Methanol plant capacity enhancement

The authors share their experience in debottlenecking a methanol plant at GNFC Ltd.

The project involved the commissioning of a state of the art Isothermal reactor from Linde.

The authors share their experiencein debottlenecking a methanol plant at GNFC Ltd.

The project involved the commissioning of a state of the art Isothermal reactor from Linde.

GNFC is located at Bharuch, Gujarat, India and is engaged in manufacturing of fertilizers.

The key products are urea, ANP, CAN, formic acid, methanol, acetic acid, and nitric acid (weak/strong).GNFC owns two (2) methanol plants.

A small, old plant called Methanol-I with acapacity of 60 MTD and another Methanol-II plant with a capacity of 300 MTD.Methanol-I was commissioned in 1985.

It was designed to operate on the feed gasfrom the rectisol wash unit of an ammonia plant.

With the methanol market improvement in the late 90s, this plant became an attractive option for a capacity increase.

Itis now producing more than 180 MTD (three times the design capacity) due toimplemented, stepwise modifications in the plant.

Originally, this plant was designed to operate on feed gas from an ammonia plant consisting of a gas mixture of 75%hydrogen, 22% carbon dioxide, 1% carbon monoxide and some inerts.

The reactionof the methanol in gas rich in CO 2 is milder as it produces water along with methanol.

The crude methanol concentration is also lower.

Waterfurther retards the rate of reaction.

The two reactions involved here are: Normally, a gas mixture of H 2 + CO + CO 2 is used in a proportion measured in terms of a R value(H 2 -CO 2 )/ (CO+CO 2 ) equal to 2.0 to get anoptimum methanol conversion per pass.

A methanol chiller was introduced in the gas cooling circuit at thereactor outlet to reduce the methanol concentration and temperature in therecycle gas which helped to increase the methanol production from 4~5 MTD up to75 MTD level.

Setting up a synthesis gasgeneration unit (SGGU) to supply CO rich gas from natural gas reformer inFebruary 1998.

This gas composition is better for methanol production compared to the rectisol wash gas which is rich in CO 2 .

The synthesis gasand distillation loops were debottlenecked by replacing of some control valves,installation of exchangers, and other modifications.

The capacity was boostedto 100 to 120 MTD.

Replacement of the refining columntrays with high capacity Superfrac trays from Kostch Glistch India Ltd inOctober 2002.

This, along with other peripheral modifications, was made toincrease distillation capacity to 145 MTD.

Replacement of the quench adiabatic methanol convertor to LindesIsothermal Reactor and debottlenecking of the distillation loops for highercapacity.

The capacity of the plant was increased to 160 MTD in September2003.

v Sustained Production Levelthroughout the catalyst life due to better conversion Compared to the expected 160 MTD production capacity, the unit has achieved a stable production level of 185~190 MTD.

A flow diagram of the new loop is shown in Figure 2 below.