Design and variable scale optimization of flare gas recovery process for hydrogen production

Abstract

Flare systems are equipped in refining and petrochemical industries to ensure operation safety. However, flare gas sent directly to the flare system for combustion wastes energy and pollutes the environment, so it is of great significance to recover and comprehensively utilize flare gas. A new process of hydrogen production with flare gas recovery is proposed in this paper, which not only solves the problem of environmental pollution but also makes rational use of energy and improves economic benefit. Firstly, the flare gas recovery process for hydrogen production is designed by coupling the poly-refrigerant integrated cycle operation method with the chemical looping combustion sorption enhanced steam methane reforming method. Secondly, key parameters such as reactor temperature, H2O/CH4 molar ratio, and CaO/CH4 molar ratio are optimized through sensitivity analysis with CH4 conversion, H2 yield, H2 purity (dry basis), and CO2 capture rate as indicators. Thirdly, computational fluid dynamics simulation is carried out to validate the above macroscopic analysis results and further optimize the process at the mesoscopic level. The effects of different bed heights on hydrogen purity are analyzed to determine the optimal bed height for the reformer reactor, which strengthens the performance of the equipment. Finally, the process is probed by an economic analysis, which shows that 68.7 tons/year of hydrogen is produced when the recovery of methane from flare gas reaches 137.3 tons/year. This determines the economic feasibility of the process. The significance of this paper lies in: a novel green process using flare gas recovery to produce high-purity hydrogen with the conversion from waste gas to new energy realized with the concept of “turning waste into treasure”; a new way of combining meso-level and macro-level, variable-scale optimization of the process parameters; the recycling of other short-chain hydrocarbon-containing waste gases.