Gasification chemical reactions

Feldmann, H. F., "The Role of Chemical Reaction Engineering in Coal Gasification," Chemical Reaction Engineering Reviews, Advances in Chemistry, No. 148, pp. 132-155 (1975). 

Although newer technologies are always under development, the basic kraft chemical recovery process has not been fundamentally changed since the issue of its patent in 1884. The stepwise progression of chemical reactions has been refined for example, black liquor gasification processes are now in use in an experimental phase. The precise details of the chemical processes at work in the chemical recovery process can be found in Smook s Handbook.12 The kraft chemical recovery process consists of the following general steps ... 

Gasification is the result of chemical reactions between carbon in the char and steam, carbon dioxide, and hydrogen in the gasifier vessel as well as chemical reactions between the resulting gases. Gasification reactions can be represented by ... 

It is not difficult to write a number of chemical equations to represent physical, thermal, and chemical reactions taking place in a gasification vessel. In theory, gasification processes can be designed so that heat release (exothermic reactions) balances the heat required by endothermic reactions. But in practice many of the above physical, thermal, and chemical reactions may take place simultaneously, making a precise prediction of the quantity and quality or composition of product gas somewhat difficult. 

In liquefaction systems wood and wood wastes are the most common fuelstocks. They are reacted with steam or hydrogen and carbon monoxide to produce liquids and chemicals. The chemical reactions that take place are similar to gasification but lower temperatures and higher pressure are used. Liquefaction processes can be direct or indirect. The product from liquefaction is pyrolytic oil which has a high oxygen content. It can be converted to diesel fuel, gasoline or methanol. 

This section concerns catalytic processes that transform chemicals from renewables by C-C bond breaking. Among these are thermochemical processes, such as pyrolysis and also gasification, catalytic reactions, such as catalytic cracking and different reforming reactions, and decarbonylation and decarboxylation reactions. Many of these reactions occur simultaneously, particularly in the thermochemical processes. Another technically important class of C-C bond breaking reactions is the fermentation processes, however, they will not be considered in this section since they do not involve heterogeneous catalysis. 

The chemical reactions taking place during the gasification of coal are well known. Some of these are listed in Table 3. 

The first case covers for example flue-gas treatment, which requires the filtration of fly-ash and the reduction of NOx, or gasification processes, where particulates and high-boiling tars have to be removed. An example of the second case is that of combustion processes, where incomplete combustion leads to the emission of carbonaceous particulates. The most relevant topic in this category is the reduction of diesel particulate emissions ( diesel soot ) by catalytic filtration. A more exotic example is the reaction cyclone for the thermal conversion of biomass, which also combines chemical reactions and separation in one apparatus, though its separation mechanism is not filtration. 

CCS uses different chemical reactions to capture carbon dioxide. The captured gas is then safely stored in such places as empty oil and gas reservoirs deep inside Earth. (A reservoir is a chamber in which something can be stored.) Storing the carbon dioxide gas so that it cannot cause harm would allow people to use gasification to make hydrogen fuel in a safe way. Currently, CCS is still in the development stages. It is a very expensive process. Scientists are exploring different technologies to make CCS more affordable. 

Combustion of char and gas occurs within the jet to provide the heat necessary for the endothermic devolatilization, gasification, and desulfurization chemical reactions. Extraction steam from the steam turbine is also fed to the gasifier. CO and H2 are the... 

The gasification process involves the combustion of coal with a restricted amount of oxygen. For the most part the oxygen is provided by a separate air separation unit (ASU) rather than air which would otherwise introduce a large amount of nitrogen into the synthesis gas. The principal chemical reactions are ... 

The theory advanced by De Ris belongs to the first group. In his model of flame spread along a horizontal surface it is assumed that the diffusion flame contacts the surface at the point where the polymer vaporization (gasification) begins. Reactant diffusion to the narrow zone of chemical reaction controls the heat generation process. If heat is transferred from the laminar diffusion flame to the surface by conduction, then the flame spread rate follows the Equations a) for thermally thin materials... 

Philcox, J.E., and Fenner, G.W., Gasification An Attraction for Chemical Reactions, available at www.praxair.com/Praxair.nsf, August 8, 2005. 

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