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Title: COAL SLAGGING AND REACTIVITY TESTING

Abstract

Union Fenosa's La Robla I Power Station is a 270-MW Foster Wheeler arch-fired system. The unit is located at the mine that provides a portion of the semianthracitic coal. The remaining coals used are from South Africa, Russia, Australia, and China. The challenges at the La Robla I Station stem from the various fuels used, the characteristics of which differ from the design coal. The University of North Dakota Energy & Environmental Research Center (EERC) and the Lehigh University Energy Research Center (LUERC) undertook a program to assess problematic slagging and unburned carbon issues occurring at the plant. Full-scale combustion tests were performed under baseline conditions, with elevated oxygen level and with redistribution of air during a site visit at the plant. During these tests, operating information, observations and temperature measurements, and coal, slag deposit, and fly ash samples were obtained to assess slagging and unburned carbon. The slagging in almost all cases appeared due to elevated temperatures rather than fuel chemistry. The most severe slagging occurred when the temperature at the sampling port was in excess of 1500 C, with problematic slagging where first-observed temperatures exceeded 1350 C. The presence of anorthite crystals in the bulk of the depositsmore » analyzed indicates that the temperatures were in excess of 1350 C, consistent with temperature measurements during the sampling period. Elevated temperatures and ''hot spots'' are probably the result of poor mill performance, and a poor distribution of the coal from the mills to the specific burners causes elevated temperatures in the regions where the slag samples were extracted. A contributing cause appeared to be poor combustion air mixing and heating, resulting in oxygen stratification and increased temperatures in certain areas. Air preheater plugging was observed and reduces the temperature of the air in the windbox, which leads to poor combustion conditions, resulting in unburned carbon as well as slagging. A second phase of the project involved advanced analysis of the baseline coal along with an Australian coal fired at the plant. These analysis results were used in equilibrium thermodynamic modeling along with a coal quality model developed by the EERC to assess slagging, fouling, and opacity for the coals. Bench-scale carbon conversion testing was performed in a drop-tube furnace to assess the reactivity of the coals. The Australian coal had a higher mineral content with significantly more clay minerals present than the baseline coal. The presence of these clay minerals, which tend to melt at relatively low temperatures, indicated a higher potential for problematic slagging than the baseline coal. However, the pyritic minerals, comprising over 25% of the baseline mineral content, may form sticky iron sulfides, leading to severe slagging in the burner region if local areas with reducing conditions exist. Modeling results indicated that neither would present significant fouling problems. The Australian coal was expected to show slagging behavior much more severe than the baseline coal except at very high furnace temperatures. However, the baseline coal was predicted to exhibit opacity problems, as well as have a higher potential for problematic calcium sulfate-based low-temperature fouling. The baseline coal had a somewhat higher reactivity than the Australian coal, which was consistent with both the lower average activation energy for the baseline coal and the greater carbon conversion at a given temperature and residence time. The activation energy of the baseline coal showed some effect of oxygen on the activation energy, with E{sub a} increasing at the lower oxygen concentration, but may be due to the scatter in the baseline coal kinetic values at the higher oxygen level tested.« less

Authors:
; ;
Publication Date:
Research Org.:
University of North Dakota (US)
Sponsoring Org.:
(US)
OSTI Identifier:
835518
DOE Contract Number:
FC26-98FT40321
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: 1 Oct 2003
Country of Publication:
United States
Language:
English
Subject:
01 COAL, LIGNITE, AND PEAT; ACTIVATION ENERGY; AIR HEATERS; ANORTHITE; CALCIUM; COAL; COMBUSTION; FLY ASH; IRON SULFIDES; KINETICS; OPACITY; STRATIFICATION; TEMPERATURE MEASUREMENT; TESTING; THERMODYNAMICS

Citation Formats

Donald P. McCollor, Kurt E. Eylands, and Jason D. Laumb. COAL SLAGGING AND REACTIVITY TESTING. United States: N. p., 2003. Web. doi:10.2172/835518.
Donald P. McCollor, Kurt E. Eylands, & Jason D. Laumb. COAL SLAGGING AND REACTIVITY TESTING. United States. doi:10.2172/835518.
Donald P. McCollor, Kurt E. Eylands, and Jason D. Laumb. Wed . "COAL SLAGGING AND REACTIVITY TESTING". United States. doi:10.2172/835518. https://www.osti.gov/servlets/purl/835518.
@article{osti_835518,
title = {COAL SLAGGING AND REACTIVITY TESTING},
author = {Donald P. McCollor and Kurt E. Eylands and Jason D. Laumb},
abstractNote = {Union Fenosa's La Robla I Power Station is a 270-MW Foster Wheeler arch-fired system. The unit is located at the mine that provides a portion of the semianthracitic coal. The remaining coals used are from South Africa, Russia, Australia, and China. The challenges at the La Robla I Station stem from the various fuels used, the characteristics of which differ from the design coal. The University of North Dakota Energy & Environmental Research Center (EERC) and the Lehigh University Energy Research Center (LUERC) undertook a program to assess problematic slagging and unburned carbon issues occurring at the plant. Full-scale combustion tests were performed under baseline conditions, with elevated oxygen level and with redistribution of air during a site visit at the plant. During these tests, operating information, observations and temperature measurements, and coal, slag deposit, and fly ash samples were obtained to assess slagging and unburned carbon. The slagging in almost all cases appeared due to elevated temperatures rather than fuel chemistry. The most severe slagging occurred when the temperature at the sampling port was in excess of 1500 C, with problematic slagging where first-observed temperatures exceeded 1350 C. The presence of anorthite crystals in the bulk of the deposits analyzed indicates that the temperatures were in excess of 1350 C, consistent with temperature measurements during the sampling period. Elevated temperatures and ''hot spots'' are probably the result of poor mill performance, and a poor distribution of the coal from the mills to the specific burners causes elevated temperatures in the regions where the slag samples were extracted. A contributing cause appeared to be poor combustion air mixing and heating, resulting in oxygen stratification and increased temperatures in certain areas. Air preheater plugging was observed and reduces the temperature of the air in the windbox, which leads to poor combustion conditions, resulting in unburned carbon as well as slagging. A second phase of the project involved advanced analysis of the baseline coal along with an Australian coal fired at the plant. These analysis results were used in equilibrium thermodynamic modeling along with a coal quality model developed by the EERC to assess slagging, fouling, and opacity for the coals. Bench-scale carbon conversion testing was performed in a drop-tube furnace to assess the reactivity of the coals. The Australian coal had a higher mineral content with significantly more clay minerals present than the baseline coal. The presence of these clay minerals, which tend to melt at relatively low temperatures, indicated a higher potential for problematic slagging than the baseline coal. However, the pyritic minerals, comprising over 25% of the baseline mineral content, may form sticky iron sulfides, leading to severe slagging in the burner region if local areas with reducing conditions exist. Modeling results indicated that neither would present significant fouling problems. The Australian coal was expected to show slagging behavior much more severe than the baseline coal except at very high furnace temperatures. However, the baseline coal was predicted to exhibit opacity problems, as well as have a higher potential for problematic calcium sulfate-based low-temperature fouling. The baseline coal had a somewhat higher reactivity than the Australian coal, which was consistent with both the lower average activation energy for the baseline coal and the greater carbon conversion at a given temperature and residence time. The activation energy of the baseline coal showed some effect of oxygen on the activation energy, with E{sub a} increasing at the lower oxygen concentration, but may be due to the scatter in the baseline coal kinetic values at the higher oxygen level tested.},
doi = {10.2172/835518},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Wed Oct 01 00:00:00 EDT 2003},
month = {Wed Oct 01 00:00:00 EDT 2003}
}

Technical Report:

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  • To obtain qualitative information regarding the operating characteristics of the two-stage entrained-flow coal gasifier, a series of cold flow tests was conducted in a scale model of the proposed prototype gasifier. Common, unreacting substances were used to simulate the flow of anticipated components in the prototype, with air representing product gas, granulated cork (between 40- and 50-mesh USS) representing both coal and char feeds, and glycerine simulating the flow of slag in the lower stage (Stage I) of the gasifier. The flow rates for these substances were determined by matching, as closely as was possible, numerical values of various dimensionlessmore » groups in the model to those expected in the prototype. Since the primary objective of the cold model was to obtain some insight into the operation of the prototype, several aspects of the flow patterns in both stages were examined, including possible problem areas concerned primarily with refractory erosion, slag drainage, and particulate agglomeration. The results of these tests, the majority of which were recorded photographically, indicated that the gas solids mixing in both stages was generally quite intense. Based upon the results, as well as the results of the previous tests, FWEC concluded that, after incorporating recommended geometry changes into the gasifier design, further tests should be conducted in a small reacting pilot plant so that more detailed information could be obtained, especially with regard to the effects of the reactions on the behavior of the flows within both the upper and lower stages.« less
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  • A survey was conducted of four utility boiler manufacturers to obtain nonproprietary information regarding criteria that they use for designing boilers to avoid slagging and fouling. A portion of the survey identified boiler design features that are influenced by coal properties. Survey results were used to identify (1) the boiler features that manufacturers consider important when designing to avoid slagging and fouling, and (2) the coal parameters that are used in determining values for the critical boiler design features. Another part of the survey was used to obtain design information for a series of 500-MW boilers intended to fire eachmore » of six coals with varying slagging and fouling tendencies. The results were compared to identify how each manufacturer alters boiler designs to compensate for firing coals with greater slagging and fouling tendencies. It was found that each boiler manufacturer judges a different one of the six coals to present more serious deposit problems. The results suggest that each manufacturer uses different coal criteria for designing boilers. A surprising result was that some of the design furnace exit gas temperatures (which were frequently cited as important design criteria) exceed the ash fusion temperatures of several of the coals; a situation presenting a potential for deposits to form on the first few rows of convection tubes. 17 refs., 35 figs., 13 tabs.« less
  • Advanced slagging combustors were assessed for market potential and cost effectiveness as retrofits for the utility industry assuming that such slagging combustors achieve 90% ash rejection and 50% SO/sub 2/ capture, with a maximum boiler derating of 10%. A 12,000 Btu/lb design coal with a 10% ash and 3% sulfur content was utilized. The cost effectiveness of the slagging combustors was based on a four-year payback period for systems meeting emission limits of 0.03 lb of particulates/MMBtu, 0.6 lb of NO/sub x//MMBtu and 1.2 lb of SO/sub 2//MMBtu. Baghouses and dry scrubbers were used to achieve these emission limits. Amore » market analysis identified 193 oil-fired utility installations (54,000 MW, 2.8 Quads) as potential slagging combustor conversion candidates. Four case study units were selected based on geographic distribution, range of capacities, and difference of manufacturer and firing type. This report discusses the results of these analyses.« less