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PRES.pptx

  1. 1. Introduction Title: Boiler Control Systems Jardel Harper Keegan Paul
  2. 2. Scope of Presentation.  Definition and explanation of Boilers, its common equipment and a control schemes used in boiler control operations.  Explanation of the principles of the combustion process.  Evaluation of types of control schemes.  Explanation of shrink/well phenomenon and its effects on boiler level control.  Design and evaluation of boiler level control schemes.
  3. 3. Boiler.  Boilers are systems used to heat a fluid (usually water) in a closed vessel. It can be boiled, heated, or vaporized. You can then use the outcome for various purposes or heating applications.
  4. 4. Components of a boiler.  Burner- this is where air mixes with the fuel source and combusts.  Combustion Chamber- this is where fuel is burned to heat the water  Heat exchanger- this transfers the heat produced by the burners within the combustion chamber.  Controls- allows the used to set water temperature, air and fuel supply mixture, internal pressure and ignition  Supply and return line- supplied line lead from the boiler and deliver the heated water or steam to distribution points, return lines bring the water back to the boiler  Circulator pump-the component that pushes the hot water out through the supply lines to the distribution lines.  Exhaust Stack- is designed to safely expel spent fuel away from the building’s exterior.
  5. 5. Combustion.  Fire is the visible effect of the process of combustion – a special type of chemical reaction. It occurs between oxygen in the air and some sort of fuel. The products from the chemical reaction are completely different from the starting material.  Combustion is when fuel reacts with oxygen to release heat energy.
  6. 6. Types of combustion schemes.  The three basic types of combustion control schemes are:  Single-point positioning.  Parallel positioning.  Metering.
  7. 7. Single- Point positioning.  This is also a single PID loop. The main jackshaft is modulated based upon the firing-rate demand. This, in turn, moves the air and fuel linkage arms, opening and closing the air damper and fuel control valve.
  8. 8. Parallel Positioning Combustion Control.  Like single-point positioning combustion control, this is also a single PID loop. Parallel positioning controls help a burner to optimize its fuel-to-air ratio by using dedicated motorized actuators for the fuel and air valves.
  9. 9. Metering Combustion Control.  The air and fuel devices are driven by individual actuators and now air and fuel flow meters are added. Metering combustion control is disclosed in which both the fuel flow rate and the combustion air flow rate are metered in a desired ratio corresponding to a master firing rate demand.
  10. 10. • Comparison of the three.  A single-point positioning scheme is the least expensive and simplest system available while a metering scheme is the most costly and complex. It also is the most efficient option.  A parallel-positioning scheme falls right in the middle of the two regarding cost and complexity.  A metering scheme is the best system for boiler efficiency.
  11. 11. SWELL AND SHRINK.  Steam flow from the boiler is controlled by the downstream process. A sudden increase or decrease in steam flow changes the pressure in the steam drum and boiler circuit. The change in pressure will cause a change in both the boiling point and density of the water and steam. These combined reactions will cause the level in the steam drum to increase or decrease rapidly. The increase and decrease in the water level caused by the pressure change are commonly referred to as the swell and shrink reactions.
  12. 12. Drum level control systems.  The three basic types of drum level control systems are:  Single element.  Two element.  Three element.
  13. 13. Single element.  This consists of a proportional signal coming from the drum level transmitter. This signal is compared to a setpoint, and the difference is a deviation value.
  14. 14. Two element. • Consist of two elements. • Level Element: a proportional signal coming from the drum level transmitter. This signal is compared to a setpoint, and the resultant is a deviation value. This signal is acted upon by the controller which generates corrective action in the form of a proportional value. • Steam Flow Element: a mass flow rate signal is used to control the feedwater flow, giving immediate corrections to feedwater demand in response to load changes.
  15. 15. Three element.  Consist of three elements  1. Level Element: corrects for unmeasured disturbances within the system.  2. Steam Flow Element: corrects for unmeasured disturbances within the system.  3. Feedwater Flow Element: responds rapidly to variations in feedwater demand.

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