Research On Pilot-scale Experiment Of The Dry Anaerobic Digestion Of Swine Manure And The Experiment Of Material Fluidity

The development of swine's scale breeding industry produces a large number of swine manures in limited region.Dry fermentation for biogas production,as an effective technical means of processing swine manure,have much advantages,such as swine manure not to be diluted,less digested effluent,easy to land ultilization.Aiming at whether continuous dry biogas fermentation of the swine manure is feasible or not in practical applications,based on previous lab-scale trial,a pilot-scale experiment of continuous dry fermentation of swine manure lasting for 17 months was conducted using steel horizontal reactor at ambient temperature.The characteristics of the fermentation residue and the material liquidity were studied as well.The following results were obtained.Monitoring results of these indexs such as daily biogas production,monthly biogas components,pH,content of TS and VS in feeding and discharging,ammonia nitrogen in digested residue,showed that the pilot-scale experiment could normally produce biogas and basically smoothly feed and discharge digested residue.Methane content in biogas stabilized at around 53%in most months.The average volumetric biogas production rate was 0.164 m3/(m3?d)and the average biogas yield of feedstock was 95 L/kgTS.The p H value ranged from 7.4 to 8.5.There was almost no inhibition of ammonia.The pilot-scale experiment indicated that the process of continuous dry biogas fermentation of the swine manure has the potential of promotion and application in biogas plant.However,the pilot-scale experiment had the low efficiency and unstable biogas production since there was no heating and insulation.After the pilot-scale experiment,the test of 12 batches of digested residues and 6 batches of raw swine manure were carried out to obtain the potential of biogas production.Common indexes relative with fertilizer and heavy metal for the digested residue were detected.The monthly results showed that the biochemical biogas potential of pilot swine manure and digested residue was 261 L/kgTS,202L/kgTS,respectively,reflecting poorly gas production of the pilot fermentation.The average digestion efficiency of swine manure in the pilot-scale experiment was only 35.7%,which indicated the digestion was low and the digested residues should be re-fermented.The fertilizer effect of the fermentation residue is more significant,and there is no safety risk as a biogas fertilizer application.The viewpoint of using the flow rate to characterize the liquidity of the digested residues is proposed.In reference to the flow rate of the transport of sludge and the minimum simulated flow rate required for the dry biogas fermentation plant,the critical flow velocity is determined to be 6 mm/s.The material characteristics and the exit hole characteristics were determined as the factors influencing the liquidity of the digested residue according to the energy conversion model when the digested residues of swine manure were discharged from exit hole.Total solid and organic content,temperature,etc,are mainly the material properties.The height differences,the loss of resistance,etc,among the characteristics of the discharge hole,are the main influencing factors.The flow rate and the loss of resistance affect each other.The effects of total solid content,diameter and height difference on the flowability of dry digested residues were studied using horizontal U-type organic glass tube designed by myself.The results showed as following.(1)The total solid content of the material has a significant effect on the flowability.The lower was the total solid content,the better was the flowability.Using the critical flow velocity 6mm/s as the standard,the solid content of final digested residues of swine manure in dry fermentation biogas plant should not exceed 21%.Taking 21%of the solid content in final digested residues as the benchmark,to ensure the successful discharge of the digested residues,the diameter of the discharge pipe should not be lower than 125mm,and the solid content of the fed swine manure should not exceed32.7%.(2)The impact of pipe diameter on the liquidity showed that the larger was the diameter,the better was the liquidity.In order to the successful discharge digested residues,when the solid content of the residue was greater,the greater diameter should be set.(3)For the same total solids content and diameter,the average flow rate of the digested residue in discharge pipe showed a tendency that the average flow velocity decreased slowly and ultimately tended to zero with the decrease of height difference.The derived approximate calculation formula (?) of the average velocity of the digested residue flowing from exit hole of dry biogas digestor,to a certain extent,could guide the design of discharge system of dry biogas digestor in biogas in practice.