Improving Plant throughput using Thermax Chillers for MEG Process

MEG (Mono-Ethylene Glycolis formed by reaction between Ethylene Oxide (EO) and water. EO has high affinity towards water and when the EO to water ratio is high, more MEG is produced. When EO to water ratio is low then DEG (diethylene glycol), TEG (triethylene glycol), PEG (polyethylene glycol) is produced.

Ethylene Oxide is made inside the EO Reactor section where vapour phase oxidation reaction takes place and the gas produced has traces of EO. This gas is only about 2% rich in EO content and has to be further enriched. For this it is removed from the reactor and taken to a section called EO Scrubber.  Water is added in this section and due to affinity of EO towards water. The EO in the gas will get absorbed while the inert gases (with left over traces of EO) are returned back to the Oxidation section (EO Reactor).Efficiency of Absorption of EO into water is dependent on the temperature of the water. Lower the water temperature better is the absorption. The refinery facility is designed so as to have optimal absorption at cooling water temperature (36 to 37 Deg C).This way, rich EO solution is created.

The rich EO solution is then taken into another section for re-gasification of EO. A Heat exchanger is located in the stream to preheat the solution using the lean water returning from the stripper section (re-gasification section).The re-gasification section is called EO Stripper. The boiling point of EO is very low at 10 Deg C and hence, the EO separates out when heat is supplied in this section. The lean residual water (with traces of EO) returns back to the Scrubber section after being cooled down in the heat exchanger and then with the cooling tower water. The EO in gaseous form (80% EO) is then moved to the MEG plant. In the MEG plant, water is added in the section called Re-Absorber. A high EO to water ratio is maintained so as to get a higher yield of MEG in the Glycol Reaction Section. After this, the water is separated out from the products (MEG, DEG, TEG and PEG) in the Evaporation Section by heating and the steam generated in this section is used in the Stripper section.

MEG

Process Improvement:  The idea is to increase the capacity without changing the existing set up. Output can be increased by improving the Absorption efficiency in the scrubber section. The principle used for the higher affinity of EO to water at lower temperature. Thus, Thermax Absorption Chiller is installed in the Lean water line returning from stripped section to the scrubber section. If the return water temperature is dropped from original 37 Deg C to 34 Deg C, the overall Absorption effect increased considerably which is sufficient to increase the plant output to 140%.The desired Chilled water temperature for this case is 25 Deg C. Also, if the Evaporation section of the MEG plant is originally over-sized, higher quantity of steam can be available at this higher output of the plant. This excess steam at low pressure @ 1.00 Kg/ cm2/g is fed to the Thermax Absorption Chiller. 

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