Energy is required not only for unit operations and processes in a chemical plant, but also for treating the waste generated. One could argue that waste treatment and disposal are just another type of process, but given the importance of their environmental impacts, and to better analyze the impacts, it warrants a separate discussion. Figure 18.10 shows some of the types of energy requirements associated with typical waste disposal methods.
Some treatment methods can be very energy intensive. Hence techniques to increase the manufacturing efficiency and reduce waste in general will not only have an impact on the waste amounts, but also on the energy and energy-related impacts generated during the treatment operations. We cover impacts from waste treatment in more detail in Chapter 19.
PROBLEMS
18.1 We discussed the fact that the high heat value (HHV) of natural gas is in general between 53 and 54 MJ/kg of natural gas, while its low heat value (LHV) is about 48 MJ/kg of natural gas. Estimate these amounts using combustion enthalphy. As a first approximation, assume that natural gas is 100% methane.
18.2 You are performing a life cycle inventory for the manufacture of a specific chemical.
How would you decide on what type of energy data to use?
18.3 Provide an example of when the energy required for purification or separation might be the dominant contributor to the total energy requirements.
18.4 Provide an example of a chemical process that utilizes fuels (oil, natural gas, coal) directly in the process.
18.5 Investigate the electricity mix for the area in which you live.
18.6 Provide examples of 10 other parameters that typically would be included in a LCI of energy sources.
18.7 The energy given the Table P18.7 is required to produce 1000 kg of benzyl chloroformate on a gate-to-gate basis.
Estimate the major emissions related to:
(a) Electricity production (b) Refrigeration systems (c) Steam production (d) Cooling water (e) Energy requirements
TABLE P18.7 Energy Requirements Energy Requirement
MJ/1000 kg Benzyl Chloroformate
Cooling water 192
Electricity 127
Refrigeration 564
Steam 106
(a) Global warming potential (b) Acidification potential (c) Eutrofication potential
(d) Photochemical ozone creation potential (e) Energy-related resource consumption
18.9 It has been estimated that there is a potential to recover a total amount of energy equivalent to 40.8 MJ/1000 kg of benzyl chloroformate. Repeat Problem 18.7 accounting for this energy recovery.
18.10 Repeat Problem 18.8 accounting for the 40.8 MJ/1000 kg of benzyl chloroformate of potential energy recovery.
18.11 The energy given in Table P18.11 is required to produce 1000 kg of benzyl chloroformate on a cradle-to-gate basis.
How much energy is required for the benzyl chloroformate on a gate-to-gate basis?
18.12 Repeat Problem 18.11 but account for the 40.8 MJ/1000 kg potential energy recovery from benzyl chloroformate on a gate-to-gate basis and a potential energy recovery of 7690 MJ/1000 kg of benzyl chloroformate on a cradle-to-gate basis.
18.13 Estimate the following environmental impacts of a typical organic chemical:
(a) Global warming potential (b) Acidification potential (c) Eutrofication potential
(d) Photochemical ozone creation potential (e) Energy-related resource consumption
18.14 Estimate the following environmental impacts of a typical inorganic chemical (a) Global warming potential
(b) Acidification potential (c) Eutrofication potential
(d) Photochemical ozone creation potential (e) Energy-related resource consumption
TABLE P18.11 Energy Requirements Energy Requirement
MJ/1000 kg Benzyl Chloroformate
Cooling water 1.01104
Electricity 3.63103
Refrigeration 5.78102
Steam 8.82103
REFERENCES
1. U.S. Environmental Protection Agency.eGRID2007 Version 1.0 Year 2005 Summary Tables.
U.S. EPA, Washington, DC, 2008.
2. U.S. Environmental Protection Agency.Emissions and Generation Resource Integrated Data- base(eGRID)for 2007. Prepared by E.H. Pechan & Associates, Inc. Contract EP-D-06-001. U.S.
EPA, Washington, DC, Sept. 2008.
3. North American Electric Reliability Corporation. http://www.nerc.com/, accessed Dec. 30, 2008.
4. Baumann, H., Tillman, A.-M.The Hitch Hiker’s Guide to LCA. Studentlitteratur, Lund, Sweden, 2004.
5. Kim, S., Overcash, M. Energy in chemical manufacturing processes: gate-to-gate information for life cycle assessment.J. Chem. Technol. Biotechnol., 2003, 78, 995–1005.
6. Jimenez-Gonzalez, C., Kim, S., Overcash, M. Methodology for developing gate-to-gate life cycle inventory information.Int. J. Life Cycle Assess., 2000, 5, 153–159.
7. Perry, R. H., Green, D. W., Maloney, J. O. Perry’s Chemical Engineers’ Handbook, 7th ed.
McGraw-Hill, New York, 1997.
8. Jimenez-Gonzalez, C., Overcash, M. Energy sub-modules applied in life cycle inventory of processes.J. Clean Products Process., 2000, 2, 57–66.
9. Griffin, E., Overcash, M.Unit Process Life Cycle Inventory (LCI) Heuristic 201: Heating and Cooling.Chemical and Biomolecular Engineering Department, North Carolina State University, Raleigh, NC, 2005.
10. Griffin, E., Overcash, M.Unit Process Life Cycle Inventory (LCI) Heuristic 117: Refrigeration Systems.Chemical and Biomolecular Engineering Department, North Carolina State University, Raleigh, NC, 2004.
11. Ecoinvent database, http://www.ecoinvent.com/, accessed Dec. 30, 2008.
12. Kim, S., Overcash, M. Unit Process Life Cycle Inventory (LCI) Heuristic 01: Electricity Emissions.Chemical and Biomolecular Engineering Department, North Carolina State Univer- sity, Raleigh, NC, 2001.
13. SIMAPRO, Life Cycle Analysis Software. PRe Consultants, Amersfoort, The Netherlands, 1998.
14. Bundesamt f€ur Umwelt, Wald und Landschaft.O¨kobilanzen von Packstoffen. Schriftenreihe Umwelt 132. BUWAL, Bern, Switzerland, 1991
15. PEMS,Life Cycle Analysis Software. Pira International, Surrey, UK, 1998.
16. ECOPRO, Life Cycle Analysis Software. EMPA (Swiss Federal Laboratories for Material Testing and Research), St. Gallen, Switzerland, 1996.
17. Dumas, R. D.Energy Usage and Emissions Associated with Electric Energy Consumption as Part of a Solid Waste Management Life Cycle Inventory Model. Department of Civil Engineering, North Carolina State University, Raleigh, NC, 1997.
18. Griffin, E., Overcash, M. Unit Process Life Cycle Inventory (LCI) Heuristic 08: Steam for Industrial Sources from Fuel(50% using natural gas and 50% using fuel oil). Chemical and Biomolecular Engineering Department, North Carolina State University, Raleigh, NC, 2002.
19. Goodwin, K. Griffin, E.Unit Process Life Cycle Inventory (LCI) Heuristic 100: Boiler Efficiency.
Chemical and Biomolecular Engineering Department, North Carolina State University, Raleigh, NC, 2002.
20. Cohen-Hubal, E. A. Net Waste Reduction Analysis Applied to Air Pollution Control Technologies and Zero Water Discharge Systems. M.S. thesis, North Carolina State University, Raleigh, NC, 1992.
22. Overcash, M.Unit Process Life Cycle Inventory (LCI) Heuristic 05: Natural Gas Combustion.
Chemical and Biomolecular Engineering Department, North Carolina State University, Raleigh, NC, 2002.
23. Walas, S. M. Rules of thumb selecting and designing equipment.Chem. Eng., 1987, 75–81.
24. Smith, J. M., Van Ness, H. C.Introduction to Chemical Engineering Thermodynamics. McGraw- Hill, New York, 1975, p. 515.
25. Woods, D. R.Process Design and Engineering Practice. Prentice Hall, Upper Saddle River, NJ, 1995.
26. DowTherm and SylTherm Heat Transfer Fluids. Form No. 176-01-545. http://www.dow.com/
heattrans/app/chem.htm, accessed Dec. 31, 2008.
27. Jimenez-Gonzalez, C., Overcash, M. LCI of refinery products: review and comparison of commercially available databases.Environ. Sci. Technol., 2000, 34(22), 4789–4796.
19