Energy integration alternatives for effective use of waste heat associated with flaring during abnormal situation

Abstract

This work reports a multi-objective optimization frame work for new/modified design solutions for energy integration to manage flares from uncertain sources during abnormal situation. It also suggests some energy integration alternatives for waste streams recovery, for combining heat and power through process integration and for flare gas utilization. This kind of robust optimization framework and energy integration alternatives are very important for utilizing unused resources of the process and for flare gas reduction. Although, governments and companies have had success in reducing flare gas with significant investments; global gas flaring has remained largely stable the past fifteen years in the range of 140-170 billion cubic meters (BCM) which is 5% of global gas production (Kazi et al., 2015). Therefore, much attention is still needed to mitigate and manage industrial flares by innovating green process engineering for sustainable energy and environment. Here, two sustainable energy integration alternatives are proposed and harnessed properly with process for flare management during abnormal situation. First one is cogeneration (COGEN) unit which has become a mainstream practice in different industries due to its high economic and energy-savings potentials. It can produce simultaneous heat and power from a single fuel source. If COGEN unit is designed properly some part of the flare streams can be used as fuel in the boiler instead of fresh fuel like NG. This will reduce the fresh fuel cost and will also increase the energy efficiency of the process itself. Moreover, it will reduce the carbon footprint from compensated fresh fuel. Another energy integration tool is thermal membrane distillation (TMD) unit, which is an emerging technology in the area of high-purity separation especially in water treatment (Elsayed et al., 2013). In TMD, low level heat like waste heat from process or COGEN unit can be used to create the driving force to separate pure water from the raw/waste water. Moreover, it needs small floor area for installation and it is modular in nature. By integrating TMD with the process, the utility costs and the waste water treatment cost can be reduced significantly. Produced water from TMD can be recycled in the process or sold to external users. Using cogeneration (COGEN) and thermal membrane distillation (TMD) unit with industrial processes can offer a potential scope of process and energy integration and can also offer the maximum utilization of flared gas streams. In this work, an ethylene base case study is solved to illustrate the applicability of the proposed optimization framework and the implementation of the proposed energy integration tools for flare management. In final output, the optimization framework provides several Pareto fronts to the policy makers. Therefore, the end user is able to make an informed choice of suitable design, operation conditions and process performances depending on economic, energetic and/or environmental considerations. The results of different scenarios demonstrate the benefits of integrating TMD and COGEN unit with the process plant for flare mitigation approach. It will ensure the maximum use of flared gas streams, reduction of cooling utility load and the creation of recycle/reuse opportunities for the treated waste water.