Comparing and improving two column and three column methanol distillation schemes

A thesis is presented for the thermal and economic comparison of two column and three column methanol distillation schemes for the purification of crude methanol. The methanol distillation schemes considered are designed to produce methanol to US federal specification O-M-232K (14.10.1998) Grade AA from crude methanol synthesized in a low pressure, natural gas to methanol process. The schemes include the conventional two column scheme comprising a topping column and a refining column, two different enrichment cascade three column schemes and a double effect three column scheme. First and second law thermodynamic analyses were applied to the distillation schemes to identify and assess practical improvements. The improvements, which include feed conditioning and intermediate reboiling, can enhance heat integration with the background process and realise reductions in both capital and operating cost, and footprint. For the three column schemes, these improvements coupled with the manipulation of the column pressures can further enhance heat integration with the background process. Footprint reduction, which is of significance to an offshore synthesis facility, is an additional benefit of tighter process integration. Conclusions are presented with respect to the application of the schemes to three competing low pressure natural gas to methanol process technologies.