Simulation And Revamp On Rectisol Process In A Coal-to-methanol Plant

Rectisol is a method which removes acid impurity gas such as CO2, H2S and COS by using the merit of low-temperature methanol that it possesses proper gas absorption properties. Due to the great impacts of the degree of syngas purification on the methanol production and the life of synthetic catalyst, and the effects of Claus gas composition on the recovery ability of sulfur, as well as the requirement for tail gas composition to meet the emission standards, the syngas purification is a crucial process in the coal-to-methanol production industry.So far there are more than100rectisol units in China. As to the problems existed in the process, the change of feed gas, and the demand of expansion, more and more revamp projects of the existing equipment will be needed. The revamp research is always set up on the basis of a correct process simulation. Using software to conduct process optimization and transformation has the advantage of saving a large amount of manual labor, material resources, energy, and time. Meanwhile, the simulation results can guide the design and production accurately. Therefore, it is of significant meaning to conduct rectisol process simulation and reform by general simulation software.A Plant producing methanol from coal adopts a foreign rectisol technology in the syngas cleaning section. The rectisol process operates at medium pressure (5MPa), in which two problems occurred including lower sulfur content in the Claus gas and higher water content in the system. According to these problems, the whole process simulation of rectisol is set up at first, in which the missing COS UNIFAC parameters have been got by defining the components in the process of simulation, and the ELECNRTL property method for ammonia washing tower has been got and the improved PSRK property method has been adopted at the medium pressure. The reasons that caused the two problems are analyzed and corresponding revamp schemes are put forward on the basis of the correct process simulation. The revamp scheme is simulated finally, and as a result the sulfur content in Claus gas has been increased to36.636%from32.326%, the water content in the circulating methanol is reduced to0.005%from0.039%, meanwhile the heat load of bottom re-boiler in methanol-water separation column is reduced to2651.83kW from3228.82kW which saves576.99kW heat load.