solid fuel model documentation

7/28/2019 Solid Fuel Model Documentation

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A

Financial Feasibility Screening Modelfor small Coal Fired Thermal Power Stations

for sizes between 600 kWe and 5,000 kWe

April 1998

For MTNT, LimitedAnd McGrath Light and Power

and

The State of Alaska

Department of Community and Regional AffairsDivision of Energy

and

Energy and Environmental Research CenterUniversity of North Dakota

by

J. S. Strandberg Consulting Engineers, Inc.Anchorage and Fairbanks Alaska


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Technology Assessment - Small Coal Plant Screening Model

List of Figures

Figure 1 Flow Schematic 5

List of Tables

Table 1 Model Input Descriptions and Values 9Table 2 - Listing of Community Utility Systems 12

Acknowledgements


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Table of Contents

1.0 EXECUTIVE SUMMARY 1

2.0 INTRODUCTION 1

2.1 The Feasibility Initiative 22.2 The Screen Model Concept 33.0 METHODOLOGY 43.1 Power Plant Model 43.2 Cost of Construction 43.3 Assessment of Operating and Maintenance Costs 63.4 Fuel Consumption The Thermal Model 74.0 MODEL DESCRIPTION 7

5.0 MODEL OUTPUT 8

6.0 CONCLUSIONS AND RECOMMENDATIONS 11

7.0 REFERENCES 13

8.0 APPENDICESAppendix 1 Modeling EquationsAppendix 2 Data InputAppendix 3 Model Output

Tabular Data OutputCost of Power ($) versus Power Plant Generation Capacity (kWe)Cost Index (CF) = 1.0, 1.3(District Heat Load (MMBTU/hr) (dh),(Cost of Coal ($/ton) (CP)

CF = 1.0, dh = 0,10, 20, 30, 40, for CP=30CF = 1.0, dh = 0,10, 20, 30, 40, for CP=40CF = 1.0, dh = 0,10, 20, 30, 40, for CP=50

CF = 1.3, dh = 0,10, 20, 30, 40, for CP=30CF = 1.3, dh = 0,10, 20, 30, 40, for CP=40CF = 1 3 dh = 0 10 20 30 40 for CP=50


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1.0 EXECUTIVE SUMMARY

Using the results of two independent processes, a simplistic spreadsheet basedfeasibility model was created for assessment of the financial viability of smallsolid fired power plants in Alaska.

The power plant would produce heat and power, and employ a fluidized bedcombustor capable of burning a wide range of solid fuels. A traditional steamturbinegenerator arrangement would generate electricity and low pressuresteam for use in process and space heating.

The model is considered valid over a range from 600 to 5,000 kWe net electricaloutput, and over a range of 0 to 40 million BTU/hr of heat by-product. This by-product energy would leave the power plant either as process steam or hotwater.

The model is founded on two elements:

A detailed feasibility study accomplished for the McGrath, Alaska privatelyowned electric utility, McGrath Light and Power. The study is for a 600kWecombined heat and power plant employing Rankine cycle steam turbines.(Reference 1)

A proposal and bid evaluation process (Reference 2) which was undertakenby the State of Alaska, Department of Community and RegionalDevelopment, Division of Energy (State DOE), and the Energy &Environmental Research Center (EERC) for the privately owned power utility

serving Tok, Alaska. This process envisioned a 1,640 kWe net outputcombined heat and power plant with Rankine cycle steam turbines and acoal-fired fluidized bed combustor.

The results of these two efforts were combined to create a spread sheet basedcomputer model which estimates the total cost of electricity for a location inAlaska. The model breaks down this cost into major components which can beeasily related to a utility budget format.

Model input data include costs of labor and fuel, district heating load, electricalload, and parasitic power requirements and boiler thermal efficiency. Thus auser may, with inputs of plant capacity and site specific economic information,compute the life cycle cost of electricity. The model, through use of a sitelocation cost adjustment factor, is applicable to a wide range of locations andapplications in the Alaskan economy


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megawatts and larger, there is very little known about the performance and costof smaller solid fuel thermal power plants. Combining this lack of information

about available technologies with the widely varying cost conditions that Alaskacommunities labor under, small utilities and other energy suppliers find itdifficult to consider solid fuel fired combined heat and power plants as a viableoption in power production planning.

This project has been accomplished to develop a simplistic computer-basedanalysis tool for those who need to consider solid fueled combined heat andpower plants in this 600-5,000 kWe range. It is expected that process plantowners and small rural power utilities will see an application of the tool.

The spreadsheet model yields a critical performance parameter for the solid fuelpower option, that of the overall cost of power production. The model considersthe long term amortization of construction cost with ongoing operations costs,periodic renewal costs, and company overhead.

2.1 The Feasibility Initiative

Two separate initiatives [Reference 1 and 2] to develop small scale coal firedpower plants have been accomplished in the past year, which have yielded basicperformance and economic feasibility data for McGrath and Tok, Alaska.

The McGrath Study

Employing a Donlee fluidized bed combustor and a separate un-fired boiler witha dual turbine arrangement, the project was designed to provide a net output of

600 kWe and just under 10 million Btu/hr of 25 psig saturated steam fordistrict heating. A complete conceptual design and a thorough estimate ofconstruction cost which incorporated coal handling and storage/thawing wasincluded in the feasibility reference. A detailed mine development plan for thelittle Tonzona coal deposit is part of the project documentation. The McGrathProject was carried to completion of conceptual design, where it was shelvedbecause costs were significantly higher than the diesel alternative.

The Tok Study

A request for proposals was advertised by Alaskan Power and Telephone (AP&T)for the placement of a somewhat larger 1,640 net kWe power plant at Tok,Alaska. AP&T is a private power utility serving a number of Alaskancommunities, and has an interest in developing solid fuel options for powerproduction at Tok and was being funded by The State DOE and EERC. The


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power options. The company also had a complete workload of hydro-poweredprojects underway at other locations.

2.2 The Screening Model Concept

While neither of the projects yielded an economically feasible design for the tworespective communities, it was realized that the cost and conceptual designdata and experience gained from McGrath and Tok were valuable .

The experience gained with the two projects indicated that other, larger ruralcenter communities might be more appropriate for solid fuel power production.The project team felt the following conditions are necessary for a solid fuel plantto achieve feasibility:

Large base load unit size Coincident process/district heating load present Competitive coal price (purchase plus transportation charges) at a price

the per million Btu cost of diesel fuel

Knowing then that a number of communities in Alaska might meet the abovefeasibility criteria, the concept of a spreadsheet based model based on theMcGrath and Tok data was pursued, to facilitate this state-wide screeningprocess.

Modeling criteria and concepts were put forth as follows:

The Tok and McGrath conceptual designs, their respective constructioncosts and data on operating costs would be adjusted to a comparableAnchorage cost basis. In doing so, power plants considered for Tok andMcGrath could be reviewed to understand how first costs vary with plantoutput. This understanding could then be used to develop regressionequations to calculate costs for other power plant sizes.

The basis of cost would include models for energy production andconsumption, operating labor and maintenance, consumables (fuel andlimestone), and capital investment, stated as a function of unit size.

A user would be able to input the physical and economic parameters thatdescribe a potential solid fuel project. Then using the models empiricalrelationships the user could compute for a specific plant size financing


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3.0 METHODOLOGY

3.1 Power Plant ModelThe power plant that is modeled includes all major equipment within the powerblock including:

Fluidized Bed Combustor, with fuel storage and handling systemsconfigured to handle solid fuels.

A traditional steam cycle including an extraction steam turbine, configuredto generate electric power and a relatively high quality process steam/water.Deaerator and pumps included.

Fans for delivering air into the fluidized be combustor. Condensing equipment for the rejection of cycle heat Particulate removal device District Heating pumping and heat transfer equipment to create a low

temperature (250 deg F) hot water heating medium. Controls and instrumentation3.2 Cost of Construction

The designs for McGrath and Tok both employ similar equipment and haveessentially the same thermal cycle, as presented in Figure 1. Thus it is possibleto review and make selective modifications to the cost estimates to arrive at thesame power plant design, but with different size, in two different communities.Then there was a need to modify the project costs (in McGrath and Tok) back toa common base, and this was done using Anchorage as the basis. Data for thiscost modification were from a study accomplished at an earlier date, and whilesomewhat old were still were felt to reflect a reasonable approach to costcomparison. Once these two actions were complete, the team had two separatepower plant projects, of very similar design, costed on an Anchorage base thatwere available for use in building a model. (Reference 3)

The McGrath cost estimate is felt to represent a complete project budget andthus was not changed prior to having the cost modifier applied to bring the

project to an Anchorage base.

In contrast, the proposal process employed for Tok Alaska resulted in thereceipt of 13 turnkey proposals which included some large variations inapproach for thermal cycle and equipment. As a part of the work, theseproposals were evaluated in a screening process, and 3 of the 13 proposals were


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another proposer submitted with a viable combustor/boiler arrangement, buthad a steam turbine system which was not felt to be workable within the

context of providing large quantities of high quality district heating. Howeverthis proposal included a full complement of fuel handling equipment that wouldbe necessary for proper operation. A decision was made to average theproposed turnkey construction costs from these three proposals to derive asingle value ($/kW) for input into the model.

Costs for the Tok powerplant (1,640 kWe net output), corrected to an Anchoragebase, and the costs for the McGrath power plant (600 kWe net output), similarlycorrected to the Anchorage base were then entered into a regression equation,

which relates unit size to cost.

The basic form of the equation is shown below:

Cn =Cr(Sn/Sr)P

Where Cn = new adjusted cost corresponding to the new size (Sn) ($)Cr = reference cost at the reference size (Sr) ($)

Sn = New Size (kWe)Sr = Reference Size (kWe)P = Power Factor, typically (0.6 to 0.8)

While some (Reference 4 and 5) suggest a constant power factor in the range of0.6 to 0.8 for use in the above equation, it was speculated that for this sizerange the power factor would also vary as a function of unit size. Recent reviewof this was supported by (reference 5). The reference generally indicate that for

very small unit sizes, the economics of scale are much more significant than forlarge size ranges. This is the reason that the curve of cost/installed capacity issteep where unit sizes are small.

Given this background and the data from the McGrath and Tok, process powerfactors in the range of 600 - 1640 kWe calculated to be 0.3, and were assumedto be 0.8 above 1640 kWe.

As a caveat, it should be noted that a literature search (Reference 6) performedby EERC did not reveal any cost data for solid fuel plants in this 600 5,000kWe range. However the developed relationships and noted power factors doappear to meet the limit data points up to the 20 megawatt level.

3.3 Assessment of Operating and Maintenance Costs


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3.4 Fuel Consumption the Thermal Model

A simplified thermal model was developed that simulates unit operation in thefollowing manner:

A base electrical load is carried throughout the year, except during a yearlyshut down period.

A district heating load is carried which varies with outside air temperature.Heating load is expressed as a peak design load that is modified by a peak toaverage factor.

The performance of the boiler system is expressed as an overall seasonalthermal efficiency, and can be specified by the user.

The performance of the steam turbine is summarized by a throttle steamequation that inputs the extraction steam requirement and the electrical loadrequirement. A 10% factor is added to cover deaerator and station heatingsystem steam requirements. A standard 5,000 kWe extraction steam turbinewith full extraction capability is used as the base model. The extraction

performance for this turbine compares favorably with the 600 kWe extractionturbine.

Power plant station power is expressed as a parasitic power factor, which is afraction of the net output of the power station and can be specified by the user.This factor is quite important in power plant economics and will be as high as30% for plants under 1000 kWe and as low as 12% at 5,000 kWe. Steamplants typically do have high station service power requirements and fluidized

bed systems tend to take considerable power to keep circulating beds in a fluidstate.

4.0 MODEL DESCRIPTION

Analyses of the Tok and McGrath projects, yielded regression relationships forperformance and costs which are used to create an interactive spreadsheet

model. The model employs the regression equations to compute performanceand costs, and data input for the model is broken into the following major areas

Power Plant Physical Characteristics Steam Cycle Parameters Costs of Consumables


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is base loaded at a set electrical load, while the heating load is assumed to varythroughout the year.

Table 1 provides an abbreviated listing of model inputs, while Appendix 2 showsa screen display of the spreadsheet input section.

5.0 MODEL OUTPUT

The output of the model is expressed in a tabular format, and is shown inAppendix 3. In addition, there is a tabular section of the spreadsheet, whichallows a user to do what if analyses when viewing a potential power plant, its

size and character.

Characteristic curves summarizing model predictions are included inAppendices 3 and 4.

Appendix 3 presents characteristic curves of overall cost of power versus unitsize, for a number of different economic conditions. Costs for construction areincluded (Appendix 4) for two primary cost factors 1.0 (Anchorage base) and

1.3 (Aleutian rural center).

As a check, the results of the model were considered with recent constructionexperience in the state of Alaska. Of specific interest was the relationshipbetween the cost of the Healy Clean Coal Project and the cost predicted by thescreening model.

The model predicts an installed price for a 5,000 kWe power plant in an

Aleutian rural center of about $2,600 per kWe. The price for the Healy CleanCoal Plant has variously been reported at $4,000 per kWe for a 55,000 kWeplant size.

While it does not seem reasonable that the unit cost for a small plant would beless than that of a larger state of the art plan in the railbelt, the project teamdid feel that there are ameliorating circumstances, as listed below:

The smaller plant employing a fluidized bed will be considerably simplerthan the Healy Clean Coal (55 MW) power plant

The Healy plant has extensive and complex combustion and exhaust gascleaning systems employing complex technologies. This may have driventhe cost up well above that which is normal for large scale plants.Costs/installed kWe for the normal 20 to 50 MW power plant in the lower 48ranges around $2,000/kWe. EPRI reports a cost of $2085/kW for a


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Table 1 - Model Input Descriptions and Values

Model Variable Units TypicalValue

Power Plant Inputs

Power Generation KWe 600

Net power generated output from plant

Capacity factor factor 0.912

Fraction (decimal equivelant) of the year the plantis in operation[Normally expressed as (kWh/yr)/(Max availablekWh/yr)]

hrs/yr 8760

no. of hours per year (calculation variable)

Parasitic Power Requirement % of netoutput

0.15

Percent of the net power generation that must beproducedin addition to net power output to power internalplant auxiliaries

District Heat MMBTU/hr

9.62

Design district heat output from the powerplant

Coal Higher Heating Value BTU/lb 8,700BTU content of the coal fuel (higher heating value)

Boiler Thermal Efficiency ratio 0.8

Overall thermal efficiency of the coal fired


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output equals the yearly average heating load.

Steam Cycle ParametersA steam turbine curve has been developed for thesteam turbine arrangement in the power plant. .These constants are used to establish boiler headersteam flowequation constant - 8.81

equation constant - 3000

equation constant - 658.18factor for DA heat/station heat - 0.1

delhfor plant (enthalpy difference for BTU/lb 1258.5

header steam as it goes from header to condenserhotwell

Economic Data:

Cost of Consumables

Coal $/Ton 52

Limestone % of CoalCost

10%

Percent of coal consumption

Ash Disposal $/Ton 20(assumed equal to10% of coal)

Operations/Maint Supplies Basis 50,000

Replacement parts Basis 50,000

Utilities (Water, Electricity) Basis 25000

A regression based factor is computed and applied

to increase these costs as unit size increases.


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6.0 CONCLUSIONS AND RECOMMENDATIONS

The model developed is shown to be an effective tool for predicting the cost of anew power station, if reasonable assumptions are made as to electricalgeneration capability, the district heat requirement, and the cost structure inthe community.

The model is easy to use and allows the user to input site-specific criteriathereby facilitating what-if types of analysis to be performed. The model can beused to generate numerous sensitivity curves.

The inclusion of process heat sales will help offset the cost of electricityproduced by the powerplant. The ability of the solid fuel plant to producemedium grade process heat as a by-product emerges as a major benefit andenhances the marketability at the plant.

Cost of fuel, labor, and installation are the major determinates in economics ofsolid fuel power plants. The dynamic relationship of cost of solid fuels in

Alaska does center around transportation costs, and it appears that a potentialcommunity where solid fuel could be feasible may need to be readily accessibleby ocean barge.

The family of curves that summarizes the modeling results for Anchorage andan Aleution Island urban center are included in Appendix 3 and 4. In theseexamples (shown in Appendix 3) costs for power production fall dramatically asunit size increases from 600 kWe to 2000 kWe. Above 2,000 kWe, prices tend

to decrease at a lesser rate, indicating that solid fuel power may find greaterapplication where a base power load greater than 2,000 to 3,000 kWe exists ina community.

The units projected in the modeling at 5 MW appear to be considerably lessexpensive than the 55 MW Healy coal fired power plant. The team feels that thesimplicity and maturity of the smaller fluidized bed combustion systemsenvisioned may be one reason for this cost differential.

In a companion activity, the Division of Energy has reviewed power utilitystatistics and has arrived at a list of communities where a base load of 2,000kWe exists. Locations where a solid fuel plant could find application are listedbelow in Table 2 Listing of Community Utility Systems.

The results reported herein are provided to illustrate the use of the model


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Table 2 - Listing of Community UtilitySystems

Utility Name Population Total Average Load

Customers (kWe)

Bethel Utility Corp Inc. 5,195 2,045 3,717

Unalaska Electric Utility 4,122 591 3,114

Nome Joint Utility System 4,067 1,680 2,973

Cordova Electric cooperative, Inc. 2,583 1,564 2,510

Kotzebue Electric Association 2,971 957 2,231

Naknek Electric Association, Inc. 1,482 860 2,112

Craig 1,729 873 1,950

Nushagak Electric Cooperative, Inc. (dilling) 2,191 1,257 1,823

Haines light and power 1,458 957 1,259

Skagway 781 680 1,073

Tok 935 686 1,068

Galena, City of 603 282 846

Yakutat Power 747 328 808

THREA--Klawock 759 420 512

THREA--Kake 727 321 499

THREA--Hoonah 911 356 481

St. Paul Municipal Electric Utility 712 217 458

Unalakleet Vallkey Electric Utility 750 303 429AVEC-- Point Hope 704 218 423

NSPB&L--Wainwright 535 188 397

Sand Point Electric Company 1,042 483 372

G&K, Inc. (Cold Bay) 185 70 337

McGrath Light & Power 495 214 328

King Cove, City of 893 244 315

Pelican Utility Company 225 232 313


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7.0 REFERENCES

1. A Feasibility Analysis of a Proposed Coal Fired Thermal Power Station forMcGrath, Alaska, for MTNT, Limited and McGrath Light and Power, by J. S.Strandberg Consulting Engineers, Inc. June 1997

2. A proposal process administrated by the State of Alaska Department ofCommunity and Regional Affairs, Division of Energy, soliciting pricedproposals for the turn-key construction of a 1,640 kWe cogeneration PowerPlant in Tok, Alaska.

3. Strandberg, J. S., Cost data for building construction in cost regions of theState of Alaska in support of research for State of Alaska, Department ofTransportation and Public Facilities to establish a life cycle cost basedthermal standards for small rural schools, 1983.

4. Popper, Herbert, ed., Modern Cost-Engineering Techniques, McGraw-Hill,New York, 1970.

5. Jenkins, B. M., A Comment on the Optimal Sizing of a Biomass UtilizationFacility under Constant and Variable Cost Scaling, Biological andAgricultural Engineering Department, University of California, Davis, CA95616, Biomass and Bio-energy Vol. 13. Nos pp 1-9, 1997.

6. Literature search, accomplished for costing of similar fluidized-BedCombustor units, by Energy and Environmental Research Center, March

1998. [Informal copy, not published]

7. State of Alaska Department of Labor, Steam Boiler Regulations8. Bhattacharya, S. C., State of the Art of Biomass Combustion, Energy

Sources, 20:113-135, Taylor & Francis, 1998


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8.0 APPENDICES

Appendix 1 Modeling equations

Appendix 2 Data Input

Appendix 3 Model OutputTabular data outputCost of Power ($/kWe) versus Power Plant Generation Capacity (kWe)

(District Heat Load (MMBTU/hr) (dh)

(Cost of Coal ($/ton) (CP)

CF = 1.0, dh = 0,10, 20, 30, 40, CP=30CF = 1.0, dh = 0,10, 20, 30, 40, CP=40CF = 1.0, dh = 0,10, 20, 30, 40, CP=50

CF = 1.3, dh = 0,10, 20, 30, 40, CP=30CF = 1.3, dh = 0,10, 20, 30, 40, CP=40CF = 1.3, dh = 0,10, 20, 30, 40, CP=50

Appendix 4 Model Output Installed Capacity (kWe) versus Capital Cost ($)Cost Index (CF) = 1.0, 1.3, dh=0,10,20


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APPENDIX 1Modeling Equations

Parasitic Power =(parasitic power requirement) (power generation)

Total Power Output =(Power Generation + Parasitic Power)

Electrical Generation Delivered =((power generation) (8760 hrs/yr) (capacity factor)) / 10 6

Header Steam Flow =(8.81 (total plant power output) +3000 + (658.18) (design heating load) * peak/ave ratio DH load) (1 + factor DA station

heat)

Fuel Burn Rate =Annual heat input to boiler / ((hrs/yr) capacity factor)

Annual Heat to Boiler =((header steam flow / boiler efficiency) (del H for plant) (hrs/yr(capacity factor)) / 106

Coal Requirement =((annual heat input to boiler / coal higher heating value) / 2000) (106)

District Heating Delivered from Power Plant =(design heating load) (capacity factor) (peak/average ratio DH load) * 8760

Useful Energy Produced by Plant =(electrical energy delivered from power plant) (3412) / (design heating load) (106) (peak to ave ratio DH load)

Electrical Work to Heat Ratio =Power generation (1 parasitic power) (3412) / (design heating load) (10 6) (peak to ave ratio DH load)

Overall Plant Utilization Ratio =Useful energy delivered by power plant / annual heat input to boiler


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J. S. Strandberg Consulting Engineers, Inc.

Capital Cost = ($3000/kW) * (1640/new kW size)0.7 * new kW size + 200,000 (new DH size/15 mmBtuhr) 0.7

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