Research On The Optimization Of Large-scale Treatment And Recycling System Of Vegetable Waste

China is a large country in the production and consumption of vegetables,in recent years,with the increase of vegetable planting scale year by year,high-quality plateau summer vegetables in the northwest,southwest and other regions have gradually formed a large-scale vegetable production and sales chain,but the matching perfect vegetable waste treatment chain has not been formed,resulting in a large number of baby vegetables,lettuce,celery,broccoli and other VW,not only caused a waste of resources but also adversely affected the environment.Compared with the problems in the process and operation of the existing VW treatment system,the large-scale treatment method of VW with constant temperature fermentation as the core is not only highly targeted for the physical and chemical properties of VW,but also can meet the requirements of large-scale treatment and recycling,so as to achieve"harmlessness,reduction and resource utilization".This paper analyzes the trial operation effect and current process problems of a large-scale VW treatment system in Lanzhou City,and proposes an optimization system for large-scale treatment and recycling of VW based on constant temperature fermentation process.On this basis,a system simulation model is constructed,and the performance difference between the optimization system and the design system is compared and analyzed,revealing the energy economy,and providing some references for the large-scale treatment process and system operation of VW.Its main research contents and conclusions are as follows:（1）According to the material balance analysis,the design system can theoretically produce about 32400m³of biogas under the condition of full load operation with a daily processing capacity of 2000t,and the biogas residue is sold to the fertilizer plant as a fertilizer raw material,and the wastewater that meets the standard is discharged to the downstream sewage treatment plant for further degradation treatment.Combined with the field investigation to obtain the operation data of the trial operation of the system in 2022,a total of 48351.72 tons of VW were treated during the period,which was equivalent to a gas production capacity of 10.85m³/t of VW,a total of 48646 m³of wastewater discharge,a total of 3901.5 tons of biogas residue,and a treatment cost of 90.95 yuan/ton.The analysis showed that there were problems in the system:sludge was generated by drug addition and it was difficult to effectively degrade,and it did not achieve true harmlessness;The design process does not conform to the physical and chemical characteristics of VW,and the system fermentation process is prone to instability.The gas production was quite different from the theoretical value,and the biogas liquid was discharged in the form of wastewater that met the standard,which did not reach the complete resource utilization of VW.During the trial operation,the original biogas internal combustion generator set in the plant did not reach normal utilization,and a large amount of waste heat was not effectively recovered,and the overall system had problems such as low efficiency,high loss and high operating cost.Therefore,the current design system has a large room for optimization.（2）In view of the problems existing in the current system design process and trial operation,an optimization system for large-scale treatment and recycling of VW based on constant temperature fermentation process is proposed,and the process of"pretreatment（crushing+hydrolysis）+constant temperature anaerobic digestion+biogas purification+biogas cogeneration+waste heat recovery unit+solid-liquid separation+aerobic aeration treatment+biogas residue for sale"is adopted.The process of using aerobic aeration treatment to produce biogas liquid that can be used as liquid fertilizer for returning to the field instead of sewage treatment degradation to generate wastewater that meets the standard,and optimizing the waste heat recovery mode,adding water source heat pump to recover the waste heat of the aerobic process.According to the existing data and design parameters of the plant,determine the capacity and selection of the main equipment of the optimization system.（3）Select the corresponding module in TRNSYS to build the simulation model of the original design system and optimization system,and write the corresponding control module.The simulation models of the original system and the optimized system were combined to calculate the thermoelectric loads of the two systems,simulate the full-load operation of the system and analyze the operation performance according to the results.Simulation results show that:during the operation period,the electric load of the optimized system is reduced by about39.84%compared with the original system,with significant energy saving effect;the power generation of the original system and the optimized system can be 93.6%and 147.2%of the total electric load,respectively,and the original system needs to make up 670190.6 k W·h;The original system requires 3.30×10⁶ k W·h of boiler make-up heat in addition to the basic waste heat recovery of the internal combustion generator set.The heat recovery utilization rate of the optimized system is 43%for the biogas combustion of the CHP unit,and the power of the water source heat pump is 292.09 k W,with an average operating COP of 4.506,which can meet the system’s own heat load demand without additional make-up heat.The system energy utilization rate and thermal effective utilization rate are 73.86%and 91.70%,130.64%and 92.88%,respectively.The optimized system achieves fuller recovery and utilization of thermal energy,and the heat balance performance is improved compared with the original system;The annual CO₂emission of the optimized system is 6431.52 t,with an average emission reduction of 4.95kg/t of vegetable waste and an emission reduction rate of 22.07%,which effectively enhances the environmental benefits;The initial investment of the optimized system was 87.78million yuan,which saved 34.0%compared with the original system,the treatment cost was24.64 yuan/t,which was 60.87%lower than the original system,respectively,which had greater economic value for the optimization of the process and control strategy.This paper innovatively applies the anaerobic digestion and aerobic aeration harmless treatment process of VW to the large-scale treatment system,and proposes an optimized system for the large-scale treatment and recycling of VW based on the constant temperature fermentation process.The process operation of the original system and the optimized system is built and simulated using the TRNSYS simulation platform,and the energy economy and environmental benefits of the large-scale VW treatment and recycling system are revealed through comparison with the new process.