Renewable Energy Technology Assessments - Kauai Island Utility ...
Renewable Energy Technology Assessments - Kauai Island Utility ... Renewable Energy Technology Assessments - Kauai Island Utility ...
Kaua’i Island Utility Cooperative Renewable Energy Technology Assessments 3.0 Renewable Energy Technology Options Kauai Outlook As discussed in the previous section, there are a large variety of potential biomass fuels on the island that could be used to supplement coal. However, the outlook for cofiring biomass with coal clearly depends on the development of a new coal-fired power plant on the island. Without coal or any near term plans for coal, cofiring is not a viable option. The last Kauai Electric Integrated Resource Plan (1997) identified a potential 24 MW coal capacity addition in 2014. Biomass could be a meaningful and cost effective contributor to the fuel mix for this plant. It is likely that up to 25 percent of the heat input could be feasibly (technically and economically) provided by biomass. This would generate about 40 GWh/yr assuming an 80 percent capacity factor. Considering this addition, the developable potential for biomass cofiring is summarized in the following table. Year Energy, GWh Table 3-5. Developable Potential from Biomass Cofiring. Capacity, MW 3 0 0 5 0 0 Notes Potential is not limited by resource, but coal capacity. Last IRP called for 24 MW of coal capacity in 2014. 10 42 6 Assumes cofiring biomass at 25 percent of 24 MW coal plant at 80 percent capacity factor. 20 84 12 Assumes another 24 MW unit is added, with similar cofiring. 3.2 Biogas The biogas technology characterization generally pertains to the products of anaerobic digestion of manure and gas produced from landfills. The following sections detail the formation of these fuels and how each can be used to produce useful energy. 3.2.1 Anaerobic Digestion Anaerobic digestion is the naturally occurring process that occurs when bacteria decompose organic materials in the absence of oxygen. The byproduct gas has 50 to 80 percent methane content. The most common applications of anaerobic digestion use industrial wastewater, animal manure, or human sewage. According to the European Network of Energy Agencies’ ATLAS Project, the world wide deployment of anaerobic digestion in 1995 was approximately 6,300 MWth for agricultural and municipal wastes. 21 March 2005 3-14 Black & Veatch
Kaua’i Island Utility Cooperative Renewable Energy Technology Assessments 3.0 Renewable Energy Technology Options This is estimated to increase to 20,130 MWth in 2010 with the majority of that growth being in municipal wastewater digestion. Applications Anaerobic digestion is commonly used in municipal wastewater treatment as a first stage treatment process for sewage sludge. Digesters are designed to convert the organic material or sewage sludge into safe and stable biosolids and methane gas. The use of anaerobic digestion technologies in wastewater treatment applications is increasing because it results in a smaller quantity of biosolids residue compared to aerobic technologies. Power production is typically a secondary consideration in digestion projects. Increasingly stringent agricultural manure and sewage sludge management regulations are the primary drivers. In agricultural applications, anaerobic digesters can be installed anywhere there is a clean, continuous source of manure. It is highly desirable that the animal manure be concentrated, which is common at dairy and hog farms. (Poultry litter is dryer and more suitable for direct combustion.) Dairy farms use different types of digesters depending upon the type of manure handling system in place at the farm and the land area available for the digester. A 600 to 700 head dairy farm generally produces sufficient manure to generate about 85 kW. Hog farms typically use simple lagoon digesters because of the wetter manure and generate approximately 50 kW for every 500 swine. Figure 3-4. 500 m 3 Digester Treating Manure from a 10,000 Pig Farm in China. 8 8 Image source: Perdue University, http://pasture.ecn.purdue.edu/~jiqin/PhotoDigester/PhotosDigesters.html. 21 March 2005 3-15 Black & Veatch
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Kaua’i <strong>Island</strong> <strong>Utility</strong> Cooperative<br />
<strong>Renewable</strong> <strong>Energy</strong> <strong>Technology</strong> <strong>Assessments</strong><br />
3.0 <strong>Renewable</strong> <strong>Energy</strong> <strong>Technology</strong><br />
Options<br />
This is estimated to increase to 20,130 MWth in 2010 with the majority of that growth<br />
being in municipal wastewater digestion.<br />
Applications<br />
Anaerobic digestion is commonly used in municipal wastewater treatment as a<br />
first stage treatment process for sewage sludge. Digesters are designed to convert the<br />
organic material or sewage sludge into safe and stable biosolids and methane gas. The<br />
use of anaerobic digestion technologies in wastewater treatment applications is increasing<br />
because it results in a smaller quantity of biosolids residue compared to aerobic<br />
technologies. Power production is typically a secondary consideration in digestion<br />
projects. Increasingly stringent agricultural manure and sewage sludge management<br />
regulations are the primary drivers.<br />
In agricultural applications, anaerobic digesters can be installed anywhere there is<br />
a clean, continuous source of manure. It is highly desirable that the animal manure be<br />
concentrated, which is common at dairy and hog farms. (Poultry litter is dryer and more<br />
suitable for direct combustion.) Dairy farms use different types of digesters depending<br />
upon the type of manure handling system in place at the farm and the land area available<br />
for the digester. A 600 to 700 head dairy farm generally produces sufficient manure to<br />
generate about 85 kW. Hog farms typically use simple lagoon digesters because of the<br />
wetter manure and generate approximately 50 kW for every 500 swine.<br />
Figure 3-4. 500 m 3 Digester Treating Manure from a 10,000 Pig Farm in China. 8<br />
8 Image source: Perdue University,<br />
http://pasture.ecn.purdue.edu/~jiqin/PhotoDigester/PhotosDigesters.html.<br />
21 March 2005 3-15 Black & Veatch
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