Optimal Sizing of Cogeneration (COGEN) System to Manage Flares from Uncertain Sources during Abnormal Process Operations

Monzure-Khoda Kazi, Fahd Mohammed, Fadwa Eljack^*

Department of Chemical Engineering, College of Engineering,

Qatar University, P.O. Box-2713, Qatar

Email: Fadwa.Eljack@qu.edu.qa

Flaring is a very common scenario in different industrial plants. Industries usually do flaring to reduce the risk during abnormal situations, to maintain the product quality or to operate safely during process start up and shut down. Negative effects of those flares are not hidden to modern society. Nowadays, everybody is concern about the environmental and social effects of those industrial flaring. Especially, the emissions of green house gas and other toxic materials during flaring have a significant impact on the environment. Therefore, various protocol and steps i.e., Kyoto protocol, The United Nations Environment Programme (UNEP), have been taken to mitigate the impact of flaring due to process upsets. Although negative impacts of flaring are known, these flare streams have significant amount of heating value. These streams can be considered as waste stream from the industrial plants and can be used as supplement of fresh fuel feed to generate require heat and power using COGEN system. Cogeneration (COGEN) system is one of the effective and efficient approaches where waste streams can be used as fuel to generate require heat and power within a process itself. In our earlier works, we showed the possible reduction of fuel demand and CO₂ emissions by using cogeneration system where flaring streams were recycled as fuel feed (Kamrava et al.). In this paper, our objective is to develop an optimization framework to determine the optimal size of a cogeneration system to manage flares from uncertain sources such as upsets streams. The ultimate results of using cogeneration system are usually reduction in overall cost of the process and GHG emissions. An optimization formulation is developed for indentifying the optimum equipment size and operating parameters of the system, the optimum energy produce for the process from cogen system by minimizing the overall cost and emissions of green house gases. The optimization formulation also helps to find out the mixing ratios of different flare streams available to cogen system, which essentially reduce the utility cost of the process. Multi-objective tradeoffs between the economic, environmental, and energetic aspects are presented through Pareto fronts. A stochastic optimization technique based on genetic algorithm is used to solve this discrete multi-objective optimization problem. This Multi-objective optimization problem was also solved using global optimization toolbox in LINGO. A base case study of ethylene plant is used to demonstrate the applicability of the proposed procedure of cogeneration sizing.  

References:

Kamrava, S., Gabriel, K., El-Halwagi, M., & Eljack, F. Managing abnormal operation through process integration and cogeneration systems. Clean Technologies and Environmental Policy, 1-10.