INTERIM TECHNICAL REPORT

September 1, 1996, through August 31, 1997

Project Title: ORGANIC SULFUR AND HAP REMOVAL FROM COAL WITH SUBCRITICAL WATER

ICCI Project Number: 96-1/1.1C-4

Principal Investigator: Mr. Chris M. Anderson, UNDEERC

Other Investigators: Mr. Ronald C. Timpe, UNDEERC

Project Manager: Dr. Ken Ho, ICCI

ABSTRACT

To date, no economically feasible organic sulfur and hazardous air pollutant (HAP) precursor removal processes have been developed, and an effective sulfur and selected HAP removal process is needed to enhance the utilization of high-sulfur coals and to comply with increasingly stringent regulations. Subcritical water has been shown by Energy & Environmental Research Center (EERC) researchers on this project to be an effective fluid for the removal of organic sulfur from IBC-102. The fourth quarter of the third year of this project was spent in obtaining Illinois bituminous coal for testing and in erecting, testing, and cleaning Illinois coal with the 4-in. packed column. Coals from two different mines in Illinois are now onsite at the EERC for testing. Several hundred pounds of the coal has been cleaned and is ready for testing. In addition, shakedown of the continuous hydrothermal process development unit (PDU) was carried out. Initial plugging problems caused by solids settling were overcome by increasing the solids loading in the coal-water feed from less than 10 wt% to greater than 30 wt%. In bench-scale testing, Co-Mo catalyst reduced sulfur content of tar from 1.60 to 0.11 wt% in an aqueous environment. On-line catalytic desulfurization of tar will be tested when operational conditions for solids desulfurization have been set.

The spring flood of the Red River of the North in Grand Forks, North Dakota, was of a magnitude never before witnessed in the region. The entire city, including the research facilities at the Energy & Environmental Research Center at the University of North Dakota, was flooded. The EERC, along with the remainder of the University, was forced to close because of water in the bottom floors of the buildings causing loss of power, water and sewer, and equipment. Technical work at the EERC was not possible between April 17 and May 8, 1997. From May 8, 1997, forward, the premises were cleaned; electricity was restored; repairs were made; and equipment replacements were begun. As equipment was put back into service, project activity gradually increased. Fortunately, the subcritical extraction equipment used in the ICCI project was not seriously damaged and was prepared for testing as operators became available. As time progressed, personnel dealt with flooded homes, limited office space and lack of equipment at work, and the mental stress brought on by both.

After careful consideration and the realization that quality work was not possible in the short time remaining on the ICCI contract, the EERC requested a 3-month no-cost project extension for the 1996-97 program to allow EERC researchers ample time to complete project objectives and put their private and professional lives back together. The extension was granted, and the project is continuing with a new end date of November 30, 1997.

EXECUTIVE SUMMARY

The primary objective of this project is to develop a continuous processing method for removing organic sulfur along with chlorine and selected hazardous air pollutants (HAPs) from physically cleaned coal with subcritical water techniques in combination with effective thermal and/or chemical treatment, if required. The goal is to produce a coal that will emit a 1.2 lb of SO2/MMBtu or less upon combustion of coals supplied by the Illinois Basin Coal Sample Bank.

Previous efforts completed by the Energy & Environmental Research Center (EERC) have indicated that subcritical extraction is an effective technique to reduce sulfur as well as HAPs. Extractions were performed at pressure and temperatures up to supercritical water conditions under constant fluid flow (dynamic) conditions. Analysis performed on cleaned samples indicated that sulfur levels can be lowered to less than 0.8 wt% sulfur with over 90% reduction in mercury content.

Using laboratory and bench-scale systems, the EERC was able to refine the process this year and construct a pilot-scale hydrothermal system capable of continuously processing coal and water at the elevated conditions. The EERC enhanced the heat exchangers and high-pressure slurry pump to maintain high residence times. The additional heat allows researchers to investigate with continuous system temperature conditions that are closer to the critical point of water (374C), where extraction properties reach an optimum point. The EERC also modified the pilot-scale system to enhance product quality and recoveries by cleaning the organic material present in the process water using a specially designed catalyst modular system. Several commercial catalysts were tested, with special emphasis on potential poisoning, efficiency, selectivity, and catalyst attrition. Initial cold slurry flow tests indicated that modified catalyst module provides sufficient slurry-catalyst contact with no apparent plugging or coal-water separation.

Near-term objectives are to treat over 500 lb of physically cleaned Illinois coal samples using the integrated hydrothermal system at conditions near supercritical. A portion of the deep- cleaned sample will then be combusted to determine particulate levels and vapor species in flue gas.

The test coals for the program will be generated using a 4-in.-diameter packed column flotation cell developed by West Virginia University and tested at Southern Illinois University (SIU). Flotation experiments will be completed at the EERC using conditions previously determined by SIU and others for Illinois coals.

Feedstock for the proposed testing was mine-washed fresh Illinois coal from two different mines. The new 4-in. packed column flotation cell was installed and tested. On obtaining satisfactory operation of the column, more than 350 lb of physically cleaned coal was prepared for continuous testing on the hydrothermal process development unit (PDU).

Shakedown testing of the PDU to determine operating parameters, including solids loading in the slurried feed, was carried out. The need for increased residence time was addressed with the Bran-Lubbe pump. Additional heat was applied with a superheater downstream from the series of three Dowtherm preheaters. Initial plugging problems caused by settling of coal were corrected by increasing the solids loading from < 10% to >30%. The coal throughput can now be continuous during operation. The PDU was successfully operated at near-critical temperature and pressure. Testing is ongoing and will involve adjustments to residence time and temperature to achieve the best sulfur and HAPs removal.

Bench-scale evaluation of commercial zeolite, Co-Mo, and Ni-Mo catalysts in aqueous environment were carried out. As expected, Co-Mo gave the best results, reducing the sulfur content in the tar from 1.60% to 0.11%. Zeolite and Ni-Mo reduced the sulfur content to 0.99% and 0.30%, respectively. Co-Mo catalyst will be tested on the PDU following finding near-optimum conditions for desulfurization of the solids. Extruded Co-Mo catalyst on alumina, of course, has reduced mechanical strength requiring an alternate support (zeolite) of a stronger configuration (cylindrical beads) to be used.