Theoretical Analysis And Experimental Study On Pressure Energy And Cold Energy Co-generation System Of Natural Gas

As clear energy,the ratio of natural gas in the primary energy consumption increases year by year in the global scale.In our country,the proportion of natural gas consumption has risen from 2.35% in 2004 to 5.62% in 2014,and is expected to reach 12% in 2035.The rapid growth of gas demand promote the development of natural gas industry.Meanwhile,the construction scale of gas pipeline and pipe networks is enlarged continuously.By 2014,the total length of main and branch pipelines is more than 8.5×104 km.Considering the economy of gas transmission process,most of the transfer pressures are over 10 MPa in the world,and the design pressure of the 2nd west-east gas pipeline project of our country is up to 12 MPa.After these gas which transported by the high-pressure pipelines arrive the city gas gate station,all must be decompressed to meet the supply pressure requirement of downstream users,through the regulator station before entering the medium or low pressure pipe networks.As a result,a mass of energy is wasted and because of the gas temperature after throttling very low,it usually needs to preheat or reheat the gas during in the process of throttling.Pressure energy and cold energy co-generation system of natural gas was proposed and designed in this paper,coupling with the pressure energy power generation technology and organic Rankine cycle power generation technology.Use screw expander replaced regulator to recycle the pressure energy and cold energy,thus to improve the energy efficiency and the operation economy of gas transmission.Theoretical analysis was carried out on both of pressure energy power generation system and organic Rankine cycle power generation system.Inlet parameters,export back pressure,the performance of expander and working fluid,which were main influences of the systems,were studied.It was conducive to improve the system capacity by increasing the inlet pressure,promoting the isentropic efficiency of expander or selecting a suitable low boiling point organic working medium.In addition,by exergy analysis,found that,the cool exergy heightened following either the increase of ambient temperature or the increase of expansion ratio.On the basis of theoretical analysis,an experimental device of the co-generation system was designed and set up,which consisted of pressure generating system with design capacity of 20 kW and cold energy power generation system with 2 kW,and high-pressure gas was replaced by air.In the case of the speed of expander keeping invariant,the dynamic change regularities were studied,which about the output of system,power generation efficiency,isentropic efficiency,drop of temperature,cool exergy and inlet pressure.Under the circumstance of same inlet pressure and different inlet temperature,the isentropic efficiency and unit mass generation of the expander were contrasted The matching degree of equipments and the flow of lubricating oil also affected the capacity of system.The result suggested that,the maximum generation capacity of pressure energy power generation system was 14.2 kW and the largest unit mass capacity was 35.73 kJ/kg.Under the inlet pressure of 1.2 MPa,the system efficiency was the highest,in which that the power generation efficiency was reached to 33.44% and the isentropic efficiency was 38.57%,and the exergy efficiency was 32.73%.After the expansion,the maximum cool exergy of air was about 785 W.