Title

Treatability of Aqueous Gasifier Effluent Using Solvent Extraction

Date of Award

5-1-1981

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Chemical Engineering

Abstract

The treatability of aqueous gasifier effluent to reduce the content of soluble organics using solvent extraction as the principal treatment step was investigated. The aqueous gasifier effluent was collected from the spray washer of the Grand Forks Energy Technology Center's slagging fixed-bed gasifier during run RA176.

Raw gasifier effluent is treatable using solvent extraction with n-butyl acetate and isopropyl ether as solvents. A total capital investment of approximately $5,494,800 can be expected for a treatment facility using n-butyl acetate as the extracting solvent, capable of purifying wastewater from a slagging gasifier plant with a large enough capacity to produce 250 million standard cubic feet methane per day. This corresponds to a rate of wastewater production of 78,600 gallons per hour. Annual operating expenses would be approximately $8,877,100 or $12.89 per 1000 gallons wastewater treated. For a similar system using isopropyl ether as the extracting solvent, a total capital investment of $9,600,700 would be needed with an annual operating expense of approximately $13,917,400 or $20.21 per 1000 gallons wastewater treated. These costs are equivalent to 9.7$ and 15.2$ per mscf methane produced (respectively) using n-butyl acetate and isopropyl ether as solvents.

The following solvents were tested: n-butyl acetate, isopropyl ether, methyl isobutyl ketone, 2-octanone, pentane, xylene, toluene, and methylene chloride. Pentane, xylene, toluene, and methylene chloride were determined to be ineffective because of low distribution coefficients. 2-Octanone was eliminated as a possible solvent on the basis of relatively high cost of the solvent; methyl isobutyl ketone was eliminated because of a high solubility in the water phase.

Isopropyl ether and n-butyl acetate were used to treat raw waste- water directly. Additional treatment consisted of steam stripping and carbon adsorption. Optimum solvent to wastewater flow ratios were 0.10 and 0.33 for the n-butyl acetate and isopropyl ether systems respectively. Ambient temperature was determined to be optimum for both solvents.

Using solvent extraction as the principal treatment step followed by steam stripping, TOC was reduced from 12,700 mg/l to less than 50 mg/l and the ammonia was reduced from 5900 mg/l to 50 mg/l.

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