An algebraic targeting approach for effective utilization of biomass in combined heat and power systems through process integration
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Green house gases (GHGs) pose some of the most profound impact on the environment. One viable alternative for reducing GHGs is the utilization of biomass to generate heat and power for processing facilities. The purpose of this paper is to address the utilization of biowaste or biomass source in a processing facility for combined heat and power (CHP). In particular, the paper addresses the following questions: How to incorporate biomass utilization in cofiring and energy production within an existing process? How to reconcile thermal demands with opportunities for power cogeneration through a process-integration framework? What are the economic factors that will insure the feasibility of biomass utilization and power cogeneration? What is the impact on GHG emissions and what are the necessary GHG emission pricing options? A systematic algebraic procedure for targeting cogeneration potential ahead of detailed power generation network design is presented. The approach presented here effectively utilizes biomass and biowaste sources as external fuel, and matches them with the use and dispatch of fuel sources within the process, heating and non-heating steam demands, and power generation. The concept of extractable power introduced by Harell and El-Halwagi AIChE Spring Meeting, New Orleans, March (2003) has been used as a basis of constructing this algebraic cogeneration targeting approach. Steam surpluses and deficits are identified by header balance. Flow balance is performed by cascade diagram techniques and extractable power is computed from net flows to target the cogeneration potential. Next, the paper discusses important economic factors (e.g., GHG pricing options) required for the cost-effective utilization of sole biomass feed or a co-fed mixture of biomass and fossil fuels for CHP. Two case studies are discussed to illustrate the presented approach. The first case study illustrates the developed targeting approach when no external fuel is required and all the higher pressure surplus streams are able to satisfy the lower pressure deficit headers. The second case shows the application of algebraic targeting to obtain the external fuel requirement when surplus headers are not able to meet the deficit demands. Further, this case shows the use of biomass for meeting the demands and the subsequent effects on economics and GHG emissions for the process.