Gasification water effluents

Waste water effluents from coal gasification facilities contained p-cresol at concentrations of 880 mg/L (Neufeld et al. 1985) and 5,120 ppb (Pellizzari et al. 1979). A coal liquefaction and a shale oil waste water effluent contained p-cresol at concentrations of 420 mg/L (Fedorak and Hrudey 1986) and 779 pg/L (Pellizzari et al. 1979), respectively, p- Cresol was emitted with the waste water of a poultry processing plant at concentrations ranging from 2.14 to 22.5 mg/L (Andelman et al. 1984). 

Waste water effluents from coal gasification plants contained p- and m- cresol at a combined concentration of 1,840 mg/L (Giabbai et al. 1985). p- and m-Cresol were detected at a combined average concentration of 1.0 yg/L for three samples of retort water from a shale oil production facility (Hawthorne and Sievers 1984). 

Benzofuran may be released to water from coal gasification facilities. 2,3-Benzofuran was detected in coal gasification facility effluents at concentrations ranging from 6 to 267 ppb, but was not detected... 

Fig. 8.3. The Shell Penetrating Separator [12] originally developed to remove soot from wash water effluent of oil gasification plants.

Water effluents are not a problem in coal gasification plants. In fact, water effluents may create fewer problems for IGCC than for direct combustion-based power generation because the steam cycle in an IGCC plant produces less than 40% of the power plant s power. Therefore, the water effluents from boiler feedwater preparation and cooling-water blowdown are significantly less than those for steam < cle-based power generation with direct coal combustion. 

Coal gasification plants have two principal sources of water effluents which are similar to those in conventional coal-fired power plants. The first source is wastewater from the steam cycle, including blowdowns from the boiler feedwater purification system and the cooling tower. The amount of this wastewater effluent depends on the hardness of the original raw water feed to the plant and the size of the steam cycle. 

The second source is process water blowdown, where the water has scrubbed coal-derived gases to remove coal ash and trace components. The raw process water in coal gasification processes contains various organic and inorganic compounds. Purification of this water removes most of the organic compounds, and the plant then recycles much of the water. The net amount of this wastewater effluent reflects the water-soluble inorganics in the feed coal (such as chlorides) and the amount of coal feed. Coal gasification (and direct coal combustion) with dry gas cleanup systems can reduce process water effluents. Coal plants also often use water effluents to control the dust and bulk density of the solid waste. 

An IGCC plant generally produces fewer water effluents than a conventional coal-fired power plant does. The amount of process water blowdown is about the same for both gasification and direct coal combustion. However, the steam cycle in IGCC power plants produces much smaller amounts of wastewater blowdown because less than 40% of the total power generated comes from the steam cycle. 

Gasification processes purify and recycle raw process liquids, and the net process water effluent is normally only a blowdown. Like cooling-water blowdown, the process water blowdown is necessary to avoid buildup of salts and other dissolved minerals. This net process water effluent is usually higher quality than the cooling-water blowdown. In fact, some plants use the process water effluent as part of the cooling-water makeup (10). 

Like air emission standards, water effluent standards for coal gasification vary significantly by application, industry, and location. Nevertheless, the most common standard is the EPA Water Quality Limitation Standard shown in Table 4-2 (14). 

Shell Oil has extensively tested water effluents at its Deer Park, Texas coal gasification demonstration facility (13) Table 4-3 summarizes the test results. The biologically treated water from this plant has demonstrated very low toxicity to fathead minnows, which are very sensitive. 

The principal source of solid waste in coal gasification is ash or slag from the feed coal. The amount of this solid waste is a direct function of the ash content in the feed coal. This ash is normally the only solid waste coal gasification generates. Plant operators commonly add (or leave in) about 20-30 wt% water to solid waste for dust control and optimum bulk density. This water may contain dissolved salts and minerals if it is part of the plant water effluents. Some zero water effluent plant designs may also add a small amount of solid salts and minerals (from water effluent evaporation) to the coal ash. 

Hexanone is released to water by industrial facilities and at hazardous waste sites. 2-Hexanone was detected in 2 of 3 effluents from coal gasification plants and in 1 of 2 effluents from oil shale processing plants at mean concentrations ranging from 7 to 202 ppb ( jg/L) (Pellizzarri et al. 1979). The compound has also been tentatively identified in 1 of 63 industrial effluents (Perry et al. 1979), the effluent from a chemical plant (Shackelford and Keith 1976), and in one municipal landfill leachate at 0.148 ppm (mg/L) in a study of leachates from 58 municipal and industrial landfills (Brown and Donnelly 1988). 

Among the other technological variants are two effluent cooling possibilities at the exit of partial oxidation or gasification, namely the generation of high pressure steam or direct water quench. The latter is uninteresting for the production of methanol, since intensive conversioa is not the ultimate objective. 

Since 1978, the use of zeolites to solve environmental pollution and energy conservation problems showed promise and was expected to increase. Natural zeolites have many commercial uses in coal gasification and natural gas purification, selectively adsorb molecules from water or air, purify sludge effluents to potable standards, extract trace amounts... 

The SGP recovers most of the heat of the gasification effluent gases by inclusion of a waste heat boiler, whereas the gasification product gases in the TGP are quenched with water which results in a reduced thermal efficiency. 

A typical example to describe the possible combinations of waste water treatment is shown in Fig. 5.7 illustrating the treatment of gas liquor from medium-temperature pressure gasification of bituminous coal. The aqueous effluent is to be used as makeup water fOT an open cooling loop so that no conflicts with environmental legislation can be tolerated either from evapwation or from blowdown. 

Gasification effluent water treatment Sulfur removal Sulfur conversion... 

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