FINAL TECHNICAL REPORT

July 1, 1996, through August 31, 1998

Project Title: THE ECONOMIC EVALUATION OF USING DEEPLY CLEANED COAL IN PC UTILITY BOILERS

ICCI Project Number: CRG27-1-96

Principal Investigator: David B. Kehoe, CQ Inc.

Other Investigators: John Molberg, Argonne National Laboratories

David Akers, CQ Inc.

Project Manager: Dr. Ken K. Ho, ICCI

ABSTRACT

The purpose of this project is to evaluate the economics of using "deeply" cleaned Illinois coal in PC utility boilers. Task 1 of the project is an initial literature search to collect recent work in quantifying the effects of ash content on power plant costs and performance. Subsequent to the assessment of the current capabilities for predicting these effects, calibrated computer models of Illinois Power's Wood River Units 4 and 5 are being constructed. Wood River was chosen because ash performance and cost effects are highly plant specific, the units were of manageable size, some CQIM boiler modeling work had already been done, and Illinois Power had already undertaken a program of monitoring maintenance costs on these units. The model was constructed using the Coal Quality Expert (CQE). The performance and costs of burning a low ash coal was projected using this calibrated model, and compared to actual performance determined in a short full scale test burn. Long term projections of the effect of low ash content on mill internal components, burners, and boiler tube wear were calculated from bench scale abrasion and erosion tests. The project team used the resultant calibrated model to establish the power plant benefits of low ash coal. An advanced physical and an advanced chemical cleaning process were selected and simulated, and laboratory-size samples were produced. These samples were analyzed, and the results used in CQE. The project team then used the power plant benefits along with estimates of coal cleaning costs and estimates of the cost of flue gas treatment to determine the amount that could be spent on advanced physical and chemical coal cleaning.

EXECUTIVE SUMMARY

Complying with clean air legislation while remaining cost competitive is the largest challenge in the electric power industry today. Utilities are faced with a complex decision involving alternatives such as coal cleaning, post-combustion flue gas treatment, and allowance purchase.

The best economic decision often involves speculation on future legislation (such as HAPs limits) and the future cost of sulfur allowances. For complying with existing legislation, most utilities have chosen to coal switch to cleaner coals. The effect of switching to these better quality coals has been difficult to determine, therefore, it has also been difficult to determine the economic trade-off between increased coal cost and power plant benefits.

Because of the sulfur content of Illinois coals, very few of these coals can be burned as-is, and either require extensive cleaning, flue-gas scrubbing or purchase of sulfur emission allowances. very little of the Illinois basin coals can be cleaned to compliance levels using conventional technology. However, advanced technologies are becoming available that may allow far greater utilization of Illinois basin coals.

The economics of using cleaned Illinois coal as the primary compliance option depend on the cost of the cleaning technology and the benefit to the power plant of using the higher quality coal that results. This project directly addresses this question. By obtaining the best commercially available coal, and deeply cleaning it, this project will establish the lower boundary of advanced physical coal cleaning. In addition, this project estimated the economics of advanced chemical cleaning as a compliance strategy.

Task 1 of the project is an initial literature search to collect recent work in quantifying the effects of ash content on power plant costs and performance. A series of conferences under EPRI sponsorship probably provide the best source of directly relevant information. These conferences have grown out of the EPRI interest in development of the CQIM and CQE. To date, five conferences have been held, most recently in 1997. In addition, an extensive literature on coal-fired plant operability exists that often identifies coal characteristics as they relate to operations. While more difficult to access and evaluate, this literature is included in the survey.

Subsequent to the assessment of the current capabilities for predicting these effects, calibrated computer models of Illinois Power's Wood River Unit 4 was constructed. Wood River was chosen because ash performance and cost effects are highly plant specific, the units are manageable size, some CQIM boiler modeling work had already been done, and Illinois Power had already undertaken a program of monitoring maintenance costs on these units. The model was constructed using the Coal Quality Expert (CQE). This program was an essential extension and integration of R&D projects performed in the past under U.S. DOE and EPRI sponsorship and it expanded the available database of coal quality and power plant performance information. In addition to cosponsoring this project, EPRI contributed its background research, data, and computer models.

In Task 2 the performance and costs of burning a low ash in a short full-scale burn were used to calibrate a CQE model. Long term projections of the effect of low ash content on mill internal components, burners, and boiler tube wear were calculated from bench scale abrasion and erosion tests. The project team used the resultant calibrated model to establish the power plant benefits of low ash coal.

In Task 3 of this project, an advanced physical and an advanced chemical cleaning process were selected and simulated, and laboratory-size samples were produced. These samples were analyzed, and the results used in CQE. The project team then used the power plant benefits along with estimates of the cost of flue gas treatment to determine the economic margin in which advanced coal cleaning must be achieved.

Raw coal was received from the Rend Lake mine, although the delay in receiving coal caused delays in the progress of the coal cleaning evaluation. A review of advanced physical and chemical cleaning technologies was performed to select the best physical and the best chemical process for Illinois coal. The best physical process was identified as column flotation in combination with gravity separation and grinding for liberation. This combination of technologies has been evaluated by researchers at Southern Illinois University. The best chemical process was identified as supercritical water leaching. This technology has been evaluated by the University of North Dakota.

The amount that a utility can pay for an upgraded coal, and hence the amount that can be spent on upgrading that coal, is highly dependent on the value placed on sulfur removal. In the past few years, sulfur allowances have been relatively inexpensive, and therefore the amount that can be spent on upgrading Illinois coal is relatively small. During Phase II, allowances prices are expected to rise, and cleaning of Illinois coals to compliance becomes more attractive.

Intense coal cleaning is even more attractive if compared to the cost of conventional flue-gas desulfurization. Scrubber cost are very high compared to the cost of sulfur allowances, particularly for a scrubber designed for such a small unit.