Study On Process Technology For Coal To Methanol

The process for producing methanol taking coal as feedstock is composed of such units as air separation, coal gasification, CO-shift, syn-gas purification, methanol synthesis and methanol rectification. This article, by taking a coal-to-methanol plant in the capacity of1,800,000t/a as a background, has set up a mathematical model centering on CO-shift, syn-gas purification and methanol synthesis units included in methanol production process taking coal-slurry as feedstock and with the simulation calculations the process configuration, scheme for heat recovery, process parameters and the size of main equipment have been studied and optimized analysis conducted.With both the thermo-dynamic and dynamic simulations the process configuration, process parameters, catalyst charges and the means for regulating the total shifted CO respectively at initial, intermediate and last phase in the shift-conversion unit have been studied and it takes that a coal-to-methanol plant can effectively regulate the total shifted CO by changing the volume of shifted gas and the quantity of loaded catalyst into the shift-conversion reactor may comparatively be less. Also calculations and analysis for the surplus-heat utilization of the CO-shift unit in the methanol plant from coal-slurry are carried out by taking process simulations and pinch technology:there is a bigger heat-transfer temperature difference in high-temperature region whereas a smaller difference in low-temperature region, by increasing the gas temperature in the shifted reactor the temperature of the reactor may reach around485℃and this may by-produce HP-steam of11.0MPaG and LP-steam of0.5MPaG; the heat-transfer temperature difference becomes smaller, but still far bigger than the minimum heat-transfer temperature difference over the full network:the hot-point temperature inside the reactor is still below the maximum service temperature for several typical S-resistant shift-conversion catalysts and the increased major investment for the by-produced HP-steam is the addition of reformer cost of manufacture and the investment increase of heat-exchanging equipment for follow-up surplus-heat recovery, the increased investment can be recovered in1.3years.Both the Rectisol and NHD(Selexol) de-sulfuration and de-carbonization technologies may be applied to coal-to-methanol plant with higher investment of the former than tie latter and lower utility consumptions of water, power and steam:the investment for Rectisol technology of Linde is a little bit higher than that of Lurgi but the consumptions of refrigeration. LP-steam and electricity lower. Since the Rectisol system involves HP-gas and material of strong polarity and there is short of thermo-dynamic method suitable for the system, the process can not be simulated with universal software for process simulation, this article has employed a cubic state equation of Soave-Redlich-Kwong and a thermo-dynamic model set up by combining with Huron-Vida mixed rule and Non-Random-Two-Liquid activity coefficient model has obtained45pairs of parameters of activity coefficient model through a data fit from the existing gas solubility and gas-liquid balance data that can be used in the simulation of Rectisol de-carbonization process and there is a good coincidence between the simulation results of both high and low pressure systems and actual industrial data. Also simulation calculations taking this thermo-dynamic model has been conducted for Rectisol scrubbing system and the results show that the CO2concentration in the purified gas can be regulated by changing the volume of barren and semi-barren liquor to make the methanol synthesis reaction proceed under best condition.A mathematical model of one-dimensional plan homogenous phase to implement a simulation calculation of methanol synthesis reactor of serial air cool-water cool type has been set up by taking methanol and CO2as key component and the hydrogenation reaction of CO and CO2as independent reaction; both the temperature and concentration distribution in each reactor have been obtained from such simulation calculation and the effect on the methanol synthesis in reactors of such type by temperature, pressure and CO2concentration in the introduced gas has been investigated. The results show that the inlet gas temperature at water-cooled reactor and the temperature of saturated boiling water have a little effect on the methanol yield, but the inlet gas temperature has a bigger effect on the temperature distribution in each reactor; with the rise of operating pressure the methanol output in water-cooled reactor increases whereas the output of methanol in air-cooled reactor reduces with the increase of total methanol output in serial reactors; with the increase of CO2concentration in the introduced gas both the outlet temperature at air-cooled reactor and the inlet temperature at water-cooled reactor increase and methanol output reduces. CO2concentration in virgin gas should not be too high. A simulation calculation is also carried out for reactors of a serial air cool-water cool type in a1,800.000t/a methanol plant at different load (50%～110%)and the results show that the reactor of such type has a better adaptability at different production load.