Simulation of a Multi-Functional Energy System for Cogeneration of Steam, Power and Hydrogen in a Coke Making Plant

In this paper a multifunctional energy system (MES) is proposed for recovering energy from the extra of coke oven gas (COG), which is usually flared or vented out as a waste stream in coke making plants. The proposed system consists of a pressure swing adsorption (PSA) unit for extracting some of the hydrogen from COG, a gas turbine for producing heat and power from PSA offgas and a heat recovery steam generator (HRSG) for generating the steam required by the plant's processes. o assess the performance of the system practically, simulations are carried out on the basis of the design and operational conditions of Zarand Coke Making Plant in Iran. The results indicate that by utilizing about 4.39 tons of COG per hour, 6.5 MW of net electric power can be approximately produced by the gas turbine, which can supply the coke making plant's total electrical power demand. Furthermore, through recovering heat from gas turbine's exhaust, close to 57% of the plant's steam demand can be supplied by the HRSG unit. It is also found that around 350 kilograms per hour of nearly pure hydrogen (99.9% purity) at 200 bar can be produced by the PSA unit. According to the sensitivity analysis results, if the hydrogen content of the coke oven gas decreases by about 10%, the gross power output of the gas turbine also declines by around 5.2% due to the reduction of LHV of the PSA offgas. Moreover, economic evaluation of the system shows that the payback period of the investment, which is estimated at 36.1 M$, is about 5.5 years. The net present value (NPV) and internal rate of return on investment (ROI) are calculated to be 17.6% and 43.3 M$, respectively.