Study On Process Of Cogeneration Of Clean Coal And Oil From Low Rank Coal

Clean and efficient use of low rank coal is an important direction of energy development in china.LFC process is the closest to viability as a large-scale commercial technology.But it has disadvantages such as large investment and high energy consumption.The LFC process cannot process pulverized coal with particle size less than 6 mm.In view of these deficiencies,our research group developed the Cogeneration of Clean Coal and Oil process and introduced the dry quenching process.The core reactor of CCCO process is a rotary horizontal reactor.In this paper,the numerical simulation of rotary horizontal reactor was carried out and the performance of rotary horizontal reactor was verified by experiments.The CCCO process was simulated and exergic analysis was carried out.Mengdong lignite and Shenmu long flame coal were selected as experimental coal species.Tube furnace experiment and thermogravimetric analysis were carried out.The pyrolysis of lignite and long flame coal under different conditions was investigated by tube furnace experiment.It was found that with the increase of particle size,the yield of semi-coke and gas increased,and the yield of tar decreased.With the increase of temperature,the semi-coke rate gradually decreased,the gas production rate gradually increased,and the yield of tar first increases and then becomes smaller.At 520°C,the yield of tar was the highest,reaching 6.82%,and the yield of semi coke was 52.36%.The tar yield of long flame coal was highest at 550°C,reached 6.51%,and the yield of semi coke was 72.42%.The pyrolysis mechanism of two kinds of raw coal was studied by thermogravimetric analysis.On the basis of analyzing the characteristics and heat transfer law of horizontal reactor.The mathematical model of one-dimensional horizontal reactor was established.The model was solved by Matlab software.The temperature distribution and heat transfer in the horizontal reactor were calculated,and the influence of operation parameters on the reactor performance was studied.The model was validated by process experiments.The results show that the temperature difference between the inner wall of the reactor and the raw coal is very small,and there is no accumulation or loss of heat.The main role of heat transfer is to increase heat transfer efficiency,and the wall thickness of the reactor can be enhanced.The effects of heat carrier gas temperature,heat carrier gas flow rate and residence time on the performance of rotating horizontal reactors were discussed.Increasing the intake temperature and increasing the intake volume can improve the pyrolysis effect of the reactor.The determination of the intake temperature and the intake volume should be taken into account in order to maximize the energy efficiency.CCCO experimental equipment was established,and the pyrolysis and upgrading experiments of lignite and long flame coal were carried out respectively to investigate the performance of the horizontal reactor.It was found by cold experiment that residence time is mainly related to speed of the horizontal reactor,and feed rate has little influence.CCCO process experiment is divided into two parts:one stage pyrolysis and two stage pyrolysis upgrading process experiment.Dudring one stage pyrolysis,long flame coal was used as raw coal.The effect of inlet temperature at 560,650 and 750°C on yield and properties of the reactor was investigated.It is found that the higher pyrolysis temperature,the deeper pyrolysis degree,the higher yield of tar and gas products.Yield of tar is between 4-9%;content of aromatics is about 50%and content of aliphatic is more than 20%.Yield of semi coke is between 60-71%,and content of S in semi coke is reduced by half compared with that of raw coal.Calorific value is about 2.90×10~4kJ/kg,which can be used as a clean coal.The raw material coal for two stage pyrolysis experiments were long flame coal and lignite.In drying stage,temperature of the heat carrier gas is 300°C and moisture content of two kinds of dry coal obtained is less than 3%.In pyrolysis stage,carrier gas temperature was 650°C,and yield of long flame coal and lignite char was 62.95%and 45.18%,respectively,and tar yield was 7.41%and 3.34%respectively.Compared with semi coke products of LFC process,the semi coke products of CCCO two stage process have lower volatility,higher fixed carbon and higher calorific value.The results show that the yield and properties of the product can reach or exceed LFC industrial data.The experiment using pulverized coal feeding,size of mass content of 0-6mm components in more than 50%of raw coal,coal powder yield experiment was less than 1.4%,the experiment shows that the transformation smoothly.It shows that most of the coal powder is pyrolyzed and transformed.The rotary horizontal reactor has a good capacity for treating pulverized coal.The horizontal reactor is a universal reactor,and has the advantages of low cost and convenient operation.The CCCO process overcomes the shortcomings of LFC and shows that the use of horizontal reactors instead of grate reactors is a significant step forward in improving the quality of low rank coals.The CCCO and LFC processes are simulated on the Aspen simulation platform,and the reliability of the model is verified by the industrial operation data of the LFC process.In CCCO process,when the amount of raw coal treatment is 1000.00 kg/h,the total amount of air is1849.02 kg/h and the total methane is 21.32 kg/h.In LFC process,the total amount of air and methane is 2115.23 kg/h and 25.12 kg/h,respectively.Compared with LFC process,CCCO increased the coke dry quenching process,recovered the heat,increased the degree of self-sufficiency of the process heat,reduced the demand for external energy,and the energy saving effect was obvious.Based on the data obtained in numerical simulation,exergy analysis was conducted.The exergy efficiency of each unit of CCCO and LFC was calculated.Exergy efficiency of CCCO is 66.92%,higher than 63.02%of LFC process,CCCO process shows that energy use efficiency is higher.Coke dry quenching in CCCO process can reduce energy loss and improve the energy efficiency of combustion heating unit,so as to improve the energy efficiency of the total system.Method is proposed to further improve the system of energy efficiency,which is a part of the heat recovery and utilization.CCCO process of total exergy efficiency increased to 70.53%,which provides theoretical guidance for further improvement of CCCO process.