Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
PROCESSES AT MEDIUM AND HIGH TEMPERATURES 160 ⢠solids: possibly small (less than 1 µm) metals and oxides from the feed material; metal parts fed to the furnace would be withdrawn as liquid. Advantages and disadvantages. One advantage of the plasma are furnace is that it acts as a two-stage system: a first detoxification reactor (the plasma arc) and a second destruction reactor (such as a burner or catalytic oxidizer). Are furnaces have very short startup and shutdown times (e.g., startup of about 5 minutes to stable operation). Disadvantages of these furnaces include their complexity and their significant labor requirements for operation (e.g., electrodes require frequent replacement, either weekly or monthly). The heat of combustion to be dissipated is the same as for incineration, but in addition, the energy drawn by the arc must be dissipated. Development needs. Although plasma technologies have been available since the late 1940s, only one chemical process has been commercialized, a duPont process for producing acetylene from methane. Only metallurgical processes have been commercialized; there is at present a large steel remelting capacity. No other technology application is fully developed. Adapting the technology to the demilitarization program would require substantial design, development, and demonstration. Gasification Processes Technology description. Several devices have been developed that partially oxidize pulverized coal with steam and either air or oxygen to produce a fuel gas. The use of air produces a gas with a low heating value (5.60 MJ/m3, or 150 Btu/ft3), whereas oxygen produces a gas with an intermediate heating value gas (11.2 MJ/m3, or 300 Btu/ft3; Shaw and Magee, 1974a,b). Pressures are usually above atmospheric, up to 400 psi (27 bar). Adding a methanizer can convert CO and hydrogen to CH4 or synthetic natural gas (SNG). Some developers of these coal gasifiers have proposed using them to destroy chemical warfare agents completely under the partial-oxidation operating conditions. Gasifiers that could be considered for this use are listed in Table 7-3. Figure 7-7 illustrates one design of a gasifier. Development status. The technologies as applied to coal gasification are either commercial or have been tested on a very large pilot scale. Their use to date has been limited by economics, namely, the low price of natural gas. None has been tested with agent or energetics.
PROCESSES AT MEDIUM AND HIGH TEMPERATURES 161 TABLE 7-3 Some Characteristics of Gasifiers Operating Conditions Process Temperature (°F) Pressure (atm) Status References Koppers-Totzek 350 1 Commercial Magee et al., 1974 Lurgi 2200 30 Commercial Shaw and Magee, 1974a Texaco 2500 20 Commercial Shaw and Magee, 1974b Toriplex 3000 30 Pilot Scale Schulz, 1992 Gasifiers for use at demilitarization sites would require design and testing of equipment of the appropriate scale. If energetics are to be included in the feed, additional pilot studies may be needed. Application to chemical weapons destruction. On the basis of available experience, agent would be broken down to such small molecules as PH3, NH3, H2S, HF, HCL, H2, and CO. Acidic molecules would then be removed by aqueous scrubbing. The agent typically represents a small fraction of the hydrocarbon fed to an industrial gasifier. The product gas would then be used for producing power in a conventional facility. The size of the gasification plant precludes its double containment. It would be feasible, however, to contain the gasifier and scrubber. Special considerations. Commercial gasifiers can accept gases or entrained liquids with air or oxygen. Solids would need to be fed with the coal. Under gasification conditions, it is reasonably certain that the agent would be destroyed if it enters the gasifier. As noted above, some gasifiers operate under considerable pressure. Some of the gases formed (e.g., PH3 and HF) may attack refractory linings. By-products and waste streams. The final products from destruction of agent or energetics would be similar to those of the baseline incineration technology: combustion products and such salts as NaF.
PROCESSES AT MEDIUM AND HIGH TEMPERATURES 162 FIGURE 7-7 Lurgi gasifier. Source: Shaw and Magee (1974a).
