Research Paper Heat exchanger application for environmental problem-reducing in flare systems of an oil refinery and a petrochemical plant: Two case studies S.M. Jokar ⇑ , M.R. Rahimpour, A. Shariati Department of Chemical Engineering, School of Chemical and Petroleum Engineering, Shiraz University, Shiraz 71345, Iran highlights  Two sever problems were investigated in a domestic oil refinery and an ethylene plant.  The problems involved in releasing of liquid hazardous waste from flare systems.  The liquid wastes analyzed and the concerned unit simulated.  The designed heat exchanger prevents slops formation in flare system of the refinery.  The heat exchanger prevents emission of 168 kg/h of droplets from the ethylene plant. article info Article history: Received 23 March 2016 Revised 4 June 2016 Accepted 8 June 2016 Available online 9 June 2016 Keywords: Oil refinery Ethylene plant Flare system Slops and droplets Heat exchanger abstract In this work, two common problems for refineries and petrochemical plants were investigated, which includes burning of unwanted components in flare systems. Although some heavy components are sep- arated in knock out drums of flare networks, separated liquids or non-separated heavy pollutants cause significant environmental problems. In the domestic refinery, the separated liquids form slops which should be treated in the waste water plant of the refinery. However, the non-separated hydrocarbons generate droplet emissions in the domestic ethylene plant site. To handle mentioned problems, the slops and droplets were analyzed, and the concerned units were simulated. Two heat exchangers were designed to reduce the water carry-over from the waste gas stream of refinery and condense the heavier pollutants of ethylene plant before flaring. The optimum condition of the heat exchangers is obtained by sensitivity analysis and economical optimization. Furthermore, the environmental benefit and cost of the new systems were investigated. The results approved the dramatic impact of the heat exchanger appli- cation on reducing the environmental problems of the flare systems. The designed heat exchanger con- denses over 60 percent of water from the vapor phase and makes it suitable for introducing to the incinerator. Moreover, preventing the emission of 168 kg/h of droplets is possible by applying the heat exchanger for the domestic ethylene plant. Ó 2016 Elsevier Ltd. All rights reserved. 1. Introduction 1.1. Flare gas and air pollution Refineries and petrochemical industry flares are major sources of air pollution which have dangerous effects on the ecosystems. In recent years, the reduction of the waste gas emissions and the recovery of the flare gas have been considered in many different processes. Davoudi et al. [1] investigated the major sources of gas flaring in Asalouyeh gas processing plants. Tamba et al. [2] and Al-Salem [3] surveyed the CO 2 emissions in the petroleum refining in Cameroon and Kuwait respectively. Some researchers tried to estimate the CO 2 and NO x emissions of refinery fired hea- ters [3–7]. Furthermore, a few studies have been carried out which attempted to prevent the loss of the refinery waste gases. Some refineries planned to construct cogeneration facilities based on gas turbines burning refinery gases [8] or refinery gases and natu- ral gas [9]. Rahimpour et al. [10,11] and Saidi et al. [12] proposed practical methods for recovery of flare gas instead of conventional gas burning in Farashband and Asalouyeh refineries. These meth- ods include (1) gas to liquid (GTL) production, (2) electricity gener- ation with a gas turbine, (3) compression and injection into refinery pipelines and (4) using flare gas as a feed of fuel cell. Abdulrahman et al. [13] investigated the improvement in Egypt’s oil and gas industry by implementation of flare gas recovery. Some http://dx.doi.org/10.1016/j.applthermaleng.2016.06.050 1359-4311/Ó 2016 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: s.m.jokar@shirazu.ac.ir (S.M. Jokar). Applied Thermal Engineering 106 (2016) 796–810 Contents lists available at ScienceDirect Applied Thermal Engineering journal homepage: www.elsevier.com/locate/apthermeng