The purpose of the Lurgi converter loop is to produce methanol using synthesis gas as the raw material. Synthesis gas from the discharge of the MUG compressor (C-328) is combined with synthesis gas from the high pressure separator (V-2359) at the suction of the recycle compressor (C-329). The discharge pressure of C-329 is controlled at approximately 846 psig.
The discharge flow from C-329 is preheated in interchanger HE-2553 (shell side) and fed to the two converters (V-2357 and V-2358) which are operated in parallel. The synthesis gas flows through the tubes of the converters, which are filled with a pellet-shaped catalyst. This catalyst is zinc/copper in an aluminum oxide base. The product is a gas stream containing methanol and synthesis gas, which was not converted due to catalyst efficiency.
Heat is evolved during this reaction is (exothermic) and is transferred to boiler feed water on the shell side of the converters. The boiler feed water comes from the Lurgi steam drum (V-2361) located above the converters. The water flows through downcomers, picks up heat in the converters, and the steam flows through risers to V-2361. The temperature of the water in the reactor shell is controlled by varying the steam pressure in steam drum V-2361 with the pressure controller (PRC-630). The product from the converters is passed through the interchanger (HE-2553) on the tube side where it is cooled by synthesis gas on the shell side. The converter product is further cooled by a final crude methanol condenser (HE-2827). Following the condenser, the flow goes to the high pressure separator (V-2359) where the liquid methanol is dropped out and the resulting synthesis gas stream is taken overhead. To provide pressure control of the converter loop, some synthesis gas from the V-2359 overhead stream is removed or "purged" from the loop. The volume of purge gas removed is controlled using PIC-231 valve based on the discharge pressure of C-329. The remaining synthesis gas from V-2359 overhead is sent to the suction of C-329. The liquid from V-2359 goes to the low pressure separator (V-2360). The overhead of V-2360 goes to the Boilerhouse as low pressure gas for firing their boilers. The base of V-2360 crude methanol goes to T-280 and T-288 via HE-2557 and HE-2569 for sales grade methanol, and to T-279 for MO grade methanol.