Mechanism Study On Pyrolytic Disposal Of Animal Biomass By Using Pork And Pig Bone As The Representatives

As a typical animal biomass,animal carcass is inevitably produced during animal husbandry,and more carcasses are produced during outbreaks of infectious diseases like Bovine Spongiform Encephalopathy(BSE),swine fever or bird flu.Once these carcasses are not disposed in time or properly,it will cause serious environmental pollution.To dispose animal carcasses quickly and safely,pyrolytic method deserves extensive application but relevant studies on pyrolytic disposal of these carcasses are limited.So,in this work,pig carcass is chosen as a representative example of a typical animal carcass,and the pyrolytic products charaterisitcs of pork and pig bone,as well as the effect of water,fat,protein and bone on both pyrolytic kinetic charaterisitcs and pyrolytic products charaterisitcs,have been studied.Meanwhile,the influence of the addition of pig carcass during operation of a large-scale pyrolytic rotary kiln has also been studied.Results are listed as follows:(1)The pyrolytic process of pork can be divided into drying(from beginning to 70?),evaporation(from 70 to 180?),the pyrolysis of protein(from 180 to 300?),and the pyrolysis of fat(from 300 to 500 ?).The drying of pork is accompanied by the volatilization of small molecule peptides,fatty acids and esters.Most of water is evaporated during the evaporation stage.The pyrolysis of protein releases inorganic gases like CO2,NH3 and HCN,as well as some organic components like amides,carboxylic acids and aromatics.The activation energy of protein varies from 61 to 92 kJ/mol.The pyrolysis of fat produces large amounts of hydrocarbons,aldehydes,fatty acids and aromatics,and the activation energy of fat varies from 143 to 182 kJ/mol.In addition,protein and fat may react to produce lots of amides,thus accelerating the pyrolysis process.The pyrolysis of bone mostly happens from 180 to 530?,and it is the protein in bone that causes the weight loss.Like protein,the pyrolysis of bone produces CO2,NH3,hydrocarbons and amides,with its activation energy varying from 97 to 158 kJ/mol.(2)Compared with the pyrolytic products of coal and lignocellulosic biomass,the pyrolysis of pork produces more CH4 in gaseous product,resulting in a higher calorific value bio-gas,which is a promising gas fuel.Meanwhile,the Brunauer-Emmett-Teller(BET)surface area of pyrolytic char of pig bone is 130.827 m2/g and it is a porous material rich in Ca and P.So,it is more adaptable to be an adsorbent or to be a potential fertilizer compared with coal char and lignocellulosic biomass char.(3)Water has a significant influence on gaseous products formed.The presence of water leads to greater CO and H2 yields through steam gasification reactions,and greater CH4 and C2H4 yields through steam reforming reactions.Meanwhile,the water can produce H radicals at high temperature,resulting in higher conversion of N containing compounds into NH3 rather than HCN.The existence of water also destroys the crystal structure of bone char,and rupture its small mesopore to produce larger mesopore,thus leading the increase of BET surface area and pore volume.(4)Tar yields are mostly determined by the products obtain from the pyrolysis of fat,which include many hydrocarbon compounds derived from the cracking,decarbonylation and decarboxylation of long chain fatty acids.When pyrolytic temperature keeps rising,more acromatic compounds are obtained in pyrolytic tar through the cyclisation of these hydrocarbons.Like water,fat may also cause the increase of BET surface area and pore volume of bone char.(5)The decomposition of protein leads to the formation of small molecules like NH3 and HCN.It can react with fat to produce long chain amides and nitriles,increasing the tar yield.These amides and nitriles can be cyclized to form more N-heterocyclic compounds under higher temperatures.The pyrolysis of protein procudes lots of smooth and flat char,thus reducing the BET surface area and pore volume of total pyrolytic char.(6)The pig bone is rich in Ca and P.The presence of minerals in bone is found to increase the CO2 yields through decarboxylation,and to promote steam gasification and steam reforming reactions,thus lowering the chance of the formation of NH3 and HCN by H radicals.Moreover,these minerals promoting the cyclisation reaction of hydrocarbons,esters,amides/nitriles to produce more aromatic O-heterocyclic and N-heterocyclic compounds,respectively.During pyrolysis,the PO43-in hydroxyapatite is carbonized,and K presents in pork participates in the crystallization of pig char,forming a new crystal compound Ca8H2(PO4)6·KHCO3(7)During the disposal of medical waste in large-scale pyrolytic rotary kiln,no extra energy is needed when the addition of pig carcass is less than 49.5 wt.%.Also,the addition of pig carcass will cause the increase of NOx in flue gas and shift the production curve to higher temperature.The water presents in pig carcass leads to the transference of Cl from bottom ash to fly ash.To keep a good working condition in pyrolytic rotary kiln,the rotate of rotary kiln should speed up with the addition of pig carcass.