Simulation And Optimization Of Pulverized Coal Gasification And Investigation Of The Gasification Molten Slag Fludity

China is one of the majority energy consumption countries who will continue the trend that coal resources are its main energy usage species.Energy and chemical engineering base in eastern Ningxia province,occupies abundant coal resources which are low-rank candle coals.This paper based on the 2000 t/d GSP entrained flow gasification process in the base,with the CFD numerical simulation method,investigates the feedstock YCW coal gasification properties,acquires the optimized operation parameters and study the fluidity of molten slag in the straight part wall of GSP gasifier.The gasifier geometry model is built according to its industrial structure and size data.For the symmetry property of the gasifier,1/4 of which is chosen to be the calculation zone and its hexahedral structure mesh profile is gained with the ICEM CFD software.Two competing rates model,Eddy Dissipation Concept(EDC)model,the random trajectory model,the un-reacted shrinking model and P1 model are used for coal devolatilization,homogenous turbulent reactions,coal particle move pathlines tracking,heterogenous reactions and radiation heat transfer process respectively.The simulation results agree well with the industrial ones.And the results show velocity flow field is divided into external recirculation zone,swirl jet zone,internal recirculation zone as well as plug flow zone.The mole fraction of H2 and CO along the gasifier height(h)increases to its maximum 23.7%and 67.4%.The temperature,which arrive at its maximum 2238 K at h=1.2 m,increases first and then decreases to stable level.Based on the verification of model validity,the optimized operation of main parameters such as the swirl number S,operation pressure,the mass ratio of coal to oxygen m(C)/m(O)and the mass ratio of steam to oxygen m(H2O)/m(O2)has been done and obtains the results.When S is 1.20,the nozzle surface temperature is moderate for long time to use and total mole fraction of H2 and CO reaches the maximum value 91.3%.With the operation pressure varies from 3.8 MPa to 4.4 MPa,the velocity in the internal recirculation zone and outlet zone decreases,which can weaken the nozzle surface erosion as well as the fly ash entrainment and increases the coal remain time in the gasifer.As the m(C)/m(O)shifts from 1.2 to 1.5,the mole fraction of CO decreases and H2 increases in the outlet zone.The temperature along the straight part wall are higher than the coal ash flow temperature 1621K and the carbon conversion reaches 96.26%when m(C)/m(O)is 1.3.With the m(H2O)/m(O2)increases from 0.05/0/95 to 0.20/0.80,the temperature in the gasifer decreases and H2 as well as CO mole fraction along h increases first and then decreases.When m(H2O)/m(O2)is 0.10/0.90,the temperature in the outlet zone is 1744 K and the syngas species H2 as well as CO achieve its maximum value.For the fludity of liquid molten slag layer,an force balance equation of the infinitesimal body is gained to calculate slag layer velocity.The results show that the liquid slag layer velocity,which increases fast first,tends to be stable in the force balance of gravity and viscous force.What's more,the maximum liquid slag layer velocity and thickness are 80 mm/s and 14.4 mm.When the slag viscosity models are changed,the slag velocity-thickness line varies apparently,especially when the liquid slag layer thickness(?)is higher than 6 mm.So it is vital to choose the accurate slag viscosity model.And for the influence of slag critical temperature Tcv,when it adds up from 1746 K to 1946 K,the liquid slag layer velocity and thickness decreases for the reason that molten ash particles' deposition probability decreases.And when it decreases from 1746 K to 1546 K,the slag velocity and thickness increases because that molten ash particles' deposition probability increases.