Abstract
P2TCP (Pollution Prevention Tool for Continuous Processes) is a computer-based system, developed to help designers systematically identify pollution prevention opportunities. The tool is applicable for continuous chemical processes and can be used during conceptual as well as retrofit design, thus facilitating the development of inherently cleaner processes. Unlike other systems, case studies are used to validate P2TCP and to identify further extensions, not as the principal knowledge source.

P2TCP is based on a novel design approach. Unlike hierarchical or step-wise design techniques, heuristics (knowledge based rules) are used to analyze each system of a chemical process (reaction and separation) independently for potential alternatives.
Effects associated with the interacting streams, i.e. streams leaving the reaction system and potential recycles, are then taken into consideration to further reduce the number of options requiring consideration.

The effectiveness of this heuristic based approach has been demonstrated in a number of pollution prevention case studies. Unlike hierarchical techniques, it is theoretically possible to consider all alternatives. Furthermore, the case studies demonstrate that the number of design alternatives requiring consideration is not inhibitive.
 

Introduction
Throughout the life span of a chemical manufacturing process, opportunities can be identified to reduce environmental impacts caused by the consumption of energy and the generation of wastes. In terms of intrinsic waste generation and energy consumption, modifications to a design are typically most effective during the conceptual stages. However conceptual design is often limited in terms of resource constraints and driven principally by economic considerations. The identification of pollution prevention opportunities is not typically practiced consistently or routinely (From 1992, Hethcoat 1990). In this paper, the prototype of the Pollution Prevention Tool for Continuous Processes (P2TCP) is presented. P2TCP is a computer-based system, developed to help designers systematically identify and compare design alternatives in the context of pollution prevention (Pennington 1997, Pennington & Yue 1998a).

P2TCP incorporates an expert system that was developed using chemical engineering principles to help designers systematically identify process modifications that may reduce energy consumption and waste generation. Unlike other tools, case studies are used for validation and to identify further extensions of the expert system, not as the principal knowledge source. The tool is applicable for continuous chemical processes and can be used during conceptual as well as retrofit design therefore facilitating the development of inherently cleaner processes.

Hierarchical or step-wise approaches are often used for the rapid synthesis of Process Flow Diagrams (PFDs). However using these approaches may not result in the identification of all feasible options. Unlike these approaches, Pennington and Yue (1998b) performed the analysis independently for each of the component systems in a process (reaction and separation) followed by consideration of their potential interactions. This approach has been adopted in P2TCP.

Using the prototype of P2TCP presented in this paper, pollution prevention opportunities have been identified and alternatives compared for a number of continuous chemical processes. Processes considered include the production of allyl chloride, the manufacture of chlorobenzenes and the separation of a mixed hydrocarbon stream generated in naphtha reforming units of oil refineries.
 

Conclusions
P2TCP (Pollution Prevention Tool for Continuous Processes) incorporates a prototype expert system, developed to help designers of chemical processes systematically identify design alternatives that may result in reduced waste generation and energy consumption. Advantages of the P2TCP expert system include: 

• the analysis performed is resource-limited and does not require the prior specification of a process flow diagram; it will facilitate the identification of pollution prevention opportunities during conceptual as well as retrofit design without rigorous simulation calculations

• the heuristics were derived systematically using fundamental chemical engineering principles; the structure developed can provide a greater depth of analysis than key-word approaches or using limited detail heuristics developed for the rapid synthesis of process flow diagrams

• case studies are not used as the principle knowledge source but for validation and for identification of further extensions to the expert system

• each system (reaction and separation) of a process is analyzed independently, not sequentially, and then potential interactions considered

It should be noted that the scope of the prototype was restricted and a number of assumptions were made to develop a core structure. Further enhancements and research could transform P2TCP into a computer-based system for the identification of pollution prevention options with a significant commercial potential.