Principal Tools for a Cleaner Chemical Technology, Process improvements have been tremendous in the last century but production volume increase will overshadow these good results in terms of resource use and environmental impact. It will be important to use the right tools in order to achieve the necessary sustainable development within the industry. These tools should be combinations of exergy analysis, LCA and economic analysis. The focus should be on the development of these combinations and on the teaching of these combinations in engineering curricula.

1. Principal Tools for a Cleaner Chemical Technology
Patrick van Schijndel and Han van Kasteren∗
Faculty of Chemical Engineering and Chemistry
Kunststoffenhuis, Eindhoven University of Technology
PO BOX 513, 5600 MB Eindhoven, The Netherlands
Summary
In our developing world-economy the need for materials and products is growing very fast. This
has an enormous effect on resource depletion and could exceed the ecological capacity of our
planet. A major challenge lies in designing better (chemical) processes, and retrofitting existing
plants. However it is a fact that economies grow much faster compared to efficiency
improvements. As world-wide the attention towards better and cleaner processes grows, also the
understanding of the principles of efficiency and environmental impact of processes becomes
more important. This can be translated into a growing need for objective and certified tools to
assess these processes. This paper focuses on the relationship between exergy, ecology and
economy of chemical processes. The tools used, i.e. LCA, exergy analysis and economic
assessment, are investigated for their usefulness in analysing, retrofitting and optimally designing
(chemical) processes. Combination of the different tools can provide more information on the
overall sustainability of processes. Therefore more attention to combination of tools in all
engineering curricula besides or integrated in the general sustainability courses should be given.
Introduction
In order to reach a sustainable society, large efforts are requested from scientists and engineers.
These are necessary to improve production chains and processes in the (chemical) industry.
However defining sustainable production is difficult. For an easier interpretation and decision
making a single sustainability indicator is necessary. However, such an indicator does not exist at
the moment. Instead of energy efficiency it is better to use exergy efficiency as it is linked with
thermodynamics and gives more information on potential process improvements. Furthermore it
has been standardised and it has been suggested that exergy efficiency would be a good candidate
for a single sustainability indicator.
According to Brundtland most important criteria for a sustainable process are:
1. More efficient use of resources, measured by thermodynamic perfection.
2. Overall decrease of emissions, harmful for humans and eco-systems.
3. Increased ratio of renewable resources against non-renewable resources.
4. Closing of cycles, taking into account the other 3 aspects.
If these criteria are used in the design of better processes it means different tools have to be used
of which the most important are exergy analysis and environmental Life Cycle Assessment. As in
the case of the design and improvement of industrial processes also economical evaluations have
to be performed. This paper will describe the use of these indicators and possible combinations to
achieve a valid sustainability tool for industrial processes.
Sustainable Process Chains
Thinking in terms of life cycles started since the energy crises in the seventies. The idea was that
the environmental burden of a product is not only situated at the actual production step but also in
the other stages of production and utility generation. For a product a simple life cycle is shown in
Figure 1.

Tel. + 31 40 247 5435; Fax: + 31 40 2475430
E-mail address: j.m.n.v.kasteren@tue.nl

2. An environmental Life Cycle Assessment of a product determines the environmental impact of all
phases in the product life cycle calculated for a certain functional unit. Every process step has to
be investigated by determining all inputs and outputs, like shown in Figure 2.
Figure 1. Process chain Figure 2. Black box model for a single process
Several authors have proposed to combine the LCA with exergy analysis of the whole product
chain, because cumulative exergy efficiency gives an indication of total resource depletion. This
is only the case if all exergy losses are connected to non-renewable exergy resources.
Exergy, Ecology and Economy
A Combination of exergy efficiency, environmental impact and an economic evaluation, the 3
E’s, would be a good indicator for sustainability according to its definition (Rivero 1997).
Exergy analysis tool
In process analyses it is important to use good defined exergy efficiency definitions (Van
Schijndel 1998). The second law efficiency of a process is the ratio of all exergy streams out and
in (Ex out / Ex in). The Fratzcher or real efficiency is defined as the ratio of utilisable product
streams and exergy in, equation 1 (Sorin, 1998):
in
ext
in
u
real
Ex
DI
1
Ex
Ex +
−==η (1)
If a larger part of the exergy input is not transformed into the useful products, it is better to use
the utilisable exergy coefficient, ηu,tr:
utrin
utrextu
u
ExEx
ExDEx
,
,
−
−−
=η (2)
In most cases it is advisable to use real or utilisable exergy efficiency instead of the second law
efficiency because the main interest lies in the efficiency in which an utilisable product is
produced. Since all production routes are linked and because thinking in cycles is getting large
attention it is obvious that cycle efficiencies should be introduced in exergy efficiency
calculations too. Szargut (1990) defined the cumulative degree of perfection as ratio of specific
exergy and CExE:
CExE
Exu
CExE =η
(3)
CExE is the consumption of exergy of natural resources in all links of a technological
manufacturing network leading from raw materials to a product. The exergy efficiency calculated
in this way also takes the upstream processes into account, which can also be extended into a full
LCA.
Some other extensions to the exergy analysis method should be made to make it more useful for
engineers working on process improvements. One important issue is to distinguish between
renewable and non-renewable exergy streams. Renewable streams, for instance solar light, wind
and biomass can be zero depletion resources. Although renewables can cause environmental
problems, the exergy losses in using renewed resources are less problematic compared to exergy
losses in non-renewable resources in terms of sustainability. A ‘renewed exergy index’ can be
raw material
extraction
material
production
final
production
use of
product
waste
processing
recycling final
waste
Process
Useful Energy
Resources
Product(s)
Wastes
Materials
and
Waste Energy
Emissions

3. defined focusing on the fact that renewed exergy streams are ‘free’ because they are generated in
a certain amount per annum:
( )renewedin
u
Ex-Ex
Ex
indexexergyRenewed =
(4)
In this equation the Exrenewed should be the net cumulative renewed exergy in. This index can be
larger than one as explained in Table 1.
Table 1. Renewed exergy index
Inde
x
Explanation
<<1 very small efficiency, low use of
renewable exergy
<1 small efficiency, low use of
renewables
= 1 fossil exergy input equals exergy
value of product (no net fossil loss)
>1 highly efficient process, high ratio
of renewables
>>1 Reversible process without waste,
large input of renewables
Biomass as sustainable resource
Plant biomass is used as both an energy carrier and a raw material (construction material,
resource for chemicals, paper production). World wide about 15% of energy use is accounted for
as biomass. Last 10 years research on biomass as feedstock has received renewed attention in an
effort to decrease the use of fossil fuels (fossilised biomass). By using biomass instead of fossil
fuel the net amount of CO2 emitted into the atmosphere will be less. Another reason to use
biomass is its composition. Biomass contains less S and N compounds compared to oil and coal,
which means their combustion, can be less environmentally unfriendly.
However, these advantages should not be generalised without a proper analysis. Biomass needs a
large ground surface to be grown (250 GJ poplar wood per hectare⋅annum as stated by
Schaidhauf, 1998). Still with increasing productivity of agricultural food production the available
area for extra biomass production is growing every year in the western world. Also, it is known
that in growing 10 MJ of biomass a fossil fuel input of about 3,5 MJ is needed through the
process chain i.e. transport, tractors, fertilisers and pesticides production. Still the switch from
fossil based to biomass resources will cause a net reduction in CO2 emissions, however not for the
full 100%. Furthermore Haberl and Geissler (2000) state that an increased use of biomass can
disturb biochemical flows (i.e. nitrogen and carbon) and decrease biodiversity regionally. Also
extended use of natural biomass sources leads to over cutting and overgrazing causing soil
erosion and related environmental problems. Because large amounts of bio waste, about 10% of
commercial energy supply, are not being used at the moment, the use of these wastes could be a
first answer to these disadvantages.
Economic evaluation
Nowadays economy is based upon ‘free’ trade and costs being determined by demand and supply.
The free economy works very well in determining prices. However many scientists argue that
certain costs are not being reflected in these prices. It is true that the price of using ecological
services like trees cleaning the air, the capacity of soil to filter groundwater, photosynthesis, and
different cycles are kept outside the classical economy. Parts of these ecological services are
being damaged by economic activities through emissions to water, soil and air, use of surface etc.
Therefore there is a need to combine both systems and internalise them. It is estimated that total
global national product lacks about 50% of money due to ecological services not accounted for.

4. However these calculations are very difficult and only give some feeling on the fact that the
economy would come to a total halt without ecological services.
The big question remains on how to internalise environmental costs in our economy. Costs to be
specified are pollution via emissions and the use of resources, which is sometimes calculated as
the entropy production or exergy loss. The costs of emissions on the environment are clear, like in
health problems, corrosion of iron and concrete structures, and damage to eco systems. But the
financial quantification of these costs is difficult. Another way to calculate costs caused by
emissions is via cleaning up costs. This can be done for instance for oil spills. But these clean up
costs are also hard to quantify. A compromise solution is to calculate prevention costs, which are
made up by the different costs of cleaner technology and end-of-pipe solution needed to cut
emissions to a more sustainable level. It is easy to understand that prevention costs are lower than
clean up costs or costs of ecological damage. For use in The Netherlands Vogtländer (2000) has
determined prevention costs for some important environmental impact categories as shown in
Table 2.
Table 2. Marginal prevention costs for important environmental impact categories
Environmental Impact Category Marginal prevention costs*
In € / kg equivalents
Acidification 6,40 € / kg SO2
Eutrophication 3,05 € / kg PO4
Summer smog 50,00 € / kg VOC
Winter smog 12,30 € / kg fine dust
Heavy metals 680 € / kg Zn
Carcinogenics 12,30 € / kg PAH
Global warming 114 € / 1000 kg CO2
*
Data calculated for Dutch situation
Environmental prevention costs can be applied to compare environmental impact of different
techniques. It is also possible to check the real economic feasibility of environmental solutions.
The calculation of depletion costs is very difficult. A certain amount of exergy is produced on
earth ‘for free’, which is called renewable. This should be left out of depletion cost calculations.
A possible way to calculate the depletion costs is by coupling the exergy values of the resource
with the price of fossil fuels. However the price of fossil fuels is not depending on the actual
proven reserves but on a ratio between production capacity and anticipated or actual demand for
oil. As oil reserves are proven to be well beyond 10 years from now there is no real effect on its
price other than a sort of psychological effect and some extra costs due to increasing complexity
of oil extraction techniques used. By combining the prevention costs, raw materials costs and
depletion costs a sort of combined triple E model based on economics can be established, which
is useful as a sustainability indicator.
Industrial cases
Within major industries there have been important developments world-wide like:
- Increase in production (see Figure 3), especially in major developing countries like China.
- Efficiency improvement and decrease of specific environmental impact mainly by instalment
of new technology.
- Overall strong increase of electricity production
- Overall strong increase in use of fossil fuels and raw materials

5. Figure 3. Total world production of some important metals and minerals
Exergy analysis of some chemical processes as carried out by Hinderink (1999) show that the
process industry still has enough potential for improvements, as shown in the adapted Figure 4.
Figure 4. Exergy losses during production of important commodities
The conclusion is that most processes have become more efficient but due to the enormous
growth (potential) the use of resources, fossil fuels and the environmental pollution has increased.
Although new technology is available many older plants remain in function and are not being
upgraded due to lack of funds or lack of government intentions and environmental law
enforcement.
Case study 1: Simple economical and environmental decision model
Biomass as a sustainable energy source within The Netherlands
This study was done to find the best technique of generating electricity using biomass in respect
of economy and the environment (van Schijndel, 1999). The available land surface within The
Netherlands is too small to make biomass farming a very large and attractive activity in the near
future. However different biomass waste streams are available in high enough quantities to built
small-scale power plants or to co-combust biomass in existing power plants. First a preliminary
literature survey was carried out to find out possible techniques for using biomass waste to
generate electricity and ranking them according to technology and market perspectives.
For the Dutch situation following top 5 ranking of techniques was found:
1. Co-combustion of biomass in a pulverised coal power plant with steam cycle.
2. Gasification of biomass in an atmospheric fluidised circulating bed and co-firing the gas in a
natural gas steam boiler system.
3. As 3 but with co-combustion of the gas in a natural gas fired combined cycle system.
0
1000
2000
3000
4000
5000
aluminium
copper
cement
methanol
polyethylene
ammonia
nitricacid
urea
hydrogen
oxygen
Exergy[kJ/mole]
exergy loss
exergy of steam-credit
exergy of product
0
400
800
1200
1600
1950 1960 1970 1980 1990 2000
Year
MillionMetrictonsperyear
0
400
800
1200
1600
Thousandmetrictonsperyear
Cement
Steel
N fertilizer
P fertilizer
Aluminium
cement
steel
N fertilizer
P fertilizer
aluminium

6. 4. As 3 but with stand-alone combustion of the gas in a combined cycle system.
5. Atmospheric stand-alone fluidised bed combustion with steam cycle system.
Three of the best-ranked techniques (1,4 and 5) were evaluated on their environmental impact
using a functional unit based upon exergy. The functional unit was defined as: Thermal treatment
of an amount of biomass equal to 966 TJ calorific value (LHV) and joined production of 424,80
TJ electricity in one year. An elaborate discussion can be found in the Entrée 1999 proceedings
(Van Schijndel 1999).
The results of the LCA on the three alternatives in Figure 5 show that the process with highest
exergy efficiency, namely co-combustion with coal, also scores best on environmental impact. In
Figure 5 the LCA scores are calculated using eco-indicator ’95 method. High scores mean high
environmental impact.
Figure 5. Results in Eco-Indicator 95 points for environmental comparison of techniques
It can be concluded that in the case of power production the exergy efficiency has a large impact
on the outcome of the LCA. A consequent ranking of technical, economical and environmental
issues is a good way to choose a sustainable option.
Case study 2: Eco costing method as a tool to internalise environmental burden
Production of container glass
The production of container glass involves basic chemicals like sand and sodium carbonate and a
large input of fossil fuels. The high temperature glass melting process has been improved
tremendously over the years by technical improvements of the kiln, re-use of exhaust gases and
not least the recycling of glass, see Figure 6.
Figure 6. Historical development of specific fuel use in container glass production
Using exergy analysis and an AspenPlus simulation model a process improvement using fuel
reforming through exhaust cooling, chemo-recuperator (TCR), has been investigated. LCA was
combined with the emission prevention methodology (Table 2) in order to calculate the total costs
for container glass production for a standard glass kiln and improved processes.
When environmental issues are internalised within the ‘normal’ production price of standard
container glass, the eco costs of emissions are about 66%. Raw material and fuel costs per kg of
glass equal about 0,09 €, environmental protection costs are much bigger since they are about
0,18 € per kg of glass. For the two types of kiln eco cost calculations are shown in Figure 7
0,00
20000,00
40000,00
60000,00
80000,00
100000,00
120000,00
140000,00
MSW incineration Co-combustion Combustion Gasification
Solid
Energy
Pesticid
S.smog
W.smog
Carcin.
H.metals
Eutroph.
Acid.
Ozone
Greenhouse
0
10
20
30
40
50
1920 1940 1960 1980 2000
specificfueluse(GJ/tonglass)

7. In this Figure, BAT stands for best available technique or best available glass kiln system. When
hydrogen is used, for instance from biomass, the eco costs are much lower. The new TCR kiln
natural gas fired system also has a better eco costs score almost equal to the hydrogen-fuelled
system. The high eco costs compared to raw materials used are clearly shown in the figure. Use of
this prevention costs model, the triple E model, can be a good one number indicator for process
improvement studies or comparison studies. The figure also shows that the ecological impact is
not solely determined by the exergy (fuel) efficiency.
Figure 7. Results for triple E costs of glass production (Van Schijndel 2000)
Besides emission also the depletion of resources should be quantified. It is hard however to
quantify the costs for depletion. A possible pricing method can be pricing the exergy value of a
resource and linking it to a specific price for instance the price of fossil fuels.
Case study 3: Relationship between exergy efficiency and environmental impact
Cement industry
This industry is a great importance for world-wide economical development as it forms the basis
for concrete, main material for buildings and other civil constructions. Figure 3 shows the
tremendous volume growth in cement production. China and India mainly caused the growth in
the nineties. The efficiency of cement making for new plants lies around 50% as shown in Figure
4, however many plants in operation are outdated and their efficiency lies around 40%. Main
environmental effects in cement making are pollution by dust particles, SO2, NOx and CO2. Large
amounts of CO2 are produced by fossil fuel combustion but also due to decomposition of the
calcium carbonate. The relationship between the exergy efficiency (eq. 1) of an oil-fired cement
kiln and the CO2 emissions is shown in Figure 8.
Figure 8. Relationship between CO2 emission and exergy efficiency of a cement kiln
0
0,05
0,1
0,15
0,2
0,25
0,3
3Ecosts(€/kgglass)
BAT gas BAT hydrogen TCR low TCR high
Environmental
Fuel
Raw materials
0,65
0,75
0,85
0,95
1,05
20 30 40 50 60 70
Exergy efficiency
CO2emission[kg/kgclinker]

8. A life cycle over the cement plant itself shows that the production phase has a much larger impact
compared to construction and demolition phase (i.e. over 90%). As a large part of external exergy
losses are caused by heat radiation most important developments have been the enlargements of
the production facilities. In Japan the hot flue gases are used for electricity generation, in other
countries these energy savings are economically non-feasible due to low electricity prices. Exergy
analysis in combination with LCA has been used to compare three plants (two in Tanzania and
one in South Africa) on their efficiency, environmental impact and low cost improvement
options. Upgrading dust filters and decreasing driving forces are the most important improvement
options. More attention also should be on the milling and grinding of the resources and final
product as their efficiencies are very low.
Figure 9. Influence of electricity generation on environmental impact of cement production
Results for the influence of exergy efficiency and choice of fuel for electricity generation on the
environmental impact are given in Figure 9. The influence of the type of electricity generation on
the environmental impact is higher than the increase of exergetic efficiency of the cement kiln.
This result clearly illustrates the importance of chain analyses when improving a process.
Results and discussion
Different tools have been introduced and discussed in the case studies. Most tools are known
although the combined use of them has not become general practice yet in industry and in the
engineering companies. Therefore focus on combination of these tools should be an important
issue in engineering education. The relationship between exergy efficiency on one hand and
environmental impact on the other hand is not very clear. Therefore exergy analysis is not a good
sustainability indicator. Another important aspect is the way renewable resources are used in
exergy analysis. As renewable streams do not deplete resources they should be treated different
from non-renewable exergy streams, like in a sort of renewed exergy index.
Conclusions
Process improvements have been tremendous in the last century but production volume increase
will overshadow these good results in terms of resource use and environmental impact. It will be
important to use the right tools in order to achieve the necessary sustainable development within
the industry. These tools should be combinations of exergy analysis, LCA and economic analysis.
The focus should be on the development of these combinations and on the teaching of these
combinations in engineering curricula.
Nomenclature
Dext external exergy loss (kJ)
Ex exergy value (kJ)
ExRenewed renewable exergy (kJ)
Extr transiting exergy (kJ)
Ex u total utilisable exergy output (kJ)
References
Haberl, H. and Geissler S., 2000, “Cascade utilization of biomass: strategies for a more efficient use of a
scarce resource”, Ecological Eng., Vol 16, pp. S111-S121.
200
300
400
500
600
700
800
0,20 0,30 0,40 0,50 0,60 0,70
Exergetic efficiency [%] (Fratscher)
Environmental impact [ micro ecopoints ]
PPC
Pretoria
TangaTPCC
Dar es Salaam
fuel mix
coal
electricity NL
hydro power

9. Hinderink, P., Swaan Arons J.d. and Kooi, H. v.d., 1999, “On the efficiency and sustainability of the
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Personalia
The author;
Patrick van Schijndel studied chemical engineering at the Eindhoven University of Technology
(TU/e) and graduated in 1994. He got his teaching degree in chemistry at TU/e in 1995. Since
1996 he is working on his PhD thesis in the field of cleaner production. He combined this work
with setting up a MSc. course and several research projects in environmental technology at the
University of Dar Es Salaam in Tanzania. He will receive his PhD degree in the beginning of
2002. In November 2001 he joined the Kunstoffenhuis group at the Dutch Polymer Institute
(DPI) as process designer and environmental consultant.
The co-authors;
Han van Kasteren studied chemical engineering at TU/e and in 1990 he received his PhD degree.
In 1990 he worked at the Inter-University Environmental Institute Brabant (IMB). From 1991 he
started working as assistant professor at the TU/e, in the field of environmental technology. From
1996-1999 he was director of the Polymer-Recycling Institute, PRI at the TU/e. At PRI economic
and technical feasibility studies of the recycling of wastes are carried out. Since 1999 he is
director of the Kunstoffenhuis at TU/e. The Kunstoffenhuis is the intermediate between the
polymer industry and knowledge institutes. Several projects running are: recycling of toner waste,
small-scale plastic waste gasification and design of environmental friendlier products in the
electronic industry.
Address:
Kunststoffenhuis, Faculty of Chemistry and Chemical Engineering
Eindhoven University for Technology, P.O. Box 513, 5600 MB Eindhoven
The Netherlands; Tel. + 31 40 247 5435; Fax: + 31 40 2475430
E-mail address: j.m.n.v.kasteren@tue.nl

10. Photos of both authors are placed in a separate file!