Study Of The Characteristics Of Semi-coke Combustion And The Harmful Emissions

In this paper,S/N transfer rule during the pyrolysis and combustion of Shenmu coal?SM coal?was studied.Results of XPS analysis for SM coal pyrolysis show that pyrite and sulfide decreases with the increasing temperature,and disappears after 600?.Sulfoxide decreases as the temperature increases and disappears after 700?.Thiophene reduces slightly with coal tar production and then continues to increase because of the polycondensation at high temperature.Sulphone increases before 600?and then begin to decompose.With the rising temperature,sulfate shows an increasing trend because of the reaction between pyrite and oxygen-containing functional groups or some other sulfur compounds in an oxidation state.N-6 first increases and then decreases.N-5decreases as temperature increases before 500?and then is transformed into the more stable N-6.N-Q and N-X decrease as temperature rises.From XPS analysis results of SM coal,semi-coke and their burning ashes,it is showed that semi-coke has the advantages of low sulfur content,high porosity and big specific surface area.Part of SO₂ produced by sulfur speciation combustion continues to react with CaO in semi-coke and to be captured as sulfate in ash,which is 3 times more than original semicoke,even 10 times more than raw coal.Besides,the content of N in semi-coke decreases significantly with increasing temperature and all nitrogen speciation transform to the gaseous products after combustion.The NO_x emissions from semi-coke combustion are significantly lower than SM coal.Consequently,burning semi-coke can reduce the emissions of SO₂ and NO_x compared with the corresponding raw coal.A modified coupling system of large scale TG and gas analyzer was used to simulate the combustion behavior in the coal burning stoves.The rapid combustion characteristics and gaseous product emissions of SM coal and semi-coke were investigated.Results show that the emissions from semi-coke combustion are reduced significantly.The production of SO₂ and NO_x from coal combustion is 2.51 and 1.71times more than semi-coke combustion,respectively.In order to investigate the feasibility of semi-coke substituting to bituminous coal and anthracite for clean combustion,several representative coals from different zones were selected for burning to compare the emissions of noxious gases?SO₂,NO_x?and particulates?PM 2.5,TPM?.The different burning facilities were used,including Shanbei stove,Beijing stove and hearth.It is found that the emissions of PM 2.5,TPM,NO_x and SO₂ for burning bituminous coal are higher than burning semi-coke.To compare with anthracite,semi-coke has advantages of low ignition point and longer burning period.Rapid combustion kinetics of particulate semi-coke and briquette semi-coke were studied using shrinking particle model and shrinking core model,respectively.The kinetic parameters were obtained using the software of ANSYS and OpenLu.For the rapid heating stage and constant temperature stage of semi-coke combustion,shrinking particle model were used to determine the kinetic parameters.The diffusion through gas film and chemical reaction were simultaneously considered in the model.For the rapid heating stage and constant temperature stage of briquette semi-coke combustion,shrinking core model was used to calculate the kinetic parameters.The three resistances were taken account the consideration including gas film diffusion controlling,ash layer diffusion limitation and chemical reaction step.Finally,the variation of the two or three step resistances during combustion was discussed.Combining the basic properties of SM coal and the technological process of the Sanjiang gas combustion rectangular retort?SJ-retort?,1000 kg of SM coal were taken as the object to investigate the heat and material balances of the SJ-retort operation.Results show that the heat required?1299.08MJ?for SM coal retorting can be provided by its retorting gas combustion and the heat released from the retorting process.About1/3 total retorting gas was utilized for retorting process while other 2/3 is surplus.