FINAL TECHNICAL REPORT

September 1, 1996, through August 31, 1997

Project Title: COMMERCIALIZATION OF SINGLE STAGE FINE COAL DEWATERING AND BRIQUETTING PROCESS

ICCI Project Number: 96-1/1.1B-2

Principal Investigator: R. L. Grayson, Department of Mining Engineering, University of Missouri - Rolla

Project Manager: K. Ho, ICCI

ABSTRACT

This research was an integral part of the ongoing ICCI series of coal preparation research projects. An important goal of these ICCI projects is to reduce the ash and sulfur content in coal by using fine grinding and other coal cleaning processes. The ultra-fine coal resulting from the grinding and cleaning operations is not only high in moisture content, but also creates problems in its storage, handling and transportation.

The objective of this research project was to combine the dewatering and briquetting process of fine coal preparation into a single-stage operation, thereby enhancing the viability of utilizing fine-coal. A bitumen-based emulsion, Orimulsion, proved to be an effective hydrophobic binder. It helps not only with the briquetting process but also in expelling water from the coal and preventing re-saturation.

Research this past year was done in the laboratory and with a pilot-scale (commercial) briquetting machine (Komarek B-220A). In using the pilot-scale machine initially, certain shortcomings were noticed concerning the briquetting of wet material. These problems were rectified early in the year by incorporating selected modifications to the machine, which enhanced dewatering of the feed material just before briquette formation.

Briquettes were produced with Illinois No. 5 coal feed material of different moisture contents, different levels of binder and solvent, and at various settings of machine parameters. Due to the fineness of certain samples (90% -400 mesh), solvents were used to dilute the binder so that a better binder distribution was achieved. The best results from testing, using -100 mesh material (with 37% -400 mesh content), required no solvent and consistently achieved low cured-moisture content (about 8%) and low deterioration (approximately 4% weight loss) of briquettes. These figures indicate quite robust products for ultimate handling and transport.

A preliminary economic analysis of the dewatering and briquetting process indicated a cost range of $3.84 to $6.90 per ton, depending on pilot-scale operating levels, i.e., 1.71 to 0.79 tph, respectively. Commercial-scale implementation would undoubtedly give an "economies of scale" effect, resulting in a reduced total unit cost. At this point, the process is ready for field testing but insufficient funds and time prevented implementation.

EXECUTIVE SUMMARY

The Illinois basin coal contains minerals that are finely disseminated in micron-size particles. The mineral matter, especially pyrite, can be liberated from the coal matrix by an ultra-fine grinding operation followed by a wet physical coal cleaning process such as column flotation. The fine-ground coal has a large surface area and therefore entraps substantial amounts of water during the column flotation process, making dewatering of the filter cake more difficult than for moderately-ground coal. Moreover, even if dry, this ultra-fine coal would create dust control problems during its transportation, handling and storage.

This project focused on overcoming the problems mentioned above by forming the fine coal into briquettes and, in the process, achieving additional dewatering. During experimentation using a commercially-available briquetting machine, water that existed between coal particles was expelled and coal was compacted to form briquettes. By adding Orimulsion, a hydrophobic emulsified bitumen, to enhance the formation and dewatering of briquettes, a robust product was consistently formed from -100 mesh coal samples (containing 37% -400 mesh material). These robust briquettes had a low cured-moisture content (approximately 8%) and low weight loss (approximately 4%). The single-stage system is intended to be located at the downstream end of the deep coal-cleaning process.

During previous research, problems encountered in using the Komarek B-220A briquetting machine were arching and caking of the feed material in the feed hopper and poor drainage of water at the rolls and inside the feed barrel. This year a number of design modifications were proposed to address these problems, and all of the problems were conceptually handled with various alternative solutions. Due to funding and time constraints, steps were taken to remedy the water-drainage problem first. Modifications of the machine included lengthening the feed screw to improve the primary dewatering, incorporating a special cage-type filter screen along the feed barrel, and providing a suction port in the feed barrel at the region of the filter screen so that the water squeezed-out could be removed by a vacuum pump. In addition, a filter-cloth mesh screen was used in place of the sliding cover at the bottom of the feed hopper. A vacuum port was provided to draw out water that collected in the screw feed. Following these changes, further tests were conducted for the remainder of the year.

During the year, Illinois No.5 coal samples, -100 mesh in size but with varying size consists, were used in different experiments. The coal used in the second and third quarters was predominantly -400 mesh in size (90%), which caused delays in progress and, consequently, later in the year a revised schedule of tasks was approved. Because of the extreme fineness of the coal, the binder had to be diluted to reduce its viscosity and thereby achieve effective distribution over all of the coal surface. This led to the issue of selecting a suitable solvent for the purpose. In the second quarter various solvents were mixed with the binder in various proportions and tests were conducted in the lab. For this, an automatic hydraulic press, SPEX Model 3630 was used. This equipment produced small pellets, and the settings had to be adjusted so that the conditions of the roll briquetting machine were approximated. Based on the results from this set of experiments, it was decided to use hexane as a solvent to reduce the viscosity of the binder. The experiments carried out with the -400 mesh coal were significant since it offered the worst case scenario of the single stage fine coal dewatering and briquetting application. It is emphasized that later research showed that the use of a solvent is not required for coarser coal.

In the fourth quarter, coal of a coarser size fraction (37% -400 mesh) was used, with the good results mentioned earlier, i.e., the consistent formation of robust (4% weight loss) and low moisture content (8%) briquettes. This time it was possible to achieve good distribution of the binder on the coal without the use of a solvent. A total of six laboratory (using SPEX 3630 machine) and two pilot-scale (using the modified B-220QC) experiments were performed.

Having overcome the dewatering problems through machine modifications and having achieved the formation of robust briquettes, the process is now ready for testing in actual conditions at a coal preparation plant. Further problems that might occur can be addressed on site.

A preliminary economic evaluation of the dewatering and briquetting process, based on the pilot-scale machine and done with Komarek's assistance, indicated a total cost for installation and operation of $3.84 to $6.90 per ton for production rates of 1.71 and 0.79 tph, respectively (using a 5-roll machine). Although not done yet, a commercial-scale implementation would reduce this cost, but until field testing is done at Kerr McGee's plant, a better estimate cannot be made.