| China is abundant in coal,and in short of petroleum and SNG.Coal is the major fossil energy source.In recent years,the SNG consumption in China showed a rapid growth trend.The SNG consumption gap is expected to reach 1075 1765 billion Nm3 by 2020.Combined with abundant coal resources and industrial advantages,the development of Coal-to-SNG is an important way to solve the problem of the SNG supply in China.Coal-to-SNG plays an irreplaceable and important role in the SNG industry of China.However,the high energy consumption of Coal-to-SNG process is a major obstacle to the vigorous development of Coalto-SNG industry.In this paper,the model of the whole process is built and the analysis of Coalto-SNG is conducted.Lurgi gasification and BGL gasification are both adaptive for coal-toSNG because of the rich content of CH4 in raw gas after gasification.In this paper,these two coal gasification units and corresponding WGS units are modeled and simulated,hereafter named as the Lurgi process and the BGL process.Depending on the simulation,technical analysis is conducted and the two processes are compared in energy and economic performance.Comparison of these two processes in this paper aims to find the most suitable gasifier for Coalto-SNG.Based on this,the low-grade waste heat in Coal-to-SNG process is quantitatively analysed.The new processes of cascade absorption heat transformer?NCAHT?and cascade absorption refrigeration?NCAR?are established to recover this part of low grade waste heat.The models of Lurgi process and BGL process are established in this paper.And then the two processes are simulated.The operation parameters and simulation parameters are analyzed.The exergy efficiency and economic performance of the two processes are compared based on the simulation results.In this paper,the whole process model of coal-to-SNG is established and the accuracy of the model is verified by comparing with the actual operating parameters,mass and energy balance data.On basis of the established model,the key parameters of the process were conducted sensitivity analysis.Based on the simulation results,the exergy analysis and economic evaluation of the process were carried out to provide theoretical support and reference for the actual production and the later process improvement.The results show that the exergy efficiency is 0.63,the total exergy loss is 2023.2 MW,and the loss of gasification unit is 1141.9 MW,which is 56.5% of the total loss.Gasification unit for the entire process of the exergy loss of the largest,should give priority to improvement.At the same time,sentisitive analysis for raw material and product are conducted.In this work,a novel cascade absorption refrigeration?NCAR?is proposed to produce-40 ? cold energy by using low-grade waste heat.The proposed sytem is composed of two subsytems: LiBr/H2O AR cycle and NH3/H2 O AR cycle.NCAR utilizes the low-grade waste heat using a cascade approach.A simulation study is conducted,based on the revised model built in Aspen Plus.The effects of feed concentration,generator temperature,HPP pressure,LPP pressure,and concentration range are analyzed to provide guidance to NCAR design.The designed NCAR aims to achieve the maximal COP.In a 4 billion Nm3/a Coal-to-SNG plant,the NCAR is integrated to use low-grade heat taken from the methanation unit.Produced cold energy is used in the Rectitsol unit to remove CO2.For the NCAR,18.0 MW of waste heat above 121 ? is used for the NH3 absorption refrigeration,while 24.2 MW waste heat from 90 to 121 ? is used for the LiBr absorption refrigeration.As a result,7.1MW of cold energy is generated for the Rectisol unit.The total investment of NCAT is 8,100,000 USD.The operational cost of the NCAR is only 14% of the conventional compression refrigeration.The payback period is 1.7 years.In addition,the economic performance of the NCAR is dependent on electricity price.The annual profit is 5,200,000 USD.When the price of electricity is higher than 0.09 $/kWh,the payback will within 2 years.It is concluded that the NCAR is promising on energy saving and making more profit.This paper proposes the NCAHT to recover low grade waste heat to produce 0.5 MPa steam.The NCAHT consists of two cycles: the LiBr/H2O AHT cycle and the NH3/H2O AHT cycle.According to the principle of energy cascade utilization,the high temperature part is the heat source of the LiBr/H2O AHT cycle and the low temperature part is the heat source of the NH3/H2 O AHT cycle.The NH3 AHT cycle produces high temperature heat fed to LiBr/H2 O AHT cycle;the LiBr/H2 O cycle produces low temperature heat fed to the NH3/H2O AHT.This heat integration in NCAHT can improve the COP for efficiently low grade waste heat recovery.The effects of feed concentration,generator temperature,HPP pressure,LPP pressure,and concentration range are analyzed to provide guidance to NCAHT design.The designed NCAHT aims to achieve the maximal COP.The maximal COP is 0.227.The low-grade waste heat above 136 ? is fed to LiBr/H2 O AHT cycle;90 to 136 ? low-grade waste heat is fed to NH3/H2O AHT cycle.The NCAHT is applied to Coal-to-SNG to recover low grade waste heat.The Financial Internal Rate of Return?FIRR?is used as the economic indicator.The cost of 12 MW NCAHT is 924,000 USD.The Financial Internal Rate of Return is 62.16%.When the steam price is cheaper than 9 USD,the FIRR will be less than 30%.Higher product price leads to shorter payback time and bigger ROI.When the cooling water price is expensive than 0.96 USD,the FIRR will be less than 30%.Higher cooling water price leads to longer payback time and smaller ROI.Production capacity load is more sensitive than cooling water price and cooling water price is more sensitive than project life.All the FIRR is larger than 30% when these three uncertain factor varies in 20%. |
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