Practical Issues of Co-Firing and Gasification of Biomass October 28, 2003

Transcription

1 Practical Issues of Co-Firing and Gasification of Biomass October 28, 2003 IEA Bioenergy Joint Task Meeting

2 Practical Issues of Biomass One Environmental philosophy: Think Globally, Act Locally For renewable energy applications in biomass this is particularly true. This presentation looks at the technical, political, economic issues associated with co-firing & gasification of biomass in the Upper Midwest region of United States

3 Outline Background of Alliant Energy fleet and biomass programs Presentation will focus on the four major issues that impact the viability of biomass for co-firing with coal and for gasification: Political drivers Economic drivers Environmental drivers Technology issues

4 Alliant Energy Generation Plants Regulated Utility - - constrained by rate-regulation Must comply with regulation Must provide the most economic generation - - including consideration for long-term reliability, fuel costs, capital costs, and operation & maintenance costs. State of Iowa has Renewable Portfolio Standard, but otherwise, there is no requirement for CO2 reduction. Biomass-fueled generation is most often not the lowest cost, but can compete with incentives, such as tax incentives.

5 Alliant Energy - Utility Fuel Mix Chart based upon energy not on capacity. Fuel mix does not include the fuels for BioFuels Corp gasification plant Gas Oil 1.78% Hydro 0.20% 0.89% Nuclear 14.46% Coal 56.63% Purchased 24.46% Wind 1.58%

6 Biomass Technologies at Alliant Direct Combustion - - at base-load coal facilities Co-firing 40,000 to 70,000 tons per year of resifil (residue from manufacture of furfural from oat hulls) co-fired with coal. Co-fire landfill gas Co-fire test of dedicated-energy crop (switchgrass) at Ottumwa Generating Station MW of biomass in 700 MW t-fired boiler Gasification - - at 6 MW stand-alone plant Uses corrugated cardboard rejects & obsolete seed corn Other projects, not included in this discussion Pyrolysis - - performed study to utilize agricultural residues for bio-chemicals and electric energy. Digesters - - to generate methane from animal wastes Electric generation from reciprocating engines and micro-turbines

7 Biomass Energy Feedstocks Midwest Biomass Sources Grain Processing Livestock Waste Bio-Crops &Ag-Waste Food Processing Municpal Waste Ethanol Dairy Poplar Trees Cheese Landfills Wet Corn Milling Soybean Swine Poultry Switch grass Corn Stover Vegetables Cattle/Hog Processing Waste Treatment Refuse Other Midwest has large volumes of biomass fuels 7

8 Political drivers United States has not committed to CO2 reductions, except with voluntary programs. However, there are tax and policy incentives that support & encourage bioenergy production. In the short term, political focus for coal is on reduction of traditional environmental pollutants plus capture of mercury from coal. In the long-term the research focus for electric generation is on near-zero emissions power plant. After September 11, 2001, focus of energy issues has shifted to security and sustainability of transportation fuels Bioenergy programs shift to bioproducts and biochemicals feedstocks

9 Economic drivers Recall that regulated utilities must provide the most economic generation. Typical fuels costs: Coal fuel costs US$ to US$ per KWHr (for typical base-load plant) Natural Gas costs US$ to US$ per KWHr (for typical peaking plant) Can renewable fuels compete with these prices, without subsidies?

10 Economic factors Green Energy Pricing Program Voluntary program for customers to pay US$ 0.02 per KWH price premium for energy derived from renewable sources. Environmental emissions credits to the extent that renewable fuels has less Sulfur than coal (all emissions of SO2 must be accompanied by an emissions allowance for which a market exists). At the present time U.S. Congress is debating changes to energy legislation that would provide a production tax credit (PTC) for biomass energy. Similar tax credit exists for wind energy (approximately US$ 0.018/KWH). Iowa requires 2% of our energy to be derived from renewable sources. We currently meet this regulation by purchase of wind energy. Therefore, biomass sources must compete with wind energy for this market.

11 Biomass Energy Economics Cost of Energy from Conventional Co-firing Combustion Cost of Electricity compared to feedstock prices, with various conditions, incentives, or subsidies Typical biomass Cost (US$ per ton) PTC proposed production tax credit Incentive, e.g., Green Pricing Premium Acknowledgement: Graph provided by Antares Group Inc 11

12 Environmental Drivers Some dedicated energy crops may provide superior environmental benefits. For example, since prairie grass is a perennial plant, it provides more complete protection from soil erosion, less impact to surface waters, and may provide more benefits for wildlife habitat. The implications for NOx, particulate, SOx, and mercury emission continues to be the subject of research. Depending upon cultivation methods, there can be emission benefits compared to coal. At the present time the United States has not made formal commitments to CO2 reductions, although Alliant Energy participates in voluntary programs.

13 Alliant Energy co-firing projects Sixth Street Station Prairie Creek Station Ottumwa Generating Station

14 Sixth Street Station Three small units originally designed for poor quality Iowa coal Furfural byproduct (resifil) is transported pneumatically from Quaker Chemical to power plant Quality: Iowa Coal PRB Coal Resifil BTU/ pound Moisture (%) to to 30 Sulfur (%) 5 to Issues Resifil has low ph and is abrasive to transport piping, diligent pipe maintenance is required. Product was co-mingled with coal for best pulverization. Separate pulverizer and separate (poorly designed) burner provided poor result.

15 Prairie Creek Station Landfill gas % methane Supplied from landfill that is several miles away Gas collection and processing by independent agent Landfill issues are water removal and disposal Hazardous constituents separation Maintenance to collection system due to subsidence Maintenance of compressor equipment due to corrosion

16 Ottumwa Co-firing Project Ottumwa Generating Station is 700 MW, T-Fired boiler. Project envisions burning 200,000 tons of switchgrass per year from 50,000 acres within 40 km radius of plant to supply as much as 5% of the energy input. Test program during year 2001 demonstrated the principle of co-firing at this plant.

17 Ottumwa Generating Station Project is expected to provide 5% of the energy input to the base-load generator from switchgrass. Quality: Heat content (BTU/pound) Moisture % Volatiles % Sulfur % K2O % P2O5 % SiO2 % PRB Coal to Switchgrass to

18 Switchgrass, a warm season grass native to Iowa, can reduce soil erosion, requires relatively low inputs, grows well on marginal soils, and adds significant amounts of carbon to the soil as a sequestering method for atmospheric CO2.

19 Environmental Impacts of Biomass Reduces soil erosion rates compared to crop production on marginal land Reduces potential for sediment and chemical delivery from land in biomass

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23 Issues from Co-firing Logistics associated with handling high-volume and low-bulk density (compared to coal). No established transport infrastructure. Because transport air to grass-burner was not preheated, and volume was predicated on transport properties, not combustion, there was no observable NOx emission benefit in early testing. Switchgrass has a node, where the leaf attaches to the stem, that is a concern for complete combustion. Agriculture industry has worked for 100 years to breed plants with high nutritional value; but we need high heat-content and low mineral content - - some plant breeding would be beneficial.

24 More Issues from Co-firing There is more experience with wood-wastes than with herbaceous products. Herbaceous has more alkali-minerals which corrosion & slagging Storage, handling, and size-reduction is very different High potassium and phosphorus content of ash

25 Gasification of biomass Biofuels Corporation project: 6 MW Idaho Products gasifier (designed for wood-chips) Boiler designed for clean fuel-gas, not syngas Fuel consumed: Obsolete seed corn Corrugated cardboard recycling rejects Issues encountered Gasifier control problems with variable fuel input Gasifier bed-agglomeration Excess boiler deposits

26 Gasification of biomass Fuels for this installation are very different. Since the delivery quantities are variable, the fuel mix varies dramatically from day to day. Fuel Characteristics: Moisture (%) Heat Content (BTU/lb) Percent of fuel mix Cardboard rejects with plastic 40 8,000 to 11, to 60 Cardboard rejects w/o plastic 50 to 60 4,000 to 5, to 20 Old seed grains Less than 15 7,000 to 8, to 30 Other (saw dust, packing materials) Less than 20 6,000 to 8,000 5 to 10

27 Summary Each biomass fuel provides a unique opportunity but also has specific characteristics that must be accommodated in the boiler. Each biomass may hold its own surprises for handling characteristics, environmental impact, and combustion performance. There are a large number of economic and political variables (some may be local circumstances). Each application must be independently evaluated because the economic of political variables may not always add-up the same. Thank you for your attention. Questions?