| The continued rise in global fossil energy consumption has caused the energy crisis and posed serious challenges to the environment and climate.Accelerating the transition to a green and low-carbon energy system is an inevitable requirement for future energy development.The use of anaerobic digestion technology to convert organic waste into biogas,which is then purified and upgraded to obtain biomethane,which on the one hand achieves the recycling of waste resources,and on the other hand,biogas can be used as a supplement to conventional natural gas to increase the share of renewable energy in the energy system.The purpose of this paper is to quantify the potential of biomethane from various types of urban organic waste and to demonstrate the feasibility of using natural gas pressure to achieve biogas upgrading and injecting into natural gas grid.The main content and conclusions of this paper are as follows:(1)The method for estimating the potential of biomethane from various type of urban organic wastes is proposed,with the aim of quantifying the energy that can be recycled from various waste materials.(2)The pressure energy cryogenic method is proposed,in which the pressure energy is converted into mechanical energy and cold energy by an expandor in the natural gas pressure reduction station,and the cold energy is used to upgrade biogas and the mechanical energy is used to generate electricity.And the upgrading process with pressure energy cryogenic method is calculated using HYSYS software.The results show that the method can increase the methane content in biomethane to more than 95%.The maximum biogas treatment capacity of the process increases with increasing natural gas inlet pressure,methane content,flow rate and biogas inlet pressure and decreases with increasing natural gas outlet pressure.Heat exchangers and expanders are the main equipments in the process that contribute to the total loss.(3)The life cycle assessment of high pressure water scrubbing method,chemical absorption method,pressure swing adsorption method,membrane separation method,traditional cryogenic method and pressure energy cryogenic method is carried out using e Footprint,an online life cycle assessment system.The results show that the primary energy consumption and water resource consumption of the pressure energy cryogenic method are much lower than that of the commonly used upgrading methods;the climate change is basically equal to that of the PSA method,which is lower than the membrane separation method,the traditional cryogenic method,the chemical absorption method and the high pressure water scrubbing method.(4)Using Changshu,a typical industrial city,as a study case.The raw data was obtained by field investigation and the research results show that the biomethane potential that can be used at scale in Changshu reaches 11.96%of its annual gas consumption in 2018.The natural pressure exergy that can be recovered at each pressure reducing stations in Changshu reaches 3.11×10~5k J,and the amount of biogas that can be upgraded is about 1.15×10~6m~3/d.For the 61215 m~3/d of biogas that can be concentrated,the pressure exergy at Xieqiao Station,which has the largest gas supply capacity,can achieve biogas upgrading and biomthane injecting into natural gas grid,with significant economic and environmental benefits. |
