Study On Conversion And Ultimate Utilization Of Waste Energy Of Temperature Swing Adsorption Cycle For Air Drying

Compressed air is the second largest power source next to electricity.The compressed air system is an energy-intensive sector in industrial enterprises,and its energy consumption accounts for about 9-15%of industrial energy consumption.Compressed air needs to be dried and dehydrated before it can be used.The airdrying system using the temperature swing adsorption(TSA)process can obtain extremely low dew points and is widely used,and its regeneration process requires a lot of energy.Therefore,improving the energy utilization efficiency of the TSA air-drying system is of great significance to the energy saving of the compressed air system.Presently,there are three major problems in the energy utilization process of the TSA air-drying system:the lack of an operating method for variable conditions leads to inefficient use of energy;the waste heat is lost due to the lack of effective recycling means;and the waste pressure is dissipated due to the lack of recycling methods.To solve the above problems,the conversion and ultimate utilization of waste energy of the air-drying TSA cycle is studied in this thesis based on the combination of numerical simulation and experimental research.(1)The dynamics of the air-drying TSA cycle are studied,and efficient operation methods of the TSA air-drying system are obtained.The adsorption equilibrium data of water vapor on activated alumina is measured experimentally,and the experiments of TSA cycle dynamics are carried out;the dual mechanism adsorption potential(DMAP)model,which is used to describe the adsorption isotherm and heat of adsorption,is innovatively introduced into the modeling of TSA cycle dynamics.Then,a novel dynamics model of the air-drying TSA cycle was established,and the accuracy of the model was verified experimentally.The parameter analysis of an industrial-scale TSA air-drying system is conducted based on numerical simulations,and then the influence of parameters such as the water content of feed air,the heating temperature,and the flow rate of purge gas on the TSA cycle is revealed.The relationship formula between the heating temperature and the purge gas flow rate is obtained,which can make the TSA air-drying system operate efficiently under different working conditions.(2)The waste heat self-utilization of the air-drying TSA cycle is studied,and a new process of waste heat self-utilization(WHSU)TSA cycle is proposed to realize waste heat recovery and self-utilization.To clarify the effect of the retrofit from the traditional TSA cycle to the WHSU TSA cycle on the performance of the air-drying system,an industrial-scale TSA air-drying system was taken as a study case,and the numerical studies were conducted on the two TSA cycles.The bed profile and history curves of various parameters of both the adsorption and regeneration steps of the two cycles were obtained through numerical simulation.The energy efficiency,drying performance,and pressure loss of the two cycles are compared and analyzed,and the effect of regeneration pressure on the energysaving potential of the WHSU TSA cycle is studied.In addition,the economic analysis of the WHSU TSA cycle is carried out.(3)The waste pressure self-utilization of the air-drying TSA cycle is studied,and a new process of waste pressure self-utilization(WPSU)TSA cycle is proposed to realize waste pressure recovery and self-utilization.The mathematical model of the WPSU TSA cycle is established,including the expander,heat exchanger,heat reservoir,and electric heater models.An industrial-scale TSA air-drying system was taken as a study case,and then the operating parameters of the WPSU TSA cycle were designed based on numerical simulation,and the drying performance and energy consumption of the two TSA cycles were compared and analyzed.In addition,the economic analysis of the WPSU TSA cycle is carried out.The results show that:(1)During the operation of the TSA air-drying system,the purge gas consumption for heating increases with the decrease of the heating temperature and the increase of the water content of feed air,but is not related to the purge gas flow rate.The purge gas consumption for cooling will not change significantly due to the change in heating temperature and purge gas flow rate,even for the different water content of feed air,the purge gas consumption for cooling will only change slightly.Through the relationship between heating temperature and purge gas flow rate,the TSA air-drying system can be efficiently operated under different working conditions.(2)Compared with the traditional TSA cycle,the WHSU TSA cycle saves about 40%energy and has the same drying performance.Economic analysis shows that the payback period for process change is about one year.(3)Compared with the traditional TSA cycle,the WPSU TSA cycle can save about 37.5%energy and has better drying performance.Economic analysis shows that the payback period for process change is 0.55 years.