166 C CHEMICAL EFFECTS : see EFFECTS OF CHEMICALS; AIR POLLUTANT EFFECTS; POLLUTION EFFECTS ON FISH CHEMICAL TREATMENT : see PHYSICAL AND CHEMICAL TREATMENT OF WASTEWATERS COAL GASIFICATION PROCESSES In spite of temporary oil “gluts,” elements of a new coal- based synthetic fuels industry are slowly emerging in oil importing nations. This coal conversion activity involves the commercial integration of process and power systems. Overcoming both process engineering and environmental problems will be crucial factors in the development of coal liquefaction and gasification plants. Depending upon proj- ect size and complexity, the associated expenditures for the total compliance effort could require multimillion dollar budgeting. The concept of gasification of coal is not a new one. John Clayton proved conclusively that gas could be obtained from coal in the early 1680s. His initial experiments were observations of the products formed upon heating coal. In the presence of air, heat will invariably be generated by burning a portion of the coal. In order to increase the yield of secondary fuels with higher hydrogen to carbon (H/C) ratio than that of coal, it is required to gasify the coal in the pres- ence of steam and an oxygen containing gas. The products formed during high yield gasification are typically hydrogen, carbon monoxide, and variable amounts of light hydrocar- bons, especially methane. Carbon dioxide may be scrubbed from the product. The coal, steam, air mixtures are contacted at temperatures above 700°C in fluidized, entrained flow or moving bed configurations. Liquefaction of coal may be accomplished by reacting with heavy oil derivative hydrocarbons at temperatures of 400 to 500°C. Contaminants are typically hydrogenated to gases which may be absorbed (sulfur to H 2 S, nitrogen to ammonia and oxygen to water). According to Quig and Granger (1983), a coal conver- sion facility impacts the environment through the handling of large amounts of coal, and discharges from the conver- sion process and associated facilities. Also, there will be impacts related to the construction and operation of any large industrial complex. The major health concerns for both occupational and offsite populations include potential exposure to particulates, sulfur compounds, trace elements, aromatic amines, and other nitrogenous compounds and radioactive nuclides. Considerations of these issues and concerns for this facility will begin with the coal handling facilities. Fugitive dust, consisting mainly of coal fines, is generated by the disturbance of the coal in the unloading, transfer and stor- age facilities. Particulates can remain airborne and be trans- ported from the site under certain meteorological conditions and therefore must be evaluated in terms of their potential impacts and control mechanisms. Coal pile runoff and coal wetting wastewater contain varying amounts of coal fines and dissolved constituents depending on variables such as rainfall intensity and duration, contact time, coal storage configuration and coal pile sealing techniques. Values of over 2000 mg/l total suspended solids and 10,000 mg/l total dissolved solids have been reported by EPA and TVA for runoff from coal piles. The magnetic separation of metal- lic materials from the coal during preliminary coal cleaning operations will generate a variable quantity of pyretic solid waste which must be addressed. The coal processing facili- ties, that is coal grinding and slurry preparation, include con- trols which minimize the discharges from these operations. © 2006 by Taylor & Francis Group, LLC COAL GASIFICATION PROCESSES 167 Some of the more important coal gasification processes include those of Texaco, Shell, Dow & British Lurgi. These are carried out at high temperature 600 to 3000°F and high pressure 25 to 80 atmospheres. The most developed process is Cool Water integrated gasification/combined cycle (IGCC) described by Holt (1988) and Spencer et al. (1986) which uses a Texaco gasifier. Makansi (1987) compares the per- formance of various systems. Important emissions data for IGCC projects are presented at the end of the current review. Additional information is presented below on the status of coal gasification environmental effects. A comparison of the impacts on water streams of various processes is given in Table 1. Pruschek et al. (1995) discusses the removal of pollut- ants from a coal gasification plant in a more efficient and economical manner than in previous designs by conserving energy in the cleaning sections of the plant. A zinc titanate catalyst is being tested for hot (1000°F) gas cleanup potential at Tampa Electric’s 260 MW coal gasification power plant in Lakeland, Fla. Waste gas emissions are reduced by scrubbing the raw gases leaving the gasifier in an acid gas removal system and converting the H 2 S (via a modified Claus process) to sulfur. Sulfur dioxide is thus drastically reduced in the final stack emissions. NO x levels are reduced by saturating the gas prior to gas turbine combustion (see Spencer 1986) or Makansi (1987). Advances in process efficiency are pos- sible, through the use of a combined cycle configuration the Shell Coal gasification process. The product gas would typically be fired in a combustion turbine followed by an HRSG and a steam turbine (i.e., combined cycle) to com- plete the IGCC. Heitz (1985) presented data on end uses of From an economic point of view it is desirable to con- struct an IGCC in phases, Le et al. (1986). In the typical scenario the first phase would be installation of simple cycle gas turbines for peaking power. As of 1989 the maximum single gas turbine output is about 150 MW. In the second phase a heat recovery boiler is used to generate steam for either cogeneration or to power a steam turbine (i.e., ordi- nary combined cycle). Zaininger Engineering (Lewis, 1988) indicate that there is an optimum time at which the gasifier plant could be added as fuel cost/availability would dictate. Normal combined cycle efficiency can be approximately 50% (LHV) whereas IGCC values range from 37 to 42%. However, new hot gas cleanup processes (such as limestone throwaway or metal oxide catalyst) are being developed which may increase IGCC efficiency to about 48%. TABLE 1 Coal gasification wastewater concentrations (mg/l, unless noted otherwise). (Adapted from Epstein, 1987) Component KILnGAS (Illinois No. 6) Moving Bed Lurgi Dry Ash (Montana Rosebud) Moving Bed Lurgi Dry Ash (High-Sulfur Eastern Coal at Sasol) Moving Bed Lurgi Dry Ash (Lignite at Kosovo) Moving Bed British Gas-Lurgi Slagger (Pittsburgh No. 8) Moving Bed Grand Forks Slagger (Lignite) Moving Bed HYGAS (Illinois No. 6) Fluidized Bed Texaco (Illinois No. 6) Entrained Flow Chemical oxygen demand (COD) 4100–6100 21,000– 23,000 12,000 20,000 20,000 25,400 4050 1100 Total organic carbon (TOC) 810–1610 — 3500 6000 — — — — Total phenols 260–660 4200–4400 3800 3000 3000 5100 710 <1 Cyanides and thiocynates 130–300 8–19 <3 80 1150 150 30 50 Total nitrogen 1200–2300 — — 4300 — 5200 3700 — Ammonia 840–1700 4000–14,000 7000 3700 3000 — — 2100 Total sulfur 430–1030 — 950 — 700 — — — Chloride 450–710 40–45 670 — 1500 — — 3500 Total suspended solids (TSS) 150–700 — ———— — — Total dissolved solids (TDS) 1070–2100 1700–4000 — 2000 7000 — — 2220 Oil and grease 25–340 — 50 900 — 300 — 6 pH 8.3–8.8 8–10 9 9 9 — — — Temp. °F, 100s — 9–12 9–12 9–12 9–12 — 16–18 24–28 © 2006 by Taylor & Francis Group, LLC various gasifier process streams (see Table 2). The analysis of a typical product gas stream appears in Table 3. and by reducing gasifier energy losses. Figure 1 illustrates 168 COAL GASIFICATION PROCESSES Holt’s (1988) review of Cool Water data, are impressively low for a coal-based plant. Sulfur dioxide in the gases leav- ing the tail gas incinerator is about one fifth the quantity leaving in the turbine exhaust stream. The turbine exhaust did not contain sulfur compounds other than SO 2 . A typical gasification process will generate both solid and liquid wastes. The solid waste retains the natural impu- rities inherent in the coal such as heavy metals, chlorides as well as organic compounds formed by the combustion of coal in the reactor. Testing, as defined in rules and regula- tions under Section 3001 of the 1976 Resource Conservation and Recovery Act RCRA, must be conducted to determine the nature of the solid waste generated by the gasifica- tion of the particular coal with the specified process. The wastewater stream exiting the carbon-ash scrubbers may contain dissolved and suspended fly ash and unconverted carbon trapped in the scrubber. The treatment of this process wastewater for discharge will generate sludge which will have to be controlled and assessed. A gasification process may not have any atmospheric emissions during normal operating conditions. Gases are processed and recirculated so that the desired discharge from the system is product gas alone. During upset conditions, however, venting will occur causing releases of gaseous wastes. Sources of non-gasifier liquid wastes which must be evaluated include blowdown from clarifiers and cooling towers, drainage from equipment and floor areas, demin- eralizer wastes and sanitary wastes. Contaminants in these streams are generally a function of the intake water quality and any chemical additives. Coal Coal Receiving and Storage Coal Milling and Drying Coal Feed System Steam to Utilization Steam to Utilization High Temperature Cooling Solids Removal and Cooling Acid Gas Removal Acid Gas to Sulfur Recovery Water Recycle Water Treatment To Biotreater Product Gas to Power Generation Slag to Utilization To Utilization Oxygen Gasifier Quench Gas BFW BFW FIGURE 1 Shell coal gasifi cation process block fl ow diagram for SCGP-1. TABLE 2 Uses of products, co-products and effluents (from Heitz, 1985) Product gas Power generation Steam General steam system Acid gas Sulfur plant/sulfur sales Slag and ash Roads, fill, other products Runoff and stripped Biotreater © 2006 by Taylor & Francis Group, LLC The stack emission values presented in Table 4, as per The main problems found with sulfur sorbents involve mechanical property degradation and/or loss of sulfur capac- ity over many sulfidation-regeneration cycles. The sorbents receiving the most attention are all zinc based. Building on the Cool Water technology, various zinc titanate formulations and proprietary materials were developed by the U.S. Department of Energy (DOE)/Morgantown Energy Technology Center (METC) and used at Tampa Electric—Swisher et al. (1995). A hot gas pilot scale desulfurization is currently operating at METC. It uses a simulated coal gas mixture at volumetric flow rates of up to 120,000 standard cubic feet per hour and 400 psia and up to 1200°F. Fluidized bed technology is ideal for reactors that continuously circulate reactive and regen- erated adsorbent. For further information and updates the reader is referred to the following publication and the DOE websites: and One of the world’s largest coal gasification plants for elec- tricity generation, a 253 MWe power plant based on the Shell IGCC process, was built and started-up in Buggenum, in the Netherlands, in 1994. Since October 2001, the installation has been owned and operated by NUON Power as a fully com- mercial electric generating unit. Pulverized coal is gasified at about 400 psi and 2700°F using pure oxygen rather than air. Fly ash bearing raw gas exiting the gasifier is passed through cyclones to remove the larger particles. The remaining fines are collected in a hot gas ceramic candle filter. The filter treats about 1 million cubic feet per hour of syngas at about 500°F and 380 psia. The filter contains tube modules with elements made from a structure of silicon carbide supporting a porous Mullite grain membrane with a pore size of about 4 × 10 −4 inch. Future plans include co-gasifying waste materials such as biomass chicken litter, wood products and sewage sludge. Further cleanup of the syngas involves removal of acid gases such as COS, H 2 S and chlorides as well as a process to pounds is included in the water treatment process. Sources of non-gasifier solid wastes include sludge from raw water treatment and spent bauxite catalyst from the Claus unit, spent cobalt/molybdenum catalyst from the tail TABLE 3 Typical treated product gas composition. (Adapted from Heitz, 1985 for SCGP-1) Component % Volume (N 2 Free) Hydrogen 30 Carbon monoxide 69 Carbon dioxide <0.1 Hydrogen sulfide <0.01 Carbonyl sulfide <0.01 Hydrogen cyanide <0.001 Ammonia <0.001 Hydrogen chloride <0.001 Hydrogen fluoride <0.001 Methane 0.03 Water 0.6 Argon 0.2 TABLE 4 Cool water stack emissions. (adapted from Holt 1988) HRSG Emissions (Lbs/Million Btu) Incinerator combustion productsPollutant U.S. EPA NSPS Cool Water Permits* Cool Water Test Results** NO x 0.60 0.13 0.056 140 ppmv SO 2 0.24 0.034 0.017 116 ppmv Particulates 0.03 0.01 0.008 0.18 g/m 3 * Cool Water Permit for Low Sulfur Coal Operation (Low sulfur coal is defined in the per mit as coal containing less than 0.7 wt.% sulfur). ** 1987 EPA Performance Test Results for SUFCo Coal, Holt (1988). COAL GASIFICATION PROCESSES 169 © 2006 by Taylor & Francis Group, LLC recover sulfur (see Fig. 1). Also removal of ammonia com- http://www.netl.doe.gov/publications/proceedings/96/ 96ps/ps_pdf/96ps1_5.pdf, http://www.netl.doe.gov/ publications/proceedings/02/GasCleaning/1.05paper/pdf 170 COAL GASIFICATION PROCESSES gas treatment, silica gel from the air separation plant, and various resins from the water treatment plant. Sources of non-gasifier atmospheric emissions are cool- ing tower evaporation and drift, and the gas turbine. The cooling tower releases will cause salt deposition in the sur- rounding area. The nature and extent must be determined and evaluated using intake water quality data, design infor- mation and mathematical modeling. The on-site gas turbine will emit low levels of NO x , SO 2 and particulates which will have to be considered. Other impacts associated with any large scale project are those related to the construction of the plant. There will be an increase in traffic by the construction work force on the existing roads. There are potential construction work force impacts related to workers immigration, shortage of cer- tain skilled labor categories, etc. which must be assessed. In addition, there is a potential for noise impacts during the construction or operation of the facility. The increase in traffic on the roads, rails and rivers near a proposed site due to coal deliveries will create additional demands on the system. The construction of a facility will have unavoidable impacts on the land use at the site. Construction and operation may impact on the surface water bodies and the potable aquifers in the area but due to the current state of waste water treatment technology, minimal impact on water quality is expected after control measures are applied. The authors wish to acknowledge the work of Quig and Granger (1983) in an earlier version of this article, some of which appears here. REFERENCES Epstein, M., Elec. Pwr. Res. Inst. Jnl. pp. 39–42 Advanced Power System, April/May (1987). Heitz, W.L., Status of the Shell Coal Gasification Process (SCGP) presented at 5th Annual EPRI Contr. Conference, Palo Alto, CA, Oct. 30 (1985). Holt, N.A., EPRI Report AP-5931, Oct. (1988). Le, T.T., J.T. Smith and M.T. Sander, Elec. Pwr. Res. Inst. EPRI Report AP 4395 Jan. (1986). Lewis, A., EPRI Report AP-5467, Feb. (1988). Makansi, J., Power, pp. 75–80, Apr. (1987). Pruschek, R., G. Oeljeklaus and V. Brand, “Combined cycle power plant with integrated coal gasification, CO shift and CO 2 washing.” Energy Conversion and Management, June/September 1995, pp. 797–800. Quig, R.H., Chem. Eng. Prog., 76, 47–54, March (1980). Quig, R.H. and T. Granger, Encycl. of Envir. Sci. and Eng. Vol. 1, 103–113, (1983). Spencer, D.F., S.B. Alpert and H.H. Gilman, Science 232, 609–612, May (1986). Swisher, J.H., J. Yang, and R.P. Gupta, Ind. & Eng Chem. Research, Vol. 34, 4463–4471 (1995). ROBERT J. FARRELL ExxonMobil EDWARD N. ZIEGLER Polytechnic University © 2006 by Taylor & Francis Group, LLC . CHEMICAL EFFECTS : see EFFECTS OF CHEMICALS; AIR POLLUTANT EFFECTS; POLLUTION EFFECTS ON FISH CHEMICAL TREATMENT : see PHYSICAL AND CHEMICAL TREATMENT OF WASTEWATERS COAL GASIFICATION. at the end of the current review. Additional information is presented below on the status of coal gasification environmental effects. A comparison of the impacts on water streams of various. the pres- ence of steam and an oxygen containing gas. The products formed during high yield gasification are typically hydrogen, carbon monoxide, and variable amounts of light hydrocar- bons,