| Liquefied natural gas(LNG)can carry out the liquid storage and transportation of NG,whose storage conditions are-162 ℃ and 0.14MPa.Before supplied to users,LNG should be regasificated to NG,which releases large amount of cold energy(about 860～883 kJ/kg).At present,the LNG receiving capacity of Yingkou port is about 3 million t/a,which accounts for about 7%of the total LNG in China.Its available cold power 65MW is equivalent to 1 billion kWh,but it has not been utilized yet.At the same time,in the Da Shiqiao area of Yingkou,the proven reserves of magnesite accounted for 82.2%of the province,accounting for 56.9%of the country,accounting for 16.3%of the world.Since every ton of MgO products can produce at least 1.1 tons CO2,in 2013 the annual CO2 emissions in the Liaoning province are 4 million tons and no effective measures have been taken to recycle it.Therefore,a large amount of CO2 emission has become one of the main factors restricting the sustainable development of Magnesite Industry Base.Because of LNG cold energy can be used for liquefying(solidifying)CO2,and Yingkou port and Da Shiqiao are in the new economic circle within 30 km around Yingkou city,we propose an integrated system for CO2 capture with the cryogenic energy of the LNG.In the existing research,the preliminary construction of the system exists many lack of research,for example,the main form of system is a series of simple Rankine cycles,circulating refrigerant is a single working substance,the cold air produced at-120℃ causing a great number of cold energy to waste.Based on the shortcomings and gaps of existing research,we improve and further optimize the existing circulating system through installation of heat recovery devices and the embedded Rankine cycles,taking organic compound as refrigerant and other measures.For the final compound cycle system,the thermal parameters of every node in the process were calculated on the basis of the physical exergy release characteristics of LNG regasification process and features of NG waste heat utilization process,and then thermal analysis of the integration process was carried out to verify the feasibility of the integration process.At the same time,we studied the effect of single parameters on the thermodynamic properties of the system.The main research contents and innovations are as follow.(1)The integration system consists of two subsystems.One of them is a circulation system that uses LNG and magnesite smelting flue gas for high and low temperature heat source,the two level nested Rankine cycle is compounded by transverse cascade Rankine cycle and nested multi-stage Rankine cycle act as the link of cold and heat source,the methane、ethylene and other organic matter blend foe organic mixtures,in accordance with the "boiling point difference method",was used for refrigerant Rankine cycle.The other is a CO2 hydrogenation methanol system that can be used for the energy utilization of LCO2 products.(2)In system integration,the system of energy efficiency and cold energy utilization rates are 56.9%and 20.81%,compared with the existing research were improved by 9.42%and 85%,and tons of LNG generating capacity(22.59 kWh)and the existing research performance parameters are at the same level;the exergy and energy loss in the heat exchangers respectively account for 94.62%and 77.76%of the total exergy and energy loss in the integrated system.(3)In the future possible range of actual production regulation,along with the increase of the LNG regasification pressure(0.2～3.0 MPa),the exergy loss of the whole process continuously decreases and the exergy efficiency continuously increases;Along with the increase of the CO2 capture pressure(0.1～1.2 MPa),all performance parameters of the system continuously rise.(4)Regenerative device makes the system of energy efficiency,cold trapping rate respectively increased 1.35%,21.91%and 26.32%and the utilization rate of CO2;mixed refrigerant makes the system energy efficiency,cold energy,cold energy utilization rate,the capture rate of CO2 system and power generation efficiency were improved by 6.01%,75.10%,18.48%,12 times and 65 times,the mixture composition of the components with a large difference in boiling point temperature has a greater impact on the performance of the system. |
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