Types of Gasifiers

The classification of gasifiers is commonly done according to the bed type. Based on this, three groups of gasifiers are known moving bed, fluidized bed, and entrained flow. These reactor types are currently in commercial operation. 

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Current Status The U.S. Department of Energy (DOE) and its private-sector collaborators have substantially advanced the development of gasification-based power systems during the last decade. This section describes the current status for the various types of gasifiers used. 

Two major types of gasifiers currently in development are direct-fired gasifiers, using air, and the indirect-fired method, where heated sand surrounds biomass and gasifies it. These design schemes are described in Chapter 3. 

The influences of various gasifier types on the product composition are summarized in Figure 3.1. A brief description of each type of gasifier is provided in Table 3.1. 

The process-related details of the various types of gasifier are not discussed here in depth. For more information, refer to the relevant literature (see, e.g., Trevino (2002) Chiesa et al. (2005) IE/IPTS (2005) BMELV (2005)). 

The common feature of coal gasification processes is that coal is contacted in a gasifier with an oxj en-containing gas and steam at a temperature of at least 700UC. The main types of gasifiers are ... 

Gasifier Types and Characteristics The three main types of gasifier reactors, moving bed, fluidized bed, and entrained bed, as shown in Fig. 24-4, are all in commercial use. The moving bed is sometimes referred to as a fixed bed, because the coal bed is kept at a constant height. These gasifiers can differ in many ways size, type of coal fed, feed and product flow rates, residence time, and reaction temperature. Gas compositions from the gasifiers discussed below are listed in Table 24-10. 

The gas from either type of gasifier contains H2, CO, and CO2. About 95 percent of the sulfur is present as H2S, and the balance as COS. Other minor components include NH3 and HCN. Carbon and ash are always present, and pyrolizers also produce oils, tars and water-soluble organics. Small quantities of oxygen, SO2, and nitrogen oxides also may be present. 

In addition to coal, gasifiers can be used on a variety of feedstocks. Almost anything that will burn can be gasified. There are many types of gasifiers. Some are fluidized beds, and others are moving beds. The coal fed to the gasifier can be dry or a coal/ water slurry. 

The reactor type strongly influences the temperature distribution and, in this way, the gas and residue products. The reaction temperature typically varies from about 800 to 1500°C, and up to a maximum of about 1900°C in entrained flow oxygen reactors. Each type of gasifier... 

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. 

Industrial gasification achievements by themselves have succeeded in upgrading munidpai wastes. Union Carbide s Purox process represents a typical technology in the field. Many developments have occurred with wood Table 1.6 provides an idea of the dry gas compositions obtained, which vary with the type of gasifier and the feedstock. 

A feature of this type of gasifier is that the temperature in the bed peaks sharply in a burning (gasification) zone about a third of the way up the coal bed. The maximum temperature is about 1,300°C. 

Carbon Feedstock in Different Types of Gasifiers Used or Planned throughout the World... 

Firing the raw gas in boilers or heat applications such as kilns after removal of dust and particulates is the simplest application since the gas is kept hot and the tar problem is avoided. However, surprising enough, there are very few known successful applications, which have been operating in a commercial environment. This market is one where all types of gasifiers can compete and more concerted efforts have to be undertaken by the gasification industry to increase the number of successful cases. 

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