12. Power and Heat Plants in General
13. Heat Plant A
14. Heat Plant B
15. Power Plant C
16. Power Plant D
17. Summary on Power and Heat Plants
18. Operation Economics by Different Prices of Fuel
19. Summary and Conclusions
In this chapter four power and heat plants will be presented. They have been designed to supply power and (or) heat for the purposes of those eleven industry mills, that were presented in chapter 3. All four power and heat plants operate on industrial wood wastes and, in case there is not enough of these to satisfy the demand, on hogged fuel wood.
The plants are non-existent and have been designed for the purpose of this study.
The prices of the various plant equipment have been obtained either as quotations by the manufacturens or from the cost files for similar installed equipment. The energy cost calculations are based on assumptions concerning wages, fuel prices, price of electricity etc., listed in chapter 2. These assumptions refer to the cost level of the fourth quarter of 1979 in the Philippines in South-East Asia.
The sensitivity analysis at the end of the chapter indicates to what extent the results of the cost calculations are affected by changes in the initial cost assumptions.
In the cases of Heat Plants A and B as well as Power Plant °C the energy costs have been calculated for various size alternatives. For instance, Power Plant C was initially designed for a power output of 250 kW and to support Sawmill No. 4 (100 m3 sawnwood per day). In this chapter calculations have also been made for an identical power plant, but with an output reduced to 125 kW. This plant supports Sawmill No. 3 (50 m3 sawnwood per day).
The investment costs of these heat and power plants with alternated output capacities have been estimated rather roughly. For this reason the capital cost figures and the energy cost figures of these plants cannot be regarded as reliable as those calculated on basis of the actual investment costs.
The energy cost tables in this chapter indicate the annual costs caused by power and heat generation by a given power or heat plant in connection with a given industry mill. In fact, they are the operation costs of the power and heat plants and they must not be confused with the operation costs of the actual manufacturing process of the industry mills.
It must finally be pointed out that neither the solutions of technical plant design nor the stated investment costs of this chapter represent the only feasible alternative. On the contrary, there is a multitude of possible solutions in designing a wood fired power and heat plant and the investment cost of such a plant may vary considerably according to plant design and for a number of other reasons as well.
13.1 Description
Heat Plant A is designed to operate at small sawmills with low requirements on thermal energy and heat temperature. The plant fires sawmill waste to produce warm water, which is pumped to the drying kiln of the sawmill. At the sawmill the drying of sawnwood stands for the major part of the heat demand, in many cases for all of it.
The wood waste from the saw is conveyed to a pile. Sawdust and small-size chips are conveyed there directly but bigger wastes such as slabs and edgings are first hogged in a chipper to meet boiler requirements.
From the pile the chips are transferred to the dumping silo next to the boiler house. This is done either by a front-end loader or by men with the aid of carts and spades.
The volume of the dumping silo is 10 m3. The silo serves both as a dumping retort and as an intermediate fuel storage.
Three screws at the bottom of the silo remove the chips onto a feeding screw, which takes the chips to the feed hopper and into the boiler. The fuel combustion takes place on an inclined grate. The flue gases are passed through a cyclon where the dust is separated and onto the 20 m stack and the open air.
The water is heated to 115...120 °C before passed over to the dryer. The temperature drop during the cycle is 20... 30 °C. To prevent the water from boiling the water-side pressure is kept at 10 bar. The boiler has a thermal output of 1 MW, which is enough to support a sawmill with an output capacity of 50 m3/d.
Fuel oil is used as pilot fuel and also to support combustion at high chips moisture or rapid load changes. The oil is stored in a 10 m3 tank next to the boiler house.
The operating personnel consists of one boilerman per shift and one cleaner per day. Depending on arrangements the fuel handling personnel varies between one man per day or two men per shift.
Heat Plant A could be supplied as a turn-key delivery. The delivery time is 6 months plus approximately 3 months for freight. Assembly and trial run counts for 2 months which totals 11 months between contract signing and commissioning.
The total transport weight of Heat Plant A is 15...20 t, including fuel handling equipment but not including a front-end loader.
13.2 Investment Costs
|
USD |
|
A. Equipment Costs (F.O.B.) |
||
1. Boiler plant |
127 000 |
|
|
1 MW warm water boiler |
|
|
10 bar, 120 °C |
|
|
Fuel feeding and combustion equipment |
|
|
Water treatment equipment |
|
|
Pumps, pipings and tanks |
|
|
Measuring and control equipment |
|
|
Electrification |
|
|
I.D. fan, dust separator and stack |
|
2. Fuel handling equipment |
87 000 |
|
|
Chips handling, incl. dumping silo and feeder screws |
|
|
Chipper 10 m3/h |
|
|
10 m3 oil tank |
|
A. Total |
214 000 |
|
B. Construction costs |
||
3. 220 m3 boiler house, foundations |
65 000 |
|
B. Total |
65 000 |
|
C. Miscellaneous costs |
||
4. Freight and insurance (7 % A) |
15 000 |
|
5. Clearing and transport to site (2.5 % A) |
5 000 |
|
6. Assembly (20 % A) |
43 000 |
|
7. Planning and supervision (6 % A+ B) |
14 000 |
|
8. Interest during construction (8 % A+ B) |
18 000 |
|
C. Total |
95 000 |
|
Total investment costs (A+ B+ C) |
320 000 |
13.3 Energy Costs
|
Unit |
Sawmill No. 3 |
Sawmill No. 4 |
||
1. Wages and salaries |
|||||
|
operating personnel |
|
3 x 3 + 1 x 1 = 10 |
||
|
unit cost |
USD/a |
490 |
||
Total |
USD/a |
4 900 |
4 900 |
||
2. Maintenance, repair and insurance |
|||||
|
3 % of equipment costs |
|
|
|
|
Total |
USD/a |
6 400 |
7 200 |
||
3. Fuel |
|||||
|
average boiler efficiency |
% |
72 |
||
|
fuel oil
|
- share |
% |
5 |
|
- price |
USD/MWh |
25 |
|||
|
sawmill waste
|
- share |
% |
95 |
|
- price |
USD/MWh |
- |
|||
|
unit cost |
USD/MWh |
1.7 |
||
|
consumption of thermal energy |
MWh/a |
5 625 |
11 250 |
|
Total |
USD/a |
9 600 |
19 100 |
||
4. Auxiliary power, lubricants etc. |
|||||
|
auxiliary power demand |
kWh/MWh |
25 |
||
|
price of electricity |
USD/kWh |
0.048 |
||
|
total |
USD/MWh |
1.2 |
||
|
lubricants etc. |
USD/MWh |
0.2 |
||
|
ash removal |
USD/MWh |
0.2 |
||
|
total unit costs |
USD/MWh |
1.6 |
||
|
consumption of thermal energy |
MWh/a |
5 625 |
11 250 |
|
Total |
USD/a |
9 000 |
18 000 |
||
5. Capital costs |
|||||
|
investment costs |
USD |
320 000 |
363 000 |
|
|
annuity factor (10 %, 10 a) |
% |
16.27 |
||
Total |
USD/a |
52 000 |
59 000 |
||
6. Electrical energy |
|||||
|
consumption |
MWh/a |
540 |
1 080 |
|
|
unit price |
USD/MWh |
48 |
||
Total |
USD/a |
25 900 |
51 800 |
||
Total energy costs |
USD/a |
108 000 |
160 000 |
||
Unit energy cost |
USD/m3 |
8.00 |
5.90 |
13.4 Fuel Oil Comparison
An oil fired heat plant of the same capacity as Heat Plant A would cost 85 000 USD which is 235 000 USD less than the price of Heat Plant A. On the other hand, the energy generation based on fuel oil would cost an additional 86 000 USD per year at present oil prices and 140 000 USD more if the oil price would rise by 50 %, other prices remaining the same.
The additional investment caused by choosing the wood fired Heat Plant A instead of the cheaper oil fired plant pays itself back in 3, 3 years at present prices and in 1.9 years in the plus 50 % case.
|
Unit |
Heat Plant A |
Oil fired plant |
|
Oil price |
||||
present |
present + 50 % |
|||
Investment cost |
USD |
320 000 |
85 000 |
85 000 |
Annual energy cost at Sawmill no. 3 (excl. capital costs) |
USD/a |
56 000 |
142 000 |
196 000 |
Annual savings by Heat Plant A operation |
USD/a |
|
86 000 |
140 000 |
Pay-back time of investment in Heat Plant A |
a |
|
3.3 |
1.9 |
14.1 Description
While the drying kiln of a sawmill operates with a water temperature of 120 °C, the driers and the hot presses in panel manufacturing require at least 150 °C but often 200 °C. At these temperatures it is preferable to supply the thermal energy in the form of steam rather than warm water. Heat Plant B is designed for this purpose. Its main application is to supply the heat needed at various types of panel plants, but it could also support an integrated plant of bigger size, which has no power generation of its own. As fuel Heat Plant B uses the wood wastes of the manufacturing process and hogged wood.
The wood handling equipment is of the same type as at Heat Plant A. For particle and fibreboard manufacturing a chipper is needed at the mill. This can be used for fuel wood hogging as well. For this reason no separate chipper is included in the heat plant delivery.
The wood waste yield of plywood manufacturing covers 90...100 %, of the fuel demand. In the case of particle and fibreboard manufacturing the figure is 5...10 %. The remaining part of the fuel wood is made up of small-size roundwood or logging residues. These are either chipped at the site of logging or transported to the plant and chipped there.
At full load the fuel consumption is approximately 1.5 m3 chips per hour. The volume of the dumping silo is 20 m3.
For steam generation a three-pass flame - fire tube boiler is applied. A furnace is connected to the boiler, in which the chips are combusted on a sloping grate. The hot flue gases leave the furnace and pass through the boiler, warming and evaporating the water, and leave through the dust separator and the 20 m stack.
The boiler has a capacity of 1.1 kg saturated 15 bar steam per second. The temperature of the output steam is about 200 °C, which is enough to meet the panel manufacturing requirements. The thermal output is approximately 2.5 MW.
Fuel oil is used as pilot and supporting fuel.
The steam is used for drying and heating in the manufacturing process. While giving off heat the steam condensates and the condensate flows back to the boiler house into the condensate tank. From there it is pumped through the deaerator into the feed water tank, from where a new cycle begins.
To compensate losses in mass flow, filtered, softened and deaerated make-up water is pumped into the water-steam cycle at regular intervals.
The operating personnel consists of two boilermen and two fuel handling men per shift. In addition there are three persons - a plant engineer, a water treatment technician and a cleaner-working in the day shift only. The work at the heat plant occupies the day shift personnel only part of the time and they can have parallel duties on the industry side as well.
Heat Plant B could be delivered by turn-key arrangement. The delivery time is 10 months of which some 3 months stand for freight. An additional 2 months is to be counted for assembly and trial run.
Total transport weight is about 40 t.
14.2 Investment Costs
|
USD |
|
A. Equipment costs (F.O.B.) |
||
1. Boiler plant |
297 000 |
|
|
Three pass flame-fire tube steam boiler, 1.1 kg/s, 15 bar, 200 °C Fuel feeding and combustion equipment Water treatment equipment Pumps, pipings and tanks Measuring and control equipment Electrification I.D. fan, dust separator and stack |
|
2. Fuel handling equipment |
61 000 |
|
|
Chips handling, incl. dumping silo and feeder screws 20 m3 oil tank |
|
A. Total |
358 000 |
|
B. Construction costs |
||
3. 1300 m3 boiler house, foundations |
65 000 |
|
B. Total |
65 000 |
|
C. Miscellaneous costs |
||
4. Freight and insurance (7 %a) |
25 000 |
|
5. Clearing and transport to site (2.5 % A) |
9 000 |
|
6. Assembly (20 % A) |
72 000 |
|
7. Planning and supervision (6 % A+ B) |
25 000 |
|
8. Interest during construction (8 % A+ B) |
34 000 |
|
C. Total |
165 000 |
|
Total investment costs (A+ B+ C) |
588 000 |
14.3 Energy Costs
|
Unit |
Panel Plant |
|||||
No. 1 |
No. 2 |
No. 3 |
No. 4 |
||||
m3/a |
8 100 |
5 400 |
6 750 |
13 500 |
|||
1. Wages and Salaries |
|||||||
|
operating personnel |
|
|
4 x 3 + 3 x 1 = 15 |
|
||
|
unit cost |
USD/a |
|
490 |
|
||
Total |
USD/a |
7 400 |
7 400 |
7 400 |
7 400 |
||
2. Maintenance, Repair and Insurance |
|||||||
|
2, 5 % of equipment costs |
|
|
|
|
|
|
Total |
USD/a |
9 000 |
9 000 |
9 000 |
9 000 |
||
3. Fuel costs |
|||||||
|
average boiler efficiency |
% |
72 |
||||
|
fuel oil
|
- share |
% |
5 |
|||
- price |
USD/MWh |
25 |
|||||
|
wood waste
|
- share |
% |
95 |
8 |
||
- price |
USD/MWh |
- |
- |
||||
|
hogged wood
|
- share |
% |
0 |
87 |
||
- price |
USD/MWh |
- |
3.6 |
||||
|
unit cost |
USD/MWh |
1.7 |
6.1 |
|||
|
consumption of thermal energy |
MWh/a |
10 350 |
15 150 |
6 750 |
13 500 |
|
Total |
USD/a |
17 600 |
92 400 |
41 200 |
82 400 |
||
4. Auxiliary Power, Lubricants etc. |
|||||||
|
auxiliary power demand |
kWh/MWh |
25 |
||||
|
price of electricity |
USD/kWh |
0.048 |
||||
|
subtotal |
USD/MWh |
1.2 |
||||
|
lubricants etc. |
USD/MWh |
0.2 |
||||
|
ash removal |
USD/MWh |
0.2 |
||||
|
total unit costs |
USD/MWh |
1.6 |
||||
|
consumption of thermal energy |
MWh/a |
10 350 |
15 150 |
6 750 |
13 500 |
|
Total |
USD/a |
16 600 |
24 200 |
10 800 |
21 600 |
||
5. Capital costs |
|||||||
|
investment costs |
USD |
|
588 000 |
|
||
|
annuity factor (10 %, 15 a) |
% |
|
13.15 |
|
||
Total |
USD/a |
77 300 |
77 300 |
77 300 |
77 300 |
||
6. Electrical Energy |
|||||||
|
consumption |
MWh/a |
1 940 |
3 240 |
2 835 |
3 375 |
|
|
unit price |
USD/MWh |
|
|
48 |
|
|
Total |
USD/a |
93 100 |
155 500 |
136 100 |
162 000 |
||
Total energy costs
|
USD/a |
221 000 |
365 700 |
281 800 |
359 700 |
||
USD/m3 |
27.30 |
|
41.80 |
26.60 |
|||
USD/t |
|
67.70 |
|
|
14.4 Investment and Energy Costs; Integrated Plants
A heat plant of the same type as Heat Plant B could be connected to an integrated plant with a production mix of sawnwood, various types of panels and further refined products derived from these.
The heat demand of an integrated plant is generally bigger than of a separate panel plant, which leads to a bigger heat generating capacity and, hence, to a more expensive heat plant than Heat Plant B.
The investment and energy costs of such a plant are estimated as follows:
|
Unit |
Integrated Plant |
|||
No. 1 |
No. 2 |
No. 3 |
|||
Consumption of thermal energy |
MWh/a |
35 100 |
40 645 |
27 450 |
|
Heat plant investment cost |
USD x 103 |
1 000 |
1 060 |
1 000 |
|
Total energy costs |
USD/a |
630 000 |
717 000 |
603 000 |
|
Unit energy costs |
|||||
|
- sawnwood |
USD/m3 |
5.80 |
5.80 |
|
|
- plywood |
USD/m3 |
23.00 |
23.00 |
27.30 |
|
- veneer |
USD/m3 |
|
|
22.10 |
|
- particle board |
USD/m3 |
21.30 |
21.30 |
|
14.5 Fuel Oil Comparison
The economics of investing in Heat Plant B instead of in an oil fired heat plant are calculated in the table below. As operation costs are used the average costs of Panel Plants No 1...4.
|
Unit |
Heat Plant B |
Oil fired plant |
|
Oil price |
||||
resent |
present 50 % |
|||
Investment cost |
USD |
588 000 |
128 000 |
128 000 |
Annual energy cost (excl. capital costs) |
USD/a |
235 000 |
366 000 |
470 000 |
Annual savings by Heat Plant B operation |
USD/a |
|
137 000 |
241 000 |
Pay-back time of investment in Heat Plant B |
a |
|
4.3 |
2.2 |
15.1 Description
Power Plant C is designed to supply both heat and power for mechanical forest mills, using the residues of the mill. The power is generated by a steam engine generator set and the heat is recovered from the back-pressure steam of the engine by running it through a heat exchanger.
Because of the low temperature of the back-pressure steam, the best applications of Power Plant C are in connection with sawmills. At a production of 100 m3 sawnwood per day the daily waste yield is about 85 m3, while the fuel demand is some 50 m3 per day.
The fuel handling equipment is of the same type as at Heat Plant B. A chipper is included in the equipment list of Power Plant D because there is no such at the sawmill and bigger size wood waste must be hogged before it is used as fuel.
The steam is generated by a two-drum water tube boiler. At the bottom of the boiler there is a sloping grate on which the chips are combusted. The boiler output is 1.1 kg of 16 bar and 350 °C superheated steam per second. This corresponds a thermal output of 2.8 MW.
Ash is removed from bottom of the grate and from the dust separator by a screw, which conveys it to a cart or a container. These have to be exchanged, and emptied at regular intervals. At full load operation the ash yield is roughly 5 m3 per week.
The output of the steam engine generator is 250 kW which-is about 75 percent of the average demand of a 100 m3/d sawmill. The rest of the electrical energy must be generated by a diesel generator set or be purchased from public utilities.
As a continuous steam flow is required for sawnwood drying and the steam engine thus also could run continuously, but the sawmill only operates in one shift, there is a surplus in power generation at off-operation time of the sawmill. The selling of this surplus would improve operation economics.
The operating personnel of Power Plant °C consists of two boilermen, one engine operator and two fuel handling men per shift. In the day shift there is further a plant engineer, a water treatment technician and a cleaner working at the power plant only or alternatively at the power plant and the sawmill at the same time. The delivery time of the boiler is 7 months plus approximately 3 months for freight. Assembly and trial run takes an additional 2 months totalling 12 months between contract signing and commissioning. The corresponding time for the steam engine is 9...10 months.
The transport weights are 40 t for the boiler and Its equipment and 5...10 t for the engine set.
15.2 Investment Costs
|
USD |
|
A. Equipment costs (F.O.B.) |
||
1. Boiler plant |
340 000 |
|
|
Two-drum water tube steam boiler |
|
|
1.1 kg/s, 16 bar, 350 °C |
|
|
Boiler feed pumps |
|
|
I.D. fan, dust separator and stack |
|
2. Steam engine plant |
175 000 |
|
|
Two-cylinder 250 kW back-pressure steam engine set with condensate oil removing device |
|
|
Steam-water heat exchanger |
|
3. Water treatment |
132 000 |
|
|
Filtering, softening and deaerating equipment |
|
|
Chemical feeders |
|
|
Feed water tank |
|
4. Fuel handling equipment |
89 000 |
|
|
20 m3 dumping silo and screw feeder |
|
|
10 m2/h chipper |
|
|
20 m3 oil tank |
|
5. Auxiliary equipment |
13 000 |
|
6. Piping and insulation |
43 000 |
|
7. Instrumentation |
105 000 |
|
8. Electrical equipment |
39 000 |
|
9. HVAC |
3 000 |
|
A. Total |
939 000 |
|
B. Construction costs |
||
10. 900 m3 plant building, foundations |
45 000 |
|
B. Total |
45 000 |
|
C. Miscellaneous costs |
||
11. Freight and insurance (7 % A) |
66 000 |
|
12. Clearing and transport to site (2.5 % A) |
23 000 |
|
13. Assembly |
241 000 |
|
14. Planning and supervision (6 % A + B) |
59 000 |
|
15. Interest during construction (8 % A + B) |
79 000 |
|
C. Total |
468 000 |
|
Total investment costs (A + B + C) |
1 452 000 |
15.3 Energy Costs
|
Unit |
Sawmill No. 3 |
Sawmill No. 4 |
||
1. Wages and salaries |
|||||
|
Operating personnel |
|
5 x 3+ 3 x 1 = 18 |
||
|
unit cost |
USD/a |
490 |
||
Total |
USD/a |
8 800 |
8 800 |
||
2. Maintenance, repair and insurance |
|||||
|
2.5 % of equipment costs |
|
|
|
|
Total |
USD/a |
16 400 |
23 500 |
||
3. Fuel |
|||||
|
ratio between boiler fuel input and output of industrial heat |
% |
51 |
||
|
fuel oil
|
- share |
% |
5 |
|
- price |
USD/MWh |
25 |
|||
|
sawmill waste
|
- share |
% |
95 |
|
- price |
USD/MWh |
- |
|||
|
unit cost |
USD/MWh |
2.5 |
||
|
consumption of industrial thermal energy |
MWh/a |
5 625 |
11 250 |
|
Total |
USD/a |
14 100 |
28 100 |
||
4. Auxiliary power, lubricants etc. |
|||||
|
auxiliary power demand |
kWh/MWh |
36 |
||
|
price of electricity |
USD/kWh |
0.048 |
||
|
subtotal |
USD/MWh |
1.7 |
||
|
lubricants etc. |
USD/MWh |
0.3 |
||
|
ash removal |
USD/MWh |
0.3 |
||
|
total unit costs |
USD/MWh |
2.3 |
||
|
consumption of industrial thermal energy |
MWh/a |
5 625 |
11 250 |
|
Total |
USD/a |
12 900 |
25 900 |
||
5. Capital costs |
|||||
|
investment costs |
USD |
1 016 000 |
1 452 000 |
|
|
annuity factor (15 a, 10 %) |
% |
13.15 |
||
Total |
USD/a |
133 700 |
190 900 |
||
6. Electrical energy |
|||||
|
consumption |
MWh/a |
540 |
1, 080 |
|
|
generation |
MWh/a |
470 |
940 |
|
|
purchased power |
MWh/a |
70 |
140 |
|
|
price of electricity |
USD/MWh |
48 |
||
Total |
USD/a |
3 400 |
6 700 |
||
Total energy costs |
USD/a |
173 500 |
283 900 |
||
Unit energy costs |
USD/m3 |
12.90 |
10.50 |
||
In case the potential power generation surplus of |
MWh/a |
745 |
1 490 |
||
was sold at |
USD/MWh |
34 |
|||
annual savings of |
USD/a |
25 300 |
50 700 |
||
would be reached. This would give the unit energy cost |
USD/m3 |
11.00 |
8.50 |
15.4 Fuel Oil Comparison
The table below shows the pay-back time of the Power Plant C investment compared with an alternative, where heat is generated by fuel oil and electrical energy is purchased from public utilities. Operation costs refer to the sawmill No. 4 case.
|
Unit |
Power Plant C |
Oil fired plant |
|
Oil price |
||||
present |
present + 50 % |
|||
Investment costs |
USD |
1 452 000 |
502 000 |
502 000 |
Annual energy costs (excl. capital costs) |
USD/a |
93 000 |
275 000 |
380 000 |
Annual savings by Power Plant C operation |
USD/a |
|
182 000 |
287 000 |
Pay-back time of investment in Power Plant C |
a |
|
7.7 |
4.2 |
16.1 Description
Power Plant D generates power and industrial heat. Power is generated by a 1 MW back-pressure steam turbine generator set and the heat is supplied in the form of medium-and low-pressure steam. With a thermal output of about 8 MW and an electrical output of 1 MW the main application of this plant is in connection with integrated units of small-size mechanical forest industry mills.
At an integrated plant one unit often uses the residues of another as raw material in its manufacturing process. For this reason, the yield of combustible wood wastes at an integrated plant generally covers only part of the fuel demand.
Power Plant D uses an amount of wood wastes corresponding to 25 to 60 percent of its total fuel consumption, the rest being hogged wood and small amounts of fuel oil.
The fuel chips are stored in a pile. The wood wastes from the different units of the integrated plant are conveyed to the pile as well as the hogged fuel wood. The hogging of the fuel wood and of bigger-size wastes is done either by the chipper of the particle board plant or by a separate one.
At the bottom of the pile there is a screw discharger, which feeds the chips onto a belt conveyor. The conveyor transports the chips into a hopper at the boiler house, from where the fuel is fed into the boiler.
The steam boiler is of the same water tube design as at Power Plant C but with a bigger capacity. Its output is 3, 9 kg of 40 bar and 360 °C superheated steam per second.
To meet the different temperature requirements of the integrated plant steam is supplied both from a turbine extraction at 10 bar and 200 °C as well as from after the turbine outlet at 3 bar and 150 °C.
The generating capacity of the power plant covers approximately two thirds of the industrial power demand. The remaining part must be generated by other means or be purchased. The power output could be raised by changing the plant design. This would, however, lead to increased initial cost and a more sophisticated technology, which might not fit the conditions of developing countries.
The operating personnel is listed in the table below:
Chief technical engineer |
1 x 1 |
Power plant engineer |
1 x 1 |
Boilermen |
3 x 3 |
Turbine operator |
1 x 3 |
Fuel handling personnel |
4 x 3 |
Maintenance technicians |
2 x 1 |
Water treatment technician |
1 x 1 |
Cleaners |
2 x 1 |
(1 x 1= one person, day shift only; 3 x 3= three persons per shift.)
The delivery time of both the boiler and the turbine is 15 months including 3 months of freight time. An additional 3 months is to be counted for assembly.
The transport weight of the equipment of the boiler plant is about 200 t while the turbine set weighs some 10 t.
16.2 Investment Costs
|
USD |
|
A. Equipment costs (F.O.B.) |
||
1. Boiler plant |
688 000 |
|
|
Water tube steam boiler 3.9 kg/s |
|
|
40 bar, 360 °C |
|
|
Boiler feed pumps |
|
|
I.D. fan, dust separator and stack |
|
2. Steam turbine plant |
130 000 |
|
|
1 MW back-pressure turbine generator set |
|
|
Steam-water heat exchanger |
|
3. Water treatment |
184 000 |
|
|
Filtering, softening and deaerating equipment |
|
|
Chemical feeders |
|
|
Feed water tank |
|
4. Fuel handling equipment |
149 000 |
|
|
Pile discharger and belt conveyors 100 m3 oil tank |
|
5. Auxiliary equipment |
56 000 |
|
|
Steam conditioning valves |
|
|
Crane |
|
6. Piping and insulation |
86 000 |
|
7. Instrumentation |
132 000 |
|
8. Electrical equipment |
79 000 |
|
9. HVAC |
8 000 |
|
A. Total |
1 512 000 |
|
B. Construction costs |
||
10. 4 500 m3 plant building, foundations |
225 000 |
|
B. Total |
225 000 |
|
C. Miscellaneous costs |
||
11. Freight and insurance (7 % A) |
106 000 |
|
12. Clearing and transport to site (2.5 % A) |
38 000 |
|
13. Assembly |
387 000 |
|
14. Planning and supervision (6 % A+ B) |
104 000 |
|
15. Interest during construction (8 % A+ B) |
139 000 |
|
C. Total |
774 000 |
|
Total investment costs (A+ B+ C) |
2 511 000 |
16.3 Energy Costs
|
Unit |
Integrated Plant |
||||
No. 1 |
No. 2 |
No. 3 |
||||
1. Wages and salaries |
||||||
|
operating personnel |
|
8 x 3+ 7 x 1 = 31 |
|||
|
unit cost |
USD/a |
490 |
|||
Total |
USD/a |
15 200 |
15 200 |
15 200 |
||
2. Maintenance, repair and insurance |
||||||
|
2.5 % of equipment costs |
|
|
|||
Total |
USD/a |
37 800 |
37 800 |
37 800 |
||
3. Fuel |
||||||
|
ratio between boiler fuel input and output of industrial heat |
% |
59 |
|||
|
fuel oil |
- share |
% |
5 |
||
- price |
USD/MWh |
25 |
||||
|
wood waste |
- share |
% |
59 |
51 |
25 |
- price |
USD/MWh |
- |
- |
- |
||
|
hogged wood |
- share |
% |
36 |
44 |
71 |
- price |
USD/MWh |
3.6 |
||||
|
unit cost |
USD/MWh |
4.30 |
4.80 |
6.50 |
|
|
consumption of industrial thermal energy |
MWh/a |
35 100 |
40 645 |
23 450 |
|
Total |
USD/a |
150 900 |
195 100 |
178 400 |
||
4. Auxiliary power, lubricants etc. |
||||||
|
auxiliary power demand |
kWh/MWh |
30 |
|||
|
price of electricity |
USD/kWh |
0.048 |
|||
|
subtotal |
USD/MWh |
1.4 |
|||
|
lubricants etc. |
USD/MWh |
0.2 |
|||
|
ash removal |
USD/MWh |
0.2 |
|||
|
total unit costs |
USD/MWh |
1.8 |
|||
|
consumption of industrial thermal energy |
MWh/a |
35 100 |
40 645 |
27 450 |
|
Total |
USD/a |
63 200 |
73 200 |
49 400 |
||
5. Capital costs |
||||||
|
investments cots |
USD |
2 511 000 |
|||
|
annuity factor (15 a, 10%) |
% |
13.15 |
|||
Total |
USD/a |
330 200 |
330 200 |
330 200 |
||
6. Electrical energy |
||||||
|
consumption |
MWh/a |
6 395 |
7 135 |
5 495 |
|
|
generation |
MWh/a |
4 515 |
5 040 |
3 095 |
|
|
purchased power |
MWh/a |
1 880 |
2 095 |
2 400 |
|
|
price of electricity |
USD/MWh |
|
48 |
|
|
Total |
USD/a |
90 200 |
100 600 |
115 200 |
||
Total energy costs |
USD/a |
687 500 |
752 100 |
726 200 |
||
Unit energy costs |
||||||
|
- sawnwood |
USD/m3 |
7.00 |
7.00 |
|
|
|
- plywood |
USD/m3 |
24.90 |
23.60 |
33.30 |
|
|
- veneer |
USD/m3 |
|
|
29.20 |
|
|
- particle board |
USD/m3 |
22.10 |
20.70 |
32.60 |
16.4 Fuel Oil Comparison
The following table shows a pay-back calculation on the economics of a Power Plant D investment.
|
Unit |
Power Plant D |
Oil fired plant |
|
Oil price |
||||
present |
present + 50 % |
|||
Investment costs |
USD |
2 511 000 |
749 000 |
749 000 |
Annual energy cost, Integrated Plant No. 2 (excl. capital costs) |
USD/a |
422 000 |
1 137 000 |
1 508 000 |
Annual savings by Power Plant D operation |
USD/a |
|
715 000 |
1 086 000 |
Pay-back time of investment in Power Plant D |
a |
|
2.7 |
1.7 |
Some of the technical and economical features of Heat Plants A and B as well as Power Plants C and D are listed in the following table.
|
Heat Plant |
Power Plant |
|||
A |
B |
C |
D |
||
Output
|
- thermal |
1 MW |
2.5 MW |
2 MW |
8 MW |
- power |
- |
- |
250 kW |
1 MW |
|
Form of energy |
hot water |
medium pressure steam |
low pressure power |
low and medium pressure steam power |
|
Fuel
|
hogged sawmill waste |
hogged wood waste and fuel wood |
hogged sawmill waste |
hogged wood waste and fuel wood |
|
fuel oil |
fuel oil |
fuel oil |
fuel oil |
||
Boiler design |
warm water |
flame-fire tube, three-pass |
two-drum water tube |
one - drum, water tube |
|
Prime mover |
- |
- |
steam engine |
steam turbine |
|
Boiler output conditions |
10 bar, 120°C |
1.1 kg/s 15 bar, sat., (200°C) |
1.1 kg/s, 16 bar, 350 °C |
3.9 kg/s, 40 bar, 360 °C |
|
Fuel consumption (chips) at full load |
0.7 3/h |
1.5 m3/h |
2.0 m3/h |
6.3 m3/h |
|
Plant building volume |
220 m3 |
1 300 m3 |
900 m3 |
4 500 m3 |
|
Time of delivery and assembly |
11 months |
12 months |
12 months |
18 months |
|
Approximate transport weight |
20 t |
40 t |
50 t |
210 t |
|
Total investment cost |
320 000 USD |
588 000 USD |
1 452 000 USD |
2 511 000 USD |
|
Pay-back time of investment compared with oil fired equipment |
3.3 years |
4.3 years, |
7.7 years |
2.7 years |
The calculation of the investment costs in the above tables is based on a number of assumptions concerning the equipment list. Some items are considered belonging to the industry mill and hence omitted in this connection. If, however, this would not be the case the revised total investment cost is obtained by adding the price of the item in question to the original investment cost. Some of these prices are listed in the following table.
Item |
F.O.B. price | |
10 m3/d chipper |
(Plant B) |
28 000 USD |
40 m3/d chipper |
(Plant D) |
46 000 USD |
Front-end loader with 4 m3 bucket |
106 000 USD | |
Compressed air system, incl. compressor |
18 000 USD | |
Diesel generator sets for on-site power generation or for stand-by power |
| |
100 kW |
|
31 500 USD |
300 kW |
|
60 000 USD |
In the following table a comparison is made on the unit energy costs of some mechanical forest industry products. The unit costs are listed both for different energy supply alternatives - including fuel oil heat generation - and for different production units.
Production Unit |
Energy Supply |
Sawnwood USD/m3 |
Plywood USD/m3 |
Veneer USD/m3 |
Fibreboard USD/t |
Particle Board USD/m3 |
Sawmill No. 1 |
Public grid |
1.00 |
|
|
|
|
Sawmill No. 2 |
Public grid |
1.00 |
|
|
|
|
Sawmill No. 3
|
Heat Plant A |
8.00 |
|
|
|
|
Power Plant C |
12.90 |
|
|
|
|
|
Power Plant C 1) |
11.00 |
|
|
|
|
|
Oil I 2) |
11.60 |
|
|
|
|
|
Oil II 2) |
15.60 |
|
|
|
|
|
Sawmill No. 4
|
Heat Plant A |
5.90 |
|
|
|
|
Power Plant C |
10.50 |
|
|
|
|
|
Power Plant C 1) |
18.50 |
|
|
|
|
|
Oil I |
10.80 |
|
|
|
|
|
Oil II |
14.70 |
|
|
|
|
|
Panel Plants
|
Heat Plant B |
|
27.30 |
|
67.70 |
26.60 |
Oil I |
|
45.40 |
|
96.50 |
36.70 |
|
Oil II |
|
57.00 |
|
122.00 |
45.90 |
|
Panel Plant
|
Heat Plant B |
|
|
|
|
41.80 |
Oil I |
|
|
|
|
50.80 |
|
Oil II |
|
|
|
|
59.90 |
|
Integrated Plant
|
Heat Plant B |
5.80 |
23.00 |
|
|
21.30 |
Power Plant D |
7.00 |
24.90 |
|
|
22.10 |
|
Oil I |
11.30 |
39.60 |
|
|
34.80 |
|
Oil II |
15.10 |
51.10 |
|
|
44.10 |
|
Integrated Plant
|
Heat Plant B |
5.80 |
23.00 |
|
|
21.30 |
Power Plant D |
7.00 |
23.60 |
|
|
20.70 |
|
Oil I |
11.20 |
39.00 |
|
|
34.70 |
|
Oil II |
15.00 |
50.40 |
|
|
44.00 |
|
Integrated Plant
|
Heat Plant B |
|
27.30 |
22.10 |
|
30.10 |
Power Plant D |
|
33.30 |
29.20 |
|
32.60 |
|
Oil I |
|
41.60 |
36.40 |
|
40.90 |
|
Oil II |
|
53.40 |
48.10 |
|
49.80 |
1) Power generation surplus sold at 34 USD/MWh.
2) Oil I = heat generation by fuel oil, power purchased from public utilities. Present oil price
Oil II = like oil I. Oil price 50 % above present oil price.
The impact of a change in the price of fuel oil on the payback time of the power and heat plants was examined in connection with the plant presentation. As it is obvions that not only the price of oil, but also the price of fuel wood and wood wastes strongly affect operation economics this question will be examined here.
The operation economics - measured by the pay-back time - will be calculated for three different cases:
- the price of wood wastes rises from zero to the price level of fuel wood, i.e. 8.5 USD/t,- the price of wood wastes as well as the price of fuel wood rise by 50 % from the previous level to 13 USD/t,
- the price of fuel wood is 13 USD/t while the price of wood wastes are zero.
In addition, the pay-back time figures for present and plus 50? % oil prices are presented for the sake of comparison.
|
Initial price assumptions |
Oil price + 50 % |
Wood waste + fuel wood 8, 5 USD/t |
Wood waste + fuel wood 13 USD/t |
Fuel wood 3 USD/t |
(1) |
(2) |
(3) |
(4) |
(5) |
|
Heat Plant A |
3.3 |
1.9 |
6.3 |
8.2 |
3.3 |
Heat Plant B |
4.3 |
2.2 |
6.1 |
19 |
9.5 |
Power Plant C |
7.7 |
4.2 |
23 |
investment not paid back |
7.7 |
Power Plant D |
2.7 |
1.7 |
3.3 |
4.4 |
2.9 |
Table 18.1 Heat and power plant pay-back times (years) by different fuel prices.
By comparing the columns (3) and (4) with column (1) of the table above, it is clearly shown that the economics of wood based energy generation heavily depends on the prices of wood wastes and fuel wood. This means that if there is an alternative way of using wood wastes instead of power and heat generation, the economical advantage of combusting the waste is not as obvious as before. Only in the case of co-generation of power and heat (Power Plant D) the pay-back figures are not crucially worsened by the higher price of wood based fuel.
Column (5) indicates that panel manufacturing (Plant B) will suffer economically from a rise of the fuel wood price (wood waste cost remaining zero). This is because of the low waste yield especially at particle board and fibreboard manufacturing, leading to a high dependence on purchased fuel wood.
The conclusion to be drawn is that economical wood based energy generation is possible only if there is no alternative use for the fuel (or there is enough of it for all applications) or that the wood could be applied to generate both industrial power and heat.
On the other hand, column (2) indicates clearly, that rising oil prices improve economics rapidly, making wood based energy generation economically feasible even at higher wood prices than those initially assumed.
The aim of this study was to investigate the potential rate of self-sufficiency in energy of small scale mechanical forest industry mills in developing countries. The study was performed as a case study, in which eleven (non-existent) industrial mills were examined.
Based on the data from these mills concerning energy consumption and yield of combustible process wastes, four wood fired power and heat plants were designed. In cases where the waste yield did not cover the entire fuel demand it was assumed that hogged fuel wood, e.g. logging residues, were combusted.
In designing the power and heat plants attention was paid to chose systems, which represent proven technology and which are suited for operation in tropical conditions. To reduce investment costs as well as the need for highly educated maintenance personnel the plants were equipped with a low level of automation.
The operation costs of wood based heat and power generation were calculated both as annual costs and as cost per unit of manufactured end-product. The costs were compared with the costs of fuel oil based heat generation and power supply from public utilities.
19.1 Technology
At the present stage of technology there is no obstacle to converting manufacturing wastes into power and heat for the use of mechanical forest industries in the developing countries. The technologies of fuel wood handling and combustion, warm water and steam generation as well as steam based power generation have all reached a proven stage a long time ago.
The flue gases from wood combustion could in some cases be used directly for heating and drying purposes instead of warm water or steam generation. It is also possible to connect a prime mover directly to some mechanical device instead of using a power generator. The suitability of these alternatives must be examined case by case. Due to their rather limited number of applications they were not dealt with in the study.
Generation of combustible gases out of wood wastes looks a very interesting solution to power and heat generation.
This is particularly the case in such remote areas, where industrial operation is 100 %, dependent on on-site power generation.
Although the development in the gasification field has been rapid during the last years, the technology of gas application is not yet at a proven stage. Therefore, a producer gas engine set cannot be recommended as a supplier - at least not as the only supplier - of power for the purposes of mechanical forest industries in the developing countries.
19.2 Economics
In general, considerable savings could be gained by using wood waste instead of oil as fuel. At present oil prices the extra cost of an investment in wood based heat generation facilities is paid back by annual savings in operation costs in 3...4.5 years.
By generating not only the heat, but also the power by fuel wood, the annual savings are still increased. The pay-back time of the 1 MW wood fired power plant examined in this study was 2.7 years.
A rising oil price causes shorter pay-back times, while rising prices of wood wastes and fuel wood - indicating a lack of these or the existence of some other profitable application - leads to longer pay-back times.
Another way of evaluating the economics of wood based power and heat generation is to study the energy unit costs. These indicate how much the energy costs, that is needed to produce one unit of some end-product.
The energy unit cost of sawnwood is 11 USD/m3 when fuel oil is used but only 6...7 USD/m3 by wood-based heat or heat and power generation. At a production of 100 m3 sawnwood per day this totals an annual sawing of about 130 000 USD.
In panel manufacturing the difference between oil based and wood based energy costs are as significant as in the sawnwood case. By using wood based heat and power from the public grid a plywood plant manufacturing 30 m3 per day approximately the same amount could be saved annually.
The economics of wood based energy generation is naturally depending on the price of fuel oil. The higher the oil price gets the bigger are the savings by wood combustion and the shorter are the pay-back times of investments in wood firing power and heat plants.
There was one exception from the rule of cheap wood based energy in this study. The heat and power generated by Power Plant C - a wood fired steam boiler connected to a steam engine set - was only slightly cheaper than the oil alternative, and in one case oil was even more economical.
This was due to the considerably high investment cost caused by the steam engine, which in turn led to high annual capital costs. Regardless of the savings in fuel cost, the pay-back time of the investment was 7.7 years. This seems to be a high figure, considering the scarcity of capital in many developing countries.
To summarize, wood based heat and power generation is economically feasible at today's oil prices.
In the case of the mechanical forest industry of developing countries the main problem is to generate the funds needed for the initial investment in wood combusting equipment. Once the investment is made and the plant is in operation, the savings in fuel costs will pay back the spent money in 2...4 years, or in an even shorter time if the oil price continues to rise.
19.3 Self-sufficiency in Energy
When the yield of combustible wood wastes is regarded the sawmills and the plywood plant are the only industrial mills of those examined in this study, that are self-sufficient in fuel. To fill the fuel gap of the other mills fuel wood must be purchased. As the price of logging residues and small-size roundwood, due to the lack of alternative applications, generally is much below the fuel oil price, the use of hogged fuel wood does not affect operation economics to any significant extent.
As long as there is fuel available the heat needed in the manufacturing process can be generated at the site for instance by a warm water or steam boiler. Thus, all the industry mills of this study could be regarded as self-sufficient in heat.
Self-sufficiency in electrical energy is, however, more difficult to reach. This is because of the fact that there is a given ratio between the power output and the output of industrial heat generated by an industrial back-pressure power plant. At the plant sizes and steam pressures coming in question in this study this ratio is 0.10... 0.15. (A power plant generating 1 MW of industrial heat has a maximum power output of 150 kW.)
The ratio between power demand and heat demand at the investigated industry mills is bigger than that, normally 0.18... 0.25.
In this case there seem to be two principal solutions of reaching self-sufficiency in power generation. One is to design a power plant which by means of a more sophisticated technology would have a generation ratio between power and heat, that corresponds to the consumption ratio.
Such a plant is expensive and needs a highly skilled operating personnel, which makes it poorly suited for operation in developing countries.
The other solution could, in spite of its slightly higher cost of operation, prove quite satisfactory in the operating conditions of developing countries. It is consisting of a power plant of simple design, which covers a certain part, say two thirds, of the power demand. The rest would be generated by a diesel set. This would lead to rather low initial costs and still to reduced energy costs as only part of the power is generated by fuel oil and the rest, plus all the heat, is generated by wood.
The diesel power could of course be replaced by power purchased from the public grid in those cases public power would be available.