Modeling and analysis for cleaner operation of a process to remove BTX from coke oven gas

Abstract

Coke oven gas (COG) is a by-product of the coke production process which can be used as a fuel or in the production of chemicals such as methanol. In this research, a model of a BTX (Benzene, Toluene, Xylene) removal process for COG purification is developed, validated with commercial-scale plant data, and applied to improve performance and reduce energy consumption. The process includes a BTX scrubbing column and a distillation column for regeneration of the washing oil. Washing oil is represented as a mixture of BTX, naphthalene and pseudo-components.Three important phenomena with implications for energy conservation were identified using the model. First, the scrubbing efficiency is higher when the ASTM D20 distillation curve of the washing oil is lower. This phenomenon can be explained by the phase equilibrium and the difference in molar volume of the washing oil components. Second, it was found that if the setpoint of the distillation column top temperature exceeds 95 °C, the temperature in the upper portion of the column will increase significantly, which increases the amount of naphthalene in the light oil and decreases its quality. Third, the total energy consuption of the distillation column can be reduced without compromising the purification efficiency if feed temperature is decreased and the low-pressure steam flowrate is increased. Plant test result and model analysis showed that for an exisiting plant with a large vapor heat exchanger and small washing oil heat exchanger, the medium-pressure steam flowrate to the preheater can be reduced without modifying any equipment.