Methanol Plant Capacity Enhancement By: Mr. C D ... - Fibre2fashion

Methanol Plant Capacity Enhancement
By: Mr. C D Bhakta, Mr. A I Shaikh, Mr. Y N Patel & Mr. S J Darjee
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.
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 a capacity 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 gas from the rectisol wash unit of an ammonia plant. With the
methanol market improvement in the late 90’s, this plant became an attractive option for a capacity
increase. It is now producing more than 180 MTD (three times the design capacity) due to
implemented, stepwise modifications in the plant.
Brief History - Enhancing the Methanol-I Plant Capacity
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 reaction of the
methanol in gas rich in CO2 is milder as it produces water along with methanol. The crude methanol
concentration is also lower. Water further retards the rate of reaction. The two reactions involved here are:
H2 + CO2 ----> CH3OH + H2O + 9.8 kcal/ kgmol
H2 + CO ----> CH3OH + 21.6 kcal/ kgmol
Normally, a gas mixture of H2 + CO + CO2 is used in a proportion measured in terms of a “R” value (H2-
CO2)/(CO+CO2) equal to 2.0 to get an optimum methanol conversion per pass.
Changes to the process included:
1. A methanol chiller was introduced in the gas cooling circuit at the reactor outlet to reduce the methanol
concentration and temperature in the recycle gas which helped to increase the methanol production from
4~5 MTD up to 75 MTD level.
2. Setting up a synthesis gas generation unit (SGGU) to supply CO rich gas from natural gas reformer in
February 1998. This gas composition is better for methanol production compared to the rectisol wash gas
which is rich in CO2. The synthesis gas and distillation loops were debottlenecked by replacing of some
control valves, installation of exchangers, and other modifications. The capacity was boosted to 100 to 120
MTD.
3. Replacement of the refining column trays with high capacity Superfrac trays from Kostch Glistch India
Ltd in October 2002. This, along with other peripheral modifications, was made to increase distillation
capacity to 145 MTD.
4. Replacement of the quench adiabatic methanol convertor to Linde’s Isothermal Reactor and
debottlenecking of the distillation loops for higher capacity. The capacity of the plant was increased to 160
MTD in September 2003.
Major advantages of Isothermal Reactor include:
Lower pressure drop in reactor
Less temperature variation
Increased life of catalyst
Narrow band of temperature differences in the reactor catalyst bed
Sustained Production Level throughout the catalyst life due to better conversion
Less by-product formation
Effective heat recovery