|
|
|
BIOMASS ENERGY State of the Technology Present Obstacles & Future Potential A Report for: United States Department of Energy Conservation and Renewable Energy Office of Energy Related Inventions Prepared by Larry Dobson Northern Light Research & Development (new address) 7118 Fiske Road Clinton, WAÂ 98236 360-579-1763 in Fulfillment of the Terms of Energy Related Inventions Grant Project Number DE-FG01-89CE15425 Project Officer: Glenn Ellis June 23, 1993 SECTION 1
|
|
|
Fast-growing biomass takes up more carbon than any other process and yields oxygen. In taking into account the total fuel cycle, several studies show that biomass energy is the only option that has a net gain over the carbon/oxygen cycle. Planting trees can reverse the CO2 buildup faster than any other means, and young forests fix more carbon than mature forests. Woody plants capture more sun and are more efficient than annual crops in temperate climates.
Woody crops actually fix over three times more carbon per field per year than a single crop of corn.
Annual crops require annual tilling, which harms the soil by killing not only macroorganisms, but by impoverishing the soil microbiota. During peak sun annual crops have at best only half their photosynthetic surface deployed. Woody plants with rapid early leaf deployment, multiple leaf layers and longer growing season can capture significantly more solar energy than traditional annual crops. Deep roots allow them to continue this even during moderate dry spells. This means more -- potentially much more -- CO2 fixed. The significance for global climate change is profound.
In our throwaway society, biomass waste is generally becoming an increasingly costly disposal problem. Landfills are filling faster and faster, and EPA's strict new regulations are expected to cost taxpayers $1 Million per acre to open new ones and force the closing of half of the nation's 5,499 dumps by 1996. From 1/3 to 3/4 of our MSW is biomass suitable for fuel which could replace nationwide 824 Million barrels of imported oil a year.
Urban wood waste processing and delivery services are springing up across the country, charging a tipping fee less than the local landfill for yard waste, tree trimmings, land clearing and demolition debris and reselling chips and compost for a tidy profit. Secondary wood product industries, tree services and agricultural processing industries are looking for alternatives to costly dumping of their residues.
"Recycle" is the buzzword of the '90s because it is generally cheaper and more environmentally sound to do so. Premium grade wood residue can be sold as fiber chips, paper recycled, and yard waste composted. But there is always a large part of our biomass waste stream that is too poor quality to recycle into products. Household garbage and low grade mixed waste paper are better recycled into energy, as long as there is no mercury present to contaminate the exhaust. In the Puget Sound region, 270,000 tons of mixed waste-paper are generated daily from recycling, and much of it landfilled because no one wants it. This would heat 75,000 homes for one fifth the cost of natural gas, and just as cleanly. Even premium grade fiber chips are a quarter to a third the price of gas. Tree trimmings and other woody residues compost slowly and would be much more economically used as fuel.
"Since 1986, 40 states have enacted legislation requiring communities to recycle parts of their waste. The effect has been dramatic. In 1980 the nation recycled only 14 million tons of its MSW and burned virtually none to produce energy. In 1988, 24 million tons were recycled, and 26 million more were incinerated to produce electricity." [62A, 1/92]
Recycling of certain materials continues to increase steadily. The country now recycles 55% of all aluminum cans. While Americans recycle one quarter of the 67 million tons of paper consumed annually, the recycling industry probably couldn't handle the remaining three quarters even if people brought it in. Because demand for recycled paper now roughly equals supply, few recycling mills are being built. [62A]
"The paper recycling process has been refined so that it's inexpensive and efficient. But recycling plastic is expensive, requires a lot of energy, and generates pollution. The furor over juice boxes epitomizes the plastic-recycling predicament: Americans purchase more than four billion of the convenient little boxes each year and recycle almost none. Made of laminated layers of paper, foil, and plastic, these so-called aseptic packages produce pulp of such a low grade that no one wants to buy it." [62A] This material would make excellent fuel in a Northern Light burner.
Communities throughout the U.S. are now accumulating mountains of recycled glass and low grade waste paper with little or no demand for these raw materials. The waste paper, along with other combustibles from municipal waste, is an excellent fuel in our Northern Light combustors to melt waste glass and turn it into useful commercial products.
Northern Light is also developing new technology to recycle glass into durable, lightweight, strong and insulating foamed building products. Currently foamed glass insulation is the monopoly of Pittsburgh Corning, does not utilize recycled glass, and is about three times the price of foamed plastic. Studies show very promising economic viability for such products.
The amount of unused biomass residue produced in this country is monumental. Most of it doesn't end up in municipal landfills.
MSW is less than 2% of the total available biomass fuel from logging, agricultural harvesting and processing, industrial and municipal waste streams.
In the Pacific Northwest alone, about one quad (1,000 trillion BTUs) of biomass residues are physically generated each year. This is equivalent to 160 million barrels of oil, or $10 billion per year in residential fuel oil. It represents the heat equivalent of 1½ times the annual electric power consumption of the Pacific Northwest. This scenario is repeated across the nation and around the world.
While fossil fuel costs are steadily increasing, the cost of wood fuels is generally declining, with increasing disposal costs for land clearing, logging cleanup, yard trimmings, and mill waste. A BPA study, Regional Logging Residue Supply Curve Project, states,
"Current indications are that recovery and transportation costs for any given piece size will decline...In no case can it be shown that there will be a significant rise in wood fuel prices for the remainder of this century."
"American demand for wood continues to rise, yet the nation's forests are growing faster than they're being harvested. In 1990, logging companies planted some 41.9 billion seedlings, according to the American Forest Council (AFC)." [22]
Dr. Harold E. Young calculated Maine's wood resources, based on utilizing the whole tree, and compared them with the U.S. Forest Service's figures, which are based only on the merchantable bole (excluding tops, needles & leaves, branches & roots). The annual production of the complete forest is 8.75 times as great as the merchantable bole harvest! This impressive number gives some indication of the increased potential for energy from logging waste.[22]
Energy crops are seriously being considered as an alternative to fossil fuels, sparked by environmental concerns about conventional forestry practices, the Clean Air Act, global climate change, soil conservation and energy needs. While only 15,000 to 20,000 acres of short-rotation woody crops are planted in the U.S. today, the feedstock potential could easily lead to more than 20 gigawatts of new capacity by 2010.
Jerry R. Allsup, director of DOE's Office of Alternative Fuels, Transportation Technologies, Conservation & Renewable Energy, says the agency "believe(s) that (wood's) role in energy is likely to grow in the future because of an increased research effort to produce faster growing trees, better utilization of the existing stands of energy and a renewed effort to utilize wood waste for energy as a part of better integrated resource planning." [Alternative Energy Retailer]
In Minnesota, short rotation intensive culture (SRIC) of trees can produce 3 to 6 dry tons/acre/year, as compared to yields of 1 dry ton/acre/year in native forest stands.[Pamphlet published by University of Minnesota, Office of Biomass Research, 10/91]
Hemp cultivation can produce 8 to 24 BDT/acre/year. Sugar cane and some tropical crops yield 40 or 50 tons per acre. [45]
Crop set-aside programs, conservation programs, emission taxes & air quality non-attainment areas have helped energy crops to become marginally competitive in some areas. Delivered energy crop production costs are now estimated at about $39 to $63/dry ton.
Energy crops could be planted on the 200 million acres of underutilized and marginal agricultural land in the United States. [62B] Much of this land could be improved with the proper balance of biomass plantations, while at the same time generating a large renewable fuel supply. BACH (Business Alliance for Commerce in Hemp) claims that if only 5% of the nation's land were devoted to hemp, it would supply all the energy, and that land doesn't even have to be arable."
Sweden demonstrates the economic viability of biomass energy. The country plans to double its present reliance on wood energy in the next decade, providing 28% of its energy needs largely from fuelwood plantations surrounding decentralized power plants located in each community.
The most expensive biomass fuel, premium grade fiber chips for paper making and chipboard, costs only one third as much as Texas intermediate crude oil at the pump and one fourth the price of commercial natural gas for the same energy content. Typical fuel-grade biomass is often one eighth the cost of fossil fuels, delivered. Additionally, Northern Light biomass energy systems extract more heat from the fuel than most fossil fuel fired systems.
By substituting Municipal Solid Waste (MSW) for imported oil, we could save an estimated $25 billion a year in foreign exchange, while at the same time creating thousands of new jobs locally and saving $10 Billion on landfill costs.
The economic benefits in other areas of biomass energy are much greater. Energy investments stay in local communities; workers of varied skill levels can be employed. Industrial wood energy utilization in the Southeastern Region of the U.S. is projected to generate approximately 97,000 jobs and $1.4 billion annually by the year 2000.
State and regional governments are waking up to the manifold possibilities of a local waste-to-energy infrastructure to provide jobs, keep energy investments from leaving the state, solve waste disposal problems and eliminate air pollution from slash and field burning. Programs to inform businesses of the advantages of biomass energy and to fund demonstration and research projects are being developed nationally and locally. The vast potential for biomass farming is receiving more and more serious consideration and funding. The net gain in the greenhouse cycle has the capacity to preserve our planet, and a growing wave of environmental concern may push biomass energy into the forefront of future energy options.
"I'm hearing from the marketplace, " says Stan Sorrell president and C.E.O. of the Calvert Group of mutual funds, "and what I am hearing is that environment is and will be the main issue of the nineties." [The Nation, 3/26/93]
Recently, tough environmental laws passed by the EPA, notably the Clean Air Act, Clean Water Act, new landfill regulations, and Woodstove Performance Standards, have dramatically changed the playing field in the biomass energy game. State and local regulations have compounded the effect in many areas.
"Changing landfill regulations have a decided impact on the availability of mill residues. More stringent disposal standards increase the cost of disposal forcing mill operators to explore additional options including potential fuel applications. Currently, some sawmills are finding disposal costs so expensive that they may be forced to close down. This situation is partially responsible for the low current (1990) price of mill residues. In fact, some mills are paying a fee to energy users to dispose of their residues. They do so because the landfill disposal costs are even higher. This is another case where environmental policy can make more material available for energy uses."[6]
The new Clean Water Act will indirectly provide significantly more biomass feedstock and need for incineration of wastes that are now polluting ground water in landfills and storage dumps. Candidates include poultry and chicken litter, manure from dairies and feedlots, onion culls, chicken carcasses, etc.[77] Because Northern Light's burners can handle such diverse wet fuels, they should serve this market well.
Title XIX of the Energy Policy Act of 1992 included tax provisions to encourage investment in renewable energy sources, including biomass. The Energy Act also provides a 1.5 cent tax credit for every kilowatt-hour of electricity produced from "closed-loop biomass" (crops grown exclusively to produce electricity).
The U.S. Department of Energy, Office of Utility Technologies, is enthusiastic about biomass energy. [62B]
"The future for biomass power looks particularly attractive given the potential for substantially expanding biomass supplies by growing new energy crops on millions of acres of underutilized land; the potential for significantly improving the performance of biomass power technologies through R&D; important environmental benefits offered by biomass power such as recycling of atmospheric carbon and its low sulfur content; as well as the potential for biomass power to provide substantial rural economic development benefits.
The growing demand for electricity, in conjunction with a new regulatorycompetitive environment and environmental pressures such as those created by the clean air act, has created a substantial target of opportunity for biomass power over the next decade. The 1980's provided a decade of technological progress to build upon."
"The plan of the DOE Biomass Power Program is to make the 1990's a decade of commercialization. The strategy is to develop advanced high-efficiency biomass power systems with competitive feed stocks and to capitalize on Clean Air Act requirements and state environmental actions."
Much more governmental support needs to be directed toward these ends than is now in the budget. Sweden has taken biomass energy seriously, and is now spending as much on R&D in this area as is the entire United States. "At the heart of Sweden's program is public support. Enlightened, environmentally-conscious citizens and an elected body free from the domination of nuclear and fossil fuel lobbyists have been essential for the progress to date." [83A]
Regional regulatory officials tend to be suspicious of poorly performing old-technology wood-fueled systems. This makes permitting difficult and time-consuming. In contrast, numerous officials in the Department of Energy, the Environmental Protection Agency, and State Energy Offices are anxious to see such clean, efficient technology as Northern Light has developed commercially available. Government funding is available for extensive emissions testing, and with the support of the EPA and DOE, local permitting should become easier than at present.
Surprisingly, this increasingly favorable renewable energy alternative is not being capitalized on and few people are even aware of it. In fact, general public and governmental attitudes are often decidedly negative. Influential environmental groups, such as The Sierra Club and Friends of the Earth, equate wood burning with noxious emissions and environmental degradation. They maintain that garbage and processing waste should either not be generated in the first place or should be recycled. Energy conversion is not considered recycling, yet the facts show it to be a better option than burning of 40 million year-old fossilized biomass, at least for the next few decades until energy becomes cheaply available without using fuel. Even then, there will always be byproducts of human endeavors that can best be disposed of by burning, and where heat is needed, combustion is the most direct approach to getting it, outside of direct solar radiation.
The New York State Energy R&D Authority gave up on trying to get any large wood-fueled installations permitted. Public sentiment is against "incineration" of any kind, and burning wood waste is seen in the same light as municipal waste.
The Northwest Power Planning Council has dismissed biomass as a potential future source of energy. In fact, in their 40 page draft plan (vol.I), only two sentences are devoted to biomass, and its projected contribution to the regional power pool is only 0.6% of the total! Cost and public sentiment seem to be keys to that decision.
Heat from waste wood in the area can directly replace electric heat - at one ninth the cost. This is not currently being factored into the Regional Power Plan, despite the fact that already one fifth of all Washington State households heat their homes with both wood and electricity, displacing up to 1,000 MWa of electric power in the region. [41A, 6] In other parts of the country, the cost advantage of wood heat over electric heat is more like 30 to 1 and rising.
Instead, 76% of the new power sources under development in the region are generators that run on natural gas, a fuel imported primarily from Colorado and Alberta. Yet the quantities of biomass residues produced each year in the region are equivalent to 7,600 MW of electric generating capacity, almost twice NPPC's projected new generator capacity requirements to the year 2010!
The standardization and coordination of regional and national regulations for biomass-fueled boilers is complicated by several factors:[80]
* Each state may require different levels of emission control to satisfy their State Implementation Plan.
* Each state has a different level of industrialization.
* Each state may pursue promotion of energy resources most abundant in their area.
* The impact of emissions varies with terrain and climatic factors.
"While the potential for conversion to wood-energy is high, fossil fuel sources will remain prominent in some areas as long as the current state regulatory scenario is perceived to be detrimental."[80]
There has been major reduction in the number of new wood-waste combustion systems installed in the Puget Sound region in the last 7 years. Much of this is due to (1) state regulations to discourage residential woodstoves and (2) Puget Sound Air Pollution Control Authority's (PSAPCA) strict 1990 emissions regulations on new wood-fueled boiler installations. The latter regulations allow new systems to emit only a tenth of the particulates that the older systems are permitted. This has prohibited small to medium sized installations of any waste-wood-fueled system now on the market because of the extremely costly cleanup equipment required to achieve compliance (cyclone separators, baghouse filters, electrostatic precipitators, etc.). Even the new state-of-the art 46 megawatt biomass power generating facilities in Kettle Falls, WA, just barely meets this standard.
Despite great improvements in residential woodstove design over the past 7 years, Most people assume that wood can never be burned cleanly. Wood smoke has become synonymous with pollution in official circles as well. A joint report by the State of Washington and the U.S. Environmental Protection Agency, "Toward 2010: An Environmental Action Agenda", recommends that Washington State "Phase out residential wood-burning stoves and inserts." The logic is that, "A decade or so ago, heating a home with wood was considered a clean alternative and an answer to the energy crisis. Today, residential wood burning is widely recognized as one of the most significant sources of air pollution--especially of small particulates--in our state."
There seems to be little interest in the results of a study commissioned by the local Bonneville Power Administration, Environmental Impacts of Advanced Combustion Systems, which proved that a residential cookstove designed by Northern Light R&D burned wood 65 times cleaner than the average woodstove and cleaner than most oil and gas fueled residential furnaces, without contributing to the greenhouse effect. The disturbing destruction of our remaining virgin forests has totally overshadowed the fact that forests can be a renewable crop and that large quantities of biomass waste of all kinds are continuously being produced and need to be disposed of.
|
|
Biomass fuels are produced wherever plant material is harvested, processed or used, generally in millions of decentralized locations throughout the country. They exists in such varied location and form as logging slash, agricultural crop residue, stockyard manure, food processing remains, demolition debris and cabinet maker scraps. No national distribution system is possible. Biomass fuels are locally generated and must be locally utilized to be cost-effective. While this has economic advantages, it does not lend itself to centralized coordination, and therefore is not so attractive to large corporations and governmental bodies.
Local processing and hauling operations are springing up wherever waste has become an expensive disposal problem, but a well-established and dependable fuel delivery service does not exist in many areas, simply because there has not been the customer base of biomass fuel users.
Without an existing fuel delivery infrastructure, potential customers are reluctant to invest in a biomass energy system. This situation also dissuades potential investors, manufacturers and marketing firms from getting involved in the biomass energy game. The prevailing attitude is, "Let the industry get further developed...Then I will get involved." Now is the time for government and industry to make major investments in the future of a decentralized biomass energy industry to get it established and over the initial hurdles.
Fully automated fuel feed systems are expensive. Currently available fuel feed systems are individually designed and fabricated for the logging industry. They are too complicated, over built, and expensive for such small-scale systems as we have determined to be the best market. This has been a major factor in preventing greater utilization of bioenergy on the commercial scale. A fully automated fuel storage/feed system of present design could make up two thirds of the total cost of an installed commercial wood-fueled boiler system of Agni size. Such an investment is not cost-effective in today's short-term investment market. Northern Light R&D has done considerable research in this area and has developed a simple system which should drop the cost by 50 to 75%. Additional funding will be needed to perfect the most economical fuel feed system and open up the market to the widest customer base.
All indications point to a very promising future for bioenergy, but the industry is not yet prepared with answers to the many perplexing problems confronting the would-be customer. Equipment is complex, costly and too often plagued with aggravating problems and limitations. Variations in fuel type, size and moisture content are not easily accommodated in any one combustion/fuel-handling system. Much of the potential fuel is too wet, too stringy, not uniform enough in size and moisture content or too high in ash and dirt content for existing systems to handle at all. Most biomass combustion systems available at present have a very narrow range of clean combustion, with a turn-down ratio of only 2 or 3 to 1. This makes them inappropriate for many applications that have seasonal variations in heat demand.
All wood-burning boilers on the market today have difficulty meeting increasingly strict emissions regulations without costly stack clean-up air pollution controls. Typical flue gas scrubbing and conditioning equipment costs average from 25 to 40% of the total capital costs of coal-fired plants and consume large amounts of power (approximately 3% of the total unit output). [Biologue, Dec'88/Jan'89]
Fuels with moisture content higher than 40% have unacceptable emissions problems, and nothing currently available can even burn fuel above 66% moisture content. Yet there are huge outdoor stockpiles of wood-waste throughout the country that are wetter than that. Because all of the moisture in the fuel is vaporized and sent up the stack, net system efficiencies drop to unacceptable levels with high moisture fuels.
Controls are generally very basic and incapable of analyzing changes in multiple variables to self-correct imbalanced conditions and optimize combustion conditions. None except the very largest industrial installations even monitor fuel/air ratios.
A boiler with fully-automated feed system is so expensive that it has not been cost-effective in sizes below 10 million Btu/hr, but this size represents the largest customer base. For a heating system the size of Agni (1.5 MBtu/hr) a fully-automated feed system could amount to 75% of the total installation cost.
If, in addition to a hassle-free fully automated feed system one requires a sophisticated microprocessor control system for feed, combustion, boiler monitoring and control, with multiple alarms; automated ash-removal; the capacity to automatically handle various low-grade fuels; a high turn-down ratio; very low emissions to meet strict governmental standards; and high efficiencies even with wet fuels; they will find nothing on the market at any price.
But most of these problems have been solved and extensively tested in the 10 prototypes Northern Light R & D has developed over the past 20 years. The remaining challenges have been addressed in the most recent improvements to the Agni design, and in new approaches to inexpensive fuel handling described at the beginning of this paper.
The experts seem to agree that, at the present time, the best way to recycle wood waste is to convert it to energy by combustion. There is not a sufficient demand for alternative uses such as composting or animal bedding to absorb the large amounts of wood waste produced in the U.S. The primary forest products industry is already doing a good job of generating its heat and process steam requirements through the combustion of its wood waste. The secondary forest products industry could generate a good deal more of its heat and process energy needs by wood combustion. Beyond that, the potential market is determined by numerous factors that have been well researched for the economics and capacities of presently available systems.
Four market studies have been carried out in different areas of the country to define the existing and potential users of commercial and industrial wood fueled boilers.[5], [48], [48A], & [77]
The SERBEP 1986 study [5], "Analyzing Market Constraints in Woody Biomass Energy Production", determined that there were about 5843 reported industrial wood energy users in the continental U.S.. A 1977 study [80] reported about 10,500 wood-fired boilers installed nationally. The discrepancy can be attributed mostly to the fact that close to half of these were smaller than industrial size. In 1977, wood-fired boilers represented only one-third of one percent of the total national boiler installations. Approximately 76% of fossil fuel boilers installed in the United states are rated at below 1.5 million Btu/hr.
The largest market for wood-fired boilers is below 1.5 MBtu/hr, but this is generally below the cutoff considered cost effective for presently available systems and below the size of concern to half of the studies. Yet this is the most appropriate market for decentralized collection and distribution of biomass wastes and application of the Stirling engine linear alternator technology for cogeneration.
The SERBEP study [5] identifies five important constraints preventing wood energy use in the Southeast:
A major constraint identified by this study is a lack of knowledge about industrial wood energy and a poor perception towards its implementation.
The lack of confidence in the availability of outside sources of wood, of funding for conversion to wood, and of incentive to convert to wood (as well as industries requiring outside wood sources) are speculative reasons for the slow growth of the wood-fired boiler population. Costs of conversion to a wood energy system is perceived as the most significant barrier.[5]
Today, conversion to a wood energy system may be two to seven times the capital cost for an oil or natural gas energy system, and twice the capital investment of a coal energy system. Fuel handling costs are a significant part of this high initial investment. However, Northern Light R&D has developed a much simpler low-cost option for automatic feed.
A study in South Carolina [77] concluded that if the cost per million Btus from wood residue is at least $3.65 less than the cost from fossil fuels, conversion for a minimum or larger industry becomes a real possibility. However, these figures were based on very costly feed system and boiler installation costs and on 65% boiler efficiencies, rather than the 90%+ efficiencies of a Northern Light system.
This means that the wood residue prices can be 38% more for the same energy yield. Taking representative commercial fuel prices from the Pacific Northwest as an example, natural gas is around $4.44/MBtu, which would give an appropriate cost for wood waste at $1.09/MBtu. The most expensive wood chips are delivered in the area for $0.94/MBtu. Therefore, even for presently available wood-fueled boilers and costly feed systems, wood energy is a profitable investment in the region.
Looking at the potential for residential cogeneration, we have a different set of economics. If a home or apartment energy system produces electricity and replaces a central heating system, hot water heater, cookstove, and perhaps also supplies refrigerator cooling and air-conditioning, hot air for the drier, and waste disposal, a more expensive system could be cost-effective. Adding up all the costs of the individual appliances that are replaced and their combined energy costs show a major investment indeed. This potential deserves serious R&D work.
Best Size System
Because biomass fuel is available in decentralized locations, and transportation costs are a big factor in both disposal costs and potential fuel delivery economics, small commercial systems afford significant advantages.
There are over 1480 landfills in the 13-state Southeast Region. 55% of these are small (<30,000 cu.yd./yr.). In MS, WV, KY, and GA there are 537 small landfills and only 3 large (600,000 cu.yd./yr.). If one third of the waste going to these landfills can be cleanly burned for energy, the average size of incinerator needed by most Southeastern counties would be less than 10 MBtu/hr. If a more decentralized cogeneration siting approach were taken, even smaller units would be appropriate.[72]
One Agni-sized boiler (1.5MBtu/hr) could serve a community of 1,500 people. (@ 5,000 Btu/lb with recycled beverage containers removed, and about 33% moisture.)
Small biomass combustion systems can have permitting advantages. In some areas, permitting for larger systems (over 12 tons/day) is much more difficult, due to classification as a potential industrial pollution source.
"Small, hospital-sized incinerators such as the Therm Tech in Fairbanks (Hospital) could provide opportunities for using solid waste to heat community buildings or schools in rural Alaska. Small communities in Alaska are experiencing difficulties in properly disposing of MSW, particularly where high water tables and lack of suitable cover cause landfill problems. Most waste-to-energy facilities use incinerators that are large, continuously fed systems that are too big for small communities. An incinerator the size of the Fairbanks unit could process 2.5 tons of solid waste per day on two shifts, providing adequate disposal for a community of 1,000 people." [3]
BioBurn Corp. of Utica, NY, is a sales representative and distributor for over ten different manufacturers of solid fuel combustion equipment ranging from 50,000 Btu/hr to 1000 boiler horsepower. They are constantly seeking and testing new equipment to find a good range of systems that can meet the needs of different users. They contend that there is no wood chip combustion equipment under 100 hp (3.3 MBtu/hr) that is both economical and technically reliable. [93]
This observation is echoed by numerous authorities in the field. The report, "Stack Emission Standards for Industrial Wood-Fired Boilers" [80], concludes,
"After review of the current situation, it is apparent that efforts to promote wood energy use is best directed to small boilers. In addition to representing over 90% of the total number of boilers, the 0-1.5 million Btu per hour capacity boiler, and small (less than 10 million Btu per hour) regulated boiler, offers the following advantages for conversion to wood-firing:"[80]
* "The greatest number of wood-fired boilers are fueled using residue generated by production at the facility. This residue does not have to be hauled off-site, thus reducing the deleterious effects of other contributors of pollution e.g. fugitive dust. There are few large facilities which generate sufficient wood residue to be energy self-sufficient."[80]
* "Wood-fired boilers fired with residue from the production facility are immune from wood shortages and fuel transportation problems."[80]
* "Small wood-fired boilers are easily switched to fossil fuel firing in an emergency situation compared to larger boilers of the same design and operation."[80]
* "Small boilers will have minimal impact on the local ambient air quality singularly or cumulatively (assuming normal distribution of small boilers). This conclusion is supported by modeling results."[80]
* "Small boilers will not impact local wood fuel supplies (assuming normal distribution of small boilers)."[80]
* "Small boilers are best suited for retrofit and are the most flexible compared to large boilers of similar design and operation."[80]
"Other findings of this study include:
* "A correlation between the wood-fired boiler population in a state and the state's particulate emissions standard is not readily apparent."
* "Potential users of biomass are not aware of the availability of wood, the operation of wood-fired systems, the applicable air pollution regulations, or the permitting process."
* "Efficient operation of the boiler and associated equipment will also result in the lowest emission rates."
* "Innovative methods of operation can eliminate the requirement for air pollution control equipment or at least reduce the cost of control equipment."
Each statement is supported by detailed discussion in the report.[80]
Greatest fuel savings and payback within 2 years can be realized in commercial installations such as greenhouses, hospitals, schools, county seats and other public buildings, laundries, factories, wood- and agricultural-processing facilities, shopping centers, hotels, resorts, and nursing homes, wherever there is nearby biomass waste and space to store the fuel.
Small, efficient, cost-effective cogeneration systems fueled with biomass promise the greatest near-term potential for solving the world's energy needs of any available renewable energy option. The energy and environmental crisis we are facing on all fronts has forced us Americans to reevaluate our "mega" approach to problem solving. Utilities are suddenly looking to conservation and efficiency as an alternative to building more power plants. Decentralized electric power cogeneration is preferred to wasteful large central power plants. We must use less, use it more efficiently, reuse it again and again. The operating principles are Conserve, Reuse, Recycle.
Applying these principles to energy and waste recycling, we must conclude that small decentralized settings are the best cogeneration sites.A community could recycle local biomass, household waste and low grade paper into energy for a recycling operation, providing heat, mechanical power, and electricity for transforming recycled glass into foamed building insulation and roofing tiles, for an aluminum foundry, pottery and glass blowing studios, etc.. The waste heat, too, could be recycled first back into the combustion air, then into process steam or used in a Laundromat, car wash, sauna, heated swimming pool or greenhouses.
By recycling waste biomass into energy, recycling waste energy back into the combustion process, and using the waste heat again and again, increases in efficiency are possible that are many times what is presently achievable.
According to the Union of Concerned Scientists, "Buildings use more than one-third of the energy consumed in the United States. Heating and cooling systems account for 60% of this energy." Of that amount about 20% is reasonably recoverable with the use of appropriate heat engines. This amounts to about 15% of the electricity requirement of the country.[37A] There are 54 million single-family dwellings in the U.S. which could take advantage of cogeneration to generate much of its power from the nation's waste .
Electric utility customers at the end of the power grid are losers for the power company. Electricity that makes it to the end may be 15% less than the power sent out of the power plant, which in turn is only about a third of the energy stored in the fuel. It would be far more efficient to generate electricity right at the remote site, with no transformer or line losses, using most of the remaining valuable heat energy for space heating, hot water, etc., by burning locally generated and continually renewable biofuels. Economical, reliable residential cogeneration systems are the key, and this is what Northern Light & Sunpower are currently investigating.
MSW has become a major disposal problem worldwide, and burying it is no longer a viable solution. Incineration has just as bad a reputation, despite the costly gas cleanup technology employed. Part of the pollution problem is poor combustion (Dioxins, Furans, PAHs, PCBs, etc.), and part of the problem is heavy metal and other contaminants. With proper source separation, heavy metals can be eliminated from most waste streams. Poor combustion requires in most cases an entirely new combustion approach. Pyrolytic gasifiers are much better technologies in this regard, but they are too costly and complex for small municipalities.
MSW incinerator plants presently tend to be very large (200 - 3000 tons/day) because of the complexity and cost of the equipment, but there are significant advantages to small, decentralized installations:
1. Waste is mainly produced in local, decentralized homes and businesses. Shorter hauling distances mean reduced disposal costs.
2. MSW is a valuable fuel which can best be burned in numerous smaller decentralized locations where heat and processing steam can be utilized, along with cogeneration.
3. Large garbage-collection sites have traffic congestion, odors, large volumes of emissions, and strong public opposition.
4. Many municipalities do not generate enough waste to support a large, expensive disposal installation.
There needs to be more thought and support given to the clean conversion of municipal waste to energy in small, decentralized community settings. Existing systems are prohibitively expensive and unreliable. Because Northern Light's technology is so clean and simple and capable of handling such a diversity of fuels, it should be ideally suited for such application.
The Biomass Energy Research Association (BERA) recently testified before the House Committee on Science, Space, & Technology, Subcommittee on Environment,
"In combustion research, a need still exists for improved solid waste incinerators that meet environmental requirements and cost goals. Research should be focused on systems that can be used for economic disposal of MSWs in small communities. Research is also needed to reduce the emissions of solid waste disposal processes..."
Northern Light R&D has done this research and has come up with a number of major improvements. Gasification and combustion processes are separated by preheating to very high temperatures the fuel and the air for pyrolysis and combustion and by controlling primary and secondary air through a microprocessor linked to various sensors and dampers. This allows extremely wet material of diverse physical properties to be burned completely without carrying ash and other particulate out the stack. In tests burning RDF (Refuse-Derived-Fuel) pellets, excess air was brought down to ½%, while maintaining low carbon monoxide emissions (0.02%). This is unprecedented in biomass combustion. Only large state-of-the-art gas furnaces approach such efficiencies.
Further advantages to this staged combustion approach are reduced NOx emissions and elimination of ash-slagging problems associated with low melting temperature ash from MSW and agricultural fuels. This latter problem has plagued the industry and is aggravated by the larger system approach.
The smokeless, odor-free exhaust is further scrubbed of fly-ash in the condensing boiler, where moisture from the fuel is precipitated out as clear water. There is no need for the costly stack clean-up equipment currently used in the industry. Because the whole system is so elegantly simple, it should be able to meet the disposal and heating needs of small municipalities at one quarter the cost of systems now on the market and easily pass the most stringent emissions regulations.
|
|
A prototype residential cook stove developed by Northern Light R.&D. (named "Helen") was officially tested by OMNI Environmental Laboratories for the U.S. Department of Energy/Bonneville Power in 1986, burning green sawdust of 44% moisture content, with no catalytic afterburner or stack cleanup of any kind. [40]
Its particulate emissions were 65 times cleaner than the average state-of-the-art woodstove, several times cleaner than the best pellet burner, and considerably cleaner than the average oil furnace.
Carbon Monoxide emissions in the stack gases were 1/7500th of the Federal Auto Emissions standard, 1/100th of the gas industry's standard for "CO-free combustion", and 1/2 of the EPA's standard for acceptable 24 hour indoor air quality.
|
|
These emissions are less than half of the most stringent PSAPCA standards for new wood and refuse burners. Since this prototype, two improved versions have been built.
The most recent 150,000 BTU/hr hot air furnace (Vaagner) is capable of burning the wettest wood (logs, chips, sawdust, etc.) extremely cleanly and efficiently. Primary and secondary air is precisely controlled by a state-of-the-art microprocessor continually monitoring input from various temperature and position monitors and an oxygen sensor in the exhaust stream.
Flue gases are usually so cool that clear water is condensed out in the heat exchanger. This reclaims the heat of vaporization and allows wet fuels with over 70% water to be burned as efficiently as dry ones. No other combustion system yet tested comes close to this capacity. (The condensate poses no disposal problems in sewers or septic tanks. It contains no sulfur and is less acid {pH 4.5} than rainfall near many fossil-fueled industrial areas of the world {pH 3.5}) The unit can be fitted with a large hopper to hold several day's fuel at one loading. It will also burn pellets cleaner and more efficiently than commercial pellet burners, and can be operated without electricity if necessary.
![]() |
State-of-the-art Silicon Carbide heat exchanger transmits heat to the incoming combustion air 6 to 10 times as fast as firebrick. Extremely strong, durable, fatigue- and shock-resistant refractory ceramics are used in the combustion areas, High-temperature ceramic fiber insulation is used along with concentric heat-exchanger shells to move the heat where it is needed to optimize pyrolysis and combustion and to eliminate excessive heat which produces slag buildup and ceramic fatigue.
Counterflow gravity-stratified condensing heat-exchangers, specifically designed for high-ash biomass fuels, scrub the exhaust & reclaim the heat of vaporization of the moisture in the fuel. Thereby wet fuels can be burned as efficiently as dry. The thermodynamic properties of these heat-exchangers increase natural draft and eliminate the need for exhaust fans (and their tendency to send unburned embers, soot and ash to clog up the heat-exchanger and increase particulate emissions). All soot is burned in the combustion zone. The remaining fly-ash is removed from the exhaust stream through a combination of centrifugal/gravity precipitation and steam-condensation entrainment, which continuously scrubs the lower heat-exchanger surfaces. We have built hot air and hot water systems and have designed a low pressure steam boiler.
A gravity feed hopper operates when the power is out and takes any size, shape and configuration of fuel without hang-ups. Counterweighted hopper flaps prevent uncontrolled combustion and heat loss in the upper hopper. They also indicate status of fuel reserves, turn on fuel feed in automatic feed systems, facilitate smoke-free loading of the hopper. The lower hopper is vertical sided with no constrictions to hang up stringy hogged fuel or logs.
We have developed a powerful but inexpensive central microprocessor control system with built-in analysis and correction routines and an alarm system. In both the commercial Agni system and the residential cogeneration system it will control the fully automated feed system, automatic ash removal system, and dual-fuel switching functions.
With the new fuel feed system, the economics of the installed package is very favorable compared to natural gas, and no contest when replacing oil or electricity. We expect to offer a complete Agni 1.5 MBtu/hr system, with condensing boiler, fully automated computer control, ash removal and fuel handling systems for under $90,000 installed. Eventually, with the development of an even more economical feed system and optimizing of all the components in the system, the total package installed cost could be substantially less.
Â
To continue reading Part II of this report, CLICK HERE
MeasureDefinition
Unit 200 cubic of uncompacted volume
Green Unit (GU) - Chips Weighs approximately 3,430 Lbs @ 30% MCWB
Bone Dry Unit (BDU) Used as a basis for payment for pulp chips. A measure of weight, not volume, defined as 2,400 Lbs @ 0% MC.
Green Ton (GT) 2,000 lbs of woody material, as received and includes the weight of water in the material.
Bone Dry Ton (BDT) 2,000 Lbs of woody material @ 0% MC. - The most accurate measure for energy purposes.
Wood density Range for Western softwoods, 23 to 28 lbs/ft3 @ 0% MC. Varies with species and location.
Cord Stack of wood, 4'x 4'x 8' or 128 gross cubic feet (usually about 80-90 net cubic feet but varies widely with log diameter)
Board foot (BF) A measure of the volume of wood fiber in lumber Lumber scale form nominally equal to 1/l2th cubic foot.
Board foot (BF) There are many varieties of log scale measuring
Log scale systems. Converting BF log scale to BF lumber scale depends upon the log scale system.
One Log Truck Load Approximately 5,500 BF, log scale.
Log Weight 1,000 BF, logs, log scale, has a weight range of from 6,463 lbs to 10,262 lbs depending upon species.
When converted to residue, 1,000 BF yields 2 units of a combination of chips, sawdust, and hog fuel.
Moisture content can be measured on a wet or a dry basis. In engineering calculations moisture content (MC) is usually expressed as a percent of the total weight. This is the wet basis method. In forest product calculations, the dry basis method is used; the moisture content is expressed as a percent of the dry weight of the wood. Thus:
MC (% Wet Basis) = (Water Weight) / (Total Weight) x 100
MC (% Dry Basis) = (Water Weight) / {(Total Weight) - (Weight of Water)} x 100
If M & D represent the moisture contents on the moist-wood and dry-wood bases respectively, then:
M = D / (1 + D) and D = M / (1 - M)
Â
|
UNIT of HEAT VALUE |
Btus |
|
 |
 |
|
1 KWhr |
3,413 |
|
1 Cubic Foot Gas |
1,000 |
|
1 Therm Gas |
100,000 |
|
1 lb Bituminous Coal |
12,500 |
|
1 lb Charcoal |
13,000 |
|
1 Gallon #2 Diesel Oil |
140,000 |
|
1 Gallon Propane |
92,000 |
|
1 Ton Whole Tree Chips |
 |
|
(50% moisture) |
8.3 to 8.8 MBtu |
|
1 quad |
1015 |
|
 |
 |
|
1 Boiler Horsepower |
33,475 (33,472) |
|
 |
= 9.8095 kW |
|
1 Btu (British Thermal Unit) |
= 0.29307 watt |
|
1 million Btu (1MBtu) |
= 293.07 kW |
|
1 lb of steam/hr |
= 0.2843 kW |
|
1 lb of steam |
= 1000 Btu |
Moisture Content Heating Value Bulk Density
Wood Fuel Wet Basis (Btu/lb) (lbs/ft3)
Whole tree chips 50% 4000 24
" 45% 4800 23
Green sawdust 50% 4000 20
Dry planer shavings 13% 6960 6
Dry sawdust 13% 6960 11
Wood pellets 10% 7200 35
" 8% 8000 45
* Source: The Industrial Wood Energy Handbook, 1984.
* Second Source: Wood Burning for Energy [92]
Throughout this report many figures will be given on volumes, weights and energy equivalents of biomass fuels. To give some feel for the size of these numbers, I will sometimes give an "AGNI" equivalent. This means roughly the amount of biomass fuel that the AGNI boiler would consume over a year operating at 50% capacity day & night, or the amount of fuel that will heat a typical 100,000 sq. ft. uninsulated industrial facility or a 200,000 sq. ft. insulated building using an AGNI Boiler in the Pacific Northwest.
*
for Footnotes and Further Information
{Footnote Numbers Correspond to Source Numbers}
{Key Categories in Italics}