Study On The Effect Of Heat And Mass Recovery On The Performance Of Vegetable Waste Treatment System At Scale

With the vigorous development of vegetable industry characterized by healthy and green,the domestic vegetable production has increased rapidly,but due to the lack of unified planning and corresponding guidance,farmers’blind disorderly planting has led to a large number of vegetables of the same kind being marketed centrally,and businessmen,in order to pursue maximum profit,usually fine-tune the processing of vegetables,resulting in a large amount of VW（vegetable waste）in circulation,at the same time,the scale treatment process of vegetable waste adopted at this stage in China cannot efficiently process and utilize VW resources.In view of the problems of instability,low efficiency and high cost of the existing VW scale treatment system,considering the nature of VW with high water content,fast acidification and hydrolysis rate and as a kind of available resource,combining with the existing research,based on the typical VW scale treatment system in actual operation,comparing and analyzing the energy consumption under theoretical and actual working conditions of the system,putting forward the problems in the operation of the system and pointing out the direction of energy saving and consumption reduction.Point out the direction of energy saving and consumption reduction.The stability and gas production of the optimized system are analyzed.The energy consumption of the system and the related parameters of the heat pump are simulated by TRNSYS software,and the operation cost is calculated.It is pointed out that the improvement of the system in terms of thermodynamic performance,economic performance and environmental benefits,and provides some ideas and references for the improvement of the quality and efficiency of the VW scale treatment system in the future.The main research contents and conclusions are as follows:（1）Based on the data collected in the field,the process and equipment power consumption of a typical VW scale treatment system operating in Songming,Yunnan Province were analyzed.The main process"pretreatment+anaerobic fermentation+digestate dewatering+wastewater treatment"has a large optimization space,which is characterized by an average p H of 6.81 in the fermenter and an internal acidification imbalance,an average temperature of30.4℃in the anaerobic fermenter,a hydraulic residence time of 7 days,low treatment efficiency,insufficient treatment capacity and low gas production efficiency.low gas production efficiency.The actual energy consumption of pretreatment subsystem and anaerobic fermentation subsystem in Songming plant is 108.44%of the theoretical energy consumption,among which the energy consumption of pressing process accounts for the highest percentage,and the theoretical electricity consumption of digestate dewatering system and sewage treatment system equipment is lower than the actual data of 79315k W·h,and the electricity consumption exceeds the standard by 31.37%.Based on the problems obtained,energy saving measures were proposed:the low and unstable working efficiency of the pressing equipment could not realize the reduction of VW.After analyzing the feasibility,the pressing and dewatering equipment was removed,and all the crushed VW and wastewater were directly input into the hydrolysis tank.The energy consumption of the pre-treatment sub-system can be reduced by 40.45%,with obvious energy-saving effect.（2）Construct a new system for large-scale VW treatment with heat and mass return,compare the heat load of the plant and the heat recoverable in the heat and mass return process,simulate the heat pump energy supply process in TRNSYS software,and the simulation results prove that using heat pump waste heat recovery system to supply heat can meet the system heat load;using heat pump direct heat exchange is more energy efficient than using heat exchanger indirect heat exchange,saving 37.17%,confirming The use of heat pump direct waste heat recovery and medium temperature anaerobic fermentation can maximize the efficiency of heat pump.Analyzing the system stability and gas production,the temperature of the inner wall surface of the fermenter is 34.9℃and the average internal p H value is 7.97,which means the internal operation is stable;returning heat and mass can increase the gas production of VW scale treatment system by 28.81%.（3）The initial investment of the vegetable waste scale treatment system with heat and mass return is 24.08%higher than that of the original system,the cost of treating each ton of vegetable waste is 64.66 yuan,and the net benefit of treating each ton of vegetable waste is 11.57 yuan,which is 21.18%lower than the treatment cost and 33.6 yuan/t higher than that of the original system in sick operation in Songming;the treatment cost is 14.93%lower and the net benefit is 15.07 yuan/t higher than that of the original system in normal operation in Songming.The average comprehensive energy utilization rate of the scale vegetable waste treatment system in Songming was 64.60%in no rmal operation,and the average comprehensive energy utilization rate of the new system was 86.49%.The average comprehensive energy utilization efficiency of the vegetable waste scale treatment system after adding heat and mass return increased by 21.89%,and the energy saving rate was 63.83%.The emissions of SO₂ and NO_x of the new system were reduced by 8.83%and 8.89%,respectively,compared with the original system,and the release of CO₂ was reduced by51.00%,and the CO₂ emission reduction was increased by 4.50%.The environmental benefits generated in reducing greenhouse gas emissions were enhanced by 5.78%,and the environmental benefits were significantly increased.High lights:（1）This paper innovatively builds a vegetable waste scale treatment system with heat and mass return against the background of an actual operating project.Through heat pump,waste heat is recovered from the high-temperature sewage inside the wastewater treatment system to meet the heat load of the core anaerobic fermentation system and enhance the treatment capacity,treatment efficiency and gas production of the system;through methane return flow,the stability of the system is enhanced and the internal p H value is maintained,which ensures VW scale treatment system is efficient,low cost and stable operation.（2）The operating costs and benefits of the vegetable waste scale treatment system with heat and mass return were calculated,and the initial inv estment,comprehensive energy utilization rate,energy saving rate and harmful gas emission of the new system were compared with the original system,and the effect of heat and mass return on the improvement of the vegetable waste scale treatment system in terms of thermodynamic performance,economic performance and environmental benefits was determined.