and traditional power generation
using fossil fuels lie in the need for
pretreatment of biomass feedstock
and in the design requirements for
biomass boilers, which guarantee
effective combustion, heat transfer
efficiency, and stable long-term
operation using crop straw residues.
Table 3.8: Scoring for Direct Crop Straw Combustion
Criteria Score Comments
Technical
Evaluation ★★★★
This technology has several advantages: a fairly large construction scale, high- energy conversion efficiency, and no secondary pollution. Several technical prob- lems still need to be solved, including boiler corrosion and slag formation, fuel pretreatment, technological localization, and domestic manufacturing develop- ment. With several new straw-fired power plants being put into operation, such technical obstacles can gradually be overcome.
Economic
Assessment ★★★
Plants require collection and transporting of large amounts of biomass to the plant site. These costs can be high and need to be managed well.
Economic and financial returns are lower than the gasification option because it currently relies on imported (expensive) technology.
A sample direct combustion power plant with 25 MW of installed capacity entails an initial investment of CNY308,420,000 and payment of CNY29,500,000 in annual operation and maintenance costs, while resulting in an annual benefit of CNY72,600,000; so the FIRR is 11% and EIRR is 16%.
Environmental
Impact ★★★
Operation of biomass power plants can significantly reduce field-burning of crop straw in rural areas, thereby reducing air pollution and improving the rural envi- ronment. Compared with the same-sized coal-fired power plant (1.38 gigawatts per year), a crop residue power plant can save more than 100,000 tons of coal
and reduce 400 tons of SO2 emissions.
Through the modern technology, burning crop residues instead of coal does not produce harmful waste gases, making desulphurization and NOx scrubbing un- necessary.
Operation of a 25-megawatt biomass power plant could reduce carbon dioxide emissions by 100,000 tons per year, compared with the same-sized coal power plant. The smoke and dust produced has no water-soluble component, so discharged wastewater needs no special treatment, except filtering of suspended particles. The ash residue from biomass combustion can be used as a high-quality potas- sium fertilizer.
Social Impact ★★★★
Farmer revenue from crop straw sales to biomass power plants can have signifi- cant economic impacts, especially in poverty-stricken agricultural counties that have sufficient biomass resources.
A household with four family members could earn about CNY600 in crop straw sales, equivalent to 40% annual income of poor farmers in western provinces. Employment opportunities will mainly come from construction and operating jobs at power plants and in collecting crop straw.
Comprehensive
Result ★★★1/2
Table 3.9: Scoring for Co-combustion of Coal and Crop Straw
Criteria Score Comments
Technical Evaluation ★★★★★
The boiler design does not need to be changed as long as energy content of the crop straw is not more than 20% of total heat input to the boiler. The critical elements of the technology are the crop straw handling, preparation, and feed equipment needed to get proper mixing of the coal and biomass to ensure good combustion of the mixture.
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Table 3.10: Cost–Benefit Analysis for Power Generation from Straw Technology Number of Plants Initial Investment (CNY) Annual O&M Cost (CNY) Annual Economic Benefit (CNY) Net Benefit (CNY) EIRR (%) FIRR (%) Benefit– Cost Ratio Payback Period (years) Direct Crop Straw
Combustion 25 308,420,000 29,500,000 72,600,000 57,543,910 16 11 1.46 5.4
Co-Combustion of Coal and Crop
Straw 32 83,570,000 7,360,000 35,162,400 47,763,394 53 30 3.55 1.7
Criteria Score Comments
Economic Assessment ★★★★★
A sample power plant for co-combustion of coal and straw with a 32-MW installed capacity entails an initial investment of CNY83,570,000 and pay- ment of CNY7,360,000 in annual operation and maintenance costs, while resulting in annual benefits of CNY35,162,400, so the FIRR is 30% and EIRR is 53%. This assumes 10% biomass co-firing (although 20% is technically possible).
Environmental Impact ★★★ Co-combustion of coal and crop straw for power generation at existing coal
power plants has good environmental and social effectiveness, as do the other crop straw technologies.
Social Impact ★★★
Comprehensive Result ★★★★
Table 3.9 continued
also be able to negotiate economic arrangements for the collection and transportation of raw materials within the power plant’s collection radius to reduce long-term supply risks and keep supply lines short. Also, crop residues are highly seasonal and arrangements are needed to store the biomass resources to ensure a stable supply to the plant over the course of a year. Farmers’ participation also relies on such arrangements.
Thus, it is important to develop clear organizational arrangements between farmers and power plants. The following two arrangements are possible:
The “company + household” model. The
power plant directly signs an agreement with rural households on annual supply of crop straws, and the power plant purchases the raw materials according to the contract signed. In this arrangement, the plant must manage a large number of contracts and organize the collection, storage, and transportation of the crop straw.
The “middlemen” model. The power plant
signs an agreement with one or more supply agents, who purchases the crop straw from the farmers and arranges for the collection, storage, and transportation to the power plant. In this arrangement, the power plant can establish a fixed price with the middleman, which provides more certainty to their economics. See Figure 3.3. The latter model may be more prevalent and has been adopted in pellet/briquette fuel production. Given the typical county-sized collection radius, county governments can also play an important role in facilitating and mediating between power plants