Experimental Study On Sludge Drying System With Heat Recovery And Double Heat Source Heat Pump

As an energy intensive industry,how to reduce its energy consumption and carbon emissions is an important issue in recent years.Sewage treatment accounts for about 0.6%of the annual electricity consumption of the United States,0.7%of the total electricity consumption of Germany and only 0.25%of the total electricity consumption of China.The unit power consumption of sewage treatment in the above countries is about 0.52 kWh/m³,0.40 kWh/m³ and 0.254 kWh/m³[1].Compared with developed countries,the energy consumption of sewage treatment in China is obviously at a low level.However,the energy consumption of sewage treatment is affected by sewage treatment level and treatment requirements.China’s sewage treatment level and scale still have a large space to rise,which means that while the scale and standard of sewage treatment in China are further improved,the energy consumption and discharge brought by sewage treatment will continue to improve.Therefore,the energy saving and efficiency increasing of sewage treatment plant is a subject of practical significance.In order to solve the problem of high cost of sludge treatment and low utilization rate of waste heat energy in sewage treatment plant,and provide technical and theoretical support for the transformation of sewage treatment plant from energy consumption unit to energy recovery unit and even further to capacity unit.Based on the recovery and utilization of waste water and the drying characteristics of sludge,this study intends to establish an energy-saving and efficient low-temperature dual source heat pump sludge drying equipment.First of all,the current sludge drying technology and sludge drying characteristics are introduced.According to the existing problems of drying equipment and sludge disposal,the research significance of waste heat recovery dual heat source heat pump low temperature sludge drying system is put forward.Then,according to the experimental study of sludge drying characteristics,a dual heat source heat pump low-temperature sludge drying system for low-temperature sludge drying was designed.According to the working principle of low-temperature sludge drying technology of dual heat source heat pump with waste heat recovery,the experimental platform of low-temperature sludge drying system of dual heat source heat pump with waste heat recovery is designed and the test system is determined from the perspective of overall optimal operation of the system.The drying and dehumidification effect of the system and the energy consumption of heat pump are analyzed by experiment.The results show that the increase of air speed in the early stage of sludge drying is much greater than that in the middle and later stage.With the increase of temperature,the time difference reduced by the increase of drying temperature decreases gradually.Under the condition of low wind speed,the increase of temperature has a greater effect on the drying speed,because when the drying enters the later stage,the drying air speed can be appropriately reduced or the drying temperature can be increased.When the temperature increases,the wood sludge in the sludge can form supporting effect and enhance the diffusion,which results in that the drying rate of the sludge in the initial stage of sludge drying is higher than that of the pure sludge.At low temperature,the sludge is not easy to produce surface fracture,which is more obvious in the modulation of sludge.This can ensure that the sludge will not fly away due to the generation of broken small particles under high wind speed,and reduce the safety risks.However,in the later stage of sludge drying,it is a disadvantage factor for sludge drying.Therefore,in the later stage of sludge drying,the drying temperature should be increased and the drying wind speed should be reduced.At the same time,the sludge should be broken twice by physical means.The maximum energy consumption of the low-temperature double source heat pump sludge drying equipment is 3.73.1kg_（H2O）/kWh after the maximum calculation of the energy consumption of the fan and water pump（using the sewage evaporator and hot air drying at 60℃）,and 3.1kg_（H2O）/kWh when using the air evaporator.It has good energy-saving performance and can be applied to a variety of adverse weather conditions.