United States Environmental Protection Agency Air and Energy Engineering Research Laboratory Research Triangle Park NC 27711 Research and Development EPA/600/S7-86/015e July 1986 v°/EPA Project Summary Coal Gasification Environmental Data Summary: Trace Elements Larry J. Holconbe, Ronald D. Achord, Robert A. Magse, and Robert M. Mann This report summarizes trace element measurements made at several coal gas- ification facilities. Most of the measure- ments were madu as part of EPA's source testing and evaluation program on low- and medium-Btu gasification. The behavior of trace element:: is discussed in light of their distribution from feed coal to various discharge, product and by-product streams. This summary piovides a basis for deci- sions concerning monitoring needs at coal gasification facilities. The stream flow data and trace element concentration measurements were typi- cally not precise or accurate enough to make quantitative conclusions concerning trace element behaviors in the gasifiers. However, some general trends in element distribution are apparent. Elements that consistently had more than 70 percent of their total inlet mass partition to the bot- tom ash or slag included aluminum, bar- ium, cobalt, potassium, uranium, tungsten, and zirconium. Other elements consistently had less than 70 percent of their mass par- tition to the bottom ash, and had signifi- cant mass flow in the overhead gas and aerosols. They included antimony, arsenic, bromine, cadmium, chlorine, germanium, iodine, lead, mercury, selenium, and thal- lium. Other elements measured in the gasifier output streams had varying be- haviors depending on the gasifier. Un- known controlling factors and the varia- bility of the processes precluded com- parisons between the trace element be- haviors in the different gasifiers. This Project Summary was developed by EPA's Air and Energy Engineering Research Laboratory, Research Triangle Park, NC, to announce key findings of the research project that is fully documented in a separate report of the same title (see Project Report ordering information at back). Introduction This summary report presents and dis- cusses trace element and other selected minor and major element distributions at the coal gasification facilities tested dur- ing eight EPA studies, and from the Kel- logg-Rust/Westinghouse (KRW) PDU, Syn- thane, and Lurgi (SASOL) process char- acterizations. The U.S. EPA data acquisi- tion studies were conducted at the follow- ing synthetic fuel facilities. • Chapman low-Btu gasifiers at King- port, TN; • Wellman-Galusha low-Btu gasifiers at the Bureau of Mines Twin Cities Met- allurgy Research Center, Fort Snell- ing, MN, and Glen Gery Brick Com- pany, York, PA; • Riley Gas Producer low-Btu gasifier at Worcester, MA; • Foster-Wheeler/STOIC low-Btu gasi- fier at the University of Minnesota, Duluth; • Koppers-Totzek medium-Btu gasifiers at Modderfontein, South Africa; • Lurgi-type medium-Btu gasifiers at Kosovo, Yugoslavia; and • Texaco medium-Btu gasifier at the Ruhrkohle/Ruhrchemie facility in Oberhausen-Holten, Federal Republic of Germany. Considerable research has been con- ducted to define trace element distribution and emissions from coal combustion faci- lities. A number of groups have researched the volatility and distribution of elements in specific ash fractions and other dis- charge streams at coal combustion plants. The data from seven of the source test and evaluation studies and results from the ------- KRW, Synthane, and Lurgi (SASOL) pro- cess characterizations were evaluated, and general behavior trends are presented in this report. Wide variations may exist between trace element behavior in the various processes; however, the general trends reported here will serve as a guideline for further source testing or discharge stream monitoring. Objectives The purpose of this report is to char- acterize the partitioning of trace elements between the various gasification process streams and to compare that partitioning among gasifier processes. This summary is based on data obtained from source testing at several coal gasification facili- ties. In some cases, enough data were obtained to close the material balance on all discharge streams and by-products. This entails having trace element concen- tration and flow data on the product gas, major cleanup streams (typically cyclone dust), solid ash, and ash sluice water. However, in most of the source tests the product gas trace element data were not available. In these cases, the trace element distributions in the discharge and by-pro- duct streams are expressed as a percent of the total trace element input in the coal. This is the same as assuming that the total trace element flow from discharge streams is equal to the total input (coal) trace ele- ment flow. This assumption is not entirely accurate due to large imprecisions in flow and concentration measurements. How- ever, in most cases the results are ade- quate to identify general trends of trace elements in the gasification processes. Conclusions Data from seven gasification processes were evaluated for trace element distribu- tions: Chapman, Wellman-Galusha (Glen- Gery), Wellman-Galusha (Ft. Snelling), Riley, Foster Wheeler/STOIC, Lurgi-type, and Texaco. In addition, data collected at the Syn- thane Pilot Plant, Lurgi (SASOL), and Kellogg-Rust/Westinghouse (KRW) PDU were included for comparison. Trace Element Distributions Trace elements enter the gasification process in the coal feed. In the gasifier the fraction of coal that does not combust moves to the bottom of the gasifier as ash or slag. The gas produced contains vapor- ous trace elements as well as dust and aerosols containing trace elements. The flow measurements and concentra- tion (mass) measurements made in these gasification tests had inherent impreci- sions. Comparisons between the total mass flow of individual elements entering the gasifier in the coal and the sum of the mass flows exiting the gasifier confirmed this imprecision in many trace element measurements. A ratio of mass flow in/ mass flow out should be unity for a perfect mass balance. Actual ratios were often much greater or less than unity, depending on the element or analytical method. De- spite these imprecisions, which include more than just analytical imprecision, general trends in trace element distribution and behavior were apparent. These trends are noted below: • Seven elements consistently had more than 70 percent of their total inlet mass partition to the bottom ash or slag (for all gasifiers evaluated): aluminum, barium, cobalt, potassium, uranium, tungsten, and zirconium. • Eleven elements had consistently less than 70 percent of their mass partition to the bottom ash. Where overhead stream measurements were made, these elements had greater than 20 to 30 percent mass flow in the overhead gas and the dust and aerosols entrained with the gas: an- timony, arsenic, bromine, cadmium, chlorine, germanium, iodine, lead, mercury, selenium, and thallium. Data were neither precise enough nor con- sistent enough to be able to make any con- clusions comparing the differences in trace element behavior between different gasifiers. Overhead gas streams are routed through control devices to remove unde- sirable constituents such as dust, heavy tar, acid gases, and organic gases. By- products, such as tar, oil, and naphtha, may also be removed. The tendency for trace elements to dis- tribute in the dust captured in cyclones was evaluated by examining data from four fixed-bed gasifier tests. The follow- ing elements were highly enriched (relative to the coal ash) in the cyclone dust: anti- mony, arsenic, bismuth, cadmium, gallium, germanium, lead, mercury, and tin. (NOTE: The enrichment factor is the ratio of the concentration of the element in the stream to that of ash in the stream, divided by the ratio of the concentration of the element in the coal to that of ash in the coal.) Ad- ditionally, thallium and zinc were enriched in the cyclone dust from the four fixed-bed gasifiers, and nickel was enriched in the gas particulate matter from KRW. Trace element concentrations were mon- itored in several gas cleanup waste and by- product streams at the Lurgi-type (Kosovo) gasifier. The gas cleanup streams moni- tored, in order of successive downstream location, were heavy tar, light tar, and medium oil. Six of the elements measured during a test at the Lurgi-type (Kosovo) gasifier showed slight depletion in the gasifier ash and a generally increasing enrichment factor in the cleanup streams successively downstream. In other words, these elements (lead, chromium, stron- tium, arsenic, selenium, and copper) were more highly enriched in the medium oil than in either the light or heavy tar. Environmental Issues Solid Waste The gasifier ash or slag carries the greatest mass of trace elements from the process. Cyclone dust, also a solid waste stream, is another vehicle for discharge of trace elements from the gasifier. The ulti- mate fate of trace elements carried from the process in the solid waste streams is a function of the method of disposal. Trace elements in the gasifier ash/slag or cyclone dust may enter the environment as a result of leaching by run-off waters from surface disposal sites or by leaching from landfills into ground water. Trace element concen- trations in mild acidic teachings (RCRA EP Toxicity Test) of gasifier ash and cyclone dust were compared to RCRA maximum permissible concentrations. All solids tested were nontoxic by the EP Toxicity criteria. Aqueous Discharges Water that is used to quench or trans- port the ash or cyclone dust is another vehicle for discharge of trace elements from the gasifier. The concentration of trace elements in the ash water depends on the form of the element in the ash, the length of time the ash is in contact with the water, and the physical characteristics of the ash. Concentrations of trace ele- ments in ash or cyclone dust sluice waters were compared to the strictest drinking and irrigation water quality criteria. Under normal procedures these criteria would not be used in a direct comparison to assess environmental risk. Some consideration for dilution or the eventual discharge of the water would be made prior to establishing pollutant discharge limits. However, the criteria provide a relative basis to identify elements which may be of environmental concern in the ash waters. Trace elements that exceeded the strictest criteria at one or more of the plants were barium, boron, chromium, mercury, manganese, and molybdenum. ------- Gaseous Discharges Gaseous discharges with trace element concentrations of possible environmental concern are fugitive emissions (pokehole gases, coal hopper vent gases, and other vent gases). Only a few fugitive emissions were measured directly. However, it can be assumed that fugitive emissions will be similar in chemical composition to the pro- duct gas, except for different particle loading. Product gas concentrations of trace elements from four fixed-bed gasi- fiers were compared to work place TLVs (Threshold Limit Values) to indicate poten- tial environmental and health concerns. In this direct comparison of product gas con- centrations to TLVs, dilution by work place air or loss, through settling, of entrained particulate matter has not been consi- dered. Elements which exceeded the TLV in at least one stream included aluminum, arsenic, barium, beryllium, cadmium, cop- per, iron, lead, mercury, selenium, silver, and tellurium. All but arsenic, copper, lead, silver, and tellurium exceed the TLV, due solely to their particulate matter contribution. Vaporous trace element concentrations were measured in the gas phase only at the KRW PDU. Considerably fewer ele- ments were analyzed at KRW than at the four fixed-bed gasifiers. Only nickel in the subbituminous coal test exceeded the TLV. L. Holcombe, R. Achord. R. Magee. andR. Mann are with Radian Corp.. Austin, TX 78766. William J. Rhodes is the EPA Project Officer (see below). The complete report, entitled "Coal Gasification Environmental Data Summary: Trace Elements," (Order No. PB 86-195 278/AS; Cost: $16.95. subject to change) will be available only from: National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at: Air and Energy Engineering Research Laboratory U.S. Environmental Protection Agency Research Triangle Park, NC 27711 ------- United States Center for Environmental Research > ',';''':-.Vr,i "~ O ? Environmental Protection Information \ /1~" ,\ "., ^'' ,C Agency Cincinnati OH 45268 ' '"' ' ••"•-- Official Business Penalty for Private Use S300 EPA/600/S7-86/015e 0000329 PS ------- |