Evolution Overview

The base case is based on the McNeil Station located in Burlington, Vermont, as described by Wiltsee and Hughes [1]. Feed composition is given in Table 3. Wood heating values are about 10 MJ/kg on a wet basis and 20 MJ/ kg on a dry basis; these values are about 40% and 80% of coal (24.78 MJ/kg [12]), respectively.

Table 3. Feedstock composition.

5%M 50%M

5%M 50%M

C, wt%

50.45

26.55

47.65

25.08

H

5.74

3.02

5.72

3.01

N

0.16

0.09

0.09

0.05

O

37.34

19.66

41.17

21.65

S

0.02

0.01

0.01

0.01

Cl

0.03

0.01

0.01

0.01

Moisture

5.00

50.00

5.00

50.00

Ash

1.26

0.67

0.35

0.19

MJ/kg (wet)

19.72

10.38

18.92

9.96

MJ/kg (dry)

20.76

20.76

19.92

19.92

Representative material and energy balances for the 1996 and 2000 cases are given by Figures 2 and 3. The nameplate efficiency ofthe McNeil Station is 25%, while the Biopower model [14] from which Figure 2 was derived, gives 23.0% efficiency.

As indicated in Figure 3, the plant efficiency is increased to 27.7% in the year 2000 (EPRI 1995) through the use o f a dryer. This increase in efficiency comes from an increase in boiler efficiency that occurs when dry feed is substituted for wet feed. For example, for a wood-fired stoker boiler, boiler efficiency is estimated at 70% for a 50% moistur e content fuel and 83% for a 10% moisture content fuel, assuming 30% excess air, 19.96 MJ/kg dry feed, and a flue gas exit temperature of 177°C (351°F) [1]. The McNeil Station boiler efficiency is 70% for a 50% moisture fuel and it s process efficiency is 23%. Wiltsee states "The boiler efficiency, multiplied by the higher heating value of the fue l burned in the boiler, determines the amount of energy that ends up in the steam, available for driving the steam turbine generator. The boiler efficiency also determines the gross station efficiency when it is multiplied by the gross turbin e efficiency. Boiler efficiency is a function of the amount of moisture in the fuel, the amount o f

Table 2. Performance and cost indicators.

Base Case

INDICATOR

1997

2000

2005

2010

2020

2030

NAME

UNITS

+/- %

+/- %

+/- %

+/- %

+/- %

+/- %

Plant Size

MW

50

60|

100|

150

184|

184|

General Performance Indicators

Capacity Factor

%

80

80

80

80

80

80

Efficiency

%

23.0

27.7

27.7

27.7

33.9

33.9

Net Heat Rate

kJ/kWh

15,280

13,000

13,000

13,000

10,620

10,620

Annual Energy Delivery

GWh/yr

350

420

700

1,050

1,290

1,290

Capital Cost

Fuel Preparation

$/kW

181

20

150

20

129

20

114

20

93

20

93

20

Dryer

0

79

68

60

49

49

Boiler

444

25

369

25

317

25

281

25

229

25

229

25

Baghouse & Cooling Tower

29

24

21

18

15

15

Boiler feed water/deaerator

56

25

46

25

40

25

35

25

29

25

29

25

Steam turbine/gen

148

123

106

94

76

76

Cooling water system

66

55

47

42

34

34

Balance of Plant

273

15

227

15

195

15

172

15

141

15

141

15

Subtotal (A)

1,197

1,073

922

816

667

667

General Plant Facilities (B)

310

257

221

196

160

160

Engineering Fee, 0.1*(A+B)

1,513

133

114

101

83

83

Project /Process Contingency

2,269

200

171

152

124

124

Total Plant Cost

1,884

1,664

1,429

1,265

1,034

1,034

Prepaid Royalties

0

0

0

0

0

0

Init Cat & Chemical Inventory

2.21

2.21

2.21

2.21

2.21

2.21

Startup Costs

53.06

53.06

53.06

53.06

53.06

53.06

Inventory Capital

11.19

11.19

11.19

11.19

11.19

11.19

Land, @$16,060/hectare

14.49

14.49

14.49

14.49

14.49

14.49

Total Capital Requirement

$/kW

1,965

1,745

1,510

1,346

1,115

1,115

1. The columns for "+/- %" refer to the uncertainty associated with a given estimate .

2. Plant construction is assumed to require two years.

3. Totals may be slightly off due to rounding

Notes:

1. The columns for "+/- %" refer to the uncertainty associated with a given estimate .

2. Plant construction is assumed to require two years.

3. Totals may be slightly off due to rounding

Table 2. Performance and cost indicators. (cont.)

INDICATOR NAME

UNITS

Base Case 1997

2000

2005

2010

2020

2030

Plant Size

Operation and Maintenance Cost

Feed Cost

Fixed Operating Costs

Variable Operating Costs Labor

Maintenance Consumables Total Variable Costs

Total Operating Costs

2.50 60

5.50

2.50 60

4.74

2.50 60

4.74

60 15

2.50 60

4.74

60 15

2.50 49

3.87

60 15

2.50 49

3.87

60 15

Notes:

1. The columns for "+/- %" refer to the uncertainty associated with a given estimate .

2. Total operating costs include feed costs, as well as fixed and vaiable operating costs.

3. Totals may be slightly off due to rounding

Direct-Fired Combustion Wood-Fired Stoker Plant 50 MW (Net)

Boiler Efficiency 71.7%

Bottom Ash 2.5 Mg/day

1112.9 Mg/day

Gross MW 55.9

Net MW 50.0

Direct-Fired Combustion Wood-Fired Stoker Plant 50 MW (Net)

Gross MW 55.9

Net MW 50.0

Boiler Efficiency 71.7%

Prep Fines - 0 Mg/day

Combustion Air 7713.2 Mg/day

Fly Ash 10.1 Mg/day

Prep Fines - 0 Mg/day

Combustion Air 7713.2 Mg/day

Fly Ash 10.1 Mg/day

Emissions

Mg/day

Flue Gas

9510.8

CO2

1720.3

CO

2.0

SO2

0.37

NOx

0.81

Part.

0.23

Solar Stirling Engine Basics Explained

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The solar Stirling engine is progressively becoming a viable alternative to solar panels for its higher efficiency. Stirling engines might be the best way to harvest the power provided by the sun. This is an easy-to-understand explanation of how Stirling engines work, the different types, and why they are more efficient than steam engines.

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