FINAL TECHNICAL REPORT

September 1, 1995, through August 31, 1996

Project Title: IN-PLANT TESTING OF A NOVEL COAL CLEANING CIRCUIT USING ADVANCED TECHNOLOGIES

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

ICCI Project Number: 95-1/1.1A-1P

Principal Investigator: R. Q. Honaker, Department of Mining Engineering, Southern Illinois University at Carbondale

Other Investigators: S. Reed and M.K. Mohanty, Kerr-McGee Coal Corporation

Project Manager: K. Ho, ICCI

ABSTRACT

A circuit comprised of advanced fine coal cleaning technologies was evaluated in an operating preparation plant to determine circuit performance and to compare the performance with current technologies used to treat -16 mesh fine coal. The circuit integrated a Floatex hydrosizer, a Falcon enhanced gravity concentrator and a Jameson flotation cell. A Packed-Column was used to provide additional reductions in the pyritic sulfur and ash contents by treatment of the Floatex-Falcon-Jameson circuit product.

For a low sulfur Illinois No. 5 coal, the pyritic sulfur content was reduced from 0.67% to 0.34% at a combustible recovery of 93.2%. The ash content was decreased from 27.6% to 5.84%, which equates to an organic efficiency of 95% according to gravity-based washability data. The separation performance achieved on a high sulfur Illinois No. 5 coal resulted in the rejection of 72.7% of the pyritic sulfur and 82.3% of the ash-forming material at a recovery of 81%. Subsequent pulverization of the cleaned product and re-treatment in a Falcon concentrator and Packed-Column resulted in overall circuit ash and pyritic sulfur rejections of 89% and 93%, respectively, which yielded a pyritic sulfur content reduction from 2.43% to 0.30%. This separation reduced the sulfur dioxide emis-sion rating of an Illinois No. 5 coal from 6.21 to 1.75 lbs SO₂/MBTU, which is Phase I compliance coal. A comparison of the results obtained from the Floatex-Falcon-Jameson circuit with those of the existing circuit revealed that the novel fine coal circuit provides 10% to 20% improvement in mass yield to the concentrate while rejecting greater amounts of ash and pyritic sulfur. Although the magnitude of the improvement may vary due to liberation characteristics, the superior separation performance provided by the advanced fine coal circuit should be achievable on the -16 mesh size fraction of most run-of-mine coals. However, for coals containing a significant amount of pyritic sulfur in the -400 mesh size fraction, a Packed-Column may be needed to replace the Jameson Cell in order to achieve maximum pyritic sulfur rejections.

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

EXECUTIVE SUMMARY

The goal of this project was to demonstrate through in-plant testing the improved separation performance and enhanced economics that may be provided by a fine coal cleaning circuit utilizing advanced coal cleaning devices. In addition, it was also a goal to develop a pre-combustion coal cleaning strategy for the production of Phase I and II compliance coal from medium-to-high sulfur Illinois Basin coals.

The fine size fraction (i.e., -28 mesh) in U. S. coal preparation plants has been given very little attention until recently. However, the production of larger amounts of fines by the increase in mine mechanization and the fact that the fine coal fraction contains the most pure coal particles in the preparation plant has created a great deal of interest in the efficient cleaning and recovery of fine coal. Several technologies have been developed and introduced to the coal industry which assist the plant operators in achieving this task. The modifications to the original spiral concentrators to treat fine coal have resulted in their recent popularity among coal producers. However, despite the units simplicity of operation, several problems exist related to their separation performance capabilities and operational/maintenance characteristics. For example, their relatively small throughput per unit (i.e., 3 tph) requires the need for a large number of units to treat a moderate size stream and, thus, a complex distribution system that often gets plugged during operation. In addition, the specific gravity cut point provided by the spiral is a relatively high 1.8 and, despite extensive efforts, has yet to be decreased. Conventional flotation is another technology commonly used to treat fine coal but also has problems with the entrainment of clay particles in the clean coal concentrate and its ineffectiveness at cleaning coals containing a significant amount of middling particles.

Tests conducted over the past two years as part of ICCI projects have identified fine coal cleaning technologies that appear to provide an improved separation performance when compared to technologies currently being used in the coal industry. The research projects evaluated three distinctly different solid-solid separation technologies, namely, hindered-bed classification, enhanced gravity concentration, and column flotation, which were found to be highly efficient for treating ranges of particle sizes that are compatible when placed in a circuit arrangement. The hindered-bed classifier, commercially known as the Floatex, was found to be the most effective on the 16 x 48 mesh size fraction. The specific gravity-cut point provided by the unit is about 1.8 while achieving a probable error value (E_p) of 0.12, which is an improvement in efficiency over spiral concentrators which yield a E_p of 0.12 to 0.20. In addition, the unit is able to treat much larger throughputs, thereby, eliminating the need for a complex feed distribution system. The operating parameters of the Floatex can be easily adjusted by a controller, which is not currently possible for spiral concentrators.

The Falcon Concentrator, an enhanced gravity concentrator, was found to be the most efficient at treating the 48 x 400 mesh coal size fraction. The specific gravity cut point was found to be easily varied by the adjustment of operating variables to achieve values between 1.5 and 1.7, which are less than those achievable by spiral concentrators. The E_p value obtained from the Falcon unit was approximately 0.12. Pyritic sulfur rejections greater than 75% were achieved while maintaining recovery values at near or greater than 90%.

A number of studies comparing the performance of column flotation with conventional flotation, which is presently the most common process used for treating the -100 mesh size fraction, has found that column flotation is more efficient in the recovery of ultrafine particles and produces much lower product ash contents. In an ICCI study, recovery values greater than 90% were achieved by a number of different flotation column units while reducing the ash contents of Illinois Basin coal containing 60% -325 mesh material from as high as 50% to below 5%. These results demonstrate the excellent desliming efficiency of flotation columns. The Jameson Cell was found to be very attractive due to its high throughput and operational simplicity. The cell is self-aspirating, using a venturi-based system to draw air into a long tube where the bubbles are intimately mixed with the coal particles. However, due to its highly efficient bubble-particle collision environment, the sulfur rejection achieved by the Jameson Cell is significantly lower than other column technologies. Thus, in this investigation, a Packed-Column was used to achieve additional pyritic sulfur and ash reductions from the product of the Floatex-Falcon-Jameson circuit.

In this project, a fine coal circuit comprised of the three aforementioned advanced coal cleaning technologies was tested in an operating coal preparation plant for the purposes of improving the efficiency of current preparation plant operations and developing a Phase II compliance strategy for medium-to-high sulfur coal. To meet this goal, the specific project objectives were: 1) To install a fine coal cleaning circuit having a mass flow capacity of approximately 5 tph at Kerr-McGee's Galatia preparation plant; 2) To test the circuit in a "real-life" environment while varying the operating conditions of the various units; 3) To compare the separation performance achieved by the circuit with the performance obtained by the circuit presently used for the treatment of the same size fraction; 4) To determine the economic benefits of the proposed circuit when compared to current circuits used to treat the same size fraction and 5) To produce Phase II compliance coal through the pulverization and re-treatment of the clean coal product from the Floatex-Falcon-Jameson circuit using the Packed-Column.

In this investigation, a novel fine coal cleaning circuit comprised of an 18 x 18 in2 Floatex, a 10-inch diameter Falcon Concentrator, and a Jameson Cell was installed at Kerr-McGee's Galatia preparation plant. The Galatia coal preparation plant treats coal from two sections of the Illinois No. 5 coal seam which have distinctly different characteristics, especially in terms of total and pyritic sulfur contents. The 16 mesh x 0 size fraction is currently cleaned by a combination of spiral concentrators (16 x 100 mesh size fraction) and conventional flotation (-100 mesh size fraction).

The results obtained in this study indicate that the Floatex-Falcon-Jameson fine coal circuit provides highly efficient cleaning of -16 mesh fine coal. For a -16 mesh high sulfur Illinois No. 5 coal, the Floatex-Falcon-Jameson circuit rejected 72.7% of the pyritic sulfur while reducing the ash content from 25.8% to 7.42% at a combustible recovery of 81.1%. The separation performance was more efficient when treating a -16 mesh low sulfur Illinois No. 5 coal for which the pyritic sulfur content was reduced from 0.67% to 0.34% while recovering 93.2% of the combustible material. The ash content was decreased from 27.6% to 5.8% which equates to an organic efficiency of 95% when compared to gravity-based washability data. The difference in the separation performance achieved on the high and low sulfur Illinois No. 5 coals is believed to be due to the oxidization of the surface of the high sulfur coal particles caused by an extensive duration in a stockpile and exposure to the atmosphere which hindered the flotation process.

Pulverization of the high sulfur product generated from the Floatex-Falcon-Jameson circuit and re-treatment in a Falcon Concentrator and Packed-Column arrangement resulted in a significant reduction in ash and pyritic sulfur contents. At a combustible recovery of 80%, the pyritic sulfur content was further reduced from 1.02% to 0.20% which corresponds to a pyrite rejection of 85.1%. Thus, for the overall treatment from the Floatex to the Packed-Column, a pyritic sulfur rejection of 93% was achieved at a circuit recovery of 72% and 96% at a recovery of 64%. The overall circuit ash reduction was from 25.8% to 2.8%. This separation resulted in a significant reduction in the sulfur dioxide emission rating from 6.21 to 1.75 lbs SO₂/MBTU.

The Floatex-Falcon-Jameson circuit provided superior separation performances when compared to those obtained from the existing conventional (spirals and flotation banks) circuit. For the high sulfur Illinois No. 5 coal, a 10.5% weight units improvement was obtained by the novel fine coal cleaning circuit while rejecting 6.5% greater amounts of ash-forming material. For the low sulfur coal, the increase in mass yield provided by the Floatex-Falcon-Jameson circuit was 23.9%. In addition to the improved yield, the novel circuit rejected 12.1% greater amount of pyritic sulfur. By comparing the metallurgical results with those obtained from the washability analyses of the -16 mesh feed coal, it was found that the organic efficiency of the novel circuit was approximately 95% while the conventional circuit efficiency was 64.0%. Based on the superior separation performance achieve on the high sulfur coal, significant economic benefits were determined for the use of the Floatex-Falcon-Jameson circuit over the conventional circuit. A $2.15 million enhancement in annual net profit was estimated by using the Floatex-Falcon-Jameson circuit over the conventional fine coal circuit despite the higher capital and operating costs of the novel circuit.

Partition curves generated from the Floatex-Falcon-Jameson circuit separations revealed that the circuit provided a highly efficient, low gravity cut point which is desirable and uncommon for fine coal separations. For the low sulfur coal treatment, the gravity cut point (D₅₀) was found to be approximately 1.42 with an excellent probable error (E_p) value of 0.10. As indicated by the metallurgical results, the E_p and D₅₀ values for the separation on the high sulfur coal were significantly higher at 0.16 and 1.6, respectively.

During the investigation, several circuit arrangements were evaluated which mainly involved the inclusion or exclusion of the Falcon concentrator. The circuits utilizing the Falcon concentrator were found to provide a superior separation performance when compared to the circuit using only the Jameson Cell to treat the -28 mesh size fractions and the Packed-Column to treat the pulverized coal sample. For the pulverized coal, the use of the Falcon concentrator resulted in a further reduction in ash content from 3.8% to 2.8% and a decrease in pyritic sulfur content from 0.75% to 0.20% at a combustible recovery of 80%. This reduction in both ash and pyritic sulfur substantially reduced the sulfur dioxide emission rating from 2.50 to 1.60 lbs SO₂/MBTU.

Another finding was the ability of the Jameson Cell to efficiently recover 28 x 48 mesh coal in a rougher-scavenger arrangement. Recovery values greater than 90% were achieved for the 28 x 48 mesh size fraction. The high recovery values obtained for the coarse coal fractions may be due to the co-current bubble-particle collision environment provided in the Jameson Cell which tends to reduce the effect of particle inertia on detachment process.

An important characteristic of the Floatex-Falcon-Jameson circuit is the ability to automate the operation using process control. An on-line nuclear ash analyzer commercially known as the AMDEL system allows the determination of solids and ash contents from multiple streams. The AMDEL system was to be evaluated as part of this project. However, licensing approval from federal and state agencies has yet to be achieved, thereby, prohibiting the evaluation of the analyzer to date. The main components of the analyzer minus the nuclear sources are at SIUC and will be tested upon receiving the licensing agreements. This event did not hinder the evaluation of the in-plant circuit.

The Floatex-Falcon-Jameson circuit is comprised of commercially available advanced fine coal cleaning technologies. The circuit was found to efficiently treat -16 mesh fine coal in an operating coal preparation plant. Comparisons of the metallurgical results with those from the existing spiral-conventional froth flotation circuit indicate a 10 to 20% improvement in the fine circuit mass yield. This is due to the effective treatment of the entire fine coal stream which is not achieved in the conventional circuit. This superior performance should be achievable for the -16 mesh size fraction of most run-of-mine coals although the magnitude of the increased improvement may vary due to liberation and surface property characteristics. However, due to the efficient particle recovery mechanisms that are characteristic of the Jameson cell, pyritic sulfur reductions may be limited when the fine coal contains a significant amount of pyritic sulfur in the -400 mesh size fraction. In these cases, a Packed-Column may be needed to replace the Jameson cell in order to ensure the maximum reduction in pyritic sulfur content.