Gasification reactor types

Gasification can be carried out in many different reactor types including ... 

The three principal reactor types employed in coal gasifier design are the moving packed bed, the entrained flow, and the fluidized bed reactor. In the discussion of gasification principles the moving packed bed (Fig. 3) was used to illustrate steam-oxygen or steam-air gasification of coal. 

Although the ASPEN process models can be put together to simulate many types of processes, it may still be necessary to use specialized or proprietary models. Such would be the case, perhaps, for a specific type of a coal gasification reactor. 

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. 

In the practical realization of gasification processes a broad range of reactor types has been and continues to be used. Although the usual classification is by bed type, there are other features to be considered and many of these can be selected independently of the bed type. The most important of these will be discussed as follows ... 

Four basic reactor types are used in gasification. They are ... 

The important factors in coal conversion are the physical and chemical properties of the coal, heat supply (autothermal or allothermal), reactor type (fixed bed, moving bed, fluidized bed, or entrained bed), gasification agent (air, oxygen, steam, or a combination thereof), and process conditions. Typically, coal conversion is carried out at high temperatures (900—1000 C) be-... 

The gasification techniques can be distinguished related to different criteria such as reactor type (fixed bed or fluidized bed), gasifying agent (air, oxygen, or steam), heat supply into the reactor (directly or indirectly heated) and reactor... 

Some mention must also be made here of the reactor types that have been used for coal gasification processes. 

Ash. Certain types of biomass contain significant amotmts of ash. Ash melts and agglomerates at about 800-950 °C. When that happens inside a gasification reactor, it forms heavy particles which fall to the bottom of the reactor, potentially leading to plugging problems. 

Table 6.2.2 Typical conditions of coal gasification in different reactor types [various sources Moulijn, Makkee, and Van Diepen (2004) Onken and Behr (1996) and Arpe (2007) Franck and Knop (1979) Falbe (1977)].

Important Characteristics of Generic Types of Gasification Reactors. 2-13... 

The amount of halides (usually chlorides or fluorides) and volatile metals in raw coal gas can vary significantly depending on the amounts in the feed coal and the type of coal gasification reactor. However, these trace components are effectively removed from the coal gas in the cooling and water washing before conventional acid gas removal. Halides removal is a potential problem for hot gas cleanup processes. 

Figure 2-1 shows the three types of coal gasification reactors along with their temperature profiles the location of their coal, steam, and oxidant (air or oxygen) inputs and the location of their coal gas and ash outputs. 

It is well-documented that with an equilibrium model, it is possible to predict the thermodynamic limits of chemical reactions that take place in the gasification process (Sharma, 2008). There is a wide variety of literature reports that proposes very similar gasification reactor models, which are based on thermochemical equilibrium and are applied to different types of feedstocks. The main difference between all literature models lies in the reactions chosen to represent the equilibrium between the gaseous compounds produced, in how the authors deal with the equilibrium of the involved reactions, and in the considerations and assumptions made. Some authors set the conversion of carbon into the gas phase or even consider 100% conversion (Zainal et al., 2001 Jarungthammachote and Dutta, 2007 Melgar et al., 2007), while others calculate it (Altafini et al., 2003 Mountouris et al., 2006 Sharma, 2008 ... 

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