Study On The Key Technologies For The Preparation Of Civil Clean Coke And Adjustment Of Coke Oven Gas Composition

The pollutants as particles matter?PM?,sulfur dioxide?SO₂?and nitrogen oxide?NOX?emitted from the combustion of civil raw coal are one of main cause of formation of haze.Haze has been hot issue concerned commonly by the public and all levels of government,as a result of the influences and harms on ecological environment and human health.It is imperative of the clean treatment of civil raw coal.Due to excess production capacity of metallurgical coke and low efficient utilization of coke oven gas,many coking enterprises has been discontinued or the enterprises benefit has been declining.With the help of coking industry,the production of civil clean fuel shows the importance.By reasons of high ignition temperature,short flame length,poor continue burning ability,and large emitting pollutant,metallurgical coke as a product of coking is difficult to apply directly in civil combustion.Because of rich in hydrogen and lack of carbon,coke oven gas can not effectively to synthesize chemicals or concentrate methane.In light of the existing problems,this paper carries on research on the key technologies for the preparation of civil clean coke and adjustment of coke oven gas composition,which includes two-step fixing sulfur and removing nitrogen as well as de-nitration,catalytic combustion-supporting,increasing carbon monoxide,and reducing hematite coupling methane enrichment.This paper has an important practical value and scientific significance.Civil clean cokes were prepared by the high pyrolysis of coal blending,which obtained from shanxi coking coal as raw coal added CaCO₃,CaO,Fe₃O₄,and potash feldspar additives or composite additives with the multipurpose.On the high temperature reaction furnace,iron box equipment and industrial coking oven at different level equipments,the influences of calcium-based type and Ca/S molar ratio on the composition and H₂/CO molar ratio of coal gas obtained by high pyrolysis of coal blending,and the influences of Ca/S molar ratio on the fixing sulfur ratio of clean coke,were investigated.The emission characteristics of the combustion of clean coke and other coal-based civil fuels were investigated and compared in the experimental horizontal furnace and different civil burning appliance.The physical and chemical properties of samples were characterized using XRD,BET,XPS,TG-MS,TG-DSC and TPR methods.The components of coal gas and flue gas were detected using GC or flue gas analyzer,respectively.The adjustment of coal gas composition,the mechanisms of two-step fixing sulfur and removing nitrogen as well as de-nitration in the preparation and application of clean coke were analyzed and discussed.Meanwhile,the experiment on coke oven gas magnetizing hematite to concentrate magnetite and methane at low temperature were carried out in a fluidized-bed reactor with stirring apparatus.These have provided reliable basis on the key technologies for the preparation of civil clean coke and adjustment of coke oven gas composition.Main research results are as follows:?1?Thermodynamic analysis results show that the adjustment of pyrogenous coal gas composition and H₂/CO molar ratio by the CO formed from the reaction of hot C with CO₂ obtained from the pyrolysis of CaCO₃,the fixing sulfur by the reaction of H₂ S and Fe S formed by the pyrolysis of coal with CaO formed from the pyrolysis of CaCO₃ during coal pyrolysis,the fixing sulfur by the reaction SO₂ with CaO and the reaction of CaS with oxygen to CaSO₄,coking oven gas magnetizing hematite to concentrate magnetite and methane,are feasible.?2?Adding CaCO₃ additive in coal may increase the total amount of pyrogenous coal gas,especially CO and CO₂,and with the increase of Ca/S molar ratio H₂/CO molar ratio decrease obviously.While coal pyrolyze at high temperature,CaCO₃ decompose into CaO and CO₂.Part CO₂ enter into pyrogenous coal gas,and Part CO₂ changing CO by the reaction of CO₂ with C enter into pyrogenous coal gas,which result the increase of the amount of CO and CO₂ and the decrease of H₂/CO molar ratio in pyrogenous coal gas.The catalytic roles of CaO improve the crack of volatile tar and decomposition of coke structure.The amount of CaCO₃ additive adding in coal as coking is calculated according to the following equation:?3?The forms of sulfur in clean coke prepared by high pyrolysis of coal blending,which obtains from raw coal added Ca-based composite additives,are CaS and organic sulfur.The influences of Ca-based additive types and Ca/S molar ratio on the total content of sulfur and fixing sulfur ratio are different.Ca-based additive in composite additives improves the total content of sulfur in clean coke.Clean coke prepared by adding CaCO₃ additive has better fixing sulfur ratio,and with the increase of Ca/S molar ratio the fixing sulfur ratio of clean coke increase gradually and is maximum at 2 of Ca/S molar ratio.On one hand,Ca-based additive promotes the decomposition of organic sulfur in coal into H₂ S and then formation the CaS fixing in clean coke,on the other hand,Ca-based additive promotes the decomposition of Fe S2 in coal into Fe S and then formation the CaS fixing in clean coke.Fe₃O₄ additive in composite additives plays a catalytic role in the decomposition of organic sulfur.Fe and Ca additive plays a catalytic role in the decomposition of nitrogen in coke into volatile nitrogen.High temperature pyrolysis of coal blending adding the Ca-based composite additives with the multipurpose has effect of fixing sulfur and removing nitrogen.?4?The fixing sulfur ratio of clean coke during combustion had a maximum as the Ca/S molar ratio increasing,the fixing sulfur ratio was nearly 100% as Ca/S molar ratio is 1.5.The influence of combustion temperature on the fixing sulfur ratio of clean coke is related with the thermo-stability of CaSO₄ formed during combustion.When burning temperature is lower than 1050?,the fixing sulfur ratio of clean coke is above 99%.The treatment of coal blinding by high temperature pyrolysis decreased the content of Cl,Hg and aromatic hydrocarbon pollutants.Due to adding combustion improver into clean coke,the ignition and burnout temperature of clean coke is the same as that of other traditional coal-based civil fuel.According to the criteria of ignition grade?ignition temperature of 600??Ti>400?,coal is inflammable?and the index of stationary combustion characteristics,clean coke is a inflammable and good combustion coal-based fuel.Carbon dioxide reaction index?CRI?of clean coke is between 48% and 58%,clean coke has better reactivity than metallurgical coke.The concentrations of PM,SO₂,NOX pollutant emitted from the combustion of civil clean coke are very low.The reasons for high effective fixing sulfur are as follows: On one hand,SO₂ emitted from the combustion of organic sulfur is captured by active CaO in clean coke to form CaSO₄.On the other hand,CaS formed during high pyrolysis is oxidized to CaSO₄ fixed in ash.The principle of fixing sulfur by clean coke is not that by traditional coal during combustion.The routes of the effective decrease of NOX emission are as follows: Route one is that NOX emitted is reduced to N2 by CO formed during combustion.Route two is that NOX emitted is reduced to N2 by hot C formed during combustion.Ca and Fe in clean coke have catalytic activity for the reduction of NOX.Comparison with the traditional civil coal-based fuel,clean coke has effect of high effective fixing sulfur and de-nitration.?5?The phases of Guangling's hematite ore are mainly hematite,limonite and quartz sand.Hematite was changed into magnetite by the low reduction of H₂.The size of magnetite crystal particles was bigger than that of hematite.Magnetite crystal particles had obvious grain coarsening and gathering structure,crustification banding and gathering structure.Although magnetite crystal particles bind up the gangue impurity,the dissemination size was big.Magnetite was prepared from hematite containing 28.63% TTe by H₂ reduction under conditions of 450? of reduction temperature,30 min of reduction time.The concentrate fines with 56.99% of iron grade and 61.93% of iron recovery were obtained from magnetite by the magnetic separation under 0.156 T of magnetic field strength.Rich CH4 was obtained from simulation coking oven gas by the low reduction of hematite ore.?6?The technology for the industrial preparation of civil clean coke is mature and reliable,and the product quality of clean coke prepared is stability.Clean coke have been list on the clean substitute for raw coal in the technical guide for the comprehensive treatment of pollutants from civil coal combustion?advanced edition?issued by the Ministry of the State Environmental Protection in 2016,and have been popularized.The industrial production of civil clean coke has achieved one million tons,which replaced the civil raw coal.As a result of application of clean coke in civil fuel,the environmental benefits were outstanding.