REFERENCES

1. Secton, R. J., M.D. Archives of Environmental Health. 1:208. 1960.

2. Solvent Refined Coal (SRC) Process: Health Programs, Research and Development (Report No. 53, Interim Report No. 24, Volume III, Part 4.) Industrial Hygiene, Clinical and Toxicological Programs. FE/496T15. January 1978.

3. Solvent Refined Coal (SRC) Process: Health Programs, Research and Development (Report No. 53, Interim Report No. 28,

Volume III, Part 4.) Industrial Hygiene,
Clinical, and Toxicological Programs.
FE/496-T19. April 1979.

4. Jackson, J. O., and J. A. Cupps. Carcenogenesis: Polynuclear Aromatic Hydrocarbons (Volume 3). New York, Raven Press, 1978. p. 183-191.

5. Schmalzer, D. K. SRC Pilot Plant: Health Programs and Observations. (Electric Power Research Institute Advisory Workshop on Carcenogenic Effects of Coal Conversion. Pacific Grove. September 26, 1978.)

Abstract

Environmental assessments reports (EARs) have been developed by the U.S. Environmental Protection Agency (EPA) to provide assistance in meeting commitments to preserve environmental quality. EARs are applicable both to emerging coal gasification and liquefaction systems. This paper addresses the environmental assessment of coal liquefaction via solvent refined coal (SRC).

An overview of the hypothetical SRC system considered is made. Potential sources of air emissions, water effluents, and solid waste discharges are identified. Applicable control alternatives for the discharges are discussed. Based on utilization of these controls, a summarized version of the multimedia environmental goals (MEGs) and source analysis models (SAMs) applied to SRC system discharges is presented, highlighting existing areas of environmental concern. Research needs for subsequent environmental assessments of SRC also are noted.

INTRODUCTION

As part of its goal of maintaining the nation's environment, the U.S. Environmental Protection Agency's (EPA) Industrial Environmental Research Laboratory at the Research Triangle Park (IERL/RTP), N.C., is directing an effort to evaluate the environmental aspects of emerging coal conversion technologies. Hittman Associates, Inc. (HAI), a prime contractor to IERL/RTP, is responsible for environmental analysis of coal liquefaction systems. Environmental assessment reports (EARs) were developed to provide best available environmental assessment data on specified coal conversion systems in a standardized format, thereby facilitating utilization by EPA personnel and other researchers in the field. This paper discusses a draft EAR prepared by HAI addressing solvent refined coal (SRC) liquefaction systems.

SRC systems convert high-sulfur coal and ash

coal into clean-burning gaseous, liquid, and/or solid fuels by noncatalytic direct hydrogenation. There are two basic system variations: SRC-I, which produces a solid, coal-like primary product of less than 1.0 percent sulfur and 0.2 percent ash by weight; and SRC-II, which produces low-sulfur fuel oil (0.2 to 0.5 percent sulfur by weight) and naphtha as primary products. Both system variations produce significant quantities of gaseous hydrocarbons, which are further processed to yield substitute natural gas (SNG) and liquefied petroleum gas (LPG) products. Some constituents formed during coal hydrogenation may be recovered as byproducts.

ENVIRONMENTAL OVERVIEW OF SRC SYSTEMS

Major inputs to SRC systems consist of coal, water, and air. Major products consist of gaseous and liquid hydrocarbons. Sulfur, ammonia, and phenols are recovered from waste streams as byproducts. The SRC-I and SRC-II systems are defined to consist of the following system operations,1 which perform specific functions essential to solvent refining:

• Coal pretreatment: preparation of the coal feed to meet system specifications for size and moisture content.

• Coal liquefaction: reaction of feed coal with hydrogen, yielding a three-phase mixture of increased liquid and gaseous hydrocarbon

content.

• Separation: includes all necessary phase separations. Gas separation and solids/liquids separation processes are employed in SRC systems.

• Purification and upgrading: a fractionation process is used to separate components of the raw liquid products mixture by distillation, because of differences in boiling points. A hydrotreating process may be optionally employed to upgrade the quality of fractionated product liquids.

In addition, SRC systems require the following auxiliary processes incidental to the functions of

the system operations:1 coal receiving and storage, water supply, water cooling, steam and power generation, hydrogen generation, oxygen generation, acid-gas removal, hydrogen/hydrocarbon recovery, sulfur recovery, ammonia recovery, phenol recovery, and product/byproduct storage facilities.

Figure 1 is a flow schematic of the SRC-I (solid product) system that shows how the system operations and auxiliary processes transform the major input materials into products and byproducts. Comparison of Figure 1 with Figure 2, the SRC-II (liquid product) system flow diagram, identifies the major differences in the two processing schemes as follows:1

• The SRC-I feed slurry consists of feed coal mixed with system-derived solvent produced in the fractionation process. SRC-II feed slurry consists of feed coal mixed with product slurry from the gas separation proc

ess.

• In the SRC-I system, solids/liquids separation precedes fractionation; in the SRC-II the sequence of these processes is reversed. Solids/liquids separation in SRC-I is most likely to be performed by filtration, producing the filter cake sent to hydrogen generation. In SRC-II, solids/liquids separation is achieved by vacuum distillation, which produces a bottom residue of high mineral matter content to be gasified in the hydrogen generation process.

Waste discharges to air, water, and land media are identified in Figure 3. Discharges specific either to the SRC-I or SRC-II system are noted. Subsequent discussions of discharge characteristics, applicable control technologies, and environmental impact assessment are based on a hypothetical SRC-II commercialscale facility, although the preliminary results may be considered representative of SRC-I.

Waste Streams to Air

As shown in Figure 3, air emissions are associated with a majority of the processes that make up the SRC systems. In addition to the air emissions sources shown, fugitive emissions, such as vapor leaks from pressurized process equipment, may occur in the SRC systems.1 Emissions shown in the figure are outlined below.

• Flue gases: flue gases are produced by com

bustion units (primarily preheaters) during liquefaction, fractionation, solids/liquids separation, hydrotreating, hydrogen generation, and sulfur recovery. Assuming the SNG and LPG products are used as fuel in these units, minimal environmental effects are anticipated.

• Coal dust: coal handling, processing, and storage in coal receiving and storage, and coal preparation result in particulate coal dust entering the atmosphere. Composition of the dust is the same as that of the raw coal.

• Dryer stack gas: to conform to system feed specifications for moisture content, feed coal is dried in the coal pretreatment operation. The stack gas produced by coal drying contains particulate coal and possible volatilized hydrocarbons present in the raw coal. • Vapors and particulates from cooling: mineral residue resulting from solids/liquids separation (in the SRC-II mode) and SRC product from fractionation (in the SRC-I mode) require cooling. Air cooling of these substances may result in emissions of particulate solids and hydrocarbon vapors. Insufficient data exist to characterize these emissions and estimate environmental effects.

• Drift and evaporation: the cooling tower loses water to the environment as water vapor. Chemical additives used in water cooling may also be present in this emission. • Boiler stack gas: presumably, coal is fired in the boilers of the steam and power generation auxiliary process. The resulting stack gas contains oxide of sulfur and nitrogen and particulates in the form of fly ash. Utilization of SRC system products is one alternative for reducing these emissions.

• Nitrogen-rich gas: the cryogenic oxygen generation process separates an oxygen-rich gas from ambient air for use in the hydrogen generation process. Other components of the air (mainly nitrogen) are discharged as an air emission.

• Carbon dioxide-rich gas: production of hydrogen by gasification produces a mixture of gases. An acid-gas removal unit separates sulfur gases (primarily hydrogen sulfide) from the gasifier product gas. This stream is sent to sulfur recovery. An additional acidgas removal stage removes a stream of near