A New Shell Dry Coal Gasification Process And Its Optimization Design With Decarburized PSA Purified Gas As Partial Feed And Water Quench

On one side,in a SMR system,the purified gas from decarburized PSA,whch is rich in H₂,CO and CH₄ generally serves as fuel for reformers instead of high-quality raw material for hydrogen production.On the other side,in a typical Shell coal gasification unit(SCGP),the circulating compressed quench gas is used to cool down syngas,enhancing the energy consumption of hydrogen production.To this end,the above two processes are integrated in this paper:First,The purified gas from SMR is compressed and sent to coal gasifier as raw material for hydrogen production,so that the purified gas can be utilizated upgradingly;Second,an additional bypass of washing and purifying water is assembled in the SCGP,and part of the washing and purifying water is self-pressurized to the outlet of the gasifier,so as to supplement the circulating compressed quench gas and adjust the temperature of syngas into the heat recovery boiler,reducing the flow rate of circulating compressed quench gas and the energy consumption of hydrogen production.Therefore,a new Shell coal gasification process is put forward in this paper,using decarburized PSA purified gas as auxiliary raw material and part of washing water as the replacement of circulating compressed quench gas.The Aspen simulation proves that the new process,in comparison with the old,has better performances in operability,hydrogen production rate,energy consumption and thermodynamic features.Furthermore,an optimization design method based on process simulation for the new SCGP procedure is developed,considering the minimum unit hydrogen production energy consumption or minimum exergy loss as the objective function,whose system decision variables are selected by partial least squares(PLS)using Matlab modeling.In order to allow the optimization calculates automatically,the integration platform of Aspen process Simulation software,Excel and genetic algorithm(GA),the optimization algorithm of this optimization design method,is developed.Most importantly,it is the Aspen Simulation Workbook(ASW)that provides a perfect interactive platform for Aspen and Excel.By coding into Excel VBA,the automation of this optimization method can be implemented under the guidance of the genetic algorithm(GA),with Aspen running under control,while the data calculated by Aspen can be read and written.As the entire process is driven by simulated data,this method is generally applicable to the multivariable optimization design of all chemical units that can be simulated.In the end,the new process and optimization design method are applied to a SCGP renovation project with synthetic gas(effective components:CO+H₂)yield of 15×10⁴ Nm³/h.The calculation shows that when the flow rate of gasifier oxygen(x₁)is 67.2 t/h,the flow rate of reactive steam(x₂)is 5.8 t/h,the flow rate of washing quench gas(x₃)is 120.8 t/h,the flow rate of quench water(x₄)is 9.7 t/h and the flow rate of PSA purified gas(x₅)is 18.85 t/h,the process exergy loss achieves the minimum value,reducing from 654.4GJ/h to 508.9GJ/h,reaching up to 22.2%;When the flow rate of gasifier oxygen(x₁)is 67.5t/h,the flow rate of reactive steam(x₂)is 8.9t/h,the flow rate of washing quench gas(x₃)is 92t/h,the flow rate of quench water(x₄)is 10.8t/h and the flow rate of PSA purified gas(x₅)is 19.98t/h,the unit hydrogen production energy consumption achieves the minimum value,reducing from11336.47×10⁴kcal/t H₂ to 6980.85×10⁴kcal/t H₂,reaching up to 22.2%,reducing 4355.62×10⁴kcal/t H₂ and reaching up to 38.42%.The result shows that the new process and optimization design method of this article is feasible and effective.