Study On Transformation Of Pressure Regulation System In Ji Nan Guide Gate Station And Analysis For Energy Conservation And Emission Reduction

The environmental pollution caused by coal,oil and other fossil energy is becoming more and more serious nowadays.Among all fossil fuels,natural gas is the cleanest one with high hydrogen / carbon ratio and the lowest carbon dioxide emissions,and it has become an environmental friendly energy.Therefore,in order to reduce the pressure on the environment and improve the energy structure,China is now vigorously promoting the use of natural gas.In recent years,natural gas in the energy structure occupies an increasing proportion.As a result,the energy saving and emission reduction is huge.Pipeline transportation is the most common mode of transport for onshore natural gas.Taking the economy of transmission process into account,long-distance pipeline transport all adopts high-pressure conveying.After a long distance transport from the gas source to the city,high-pressure gas need to be transferred to medium-pressure in regulator station before entering the city gas pipe networks for users.Regulation through throttle is the traditional means to adjust pressure.Due to the existence of Joule-Thomson effect,the temperature of nature gas will decrease after the throttling process.Especially in the freezing areas of the north,the temperature of natural gas will be twenty degrees Celsius below zero or even lower because of high pressure throttling,which leads to frost and ice blockage in pipeline system and equipment and also posts a great challenge for safe operation of gate station.On the other hand,high-pressure natural gas contains huge pressure energy,while the traditional means of throttle depressurization makes a large part of the energy consumed in vain.In this paper,the current analysis methods commonly used in thermodynamics and energy applications are introduced,and the traditional energy analysis and exergy analysis methods are compared.After that,the process of adjusting pressure is modelled and the exergy analysis from the point of thermodynamics was made for the pressure adjusting process.The exergy efficiency of turbines is better than throttle valves,with 0.861 and 0.721,respectively.Then the original pressure regulation process,preliminary transformation and the second transformation process of Jinan Guidemen station are introduced.The preliminary transformation solved the pipeline frosting by way of adopting natural gas boiler and tube heat exchanger,and the regulator outlet temperature rised from-22.0? to 17~40?,but with huge energy consumption.The second transformation added flowrate control system and heat storage tank with the regulator outlet temperature dropping to 5 ?.Then though the analysis of preliminary transformation and the second transformation process of Jinan Guidemen station,it is found that the existing transformation process only solves the low temperature problem after natural gas pressure regulation,The main irreversible loss of the regulator is still very large due to the existence of throttle valves,81.3% and 84.6% respectively.Finally,the analysis of energy saving and efficiency and economic benefits after the initial and second transformation is performed from the practical engineering point of view.It is found that the second transformation will increase the investment cost compared to the first one,but save 46.2% of the operating cost per year,and it will be able to recover all the investment costs in two years,so the economic benefits are significant.And it is also environmental friendly since the annual carbon dioxide emission reduction is 14.7t.Based on the analysis of the available energy properties in the natural gas pressure regulation process and the natural hydrate gas storage and peak-shaving process,it is recommended to establish coupling in the above two process.A system flow of coupling scheme is proposed,which can realize not only the natural gas pressure regulation process but also the gas storage and peak-shaving.The system has a good prospect from the perspective of comprehensive utilization of energy,but there is no practical application.Industrial applications need further technical and economic verification and natural gas hydrate synthesis technology as a support.