A hierarchical decision procedure for the conceptual design of pollution prevention alternatives for chemical processes

• Main Author: Schultz, Michael Anthony
• Language: ENG
• Published: ScholarWorks@UMass Amherst 1998
• Subjects: Chemical engineering|Management|Environmental engineering
• Online Access: https://scholarworks.umass.edu/dissertations/AAI9909218

The need for a procedure to design chemical plants for pollution prevention results from a recent emphasis on pollution prevention at the source. The conceptual design procedure of Douglas (1985) has been extended to consider process alternatives for pollution prevention. Waste penalties become another criteria in the economic evaluation of flowsheet alternatives. New heuristics are presented that lead to process alternatives that reduce or eliminate waste streams. Twenty processes comprising a total of 79 individual plants have been studied, and their waste loads have been summarized. This analysis shows that the majority of the waste from chemical processes can be classified as either waste from the reaction chemistry or waste from the separation system. Because much of this waste is waste water, water reuse should be considered to reduce the total waste load. The aqueous waste load from these twenty processes could be reduced by an average of 63% if all fresh water streams could be replaced with recycled water. By identifying the decisions having the greatest impact on waste loads in a chemical processes, alternative decisions for pollution prevention can be made, leading to alternative flowsheet designs. This is shown through a discussion of the styrene process, in which flowsheet alternatives using steam as a heat carrier are compared to those using either methane or toluene. Several feasible flowsheets are for each case, each having roughly the same economic potential. Heat integration should be considered to identify to best few candidates for a more rigorous design. The StreamCosts screening method targets wasteloads resulting from the reaction chemistry, by screening reaction pathway alternatives based on the costs of the feed and exit streams, including the waste penalties. Those pathways with large amounts of waste byproducts can be eliminated early in the design procedure. Finally, the PIPII computer package has been extended for pollution prevention. The production of Bis (2-Hydroxyethyl) Terephthalate serves as a case study to demonstrate the use of the code. The total waste penalty of 58.5 MM$/yr for the base case alternative leads to an economic potential of $-$47.3 MM\$/yr, showing a strong incentive for waste reduction.