James K. Ferrell

Modeling a pilot-scale fluidized bed coal gasification reactor

A steady-state model has been developed to simulate the North Carolina State University pilot-scale fluidized bed coal gasification reactor. The model involves instantaneous devolatilization of coal at the top of the gasifier (freeboard region) and char combustion and gasification in the fluidized bed. A two-phase (emulsion-dilute gas) representation of the fluidized bed incorporates the phenomena of jetting, bubbling, slugging, and mass and heat transfer between phases, and enables the prediction of individual species flow rates and temperature profiles within the bed. The model has been successfully used to simulate the gasification of a devolatilized Western Kentucky bituminous coal and a New Mexico subbituminous coal and to predict effects of various operating parameters on key gasifier performance variables.

Analysis of nitrogenous compounds in the effluent streams from a fluidized bed coal gasification reactor

A Texas lignite and a New Mexico subbituminous coal were gasified with steam and oxygen in a pilot-scale fluidized bed reactor at pressures from 770 kPa to 830 kPa, and temperatures form 795°C to 980°C. The make gas passed through a cyclone separator, and then a venturi scrubber in which condensable and water-soluble compounds were removed. The gasifier effluents (spent char, cyclone fines, tar, wastewater, and dry make gas) were analyzed for nitrogenous compounds. For both coals, 6–12% of the nitrogen in the feed was retained in the spent char, with greater quantities being retained in the subbituminous coal char. Of the nitrogen volatilized from both coals, roughly 5% appeared in the tar, less than 0.2% appeared in the dry make gas as ammonia and NOx, and the balance appeared in the wastewater as ammonia (60%), hydrolyzable nitrogenous compounds and possibly cyanate (10–15%), thiocyanate (1%), cyanide (0.5%), and other compounds (3–10%). The average concentration of NOx in the dry gas was 7 ppm for lignite. No NOx data for subbituminous coal were obtained. Reactor conditions (temperature, pressure, steam-to-carbon feed ratio) had no measurable effect on the production rates of nitrogenous compounds over the range of conditions investigated.

How clean gas is made from coal.

Project objective The overall objective of the project is to characterize completely the gaseous and condensed-phase emissions from the gasification-gascleaning process, and to determine how emission rates of various pollutants and methanation catalyst poisons depend on adjustable process parameters. Specific tasks to be performed are as follows: Identify and measure the gross and trace species concentrations in the gasifier product, including concentrations of sulfur gases (H&, COS); organics (such as benzene, toluene and xylene, and polynuclear aromatic hydrocarbons); water-soluble species (for example, ammonia, cyanates, cyanides, halides, phenols, sulfates, sulfides, sulfites, and thiocyanates); and trace metals (antimony, arsenic, beryllium, bismuth, cadmium, lead, mercury, selenium, and vanadium). environmental impact of the widespread implementation of gasification technology is not yet understood. Recognizing this problem, the Environmental Protection Agency (EPA), in 1977, contracted for the design and construction of a pilot-plant coal gasification-gas-cleaning test facility a t North Carolina State University, to be operated by the faculty and staff of the Department of Chemical Engineering. Construction began in January 1978 and was completed and turned over to the university in the summer of 1978. Details of the plant facilities and operating procedures may be found in a recent EPA technical report (Ferrell et al., EPA-600/7-80-046a, March 1980). This paper presents a brief de-

Permeation of sulfur dioxide through polymeric stack sampling interfaces.

of the sediment and no permeation of water containing ABS into the sediment have occurred since the beginning of the deposition of ABS, the average rate of sedimentation can be calculated from the thickness of ABS-containing layer and the number of years of ABS use. The date of the beginning of the deposition of ABS in Tokyo Bay was estimated to be about 10 years before the time of sampling of the sediment, according to the data on the production of synthetic detergents in Japan and the secular change of ABS in the water of the River Tama, one of the main polluted rivers flowing into Tokyo Bay. The average rate of sedimentation was calculated as 3 cm/year in this point, and one of the examples of the usefulness of ABS as a geological tracer was presented. Though the time range in which ABS can be used is limited to only 10-20 years, such an estimation by a manmade substance is promising to apply in the area where the sedimentation process is very rapid, as in an estuary. Acknowledgment

Physical Absorption of CO2 and Sulfur Gases from Coal Gasification: Simulation and Experimental Results

Abstract High partial pressures of CO2, H2S and certain other constituents produced in coal gasification tend to make the use of physical solvents in associated acid gas removal systems more attractive than the use of chemical solvents. In the research program described in this paper operating data obtained on a pilot plant system employing refrigerated methanol as a solvent will be presented. A mathematical model of the packed absorber used in the process was developed. Predictions of system performance for a feed gas consisting of CO2 and nitrogen compared favorably to experimental data obtained on the system. In addition, there was very good agreement between predicted and observed distributions of nine of the major components in a feed gas synthesized in a coal gasification reactor. The results show the validity of the modeling procedure and may be used in understanding the general characterists of packed absorbers and strippers.

Conditioning coal gas with aqueous solutions of potassium carbonate: Model development and testing

Abstract A mathematical model describing the performance of an acid gas removal system that used hot potassium carbonate as a chemical solvent was developed and tested against operating data. The model has several parts, including algorithms for describing absorption, stripping and flash operations in which chemical reaction is occurring. The approach adopted rests on assumptions that allow the influence of chemical reactions on mass transfer coefficients to be calculated from correlations found in the literature. Predictions of the composition of the conditioned gas compared favourably with those obtained in experiments on an acid gas removal pilot plant. Although developed specifically for describing the performance of acid gas removal systems that utilize potassium carbonate solutions as a solvent, the approach can be extended to other chemical solvents.

CONDITIONING COAL GAS WITH REFRIGERATED METHANOL IN A SYSTEM OF PACKED COLUMNS

Experience with the operation of a pilot-scale unit is used to outline potential difficulties in the operation of acid gas removal systems on gases produced from coal. The pilot plant has been used to condition gases produced from subbituminous coal, devolatilized char, peat and lignite. The solvent used in the acid gas removal system has been refrigerated methyl alcohol. Data from this study document accumulation of hydrocarbons, sulfur and nitrogen compounds, and mercury in the circulating solvent.