Characteristics Study Of Steam Gasification For Carbonized Briquette Of Lignite

Due to the production of the low-level pulverized coal such as ligniteincreased year by year, and the ecological environment problems areincreasingly prominent, the clean and efficient utilization technology oflow-level pulverized coal has attracted widespread attention. Positivedevelopment of the clean utilization technology of pulverized coal has positivesignificance in solving the supply and demand tension of resources, protectingthe ecological environment, safeguarding country’s energy security strategy andso on. Though the molding-pyrolysis-gasification classification utilization of thelow-level pulverized coal such as lignite as one of the best way of pulverizedcoal’s resource utilization, a series of problems are still exist for the briquette,such as low mechanical strength, easily broken and poor thermal stability. In thispaper, the carbonized briquette of carbonization reactor developed in preparationfor the fixed-bed gasifier of steam gasification characteristics and kinetics, andusing a variety of characterization means to analyze the physical and chemicalproperties of carbonized briquette. In order to provide scientific theoretical basisfor classification-conversion-efficient-utilization of the low-level pulverized coal such as lignite. The conclusions can be summarized as follows:1. Preparation conditions including molding pressure, carbonization heatingrate, carbonization temperature and carbonization holding time have asignificant influence on the gasification characteristics of the carbonizedbriquette. The carbon conversion rate will firstly increase then decrease withincrease of molding pressure, and the molding pressure by60MPa is the mostappropriate. The faster of carbonization heating rate, the faster of carbonconversion rate. And the slower of carbonization heating rate, the higher ofgasification gas production rate； Carbonization heating rate of5℃/minpreparation of carbonized briquette gas production rate of gasification than othercarbonization heating rate, at least by6.69%. The gas production rate ofgasification will obviously increase with the increase of carbonizationtemperature, and gas production rate is increased by7.86%when carbonizationtemperature increased from550℃to650℃. The slower of carbon conversionrate when the longer of carbonization holding time. When the granularity is inthe range of2to9mm, the change of granularity of carbonized briquette doesnot much influence on gasification characteristics.2. When the carbon conversion is in the range of0to85percent, thegasification temperature has a significant influence on the gasification reactionof the carbonized briquette. When the reaction for5minutes to8minutes, thegasification rate reaches maximum, and there is an inverted V-shapedrelationship between reaction rate and time. Gas production rate will decline with the rise of gasification temperature, and the gases are mainly composed ofH2, CO and CO2, and the total content of CH4and C2H6is less than1.00percent.With the increase of reaction temperature, the content of CO will increase, butthe content of CO2will decrease, and the content of H2will have to bemaintained between58.00percent and61.00percent.3. When the water vapor flow increases, the carbon conversion rate willaccelerate, and the largest gasification reaction rate will increase, and the timerequired to complete reaction will be reduced, and the accumulation speed of therate of producing gas will increase obviously, but little impact on final rate ofproducing gas. At the same time, the production of H2and CO2will inecrease,but the production of CO will decrease.4. Under the different heating rate of gasification, with the gasificationreaction of carbonized briquette, the relation curves between the reaction rateand the reaction time all appear two consecutive peaks. With the speeding up ofthe heating rate of gasification, the production of H2and CO2will decrease, butthe production of CO will increase.5. The carbonized briquette and four different metamorphic degree of coalgasification experiments show： the carbon conversion rate of carbonizedbriquette is much larger than higher-order coal, but similar to lignite, and bothhave higher gasification reactivity and the faster speed of producing gas. Thecarbon conversion of carbonized briquette has the lowest rate of producing gas,around3000mL/g. The content of H2in gases is1.0to5.0percent higher than lignite, Heishan bituminous and Jincheng Anthracite. The content of CO2isabout13.5to18.0percent, similar to lignite, Yimeng sub-bituminous andHeishan bituminous. The content of CO in gases of carbonized briquette is about22.0to27.0percent; and3.0to9.0percent lower than lignite, Heishanbituminous and Jincheng Anthracite.6. Alkali metal and alkaline earth metal (AAEM) of ash have aself-catalytic for the gasification reaction, this makes the carbonized briquettehas higher gasification activity than high metamorphic degree of coal. Thegreater of molding pressure, the higher of carbonization temperature, the lowerof pyrolysis heating rate, and the longer of pyrolysis holding time, the better ofthermal stability and compressive strength of carbonized briquette. Afteroptimization of the preparation conditions, the TS+6of carbonized briquette ismore than90percent, this is the high thermal stability of briquette.7. Surface of the carbonized briquette has a larger pore aperture hole, andthe surface structure is loose. Compared with the dense structure of lump coal,carbonized briquette has a larger specific surface area, increasing the contactarea between vapor and carbon, which the gasification reactivity is better thanlump coal.8. During pyrolysis of carbonized briquette, the relative content of phenolsor ethers carbon, carbonyl carbon and carboxyl carbon decreased obviously, andthe relative content of aromatic structures or alkyl carbon increased gradually.The relative content of hydroxyl oxygen or ether oxygen is the biggest, and the relative content of carboxyl oxygen will decrease with increase of carbonizationfinal temperature. Pyridine nitrogen and pyrrole nitrogen are the main mode ofoccurrence of nitrogen, the relative content of protonated pyridine nitrogen andnitrogen oxides decrease with different degrees. Thiophene sulfur and inorganicsulfur are the main mode of occurrence of elemental sulfur, and the content ofthiols, sulfide and Sulfur oxides are low. In the carbonization process ofbriquette, aromatic ring undergo cracking, and removing a lot of paraffins aswell as oxygen-containing functional groups; with the increase of carbonizationtemperature, the total moisture of carbonized briquette gradually lose, resultingthe hydrogen bonds of coal are broken.9. The shrinking un-reacted core model (SUCM) can fit the kineticsparameter of gasification reaction of carbonized briquette. In the chemicalreaction control area, apparent activation energy ranged from93.83kJ/mol to104.11kJ/mol; The apparent activation energy and pre-exponential factor existskinetic compensation effect. In the internal diffusion control area, when thedegree of turbulent airflow within the reaction system increases, or the diameterof the carbonized briquette decreases, the ash layer resistance can be reduced,and gasification effect can be strengthened.