Abstract:

A novel process of three-column (pre-distillation, low-pressure, and high-pressure) distillation was proposed for the purification of synthetic methanol. In the new process with double-effect distillation, the reboiler duties of both pre-column and low-pressure column were provided by the vapor distillate of the high-pressure column, which achieved complete heat-integration of heating steam to reduce the total heat consumption of the whole distillation process. At the same time, the soft water from the bottom of the low-pressure column and part of the salt water from the bottom of the high-pressure column were recycled to the pre-column as the extracting water, which achieved complete integration of soft water in the process and eliminated the consumption of fresh soft water and reduced the amount of waste water. A comparative case study by steady-state simulation was carried out for the present Lurgi process, the W-C process in literature and this Z-W process. The result showed that the Z-W process reduced the heat consumption by 21. 4 % of the Lurgi process or by 11. 7 % of the W-C process，reduced the waster water by 81. 4 % of the Lurgi process or by 68. 5 % of the W-C process and eliminated the soft-water consumption by 100 % of both Lurgi process and W-C process.