EPRI Ash Dep Impacts on Power Ind

Ash Deposition Impacts in the Power Industry

1010315

Effective December 6, 2006, this report has been made publicly available in accordance with Section 734.3(b)(3) and published in accordance with Section 734.7 of the U.S. Export Administration Regulations. As a result of this publication, this report is subject to only copyright protection and does not require any license agreement from EPRI. This notice supersedes the export control restrictions and any proprietary licensed material notices embedded in the document prior to publication.

Ash Deposition Impacts in the Power Industry

1010315 Technical Update, February 2006

EPRI Project Manager D. O’Connor

ELECTRIC POWER RESEARCH INSTITUTE 3420 Hillview Avenue, Palo Alto, California 94304-1395 ▪ PO Box 10412, Palo Alto, California 94303-0813 ▪ USA 800.313.3774 ▪ 650.855.2121 ▪ [email protected] ▪ www.epri.com

DISCLAIMER OF WARRANTIES AND LIMITATION OF LIABILITIES THIS DOCUMENT WAS PREPARED BY THE ORGANIZATION(S) NAMED BELOW AS AN ACCOUNT OF WORK SPONSORED OR COSPONSORED BY THE ELECTRIC POWER RESEARCH INSTITUTE, INC. (EPRI). NEITHER EPRI, ANY MEMBER OF EPRI, ANY COSPONSOR, THE ORGANIZATION(S) BELOW, NOR ANY PERSON ACTING ON BEHALF OF ANY OF THEM: (A) MAKES ANY WARRANTY OR REPRESENTATION WHATSOEVER, EXPRESS OR IMPLIED, (I) WITH RESPECT TO THE USE OF ANY INFORMATION, APPARATUS, METHOD, PROCESS, OR SIMILAR ITEM DISCLOSED IN THIS DOCUMENT, INCLUDING MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, OR (II) THAT SUCH USE DOES NOT INFRINGE ON OR INTERFERE WITH PRIVATELY OWNED RIGHTS, INCLUDING ANY PARTY'S INTELLECTUAL PROPERTY, OR (III) THAT THIS DOCUMENT IS SUITABLE TO ANY PARTICULAR USER'S CIRCUMSTANCE; OR (B) ASSUMES RESPONSIBILITY FOR ANY DAMAGES OR OTHER LIABILITY WHATSOEVER (INCLUDING ANY CONSEQUENTIAL DAMAGES, EVEN IF EPRI OR ANY EPRI REPRESENTATIVE HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES) RESULTING FROM YOUR SELECTION OR USE OF THIS DOCUMENT OR ANY INFORMATION, APPARATUS, METHOD, PROCESS, OR SIMILAR ITEM DISCLOSED IN THIS DOCUMENT. ORGANIZATION(S) THAT PREPARED THIS DOCUMENT N. S. Harding & Associates Electric Power Research Institute

This is an EPRI Technical Update report. A Technical Update report is intended as an informal report of continuing research, a meeting, or a topical study. It is not a final EPRI technical report.

NOTE For further information about EPRI, call the EPRI Customer Assistance Center at 800.313.3774 or e-mail [email protected]. Electric Power Research Institute and EPRI are registered service marks of the Electric Power Research Institute, Inc. Copyright © 2006 Electric Power Research Institute, Inc. All rights reserved.

CITATIONS This document was prepared by N. S. Harding & Associates 1019 East Eaglewood Drive North Salt Lake, UT 84054 Principal Investigator N. S. Harding

Electric Power Research Institute 3420 Hillview Avenue Palo Alto, CA 94304 Principal Investigator D. O’Connor This document describes research sponsored by the Electric Power Research Institute (EPRI). This publication is a corporate document that should be cited in the literature in the following manner: Ash Deposition Impacts in the Power Industry, EPRI, Palo Alto, CA: 2006. 1010315.

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ABSTRACT EPRI has played a major role in advancing the understanding of the slagging and fouling phenomena. Unfortunately as fuel quality changes due to coal pricing, mine closures, government regulations, market forces, etc., boilers and boiler operators continue to be plagued by poorer operating performance than desired. While improvements have been made, the need to address fundamental coal quality issues and how they affect deposition, emissions, handling, and combustion continues to be relevant. This study was undertaken to combine current coal quality concerns of member utilities with an assessment of how prevalent coal quality issues are to the power generation industry in general. To accomplish this, a two pronged approach was developed. First, a coal quality questionnaire was prepared and sent to several EPRI-member utilities to obtain first-hand information on specific problems as well as to seek guidance on future research and development needs. Second, a reliability and availability assessment of the NERC GADS database for the years 1995 to 2004 was completed. This database was used to determine the lost generation through either forced outages, forced derates or planned outages and derates due to coal quality or slagging and fouling issues. Conclusions from this interim report include the following: •

•

• •

•

•

Slagging and fouling continue to be the leading coal quality concerns of utility personnel. Issues with ash chemistry resulting from fuel blending and new coals being utilized continue to be the main area for needed utility support. Nearly all respondents listed slagging as one of the top five problem areas in their respective power plants. There were many research needs provided by the utility respondents. Most mentioned the need for applied rather than fundamental research – how can the results help me now and at my plant. General topics suggested for further research include fuel preparation, handling and on-line analysis; fuel and ash characterization; boiler optimization with new fuels; and development of fundamental and cost/performance models of ash deposition phenomena. There was a strong interest in supporting an EPRI Coal Quality Interest Group. The main concern was that the information be applied and factual rather than sales-oriented. An availability assessment of coal- and lignite-designed boilers showed that slagging and fouling continue to be areas of economic impact in the power industry. Older boilers did not appear to be more problematic than newer boilers and pulverized coal units (wall and tangential) tended to have less problems per boiler than cyclone units; however because of the larger number of pc-units, the economic impact was much greater. An estimated annual economic impact of over $1.2 billion was calculated for all coal- and lignite-fired boilers in the US based on coal quality and deposition causes. This number is obviously based on many assumptions, some of which will increase the number, others which will decrease the number. While this annual economic loss is huge, coal quality and deposition outages and derates account for only about 1.6% of the total number of outages and derate occurrences and 2.5% of the total lost MW-hr generation. This is based on all boilers in the NERC GADS database firing either coal or lignite and employing all firing modes used in this study.

v

•

An annual evaluation of the coal quality and deposition-based outages and derates did not show a clear trend. In fact, the coal quality-based outages and derates generally increased over the ten-year period. This evaluation was completed for all boilers greater than 100 MW.

Two prominent recommendations are: •

•

The NERC GADS database should be re-evaluated in a couple of years once the current fuel quality information is required to be provided by the participants. This will allow a much more direct cause and effect relationship to be developed between fuel quality and economic impact. Short-term (2-3 year) and long-term (5-7 year) research and development plans should be prepared and presented to utility respondents as part of the EPRI Coal Quality Interest Group agenda.

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CONTENTS 1 INTRODUCTION ....................................................................................................................1-1 2 COAL QUALITY SURVEY .....................................................................................................2-1 Introduction ..........................................................................................................................2-1 Suggested Research and Development Needs ...................................................................2-3 Pre-combustion Coal Quality Research Needs..............................................................2-3 Combustion Coal Quality Research Needs....................................................................2-4 Post-combustion Coal Quality Research Needs ............................................................2-5 Coal Quality Interest Group..................................................................................................2-5 3 COAL QUALITY SIGNIFICANCE ..........................................................................................3-1 NERC GADS Data ...............................................................................................................3-1 Boiler Evaluation Parameters...............................................................................................3-2 Cause Codes Used in Analysis............................................................................................3-4 Results of the NERC GADS Analysis ..................................................................................3-5 Coal-fired, Old Units Less Than 500 MW.......................................................................3-5 Coal-fired, Supercritical Units Greater Than 500 MW ..................................................3-13 Coal and Lignite Comparisons ...........................................................................................3-21 Boilers Greater than 500 MW.......................................................................................3-21 Boilers Greater than 100 MW.......................................................................................3-24 All Boilers .....................................................................................................................3-28 Annual Evaluation ........................................................................................................3-31 4 CONCLUSIONS AND RECOMMENDATIONS ......................................................................4-1 A COAL QUALITY QUESTIONNAIRE .................................................................................... A-1

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1 INTRODUCTION EPRI has played a major role in advancing the understanding of the slagging and fouling phenomena. Unfortunately as fuel quality changes due to coal pricing, mine closures, government regulations, market forces, etc., boilers and boiler operators continue to be plagued by poorer operating performance than desired. While improvements in overall boiler performance have been made, the need to address fundamental coal quality issues and how they affect deposition, emissions, handling, and combustion continues to be relevant. This study was undertaken to combine current coal quality concerns of member utilities with an assessment of how prevalent coal quality issues, and in particular slagging and fouling, are to the power generation industry in general. To accomplish this goal, a coal quality questionnaire was developed and sent to several EPRI-member utilities to obtain first-hand information on specific problems as well as to seek guidance on future research and development needs. To try and assess the impact of coal quality, slagging and fouling on the power industry in general, an analysis of the NERC GADS database for the years 1995 through 2004 was undertaken. This database was used to determine the number of MW-hrs lost through either forced outages, forced derates or planned outages and derates due to coal quality or slagging and fouling occurrences in boilers. Section 2 of the report describes the coal quality questionnaire and provides an analysis of the responses received. This includes suggestions from the respondents for future research and development needs as well as their desire to participate in a potential EPRI interest group on coal quality. Following the discussion of the utility contacts, Section 3 presents the NERC data analysis. This section provides a brief description of the database as well as the boiler criteria used to make the coal quality and deposition assessments. Section 4 provides conclusions and recommendations for this project.

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2 COAL QUALITY SURVEY Introduction Deposition affects power plant operations in many ways; coal quality changes as a result of coal yard practices or inability to blend coals may result in unforeseen boiler derates or outages. The need to burn a coal or blend of coals not originally meeting the design specifications for the boiler may also contribute to derates and outages attributed to deposition. As part of this study, a questionnaire was developed and sent to utility personnel intimately involved with boiler coal quality effects. The intent was to solicit their insights of coal quality effects at their plants and to provide some suggestions for future research and development needs. Appendix A contains a copy of the questionnaire. Rather than send this questionnaire to all EPRI member utilities, it was decided to send it to a select group of utility personnel who have been active or are currently active in the area of coal quality issues as they relate to deposition, outages and derates. Therefore, the questionnaire was sent to 36 individuals from 30 different utilities as shown in Table 2-1 below. Table 2-1 Utilities Receiving Questionnaire Utility

Utility

Alabama Electric

Allegheny Power

Detroit Edison

Ameren

Cinergy

Conectiv

Constellation Energy

Consumers Power

Dairyland Power

Alliant

Duke Energy

Dynegy

EKPC

Entergy

Excelon Power

Great River Energy

Hoosier

Kentucky Utilities

NIPSCO

OGE

Omaha Public Power

PacifiCorp

PNM

PowerGen

RG&E

Salt River Project

Xcel Energy

TXU

Western Resources

Southern Company

2-1

From the list of 36 contacts, 21 completed questionnaires were received; a response rate of nearly 60%. This response rate is considered to be excellent. Figure 2-1 plots a histogram of the number of individual responses for each category listed in the questionnaire. In addition, the opportunity was provided for a respondent to insert non-listed categories that are of importance to them. This is shown in red as the “other” category; these included CO emissions, cyclone tapping, on-line coal analysis, foam index, fuel variability, coal cleaning, coal yard management, hammer mills and ash sales. 20

Number of Responses

16

12

8

4

0 l I r e n s g s g g y ty es ns ng te sa lit in te er lin ci us lin LO sio m gi la sio ea po ua nd riz la pa nd ro ho ou u s s r e i H ag e i c Q a g F l l F O r D lv S B s/ rti Co er Ba lH Em Ai h er el Pu at Pa P/ ue As rn as S Fu W F u G E B Coal Quality Category

O

er th

Figure 2-1 Number of Responses for Individual Categories

Nearly all of the respondents listed slagging as one of their main coal quality issues at their plants (18 of 21). In addition to slagging, at least half of the personnel listed fouling and pulverizers as principal areas of concern with fuel quality. These were closely followed by fuel blending which was noted on nearly half of all respondents. The questionnaire asked the contacts to rank just the top five categories in terms of importance. Therefore it is not possible to state whether the individual utilities have concerns with any or all of the different categories. It is interesting to note that each of the categories listed in the questionnaire received at least one ranking. This signifies the wide range of issues that are affected by fuel quality at the power plant. As mentioned above, the questionnaire asked the contacts to rank the top five coal quality categories in terms of challenges at their plants. Using this system, an importance ranking for

2-2

each individual category could be calculated. This is shown in Figure 2-2. Note that in this figure all the “Other” issues are listed separately. 60

Importance Ranking

50

40

30

20

10

Sl ag gi n Fu F o g el uli n ES Bl g P/ end Ba in g g Pu hou l v se er iz er G s as Em LO is I si o O ns Pa pa Bu rti city rn cu er lat e s/ Fl s a C me or s ro Ai sio r n Fu H el ea Fu Ha ter el nd O Va lin g nlin riab e i An lity Fo aly am sis As I h nde D is x po s H Ta a l am pp m ing er M ills W at C e C rQ O o u C al C ali oa ty l Y lea ar nin d g M As gm t. h Sa le s

0

Coal Quality Category

Figure 2-2 Importance Ranking for Individual Categories

Clearly slagging dominates as the most important coal quality issue facing the utility respondents followed by fouling and fuel blending. Undoubtedly this is because of how changes in fuel quality can effect furnace deposition and lead to problems in many areas of the boiler. Suggested Research and Development Needs The questionnaire provided a blank field for the respondents to propose areas where they feel additional research and development are needed. The responses focused on plant needs and several comments were made to the fact that they are interested if the work is applied research that is useful to the industry. The responses have been grouped into three broad areas: pre-combustion, combustion, and post-combustion. They focus on coal quality needs as they relate to the specific topic. Pre-combustion Coal Quality Research Needs There are four main topics suggested for research needs in this area. They are:

2-3

• Transportation • Cleaning Processes (especially dry processes) • Fuel Blending • Use of On-line Analyzers These topic areas deal with issues of optimizing the fuel to the boiler in order to reduce the impact the fuel has on operations. Some utilities are forced to blend multiple coals including coals received from overseas. As a result, there are issues with transportation of dusty, more volatile coals and methods to properly blend and account for the correct fuel quality are needed. A couple of utility respondents mentioned the need for improved coal cleaning processes, especially those that don’t increase the moisture content of the coal. The target of these cleaning processes is not only to produce a more uniform product, but to also remove some of the undesirable species such as ash, sulfur and mercury. Some interest by a few of the respondents was in the use of on-line analyzers for tracking the fuel quality going into the bunkers and boilers. This is an important advancement to most utilities as the current practice is to find out the coal quality one to several days after an incident has occurred. The ability to know what the fuel quality is prior to it being consumed will allow the operators to prevent many fuel-related derates and unforced outages. Combustion Coal Quality Research Needs The most significant number of research and development needs related to coal quality is in the area of the boiler and subsequent combustion of the fuel. These have been grouped under the heading of combustion; as they are a direct result of burning the fuel. • •

Fuels Characterization Ash Chemistry • Slagging • Fouling • Corrosion • Additives • Boiler Optimization (OFA, SOFA, CCOFA, High Heat Density Furnaces) • Intelligent Sootblowing • Modeling • Fundamental Deposition • Cost and Performance Many contacts mentioned the need for applied research as opposed to strictly fundamental research in these areas. The need is to develop models or correlations which can be applied to individual boilers to maximize combustion efficiency and optimize performance.

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Post-combustion Coal Quality Research Needs The final grouping of suggested research needs was in the area of downstream control. These specific topics included: • Ammonia/SO3 control for back end corrosion • Loss-on-ignition • ESP Performance • Plume Opacity • CO2 Capture with Existing Boilers • Foam Index for Ash Sales Most of the respondents who listed post-combustion issues as areas for research needs did so because their concerns were a direct result of fuel quality conditions. These may have included blends of multiple coals or changes in coals being fired due to economic reasons, etc. Other suggestions were made of how operating changes to reduce regulated emissions have caused changes in ash chemistry as well as particulate collection efficiencies. Coal Quality Interest Group The final question on the survey discussed the issue of EPRI organizing a Coal Quality Interest Group (CQIG) with periodic web casts of in-house, funded and vendor coal quality activities. The intent was to determine if there was sufficient interest on the part of utility personnel to organize this group. All of the respondents who are not retiring their coal-fired units within the next 1-1½ years were interested in this concept. The areas mentioned for discussion were very similar to those listed as their desired research topics. These included: • • • • • • • •

Fuel selection process including on-line analyzers, blending, handling Methods to tie operations to fuel quality Improved capabilities of models such as VISTATM Slagging/Fouling/Corrosion predictions and mitigation techniques Methods to improve operations with overfire air and reduce LOI A better understanding of the fundamentals of the foam index Methods to improve hot-side ESP performance with subbituminous coals Methods to increase mercury capture or removal

There is clear evidence from the many respondents to the survey that there is continued interest in better understanding fuel quality and its impacts on the entire steam generation process. This begins with coal purchases and continues through to the use or disposal of the incombustible ash material.

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3 COAL QUALITY SIGNIFICANCE A number of authors have indicated that ash deposition is a sizable problem. For example, Devir [3-1] states that “slagging costs the global utility industry several billion dollars annually in reduced power generation and equipment maintenance.” However, other than a few similar generic statements about the significance of the problem worldwide, there is very little published economic/cost data pertaining to ash deposition. A recent joint EPRI/DOE publication on guidelines for solving ash deposition problems [3-2] provides an excellent discussion on deposition occurrences and gives some general economic impacts. In addition, given the nature of today’s power markets, the precise analysis of cost will be quite incident specific, depending on market considerations, along with utility-specific economic drivers. This section will review some industry-wide information derived from an analysis of the NERC GADS (Generating Availability Data System) data using the NERC pc-GAR program updated to include 2004 data. This database provides a tremendous amount of information, so a brief discussion of the underpinnings of the program as well as the criteria used in this analysis is given. NERC GADS Data A significant source of utility reliability, availability and maintainability information is the NERC GADS database [3-3]. This database is updated annually and contains operating histories on more that 5000 generating units, and according to NERC, represents about 90% of the installed generating capacity in North America. The NERC GADS database receives information from nearly 80% of the coal-fired generating units within the US [3-4]. The database contains basic information on the boiler including primary and secondary design fuels, boiler type, burner, steam pressure, year the boiler was commissioned, MW rating of the turbine, and all different types of specific information for all reporting boilers. These data are essentially “hardware” and to not change on a regular basis. In addition, the annual availability performance of the boiler is recorded. From the “hardware” data, boilers can be grouped according to design specifications and their group performance can be evaluated based on cause codes. These codes are defined as the primary cause of a reported event. For example, a derate due to a slag fall from a given unit will trigger a cause code and the MW-hrs the boiler was derated can be calculated. Summing up all boilers in a given group that had a derate due to a slag fall gives the total MW-hrs lost due to slag falls within that group. The information is generic in that one of the stipulations for utility personnel to provide the data is that the performance of individual units cannot be determined, only groups of similar units. In fact, the smallest number of boilers in a group that can be evaluated is five. Therefore, if a set of boiler criteria are so restrictive as to have less than 5 boilers meet all criteria, no reliability analysis can be made. One of the limitations to the NERC GADS database is that the current coal quality information is optional for contributors. Only 20% of the boiler operators provide their current coal quality

3-1

information. However, proposals are underway within NERC GADS to require the current coal quality information on an annual basis. This suggestion will be reviewed and voted on in the next couple of years. Boiler Evaluation Parameters The focus of this study was to evaluate the impacts of coal quality and deposition on boiler performance and to provide some estimates of the financial impact to the industry. The earlier EPRI/DOE study [3-2] provided a useful beginning for this work as the GADS database has been updated and this earlier study revealed certain information which indicated a more detailed follow-up study would be useful. The boilers that were used in this study would be only those fired with coal or lignite (PRB, or any particular coal source, is not listed separately, they are all included as coal). Within the coal/lignite-fired boilers, the impact of MW output, main steam pressure (subcritical vs. supercritical), boiler age and firing method (single-wall, opposed-wall, concentric, tangential, or cyclone) were also evaluated. There were two sizes of boilers compared, those less than 500 MW but greater than 100 MW and those greater than 500 MW. The age of the boiler was defined as those coming on-line between 1900 and 1970 and those newer units coming on-line after 1970. The firing methods evaluated (wall, tangential, cyclone) were used to determine performance differences between the firing modes; note however, that single-wall, opposed-wall and concentric firing were grouped and labeled as “wall”. No other firing types (roof, arch, turbo, stoker, FBC, etc.) were considered in this study. Therefore, the combination of all criteria resulted in 69 cyclone, 347 wall-fired and 383 tangential-fired boilers being evaluated in this study. The performance period for this evaluation was the most recent 10-year data, 1995 to 2004. As was mentioned previously, if less than five boilers met the combination of criteria, that group could not be further evaluated. Given the five boiler evaluation parameters and the ranges of each to be studied, a full factorial test matrix contains 48 different combinations. All of these combinations as well as some selected other evaluations were made. Table 3-1 summarizes the five criteria and the abbreviations used to distinguish each. The complete set of boiler runs made is listed in Table 32 with the number of units and utilities contained in each of the test runs. The line shown after Run No. 48 denotes the additional runs made after the full test matrix had been completed. These additional runs grouped certain parameters as noted to allow comparative evaluations to be made. Again, groups with populations less than 5 were not evaluated due to the confidentiality restrictions in the program. Table 3-1 Parameters and ranges used in boiler performance evaluations Value 1 Value 2 Parameter Range Symbol Range Symbol Boiler Age Boiler Size, MW Steam Pressure, psig Coal Type Firing Method

1900-1970 100-499.9 0-1500 Lignite Cyclone

Old Small SubC Lig Cyc

1971-2005 500-1500 1501 - 5000 Coal Tangential

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New Large SuperC Coal Tang

Value 3 Range Symbol ----Wall

----Wall

Table 3-2 Evaluation Matrix for Study Run No.

Coal Type

Age

Size

Pressure

Firing Type

Units

Utilities

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

Lig Lig Lig Lig Lig Lig Lig Lig Lig Lig Lig Lig Lig Lig Lig Lig Lig Lig Lig Lig Lig Lig Lig Lig Coal Coal Coal Coal Coal Coal Coal Coal Coal Coal Coal Coal Coal Coal Coal Coal Coal Coal Coal Coal Coal Coal Coal Coal Lig Lig Lig Lig Lig Lig Lig Lig Lig Lig Coal + Lig Coal + Lig Coal Coal Coal Coal Lig

Old Old Old Old Old Old Old Old Old Old Old Old New New New New New New New New New New New New Old Old Old Old Old Old Old Old Old Old Old Old New New New New New New New New New New New New New + Old New + Old New + Old New + Old New + Old New + Old New + Old New + Old Old New New + Old New + Old New + Old New + Old New + Old New + Old New + Old

Small Small Small Small Small Small Large Large Large Large Large Large Small Small Small Small Small Small Large Large Large Large Large Large Small Small Small Small Small Small Large Large Large Large Large Large Small Small Small Small Small Small Large Large Large Large Large Large Large Large Small Small Large+Small Large+Small Large Small Large+Small Large+Small Large+Small <99.9 MW Large Large+Small Large Large+Small Large+Small

Sub C Sub C Sub C SuperC SuperC SuperC Sub C Sub C Sub C SuperC SuperC SuperC Sub C Sub C Sub C SuperC SuperC SuperC Sub C Sub C Sub C SuperC SuperC SuperC Sub C Sub C Sub C SuperC SuperC SuperC Sub C Sub C Sub C SuperC SuperC SuperC Sub C Sub C Sub C SuperC SuperC SuperC Sub C Sub C Sub C SuperC SuperC SuperC SuperC Sub C SuperC Sub C SuperC Sub C Sub+SuperC Sub+SuperC Sub+SuperC Sub+SuperC Sub+SuperC Sub+SuperC SuperC SuperC Sub C Sub+SuperC Sub+SuperC

Cyc Tang Wall Cyc Tang Wall Cyc Tang Wall Cyc Tang Wall Cyc Tang Wall Cyc Tang Wall Cyc Tang Wall Cyc Tang Wall Cyc Tang Wall Cyc Tang Wall Cyc Tang Wall Cyc Tang Wall Cyc Tang Wall Cyc Tang Wall Cyc Tang Wall Cyc Tang Wall Cyc+Tan+Wall Cyc+Tan+Wall Cyc+Tan+Wall Cyc+Tan+Wall Cyc+Tan+Wall Cyc+Tan+Wall Cyc+Tan+Wall Cyc+Tan+Wall Cyc+Tan+Wall Cyc+Tan+Wall Cyc+Tan+Wall Cyc+Tan+Wall Cyc+Tan+Wall Cyc+Tan+Wall Cyc+Tan+Wall Cyc+Tan+Wall Cyc+Tan+Wall

0 0 0 0 0 1 0 0 0 0 0 0 0 3 0 1 1 1 0 0 0 0 0 5 10 173 138 10 37 26 0 0 0 10 33 19 0 0 1 3 49 50 0 0 0 7 82 106 13 2 5 3 18 3 5 13 2 16 799 140 257 710 257 781 18

0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 1 1 1 0 0 0 0 0 3 7 45 47 7 17 13 0 0 0 6 20 11 0 0 1 0 29 29 0 0 0 5 37 42 5 1 5 1 10 1 5 5 2 8 123 45 80 116 80 18 10

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Following the completion of these 10-year evaluations, a study of the annual outages and derates was done using all boilers greater than 100 MW (Run No. 59) for each of the 10 years. The purpose of this analysis was to see the trends in outages and derates caused by coal quality and deposition. Cause Codes Used in Analysis Once all of the boiler groups were determined, an evaluation of the operability and reliability information of the various groups could be completed. This is done by using “cause codes.” A cause code is defined as the primary cause for a reported event such as a maintenance outage, a forced derate, etc. As this evaluation was focused on coal quality and deposition, the only included cause codes were those related to fuel quality (Cause Codes 9200-9290) and boiler tube fireside slagging and fouling (Cause Codes 1100 – 1210; 1330). Table 3-3 lists the specific cause codes used in this analysis. The individual cause codes were grouped since the focus was on overall fuel quality and deposition (slagging and fouling) rather than specific causes. Note however, that it is possible to get outages and derates occurring as a result of fuel quality or deposition in any one of the listed cause code areas. Table 3-3 NERC GADS Cause Codes Included in Analysis

Cause Code 9200 9210 9220 9240 9250 9270 9280 9290 1100 1105 1110 1120 1130 1140 1150 1160 1170 1180 1190 1200 1330

System/Component Fuel Quality High ash content Low grindability High sulfur content High sodium content Low BTU content Wet coal Frozen coal Other fuel quality problems Boiler Tube Fireside Slagging or Fouling Furance wall Generating tube Cyclone furnace (in cyclone area only) Convection pass wall Boiler screen, wing wall, or slag screen (water tubes only) First superheater Second superheater First reheater Second reheater Economizer Other tube slagging or fouling Operation at reduced power to avoid slagging/fouling Miscellaneous Boiler Tube Problems Slag fall damage

These are the cause codes used in this study; however there are other similar cause codes such as tube leaks, ash or slag removal that may have their root in coal quality issues. However, if the 3-4

utility did not report the primary cause of an event as one of the listed cause codes, the event would not be counted; this most likely results in an underreporting of the actual impacts of fuel quality on performance. In fact, the NERC GADS system does not require (or even accept) root cause analysis, so even if a utility knew a tube failure was caused by sootblower erosion, it would not be recorded as a fuel quality problem, it would be simply recorded as a tube failure. Similarly, derating during non-peak hours to shed slag is rarely recorded as lost generation, though the practice is quite common. Results of the NERC GADS Analysis The results of the NERC GADS analysis showed many interesting insights into the frequency and duration of boilers having outages and derates due to coal quality and/or slagging and fouling. The data have been grouped into three categories: forced outages, forced derates and planned outages and derates. The cost to a utility for a forced outage or forced derate can be significantly higher than the cost for a planned outage or derate. In general, a utility purchases ahead of time excess energy from other utilities during their planned outages; for this reason most scheduled outages do not occur during the peak generating seasons (hot summers or cold winters) since the generation from all systems is high. This cost of generation may be in the $25-$35 per MW-hr range. However, if a unit is taken off-line or derated unexpectedly, the price of a MW-hr of power is significantly higher. In fact, on Friday, December 16, 2005 the cost of a MW-hr of power was $103.84 according to the Locational Marginal Pricing index. This price fluctuates considerably depending upon whether a large unit goes off-line or weather conditions, etc. For this study, an average cost of power for a forced derate or forced outage over the ten year study period was assumed to be $50/MW-hr. Therefore, a planned outage or derate, in this evaluation, costs $30/MW-hr while a forced outage or derate costs $50/MW-hr. Using this pricing structure and the fact that fuel quality and deposition occurrences most likely are underreported, a conservative estimate of the cost of coal quality and/or deposition to the utility industry can be determined. The next sections discuss the results of similar types of evaluations. Again, note that when the evaluation group had less than five boilers, it could not be further analyzed. Coal-fired, Old Units Less Than 500 MW Deposition Related Occurrences Figures 3-1 to 3-3 show the results of the deposition evaluation comparing firing method and main steam pressure for the coal-fired, older units (commissioned before 1971) with a nameplate rating between 100 and 500 MW. Figure 3-1 shows the average MW-hrs lost for forced outages due to the deposition cause codes, Figure 3-2 is for forced derates and Figure 3-3 is for planned outages and derates.

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Average MWh Lost/Forced Outage (Coal Fired, Old, Small)

Subcritical Supercritical ## No. Outages

183 16000

96 190

14000

MW-hr/Outage

12000

10000

44 41

8000

69

6000

4000

2000

0

Cyclone

Wall

Tangential

Figure 3-1 Average MW-hrs lost per forced outage in coal-fired, older small units

Several items are noteworthy in Figure 3-1. First the numbers on top of each bar are the number of reported occurrences over the ten year study for each case. There are many more events with the supercritical wall- and tangential-fired units due to the larger number of boilers with these firing methods compared to the cyclone-fired boilers. Even though the number of events differ between the cyclone and other firing methods, the average MW-hrs lost per each outage event is relatively constant. As one would expect, the average MW-hrs lost is significantly higher for the supercritical units than for the subcritical ones. In this case, the cyclone units have nearly the same number of events even though the boiler population is much smaller than the wall- and tangential-fired units. Figure 3-2 is a similar plot to Figure 3-1 except that it shows the average MW-hrs lost due to forced derates rather than forced outages. Note that the scale remains the same so that a quick glance shows that the average MW-hrs lost due to forced derates is about ten times less than for forced outages. Here the number of forced derate events is significantly increased compared to the number of forced outage events, as expected. This is especially true for the supercritical units. In this case the cyclone-fired units have the highest average MW-hr lost, but have the fewest reported events. Again this is a function of the number of boilers. However, for the subcritical boilers, the cyclone units do have a significantly higher number of forced derate occurrences compared to the wall- and tangential-fired units even though the number of boilers is significantly less.

3-6

Subcritical Supercritical ## No. Derates

Average MWh Lost/Forced Derate (Coal Fired, Old, Small)

16000

14000

MW-hr/Derate

12000

10000

8000

6000

4000

1127 2000

2018

564

142

Cyclone

Wall

2560

51

0

Tangential

Figure 3-2 Average MW-hrs lost per forced derate in coal-fired, older small units

Figure 3-3 shows the MW-hrs lost during planned outages or derates. One obvious fact is that for the subcritical units, there were nearly 500 more planned events for the cyclone-fired units than for the wall- or tangential-fired units. Knowing that there are only 10 cyclone boilers in this group gives an average of 49 planned events over the 10-year evaluation period. This corresponds to nearly 5 scheduled events per year per boiler. For the supercritical units, number drops to about 3 planned outages or derates every two years. Figures 3-4 and 3-5 show the total distribution of lost MW-hrs for the subcritical (Figure 3-4) and supercritical (Figure 3-5) boilers. In these figures, the number on top of each bar represents the number of boilers in the study group. For the subcritical units, the cyclone boilers have nearly three times the total lost MW-hrs compared to the wall and tangential boilers. For the supercritical units, the trend is reversed and the tangential-fired boilers have the greatest lost MW-hrs. Using the cost estimates of $30/planned MW-hr derate or outage and $50/forced MWhr derate or outage, the annual average cost of slagging and fouling is shown in Table 3-4. This estimates the cost of slagging and fouling at just over $8 million per year for the subcritical boilers and nearly $73 million per year for the supercritical units.

3-7

Subcritical Supercritical ## No. Planned

Average MWh Lost/Planned Outage & Derate (Coal Fired, Old, Small)

16000

MW-hr/Planned Outage & Derate

14000

12000

10000

8000

48

6000

4000

2000

491

1412

615 1

0 0

Cyclone

Wall

Tangential

Figure 3-3 Average MW-hrs lost per planned outage and derate in coal-fired, older small units

Distribution of Lost MW-hrs (Coal Fired, Old, Small, Subcritical) Forced Outages Forced Derates

8.0E+06

Planned ## No. of Boilers

MW-hrs

6.0E+06

4.0E+06

10

2.0E+06

26

37

0.0E+00

Cyclone

Wall

Tangential

Figure 3-4

3-8

Distribution of lost MW-hrs in subcritical, coal-fired, older small units . Distribution of Lost MW-hrs (Coal Fired, Old, Small, Supercritical)

8.0E+06

Forced Outages Forced Derates

173


6.0E+06

MW-hrs

138

37 4.0E+06

2.0E+06

0.0E+00

Cyclone

Wall

Tangential

Figure 3-5 Distribution of lost MW-hrs in supercritical, coal-fired, older small units

Table 3-4 Annual estimated cost of slagging and fouling for coal-fired, small older boilers Firing Method

Subcritical

Supercritical

Cyclone

$4.7 MM

$17.4 MM

Wall

$1.8 MM

$23.2 MM

Tangential

$1.6 MM

$32.2 MM

Total

$8.1 MM

$72.8 MM

The final figure (Figure 3-6) in this series shows the average MW-hrs lost per boiler. This clearly shows that the cyclone-fired units average nearly three times the MW-hr lost per boiler compared to the wall- and tangential-fired boilers. In this figure, the subcritical cyclone-fired units have a higher average MW-hrs lost compared to the supercritical cyclone units; the reverse is true for both the wall- and tangential-fired boilers.

3-9

Average MW-hrs Lost per Boiler (Coal Fired, Old, Small)

1.2E+05

Subcritical Supercritical ## No. Boilers

10 37

1.0E+05

MW-hrs/Unit

8.0E+04

6.0E+04 173 138 4.0E+04

26 2.0E+04

37

0.0E+00

Cyclone

Wall

Tangential

Figure 3-6 Average MW-hrs lost per boiler for coal-fired, older small units

Coal Quality Related Occurrences A similar analysis can be done using the coal quality cause codes mentioned earlier. These include incidents of wet coal, frozen coal, high sulfur or sodium coal, low heating value coal or some other generic fuel quality effect. While the coal quality being utilized at a station is not currently a requirement for the GADS database, if the utility deems that coal quality was the root cause of an outage or derate, it can be designated as such. Therefore, this is not all-inclusive regarding strictly coal quality on unit performance but does provide an interesting first attempt at quantifying the direct costs of fuel quality on performance. The coal quality information is slightly different in that the specific number of occurrences for forced outages and derates was not obtained. However, the total number of occurrences is provided. Figure 3-7 shows the number of coal quality occurrences for the coal-fired units coming on-line before 1970 and less than 500 MW. As one expects, the supercritical boilers have significantly more fuel quality related issues than do the subcritical units. Due to the larger number of wall- and tangential-fired boilers, there are substantially more coal quality related outages and derates than for cyclone-fired boilers. Also, cyclone-fired boilers are able to utilize a wider fuel specification, thus reducing the number of fuel quality incidences.

3-10

Number of Coal Quality Occurrences (Coal Fired, Old, Small)

Subcritical Supercritical

8000

7000

6000

Number

5000

4000

3000

2000

1000

0

Cyclone

Wall

Tangential

Figure 3-7 Number of coal quality occurrences in coal-fired, older small units

Using the data, the MW-hrs of lost generation can be determined for forced outages, forced derates as well as planned outages and derates. These are shown in Figure 3-8 (subcritical) and Figure 3-9 (supercritical). Note that the scales are the same so that it is readily apparent that the supercritical boilers lose significantly more MW-hrs due to coal quality related outages and derates than do the subcritical units. By comparing Figures 3-5 and 3-9, the MW-hrs lost due to coal quality is similar to the MW-hrs lost by deposition. In fact, the tangential units have a slightly higher lost MW-hrs due to fuel related outages than due to deposition. Table 3-5 shows the estimated cost of poor fuel quality for the coal-fired, small older boilers. Comparing Table 3-4 and Table 3-5 demonstrates that the annual estimated cost between fuel quality and deposition to this group of boilers in the utility industry is similar for supercritical boilers, but the fuel quality costs are nearly twice as high as the deposition costs in the subcritical units. Figure 3-10 shows the average MW-hrs lost per boiler due to coal quality issues. Clearly the wall- and tangential-fired units have the greatest average loss compared to cyclone units. This is not surprising since cyclone-fired boilers tend to have wider fuel specifications than do wall- or tangential-fired boilers.

3-11

Distribution of Coal Quality Lost MW-hrs (Coal Fired, Old, Small, Subcritical)


1.2E+07

Planned ## No. of Boilers 1.0E+07

MW-hrs

8.0E+06

6.0E+06

4.0E+06 26

37

2.0E+06 10

0.0E+00

Cyclone

Wall

Tangential

Figure 3-8 Distribution of lost MW-hrs due to coal quality in subcritical, coal-fired, older small units

Distribution of Coal Quality Lost MW-hrs (Coal Fired, Old, Small, Supercritical)

1.2E+07


173


138

MW-hrs

8.0E+06

6.0E+06

4.0E+06

2.0E+06

37

0.0E+00

Cyclone

Wall

Tangential

Figure 3-9 Distribution of lost MW-hrs due to coal quality in supercritical, coal-fired, older small units

3-12

Table 3-5 Annual estimated cost of coal quality for coal-fired, small older units Firing Method

Subcritical

Supercritical

Cyclone

$0.7 MM

$4.9 MM

Wall

$6.0 MM

$40.4 MM

Tangential

$9.1 MM

$30.3 MM

Total

$15.8 MM

$75.6 MM

Coal-fired, Supercritical Units Greater Than 500 MW Deposition Related Occurrences A similar deposition comparison was made between firing methods and boiler age for coal-fired, supercritical boilers greater than 500 MW. Figures 3-10 to 3-12 show the average MW-hrs lost per forced outage, forced derate and planned outage or derate, respectively. An interesting observation from Figure 3-10 is that the older units have fewer occurrences of forced outages than do their corresponding newer units. However, the average MW-hr lost is higher for the older units’ outages except for the wall-fired boilers.

Average MWh Lost/Forced Outage (Coal Fired, Large, Supercritical)

Pre - Dec 1970 Post - Dec 1970 ## No. Boilers

155

70000

24

23 60000 46

MW-hr/Outage

50000

203

40000

24

30000

20000

10000

0

Cyclone

Wall

Tangential

Figure 3-10 Average MW-hrs lost per forced outage in coal-fired, supercritical large units

3-13

In Figure 3-11, the newer wall-fired boilers have an extremely high average MW-hr derate loss; in reviewing the evaluation summary, there were a few very significant events that resulted in very high lost MW-hrs. As a consequence, the wall-fired units had an average MW-hr derate loss nearly 50% that of the forced outage MW-hr loss. In the previous case (coal-fired, older <500 MW units) the average forced derate loss was only about 10% of the forced outage loss. Note also that the new units again have a considerably greater number of events over the same time period than do the older units. This is somewhat accounted for in the greater number of newer boilers in this classification compared to older boilers. Average MWh Lost/Planned Outage & Derate (Coal Fired, Large, Supercritical)


18

90000

80000


70000

60000

50000

40000

30000 159

20000

10000

39

1

646

344

0

Cyclone

Wall

Tangential

Figure 3-11 Average MW-hrs lost per forced derate in coal-fired, supercritical large units

Figure 3-12 highlights the average MW-hrs lost from planned outages or derates. Here the newer cyclone-fired boilers have a considerably greater average MW-hr loss than any other group of boilers in this set. This suggests that the planned outages and derates were of a significant duration. There were not that many planned events, but they were of a long duration. However, just to note there are only seven boilers in this specific category.

3-14

Pre-1971 Post-1971 ## No. Planned

Average MWh Lost/Planned Outage & Derate (Coal Fired, Large, Supercritical)

1.0E+05 18


8.0E+04

6.0E+04

4.0E+04

159

2.0E+04 39

1

646

344

0.0E+00

Cyclone

Wall

Tangential

Figure 3-12 Average MW-hrs lost per planned outage and derate in coal-fired, supercritical large units

Figures 3-13 and 3-14 show the distribution of lost MW-hrs for the older units (Figure 3-13) and for the newer units (Figure 3-14). The number on each bar represents the number of units in the specific category. The newer wall-fired units have the largest lost MW-hrs due to the high forced derate losses. Using the cost estimates for planned and forced outages or derates as before, the estimated annual cost of deposition in the large older units is $37.3 million and for the large newer units is a staggering $750.6 million. The breakdown is shown in Table 3-5. The final figure (Figure 3-15) shows the total average MW-hrs lost per boiler. Again the cyclone-fired boilers have a greater MW-hr loss for the older units and a much higher MW-hr loss than the tangential-fired boilers, but less than the wall-fired boilers for the newer units.

3-15

Distribution of Lost MW-hrs (Coal Fired, Large, Supercritical, Old) Planned Forced Derate Forced Outage

1.0E+08

8.0E+07

MW-hrs

6.0E+07

4.0E+07

2.0E+07 10

19

33

0.0E+00

Cyclone

Wall

Tangential

Figure 3-13 Distribution of lost MW-hrs in supercritical coal-fired, older large units Distribution of Lost MW-hrs (Coal Fired, Large, Supercritical, New) 106 Planned Forced Derate

1.0E+08

Forced Outage

8.0E+07

MW-hrs

6.0E+07

4.0E+07

82 2.0E+07

7

0.0E+00 Cyclone

Wall

Tangential

Figure 3-14 Distribution of lost MW-hrs in supercritical coal-fired, newer large units

3-16

Table 3-6 Annual estimated cost of slagging and fouling for coal-fired, large supercritical boilers Firing Method

Pre-Dec 1970

Post-Dec 1970

Cyclone

$9.2 MM

$27.1 MM

Wall

$11.2 MM

$647.0 MM

Tangential

$16.9 MM

$76.5 MM

Total

$37.3 MM

$750.6 MM


Total MW-hrs Lost (Coal Fired, Large, Supercritical)

106

1.4E+08

1.2E+08

MW-hrs

1.0E+08

8.0E+07

6.0E+07

4.0E+07 82 2.0E+07

10

7

19

33

0.0E+00

Cyclone

Wall

Tangential

Figure 3-15 Average MW-hrs lost per boiler for coal-fired, supercritical large units

Coal Quality Related Occurrences A similar analysis was done on the coal-fired, supercritical boilers over 500 MW using the coal quality cause codes. These results are highlighted in Figures 3-16 to 3-19. Figure 3-16 shows the number of occurrences in this group for the three classifications of boilers. The data clearly show that the new pulverized coal boilers have considerably more fuel quality related outages and derates than the older units. One potential reason is the smaller furnaces that have been built do 3-17

not allow for such a wide deviation from the original coal specification for the unit. That is, the older units tend to be more forgiving as do the cyclone units compared to the pulverized coal units. Number of Coal Quality Occurrences (Coal Fired, Large, Supercritical)

Pre - Dec 1970 Post - Dec 1970

6000

5000

Number

4000

3000

2000

1000

0

Cyclone

Wall

Tangential

Figure 3-16 Number of coal quality occurrences in coal-fired, large supercritical units

Figures 3-17 and 3-18 show the distribution of lost MW-hrs for the older and newer units, respectively. Again, the newer units are showing nearly eight times more lost MW-hrs than are the older units. Comparing these results with the results from the deposition-based lost MW-hrs shows that the coal quality related lost MW-hrs are about one order of magnitude less than those from the deposition related lost MW-hrs. However, these data are greatly affected by the large wall-fired loss in the newer units.

3-18

Distribution of Coal Quality Lost MW-hrs (Coal Fired, Large, Supercritical, Old)

Forced Outages Forced Derates 1.2E+07


1.0E+07

MW-hrs

8.0E+06

6.0E+06

4.0E+06

19 33

2.0E+06

10

0.0E+00

Cyclone

Wall

Tangential

Figure 3-17 Distribution of coal quality lost MW-hrs in supercritical coal-fired, large older units Distribution of Coal Quality Lost MW-hrs (Coal Fired, Large, Supercritical, New)

106

Forced Outages Forced Derates Planned ## No. of Boilers

1.2E+07

1.0E+07

MW-hrs

8.0E+06

82

6.0E+06

4.0E+06

7

2.0E+06

0.0E+00 Cyclone

Wall

Tangential

Figure 3-18 Distribution of coal quality lost MW-hrs in supercritical coal-fired, large newer units

3-19

When the total MW-hrs lost are normalized by the number of boilers in the study set, the cyclone-fired units show a significantly higher average than do the pulverized coal units. This is shown in Figure 3-19. Average Coal Quality MW-hrs Lost per Boiler (coal Fired, Large, Supercritical)

Pre - Dec 1970 Post - Dec 1970

7 7.0E+05

6.0E+05

MW-hrs/Unit

5.0E+05

4.0E+05

3.0E+05 10 2.0E+05

106 19 33

1.0E+05

82

0.0E+00

Cyclone

Wall

Tangential

Figure 3-19 Average coal quality MW-hrs lost per boiler for supercritical, coal-fired, large newer units

Using the data from the previous figures, the estimated cost of coal quality related outages and derates can be calculated. This is shown in Table 3-7 below. These results are significantly lower than the estimated cost from deposition, primarily due to the extraordinarily high wall-fired costs for the newer units. The older units have a coal quality cost about one-half that of the depositionrelated costs. Table 3-7 Annual estimated cost of poor coal quality for coal-fired, large supercritical boilers Firing Method

Pre-Dec 1970

Post-Dec 1970

Cyclone

$7.1 MM

$15.0 MM

Wall

$5.0 MM

$50.5 MM

Tangential

$6.6 MM

$14.3 MM

Total

$18.7 MM

$99.8 MM

3-20

Coal and Lignite Comparisons This section will compare some of the deposition and coal quality losses between coal and lignite as the primary fuel. Because of the lack of lignite-designed boilers relative to coal-designed boilers, individual groupings of parameters did not result in a sufficient number of boilers to perform the availability assessment. Therefore, there are only two sets of comparisons that could be done, the first is for larger boilers (greater than 500 MW) and the second is for all boilers greater than 100 MW. Boilers Greater than 500 MW Deposition Related Occurrences Figures 3-20 and 3-21 show the distribution of lost MW-hrs due to slagging and fouling between coal-designed and lignite-designed boilers over the ten-year study. Figure 3-20 shows the number of events of each type of outage or derate, while Figure 3-21 shows the total lost MWhrs for each fuel with the corresponding number of boilers used in the assessment. Because of the large discrepancy in the number of boilers, there are considerably more events and a much greater total MW-hr loss for coal-designed boilers. When the number of boilers is taken into account, the average MW-hrs lost per boiler is more comparable, as shown in Figure 3-22. Nonetheless, the coal-designed boilers still have about three times the average MW-hrs lost per boiler for all outages and derates compared to the lignite-designed boilers. Applying the same cost information to these data, results for the coal-designed boilers having an average annual lost generation cost due to slagging and fouling of $787.8 million while the lignite-designed boilers have an average annual lost generation cost of $9.9 million. Average MWh Lost - +500 MW (All Ages, Firing Modes, Steam Pressure) Forced Outages Forced Derates

6.E+04

Planned ## No. of Occurrences

476

5.E+04

10

MW-hr

4.E+04

3.E+04

8474

2.E+04

1207

1.E+04

1396

0.E+00

Coal

Lignite

Figure 3-20

3-21

93

Average MW-hrs lost for larger (>500 MW) boilers Distribution of Lost MW-hrs - Large Boilers (All Ages, Firing Modes, Steam Pressure) 257

Forced Outages Forced Derates Planned ## No. of Boilers

1.6E+08

MW-hrs

1.2E+08

8.0E+07

4.0E+07 13

0.0E+00

Coal

Lignite

Figure 3-21 Distribution of lost MW-hrs lost for larger (>500 MW) boilers Average MW-hrs Lost per Boiler (All Ages, Firing Modes, Steam Pressure)

## No. Boilers 257 7.E+05

6.E+05

MW-hr/Unit

5.E+05

4.E+05

3.E+05

13

2.E+05

1.E+05

0.E+00

Coal

Lignite

Figure 3-22 Average MW-hrs lost per boiler for larger (>500 MW) boilers

3-22

Coal Quality Related Occurrences A similar analysis was completed using coal quality parameters; the distribution of lost MW-hrs is shown in Figure 3-23. These results show that the coal quality related outages and derates are about 5-6 times less than the deposition derates and outages. When the lost MW-hrs are normalized with the number of boilers, as shown in Figure 3-24, the lignite units have about four times the average lost MW-hrs compared to the coal units. From these data, the annual estimated cost of coal quality related outages and derates can be determined. Using the same $50 per MW-hr for forced derates and outages and $30/MW-hr for planned outages and derates, the coal-based boilers have an annual expense of $98.7 million while the lignite-based boilers cost about $14.7 million dollars. The coal quality based costs for coal-fired boilers is about 12% that of deposition-based costs. The lignite boilers have the opposite trend, the coal quality costs are nearly 50% higher than the deposition-based costs for the same set of boilers. Distribution of Coal Quality Lost MW-hrs - Large Boilers (All Ages, Firing Modes, Steam Pressure) Forced Outages Forced Derates 257


2.5E+07

2.0E+07

MW-hrs

1.5E+07

1.0E+07 13 5.0E+06

0.0E+00

Coal

Lignite

Figure 3-23 Distribution of coal quality related loss of MW-hrs for larger (>500 MW) boilers

3-23

Average Coal Quality MW-hrs Lost per Boiler (All Ages, firing Modes, Steam Pressure)

## No. of Boilers

13

2.5E+05

MW-hrs/Unit

2.0E+05

1.5E+05 257

1.0E+05

5.0E+04

0.0E+00

Coal

Lignite

Figure 3-24 Average coal quality related MW-hrs lost per boiler for larger (500 MW) boilers

Boilers Greater than 100 MW Deposition Related Occurrences This assessment was done to include all boilers larger than 100 MW. This was done to try and include more boilers in the evaluation. Figures 3-25 and 3-26 show the distribution of lost MWhrs between coal-designed and lignite-designed boilers over the ten-year study. Figure 3-25 shows the number of events of each type of outage or derate, while Figure 3-26 shows the total lost MW-hrs for each fuel with the corresponding number of boilers used in the assessment. Again the large discrepancy in the number of boilers tends to over-emphasize the coal-designed boilers. However, by including the small boilers, the average MW-hr loss per boiler is nearly the same between the coal-designed and lignite-designed boilers as shown in Figure 3-27. For this condition, an assessment was done to determine the fraction of total forced outage occurrences and the corresponding lost MW-hrs that could be attributed to deposition. Only the forced outages could be evaluated since only one cause code can be assigned to a forced outage. The number of total forced outage occurrences for all causes was 85,902 and the corresponding total generation loss was 1,496,803,056 MW-hrs over the 10-year period! The deposition-only number of forced outages was 1342, or 1.6% of the total and the lost generation was 36,562,945 MW-hrs or only 2.4% of the total.

3-24

Applying the cost information to these data results in the coal-designed boilers have an average annual lost generation cost due to slagging and fouling of $920.9 million while the lignitedesigned boilers have an average annual lost generation cost of $16.4 million. Forced Outages Forced Derates

Average MWh Lost - All Boilers

Planned ## No. of Occurrences

13 3.5E+04

3.0E+04

1329

MW-hrs

2.5E+04

2.0E+04

1.5E+04

20843

1.0E+04

3925

5.0E+03

1706 102

0.0E+00

Coal

Lignite

Figure 3-25 Average MW-hrs lost for all (>100 MW) boilers Distribution of Lost MW-hrs - All Boilers Forced Outages Forced Derates

781


2.0E+08

1.6E+08

MW-hrs

1.2E+08

8.0E+07

4.0E+07

18

0.0E+00

Coal

Lignite

Figure 3-26

3-25

Distribution of lost MW-hrs lost for all (>100 MW) boilers Average MW-hrs Lost per Boiler

781

## No. Boilers

2.5E+05 18

MW-hrs/Unit

2.0E+05

1.5E+05

1.0E+05

5.0E+04

0.0E+00

Coal

Lignite

Figure 3-27 Average MW-hrs lost per boiler for all (>100 MW) boilers

Coal Quality Related Occurrences Figures 3-28 and 3-29 show the coal quality related outages and derates for all boilers greater than 100 MW. These trends are similar to the deposition related outages and derates; however, the absolute level of coal quality MW-hrs lost is about one-third that of the deposition MW-hrs lost. The difference comes when the values are normalized by the number of units; now the lignite-fired units have about three times the average MW-hrs lost compared to the coal-fired units. With these data, the annual cost of coal quality related outages and derates is approximately $203.2 million for the coal-fired boilers and $14.7 million for the lignite-fired units. The lignite-fired units have about the same annual lost generation cost from coal quality causes as do the lignite units having deposition related outages. However, the coal quality outages in the coal-fired boilers are about 20% of the deposition outages for the same units. As mentioned previously, an assessment was done to determine the fraction of total forced outage occurrences and the corresponding lost MW-hrs that could be attributed to coal quality issues. Since the individual number of forced outages was not obtained for the coal quality causes, only the total lost generation could be compared. And, as mentioned previously, only the forced outages could be evaluated. The total forced outage generation loss over the 10-year evaluation period was 1,496,803,056 MW-hrs! The coal quality-only forced outage lost generation was 1,597,032 MW-hrs or only 0.1% of the total!

3-26

Distribution of Coal Quality Lost MW-hrs - All Boilers Forced Outages Forced Derates

781


5.0E+07

4.0E+07

MW-hrs

3.0E+07

2.0E+07

18 1.0E+07

0.0E+00

Coal

Lignite

Figure 3-28 Distribution of coal quality lost MW-hrs for >100 MW boilers

Average Coal Quality MW-hrs Lost per Boiler

## No. of Boilers 2.0E+05

18

MW-hrs/Unit

1.6E+05

1.2E+05 781 8.0E+04

4.0E+04

0.0E+00

Coal

Lignite

Figure 3-29 Average MW-hrs lost from coal quality for all >100 MW boilers

3-27

All Boilers Deposition Related Occurrences The final area of evaluation was to determine the effect of ignoring the small, <100 MW boilers in this assessment. Therefore, all boilers designed for either lignite or coal and commissioned between 1900 and 2005 with all firing modes and subcritical or supercritical steam pressures were evaluated using both the deposition and coal quality cause codes. The results for the deposition-based cause codes are shown in Figures 3-30 to 3-32. Figure 3-30 shows the number of events reported for the forced outages and derates as well as the planned outages and derates. The small boilers account for only 1.5% of the total events recorded. In terms of total MW-hrs lost, the small boilers only account for 0.6% of the total. Therefore, ignoring the small boilers has an insignificant effect on the previous results. In addition, there are only 140 small (<100 MW) boilers in the evaluation group compared to 799 boilers greater than 100 MW. One important bit of information from this evaluation is the ability to calculate the total estimated annual cost of slagging and fouling for all boilers using coal or lignite fuel and employing either wall-, tangential- or cyclone-firing. Using the estimates previously described, the conservative estimated annual cost to the power industry in lost generation due to slagging and fouling is just under $1 billion at $943 million! Again this is based on several assumptions, some of which would increase the number, some of which would decrease the number. Average MWh Lost - All Conditions

3.0E+04


1342

Planned ## No. of Occurrences 2.5E+04

MW-hr

2.0E+04

1.5E+04 22 1.0E+04

22549 191 4027

5.0E+03

218

0.0E+00

+100 MW

<100 MW

Figure 3-30 Average MW-hrs lost for all boilers due to deposition cause codes

3-28

Distribution of Lost MW-hrs - All Conditions Forced Outages Forced Derates

799


1.6E+08

MW-hrs

1.2E+08

8.0E+07

4.0E+07

140

0.0E+00

+100 MW

<100 MW

Figure 3-31 Distribution of deposition related lost MW-hrs lost for all boilers Average MW-hrs Lost per Boiler - All Conditions

799

## No. Boilers

2.5E+05

MW-hrs/Unit

2.0E+05

1.5E+05

1.0E+05

140 5.0E+04

0.0E+00

+100 MW

<100 MW

Figure 3-32 Average MW-hrs lost per boiler for all boilers from deposition related cause codes

3-29

Coal Quality Related Occurrences To verify that ignoring the less than 100 MW boilers would not have an effect on the results of the coal quality related outages and derates, the same analysis was done as previously described using the deposition cause codes. Figure 3-33 clearly shows that the total MW-hrs of the +100 MW is clearly dominant; in fact the lost MW-hrs for the <100 MW boilers is only 1.3% of the >100 MW boilers. Even normalizing by the number of boilers only increases the percentage to 7.7%. The important outcome from the cost perspective is that the coal quality related costs for all boilers is $267.3 million or about 30% of the costs from deposition related occurrences. Therefore, the combination of slagging and fouling outages and derates and coal quality outages and derates costs the utility industry in lost generation in excess of $1.2 billion annually! Distribution of Coal Quality Lost MW-hrs - All coals (All Ages, Firing Modes, Steam Pressure) Forced Outages Forced Derates Planned ## No. of Boilers

799 6.0E+07

5.0E+07

MW-hrs

4.0E+07

3.0E+07

2.0E+07

140

1.0E+07

0.0E+00

+100 MW

<100 MW

Figure 3-33 Distribution of coal quality lost MW-hrs for all boilers

3-30

Average Coal Quality MW-hrs Lost per Boiler (All Ages, Firing Modes, Steam Pressure)

## No. of Boilers 8.0E+04

799

MW-hrs/Unit

6.0E+04

4.0E+04

2.0E+04

140

0.0E+00

+100 MW

<100 MW

Figure 3-34 Average coal quality MW-hrs lost for all boilers

Annual Evaluation Since all previous evaluations had been grouped over the most recent ten-year period, an assessment was made using one set of conditions each year for the ten years. The intent was to determine whether improvements have been made to lower incidences of deposition- and coal quality-based outages and derates. The condition chosen included all boilers greater than 100 MW (i.e., Run No. 59 in Table 3-3). Figures 3-35 and 3-36 show the number of occurrences, by year, for forced outages, forced derates and planned outages and derates. Figure 3-35 is for deposition-based occurrences and Figure 3-36 is based on the coal quality parameters. Note that only the total number of occurrences was available for the coal quality-based evaluation. Unfortunately, there does not appear to be a consistent trend for the deposition-based occurrences! As expected, the number of forced derates was significantly larger than the number of forced outages and planned outages and derates. However, the total number of occurrences is approximately the same for the two types of evaluations. The coal quality occurrences appear to show an increasing trend over the ten year period. Additional evaluations need to be done to determine which of the coal quality parameters is resulting in the greatest number of derates/outages. The trend clearly confirms the survey responses of the need for research. Figures 3-37 and 3-38 are the lost MW-hrs, by year, for the deposition and coal quality causes, respectively. Clearly, the lost MW-hrs due to deposition is significantly greater than the lost MW-hrs due to coal quality issues. It is interesting that there appear to be more planned outages and derates based on coal quality than deposition. The total of these lost MW-hrs were plotted in Figure 3-26 (deposition) and 3-28 (coal quality). 3-31

Annual Number of Outages and Derates Due to Deposition (All Boilers Greater than 100 MW)

5000


4500

Planned Outages & Derates

4000 3500

Number

3000 2500 2000 1500 1000 500 0 1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2003

2004

Year

Figure 3-35 Annual total number of deposition related occurrences

Annual Number of Forced and Planned Outages and Derates (All Boilers Greater Than 100 MW) 5000 4500 4000 3500

Number

3000 2500 2000

1500 1000 500 0 1995

1996

1997

1998

1999

2000

2001

Year

Figure 3-36 Annual total number of coal quality related occurrences

3-32

2002

Annual MW-hrs Lost Due to Deposition (All Boilers Greater than 100 MW) 4.5E+07 Planned Outages & Derates Forced Derates Forced Outages

4.0E+07

3.5E+07

MW-hrs

3.0E+07

2.5E+07

2.0E+07

1.5E+07

1.0E+07

5.0E+06

0.0E+00 1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

Year

Figure 3-37 Annual total MW-hrs of deposition related occurrences Annual MW-hrs Lost Due to Coal Quality

4.5E+07

Forced Outages Forced Derates Planned Outages & Derates

4.0E+07

3.5E+07

MW-hrs

3.0E+07

2.5E+07

2.0E+07

1.5E+07

1.0E+07

5.0E+06

0.0E+00 1995

1996

1997

1998

1999

2000 Year

Figure 3-38 Annual total MW-hrs of coal quality related occurrences

3-33

2001

2002

2003

2004

References 3-1.

Devir, G.P. , Pohl, J. H., Creelman, R. A., “Development of Quantitative Techniques to Characterize Mineral Matter Transformations in a Pulverized Coal Fired Boiler,” Proceedings of the JPGC’01, 2001 International Joint Power Generation Conference, New Orleans, LA, June 4-7, 2001.

3-2.

Zygarlicke, C., “Guidelines for Solving Ash Deposition Issues in Utility Boilers: Volumes I – III,” EPRI, Palo Alto, CA and U.S. Department of Energy, Pittsburgh, PA, 2003, 1004891.

3-3.

North American Electric Reliability Council, “Generating Availability Data System: Data Reporting Instructions,” NERC, Princeton, NJ, October 2000.

3-4.

Personal Communication with Mr. G. Michael Curley, Manager – GADS Services, NERC, November 22, 2005.

3-34

4 CONCLUSIONS AND RECOMMENDATIONS The combination of gathering coal quality concerns from utility personnel who solve these and other ash deposition problems on an ongoing basis with an analysis if historical reliability data for a significant share of the US coal-fired power generation market has resulted in detailed information on the current status of the economic impact of fuel quality and deposition as well as provided guidance for future studies to reduce this economic impact. There are several conclusions and recommendations that can be drawn from this preliminary assessment of coal quality and ash deposition impacts in the power industry. These are highlighted below. •

•

•

• •

•

•

•

Slagging, fouling and fuel blending continue to be the leading coal quality concerns of utility personnel. Issues with ash chemistry resulting from fuel blending and new coals being utilized continue to be the main area for needed utility support. Nearly all respondents listed slagging as one of the top five problem areas in their respective power plants. Many fuel quality impacts are specific to individual boilers based on the equipment available, the regulatory pressures, and market conditions. However, many issues have a similar root cause which needs to be further investigated. There were many research needs identified by the utility respondents. Most mentioned the need for applied rather than fundamental research – how can the results help me now and at my plant. General topics suggested for further research include fuel preparation, handling and on-line analysis; fuel and ash characterization; boiler optimization with new fuels; and development of fundamental and cost/performance models of ash deposition phenomena. There was a strong interest in supporting an EPRI Coal Quality Interest Group. The main concern was that the information be applied and factual rather than “sales-oriented.” An availability assessment of coal- and lignite-designed boilers showed that slagging and fouling continue to be areas of major economic impact. Older boilers did not appear to be more problematic than newer boilers and pulverized coal units (wall and tangential) tended to have less problems per boiler than cyclone units; however because of the larger number of pc-units, the economic impact was much greater. In general, the coal quality impacts resulted in approximately the same number of outages and derates as did the deposition impacts; however the economic result was less since the duration of the incidences was less. An estimated annual economic impact of over $1.2 billion was calculated for all coal- and lignite-fired boilers in the US based on coal quality and deposition causes. This number is obviously based on many assumptions, some of which will increase the number, others which will decrease the number. While this annual economic loss is huge, coal quality and deposition outages and derates account for only about 1.6% of the total number of outages and derate occurrences and 2.5% of the total lost MW-hr generation. This is based on all boilers in the NERC GADS database firing either coal or lignite and employing all firing modes used in this study.

4-1

•

•

•

An annual evaluation of the coal quality and deposition-based outages and derates did not show a clear trend. In fact, the coal quality-based outages and derates generally increased over the ten-year period. This evaluation was completed for all boilers greater than 100 MW. The NERC GADS database should be re-evaluated in a couple of years once the current fuel quality information is required to be provided by the participants. This will allow a much more direct cause and effect relationship to be developed between fuel quality and economic impact. Short-term (2-3 year) and long-term (5-7 year) research and development plans should be prepared and presented to utility respondents as part of the EPRI Coal Quality Interest Group agenda.

4-2

A COAL QUALITY QUESTIONNAIRE The following shows the questionnaire developed as part of this project and sent to select utility personnel. Coal Quality Effects on Power Generation Survey Questionnaire Name: _______________________________

Date: ___________________

Station(s): _____________________________________________________________________ 1. Of which EPRI Target Group(s) is your company a member? 2. With regard to coal quality issues at your plant(s), which of the following present challenges: _____ Fuel Handling

_____ Fuel Blending

_____ Pulverizers

_____ Burners/Flames

_____ Slagging

_____ Corrosion

_____ Fouling

_____ Unburned Carbon (LOI) _____ Air Heater

_____ ESP/Baghouse

_____ Particulate Emissions

_____ Gas Emissions

_____ Plume Opacity

_____ Ash Disposal

_____ Water Quality

_____ Other (Describe) ___________________________________ In the preceding list, please rank the top 5 (five), with 1(one) being the most problematic. May we call and follow-up with specific examples? Yes______ Phone: _________________ 3. What areas of coal quality do you feel need research and development as it applies to power generation?

4. EPRI is contemplating a Coal Quality Interest Group (CQIG) with periodic web casts of inhouse, funded and vendor coal quality activities. Initially, there would be no charge for participation in CQIG; would you be interested in membership? Which specific topics would be of most interest to you?

Figure A-1 Questionnaire sent to selected utility personnel

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