Technical Aspects of the Development of Dendro-power
There is a range of well proven and established technologies that can be used for either the production of usable heat or for power, or for both. The choice depends on the power required and the level of support that can be provided. For situations where the power requirement is geared towards a small community or estate (100 kW) then the developer
has the choice of :-
- Small-scale gasifiers linked to an internal combustion (IC) engine
- Pyrolysis linked to an IC engine
- Fuel substitution using bio-diesel or ethanol
- Stirling engine
As well as the basic steam-based power unit.
At a larger scale (around 2MW) then the choices change to :-
- Steam turbine
- Gasifiers linked to gas turbines
As size of the installation increases then more advanced gasifier technology is appropriate with fluid bed systems becoming more appropriate for systems over 5MW. Any choice of biomass fuelled power plant will depend upon the scale of operation and the feedstock characteristics. An analysis of the current situation of developments in the technology is presented in the conference paper prepared by A. Hollingdale of NRI.
View Paper [PDF 389Kb]
In terms of experience gained in Sri Lanka, reference should be made to the conference paper prepared by Mr L.P. Jayasinghe, the President of BEASL.
View Paper [PDF 511Kb]
Target characteristics and specification of parameters for a 3 MW rated biomass-fired steam turbine system would typically be:
| Annual operational hours | 8,000 hours per year |
| Fuel rating at 20% moisture | 4 tonne/hour |
| Average LHV of biomass fuel | 3,300 Kcal/kg |
| Working temperature of furnace |
950- 1000 deg C |
| Minimum volume of combustion chamber |
75 m3 |
| Capacity of starter burner |
800,000 Kcal/hour |
| Starter fuel consumption |
150 kg diesel oil |
| Superheated steam temperature |
500 deg C |
| Superheated steam pressure |
41 bar |
| Steam produced |
13.4 tonne/hour |
| Flue gas flow |
34,000 Nm3/hour |
| Turbine power output |
3,000kW |
| Internal system power requirements |
300kW |
| Energy efficiency of system |
20% |
| Ash disposal |
< refuse standards |
| Gaseous emissions (CO, dust, NOx, SO2, volatile organics, etc.) |
< pollution standards |
The basic elements of a biomass-fired steam turbine technology system are typically:
- Fuel storage and pretreatment (drying or size reduction) as required
- Screw feeder to transport fuel onto grate
- Combustion chamber and steam generator
- Axial flow steam turbine
- Condenser
- Flue gas treatment and chimney
- Water treatment for boiler feed water
- Cooling water supply
In looking at the choice of appropriate technologies, attention has to first be made to whether the unit is to serve the community directly in an off-grid capacity or whether the intention is to establish a commercial unit capable of feeding the grid. This aspect is considered from the following links. From this page, the types and units available and the variables that need to be considered and issues related to connectivity is made, as well as a review of future trends in generation within the Sri Lanka context.
More information on grid connection and off-grid generation
As part of the whole issue of planning the future location of dendro-power units (whether they be linked to the grid or to serve a community with no short-medium term expectation of being connected to the national grid), there are a series of variables that need to be considered: for example; population distribution, land availability for fuelwood production, growth conditions for the crop (rainfall, soils) as well as the perceived demand and interest of the community taking part in such a venture. One way of assisting in national and regional planning is to overlay as many of these variables as we can in the form of Geographical Information System (GIS) and to get a combined integrated view of what seems to be the most economically viable locations.
As well as the role of wood and agricultural waste in the development of electrical power, an important aspect is the continuing role of such material for heat energy. This is particularly important in S. Asia where fuelwood and such material as rice husk has been used for tea and tobacco drying. Further consideration of the industrial use of heat energy is provided with particular emphasis on the situation in Sri Lanka.
More Information on industrial heat energy
In terms of the overall energy budget, the use of wood still dominates the energy equation of most developing countries. This particularly relates to the household sector and small enterprises making use of wood for cooking and fuelling kilns. An analysis of the household sector is provided for Sri Lanka including an assessment of the role of biogas.
More Information on the household sector
As the cost of fossil fuels become more and more expensive, the economics of using biofuels becomes more desirable. In Europe, a directive on the Promotion of the use of Biofuels for Transport proposes a target of 5.75% for the share of biofuels to be used in the transport sector by 2010. In Cambodia for example, there has been recent interest in the use of the crop Jatropha curcas for bio-diesel as well as in such places as Indonesia and India. This is discussed further in a paper prepared by Andrew Williamson of the Cambodian Research Centre for Development.
View Paper [PDF 508Kb]
Consideration of the issues related to the development of bio-fuels for Sri Lanka are considered further on the webpage covering The Transport Sector.
More information on the Transport Sector
The Economics of Dendro-Power
In this section we examine the economics of dendro-power and ask the quetion how much will it cost to establish a moderate-sized generation plan, how much will it cost to operate and how will this compare to operation from the use of coal. Again the examples are drawn from Sri Lankan and Indian experience. Costs are given in Sri Lankan rupees (Rs), which can be taken to be equivalent of a US cent, i.e. 100 Rs = 1 US$, or more precisely 102 Rs = 1 US$.
| Dendro | Coal | Biomass | |
| TECHNICAL | |||
| Plant Capacity MW | 10.00 | 10.00 | |
| Dollar Parity Rs/ Us$ | 102.00 | 102.00 | |
| Cost of fuel delivered /kg dry | 2,000.00 | 6,000.00 | |
| Interest rate | 10.00% | 10.00% | |
| O D Rate | 12.00% | 12.00% | |
| Capital Cost US$/KW | 1,000.00 | 1,200.00 | |
| Tariff Rs/KWh | 8.50 | 8.50 | |
| Internal Consumption % | 10.00% | 10.00% | |
| No of Days Run/Yr | 330 | 330 | |
| Specific Fuel Consumption kg/kwh | 1.50 | 0.50 | |
| Calorific value Kcal/kg | 3,700.00 | 6,000.00 | |
| Overall Efficiency | 15.52 | 28.71 | |
| FINANCIAL | |||
| ROC (Return on Capital) | 17.65% | 12.43% | |
| ROSE | 93.31% | 35.52% | |
| IRR over 7 years | 13.06% | 7.85% | |
| IRR over 20 years | 19.42% | 15.20% | |
| Payback Period (Yrs) | 5.67 | 8.05 |
A detailed breakdown of the capital and recurrent costs involved with the establishment and operation of a dendro-power unit of 10MW can be accessed here. As indicated above, the figures suggest that the IRR over 20 years is expected to be close to 19%, with a payback period of 5.7 years. Total capital costs would be of the order of $11.8 million.
The main assumptions made for this calculation are provided on the spreadsheet. It is assumed that the wood consumption of 1.5 kg/kwh. The plant would produce an output of 71,280,000 KWh on the basis of operation of 330 days/year with 10% of the power being used internally. Total amount of wood that will be required will equal 118,800 tonnes/year at a cost of Rs. 2,000/tonne.
View Paper [PDF 154Kb]
A similar spreadsheet has been prepared for a similar plan operating from coal. Capital investment of around $14.4 million will be required. The figures are based on the consumption rate of 0.5 kg/kwh. The IRR is estimated to be around 15% over 20 years with a payback period of 8.0 years. The cost of coal is taken to be Rs. 6,000/tonne For simplicity, in both cases a constant rate of Rs. 8.50/kwh - the current rate.
View Paper [PDF 160Kb]
Subsections
Supported by the European Union under the Asia Pro-Eco Programme