Reaction char-hydrogen

Hydrogen-Char Reaction. The hydrogen-char reaction in the first phase may be represented by ... 

Figure I. Approximate trend of the equilibrium constant as a function of conversion for the hydrogen-char reaction at 1300°F. and 2000 p.s.Lg.

Figure 2. Rate of hydrogen-char reaction during the first-phase reaction at 1600°F.

Hydrogen-Char Reaction. As discussed previously (36, 37), the reaction under experimental conditions in the pilot-plant, continuous flow reactor may be affected by gas diffusion since the gas flow rates employed were extremely low and there was evidence that considerable gas channeling, predominantly along the vessel wall, occurred in this type of reactor. 

Figure 9. Effective mass transfer factor for hydrogen-char reaction and Reynold s number relation indicating the possibility of diffusion-control mechanism...

Analogous to the hydrogen-char reaction in the second-phase, the rate of the steam-char reaction in the continuous-flow moving-bed reactor is probably controlled by gas diffusion and may be characterized as ... 

NO-Char reaction system. Therefore an excess in hydrogen is expected to play an important role in NOx reduction if the fluidized bed combustor is operated under staged air firing. 

The active reduction in weight, which is caused by the active oxidative decomposition reaction, of the sawdust of every wood species is, thereafter, observed in the range of about 200 "C to about 300 C. That is, it is thought that the charring reaction of the sawdust of every wood species ceases by about 300 C. According to elemental analysis of some char, it is, however, known that a small amount of hydrogen and oxygen are still included in the char... 

Because it requires many possible variables, such as temperature, pressure, the nature of chemical reaction, and the character of the solid surface, and because it incorporates many constants which require experimental evaluation, the general mathematical model to estimate the product gas distribution for different levels of carbon conversion can become exceedingly complicated. Practical application of this model is particularly difficult when a choice has to be made between reaction mechanisms, each of which can generate complex functions with a sufficient number of arbitrary constants to fit any given experimental curve. The purpose of the work discussed in this paper was to study the influence of temperature and the partial pressure of hydrogen and steam on the rate of steam-hydrogen and coal char reactions based on the previous pilot plant data obtained at IGT (10, 11) and to develop a correlation to estimate the performance of a hydrogasification reactor in terms of its product gas distribution for different levels of carbon conversion. 

Equilibrium. The coal char-hydrogen reaction has been shown to exceed the carbon-hydrogen-methane equilibrium at low conversion and to reach the carbon-hydrogen equilibrium at nearly complete conversion (36, 37). From the equilibrium composition of the hydrogen-char system, a pseudo-equilibrium constant, Kp, is defined as ... 

The coal char reaction with a hydrogen and steam mixture is represented by the first-phase and the second-phase reactions. The first-phase reaction is related to the amount of volatile matter and may be regarded as a volume (or mass) reaction. The second-phase reaction is characterized by the heterogeneous reaction at the carbon surface—a reaction which seems to be controlled by gas diffusion for the range of operating conditions in the continuous moving-bed reactor. 

The char-hydrogen reaction and the steam-char reaction are considered as taking place independently so that the rates of the reactions are additive. 

Concomitant extensive hydrogen transfer reactions may account for the high amount of char residue generated in the pyrolysis of PEI. 

ESR can equally be used for detection of radicals in masticated rubber their identification in relation to the chemical structure might be approached with specific techniques such as electron nuclear double resonance (ENDOR). ESR studies also contribute to the understanding of the char forming process of various polymers [815], to the study of mechanical fracture, which produces free radicals, grafting reactions, etc. Pedulli et al. [816,817] have determined the bond dissociation enthalpies of a-tocopherol and other phenolic AOs by means of ESR. The determination of the O—H bond dissociation enthalpies of phenolic molecules is of considerable practical interest since this class of chemical compounds includes most of the synthetic and naturally occurring antioxidants which exert their action via an initial hydrogen transfer reaction whose rate constant depends on the strength of the O—H bond. 

Newer coal-based methods of acetylene manufacture under development include the AVCO process, based on the reaction of coal in a hydrogen plasma. Finely divided coal is passed through a hydrogen plasma arc generating temperature gradients of up to 15,000 K. About 67% of the coal is consumed, yielding char and acetylene in concentrations up to 16%. An energy requirement of 9.5 kW h/kg acetylene has been reported (33). 

Secondary gasification involves gasification of the char from the primary gasifier, usually by reaction of the hot char and water vapor to produce carbon monoxide and hydrogen. 

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