Most Gasification Plant

Euture large gasification plants, intended to produce ca 7 x 10 m standard (250 million SCE) of methane per day, are expected to be sited near a coal field having an adequate water supply. It is cheaper to transport energy in the form of gas through a pipeline than coal by either rail or pipeline. The process chosen is expected to utilize available coal in the most economical manner. 

In a coal gasification plant, the "Claus unit is nearly the last in a chain of process steps, and the foregoing steps can have a major effect on the Claus in a number of ways. Most of this paper will be examining the kind of Claus feed, but at the outset re should note that a Claus plant is sensitive to variations in feed rate, and that relatively minor ups and downs in upstream units will tend to amplify into wild fluctuations in the Claus plant. Accordingly our Claus-type plant should be inherently stable, if possible, able to ride through large changes in feed rate as well as composition. 

Of the indirect liquefaction procedures, methanol synthesis is the most straightforward and well developed [Eq. (6)]. Most methanol plants use natural gas (methane) as the feedstock and obtain the synthesis gas by the steam reforming of methane in a reaction that is the reverse of the methanation reaction in Eq. (5). However, the synthesis gas can also be obtained by coal gasification, and this has been and is practiced. In one modern low-pressure procedure developed by Imperial Chemical Industries (ICI), the synthesis gas is compressed to a pressure of from 5 to 10 MPa and, after heating, fed to the top of a fixed bed reactor containing a copper/zinc catalyst. The reactor temperature is maintained at 250 to 270°C by injecting... 

By the mid-1950s, the availability of inexpensive natural gas and petroleum had led to the abandonment of most coal gasification units. However, even as oil and natural gas use increased, coal gasification plants continued to be built on a limited scale in certain areas of the world, particularly in countries with a limited supply of petroleum. 

The various gasification applications for power and or heat are shown in Fig. 6 in terms of their market potential and overall technology reliability. Each of these applications will be discussed in the subsequent sections and the most advanced plants in each application will be presented in terms of their status and future prospects. It is of course beyond the scope of this overview to present all known activities, however, the most significant of these will be discussed as a means of presenting their achievements for the benefit of the other projects, which are still in the development stage. All demonstration projects had to overcome numerous teclinical and non-technical barriers as this is an emerging technology, however, many of these problems are common to all projects in the same application field and thus the projects still in the development face could learn from the experiences of the others. 

Fourier Transform Infra Red (FTIR) Spectroscopy is a promising and versatile technique for gas analysis which lately has moved from the laboratory to industrial applications such as emission monitoring of combustion and gasification plants [2]. The single most important advantage of the FTIR is its capability to analyse in-situ virtually all gas species of interest in flue and fuel gas applications. In this way potential sampling artefacts can be avoided. 

The current producers of partial oxidation processes are BASF, Texaco, Shell, and Hydrocarbon Research. A process block diagram showing the three process steps can be seen in Figure 2.18 [30]. The first step is the gasification process with the addition of oxygen and water. A detailed schematic of the Shell Gasification plant (SGP) is shown in Figure 2.19 [28]. The most important features of the process are the reactor, waste-heat-boiler, carbon catcher,... 

Ambient-Temperature Removal. The vast majority of acid gas removal processes operate at high ambient temperatures (90-120°F). These systems are almost as efficient as cold systems, but have lower capital cost and are much simpler. These processes can reduce H2S to about 10-50 ppmv. The key operating cost is the large heat requirement for stripping. This cost is minor in most coal gasification plants because of the ample supplies of low-pressure steam and low-level process heat in the plants. Commonly used acid gas removal processes at these conditions include MDEA (methyldiethanolamines) and Sulfinol. 

Tail-gas treating processes are generally unnecessary in coal gasification plants that require less than 95% overall sulfur recovery/reduction (26). A well-designed acid gas removal system can easily and effectively remove most of the sulfur from coal gas, and can readily attain this standard with a Claus plant. 

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