Simulation Of600000t/a Methanol Device And Energy Efficiency Optimization

Methanol is a very important basic organic chemical raw material and can beused in the production of formaldehyde, acetic acid, dimethyl ether, methyl formateand other chemical products. In recent years, with the growing shortage of oilresources, using methanol as an alternative fuel has become a focus in the worldwide.Influenced by this, the number of domestic methanol devices is growing and the scaleis gradually expanding. But compared with the methanol enterprises abroad, domesticenterprises generally have the problem of high production cost and large energyconsumption.Based on the second law of thermodynamics, Pinch technology treats the deviceas an organic whole to carry on energy analysis and find the places of unreasonableenergy use. On this basis, the reasonable design and retrofit schemes are put forward.So far, Pinch Technology has been used throughout the world. Based on a600000t/amethanol device, the energy saving reconstruction was carried by Pinch Technologyand the main works carried on as follows:（1）The processes of gasification, shift, methanol synthesis and methanoldistillation were simulated by Aspen Plus. All models were in good agreement withprocesses data and could be used for subsequent process optimization;（2）The water-coal slurry gasifier model of GE was established by the Gibbsfree energy minimization method and the influence on gasification of slurryconcentration, oxygen/coal ratio and gasification temperature was analyzed with thismodel: Under the guarantee of gasifer not over temperature, slurry concentration canbe increased as much as possible; the appropriate oxygen/coal ratio is chosen underthe consideration of effective gas concentration and slag tapping; The appropriategasification pressure is chosen according to the design load and matching process;（3）Two improved processes were proposed for distillation unit optimization:Process1reduced energy consumption by7.6%compared with the traditionaltechnology through fully recovering waste heat of pressurized column product andbottom stream; Process2reduced energy consumption by33.8%through adjustingpressure of atmospheric and pressurized columns to realize thermal coupling bettweenatmospheric and pre-rectifying column. （4）The whole methanol device was analyzed by Pinch Technology. Shiftconversion unit was optimized utilities match separately and methanol synthesis anddistillation units were heat-integrated through comprehensive trade-off betweenenergy saving effect and retrofit difficulty.Shift conversion unit increased by-product of2.5Mpag medium-pressure steam55.5(t/hr) through steam level adjustment.There were two heat integration schemes for methanol synthesis and distillationunits: Scheme one saved34.8%of low pressure steam and21.1%of cooling water;Scheme two saved30.8%of low pressure steam and18.7%of cooling water.For a new device, Pinch Technology can optimizes the heat exchanger networksand utility consumption to save equipment investment and operation cost. Meanwhile,for an existing one, Pinch Technology can find the places of unreasonable energy usesto guide enterprises retrofitting and achieve the purpose of increase production andenergy saving.