Section 12.    COAL, COKE, AND POWER PLANT WASTES
EDS COAL LIQUEFACTION WASTEWATERS:
ZERO-DISCHARGE TREATABILITY STUDIES
Stan A. Kaczmarek, Project Engineer
Francis L. Robertaccio, Engineering Associate
Exxon Research and Engineering Company
Florham Park, NJ 07932
INTRODUCTION
This paper describes research to verify the commercial readiness of a zero-discharge treatment
scheme for wastewaters produced by the EDS coal liquefaction process. The potential need to operate
with zero-discharge wastewater is due to the uncertainty of future regulations and the possibility that
these industries would be located in arid regions where water reuse is desirable.
The EDS process, outlined in Figure 1, was proposed in the later 1960s. It directly converts coal to
a range of clean hydrocarbon products by contacting the coal with hydrogen in the presence of a
hydrogenated donor solvent. The commercial readiness of this technology has recently been demonstrated for certain coals and operating conditions under a jointly funded government/industry development effort. The effort included testing of two pilot plants: a batch-fed 1 metric ton per day unit
called CLPP in 1978, and a 225 metric ton per day, continuous feed prototype unit called ECLP during 1981 and 1982. Wastewater characterization and treatability tests were included in both of these
efforts.
Earlier studies on pollution control in the EDS process focused on wastewater reduction schemes,
as well as characterization and treatability of samples collected from CLPP. Those results have been
presented elsewhere [1]. This paper provides results of more recent and more detailed treatability
studies performed on wastewaters collected from ECLP, which is considered to be scaleable to commercial size for those parts of the process represented in ECLP (coal preparation, liquefaction, solvent hydrogenation and fractionation).
The characteristics of EDS process wastewaters are detailed in Table I. Raw process wastewaters
contain considerable levels of acid gases, ammonia, organic compounds, and inorganics consistent
with minerals in the feedstock. The major raw wastewater organic contaminants are phenolics, not
unlike other coal conversion wastewaters. There are also large amounts of organic acids, and lesser
quantities (e.g., 100 to 1000 mg/1) of aldehydes, ketones and various organo-nitrogen and sulfur compounds.
ZERO-DISCHARGE TREATMENT SCHEME
The zero-discharge treatment scheme chosen for this study is shown in Figure 2. Its goal is to consistently produce water suitable for use as cooling tower makeup. The cooling tower services heat exchangers are part of the EDS process equipment. A shortened version of this train might meet
regulated discharge limits in a location where wastewater discharge was allowed, or short water supplies did not require reuse.
The first treatment step, two-stage sour water stripping, removes hydrogen sulfide, carbon dioxide, and ammonia. Caustic injection in the second stage is necessary to free ammonia that appears
"fixed" in the water (i.e., not easily stripped).
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