Computers and Chemical Engineering 76 (2015) 76–86 Contents lists available at ScienceDirect Computers and Chemical Engineering j our na l ho me pa g e: www.elsevier.com/locate/compchemeng Multi-objective optimization methodology to size cogeneration systems for managing flares from uncertain sources during abnormal process operations Monzure-Khoda Kazi, Fahd Mohammed, Ahmed Mhd Nabil AlNouss, Fadwa Eljack ∗ Qatar University, Department of Chemical Engineering, College of Engineering, P.O. Box-2713, Doha, Qatar a r t i c l e i n f o Article history: Received 18 September 2014 Received in revised form 10 February 2015 Accepted 18 February 2015 Available online 25 February 2015 Keywords: Flare minimization Cogeneration Optimal sizing Process integration Greenhouse gas emissions Uncertainty a b s t r a c t Flaring is common practice in industries to reduce the risk during abnormal situations, to maintain the product quality or to operate safely during process start up and shut down. Due to its large negative impacts on the environment and society, various protocol and steps, i.e., Kyoto protocol, the United Nations Environment Programme, have been created for future mitigation. There is significant amount of heating value lost during flaring events. A cogeneration (COGEN) system can use waste flare streams as fuel to generate heat and power within a process. The objective of this work is to develop an optimization framework for sizing a COGEN unit to manage flares from uncertain sources by minimizing the overall cost and emissions of greenhouse gases. Multi-objective trade-offs between the economic, environmental, and energetic aspects are presented through Pareto fronts for a base case ethylene plant using a stochastic optimization technique based on genetic algorithm. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Flaring is a very common practice across all industrial plants. Industries usually flare to reduce the risk during abnormal situa- tions, to maintain the product quality or to operate safely during process start up and shut down. Industrial flaring is a contentious economic, environmental and social issue because it does not only waste potentially valuable source of energy, it also adds signifi- cant carbon emissions and other toxic materials to the atmosphere that have been linked to cause cancers, asthma, chronic bronchi- tis, blood disorders, and other diseases in human health (Davoudi et al., 2013; Nwankwo and Ogagarue, 2011). Emissions from indus- trial flares contribute to global warming. The implications of global warming have been linked to the melting of ice and the rising of sea level, which can lead to flooding and tsunamis across the globe (Anomohanran, 2012; Azam and Farooq, 2005; Edino et al., 2010; Hassan and Kouhy, 2013; Joseph et al., 2011; Nordell, 2003; Yuqin et al., 2010). Therefore, industrial flaring and its effect on the environment, ecosystem and society have gained the attention of researchers, environmentalists and policy makers. Numerous protocol, ∗ Corresponding author. Tel.: +974 404 4141; fax: +974 485 2491. E-mail address: Fadwa.Eljack@qu.edu.qa (F. Eljack). international agreement and steps such as the Kyoto proto- col, the United Nations Environment Programme (UNEP), World Bank Global Gas Flaring Reduction (GGFR) Programme have been initiated to mitigate the impact of industrial flaring. This is essential to avoid dangerous anthropogenic interference with the climate system. Many industrial countries around the world such as United States (US), France, and Saudi Arabia have attempted different alternatives to reduce the amount of gas flared in their coun- try (Anomohanran, 2011, 2012; Jegannathan et al., 2011; Sharma et al., 2011). The US was able to reduce their emission level by 5.8% between 2008 and 2009 (Anomohanran, 2012; EIA, 2011). Some governments and legislation authorities have tightened their considerable limit. The State of Qatar has changed the acid gas flar- ing limit from 1% to 0.06% (Homssi et al., 2012). In an attempt to stop the flaring of associated gas, the Nigerian government established the Nigeria Liquefied Natural Gas plant to prevent the release of millions of tons of CO 2 into the atmosphere. Oil com- panies operating in Nigeria have established several alternatives to reduce gas flaring, i.e., Shell Petroleum Development Company of Nigeria (SPDC) installed equipment to capture gas from its facilities. Between 2000 and 2010, SPDC claimed that their flar- ing quantity dropped by half (Anomohanran, 2012; SPDC, 2011). France is an example where the introduction of nuclear power was able to reduce the emission drastically. Although, govern- ments and companies have had success in reducing flare gas with http://dx.doi.org/10.1016/j.compchemeng.2015.02.012 0098-1354/© 2015 Elsevier Ltd. All rights reserved.