Numerical Simulation And System Optimization Of Coal Gasification And Sensible Heat Recovery Plant Of High Temperature

With the development of Chinese economy, the amount of fossil resources suchas coal, oil and natural gas we consumed has been increasing year by year. In2011,the coal count about78%of the consumed primary energy, most of which isdirectly used for combustion and a large amount of noxious gases like SO2and NOXare released. At the same time, the greenhouse effect has been aggravated by theemission of CO2. On this condition coal gasification has won much more attentionas a kind of new clean technology for coal and has been used in the IGCC powerplant and new coal chemical industry. Coal gasification has also shown itsimmeasurable economic benefits nowadays when the coal price is low. But we haveto admit that the coal gasification system is not stable as the gasifier and radiantsyngas cooler are easily got troubled. So it is necessary to have a deep research onthe system composed by gasifier and radiant syngas cooler.This thesis mainly uses the numerical simulation method to study the gasificationsystem composed by Texaco gasifier and radiant syngas cooler. As to Texacogasifier， the thesis pays more attention to the internal flowing field andtemperature arrangement. In additional to those, this thesis has also studied thearrangement of syngas in the Texaco gasifier. During the numerical simulation ofTexaco gasifier, this thesis has used two methods named species transport methodand probability density function(PDF) method which belongs to the non-premixmodel and has compared the differences between the two methods. As to the radiantsyngas cooler, this thesis has been focused on the points like the temperature andflow arrangement. At the same time this thesis also has a deep research on theradiative heat transfer between the ash particles and water wall in the cooler by theEulerian-Lagrangian method and the evaporation of water seal by multiphase model.At last this thesis has studied the parametric sensitivity of the gasification systemlike water slurry concentration and oxygen-coal ratio by Aspen Plus. In addition,this thesis also has calculated the heat duty of radiant syngas cooler and convectivesyngas cooler on different conditions and optimized the feed-water quantity of thetwo coolers.The research result shows that the Texaco gasifier has3zones named jet flowzone, back flow zone and tubular flow zone and the first two zones are mainly for combustion and gasification. The maximum temperature of Texaco in the gasifier isabout3400K and is stable at1700K in the other place simulated by speciestransport model. While the CO and H2counts about32.66%and22.65%respectively in volume of the total output of syngas. The carbon conversion is93.07%and the cold efficiency is75.21%. The research also shows that theoptimized oxygen-coal ratio is0.75and the water slurry concentration should notbe too large which is usually around62%. The research on the radiant syngas coolershows that the inner tank is also divided by jet flow region and back flow regionand the height of the latter zone is about2.7m.Much more back flow regions arefounded in the outer tank and expansion zone. The radiative heat transfer betweenthe water wall and ash particles is2.43MW counting about8.76%of the totalradiative heat transfer. The research also shows that the evaporation amount of thewater seal is0.18kg/s when the time is600s and the total heat duty of radiantsyngas cooler and convective syngas cooler is25.36MW when the system is stable.At last the research shows that the optimized amount of feed-water for the boilereconomizer is10.07kg/s.