生物质热电技术简介（英文版）_28页-1mb

Summary of Biomass for Heat and Power

Core Content

Biomass, defined as organic matter from plants or animals, plays a significant role in energy production, encompassing traditional uses like heating and cooking, as well as modern applications such as combined heat and power (CHP) generation and biofuels. It accounts for approximately 10% of global energy demand, or 51 EJ, with a large portion (27 EJ) used in traditional woodstoves in developing countries. Modern biomass-based electricity generation supplies about 1.5% of global electricity demand, equivalent to 280 TWh.

Main Views and Key Information

Biomass Utilization and Its Characteristics

• Multi-dimensional role: Biomass is used for food, feed, fibre, and energy, often on the same land, and supports ecological goals such as biodiversity, GHG emission reductions, and landscape development.
• Efficiency and cost: Biomass has lower energy density than fossil fuels, and its use is economically viable when local resources are available and coal needs to be imported.
• Seasonal fluctuations: Due to its biological nature, biomass supply can vary seasonally and annually, making feedstock availability and cost a critical factor for project sustainability.
• Policy importance: An effective policy mix is necessary to enhance biomass utilization while mitigating trade-offs. National targets and economic incentives like Feed-in Tariffs (FITs) or tax credits are commonly used, but must be carefully managed to avoid financial burdens.

Technology and Process Status

• Traditional vs. modern uses: Traditional uses are prevalent in developing countries, while modern high-efficiency technologies such as CHP and gasification are growing globally.
• Key technologies: Fluidised bed combustion (FBC), co-firing with coal, and CHP are the most widely used technologies. FBC includes bubbling fluidised-bed combustion (BFBC) and circulating fluidised-bed combustion (CFBC), both offering high efficiency and low emissions.
• Boiler types: Water-cooled vibrating grate (VG) boilers are common for wood residues, with capacities around 10 MWe. CFBC is suitable for both large and small-scale applications due to its flexibility.
• Efficiency ranges: Biomass-based CHP plants have overall efficiencies between 70%–90%, while biomass co-firing in coal plants can achieve 36%–44% efficiency.

Pre-treatment and Upgrading Technologies

• Common pre-treatment methods: Drying, pelletisation, and torrefaction are used to improve biomass handling, transportation, and combustion efficiency.
• Torrefaction benefits: Increases energy density by 25%–30% and makes biomass properties closer to coal.
• Pyrolysis: Produces bio-oil with twice the energy density of wood pellets, suitable for long-distance transportation.

Cost Analysis

• Investment costs: Range from USD 4000/kW to USD 7000/kW for biomass-based power and CHP.
• Retrofitting costs: For co-firing in coal plants, retrofitting costs range from USD 140–850/kW.
• O&M costs: Typically between 3%–5% of capital costs, depending on plant size.
• Feedstock costs: A major component of total electricity production costs, ranging from negative to no-cost for waste, USD 0–4/GJ for processing residues, USD 4–8/GJ for local feedstock, and USD 8–12/GJ for internationally traded feedstock.

Potential and Barriers

• Biomass availability: A key factor for bioenergy utilization. It is widely used in regions with ample wood or agricultural residues.
• Market stability: Essential for investors and developers. Policies such as FITs help in market expansion but must remain stable to ensure long-term viability.
• Sustainability challenges: Competition with non-energy uses, GHG emission trade-offs, and environmental/social impacts (e.g., biodiversity, food security) need to be managed through comprehensive sustainability frameworks and certifications.

Case Studies and Examples

• Biomass CHP plants: Examples from countries like Germany, Finland, and the UK show varying capacities and efficiencies, with most operating between 2–100 MWe.
• Electric efficiency: Varies by feedstock and technology, with advanced steam parameters contributing to higher efficiencies.
• Emissions: Biomass CHP plants must comply with strict EU emission limits, with NOx, SOx, CO, and particle emissions reported in Table 2.

Co-firing in Coal Plants

• Advantages: High efficiency, existing coal infrastructure, and potential for reduced GHG emissions due to lower nitrogen content in biomass.
• Challenges: Requires boiler retrofitting, specific logistics, and tailored flue gas cleaning equipment.
• Emission levels: NOx emissions range from 150–300 mg/Nm³, depending on the technology and retrofitting level.

Anaerobic Digestion for Wet Biomass

• Small-scale application: Anaerobic digestion is used to produce biogas from wet biomass, which can then be used for CHP or upgraded to biomethane for use in gas grids or vehicles.
• Efficiency: In the Netherlands, gas engines using biogas have electric and thermal efficiencies reported in Figure 10.

Conclusion

Biomass offers a versatile and renewable energy source with a wide range of applications, from traditional heating to modern CHP and electricity generation. While its low energy density and seasonal supply fluctuations pose challenges, proper pre-treatment, efficient logistics, and supportive policies can enhance its viability. A balanced approach that considers economic, environmental, and social impacts is essential for sustainable biomass utilization.