CHAPTER 2 BIOMASS SOURCES

Transcription

1 CHAPTER 2 BIOMASS SOURCES 2.1 BIOMASS SOURCES University-generated biomass considered for the CURBI project includes renewable energy crops, food waste from the dining halls, manure and bedding from various animal research operations, woody biomass from University-owned forests, and crop wastes. Although Cornell University owns agricultural research facilities throughout New York State, only biomass generated within a 25-mile radius of the proposed CURBI site was considered for this feasibility study. A map of the potential biomass feedstock source locations is shown as Figure 2-1, showing the relative travel distances from the CURBI facilities. Biomass yield and cost information included in this chapter was obtained from Cornell University summaries prepared by Peter Woodbury, Andrew Lewis, and Paul Jennette, based on 2008 estimates. A. Renewable Energy Crops. Cornell University operates over 3,500 acres of agricultural research fields that produce a variety of biomass feedstocks. Using a conservative estimate of 4 dry tons/acre/year yield (typical for switchgrass in the Northeastern U.S.) produced on 2,000 acres of Cornell cropland, 8,000 dry tons/year of renewable energy feedstock could be available to feed the CURBI processes. Field trials of willow biomass in Central New York have produced yields of 3.7 to 5.2 dry tons/acre/year. Establishment costs of switchgrass and meadow grass have been estimated at $210/acre, while for willow they are $1,100/acre, including seed, machinery operating costs, fertilizer, and chemical treatments. On a short-term basis, use of grass for biomass feedstocks is less expensive; the advantage of willow is that it can be harvested on a three-year rotation for up to six or seven rotations without requiring re-establishment. Additional development of harvesting and feedstock preparation equipment will facilitate increased use of willow biomass feedstock for biomass-to-energy projects. A summary of the most recent estimate of available biomass is included as Table 2-1. At the production rate and energy content shown in the table, Cornell produces a potential energy source of nearly 300,000 million BTUs/year from University-owned land and facilities

2 B. Organic Waste. Cornell currently treats over 8,000 tons/year of organic waste using static compost piles located on Stevenson Road, approximately 2 kilometers from the University s central campus. Currently, the organic compost is used for University landscape operations and is sold to local residents and landscaping businesses. Most of the waste currently used for compost could be converted to energy using the CURBI processes. The composting process would be the standby treatment process for the crop wastes and dining hall wastes if the processes need to be shut down for maintenance activities. 2.2 BIOMASS CHARACTERISTICS Biomass feedstocks vary widely in seasonality, moisture content, and handling characteristics. CURBI would employ a variety of alternate biomass-to-energy technologies to take advantage of varying characteristics of the biomass feedstocks. A graphical depiction of the varying biomass characteristics is shown in Figure FIGURE 2-2 BIOMASS CHARACTERISTICS Ash Content (percent) 30 Bedded Manure Cow Manure Pig Manure Straw Wood Grass Green Waste Moisture Content ( percent) Adapted from Phyllis Database, Energy Research Centre of the Netherlands, From Figure 2-2, two sorts of biomass streams can be characterized. Dry streams would include sawdust, wood, straw, and dried grass crops. Wet streams would include manure, food waste, green crops, and alkaline hydrolysate from the Cornell College of Veterinary Medicine

3 (CCVM) operations. It is a goal of CURBI to advance research on combining wet and dry streams to provide biomass sources with optimal characteristics for energy production. Dry streams are regarded as most suitable for thermo-chemical processing technologies, such as direct combustion and pyrolysis, since removing moisture from wet wastes consumes energy by the heat of vaporization, and therefore reduces the available amount of energy from the process. Anaerobic digestion and dry fermentation produce energy in the form of biogas under similar conditions. Wet anaerobic digestion can be used to produce energy from liquid manure, food waste, and alkaline hydrolysate, while dry fermentation is appropriate for drier biomass such as pack manure, grass, and drier food wastes. Excess heat from the processes is used for local thermal needs or to dry wet biomass streams in order to take advantage of dry biomass-to-energy processes. For the purposes of this study, biomass has been roughly divided into feedstocks for various biomass-to-energy processes based on moisture content. It is important to note that most biomass can be converted to energy using several alternative processes, and that the proposed CURBI facilities would allow a wide variability in the allocation of feedstocks to alternate processes. Since biomass in general can have widely varying moisture contents ranging from nearly dry to saturated, it is important that the correct biomass-to-bioenergy process be matched to the particular feedstock. This has been a critical obstacle to the adoption of regional small to midsize biomass-to-bioenergy systems. For example, many agricultural biomass feedstocks are too wet to burn in a direct combustion unit, and are too dry to flow through an anaerobic digester. CURBI research on alternate processes such as dry fermentation and pyrolysis will address many of the obstacles to expanding the use of biomass-to-bioenergy processes to commercial application beyond the University. Figure 2-2 also shows the relative ash content of the various biomass sources. Ash content affects the efficiency of combustion and gasification. Inherent ash value is approximately 0.5 percent for wood; 5 to 10 percent for agricultural crops; and up to 30 to 40 percent for manure and municipal biosolids. Although the use of municipal wastewater biosolids is not proposed for the CURBI project, the use of this reliable feedstock for production of bioenergy is a significant research opportunity. At high temperatures, melted ash becomes sticky and can cause operating problems with combustion and gasification reactors. Higher ash content results in a larger need for disposal of combustion by-products, which can increase costs and reduce sustainability of the processes through increased demand for landfill disposal of residuals

4 Bulk density and moisture content are significant factors for transportation and preparation of feedstocks for the various processes. Relatively wet feedstocks, such as liquid manure, alkaline hydrolysate, and food wastes, are not suitable for thermo-chemical processes such as combustion or pyrolysis and are economically limited to relatively short haul distances. However, these feedstocks are well suited for conversion to biogas by anaerobic processes. Drier, more dense feedstocks such as baled hay or woody biomass are better suited for thermo-chemical processes and longer haul distances. With the exception of dining hall wastes, biomass produced by University operations is of fairly consistent quality. Dining hall wastes for the CURBI project would be primarily pre-consumer (kitchen) wastes with minimal inorganic contaminants. Dining hall wastes pose concern because of the minor presence of contaminants, such as plastic or metal objects (cutlery, for example), which could interfere with the biomass-to-energy processes. Dining hall wastes for anaerobic digestion should be restricted to clean pre-consumer wastes, while dry fermentation would be tolerant of a much wider range of pre- and post-consumer wastes. 2.3 ALKALINE HYDROLYSATE An unusual biomass feedstock available to the CURBI project is alkaline hydrolysate waste produced by a chemical process incorporated by the CCVM to liquefy animal remains. This process, which was recently implemented, uses a strong base (potassium hydroxide) high pressure and high temperatures to liquefy solid remains as an alternative to incineration or landfill. The process at CCVM is currently capable of disposing of approximately 600,000 pounds/year of animal remains, resulting in production of approximately 250,000 gallons of alkaline hydrolysate. Hydrolysate is the result of a batch process of approximately 3,000 gallons/batch; however, weekly output of hydrolysate is highly variable, depending on needs for disposal of animal remains. Hydrolysate output could vary from as much as 1,000 to 20,000 pounds/week. Available information indicates that the average COD concentration for alkaline hydrolysate is approximately 88,000 mg/l compared with approximately 100,000 mg/l for dairy manure. If buffered to an acceptable ph range, it is expected that alkaline hydrolysate could be processed in a complete mix anaerobic digestion system. Other facilities that use alkaline hydrolysate for carcass disposal currently discharge the alkaline hydrolysate to sanitary sewers for treatment in municipal wastewater treatment plants (WWTP)

5 The current plan is for this waste to be treated at a municipal WWTP. Introduction of alkaline hydrolysate to the Cornell CURBI project could result in a lower cost disposal method which would provide additional feedstock for production of biogas for bioenergy. Characteristics of the hydrolysate are fairly consistent, but oil and grease concentrations can vary depending on the type of animal dissolved in the process. Alkaline hydrolysate from this process includes a fairly high energy density and, with the possible need for treatment to an acceptable ph range (subject to field tests), could be incorporated into the proposed anaerobic digestion process for the CURBI project. A model digester experiment performed by the City of Ithaca Environmental Laboratories determined that alkaline hydrolysate can effectively be used in a wet anaerobic digestion process. 2.4 SEASONAL AVAILABILITY Several of the biomass feedstocks proposed for the CURBI project have highly variable availability during the course of the year, including the following: 1. Dining hall waste production is proportional to the resident student population. Waste production is fairly consistent through the year, but drops significantly in January, early June and early June through mid-august. Since dining hall wastes cannot be effectively stored due to odors and pests, this waste must be processed on a daily basis throughout the year. 2. Alkaline hydrolysate waste production varies widely from as little as 3, gallons/week to more than 20,000 gallons/week, depending on animal mortality at the CCVM. Since this waste is very odoriferous and decomposes quickly, it should be treated when produced or stored in sealed vessels with odor control facilities for a short period of time. 3. Energy crops such as grasses are harvested in the summer months and can readily be baled and stored for year-round use. Similarly, woody biomass can be chipped and stored for year-round use. Storage issues are discussed below

6 2.5 CURRENT BIOMASS MANAGEMENT PROGRAM Cornell University has successfully composted most of the organic biomass wastes produced on the campus for several years. Quantities and characteristics of various biomass sources are summarized in Table 2-1. Currently, a total of approximately 8,000 tons/year of biomass waste is aerobically composted at the Stevenson Road compost location. Biomass wastes currently being composted include animal manure and bedding from the CCVM, Animal Science Center, polo fields, and poultry buildings. Plant material from the University greenhouses, Plant Science Center, and Cornell Plantations is also composted, along with pre-ground wood pallet waste and food waste from the dining halls. Pig manure from the pig research farm is applied to cropland as fertilizer. The recently completed alkaline hydrolysate waste disposal process from the CCVM relies on trucking to a municipal WWTP for disposal. Waste vegetable oil from the dining halls is collected and converted to biodiesel fuel by a sawmill operator in a nearby township. Two feedstocks under consideration for the CURBI process are not currently in the management program. Cornell cropland is currently used to produce forage crops and grain for use as feed for University animals and for sale on the agricultural commodities market. The proposed CURBI project would include approximately 8,000 tons/year of dedicated energy crops (most likely switchgrass) which could provide feedstock for the CURBI processes. The proposed CCVM Dairy Center, to be located adjacent to the CCVM, will produce approximately 5,000 tons/year of liquid manure. Some biomass wastes produced by the University were determined not to be applicable to the CURBI facility. These include approximately 26,000 tons/year of liquid dairy manure from the Teaching and Research (T&R) Farm, which is located approximately 15 miles from the CURBI site. Transportation of this quantity of liquid manure for anaerobic digestion would not be cost effective, although it would be feasible to locate a second anaerobic digester at the T&R Farm for local treatment of the manure, as well as utilization of the combined heat and power produced by the system. An unknown quantity of summer lawn clippings is generated on University grounds, but collection and transportation of these clippings is not justified for the marginal energy content of this biomass. The University generates approximately 4,600 tons/year of various types of waste which must be disposed in an approved sanitary landfill. Introduction of this type of waste to the CURBI process could limit the agricultural application of the byproducts from the system

7 2.6 FUTURE FEEDSTOCKS In the future, Cornell University could expand the production of agricultural biomass energy crops to increase the production of renewable energy, and reduce the University s carbon footprint. Cornell is currently involved in the development of several alternative biomass crops for energy production, which could provide additional research opportunities at CURBI for processing the biomass to renewable energy. Currently, over 3,500 acres are available for biomass crop production. Potential biomass production and energy yield from various biomass feedstock crops is based on information obtained from Cornell University and the SUNY School of Environmental Science and Forestry. Although only biomass produced by Cornell University has been considered as potential feedstock for the CURBI facility, future expansion of the processes could provide opportunities for increased renewable energy production and carbon sequestration using feedstocks within a larger radius from the CURBI site, consistent with Cornell s Land Grant mission to help create rural jobs and promote sustainable agricultural practices beyond the campus borders. This would also provide potential economic benefit to the communities surrounding CURBI if farmers, local businesses, and/or landowners sell biomass to Cornell