Turboexpanders Installed at an Older Methanol Producing Plant Provide Major Energy Savings

CASE 2 TURBOEXPANDERS INSTALLED AT AN OLDER METHANOL PRODUCING PLANT PROVIDE MAJOR ENERGY SAVINGS 

However, not all the hydrogen that is produeed is used in the produetion of methanol. To prevent an exeessive buildup of hydrogen in the reeireulating methanol synthesis loop, a slipstream is drawn off eonsisting of hydrogen and some CO and CO2. It is fed to the boiler as supplemental fuel to the main natural gas fuel supply. The slipstream is at approximately 800 psi pressure and must be redueed to 75 psi before it ean be fed to the boilers. 

Three turboexpanders were installed at the plant to reduee the slipstream pressure from 800 psi to 100 psi and to thus eapture the kinetie energy made available. The energy eaptured by the turboexpanders provides 40,000 kWh of eleetrie energy per day. One 23,000 rpm turboexpander with a 2 1 pressure reduetion ratio takes the gas stream from 800 psi to 400 psi. A seeond 19,000 rpm turboexpander with the same 2 1 ratio takes the 400 psi gas down to 200 psi, and a third 19,000 rpm turboexpander with a 2 1 ratio takes the 200 psi gas down to 100 psi. 

The units have been disassembled for maintenanee by plant engineering personnel on a seheduled 3-year basis. Although a preventive maintenanee philosophy was used where others might have opted to employ the predietive maintenanee approaeh, the maehines have operated well with an on-stream faetor in exeess of 99%. 

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