Temperature profile, gasifier

SL/RN Process. In the SL/RN process (Fig. 4), sized iron ore, coal, and dolomite are fed to the rotary kiln wherein the coal is gasified and the iron ore is reduced. The endothermic heat of reduction and the sensible energy that is required to heat the reactants is provided by combustion of volatiles and carbon monoxide leaving the bed with air introduced into the free space above the bed. The temperature profile in the kiln is controlled by radial air ports in the preheat zone and axial air ports in the reduction zone. Part of the coal is injected through the centerline of the kiln at the discharge end. The hot reduced iron and char is discharged into an indirect rotary dmm cooler. The cooled product is screened and magnetically separated to remove char and ash. 

FIG. 24-4 Gasifier types and temperature profiles a) fixed bed (dry ash) h) fluidized bed (c) entrained flow. This figure teas published in N. Holt and S. Alpert, Integrated Gasification Combined-Cycle Po-werG vol. 7, pp. 897-905, in Encyclopedia of Physical Science and Technology 3d ed. Copyright Elsevier, 2002.)... 

A model for transient simulation of radial and axial composition and temperature profiles In pressurized dry ash and slagging moving bed gasifiers Is described. The model Is based on mass and energy balances, thermodynamics, and kinetic and transport rate processes. Particle and gas temperatures are taken to be equal. Computation Is done using orthogonal collocation In the radial variable and exponential collocation In time, with numerical Integration In the axial direction. 

Gasification processes can be separated into three major types (1) moving-bed (counter-current flow) reactors (2) fluidized-bed (back-mixed) reactors and (3) entrained-flow (not back-mixed) reactors. Figure 19.11 shows the types of gasification reactors together with temperature profiles and locations of feed and product streams. Table 19.12 summarizes the important characteristics of each type of gasifier, and Table 19.13 presents the performance characteristics of selected gasifiers. 

Figure 4 Temperature profiles in the riser of a CFB gasifier using different fuel sizes, el has been fed 1 meter above the bottom of the reactor. 

Figure 4.24. Typical temperature profile in a fluidized-bed gasifier.

Figure 5.2 Schematics of different coal gasifiers and their temperature profiles for coal particles and gas phase (a) entrained flow gasifier (b) fluidized-bed gasifier (c) moving/fixed bed gasifier (Phillips, 2006).

Graphical representation of a gasifier with the resultant temperature profile observed in the gasifier [19,20]. 

Roll and Hedden developed a one-dimensional model for the semi-technical gasifier. This model describes (i) the trajectories of the reed particles, (ii) the axial temperature profiles of the gas phase and of the reactor wall, (iii) the conversion of the reed particles by pyrolysis and gasification of the char formed, and (iv) the quantity and composition of the product gas. 

Bunt, J., Joubert, J., and Waanders, F. (2008) Coal char temperature profile estimation using optical reflectance for a commercial-scale Sasol-Lurgi FBDB gasifier. Fuel, 87, 2849-2855. 

The required initial conditions for the dynamic model are the temperature and flux profiles of the gas and the solids streams down the entire length of the gasifier at time zero. 

Figure 6.2.25 Semi-technical gasifier of Chinese reed calculated profiles of gas phase and wall temperature and carbon conversion (a) and profiles ofthe product gas composition (without nitrogen), symbols measured values (b) (Roll, 1994 Roll and Hedden, 1994).

Borowiec et al. (XL) presented a steady state model for a counterCTjrrent moving-bed gasifier by considering the effect of interphase heat transfer coefficient on temperature and composition profiles, and on the location of the combustion zone. 

---