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Attachment 10 Initial Design Boiler Heat Input Rating VS. As Built Boiler Heat Input Rating

## "INITIALDESIGN" BOILERHEAT INPUT RATING 

# VS "AS BUILT" BOILERHEAT INPUT RATING

George W. Bouton January, 

## 2001Experience & Background George W. Bouton is an expert witness on [he subject ofutility boilerdesign based on his
more than 50 years expe:ience in this area. He was graduated from Cornell University in June 1942 with abachelor ofmechanical engineering (BME) degree andjoined Babcock & Wilcox that same month in their student engineertraining program. He left B&W in February 1943 to spend 3-1/2 years in the US Navy. He returned to B&W in September 1946 at theirNew York StaffEngineering Depanment. He was in the perfonnance methods section, which had the responsibility ofdeveloping performance methods used in the design ofB&W Boilers. This involved running circulation tests and other performancetests on operating units and applying those results to the development of B&W's standards. [n 1958 B&W's engineering departments were combined in Barberton, Ohio and at thattime George Bouton was named Manager, Utility Boiler Design Engineering Technology. TheTechnology Section was responsible for developing all the functional standards (heat transferand fluid dynamics) used in the design ofB&W boilers. He remained in this position until 1970 when he was made the managerofUtility BoilerDesignEngineering.
GeorgeBouton retired from B&W in May 1983 after41 years ofservice, mostly in some phase ofutilityboiler design. Since 1983 he has been doing power plant consulting for boiler manufacturers and utilities. The boilercompanies includeBabcock & Wilcox, Combustion Engineering, Riley Stokerand Zum Industries. Utility companies include Associated Electric Cooperative, Baltimore Gas & Electric, Basin Electric, Kansas City

2

### Power

### & Light, Minnkota PowerCooperative, MinnesotaPower, Nonhem States Power and Wisconsin Power & 

### Light.

BoilerDesign Boilerdesign is based on: I. The required heat input to theboiler. 

### 1.. The characteristics ofthe fuel to be fired
. .J.... 

### Specifications prepared by the purchaseror his consultant.

The required heat inputto the boiler is based on the capacity specified bytheutility in terms ofmain steam and reheat steam flow and the associated pressures and temperatures related to these flows as well as the feed watertemperature. Using these conditions and the boiler efliciency, either specified bythepurchaserordeemed optimum by the boiler manufacturer, the heat input to the boilercan be determined.

The characteristics ofthe fuel to be fired determine the design parameters used bythe boiler manufacturer. Forexample, for agiven boiler heat input, the size ofthe furnace will be greaterwhen acoal with high slagging characteristics is specified.

The specifications prepared bythe ownerorhis consultant often determinethe design parameters used bythe boiler manufacturer. For example, for agivenboiler heat input and given fuel characteristics, the sizeofthe furnace may begreaterdueto the specifications than believed necessary by the boiler manufacturer.

)

### The boilerspecifications prepared forMilton R. Young Units I & 2were very similar, exceptforthe capacity requirements, and were very comprehensive. They included: 1. 

### The normal maximum full load 

### steam conditions. 2. The peak maximum overload steamconditions. 3. The performance fuel and range offuels to be designed for. 4. The furnace should be sized (Q 

### limit the maximum gas temperature leaving the furnace and entering the superheaterto 1950

### ofatthe nonnal full load capacity. The method for measuring thisgas temperature is defined. 5. 

### Design (safety) margins to be applied to auxiliary equipmentfurnished by the boiler manufacturer, such as: (a) The cyclone furnaces, includingthecoal crushers and related fuel-handling equipmentmustbe capableofsupplying 125% ofthe nonnal full load 

### capacity for Unit 1and 110% ofthe 

### nonnal full load 

### capacity forUnit2. In addition, with one cyclone furnace outofservice, enoughcapacity should be availableto obtain at least 100% ofthe full load normal capacity forthe range offuels specified. (b) 

### The forced draft, induced draft and gas recirculating fans shouldbesized for 115% to 120% ofthe required maximum load capacity and }32% to 144% ofthe required maximum load staticpressure.
While the heat input to theboileris fundamental to the design, itgenerally is not guaranteed. The maximum capacityoftheboilerin terms ofsteam flow, steam temperature and feedwaterflow is guaranteed. To insure that theguaranteed capacity of

### f theboilerwill be met, the boiler manufacturerincorporates design margins in the components ofthe boiler and the related auxiliary equipment supplied.
Design margins are incorporated to permit theboilerto operate satisfactorilyunder less than optimum conditions. For instance, fuel input to thefurnace may not bewell balanced due to equipment problems oroperatorerror. The boiler manufacturertakes into account typical unbalances with design margins on such parameters as furnace exit gas temperature, flue gas flow oversections ofthe superheater, now through the superheatertubes, etc.

Theboiler manufacturer also applies capacity margins, similarto those covered inthe hailer specifications, to auxiliary equipment such as forced and induced draft fans, recirculating fans, boilercirculating pumps, fuel preparation and burning equipment, etc. The largerofthe margins specified by the engineer, ornormally provided bytheboiler manufacturer, would be used. The margins normally will range from 10% to as much as 40%, depending upon the type ofequipment involved.
Optimum Maximum Load. The actual maximum load (heat input) that the boiler is capable ofachieving is expected to be 100.10 ormore higherthan the maximum design load (heat input) due to one or more ofthe following: 

### I. Margins incorporated in the boiler manufacturer's design.

52. Specifications prepared by the owner or his consultant that stipulate design margins greaterthan those nonnally used by theboiler manufacturer. 3. Use ofa fuel with more favorable characteristics than that specified by the owner or his consultant. 4. More careful operation by the owner than that assumed as typical by the boiler manufacturer.

In many instances the maximum load (maximum heat input) is determined byrunning maximum load tests on the boiler/turbine system. This allows the limiting components in either the boilerorturbine to beidentified. Such tests may be run periodically to determine the maximum load under different operating conditions. When burning severe slagging and fouling fuels, such as North Dakota lignite, periodic cleaning outages may be required to permitoperation at maximum load for extended periods oftime. The maximum load attainable immediately following acleaning outage will be greaterthan thatattainable afteroperating for extended periods oftime at maximum loads.



### "AS BUrLT" MAXIMUM HEAT INPUT ForUnit 1. the maximum design capacity (heat input) is based on operating at the 5% overpressurecondition. The designboiler heat input atthis maximum load is 25

### to MKBlHr.. Considering the design margins discussed above, theboiler is expected to be capable ofoperating at capacities (heat inputs) up to 10% or more higher than the design maximum boilerheat input.

6For Unit 2, the maximumdesign capacity (heat input) is based on operating at the 5% overpressure condition. The maximum design boiler heat input at this condition is 4700 MKBlHr
.. Considering the design margins discussed above, the boiler

### is expected to be capable ofoperating at heat inputs up to 10% or more higherthan the design boiler heat input.



### Due to the reasons 

### elaborated previously, the actual maximum heat input capability 

### for a particular boiler design is best determined, not by the boiler manufacture's design "targeu", butratherby the actual operation ofthe boiler. 

# P /l / 

# /**/:1~** 

# .../;' /..>W,4/' George W. Bouton 

### t'J'1l January 5, 2001

7Attachment 11 Expert Opinion Report, Maximum Boiler

Heat Input Capacity, Units 1 and 2, Milton R. Young Station, Minnkota Power Cooperative, Inc. Center, ND 58530

# Expert Opinion Report
Maximum Boiler Heat Input Capacity
Units 1 and 2 Milton R. Young Station
Minnkota Power Cooperative Inc. Center, N.D. 58530

Robert 

# L. Pearson, Ph. 

# D., PE CH2M 

# HILL 100 Inverness Terrace East Englewood, CO 80224

# Introduction This is an expert opinion report regarding the as designed and as built maximum heat input capacity ofMillon R Young Station. The report is an expert opinion ofDr. Robert L. Pearson, Vice President ofUtility Practice, CH2MHILL in Denver. Dr. Pearson is a registered professional engineer with 28 years ofexperience in the electric utility industry. For 19 years he was both a Senior Environmental Engineer and Administrator of Environmental Affairs for the Public Service Company ofColorado (now Xcel Energy). He bas also been a project manager for Radian International specializing in the electric utility industry, and most recently he became Vice President, Utility Practice for CH2MHILL. Dr. Pearson has been qualified as an expert witness in several administrative andjudicial proceedings including twojudicial proceedings where he presented his opinion about the operation ofcoal fired electric utility power plants. He bas also testified before Congress three times on the impact ofnew federal envirorunental regulations on the electric utility industry. See Attachme'nt 2 for Dr. Pearson's complete resume. 

# Description ofthe Plant The Milton R Young Station is a two-unit lignite fired power station located at Center. North Dakota. Unit 1. brought on line in 1970 is listed in its air permit as having 235 MW net generation capacity with a heat input raling of2500 millioo BTU per hour (MMBTUfhr). Unit 2 brought on line in 1977 is listed at 440 MW net generation capacity with a heat input rating of4696 MMBTUlhr. Both sets ofnumbers are based on the original anticipated fuel firing rate ofthe units. The Milton R Young Station uses North Dakota lignite coal as fuel. This coal is relatively low in heating value (nominally 6500 BTU per pound) compared to bituminous coal used 

### in most U.S. power plants which has a heating value ofover**1ססoo** BTU per pound. Also, the chemical composition ofthe ash 

### in the lignite coal causes the ash to melt during combustion of the coal creating a molten slag. which can cause severe fouling ofthe boiler tubes. Both ofthese characteristics ofthe coal require the boiler to be designed to be able to U(ilize this fuel. One boiler type that can burn lignite is acyclone boiler, with the initial combustion ofthe coal taking place in cyclone burners, located to the side ofthe main combustion zone. The molten slag from the cyclone burner runs down to the bottom ofthe boiler where it is quenched and removed for disposal. The coal combustion products enter the main combustion chamber ofthe cyclone boiler where the heat is extraCled by several sets oftubes making sleam which is used to turn a turbine generator producing power. The flue gas exits Lhe rear ofthe boiler and passes into the atmosphere after being processed through the plant's air pollution control equipment.

# Original Design Considerations for Boilers Coal fired electricity plants are designed as asystem with

# all components specified to work IOgeLher. For instance, the boiler is designed to provide the amount and quality ofstearn the turbine generator requires. The coal handling system is designed to provide the amount and quality ofcoal the boiler requires, etc. Each equipment vendor makes a guarantee thathis equipment will operate according to specifications. The vendors need to demonstrate compliance with their guarantees or face paying penalties to lhe plant owner. Therefore, the vendors usually design their equipmentwith a margin to allow for changed circumstances in the plant and still perform as specified. These design margins vary with the vendor and the type ofequipment but usually range from 5% to 10%. At Ihe lime ofconstruction ofUnit 1 in the late '60's. few other power generation boilers had been buill to burn mis fuel. Therefore, the boiler vendor, Babcock and Wilcox had to base the design ofthe Unit 1boiler on the limited infonnation available at the time. They also had 10 design the boiler to meet the purchase specifications set by Minnkota and their architect engineer. In the case ofthe Milton R Young Station, the boilerdesign chosen to meetthese constraints contained many conservative assumptions including the anticipated heat-input capacity ofthe boiler. 

# Comparison ofOriginal Anticipated Heat InputtoActual as Built Operation
Unit 1 Actual operalion ofthe plant has shown these original anticipated heat input assumptions LO be very conservative. Unit 1 had an initial anticipated heat input rating of2500 MMBTU/hr. During a perfonnance tcst on December 2, 1983 thc unit demonstrated an actual maximum heat input rating of2863 MMBTUlhr., a 14% inerease over the antieipated fuel firing rate. Figure 1below is a plot ofthe maximum heat inputs for Unit 1 for each month ofme first twenty years ofoperation from December 1970 to January \990. The horizontal line at 2500 MMBTU/hr represents the original anticipated maximum heat input figure. Note Lhat the unit routinely exceeded this anticipated maximum heat input figure during this period ofnonnal operation and on several occasions even exceeded 3()(x) MMBTU/hr.

### Figure 1. 

### Monthly maximum heat inputs for Unit I, December 1970 to January 1990.
Minnkota PowerCooperative Milton R. Young Station Unlt" Calculated URGE Bolter Heat Input Pr1l1990 Maximumof 3.128 occurred in Jan-79 3.500

### r---------.!===~===~~==!.---------, 3,000 "'

2
.... 

# l 2.000 

## 3- 

## • 

# i 1,500 ••
1,000 ••



# ... ..

o 

# l'/'·/:/·/'/'//·,l/l/',l/'/·.l'./·/·,,"·//./',»///
....

///////'.,.>'///1' In a letter dated November 20. 1995 from John T. Graves ofMinnkota Power to Mr. Dana 

### Mount ofthe Division ofEnvironmental Engineering, North Dakota Depanmenl ofHealth, a comparison was made between the initial anticipated heat input figures used in the plant's 

### pennit to operate and actual figures measured in 

### recent operating tests. The letter references a performance test on May 30, 1995 lIlatdemonstrated lbe actual maximum beal 

### inputrating was 

### 3001.6 MMBTUIhr., a 

### 20% increase over the 

### original anticipated heat input. This figure bas been seen or exceeded several times prior to 1990 as shown in Figure 1. Unit2 For Unit 2, the original anticipated heat input value is 4696 MMBTUlhr. OnJune I, 1990 Unit 2 had a measured maximum heat input rating of4909 MMBTU/hr., a 5% increase over tbe original figure. Figure 2 below is aplot ofthe maximum heat inputs for Unit2 for an 18 year period from May 1977 to March 1995. This period 

### endsjuS! before an outage in 

### 1995 when some major maintenance work was done on the boiler. The horizontal line al 4696 represents the anticipated fuel firing rale maximum heat input figure. Note that this unit also frequentlyexceeds this maximum heat input figure during normal operation and on several occasions has exceeded 5000 MMBTU/hr. The maximum value is 5401 

### in September 1991 with a second high value of5177 MMBTUlhr in July 1986 and another high value of5168 MMBTU/hr ill December 1980. Figure 2. Monthly maximum heat inputs for Unil2. May 1977 10 Marcb 1995.
Mlnnkola PowerCooperative Mitton R. Young Station Unit 112 Calculated URGE Boller Heal Input Pre 1995 Maximum of 5,401 ocaJrred In Sep-91 e.ooo ,-**.b~~~~~** __**~;.......!** ___,

.5.000
.

'.000 

### i 3.000 

# " • 2.000

1.000
..

o

## \#~"~.j!~~~~~'l**/...?~/it./-r>~/ ~.J'~~/** **/...J''':/''/-r>~.?X;jC<f'-r>v~#OJ'./~OJ~~<P~<¥,ii' "~.j!o,"** 
For Unit 2. the November 20 lener from Mr. Graves to the Division ofEnvironmental Engineering listed a CEM measured maximum heat input of6261 MMBTU/hr. This value compares to the original anticipated heat input of4696 MMBTU/hr. a 33

### %increase. These comparisons clearly demonstrate that both Units 1 and 2 can and do operate well above their original anticipated maximum beat input values. The original anticipated heat levels are very conservative and are not representative ofactual operation as shown in these data and in the referenced performance tests. Another consideration is the way that the heat input to the boiler is currently calculated. The heat input data shown above 

### in Figures 1 and 2 is based on the monthly maximum power generation level multiplied by the average energy conversion efficiency (heat ratc) for that month. Since 1995, the permits for these units require that the continuous emission monitors

## , be used to calculate fuel input values. The CEM uses EPA Method 19 (also known as the F factor method) to convert several Oue gas constituent concentration and flue gas flow measurements into an estimate ofheat input to the boiler. The problem is that one component ofthe flue gas volume calculation uses the velocity measurements offlue gas exiting the boiler. It 

### is well known thatflue gas flow in 

### adUCIexiling aboilercan be 

### very non-uniform. Ifone were to lake one oreveD a few measurements offlow velocity 

### in Lhe dUCI using EPA Method 2 or an equivalent test method and calculate the total volumetric flow offlue gas in lhe dUCI from 

### these measurements. errors in flue gas volume can result 

### These errors can be 

### as high as 20%. In 1999, the EPA promulgated Methods 2F, 20, and 2H tn help address these errors in measuring stack gas velocities. Theseerrors can result 

### in a considerabledifference between Slack-measured power plant heat rates and combustion-calculated heat rates. An EPA memorandum, dated AUguSl26, 1999, discussing the background and applicability ofthe new methods is attached, For the period from January 1995 to October2000, a comparison was made ofthe monthly average heat inputderived from the CEM calculation ofheat inputcompared to the calculation based on power generation. For Unit 1 the CEM derived estimate ofbeat input ranged from 89% to 107% ofthe power generation derived estimate with an average value of97%. For Unit 2, the comparison ranged from 95% to 121 

### % with an average of III

### %. These comparisons demonstrate that these two methods ofcalculating the fuel input to the boiler do not agree. Therefore, any use ofthe calculated heat input to the boiler needs to take into account the uncertainty resulting from the disagreement belWeen the methods. 

# Consequence of Using Anticipated Maximum Heat Inputs in Determining TitleVPermitCondition. The operating pennit for each unit will base the allowed pounds per hour ofS02 emissions on an emissions factor times the pounds per million BTU ofmaximum fuel firing capacity. This calculation results in a maximum allowed S02 emission rate for each unit expressed in units of pounds of502per bour. Ifthe fuel firing capacities used for this S02emission calculation are the original anticipated fuel firing rates that are below the measured firing rates for the boiler then the allowed 502 emission rates 

### in pounds per hour will also be set too low. This is indeed the case for the Milton R. Young Station. The boilers can and do fire at a much higher firing rates than the original anticipated values as demonstrated 

### in this repon. The calculated pounds per hour S02emission limits should be calculated from the more representative measured firing rates rather than the original anticipated firing rates. These calculated maximum 502emission rates should also have an allowance to account for the uncertainties in the methods ofcalculaling the fuel frring rate as discussed above.

# Conclusion The Milton R. Young Station Units 1 and 2 frequently operate at heat input levels well in 

### excess oftheir original anticipated fuel-firing rate. The marginofthis difference is up (Q 

### 33

### % above original anticipated levels. Therefore, the use ofthe original anticipated heat input values for the Millon R. Young boilers is not representative ofactual as built operation as 

### demonstrated by 

### actual performance tests and the operating data plotted in Figures I and 2. The maximum heat input levels referenced in lbe November 20. 1995 letter from 

### Me. Graves are more representative ofdemonstrated maximum operating heat inputs and sbould 

### be used 

### for the purpose ofcomputing permit S02cmission limits for I.he units' operation. Should the permitting aulbority continue to see the need to use these heal 

### inputnumbers to calculate emission rates that are placed into an air permit, it is our opinion thatthe measured maximum heat inputs should be used for (his calculation, not the much lower original anlicipa(ed heat inputs. The maximum values shown in Figures 1 and 2 should

### be used instead. These values are 3128 MMBTUlhr for Unit 1 and 5401 MMBTUlhr for Unit2. The pollution emission rates stated in lhe permits should 

### be based on lhese measured maximum firing rates.