FINAL TECHNICAL REPORT

September 1, 1995, through August 31, 1996

Project Title: INNOVATIVE PROCESS FOR CONCENTRATION OF FINE PARTICLE COAL SLURRIES

DOE Cooperative Agreement Number: DE-FC22-92PC92521 (Year 4)

ICCI Project Number: 95-1/5.2A-3P

Principal Investigator: Marcus Rajchel, Williams Technologies, Inc./Clarke Rajchel Engineering Joint Venture (WTI/CRE-JV)

Other Investigators: Henry P. Ehrlinger, Consultant; Dan Harnett (WTI); Dr. Anthony Fonseca, Consol; R. Maurer, Destec Energy.

Project Manager: Dr. K. Ho, ICCI

ABSTRACT

Williams Technologies, Inc. And Clarke Rajchel Engineering are developing a technology (patent pending) to produce high quality coal water slurries from preparation plant fine coal streams. The WTI/CRE technology uses the novel implementation of high-shear cross-flow separation which replaces and enhances conventional thickening processes by surpassing normally achievable solids loadings. Dilute ultra-fine (minus 100 mesh) solids slurries can be concentrated to greater than 60 weight percent and re-mixed, as required, with de-watered coarser fractions to produce pumpable, heavily loaded coal slurries. The permeate (filtrate) resulting from this process has been demonstrated to be crystal clear and totally free of suspended solids.

The primary objective of this project was to demonstrate the WTI/CRE coal slurry production process technology at the pilot scale. The technology can enable Illinois coal producers and users to realize significant cost and environmental benefits both by eliminating fine coal waste disposal problems and producing an IGCC fuel to produce power which meets all foreseeable clean air standards. Testing was also directed at concentrating mine tailings material to produce a tailings paste which can be mine-back-filled, eliminating the need for tailings ponds.

During the grant period, a laboratory-scale test apparatus (up to 3 GPM feed rate) was assembled and operated to demonstrate process performance over a range of feed temperatures and pressures. A dilute coal/water slurry from Consol, Inc.'s Rend Lake Preparation Plant was concentrated with the process to a maximum recorded solids loading of 61.9% solids by weight. Analytical results from the concentrate were evaluated by Destec Energy for suitability as an IGCC fuel.

"U.S. DOE Patent Clearance is NOT required prior to the publication of this document."

EXECUTIVE SUMMARY

It has been estimated that the Illinois coal industry discards over 4,000,000 tons of coal fines into tailings impoundments each year. Much of this coal is of fairly high quality due to a high degree of inherent natural mineral liberation. As such, this coal might be considered "pre-prepared" for a number of various fine coal beneficiation processes. Also, it does not require milling for feed to such processes as IGCC or co-firing with pulverized coal in utility boilers. Coal fines most often go under-utilized because of inadequate means of de-watering and because of associated filter-cake handling problems. Williams Technologies, Inc. and Clarke Rajchel Engineering are developing a technology (patent pending) to produce high quality coal water slurries from preparation plant fine coal streams.

In this engineering study, recovered fine coal from Consol Inc.'s Rend Lake Preparation Plant was concentrated with the WTI/CRE process. The highest recorded slurry concentration was 61.9 weight percent solids slurry. Flotation concentrate feed slurry from the Rend Lake fine coal cleaning circuit which had been cleaned (via flotation) to less than 6.5% ash and 1.3% sulfur and with a nominal concentration of 15 weight percent, and of a size suitable for feed to Destec's slurry fed coal gasification plant was utilized in this demonstration.

The primary objective of this project was to demonstrate the WTI/CRE coal slurry production process technology at a pilot plant scale. It is hoped that the technology will enable Illinois coal producers and users to realize significant cost and environmental benefits both by eliminating fine coal waste disposal problems while producing an IGCC fuel which will meet all foreseeable clean air standards. In addition, testing was also directed at concentrating mine tailings material to produce a tailings paste which can be mine-back-filled and thus eliminate the need for tailings ponds.

Central to the WTI/CRE process technology is the novel implementation of high-shear cross-flow separation which replaces and enhances the thickening process by surpassing normally achievable solids loadings. Dilute ultra-fine (minus 100 mesh) solids slurries can be concentrated and re-mixed, as required, with de-watered coarser fractions to produce pumpable, heavily loaded coal slurries. The permeate (filtrate) resulting from this process has been demonstrated to be crystal clear and totally free of suspended solids.

The project team was assembled to present a "total technology approach" to provide a package which addresses the interests of the Illinois power generation industry. The project team includes the proposers, Williams Technologies, Inc./Clarke Rajchel Engineering Joint Venture; Consol, Inc. coal company of Illinois; Destec Energy, Inc., and Southern Illinois University. An example of the target interest is represented by the planned Franklin County Industrial Park which has shown interest in providing an environmentally friendly supply of power to their users while maintaining the support of the Illinois Coal industry.

The specific goals of the effort are:

o To improve the overall plant efficiency of Illinois coal preparation facilities and thus reduce overall costs by reducing wastes and lowering plant capital and operating costs.

o To provide the slurry production technology to produce a fuel suitable for the Destec slurry fed gasification process using recovered preparation plant fines.

o To demonstrate a process which will reduce or eliminate the need for large tailings impoundments.

o To gather data which will provide the engineering information required to design a demonstration-scale process facility for the production of coal-water slurry fuels from preparation plant fines which is suitable for the Destec slurry fed IGCC process.

o To produce a cleaner fuel by taking advantage of the natural mineral liberation associated with preparation plant coal fines.

o To demonstrate the utility of the technology in producing a tailings paste which is suitable for mine back-filling.

The specific tasks involved in achieving these goals included:

A. Process Set-up

A model process plant was assembled and operated at the SIUC Coal Research Center, Carterville, Illinois. The test setup included a membrane separator, feed tanks and piping, and a steam generator.

B. Ambient Temperature Tests

This testing had, as goals, both equipment shake-down and base-line testing. Early in the testing it was found that pilot-scale filtration efficiency was substantially lower than previous lab-scale observations. This scale-up problem was traced to design differences in the vendor-provided separation unit. Re-design of the pilot-scale separator was beyond the scope and resources of this project. The test plan was modified to include a combination of lab scale ("L-Mode") and pilot scale ("P-Mode") testing:

L-Mode To determine maximum achievable unit water removal rates.

P-Mode To investigate maximum achievable slurry loading and other operations and process control issues presented by a multi-membrane separator.

C. Elevated Temperature Tests

Elevation of feed slurry temperature has an effect linked to reduced slurry carrier fluid viscosity. Unit water removal rate was observed to increase in a linear relationship with temperature between 65 and 200F.

D. Optimum Vibrational Frequency Tests and Feed Pulse

It was found that vibrational frequency (and thus vibration amplitude) had little effect on dewatering performance above a minimum value.

Feed pulsing is a strategy to increase flux (water removal) rate by disturbing the fines bed on the membrane surface. The effect of feed pulsing could not be established in the pilot configuration during the test program, primarily because the P-scale separator package would not allow rapid pressure/flow pulsations because of flow restriction.

E. Process Control Strategy Tests

Optimal operations in a commercial plant will most likely include some level of instrumentation which will aid in start-up, shut-down, normal run-mode operation, and product quality control. Process control strategies were developed to provide smooth start-up and reliable operation, including procedures to detect and prevent plugging and membrane damage.

F. Equilibrium Flux Rate at Elevated Slurry Concentration

(Formerly "Long Duration Testing")

This task was modified from the original proposed scope during the project. The original objective was to perform a set of long-duration tests to demonstrate equilibrium performance and investigate membrane degradation over a period of 100 hours or more. However, long duration tests proved to be impractical owing to equipment limitations of the test apparatus.

Rend Lake Flotation Concentrate feed slurry was concentrated at both ambient and elevated temperatures in the pilot-scale apparatus. Measurements at system equilibrium were taken at various values of feed slurry solids concentration to observe the variation of flux rate versus solids loading.

After system startup, flux rates were observed to decline from a high initial value to a stable equilibrium rate after about 15 minutes. Flux rate was fairly constant as concentration increased from 25 to over 40% solids.

G. Tailings Paste Production

Tailings material was concentrated to determine whether a paste suitable for mine back-fill can be produced or if the material can be concentrated such that a better feed for belt filtration and subsequent tailings pile stacking can be achieved.

A dilute tailings slurry from the Rend Lake Preparation Plant was concentrated from 1% to 3.5% solids. Further concentration was not attempted due to insufficient quantities of feed slurry. In addition, the tailings slurry tested was apparently not a representative sample of the Rend Lake waste product.

Limited L-Mode testing with the material showed that dewatering performance of the equipment did not appear economically interesting. However, this assertion is somewhat dubious in the absence of testing with a more representative sample.

H. Destec Slurry Fuel Evaluation

Samples of coal/water slurry fuel made from the Rend Lake Flotation Concentrate were prepared and analyzed. The fuel was a mixture of concentrated fine-coal slurry and screen-dewatered coarse (-28 x 100 mesh) coal. Analytical results were evaluated by Destec Energy, Inc. to determine gasifier acceptability and estimated IGCC heat rate for the fuels. Destec's analysis indicated that the best fuel sample, which was 61.9 wt% solids, would make an acceptable gasifier fuel with an estimated IGCC heat rate of approximately 8,000 Btu/KWH.