Environmental Engineering Reference
In-Depth Information
with the highest recovery of toluene from the gaseous stream. The acid rain potential,
I ARP , shows a slow steady increase with oil flow rate and relates only to the increased
process utilities emission of NO x at high oil flow rates. The optimum value appears
to be about 100 kg mol/h for this case. The noncarcinogenicity indices, I INGTP and
I INHTP , show similar behavior and decrease considerably above 100 kg mol/h oil flow
rate. The reductions in inhalation and ingestion toxicity are both related to the removal
of benzene and toluene from the process waste stream that would otherwise enter the
general environment. Thus, a single value of oil flow rate, which minimizes the overall
environmental index, appears to be not realizable. However, a value between 50 and
100 kg mol/h appears to be a good compromise for the process.
Note that in the above illustration of green engineering principles, we have utilized
concepts from Chapters 2 and 3 in the estimation of physicochemical properties
of chemicals and the fugacity Level II model to obtain the environmental F&T of
chemicals. Additionally, in the more general case of fugacity Level III model, we
will also have to utilize rate constants in air, water, and soil that were the topics of
Chapter 5. This should serve as another application of the basic concepts of chemical
thermodynamics and kinetics in environmental engineering that we have touched
upon in this topic.
6.6.2 L IFE C YCLE A SSESSMENT
Another important aspect of green engineering is the so-called LCA. This process
involves following the so-called “cradle-to-grave” cycle of any component within a
complete manufacturing, usage, and disposal of a product. This is best illustrated in
Figure 6.77.A material such as, for example, a metal is used in several manufacturing
operations. One follows the metal from its raw material supply chain to the production
process, and further to the usage of the product in several forms. Ultimately, the
manufactured products are disposed after use. During the various stages, we have the
Emissions to air, soil or water
Inputs
Raw
material
supply
Products
Production
Usage
Disposal
Recycle
Remanufacture
Reuse
Life cycle analysis (LCA)
FIGURE 6.77 Steps in the life cycle assessment for a metal.
 
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