Gasification rates

Fig. 4 Arrhenius plot of the gasification rate Fig. 5 Effect of the steam partial...

Fig. 6 ComparisoB of the model Fig. 7 Arrhenius plot of the gasification rate predictions with the experimental data. for the gingko nut shell char. (HjOrO.datm)...

The conversion of the parent hydrocarbon and the gasification rate is calculated from the following equation ... 

This paper describes a simulator which has been developed at the Alberta Research Council and permits gasification in a two-ton coal block. Initial gasification experiments with air, steam and carbon dioxide are summarized, and data for product gas composition, heat propagation through the coal block, and gasification rates as functions of the geometry of the reaction channel are presented. 

Unfortunately, insofar as a clear understanding of the true orders of gas-carbon reactions is concerned, the problem is made more difficult when the gasification rate is affected by product retardation and by the rate of mass transport of reactants to the surface of the solid. Product retardation can result in the obtaining of orders of reaction which are too low, while mass transport retardation can either raise or lower the apparent order depending upon the true order of reaction and the nature of the mass transport control. In Secs. V and VI, these complicating factors will be discussed in more detail. In the remainder of this Section, pertinent references on the orders of gas-carbon reactions will be given. 

Austin, P.J., Buch, R.R., and Kashiwagi, T., Gasification of silicone fluids under external thermal radiation part I. Gasification rate and global heat of gasification, Fire Mater. 1998, 22, 221. 

If the pore diameter and process conditions are well defined, the rates of internal and film diffusion can be calculated. The temperature dependency of the rate can be presented in the form of an Arrhenius plot, that is, log rate vs. reciprocal absolute temperature. Gasification rates can be divided into three zones, depending on whether reaction rate is controlling,... 

Differences in gasification rates are due to the heterogeneous pore structure and the inhomogeneous iron distribution in the coal matrix. 

G D ratios greater than 1.0 sometimes occurred with Incoloy 800, and stainless steel 410 and 304 reactors. Initially, dry ethane was pyro-lyzed in a new reactor and then wet ethane was used, resulting in high G D ratios. In such cases, 90% or more steam reacted, but the deposition rate did not appear to change markedly. After a short period of time, the gasification rate dropped to produce G D ratios less than 1.0. As this occurred, the deposition rates increased to large values. 

Figure 8. Gasification rate vs. deposition rate at surface steady state (Kpseudo constant). 800°C 1 atm 50 mol % steam.

Pick diffusivity for species i relative to mixture molecular mean-free-path (we assume Rp /) latent heat of fuel vaporization (per g) interparticle separation dimensionless interparticle separation, L/Rp Lewis number (mass/heat diflFusivity ratio) individual particle gasification rate fuel particle number density total number of particles in cloud total pressure... 

The diversity in evaluation of the results from char reactivity experiments is large. The definition of gasification rate varies among researchers and so does the criteria to select the reactivity values from the experiments. Few authorshave concerns regarding this. 

With respect to reactivity, the results have shown no large differences between birch and beech, There are however certain differences regarding the effect of temperature on the reactivity profile, and the shape of the profile itself. Fig. 8 shows several reactivity profiles, normalised with respect to their reactivity at 20% conversion to allow comparison. The final increase in gasification rate is more drastic for beech than for birch, especially noticeable for beech at lower temperatures. 

Kannan, M.P. Richards, G,N.(1990). Gasification of biomass chars in carbon dioxide dependence of gasification rate on the indigenous metal content. Fuel,... 

Cerfontain et ai. also show that the gasification rate for activated carbon only depends on the ratio Pco/Pco2 and not on Pco2 or Pco. 

The length and position of the zones described above depend on numerous parameters that interact with each other pyrolysis rate, gasification rate, rate of ash/inert char removal, temperature profile, heat available for reaction, fuel feeding rate, air feeding rate, heat losses, etc. 

The fuel consumption rate is a direct measure of cooking power, provided all the gas is subsequently burned in the burner section. The heating value of most biomass with 5-10% moisture (Denver dry) is -18 kj/g, The stove typically produces 20-25% charcoal after the volatiles have been burned. The charcoal typically has a higher heating value of -24 kJ/g. In the tables the power level is calculated from these values. A gasification rate of 10 g/m gives 2.5 kW, coit )arabIe to the large burner on modem gas or electric stoves. 

---