Sutdy On Total Site Heat Analysis And Integration Of Coal To Synthetic Natural Gas Process

Natural gas is an important clean energy and chemical raw material.The development of the coal-to-gas industry plays an important role in alleviating the contradiction between China's natural gas supply and demand.Coal to synthetic natural gas(coal-to-SNG)process is consist of several sub-units,and energy system of the process is complex.Meanwhile,the existing heat recovery scheme for the coal-to-SNG project is designed by individual process.It is failed to achieve the step utilization of energy from a holistic view.There are several unmatched joints in existing energy system configuration of coal-to-SNG process,and the energy utilization efficiency still has room for improvement.Studying on the bottleneck problem of energy system could produce a positive effect on the further upgrading of China's coal-to-SNG project and the sustainable development of the industry.This study established a basic model for each sub-unit of the coal-to-SNG process,including both chemical process and utility system,and the industrial data are used to check the model parameters.With accurate models,mass and energy balance of coal-to-SNG process is simulated.Based on this,the technical and economic performance of the typical coal-to-SNG process is analyzed,and the bottleneck problems of the material and energy utilization are clarified.The result shows that the utility system of coal-to-SNG process has a high energy consumption and carbon emissions: consume 2.27 kg of standard coal to produce one cubic meter of synthetic natural gas,of which the utility system's fuel coal consumption accounts for 28.8%,the carbon emission of the average unit product is 4.94 kg,of which the utility system's carbon emissions accounted for 42.4%.Therefore,energy system integration is an important way to achieve the quality improvement and efficiency of coal-to-SNG projects and the process of energy conservation and emission reduction.The Total Site Analysis method is a graphical methodology for heat integration study on large industrial processes.It has achieved great success in petrochemical industry.However,in that case,only the latent heat of steam is considered,while the heat for boiler feed water preheating and steam superheating is neglected.This leads the amount of heat recovered globally is significantly overestimated compared to the theoretical maximum heat recovery value.Besides,utility system designed cannot meet requirements of the chemical process,when the Total Site Analysis method calculated in the high-temperature coal chemical process energy integration.In this work,we propose a Total Site Analysis method considering sensible heat for heat integration of processes with high temperature and can be applied to energy integration in coal chemical processes.By take method proposed in this paper,a utility system which meets the requirements of the process better can be obtained.Therefore,for the total site heat integration of coal chemical process with high temperature,the total site analysis method considers sensible heat,which is much valuable in both theoretical model and engineering practice.The purpose of our study is to solve the bottleneck problem and propose a corresponding energy-saving transformation plan to achieve the improvement of the energy utilization efficiency.Firstly,the pinch point technology is used to carry out detailed energy analysis of each unit process,then,using the Total Site Analysis method to consider sensible heat.The energy system of the existing coal-to-gas natural plant is analyzed to determine the energy bottleneck of the whole plant and the direction of energy system transformation.It is proposed to carry out energy-saving transformation from three aspects: heat union between equipment,low-temperature heat recovery and utilization,and steam power system optimization.By combining the water gas shift unit and the methanation unit,the enthalpy efficiency is increased by 15.8%;the whole plant low-temperature organic Rankine cycle power generation system was constructed to realize 4.32 MW of electricity production.The steam power system was modified correspondingly with the change of steam production and use,and the fuel coal saved 14.3%.Through the integration of the entire plant energy system,the annual income can be 19.44 million yuan,and the investment recovery period is 2.3 years.