Study On Performance Optimization Of Wastewater Tank In Wastewater Recovery System Based On Discontinuous Bath Wastewater

With the global climate change becoming increasingly prominent,the proportion of building energy consumption in the national energy consumption will become larger and larger,and air conditioning and hot water systems are the major energy users in building energy consumption,so more attention should be paid to the use of low-carbon energy.China has a huge amount of wastewater discharge and abundant thermal energy resources.Wastewater waste heat utilization has the advantages of environmental protection,high efficiency and energy saving.However,small and medium-sized,dispersed and intermittent bathing methods in daily life lead to the direct discharge of bathing wastewater,which not only wastes energy,but also causes environmental pollution.Based on the engineering background of bathroom renovation in a factory,this paper tests and optimizes the performance of the intermittent bathroom wastewater waste heat utilization system by combining experimental and theoretical research.Firstly,an experimental platform for waste heat utilization system of intermittent bathing wastewater was built,including hot water preparation and supply system,sewage heat exchange system,data acquisition and control system.After debugging the experimental system and checking the test errors,the operation performance of the system was tested.It was found that the system had some problems,such as excessive temperature drop of sewage in the sewage tank,large fluctuation of hot water temperature and COP in the system preparation,and gradual decrease.The experimental results show that the power of each pump is relatively stable,and the flow rate of sewage heat exchange pump decreases gradually with the decrease of the temperature of sewage pool.The highest temperature of hot water prepared is 54.4 C,but the temperature of hot water prepared after working for about 5 hours decreases by 10 C.The maximum temperature of the top sewage in the sewage tank is 25.1 C,but the temperature of the middle and bottom sewage increases about 1.4 C and 0.8 C respectively,and the temperature of the top sewage decreases rapidly.The temperature of the top sewage decreases to 10 C before the unit stops working in the afternoon.This shows that the current sewage flow situation in the sewage tank leads to poor overall temperature environment of the sewage tank,more waste heat loss,and the unit can not prepare the temperature for a long time.High hot water.How to slow down the rate of temperature reduction in the sewage tank is the key to improve the performance of the unit.Secondly,in order to improve the temperature environment of sewage in the sewage tank,a three-dimensional unsteady mathematical model of the sewage tank was established.After reasonable assumptions were made on the simulation conditions,the heat transfer process of five different inlet and outlet positions of the sewage tank model was simulated by FLUENT software.By comparing and analyzing the temperature environment of five models at different depths and at different time,the best model of heat transfer process temperature environment is selected.The mathematical model of each equipment is obtained by regression of the first experimental data,and the TRNSYS simulation platform of the intermittent waste heat utilization system is established,and the operation before the improvement is simulated.Compared with the simulation and experimental results,the reliability of the simulation platform is verified.After the improved sewage parameters are input into the simulation system,the simulation results show that the heat production of the improved system is 14.77% higher than that of the original system,and the average COP of the heat pump unit is 14.46%.Finally,according to the simulation,the optimal sewage pool model was obtained,and the position of the inlet and outlet of the sewage pool was reformed,and the operation of the system after the reformation was tested.After modification,the hot water temperature prepared by the heat pump unit is higher than that before modification,and the top temperature of the sewage pool is basically the same when bathing,but in the non-bathing period,the top temperature reduction rate decreases significantly after modification.After the improvement,the temperature of the middle sewage is obviously higher than that before the improvement,and it can provide heat for the top sewage heat transfer.After improvement,although the power of each equipment increases slightly,the COP of heat pump unit and system is 0.3-0.6 higher than that before improvement.