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Ventilation of underground mine

Lecture 6: FANS

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Ventilation of underground mine

  1. 1. VENTILATION OF UNDERGROUND MINE © Hassan Harraz 2016 Hassan Z. Harraz hharraz2006@yahoo.com Spring, 2016
  2. 2. Follow me on Social Media http://facebook.com/hzharraz http://www.slideshare.net/hzharraz https://www.linkedin.com/in/hassan-harraz-3172b235 © Hassan Harraz 2016
  3. 3. Ventilation 1) Background •The main objective of an underground mine ventilation system is clear: ➢ to provide air flows in sufficient quantity and quality to dilute contaminants to safe amounts/concentrations where personnel are required to travel and work. ➢ To Supply of oxygen men and machines; ➢ To Dilute toxic gas / explosive and dust originated in production operations; ➢ To Assist in temperature control and humidity. • This requirement is integrated into the mining law of those nations who possess that type of legislation. • The degree of "quality' and "quantity" varies with regulations set from nation to nation, depending on a number of parameters: mining history, contaminants of greatest concern, the apparent dangers associated with those hazards and the political/social structure of the nation. • The general requirement is for any personnel to work and travel in an environment that is safe and comfortable. 3
  5. 5. References• Hartman, H.L., Mutmansky, J.M., Wang, Y.J., eds.,(1997). Mine Ventilation and Air Conditioning, 3rd. Ed., John Wiley & Sons, ISBN 0- 471-05690-1. • McPherson, M. J. (1993). Subsurface Ventilation and Environmental Engineering, Ed. Chapman & Hall, London. • Kennedy, W.R. (1999). Practical Mine Ventilation, 2nd. Ed., Intertec Publishing Corp., ISBN 0-929531-50-7. • Mutmansky, J.M., Ramani, R.V. (1992). “Environmental Health and Safety”, SME Mining Engineering Handbook, 2nd edition, Vol.1, AIME, N.Y., section 11. • John Wiley and Sons. "Metal Mine Ventilation Systems." John Wiley and Sons, 1997. p. 524 - 548. • McElroy., G. W.(1954). "A Network Analyzer for Solving Mine Ventilation Distribution Problems" U.S. Bureau of Mines Inf. Circ. 7704, 1954. p. 13. • McPherson, M.J. (1984). "Mine Ventilation Planning in 1980s." International Journal of Mining Engineering Vol 2, p. 185 - 227. • Atkinson , J.J (1854). "Theory of Ventilation of Mines." North of England Institute of Mining Engineers No 3, p. 118. • Hartman, H.I. and Wang (1967). "Computer Solutions of Three Dimensional Mine Ventilation Networks with Multiple Fans and Natural Ventilation". Int. J. Rock Mech. Sc.Vol.4. • Cross, H. (1936). "Analysis of Flow in Networks of Conduits or Conductors." Bull. Illinois University Eng. Exp. Station. No. 286. • De Souza, E.M.. Fundamentals of Airflow. In E. De Souza, Mine Ventilation, n.d. • Goldstein, M. (2008). "Carbon Monoxide Poisoning" Journal of Emergency Nursing, Volume 34, Issue 6. • Earle, R.L.(1966). "Unit Operations in Food Processing." Chapter 7 Figure 7.3. • NR-22 and NR-15 standards, Ministry of Labour and Employment, Brazil, 2010. External Sources • http://en.wikipedia.org/wiki/Wikipedia:Citing_sources • https://www.minedesignwiki.org/index.php/McPherson_Subsurface_Ventilation_Chapters • http://library.queensu.ca/ • http://www.bacharach-inc.com/sling-psychrometer.htm • http://www.bestech.com/Downloads/ProductSheets/BESTECH_NRG1-ECO.pdf • http://www.engineeringtoolbox.com/pitot-tubes-d_612.html © Hassan Harraz 2016 5
  6. 6. Lecture 1: Pollutant underground mines Hassan Z. Harraz hharraz2006@yahoo.com Spring, 2016 © Hassan Harraz 2016
  7. 7. Lecture 7: VENTILATION CONTROL Hassan Z. Harraz hharraz2006@yahoo.com Spring, 2016 © Hassan Harraz 2016
  8. 8. Objectives:Objectives: ➢ Flow rate ➢ Airspeed ➢ Pressure ➢ Temperature ➢ Humidity ➢ Contaminants (gas and dust) © Hassan Harraz 2016 8 What should we measure? ➢Maintain hygiene and safety of workers
  9. 9. 1) GASES IN UNDERGROUND MINES  As air travels through a ventilation circuit in an underground mine, it may become contaminated with one or more potentially harmful gases. These gases come from a variety of sources and must be carefully monitored to prevent mine workers from being exposed. Because ventilation systems must be designed to eliminate the hazards created by these gases, it is important for ventilation engineers to be familiar with the gases that may be present, their sources, and the hazards associated with them.  All of the hazardous gases discussed in this section can cause serious health issues and fatalities if they are present in significant quantities. Fortunately, modern ventilation systems in underground mines have made great steps in limiting worker exposure and creating an overall safer working environment. © Hassan Harraz 2016 9
  10. 10. 1.1) Fresh Air  'Normal' atmospheric air is composed primarily of nitrogen (78.10%) and oxygen (20.93%). Nitrogen is quite inert, and does not pose any direct threat to worker safety aside from the possibility of oxygen displacement leading to asphyxiation.  Presence of oxygen is critical for human respiration. While normal fresh air contains approximately 21% oxygen, this number can be changed significantly when workers and equipment operate in confined areas. The amount of oxygen that a worker needs for respiration varies with changing levels of muscular exertion. A miner working vigorously will consume more oxygen and produce more carbon dioxide than one who is at rest. In most mining situations, however, the rate of oxygen consumption and carbon dioxide production by the workers is negligible when compared to the gas exchanges occurring in equipment with internal combustion engines, and the effects of oxygen displacement from other gas sources. A well-designed ventilation system should ensure that workers always have an adequate supply of fresh air to breathe. © Hassan Harraz 2016 10 These percentages will be reduced in the presence of water vapor in the air, which can reach a maximum of 4%. % in volume Oxygen 20.93 CO2 0.03 Nitrogen 78.10 Argon 0.94 Total 100.00 Composition of normal air (clean, dry):
  11. 11. 1.2) Carbon Dioxide (CO2)  Normal fresh air contains approximately 0.04% CO2.  The gas itself is not toxic, but it can become dangerous at high concentrations primarily due to its displacement of oxygen. Because of its high solubility, CO2 also acts as a respiratory stimulant.  This combination of effects can lead to rapidly increased breathing rates and a lower availability of oxygen for respiration.  Workers exposed to air containing 10 to 15% CO2 will experience intolerable panting, severe headaches, rapid exhaustion and eventual collapse. While extended exposure (and deprivation of oxygen) can be extremely dangerous or fatal, administration of oxygen and rest can usually reverse any symptoms fairly rapidly. [3  LIMITS OF TOLERANCE CO2: The main source of CO2 in the mines is the use of explosives; the tolerable limit is 0.39% by volume or 3900 ppm.  The table below shows the contamination ranges in volume with its symptoms. © Hassan Harraz 2016 11 % Symptom 1% faster breathing without prejudice to health, rapid exposure 1-2% Breathing doubled, quick fatigue 2-5% tripled and difficult breathing 5-6% Shortness of breath (apnea), weakening 6- 10% Fainting Risk 20% Life threatening after a few minutes
  12. 12. 1.3) Carbon Monoxide (CO)  Carbon monoxide is a colorless, odorless, and highly toxic gas.  Even very low levels of carbon monoxide (35 ppm) can cause headaches and dizziness with prolonged exposure over 6-8 hours. Symptoms progress more quickly and become more severe with increasing concentrations. Death can occur in less than 3 minutes at levels 12,800 ppm. [8]  Carbon monoxide is absorbed very readily by the hemoglobin in human red blood cells. When this occurs, a stable compound known as carboxyhemoglobin is formed in the blood stream and does not decompose quickly. Because of its stability, carboxyhemoglobin can gradually build up in the blood stream even when only low levels of carbon monoxide are present. As this compound builds up, the number of red blood cells available to transport oxygen within the body decreases, and vital organs become deprived of oxygen. [3]  In mines, carbon monoxide can be generated in large quantities during explosions or fires. On a more regular basis, the gas is also formed in smaller quantities by internal combustion engines and by blasting activities.  LIMITS CO TOLERANCE: The tolerance limit for up to 48 hours per week of exposure is 39 ppm (43 mg/m3), or 0.0039% in volume.  Table below shows the contamination levels in ppm, with their symptoms. © Hassan Harraz 2016 12 ppm Symptom <50 Health risks in jobs that require a lot of effort 50 - 100 mild headaches, breathing difficulties after two hours of exposure 100 – 200 headaches, breathing difficulties, dizziness, decreased visual capacity and vomiting 500 – 1000 Risk of life after one hour of exposure >1000 - 10000 Risk life after 3 to 5 minutes
  13. 13. 1.4) METHANE (CH4)  Methane is a non-toxic gas that has no odor.  It is a combustible gas that occurs in deposits of organic origin such as coal.  The methane in the natural state, is confined in the carbon layer, either as free molecules of gas occupying pores, voids or cracking adsorption effect on the surfaces of these cavities being slowly released in the mining fronts or faster when coal is crushed.  It is commonly found retained in rock fractures, pores, or adsorbed on mineral surfaces.  Methane gas is particularly common in underground coal mines because it is formed gradually by decomposition of organic material.  Methane is very dangerous in mines because of its extreme flammability and explosive qualities.[3]  Methane burns cleanly to produce carbon dioxide and water vapor in open-air environments with sufficient oxygen presence. In most mine fires or explosions, however, this is not the case. The combustion is starved of oxygen, which leads to the production carbon monoxide. Indeed, many of the fatalities associated with methane fires and explosions in mines are caused by carbon monoxide poisoning.[3]  In mines with high methane release, there is a risk of gas explosion.  The methane concentration in the workplace should be <1%. © Hassan Harraz 2016 13
  14. 14. Methane explosion In the mine atmosphere conditions can occur in which methane burst are indicated in the graph known as "Triangle Coward", delimited by the points table below. © Hassan Harraz 2016 14 Points Oxygen (%) Methane (%) B 20 5 C 18 14 E 12 6 Explosive conditions of methane
  15. 15. 1.5) Hydrogen Hydrogen is also a non-toxic gas, but it is even more explosive than methane. Hydrogen can occasionally be found in surrounding strata, but not usually in dangerous concentrations.  Battery charging areas likely create the most risk for dangerous accumulations of hydrogen, especially if they are poorly ventilated. [3] © Hassan Harraz 2016 15
  16. 16. 1.6) Sulfur Dioxide (SO2)  Sulfur dioxide is a highly toxic gas that presents an immediate risk of death at concentrations as low as 400 ppm.  It is a toxic gas, colorless, non-flammable, which irritates eyes and throat even at low concentrations.  Unlike carbon monoxide, the presence of sulfur dioxide (even at concentrations as low as 1-3 ppm) can be easily detected by its acidic taste and odor.  In underground mines, sulfur dioxide is generated by oxidation of sulphide minerals and by internal combustion engines.  Workers exposed to sulfur dioxide should be immediately administered oxygen, immobilized, and kept warm.[3]  LIMITS OF TOLERANCE FOR SO2: the exposure limit to 48 hours per week the value of 4 ppm. © Hassan Harraz 2016 16 ppm symptoms 3 - 5 Detectable by smell (sulfur) 20 Irritation of eyes, nose and throat 50 Pronounced irritation of eyes, throat and lungs > 700 Risk of death in minutes
  17. 17. 1.7) Nitrogen Dioxide (NO2)  Of the three common oxides of nitrogen (nitric oxide, nitrous oxide, and nitrogen dioxide), nitrogen dioxide is the most toxic gases. Unfortunately, it is also the variation that is most commonly found in underground mines. Nitrogen dioxide can be recognized by its characteristic brown fumes. [3]  Nitrogen dioxide is very soluble in water, where it forms acids that can have irritating and corrosive effects. Concentrations of nitrogen dioxide greater than 200 ppm can be fatal. [3]  The oxides of nitrogen are most commonly generated by blasting and internal combustion engines. © Hassan Harraz 2016 17 LIMITS OF TOLERANCE FOR NO2  Toxic gas.  In Brazil the tolerance limit is 4 ppm or 0.0004% in volume.  The table below summarizes the levels of contamination with their symptoms Content (ppm) symptoms 2.8 - 5 No irritation of the respiratory system, changes in blood 5 - 10 Possible lung diseases 10 - 20 Respiratory irritation, symptoms disappear after adjustment 20 - 30 Increased hemoglobin 30 - 35 Long period of adjustment but with all the risks described above 35 - 54 strong respiratory irritation with cough, early intoxication 55 - 120 After 3 to 5 minutes, chest distress 120 - 200 Risk of life after one hour of exposure 200 - 300 Death
  18. 18. 1.8) Hydrogen Sulphide (H2S)  Hydrogen sulphide is a very toxic gas that can be fatal to exposed workers at concentrations of 600 ppm.  Workers who recover from hydrogen sulphide exposure are often afflicted with long-term health issues such as bronchitis and conjunctivitis. [3]  Hydrogen sulphide gas can often easily be recognized by its characteristic 'rotten eggs' smell, but relatively high concentrations of the gas can actually cause temporary paralysis of an exposed worker’s sense of smell. Scent detection alone should not be relied on to detect dangerous levels of hydrogen sulphide.  Exposure causes irritation of mucous membranes, eyes and respiratory system. It attacks the nervous system.  In mines, hydrogen sulphide is often generated by acidic breakdown or heating of sulphide ores. Areas with stagnant water pose especially high risks, especially when poorly ventilated.  LIMITS OF TOLERANCE FOR H2S: the exposure limit to 48 hours per week the value of 8 ppm. © Hassan Harraz 2016 18
  19. 19. 1.9) Radon Gas  Radon gas is a by-product of the radioactive decay of uranium. Uranium is commonly found throughout the upper surface of the earth at an estimated average grade of 4 grams per tonne in crustal rocks. Uranium gradually decays through a series of steps which emit ionizing subatomic particles. While most of the products of these steps are solid elements, radon is not. The gaseous properties of radon allow it to more easily 'escape' from the rock masses it forms in, and also make it significantly more dangerous to underground mine workers than other products of radioactive decay. [3]  Radon gas can freely flow into the airways of underground mines, where it will then decay into microscopic radioactive particles. These particles can be breathed in by mine workers and retained in their lungs where they will further decay and continue to emit radiation. Over the long term, exposure to radon can cause lung cancer. [3] © Hassan Harraz 2016 19
  20. 20. 1.10) Oxygen  It is a gas that has no color, taste or smell, with a density of 1.10 compared to air.  The minimum content which should be present in volume in the working environment, as 19%.  It is considered serious and imminent risk values below this level.  You can work at concentrations below 19%, but at risk to health because the blood does not fully absorbs oxygen, affecting the central nervous system.  Below 10% there is a risk of life. © Hassan Harraz 2016 20
  21. 21. 1.11) NH3 Toxic gas. The exposure limit to 48 hours weekly value of 20 ppm or 14 mg/m3. Acute exposure to ammonia produces tissue injury. It is very soluble in water and thus acts in the mucosa moist upper airways and eyes. © Hassan Harraz 2016 21
  22. 22. The air flow required to dilute a dopant determined, considering the situation in which the flow of dopant is constant over time is given by: Q = Qg (1 – VL) / (VL – Bg) Where: VL = maximum allowed value for the concentration of the contaminant (fraction); Qg = contaminant flow in the mine atmosphere (m3/s); Bg = the contaminant concentration in the Q flow (fraction); Q = flow of air required for dilution (m3 / s). 22 Contaminants Gas Dilution Calculations : © Hassan Harraz 2016
  23. 23. 1) A coal mine methane releases forward at a rate of 0.5 m3 / s. Assuming that the maximum permissible concentration of methane gas in the work area is 1%, calculate the minimum flow of fresh air required for dilution. Q = 0.5 (1 – 0.01) / (0.01 – 0) = 49.5 m3/s 23 2) Assuming that the air intake in the previous situation, is already contaminated with methane, with an initial concentration of 0.2%. What dilution flow forward plowing? Q = 0.5 (1 – 0.01) / (0.01 – 0.002) = 61.9 m3/s Example: © Hassan Harraz 2016
  24. 24. Summary Table mine of polluting gases (Hartman et al., 1997 Mine Ventilation and Air Conditioning) © Hassan Harraz 2016 24
  25. 25. I) AIR IN UNDERGROUND MINES • The mine ventilation system demand, to the extent possible, play the composition of air on the surface. The gases and vapors present in the air that effects on the human body can be classified as: a) Simple Asphyxiating b) Toxic gases © Hassan Harraz 2016 25
  26. 26. a) Simple Asphyxiating  They are physiologically inert gases, whose danger is linked to its high concentration, by reducing the proportion of oxygen in the environment. Are chemicals that have the common property of displacing oxygen from the air and cause suffocation by lowering the concentration of oxygen in inspired air, without presenting other characteristic level of toxicity.  Examples of chemicals with simple asphyxiating effects: ethane, methane, carbon dioxide (CO2), acetylene, nitrogen, hydrogen, etc.  They are physiologically inert gases, whose danger is linked to its high concentration, by reducing the proportion of oxygen in the environment. Are chemicals that have the common property of displacing oxygen from the air and cause suffocation by lowering the concentration of oxygen in inspired air, without presenting other characteristic level of toxicity.  Examples of chemicals with simple asphyxiating effects: ethane, methane, carbon dioxide (CO2), acetylene, nitrogen, hydrogen, etc. © Hassan Harraz 2016 26
  27. 27. b) Toxic gases Gases are even present in small concentrations, produce several harmful health effects. A toxic gas example is carbon monoxide (CO). CO is a chemical asphyxiating, producing tissue anoxia (low oxygenation of tissues), interfering with the use of oxygen by the cells. In the practice of mine ventilation, there is the prospect of reaching an overall purity of the air, but to reach out to a purity, based on the concentration of contaminants in the air, which does not offer risks to workers' health. © Hassan Harraz 2016 27 Which gases should we measure? This depends on the type of mine, ore interest and equipment used in mining.
  28. 28. Contaminants that occurs frequently:  CO and CO2: incomplete combustion of carbonaceous material, the exhaust gases of diesel engines and detonation;  NO and NO2: formed in incomplete detonation and exhaust gas of diesel vehicles;  SO2: formed on detonation of sulfur ores during fires involving sulfides (e.g. pyrite) and diesel vehicles gas.  Methane (CH4): mineral deposits of organic origin (coal) or wood rot used in shoring;  H2S: present in mineral deposits of organic origin (e.g., coal strata);  NH3: released in the detonation of explosives based on ANFO. © Hassan Harraz 2016 28
  29. 29. Standards for pollution control in mine... Each country sets its own rules regarding the allowed concentrations for contaminants in the workplace. In Egypt,.......... establishes allowable concentrations.....? © Hassan Harraz 2016 29
  30. 30. © Hassan Harraz 2016 II) DUST IN UNDERGROUND MINES Dusts:  consist of solid particles suspended in a gas and its presence in underground mine is a common problem;  Are formed in rock fragmentation processes;  The diameter of the dust particles may range from 1 to 100 μm, but the range is usually 1 to 20μm;  Dust can harm the health of workers and present explosive;  An example of disease caused by continuous exposure to dust is silicosis, which is caused by the accumulation in the lungs, containing silica particles;  Suspended dust particles which have diameters smaller than 5 m are called "respirable dust“. 30 Types of Dust: 1) Fibrogenic: silica, beryllium ore, iron ore, coal, etc. 2) Carcinogenic: asbestos, decay products of radon, silica, DPM's, etc. 3) Toxic: lead ores, beryllium, arsenic, mercury, radioactive ores, etc. 4) Radioactive: uranium ores, radio, thorium, etc. 5) Explosive: coal, sulphide ores, ..etc.
  31. 31. © Hassan Harraz 2016 Dust explosion: It consists of a very rapid combustion of dust. The initiation may occur by a flame or detonation (methane gas explosions are common initiators of dust). Conditions for coal explosively: a) Particle diameter below 850 μm b) Concentrations above 60 g/m3 c) Explosiveness decreases by increasing the% ash. 31
  32. 32. © Hassan Harraz 2016 The regulatory norms of the Ministry of Labor in Brazil (NR-15) lay down the maximum level in the work environment. ➢ Maximum levels of solids concentration in the air, according to NR-15, for the case of the presence of crystallized silica (eg coal mine): LT (Threshold Limit in mg/m3) for the total dust (respirable + non-breathable) ... LT = 24 / (3 + Qz%). LT for respirable dust ... LT = 8 / (Qz% +2). 32 Alternatives to control dust in the environment:  Using water in the rock fragmentation process, moistening the walls of the work fronts (before and after blasting), and the comminuted material;  Make the collection of dust (eg in dry drilling);  Use sprays water in places where there is dust formation;  Use personal protective masks.
  33. 33. © Hassan Harraz 2016 III) DIESEL PARTICULATE MATTER (DPM)  Diesel particulate matter (DPM) is part of the complex mixture formed in the exhaust of the fuel consumed by vehicles, machinery and equipment powered by diesel oil.  In diesel exhaust are gases and particles resulting from the incomplete combustion of diesel. The particulate generally has a diameter smaller than 1μm, with carbon as a primary component, and other adsorbed compounds (benzene, aromatic hydrocarbons, sulfates, nitrates, ...).  Occupational problems generated by DPM are related to short and long exposure, as well as concentration and individuality of each employee: ➢ The emissions can cause irritation to the eyes, nose, throat, lungs. ➢ There is considerable evidence that these diesel emissions are carcinogenic. 33
  34. 34. © Hassan Harraz 2016 Measures to minimize DPM:  use electrical equipment (if possible);  avoid keeping the engine when the vehicle is stationary;  maintain reviewed and adjusted equipment;  use DPF filter (filter for diesel particles) with correct dimensioning and validity of the filter element for each equipment;  keep the mine ventilation in appropriate standards defined in the standards. Exposure limits:  The legislation was more rigid in recent years as the daily exposure of underground mine workers,  especially in countries with mining tradition such as Germany, Canada and the United States.  In Germany, the tolerance limits for underground work are 0.10 mg/m3 elemental carbon.  In Switzerland this limit corresponds to 0.20 mg / m3, total carbon contained in th  American Institute Mine Safety and Health Administration (MSHA) is a bit more tolerant and daily exposure ranges vary 0:16 to 0:40 mg/m3 total carbon.  In Canada, as the Canadian ad hoc Diesel Committee, the limit was set at 1:50 mg/m3, which appears to be somewhat high relative to other countries, but the method used by Canadian takes into account all the particulate matter and not somento the carbon. 34
  35. 35. 2) TEMPERATURE AND HUMIDITY Climate parameters in the basement: ❖ Dry Bulb Temperature (ts); ❖ Air humidity, which can be characterized by the Humid Temperature (tu) and Barometric Pressure (p); ❖ Air velocity (v) close to the human body © Hassan Harraz 2016 35 2.1) Introduction Thermal comfort indexes: There are several indices used to represent the workers of thermal comfort, among the most common are the Effective temperature and the IBUTG. ➢The index to be used depends on the country or region.
  36. 36. 2.2) Effective temperature (te) © Hassan Harraz 2016 36 Definition:  The Effective Temperature (te) was designed by the American Society of Heating and Ventilating Engineers to characterize the thermal comfort of workers.  The effective temperature is an index used in many countries to determine the thermal comfort.  te determined by using equipment: Psychrometer or Anemometer.  The te value is determined from the values you, ts and air velocity, using the abacus right chart.
  37. 37. 2.3) IBUTG Index  In Brazil, this index is used in industry for specifying levels of exposure to hot environments for workers. It was regulated by the standard of the Ministry of Labor NR-15, Appendix 3.  It is an index obtained from the measurement of the natural wet bulb temperature and globe temperature, and represents the weighted average of these measures (Clezar, 1999 p. 253). ❖ Natural wet bulb thermometer→It is a wet bulb thermometer differs from those used in psychrometers by not imposing a forced air speed and the bulb not be protected against thermal radiation. ❖ Globe thermometer →consists of a thermometer whose bulb is positioned at the center of a hollow metal sphere with fifteen centimeters in diameter, with its painted outer surface of matte black. ❖ Indoors or outdoors without solar charging: IBUTG = 0,7 tun + 0,3 tg • Where: ❖ tun = natural wet bulb temperature ❖ tg = globe temperature © Hassan Harraz 2016 37
  38. 38. 3) PYSCHROMETRY Psychrometry is the study of gas-vapor mixtures. In underground mining, the most interest is in investigating the properties and behaviors of water vapor and air mixtures in environments with variable temperatures and pressures. All around the world, the composition of “dry air” is remarkably constant. “Dry air” refers to the mixture of gases that is all around us, assuming that no water vapor is present. With only slight local variation, the dry air of our lower atmosphere is comprised of approximately 78% nitrogen and 21% oxygen, with small amounts of other gases. Although the gas proportions remain fairly constant, the amount of moisture in the air (from water vapor) is highly variable.[3] Underground mines are typically wet environments. Water is commonly used for dust suppression, and it can often been seen seeping out of wall rocks. Water is also used by certain types of underground drilling equipment. Under varying temperatures, pressures, and humidity levels, some of this liquid water can evaporate and be carried along by the ventilation systems in the mine. When conditions change, the water can condense back into liquid form. It is important to understand these thermodynamic processes in order to accurately calculate and predict their effects on the local underground 'climate'. © Hassan Harraz 2016 38 3.1) Introduction
  39. 39. 3.2) Basics of Pyschrometric Analysis  Psychrometric calculations are performed on a basis of mass, rather than volume, because the volume of a gas is subject to variation under changing temperatures and pressures. In a dry air system, the mass flow (of air) in an independent airway remains constant at all points. This assumption is not always true in wet systems such as mines, because water is present which can evaporate and add to the mass flow, or condense and take away from it. Because of this complication, most calculations are performed using a basis of a fixed mass flow of dry air, and a variable concentration of water vapor. The concentration of water vapor in the air mixture (usually expressed as kg water per kg dry air) is known as the moisture content or specific humidity of the air. [3]  As more and more water vapor is added to a system by evaporation, the air (or more correctly, the system) is said to become increasingly saturated. At a certain point, the partial pressure exerted by the water vapor reaches a limit and no more vapor can be added to the system. This limit changes with temperature and is known as the saturation vapor pressure. When this level is reached, the system is said to be fully saturated.  Related to this idea is the concept of the “dew point.” If an unsaturated air/vapor system is cooled under constant pressure, its saturation vapor pressure will gradually decrease without any change in the vapor pressure from the water present. Eventually the system will be cooled enough that it will become fully saturated. The temperature at which this occurs is known as the dew point. Cooling the system beyond this point would cause condensation to begin to occur. © Hassan Harraz 2016 39
  40. 40. 3.3) Humidity  In psychrometric analysis, humidity is calculated in two ways: relative humidity and percentage humidity.  Relative humidity (%) is calculated based on the vapor pressure of the system compared to the saturation vapor pressure of the system at the same temperature.  Percentage humidity is very similar, but is calculated from the moisture content of the system compared to same system’s moisture content at the point of saturation.  Over the normal atmospheric range, these two calculation methods give similar results. [3] © Hassan Harraz 2016 40
  41. 41. 3.4) Pyschrometric Measurements  In underground mining, the most common tool used for measuring the presence of water vapor in air is known as a wet and dry bulb hygrometer (or psychrometer). The device consists of two thermometers, one of which has its bulb covered in a thin, water- soaked cloth. The dry bulb thermometer registers the air temperature as any regular thermometer would, while the wet bulb thermometer is cooled slightly due to the evaporation of the water. All relevant psychrometric parameters can be calculated based on knowledge of these two temperatures and the barometric pressure.  In order to measure accurately, these devices must have a constant flow of air over the wet bulb to prevent the establishment of a pocket of more saturated air. Static hygrometers simply rely on the air velocity at the site of their location to provide the required flow. “Whirling” psychrometers are commonly used in mine surveys, and are spun around a handle to provide sufficient airflow. Aspirated psychrometers provide the best accuracy and most consistent results by using small fans to draw air into the shielded container which contains the thermometers. [3] © Hassan Harraz 2016 41
  42. 42. Psychrometer: • equipment that combines a dry bulb thermometer and other wet bulb. © Hassan Harraz 2016 42 Modern pyschrometer
  43. 43. 3.5) Pyschrometric Charts  Knowing the barometric pressure dry and wet bulb temperatures, it is possible calculate many relevant parameters (including moisture content, relative humidity, vapor pressure, enthalpy and more) using a set of equations known as the psychrometric equations. Without access to programmable calculators or spreadsheet software, these equations can be very cumbersome and intimidating to use.  For convenience, visual representations of the psychrometric relationships were created for various barometric pressure. These plots are known as psychrometric charts (see image to left).  These charts can be used to quickly determine psychrometric parameters based on field measurements, and they provide an opportunity to better understand the relationships between the parameters as an air/vapor mixture undergoes thermodynamic change. © Hassan Harraz 2016 43 Modern Pyschrometric Chart[9]
  44. 44. © Hassan Harraz 2016 44 Psychrometric chart: Lists ts and you with the relative humidity (psychrometric the cards are sold with the equipment and can be found in the mine ventilation literature).
  45. 45. 4) PRESSURE • Objetives:  Estimate the total equivalent resistance and stretches of the ventilation circuit: ➢ Find leaks in the ventilation circuit; ➢ Check the operating points of the main fans of mine in his characteristic curve P x Q ➢ pressure difference measured between two points are made using differential pressure gauges.  The measurement of absolute pressure at a point is performed with the use of barometers.  Methods to measure the pressure difference between two points of the ventilation circuit: direct methods and indirect methods. © Hassan Harraz 2016 45 Measures air pressure differences between different points within the mine give information about the pressure loss in the ventilation circuit.
  46. 46. 4.1) Direct pressure measurement methods © Hassan Harraz 2016 46 Direct methods using differential pressure gauges for measurement. The purpose of differential pressure measurements to evaluate the pressure loss in certain stretches of the ventilation circuit or the circuit as a whole. For practical purposes, the equipment must have sensitivity around 1 mmCA (+/- 10 Pa). lower sensitivity may be permitted in gauges that make monitoring of the main fans.
  47. 47. 4.2) Indirect methods of measurement of pressure © Hassan Harraz 2016 47  Indirect methods of measurement of pressure using Aneroid Barometers or Altimeters.  These devices measure the absolute static pressure at one point. pressure drop between two points is calculated by difference and need corrections.
  48. 48. 5) FLOW RATE (Q) The flow control is to:  Check that the air and speed limits needs are being met;  Find leaks in the ventilation circuit;  Check the operating point of mine fans (main and auxiliary). Q = V · A (m3/s or m3/min) V = velocity of air flow; A = cross-sectional area of the gallery. ❖ Depending on the air flow speed, different types of measuring equipment may be used. ❖ The equipment most commonly used in mining is the anemometer blades. © Hassan Harraz 2016 48 ➢It is the main measure of ventilation.
  49. 49. 5.1) Instrumentation  Ventilation is a requirement to provide enough fresh air to eliminate harmful fumes from blasting and diesel engine combustion. To ensure sufficient oxygen and limited harmful gases instrumentation has been developed to ensure safe working conditions. There are numerous types of instrumentation that can be used for ventilation measurement and related tasks in a mine setting. Common instruments used to measure the airflow are smoke tube, velometer, vane anemometer, and pitot tube. Additionally, instrumentation can be used to test for harmful gases and fumes such as sophisticate hand held devices or a simple safety lamp.  Ventilation on Demand allows the optimization of airflow to each section of the mine based on the real time positioning requirements of equipment. Based on the location and ventilation requirements of each piece equipment auxiliary fans can be used to redirect airflow to provide the required level of ventilation. Currently there are a couple of companies providing this solution. Simsmart Technologies has developed a product called SmartEXEC and BESTECH has a similar product called NRG1-ECO. © Hassan Harraz 2016 49
  50. 50. 5.2) Air Velocity Instrumentation Below is a summary of the recommended range of velocity that can be measured with each of the outlined instrumentation discussed: Instrument, Velocity (m/minute), Accuracy ❖Smoke Tube , 3-45 , ±10% ❖Velometer , 0-3000 , ±10% ❖Vane Anemometer , 0-1800 , Single point: ±3% Grid: ±2% ❖Thermal Anemometer , 0-1800 , ±2% ❖Vortex Airflow Sensors , 0-3000 , ±0.5% ❖Pitot Tubes , >760 , ±1-2% © Hassan Harraz 2016 50
  51. 51. Anemometer blades © Hassan Harraz 2016 51 Thermoanemometer Thermometers; Smoke tube; Velometer; Pitot Tube. Other equipment for flow measurements:
  52. 52. © Hassan Harraz 2016 52
  53. 53. 5.3) Types of Measuring Devices5.3.1) Smoke Tube  Smoke tubes can be used to determine the direction and low velocity measurements of airflow. Measurements are determined by timing a cloud of smoke as it travels over a set distance. In addition, smoke can be used to determine areas of leakage.  One person releasing the smoke cloud at the beginning of a 10m marked distance generally performs timed measurements as the cloud reaches the other marker. The second person waits downstream and records the time taken by the cloud to travel the known distance. If a measurement is taken from only one position, a correction factor of 0.8 should be used for the velocity. The corrected velocity can then be multiplied by the area of the drift to determine the flow volume. For higher accuracy, multiple readings should be taken in a grid pattern in the mine opening and the values can be averaged.[7] 5.3.2) Velometer  Readings at high velocities up to 3000 m/ minute can be achieved using a velometer. A direct reading of the linear velocity is taken as the vane deflects with the airflow. An analog measurement is taken and can be output to a data acquisition unit. The velometer has a low ±10% accuracy and therefore should be used in conjunction with another test or can be used as a reference test where reliability of output is not of vital importance. Velometers are commonly used to check ventilation in ducts as additional fittings can be used to reach into a duct. To provide a more accurate measurement for a large passageway, a traverse method should be employed in taking the reading. The average velocity of the traversed cross-section is considered a more accurate reading.[7] 5.3.3) Vane Anemometer  Vane anemometers generally are suited to measure mid-range velocity flow rates. The reader consists of a rotating vane or spinner and a rotation counter. Velocities are determined based on the rotation counting mechanism. Either output readings can be a direct mechanical reading or digital vane anemometers are also available. Vane anemometers are sensitive to flow hindrances and must be held a distance of at least 0.9m away for the body of the technician.[7] 5.3.4) Thermal Anemometer  A thermal anemometer can provide a more accurate reading than the vane type of anemometer. Air flows are measured using the changes in the resistance of a heated wire. As the air passes by and cools the wire, the relationship between the resistance and cooling change, can be used to determine the airflow. Thermal anemometers require correction for density. The result is a highly accurate reading of ±2% for velocities below 1800m/ minute. 5.3.5) Vortex Airflow Sensors  Vortex airflow sensors use ultrasonic sensing units and a direct reading analog velocity meter. Analyzing the rate of vortex formation in airflow with a disturbance can be used to directly calculate the airspeed. 5.3.6) Pitot Tubes © Hassan Harraz 2016 53
  54. 54. Measurement procedures of Anemometers © Hassan Harraz 2016 54 It depends mainly on the type of equipment available. Anemometers instant measurement: have very short integration time, measuring the instantaneous velocity of flow of air passing through the equipment. Positioning the anemometer in the gallery Anemometers integrators: measure the average speed of air flow after a certain integration time (1 minute, for example).
  55. 55. Example flow survey... © Hassan Harraz 2016 55
  56. 56. Example of flow survey records... © Hassan Harraz 2016 56
  57. 57. Pitot tube  Pitot tubes are configured to simultaneously measure static and total pressure. The configuration is described below. The difference in the two readings reflects the velocity pressure. Pitot tubes are generally use to measure high velocity air flows in air ducts or ventilation tubing. Pitot tubes are capable of accurate measurements of velocities of greater than 760m/minute with an accuracy of ±1%.[7]  Pitot tubes consist of two concentric tubes mounted one inside the other. The arrangement consists of one end perpendicular to the center of a shaft. The other end of the inner tube is open at the end to measure the total pressure of an airstream. The other end of the outer tube is closed to measure the static pressure through an array of pinholes.  It is a device used to measure total pressure (PT), static pressure (PS) and velocity pressure (PV) in ventilation ducts or fans. You must be connected to a manometer to perform pressure measurements.  It can be used to calculate the air flow velocity as PV = PT – PS = ρv2/2, then v = (2 PV/ρ)1/2 . The use is limited to situations where the air speed is sufficiently high. © Hassan Harraz 2016 57
  58. 58. © Hassan Harraz 2016 58 Modern pitot tube design
  59. 59. Diagram simplified Pitot tube use to perform full and static pressure measurements in a mine exhaust fan positioned on the surface. © Hassan Harraz 2016 59
  60. 60. 5.4) Measuring Equipment: © Hassan Harraz 2016 60
  61. 61. Measuring Equipment the Concentration of Gases present in the Air - Detection Principles : Catalytic Oxidation: used for combustible gases such as ethanol and CO. In this technique, measured by the heat generated during the oxidation of the gas or exchange of a resistance component of an electrical circuit when the gas is burned. Electrochemical sensors: applied in determining the concentration of oxygen, CO, H2S (hydrogen sulfide) and NOx The measured gas reacts with a special electrode in an electrolyte. This reaction generates electric current that is proportional to the gas concentration. Optical detectors: used for methane, for example. Two principles used: a) Different gases absorb light at different wavelengths; passing light through a gas mixture and measuring their absorption, determine the gas concentration. b) Gases have different refractive indices. A beam of light is divided, part goes into a chamber containing air and another part in a chamber containing gas. The difference in velocity of light beams is proportional to the gas concentration of interest. Methods of detection using semiconductor: use elements (semiconductor) that uses conductivity in the presence of certain gases. the change in conductivity is measured, which is proportional to the gas concentration. colorimetric tubes: use a proprietary chemical reaction of a gas with specific chemical compounds, which reaction causes color change in such compounds. The color change is proportional to the gas concentration which is measured directly into a tube containing particular chemical compound. © Hassan Harraz 2016 61
  62. 62. References 1)John Wiley and Sons. "Metal Mine Ventilation Systems." John Wiley and Sons, 1997. p. 524 - 548. 2)G.W McElroy. "A Network Analyzer for Solving Mine Ventilation Distribution Problems" U.S. Bureau of Mines Inf. Circ. 7704, 1954. p. 13. 3)M.J McPherson. "Mine Ventilation Planning in 1980s." International Journal of Mining Engineering Vol 2, 1984. p. 185 - 227. 4)J.J Atkinson. "Theory of Ventilation of Mines." North of England Institute of Mining Engineers No 3, 1854. p. 118. 5)H.I Hartman and Wang. "Computer Solutions of Three Dimensional Mine Ventilation Networks with Multiple Fans and Natural Ventilation". Int. J. Rock Mech. Sc.Vol.4, 1967. 6)H. Cross. "Analysis of Flow in Networks of Conduits or Conductors." Bull. Illinois University Eng. Exp. Station. No. 286, 1936. 7)E.M De Souza. Fundamentals of Airflow. In E. De Souza, Mine Ventilation, n.d. 8)M. Goldstein. "Carbon Monoxide Poisoning" Journal of Emergency Nursing, Volume 34, Issue 6, 2008. 9)R.L Earle. "Unit Operations in Food Processing." Chapter 7 Figure 7.3, 1966. © Hassan Harraz 2016 62
  63. 63. Follow me on Social Media http://facebook.com/hzharraz http://www.slideshare.net/hzharraz https://www.linkedin.com/in/hassan-harraz-3172b235 © Hassan Harraz 2016
  64. 64. Lecture 2: Rules for calculation of air requirements in underground mines Hassan Z. Harraz hharraz2006@yahoo.com Spring, 2016 © Hassan Harraz 2016
  65. 65. 2. Rules for calculation of air requirements in underground mines  The main parameter of the mine ventilation system is the flow of fresh air to be blown in the workplace.  From the supply point of view of oxygen requirements for human consumption and internal combustion engines (diesel), there are specific rules to be observed which are adopted in each country.  The common reasoning for the calculation of fresh air flows (air requirements) involves the following variables: ➢ the number of workers present in the subsurface; ➢ diesel power equipment in the mine; ➢ the production rate (+ barren ore) mine; ➢ other specific elements (concentration of polluting gases, coal mine or coal-ñ, mass explosives, the presence of electrical equipment, etc.)  A very simple example will be used below to show the calculation of air requirements using the NR-22 standard (Brazil), considering ñ-coal underground mine. © Hassan Harraz 2016 65
  66. 66. The coal mine: Elements for calculating air requirements. As the NR-22, one should choose the largest value among the items (a), (b) and (c) of Table II. © Hassan Harraz 2016 66
  67. 67. Example application of NR-22 for ñ-coal mines ... Suppose in a gold mine stope work simultaneously in the most critical situation, the first diesel truck (300cv), LHD 1 diesel (150cv) and 4 workers. Consider also that this stope uses 120kg of explosives in their dismantling, and produces monthly 5,000 tonnes of ore and waste. To estimate the flow rate required by the NR-22. © Hassan Harraz 2016 67
  68. 68. Example application of NR-22 to a panel of mining coal mine ... Resp .: Item (a) Table II ... Flow w / men and machines will be equal to 2m3 / min x 4 + 3.5m3 / min / hp (300cv 150cv +) = 1583 m3 / min. Item (b) of Table II ... The air flow according to the mass of explosive used in blasting is calculated for a 30 minute aeration time: Q = 0.5 x 120kg / 30 minutes = 2 m3/min. Item (c) Table II ... air flow according to the panel production, assuming 180m3 / min / 1000t per month: Qt = 180m3 / min / 1000t x 5000 t / month = 900 m3 / min. In this case, the need for enhancement air is 1583 m3 / min as calculated in item (a). © Hassan Harraz 2016 68
  69. 69. Limits for the air velocity in the subsoil: Seek to ensure that the air velocity is sufficient to remove contaminants from the work place, but without overextending the transport of dust or impair the thermal comfort of workers. Remember that: Q = vA Q = flow of air in the gallery (m3 / s); v = air velocity (m / s); A = gallery section area (m2). © Hassan Harraz 2016 69
  70. 70. Follow me on Social Media http://facebook.com/hzharraz http://www.slideshare.net/hzharraz https://www.linkedin.com/in/hassan-harraz-3172b235 © Hassan Harraz 2016
  71. 71. Lecture 3: Dividers air flow in underground mine Hassan Z. Harraz hharraz2006@yahoo.com Spring, 2016 © Hassan Harraz 2016
  72. 72. © Hassan Harraz 2016 72
  73. 73. 3. Dividers air flow in underground mine In ventilation circuit underground mines, fresh air needs to be directed to the work fronts. This is done using particular elements, generally known as the airflow splitters. Each working section of a mine has its own dividers, to obey a general organization. © Hassan Harraz 2016 73
  74. 74. Types of flow dividers:  Dams: Dams are usually walls of masonry or wood, built in galleries or between ore pillars to prevent mixing of fresh air (input) with the contaminated air (return). Temporary dams are used close to the work fronts and with the advancement of mining, they will then be replaced by permanent dams. © Hassan Harraz 2016 74
  75. 75. permanent dams made of masonry (coal mine): temporary dam made of wood (coal mine): © Hassan Harraz 2016 75
  76. 76. ▪ Siding Lines ▪ Siding lines are used to move air up to the last junction face. ▪ They are made of flexible material structures, much used in ventilation forward service that uses continuous mining, coal mining. © Hassan Harraz 2016 76
  77. 77. Auxiliary Ventilation Siding line: The placement of a siding line longitudinally in a gallery divides this into two opening for ventilation purposes. It is usually attached to the ceiling and is always subject to leaks (leaks). © Hassan Harraz 2016 77
  78. 78. Divisores do fluxo de ar em mina subsolo Curtains ▪ The curtains are temporary structures to control the flow of air. This is simply a curtain, which can be readily suspended in the direction of air flow where needed. The curtains are used temporarily also as dam. In some situations it may be necessary to switch men and / or equipment through the curtain. This is accomplished by cutting the curtain. © Hassan Harraz 2016 78
  79. 79. Divisores do fluxo de ar em mina subsolo ▪ Portas Quando o acesso entre galerias de entrada e retorno de ar deve permanecer disponível, são usadas as portas de ventilação, que podem ser feitas de metal ou madeira, dependendo da finalidade. Portas localizadas entre entradas e saídas principais de ar são usualmente construídas aos pares, para garantir segurança e impedir a passagem do ar mesmo quando uma das portas encontra-se aberta (ver disposição específica na NR-22). © Hassan Harraz 2016 79
  80. 80. Divisores do fluxo de ar em mina subsolo ▪ ventilation ports... Gate madeof metal Gate made of wood © Hassan Harraz 2016 80
  81. 81. © Hassan Harraz 2016 81
  82. 82. Divisores do fluxo de ar em mina subsolo  Crossings (Air Crossings) ▪ These structures are used where necessary, although complex, at intersections where it is desired not to mix the incoming air with return flow. Can be overcast or Undercast type. The Undercast structure is generally not used because of presence of water that may occur in the gap, tending to block the air flow. ▪ It is a characteristic structure in coal mines. © Hassan Harraz 2016 82
  83. 83. Air Crossing (overcast type) © Hassan Harraz 2016 83
  84. 84. Diagram gathering various types of air dividers and coal mine ventilation circuit. © Hassan Harraz 2016 84
  85. 85. Examples of symbols for elements present in mine ventilation circuit © Hassan Harraz 2016 85
  86. 86. Diagram showing the flow dividers ventilation circuit. © Hassan Harraz 2016 86
  87. 87. ▪ REGULATORS ▪ The amount of air flow can be controlled by so called regulatory elements. ▪ A regulator consists of a frame with an opening for the passage of air, which may be large or small. The small gap reduces the passage of air. ▪ Approximate calculation of the opening area of a controller: a = 1,21 / R1/2 ; in which R em Ns2m-8, the in m2. © Hassan Harraz 2016 87
  88. 88. © Hassan Harraz 2016 88
  89. 89. © Hassan Harraz 2016 89
  90. 90. Sliding door regulators © Hassan Harraz 2016 90
  91. 91. Typical air flow model of an exhaust system (dual division) © Hassan Harraz 2016 91
  92. 92. ____________ © Hassan Harraz 2016 92
  93. 93. Auxiliary Ventilation In ventilation work fronts occur situations in which the air flow from the main ventilation is inadequate or unavailable. In these cases, a reinforcement should be arranged as a means to ensure the correct air supply. This reinforcement system located is called auxiliary ventilation. The main applications of the auxiliary ventilation are: 1) Ventilate galleries in development (fund-de-sac). 2) Providing an additional flow to watch a part of the primary circuit, via a stiffener (generically called booster). © Hassan Harraz 2016 93
  94. 94. Auxiliary Ventilation Ventilation galleries in cul-de-sac: It is the most frequent and important application of the auxiliary ventilation. Almost always it is needed where mining is taking place, and may constitute the only way to meet the needs of quality and quantity of air. The entire opening galleries, wells, inclined planes, raises and winzes always require auxiliary ventilation. In coal mines, all fronts require ventilation help as soon exceed the last indent (generally, the NR-22 standard establishes the mandatory ventilation in the cul-de-sac). © Hassan Harraz 2016 94
  95. 95. Auxiliary Ventilation Example of ventilation cul-de-sac in coal mine panel (Chambers and Pillars), with small auxiliary exhaust fans running for connected non-collapsible pipes. pipes fans curtains dams. © Hassan Harraz 2016 95
  96. 96. Auxiliary Ventilation Example of ventilation cul- de-sac with siding lines and curtains (coal, method room and pillar). © Hassan Harraz 2016 96
  97. 97. Auxiliary Ventilation Example of organization ventilation assist in coal mine panel (Criciuma- SC-BRA), with fans fixed on the ceiling and acting for inflation. © Hassan Harraz 2016 97
  98. 98. Auxiliary Ventilation Position the equipment in coal mine panel (Criciuma-SC- BRA) in the previous slide. 1 2 3 4 5 9 6 8 7ARLIMPO © Hassan Harraz 2016 98
  99. 99. Auxiliary Ventilation Auxiliary fans with pipes or lines of sidings are the main means to ventilate the work fronts in the cul-de-sac, but there are other devices that can be used or added to special control purposes of dust or special air movement. A very important factor to be considered in the design and selection of auxiliary fans is the need to ensure that the recirculated air does not occur. Auxiliary fans and pipes: both axial fans and centrifugal can be used in auxiliary ventilation systems. Axial fans are preferred due to its compact size and ease of staging. The most commonly used materials for rigid pipes are steel alloys, braided steel mesh, fiberglass and resins. © Hassan Harraz 2016 99
  100. 100. Auxiliary Ventilation not rigid pipes (flexible and collapsible) are usually nylon. Pipes are available in wide range of diameters, with circular or elliptical sections. The most common placement of the pipes is usually high, being close to the central section to the rounded galleries and corners for rectangular sections. pipes pipes © Hassan Harraz 2016 100
  101. 101. Auxiliary Ventilation Examples of positioning collapsible pipes (Mina Cuiabá – MG/Brasil - AngloGold Ashanti) © Hassan Harraz 2016 101
  102. 102. Auxiliary fans coupled to piping : auxiliary fans for installation on the ceiling galleries  auxiliary fans associated in series and connected to flexible pipes. © Hassan Harraz 2016 102
  103. 103. Auxiliary fans coupled to piping : Example flexible and non-collapsible pipe, which can be used in exhaust systems for ... © Hassan Harraz 2016 103
  104. 104. Auxiliary Ventilation The use of curtains and siding lines is more common in coal mines, where it is common to mining front operate with mechanical fragmentation equipment (continuous miners). In metalliferous mines are underutilized because they are more subject to damage related to the use of explosives. The next detonations dams can also suffer damage to the vibration produced by explosives. © Hassan Harraz 2016 104
  105. 105. Auxiliary Ventilation Scrubbers: They are dust collectors that can solve problems of dust suppression, both mounted on machines like fans associated with suitable for this purpose. Example scrubbers equipping continuous miner  © Hassan Harraz 2016 105
  106. 106. The main sources of dust in coal mines are the continuous miners (coal fragmentation) and roof bolters (ceiling parafusadoras). continuous miner Roof Bolter Scrubbers... © Hassan Harraz 2016 106
  107. 107. The new models of continuous miners are almost all equipped with scrubbers. The total efficiency varies from 60 to 75%. When the dust is excessive, the scrubber requires frequent maintenance. filter cleaning and duct are required. Scrubbers... © Hassan Harraz 2016 107
  108. 108. Scrubbers AND VENT FOR INFLATE : Ventilation by insufflation, fresh air is directed through the curtain toward the face. This fresh air dilutes and displaces dust into the face of mining. After the dust removal air is discharged from the rear of the scrubber. remote operator controlling the miner cont. © Hassan Harraz 2016 108
  109. 109. Scrubbers AND VENT FOR INFLATE : The operator position has a great influence on how it will be affected by contaminated air. Studies show that changing the operator to position 2, a saving of 94% of this exposure level. Factors that cause high levels of dust:  position of the operator;  maintenance of the scrubber;  ventilation and sprays;  fresh air flow. © Hassan Harraz 2016 109
  110. 110. Scrubbers and exhaust ventilation :  Both the position as the B position are located parallel to the curtain line end.  In the case of the operator to position the move, the exposure level does not change much. However, should the operator in position B, the exposure level increases greatly as it will leave the fresh air zone. Ventilation assist by using exhaust scrubbers, the operator position also influences the level of exposure that is suffering. The options are better, because there are more places to the worker position. © Hassan Harraz 2016 110
  111. 111. ____________ © Hassan Harraz 2016 111
  112. 112. Auxiliary Ventilation Sprays are spray water generators. In modern coal mines, most cutting machines, loading and continuous miners have atomizers for dust suppression. The use of water after the dismantling is very important because fine particles of dust are generated. Thus, small particles become trapped on the surfaces of the galleries and not dissipated in the air and the water can remove them. Of course, excessive use of water can generate a high level of humidity, which can mean problems as difficulties in the management of materials and operating problems. © Hassan Harraz 2016 112
  113. 113. Auxiliary Ventilation Arrangement of the auxiliary ventilation system: Curtains, special fans and ventilation devices can be arranged in a wide variety of configurations depending on the contaminants involved, space limitations, mining equipment being employed, noise limitations, and cost and practicality considerations. © Hassan Harraz 2016 113
  114. 114. Ventilation aid by insufflation and exhaust Ventilation assist in cul-de-sac may be: - By insufflation - Exhaustion. Selecting a system by blowing or exhaust should be considered carefully. Insufflation applies to systems where higher flow velocities are directed to face both the narrow side of a curtain as a pipe with a positive pressure. When the air is sucked from the face by both pipe negative pressure as the narrow side of a curtain system is the exhaust. © Hassan Harraz 2016 114
  115. 115. Auxiliary Ventilation Ventilation aid Insufladora Ventilation aid Exhaust © Hassan Harraz 2016 115
  116. 116. Uses the auxiliary ventilation: cul-de-sac in ramp development phase! © Hassan Harraz 2016 116
  117. 117. Uses the auxiliary ventilation: cul-de-sac in shaft opening phase! © Hassan Harraz 2016 117
  118. 118. Auxiliary Ventilation The following factors should be considered in selecting an inflation system or exhaustion: 1- The higher speed of the resulting air insufflation is more effective for distances greater output than in exhaustion. This disadvantage of the exhaust system can only be overcome by placing the nearest inlet face, which is not always possible; 2- by insufflation tubing can fetch the air in any place of origin and take it to the point of use without suffering contamination in the way, whereas in the exhaust air can pass through transport galleries and even mined areas or other work fronts, reaching pre- contaminated to the point of use; 3. The conventional insufflation causes contamination with dust and / or gases, taking them beyond the face and may even increase the rate of dust in suspension. The exhaust removes the contaminants as they are generated on the face and may even improve visibility; 4. The inflator permits the use of collapsible tubing, which is easier to handle and cheaper than the rigid pipe; 5. The inflator produces lower concentrations of contaminants flammable / explosive passing through the fan; 6. The thermal sensation may be of lower temperature when it is used insufflation. © Hassan Harraz 2016 118
  119. 119. Auxiliary Ventilation Ventilation aid Insufladora Combinations (superpositions) in the auxiliary ventilation: You can use a combination of inflation and exhaust to achieve greater effectiveness in situations where a single fan does not have sufficient capacity to provide the required flow on very long pipelines.© Hassan Harraz 2016 119
  120. 120. Auxiliary Ventilation Combinations in the auxiliary ventilation: The layout and flow of the combined arrangements are not correct, dust recirculation problems and gas will occur. Next, two situations where the superimposition is not properly configured. © Hassan Harraz 2016 120
  121. 121. ____________ © Hassan Harraz 2016 121
  122. 122. Cargo Loss Estimates in Auxiliary Ventilation Ducts: You can calculate the losses in ventilation ducts help from the friction loss equations and turbulence seen before. However, the flexible pipe manufacturers usually provide good value for the losses sustained in their material. A presentation of the loss is on the next slide abacus. © Hassan Harraz 2016 122
  123. 123. Abacus to calculate the loss of pressure flexible duct meter (Vinivento-Sansuy manufacturer): © Hassan Harraz 2016 123
  124. 124. Example: duct diameter 1000mm, air flow through the duct: 30 m3 / s (108,000 m3 / hour); pressure drop in the pipeline : 2.7 mmCA / meter. Obs.: A loss of load indicated in the abacus refers to straight segments. Folds in the duct increase the pressure loss considerably. © Hassan Harraz 2016 124
  125. 125. Exercises: a) Suppose that an axial fan is capable of providing 30m3 / s at a static pressure 120mmCA (free "stall"). What is the maximum length of ventilation ducts auxiliary diameter 1000mm to which this fan can be connected, so that still maintain a minimum flow rate of 30m3 / s ? A: 44 meters. b) For the same conditions (30m3 / s and 120mmCA), the maximum length of ventilation ducts auxiliary 1200mm in diameter that can be connected, keeping the minimum flow rate of 30m3 / s? A .: 133 meters. c) Suppose the situation (a) an attempt is made to use two flexible pipes of 600mm diameter installed in parallel, replacing the duct 1000mm. What is the maximum possible length of the ducts of 600mm, to provide the same flow (30m3 / s)? A .: 15 meters. © Hassan Harraz 2016 125
  126. 126. Follow me on Social Media http://facebook.com/hzharraz http://www.slideshare.net/hzharraz https://www.linkedin.com/in/hassan-harraz-3172b235 © Hassan Harraz 2016
  127. 127. Lecture 4: SETTINGS VENTILATION Hassan Z. Harraz hharraz2006@yahoo.com Spring, 2016 © Hassan Harraz 2016
  128. 128. 4- Layouts ventilation Ventilation systems in mines  Components of the ventilation system: ➢ Mechanical ventilation vent. Natural ➢ Galleries and other connected openings ➢ Control elements of the air flow (dams, fences, doors, regulators, etc.)  The air distribution in the mine should be effective: the direction and amount of air should be controlled. Directing the air flow subsurface:  At least two openings must be present in the mine: input and output air (exception - development work).  Access routes and return to work fronts covered by workers must be made in fresh air galleries. Mapping the mine ventilation You should periodically check the flow of ventilation to:  Improve the efficiency of air distribution in work areas (to the flow balance);  Locate and determine the cause of galleries with high strength;  Locate and determine the cause of leakage of air and recirculating losses;  Plan the likely direction of flow for new galleries and the lease of fans. © Hassan Harraz 2016 128
  129. 129. Layouts ventilation leaks: Are flow losses of the air intake circuit for the return, which occur unintentionally. Leaks are the most common cause of inefficiency in the distribution of air in underground mines. Points to leak... © Hassan Harraz 2016 129
  130. 130. Layouts ventilation Where leaks occur: Occur in gaps and / or cracks located in ventilation ports, dams, crossings and sidings. At Sometimes fractures in massive own (eg pillars) can cause air leakage. The intensity of the leak depends on the state of conservation and air splitters of finish and also the pressure differential to which they are subject (higher pressure differential leaky). Leaks in coal mines: they represent on average 50% of the total flow of the mine. Trails metalliferous mines: 25% on average. © Hassan Harraz 2016 130
  131. 131. Layouts ventilation Studies concerning leakage (leakage) in sets of dams (stoppings) adjacent coal mine showed the following results: Trail flow Number of adjoining dams L = length monitored gallery H = pressure difference across the dam © Hassan Harraz 2016 131
  132. 132. ____________ © Hassan Harraz 2016 132
  133. 133. Layouts ventilation Main Fan Underground Mines: Much of the mines currently organizes the ventilation circuit to operate for exhaustion, with the main fans positioned on the surface. To reduce resistance, one should use only the exhaust wells for ventilation without handling functions production personnel and materials. © Hassan Harraz 2016 133
  134. 134. Layouts ventilation Advantages in positioning the main fan on the surface ... Ease of installation - surface there is more space to install the equipment; Ease of access - the fan has more immediate access in case of maintenance or disaster (fire and floods); Security - the fan is less vulnerable to disasters and the rock mass instability problems. © Hassan Harraz 2016 134
  135. 135. Layouts ventilation However, surface ... - There will be more noise generation and potential problems with neighbors. There earmuffs noise that can be installed on the fans, but these devices decrease the flow of equipment. - Building surface surrounding the fan can leak, eventually to 20% (in this case, in relation to the total flow moved by the fan, the air would be only 80% from the mine). © Hassan Harraz 2016 135
  136. 136. Airspeeds recommended for wells: vertical wells used exclusively for ventilation (not fitted) = 18 to 22m / s; vertical wells equipped = 10 to 12m / s. (Ref.: The mine ventilation practitioner's data book; ed. Dr. A.M. Patterson; Mine Ventilation Society of South Africa, 1992) For primary fan, it is preferable to install two units in parallel than a single unit. The reason is that, in parallel association, a fan will produce 66% of the flow while the other is blocked for repairs. (The Hard Rock Miner’s Handbook, Ed. 3, 2003 McIntosh Engineering Limited) © Hassan Harraz 2016 136
  137. 137. ____________ © Hassan Harraz 2016 137
  138. 138. Layouts ventilation Differences between ventilation metalliferous mines and coal: -diferem by mining method of the characteristics and types of polluting gases. Coal →flatter Tabular deposits; mining methods ... Room and pillar; Longwall. Metalliferous mines → verticalized bentonite deposits are common. mining methods ... R & P, & Stope pillar, SLS, Shrinkage, Sublevel caving, Block caving, Cut and Fill, etc. © Hassan Harraz 2016 138
  139. 139. Layouts ventilation Differences of air contaminants: In many coal mines, the primary pollutant is methane (explosive). In metalliferous mines, gases generated by detonations and diesel use are the primary pollutants. Ventilation is the highest priority in coal mines than metal-bearing, with higher costs in the coal. © Hassan Harraz 2016 139
  140. 140. Layouts ventilation Characteristics of ventilation of coal mines: Use of leased extractors on the surface, causing depression in the underground environment; Great air leakage; Large number of dams (and conservation problems); large need for air (presence of methane and dust); the system of bleeders; boosters in the basement are allowed in Brazil. © Hassan Harraz 2016 140
  141. 141. coal mines Positioning the main access (inclines and pits) in coal mines:  optimal positioning seeks to maintain approximately constant equivalent resistance of the circuit along the life of the mine;  this can be achieved by placing the main lines in the center of the area to be mined;  if the central positioning is not possible, the equivalent circuit resistance will increase and also the air loss (leakage) due to elongation of the ventilation circuit, making it difficult to maintain the required flow in the service fronts;  when the circuit lengthens one can drill additional wells in the periphery of mineable areas, serving as inlets or air outlets, reducing leakage and the resistance of the ventilation circuit. © Hassan Harraz 2016 141
  142. 142. coal mines Positioning the main access from the center of the mined area ... © Hassan Harraz 2016 142
  143. 143. Example coal mine with main access from the center of the mined area (mine SC) © Hassan Harraz 2016 143
  144. 144. Examples of ventilation systems on shafts and mining panels ...  "U-tube" (Fig. Left).  direct ventilation through the panel (fig. dir coal mines © Hassan Harraz 2016 144
  145. 145. Examples of ventilation circuit panels using ventilation systems "U-tube". coal mines © Hassan Harraz 2016 145
  146. 146. Coal mining Detail the organization of a mining panel and its development axis with connection (coal mine in S.Catarina, method room and pillar). Ventilation "U-tube" in the panel. © Hassan Harraz 2016 146
  147. 147. charcoal Detail of ventilation in front of production in coal mine in S. Catarina: © Hassan Harraz 2016 147
  148. 148. Layouts charcoal  Boosters for ventilation circuits:  alternative economical general to change the distribution of flows in specific areas of the mine (it's more interesting than the main increase ventilation or use regulators to move part of the flow from one sector to another mine);  the boosters can be low power fans (eg coal when used to provide flow in specific mining panel) or higher powers (in other mines where several boosters can be connected in parallel, supporting the main ventilation);  whenever possible, the boosters are positioned in return air galleries, leaving the free fresh air circuit for access; © Hassan Harraz 2016 148
  149. 149. Layouts charcoal Example boosters installation (parallel association) in underground gallery... © Hassan Harraz 2016 149
  150. 150. Layouts charcoal Example boosters use in coal mine (figure below): - Circuit consisting of a main entrance via incline mine shafts + + + mining panels general exhaust per well; clean air circuited (blue) and contaminated air (red); © Hassan Harraz 2016 150
  151. 151. Layouts charcoal desired air flow / obtained (m3/s): That is, panels 1 and 3 are insufficient to flow; Panel 4 is to excessive flow. To solve the problem … use boosters in panels 1 and 3, redistributing the flow ! Flow rate desired Flow rate obtained Panel 1 25 19.1 Panel 3 25 20.8 Panel 4 15 31.6 © Hassan Harraz 2016 151
  152. 152. Layouts charcoal  Bleeders: ventilation technique used to dilute the methane during mining backward in Longwall method or recovery pillars (in chambers and pillars). It is to ventilate the area already mined (gob) panel still active to prevent the concentration of methane. This is done using controls in the panel and existing permeability in the mining area. Bleeders may be assisted by degassing by boreholes. © Hassan Harraz 2016 152
  153. 153. Layouts Coal mines: bleeders in Longwall retreating. © Hassan Harraz 2016 153
  154. 154. Layouts charcoal systems changes to coal mines employing Longwall .. © Hassan Harraz 2016 154
  155. 155. Layouts charcoal Two common variations to longwall retreating in fields with significant presence of methane, are shown in the diagrams (c) and (e). The side access panel may be composed of two or more galleries. The common air flow rates through the Longwall face are of the order of 25 - 35m3 / s in high production fronts (flow rates depend on the methane release rate). © Hassan Harraz 2016 155
  156. 156. Layouts ventilation Ventilation metalliferous mines: In modern metalliferous mines, the practice is to use multiple fans: main fans on the surface and in underground boosters to direct the flow to work areas. Disadvantages of using multiple fans: it is more difficult to control and analyze the ventilation circuit. However, if there is failure of a fan, the impact on the circuit is smaller and easier to remedy. -Use of diesel equipment; -minor leaks; -the galleries are designed with the smallest possible section area due to high development costs (largely done in sterile material). This leads to circuits with higher aerodynamic resistance. © Hassan Harraz 2016 156
  157. 157. Layouts ventilation Example metallifer mine: main fans (shaft 3:04) on the surface and acting for exhaustion. © Hassan Harraz 2016 157
  158. 158. Layouts ventilation Metalliferous mines: General characteristics of layouts in metalliferous mines ... Check ventilation and outlet on opposite sides of the stopes, which eliminates background ventilation-de-sac in production. Up ventilation (the lowest level to the highest) in verticalized bodies, with the air being conducted by raising (chimneys) to the upper levels. © Hassan Harraz 2016 158
  159. 159. Layouts ventilation metalliferous mines: simplified configuration. © Hassan Harraz 2016 159
  160. 160. Layouts ventilation Metalliferous mines: configuration in which clean air enters the main ramp and is distributed by levels, leaving the well of exhaustion. © Hassan Harraz 2016 160
  161. 161. Layouts ventilation Metalliferous mines: details of the stops on the mining method Shrinkage © Hassan Harraz 2016 161
  162. 162. Layouts ventilation Metalliferous mines: details of the stops on the mining method Sublevel Stoping © Hassan Harraz 2016 162
  163. 163. Layouts ventilation Sublevel stoping: Orosur – San Gregorio – Uruguay (2013) © Hassan Harraz 2016 163
  164. 164. Layouts ventilation Metalliferous mines: details of the stops on the mining method Cut-and-Fill Main entrance ramp of fresh air upcast shaft © Hassan Harraz 2016 164
  165. 165. Layouts ventilation General ventilation scheme in the Cut-and Fill mining method: clean air from the surface is provided by the ramp, through the enhancement (inside the stope), then is directed to the exhaustion raises. Raise Raise Stress Dish Rampa © Hassan Harraz 2016 165
  166. 166. Layouts ventilation ventilation schemes in Cut-and-Fill - Cuiabá (AngloGold Ashanti, Minas Gerais): © Hassan Harraz 2016 166
  167. 167. Layouts ventilation ventilation schemes in Cut-and-Fill - Cuiabá (AngloGold Ashanti, Minas Gerais): © Hassan Harraz 2016 167
  168. 168. Layouts ventilation ventilation schemes in Cut-and-Fill - Cuiabá (AngloGold Ashanti, Minas Gerais): © Hassan Harraz 2016 168
  169. 169. Layouts ventilation Metalliferous mines: mining method details Sublevel Caving © Hassan Harraz 2016 169
  170. 170. Layouts ventilation metalliferous mines: detail of the stops on the VCR mining method © Hassan Harraz 2016 170
  171. 171. Layouts ventilation metalliferous mines : © Hassan Harraz 2016 171
  172. 172. Follow me on Social Media http://facebook.com/hzharraz http://www.slideshare.net/hzharraz https://www.linkedin.com/in/hassan-harraz-3172b235 © Hassan Harraz 2016
  173. 173. Lecture 5: LAWS OF VENTILATION Hassan Z. Harraz hharraz2006@yahoo.com Spring, 2016 © Hassan Harraz 2016
  174. 174. 5. Ventilation laws During the air flow in the underground mine galleries, it loses pressure (suffering "load losses") in two ways: - Friction of the fluid against the surface of the galleries (Hf losses); - Turbulence (changes of direction in curves, flares and nips of galeiras; Hx losses).  The total loss is given by : Ht = Hf + Hx  The load loss is a parameter used in the selection of fans! Hf Hf friction losses (Atkinson equation): Hf = _k P L_ Q2 A3 In the International System of Units (S.I.), has : Hf in Pa (N/m2); k, friction factor, given in Ns2m-4; P, gallery perimeter, given in m; L, gallery length, given in m; A gallery section area, given in m2; Q, air flow, given in m3/s © Hassan Harraz 2016 174
  175. 175. The friction factor k is an important parameter and can be obtained from tables or by means of measurements carried out on places of interest. In general, the value of k is presented between 00:01 and 12:02 Ns2m-4. The following table, taken from Hartman et al. (1997 chap.5) serves to estimate k galleries of coal mines. Type Gallery Rectilinear Sinuou Clean Little blocked Moderadam blocked Clean Little blocked Moderadam blocked Smooth finish* 0.0046 0.0052 0.0061 0.0055 0.0069 0.0076 Conventional Remove 0.008 0.0091 0.0110 0.0110 0.0121 0.0140 With wooden shoring 0.012 0.0134 0.015 0.0160 0.0164 0.0170 All values of k are in Ns2m-4. * smooth finish refers to galleries performed with continuous mining, roadheader, it raises or drill TBM. © Hassan Harraz 2016 175
  176. 176. k values for galleries coal mines are in the table below: Type Gallery Rectilinear Sinuou Little sinuous moderately twisty Much sinuous Finishing Soft 0.0037 0.0056 0.0065 0.0083 Sedimentary rocks 0.0111 0.0130 0.0139 0.0158 Shoring wooden 0.0185 0.0204 0.0213 0.0232 Igneous rocks 0.0278 0.0297 0.0306 0.0325 k values for pipes used in the auxiliary ventilation galleries developed in the cul-de-sac: © Hassan Harraz 2016 176
  177. 177. The k values described in the tables above are for a specific mass standard condition of air, corresponding to 1.201 kg/m3 (or 0.075 lb/ft3), recorded when the air is at the sea level and a temperature in 21.1oC. If air density (ρ) in the condition of interest is different from the standard condition, one should correct the value of k, as follows: kcorrected = ktabulated (ρ/1.201) . The variables _k P L_ They may be condensed into A3 Rf a single parameter called "gallery of resistance." Rf .... It is given (SI) in Ns2m-8. Thus, Hf It can be written as : Hf = Rf Q2 = _k P L_ Q2 A3 © Hassan Harraz 2016 177
  178. 178. Example: Calculate the loss of friction pressure caused by the passage of 200 m3/s of air through a gallery section 4 x 5m and 100m in length. Assume: k = 0.01 Ns2m-4. Hf = Rf Q2 = _k P L_ Q2 A3 P = 5x2 + 4x2 = 18m L = 100m A = 4x5 = 20 m2 Rf = 0.01 x 18 x 100 = 0.00225 Ns2m-8 203 Hf = 0.00225 (200)2 = 90 Pa . © Hassan Harraz 2016 178
  179. 179. the gallery section of area 1.7 x 2m ? Continuation: Keeping the data from the previous example, that the loss of friction pressure changing only P = 1.7x2 + 2x2 = 7.4m A = 1.7x2 = 3.4 m2 Rf = 0.01 x 7.4 x 100 = 0.188 Ns2m-8 3.43 Hf = 0.188 (200)2 = 7520 Pa . © Hassan Harraz 2016 179
  180. 180. Pressure losses Hx by air turbulence:  Obtaining estimates for Hx is by no means a simple equation as Hf. In general, they use up tables or abacuses with experimentally derived values.  Losses due to turbulence ("shock losses") can be transformed into resistors (in this case, Rx) whereas the pressure loss is expressed as follows: Hx = Xρv2 / 2 , where ρ = density of air (kg/m3), v = average velocity of air flow (m/s), X = loss factor turbulence (dimensionless). Rewriting Eq Atkinson only for pressure losses as "shock", we have: Hx = Rx Q2 = Rxv2 A2 = Xρv2 / 2. Then, Rx = Xρ / (2 A2), such that Rx is the resistance due to air turbulence. The X factor is estimated from tables from the literature. Some examples of common settings in underground mine are presented below, with its value X. An important observation is that small variations in the geometry of the galleries can cause significant changes in X in relation to approximations obtained in tables. © Hassan Harraz 2016 180
  181. 181. X Factor for losses by turbulence in some situations : (Ref.: McPherson, M. J., 1993, Subsurface Ventilation and Environmental Engineering, Ed. Chapman & Hall, London, Cap.5.3)  Air intake with well-defined edges X = 0.5  air intake duct for a X = 1.0  air intake with rounded edges X = 0.03 for r/D ≥ 0.2 © Hassan Harraz 2016 181
  182. 182.  Air exit X = 1.0  Gallery abrupt enlargement A = section area v = air speed X2 = [A2/A1 -1]2; for section 2. If A2 >> A1, X1 = [1- A1/A2]2; for section 1. © Hassan Harraz 2016 182
  183. 183.  Abrupt narrowing gallery X = 0.5 [1- A2/A1]2 Rx = Xρ/(2A2 2)  90o curve in rectangular gallery  divergent flow gallery to pit X = 0.5 [1 + 2.5 v2/v1] Rx = Xρ/(2A1 2) © Hassan Harraz 2016 183
  184. 184. Hx calculation by the equivalent length method: In this case the turbulent losses are expressed in terms of an equivalent length of a straight line the gallery and constant geometry. That is, determine an additional length Lx (Hx providing a load loss) which will add to the length L of the gallery. Thus, the total losses of load for a particular gallery that shows friction loss and "shock", takes the form: Ht = Hf + Hx = _k P (L+Lx) Q2 . A3 The table on the next slide contains some suggestions for Lx, according to the various sources of Hx losses. © Hassan Harraz 2016 184
  185. 185. Lx values for some sources of losses Hx: loss of Origin Lx(m) loss of Origin Lx(m) Air entrance 6 gradual expansion 1 Output (discharge) 20 abrupt expansion 6 Curve 90o, with rounded corners 1 bifurcation with divergent gallery (90o) 60 Curve 90o, with many well-defined 20 Crossing with poor finish 290 contraction gradual 1 Crossing with good finish 65 abrupt contraction 3 © Hassan Harraz 2016 185
  186. 186. curva característica 0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 vazão perdadepressão Characteristic curve of a gallery : The total resistance of a gallery (friction + Turbulence) is given by Rt = Rf + Rx. The total head loss takes the form... Ht = Rt Q2. It is often graphically represent the behavior of a gallery (or set of pipes connected to each other) for different flow rates, the following way. From the observation of the anterior slide curve, called gallery characteristic curve (curve or the mine when this is the resistance of a complete circuit), it is concluded that at high flow rates too high pressure drops are generated. © Hassan Harraz 2016 186
  187. 187. Example: Compare the pressure loss observed in a resistance gallery Rt = 0.1 Ns2m-8 when draining, in a first situation, 50 m3 / s of air with another situation in which drain 100 m3/s . Ht by 50m3/s ... Ht = 0.1 (50)2 = 250 Pa; Ht by 100m3/s ... Ht = 0.1 (100)2 = 1000 Pa. That is, for a flow rate of 100m3 / s, losses were 4 times higher. © Hassan Harraz 2016 187
  188. 188. The Rt value for a particular gallery or set of galleries is approximately constant and does not depend on the flow of air that flows in the passage. As a result, one can determine the pressure loss of a gallery for any flow rate using the equation Ht = Rt Q2 . In galleries where the Rt value is greater, the greatest difficulty to the passage of air. The cost of passing a given flow rate Q in a gallery also depends directly on Rt: greater resistance mean larger ventilation costs. © Hassan Harraz 2016 188
  189. 189. Example: Calculate the equivalent resistance of the ventilation circuit following figure. Consider: A1=20m2; perím.=18m A2=15m2; perím.=16m k=0.01 Ns2m-4 ρ=1.2kg/m3 Solution Frictional resistance... R1= kS/A3 = 0.01 x 18 x 500 / 203 = 0.011 Ns2m-8 R2= 0.01 x 16 x 500 / 153 = 0.024 Ns2m-8 Resistances for shock ... Check : X=0.5; Rx1=0.5 x 1.2 / (2 x 202) = 7.5x10-4 Ns2m-8 Output : X=1.0; Rx2=1.0 x 1.2 / (2 x 152) = 0.0027 Ns2m-8 Contraction A1/A2: X=0.5 [1 - 20/15]2 = 0.055 Ns2m-8 Rx3=0.055 x 1.2 / (2 x 152) = 1.5x10-4 Ns2m-8 Req = R1 + R2 + Rx1 + Rx2 + Rx3 = 0.038 Ns2m-8 © Hassan Harraz 2016 189
  190. 190. Relationship between pressure and pressure drop for fluid flow For the situation in which a fluid such as air flows in a gallery, the following pressures are defined: Static pressure (PVS) - is the pressure which also acts in all directions and results of the thermodynamic state of agitation of the molecules of air. Velocity pressure (PV) - is the pressure resulting from the kinetic energy of the air molecules moving with a certain velocity v. PV = ρv2/2 , ρ is the air density and v the flow velocity. Total pressure (PT) - is the sum of PS and PV, PT = PS + PV . © Hassan Harraz 2016 190
  191. 191. Assuming that the air flows with velocity v in a gallery whose shape and roughness cause losses Hf and Hx (Ht = Hf + Hx), it is the following relationship: PT1 = PT2 + Ht , PT1 and PT2 which are the total pressures observed in points 1 and 2. The components of the total pressure PT can be measured according to the following illustration, where they were used column manometers d'tube-type water U. © Hassan Harraz 2016 191
  192. 192.  equivalent resistance ducts associations (galleries) Ventilation:  In a mine galleries with different R are connected to each other. Depending on the configuration of the mine and so the connections are made, it may be possible to find a single value of R representing the entire air circuit (these are called "equivalent resistance" circuit).  To determine the equivalent resistance of the circuit, it is necessary to identify the products associations (galleries) ventilation. © Hassan Harraz 2016 192
  193. 193. Types of simple galleries associations: In series - the same flow passes through R1 and R2; loss total load is the sum of losses in R1 and R2. In parallel - the flow that passes in each gallery is a fraction of the total flow; the pressure loss in R1 is equal to R2 loss. © Hassan Harraz 2016 193
  194. 194. Calculation of equivalent resistance : In series... In parallel... Obs .: in a combination of two galleries in parallel flow in the gallery 1 is given by... (QT = Q1 + Q2) ... 111 21  RRReq ...21  RRReq TQ R R R R Q               1 2 1 2 1 1 © Hassan Harraz 2016 194
  195. 195. Whenever possible, you should drive the air by galleries in parallel. The parallel association greatly reduces the value of the equivalent resistance of the passage, so that air convection causes less pressure loss. Example: Calculate the pressure loss caused by passing 50 m3 / s of air with a gallery resistance total R = 0.1 Ns2m-8. Ht = R Q2 ; Ht = 0.1 (50)2 = 250 Pa © Hassan Harraz 2016 195
  196. 196. Example: Suppose that it is possible to parallelize two galleries, each with R = 0.1 Ns2m-8. What pressure drop by passing 50 m3/s ? 21 111 RRReq  821 025.0 4 1.0 4   mNs R Req PaxQRH eqt 5.6250025.0 22  © Hassan Harraz 2016 196
  197. 197. Static power ventilation: It is the product of Ht pressure loss by flow passing in particular gallery section. The static power vent is the mechanical energy per unit of time, associated with flowing air. (SI unit: watt) Pot = Ht Q Note: Static power ventilation (Pot) is not equal to the actual electrical power that will be needed to move a given flow rate. To obtain the actual electrical power, we must still consider PV velocity pressure and the characteristic revenues of fans and motors used in the system. Example: What static power ventilation employed when there is flow of 50 m3/s of air by a gallery in which there is a pressure drop 62.5 Pa? Pot = Ht Q = 62.5 x 50 = 3125 W. © Hassan Harraz 2016 197
  198. 198. General exercises on laws of ventilation: 1 - What is the pressure required for a flow rate of 5 m3 / s of air flow through a circular gallery of 3 m in diameter and 1,200 m in length (k = 0:02 Ns2m-4)? Resp .: 16 Pa. 2 - A gallery 1000 m in length has a 125 Pa pressure difference which pressure ventilation required to obtain the same flow rate when the extent of the gallery is 1800 m.? Resp .: 225 Pa. 3 - When the diameter of a well move from 4 m to 6 m, which required ratio (p2 / p1) in the pressure ventilation to keep the same rate? Resp .: p2 / p1 ≈ 0:13. 4 - A hood which provides 100 m3 / sec and a vacuum of 8000 Pa is replaced with a new offering 18, 000 Pa Calculate the amount of new air that circulates in the mine.. Resp .: 150 m3 / s. 5 - 1000 Pa If are needed to circulate 20 m3 / s, that the pressure required to move 40 m3 / s? Resp .: 4000 Pa. 6 - What is the static power ventilation when 55 m3 / s circulating under 900 Pa pressure? Ans .: 49.5 kW. 7 - moving a mine 120 m3 / s of air at a pressure of 3000 Pa Calculate the equivalent circuit resistance and ventilation power.. Resp .: 360 kW. 8 - Calculate the combined resistance of two parallel galleries with R1 = 3:47 Ns2m-8 and R2 = 12 Ns2m-8. Resp .: 1:46 Ns2m-8. 9 - Two parallel galleries same cross section have 1000m and 500m long. The total air flow is 51 m3 / s. Calculate the flow in each gallery. Resp .: Q1 = 21.13m3 / s; Q2 = 29.87m3 / s. 10 - Calculate the equivalent bore of a mine in which circulates 120 m3 / s, at 2400 Pa pressure ventilation. Resp .: a = 02.03 m2. 11 - For the ventilation circuit of figure below, to determine the equivalent resistance and the pressure (static) required to move a flow rate of 47.2 m3 / s. Finally, calculate the air flow in each circuit section. © Hassan Harraz 2016 198
  199. 199. Resistances (in Ns2m-8): R1=0.0559; R6=0.1453; R2=0.1342; R7=0.1062; R3=0.1118; R8=0.1677; R4=0.0838; R9=0.1509; R5=0.1399; R10=0.0447. © Hassan Harraz 2016 199
  200. 200. Solution: Ra = R4 + R5 + R6 = 0.3689 Ns2m-8 Rb = R7 + R8 + R9 = 0.4248 Ns2m-8 Rc = Ra // R3 (parallel association between Ra and R3) Rc = 0.047 Ns2m-8 Rd = R2 + Rc = 0.1811 Ns2m-8 Re = Rb // Rd (parallel association between Rb and Rd) Re = 0.066 Ns2m-8 circuit equivalent resistance... Rf = R1 + Re + R10 = 0.1666 Ns2m-8 Static pressure to circulate a flow 47.2 m3/s ... H = Rf Q2 = 0.1666 (47.2)2 = 371 Pa. © Hassan Harraz 2016 200
  201. 201. Flow rates in each section : Q1 = Q10 = 47,2 m3/s Q2 = 28,6 m3/s Q3 = 18,4 m3/s Q4 = Q5 = Q6 = 10,2 m3/s Q7 = Q8 = Q9 = 18,6 m3/s © Hassan Harraz 2016 201
  202. 202. Follow me on Social Media http://facebook.com/hzharraz http://www.slideshare.net/hzharraz https://www.linkedin.com/in/hassan-harraz-3172b235 © Hassan Harraz 2016
  203. 203. Lecture 6: Fans Hassan Z. Harraz hharraz2006@yahoo.com Spring, 2016 © Hassan Harraz 2016
  204. 204. 6. Fans  Fans are the devices que Provide the energy required to air for it to move inside the galleries. Fans cause a pressure difference at the mine environment; air moves due to this pressure difference. © Hassan Harraz 2016 204
  205. 205. fans The equipment is designed to move large quantities of air at moderate pressures (usually below 3 kPa). Types of axial and centrifugal fans ... thrust: In such fans, air flow direction is approximately parallel to the rotor axis. It is a device that allows adjustment of the angle of attack of the blades (pitch) of the rotor, providing a significant increase in flow (versatility), depending on the selected pitch for the operation. Are the fans most commonly used in underground mine. © Hassan Harraz 2016 205
  206. 206. Device adjustment of the blade angle of attack (pitch) of the rotor of an axial fan  Axial fans of various sizes and configurations axial fan installed in underground mine © Hassan Harraz 2016 206
  207. 207. Curves fans features:  Each fan type has a set of curves which characterize their performance. There are pressure curves, power and efficiency in line flows produced by the equipment.  Example of characteristic curves  (See next slide) ... © Hassan Harraz 2016 207
  208. 208. A disadvantage of axial fans, centrifugal compared to when operating at high pressures: there is an operating instability zone in its flow rate x pressure characteristic curve, represented by E-D portion in the figure below. Under these conditions (called stall condition), as well as reduced efficiency, there is a tendency of increased vibration in the rotor, causing premature wear of parts. The manufacturer recommends not operate in this range of flow rates. © Hassan Harraz 2016 208
  209. 209. Example characteristic curves of an axial fan, for various angles of attack of the rotor blades. (Obs .: increasing the angle of attack requires greater power of the electric motor, which must be suitably dimensioned). Curves for various angles of attack © Hassan Harraz 2016 209
  210. 210. Curves of an axial fan 75 cv, sold commercially. © Hassan Harraz 2016 210
  211. 211. Some questions about the 75cv fan whose curves appear in the previous slide: - What is the pressure developed by the fan when the flow moved by it's 20 m3 / s? (1 mmWG = 9.81 Pa) Resp .: 200 mmWG (total pressure). - What is the power consumed by the electric fan motor when the flow rate is 20 m3 / s? Resp .: 50 kW. - What is the cost of electricity per day of operation of this fan, assuming it moves 20 m3 / s during the period (24 hours), whereas the value of the energy is R $ 0.20 / kW-h? (Assuming that the power consumed equals power obtained from the mains) Resp .: 0:20 x 24 x 50kW = R $ 240.00. © Hassan Harraz 2016 211
  212. 212. Noise reduction in axial fans: Some situations require noise reduction by the axial fan (ex .: fan installed inside mine; vent near urban areas, ....). In this case, the manufacturers provide devices that reduce the noise emission of the fans. These devices cause some loss of flow, which must be checked with the manufacturer. © Hassan Harraz 2016 212
  213. 213. noise reducing ... Fan © Hassan Harraz 2016 213
  214. 214. Pressures in a fan:  The total pressure (PT) of a fan for a given flow rate, refers to the sum of the static pressure (PS) and the velocity pressure (HP) carried by the machine. PV = PS + PT  Obs .: in the calculation of PV, it uses the air velocity in the machine's rotor output. In English units, PV = (CFM/4005 x Área)2. © Hassan Harraz 2016 214
  215. 215. fans Centrifugal fans: Are devices in which the air penetrates in the direction of the rotor and is discharged radially. Currently, its application in underground mine is linked to the need to obtain high pressures. They are more robust fans (less maintenance), but are of higher cost and do not allow pitch adjustment. © Hassan Harraz 2016 215
  216. 216. Operating Point of a Fan:  It is the balance between the static pressure (PS) supplied by the fan and total pressure loss (Ht) caused during the air flow (then PS = Ht). The operating point defines the operating speed of the equipment in terms of pressure and flow rate when connected to a ventilation circuit.  To obtain the operating point, the mine curve superimposed and the fan characteristic curve on a graph Q x P.  The operating point of a fan may change during operation. It is common changes occur in the ventilation circuit and these changes induce changes in equipment operation point.  Stretches of ventilation circuits cause increased equivalent resistance, so that the fan will respond with flow reducing these changes (... and increased operating pressure).  In other situations, the opening gates or dams will cause the ventilation circuit has a reduced resistance, causing increased flow in fans. © Hassan Harraz 2016 216
  217. 217. Exercise: Calculate the equivalent resistance (REQ) of the ventilation circuit of the figure to the side, considering the losses and the flow of each segment are broken down directly in the diagram. Finding the operating point of the fan characteristic curve which lies in Table A, when connected to the circuit. Pressure static(Pa) Flow rate (m3/s) 500 30 1000 20 1500 2 Table A: characteristic curve of the fan © Hassan Harraz 2016 217
  218. 218. Solution: REQ = RAB + RCD + RDE RAB = 61/(18.8)2 = 0.17 Ns2m-8 RCD = 124/(18.8)2 = 0.35 Ns2m-8 RDE = 88/(18.8)2 = 0.25 Ns2m-8 REQ = 0.17 + 0.35 + 0.25 = 0.77 Ns2m-8 operating point (cf. graphics solution side.): H = 610 Pa (fan pressure) Q = 27 m3/s © Hassan Harraz 2016 218