Experimental Study On Pyrolysis Carbonization Characteristics And Equipment Of Seafood Waste

Seafood is an important part of the food chain system,and seafood processing has become an important economic activity in the world.A large amount of seafood waste,about 433.21million tons,is produced in the process of seafood processing and consumption in the world every year.If these seafood wastes are used,it will produce tens of millions of industries.The huge economic value and people’s requirements for the environment make the follow-up treatment of seafood waste become the focus of attention.Pyrolysis is a simple and convenient method to treat solid waste,which has the characteristics of short treatment time,harmless treatment at high temperature and products with additional industrial value.Pyrolysis has obvious advantages in solid waste reduction,harmless treatment and resource utilization,and has been widely used to treat various solid wastes.In this thesis,three typical seafood wastes,fishbone（FB）,shrimp shell（SS）and laminaria japonica（LJ）,were taken as the research objects,and the pyrolysis carbonization characteristics of three kinds of seafood wastes were studied,the kinetic analysis was carried out,focusing on the influence of pyrolysis and carbonization conditions on product distribution and the migration and transformation of nitrogen during pyrolysis.In order to solve the problem of large-scale continuous treatment of seafood waste,a moving bed pyrolysis carbonization device with pretreatment capacity of 20-30 kg/h was designed,and the pyrolysis carbonization experiment of seafood waste was carried out with the device.The specific research results are as follows:Based on the elemental analysis,industrial analysis and composition analysis of seafood waste,the pyrolysis characteristics of seafood waste at different heating rates and the influence of heating rates on the pyrolysis process of seafood waste were obtained by thermogravimetric analyzer.The results show that the pyrolysis process of three kinds of seafood wastes can be divided into three stages:drying and dehydration,organic matter decomposition and volatilization analysis,carbonization and inorganic matter decomposition.The decomposition and volatilization analysis of organic matter are the main weight loss stages of pyrolysis.At this stage,the weight loss rates of fish bones,shrimp shells and laminaria japonica are about 40%,50%and 60%respectively,and the maximum weight loss rates are 0.25%/min,0.30%/min and0.70%/min respectively.At the same heating rate,the pyrolysis start temperature,maximum weight loss rate temperature and end temperature of fish bones and shrimp shells are higher than those of laminaria japonica.With the increase of heating rate,the thermal degradation process of three kinds of seafood wastes shows the same change law,TG and DTG curves move to high temperature area,and the pyrolysis characteristic parameters of raw materials increase.The comprehensive pyrolysis characteristic index value increases with the increase of heating rate,and the higher heating rate makes the generation and release of volatiles in raw materials faster,which is beneficial to the rapid pyrolysis.Coats-Redfern model fitting method and Flynn-Wall-Ozawa conversion method at non-isothermal rate were used to analyze the pyrolysis kinetics of seafood wastes.The results showed that the pyrolysis mechanisms of fishbone,shrimp shell and laminaria japonica belonged to first-order,first-order and third-order chemical reactions,respectively.The pyrolysis mechanism of laminaria japonica was more similar to that of cellulose or polysaccharide biomass,and the average apparent activation energies of fishbone,shrimp shell and laminaria japonica were 226.73 k J/mol,263.52 k J/mol and 194.54 k J/mol,respectively.The study on the influence of pyrolysis carbonization conditions on the distribution of pyrolysis products of seafood wastes shows that with the increase of reaction temperature,the yield of solid products gradually decreases;The yield of liquid products increased before 500℃,and then decreased gradually with the increase of temperature.The highest yields of liquid products from fish bones,shrimp shells and laminaria japonica pyrolysis were about 34.53%,18.94%and 15.33%respectively.The amount of gas phase products increased gradually.With the extension of pyrolysis residence time,the yield of solid products gradually decreased;The yield of liquid products increased first and then decreased,and the highest yield was obtained when the residence time was 1 h.The amount of gas phase products increased gradually.With the increase of reaction temperature,the nitrogen in the pyrolysis products of seafood wastes gradually transferred from solid to liquid and gas.When the temperature continued to increase,the nitrogen in the liquid products obviously transferred to the gas products.The results of nitrogen migration and transformation show that the nitrogen-containing functional groups in pyrolysis solid products are mainly protein nitrogen N-P,pyridine nitrogen N-6,pyrrole nitrogen N-5 and quaternary ammonium nitrogen N-Q,and the changes of each nitrogen-containing functional group are similar to some extent.Nitrogen-containing compounds in pyrolysis liquid products are mainly nitrogen-containing heterocyclic compounds,amines,amides and nitriles,among which amines and amides have the most kinds and the highest relative content.The nitrogen-containing gases generated by pyrolysis are mainly NH₃and HCN.With the increase of reaction temperature,the output of NH₃and HCN increases gradually,but the output of NH₃is obviously higher than that of HCN.The designed moving bed pyrolysis carbonization device requires little carrier gas,and can continuously treat seafood wastes with high water content and high ash content in large quantities,converting them into high value-added carbonized products,which has good feasibility and application prospects.In order to ensure the stability of the device during operation and ensure the full pyrolysis and carbonization of raw materials,the screw speed should be set below 8 r/min,and the actual treatment capacity of the device should be controlled between 20-25 kg/h.When the temperature of pyrolysis carbonization device is 400℃and the screw speed is 5 r/min,the distribution of pyrolysis products of three kinds of seafood wastes in moving bed is similar to that in tube furnace experiment.High solid product yield can be obtained by continuously treating seafood wastes in large quantities by this device,and the highest yield of mixed seafood wastes can reach 52%.