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Biomethanation We provide Methane Gas Recovery products and services which provide fuel for generating power as well as cogeneration and trigeneration systems. BioMethane is generated from Anaerobic Digesters, Anaerobic Lagoons, Biomass Gasification, Biogas Recovery, BioMethane, Concentrated Animal Feeding Operations Landfill Gas to Energy, and Methane Gas Recovery. Unlike most companies, we are equipment supplier/vendor neutral. This means we help our clients select the best equipment for their specific application. This approach provides our customers with superior performance, decreased operating expenses and increased return on investment. Renewable Energy Technologies provides products and services relating to the biomethane produced from Publicly Owned Treatment Works and Wastewater Treatment plants. Cooler, Cleaner, Greener Power & Energy Solutions project development services are one of our specialties. These projects are Kyoto Protocol compliant and generate clean energy and significantly fewer greenhouse gas emissions. Unlike most companies, we are equipment supplier/vendor neutral. This means we help our clients select the best equipment for their specific application. This approach provides our customers with superior performance, decreased operating expenses and increased return on investment. Renewable
Energy
Technologies provides
project development services that generate clean energy and significantly
reduce greenhouse gas emissions and
carbon dioxide emissions.
Included in this are our
turnkey "ecogeneration"
products and services which includes renewable
energy technologies, waste to energy,
waste to watts and waste
heat recovery solutions. Other project development
technologies include; Anaerobic Digester,
Anaerobic Lagoon, Biogas
Recovery, BioMethane, Biomass
Gasification, and Landfill Gas To
Energy, project development services.
For more information: call us at: 832-758-0027 We are Renewable Energy Technologies specialists and develop clean power and energy projects that will generate a "Renewable Energy Credit," Carbon Dioxide Credits and Emission Reduction Credits. Some of our products and services solutions and technologies include; Absorption Chillers, Adsorption Chillers, Automated Demand Response, Biodiesel Refineries, Biofuel Refineries, Biomass Gasification, BioMethane, Canola Biodiesel, Coconut Biodiesel, Cogeneration, Concentrating Solar Power, Demand Response Programs, Demand Side Management, Energy Conservation Measures, Energy Master Planning, Engine Driven Chillers, Geothermal Heatpumps, Groundsource Heat Pumps, Solar CHP, Solar Cogeneration, Rapeseed Biodiesel, Solar Electric Heat Pumps, Solar Electric Power Systems, Solar Heating and Cooling, Solar Trigeneration, Soy Biodiesel, Trigeneration, and Watersource Heat Pumps. What
is BioMethane, BioMethanation and
Methanogenesis? BioMethane, after installation of the requisite equipment, is essentially free, as opposed to buying natural gas, presently costing around $6.00/mmbtu. Methanogenesis
is the production of CH4 and CO2 by biological processes that are carried
out by methanogens. More
About Biomass Gasification and BioMethanation Technology The production and disposal of large quantities of organic and biodegradable waste without adequate or proper treatment results in widespread environmental pollution. Some waste streams can be treated by conventional methods like aeration. Compared to the aerobic method, the use of anaerobic digesters in processing these waste streams provides greater economic and environmental benefits and advantages. As
previously stated, Biomethanation is the process of conversion of organic
matter in the waste (liquid or solid) to BioMethane (sometimes referred to
as "BioGas) and manure by microbial action in the absence of air,
known as "anaerobic digestion." Interest
in BioMethanation as an economic, environmental and energy-saving waste
treatment continues to gain greater interest world-wide and has led to the
development of a range of anaerobic reactor designs. These high-rate,
high-efficiency anaerobic digesters are also referred to as "retained
biomass reactors" since they are based on the concept of retaining
viable biomass by sludge immobilization. More and more, cities, counties and municipalities are faced with greater environmental compliance issues relating to their municipally-owned landfills, Publicly Owned Treatment Works ("POTW's") or Wastewater Treatment Systems. A city's landfill and/or POTW provides an excellent opportunity for cities to reduce their emissions as well as provide an additional revenue stream. These facilities may have valuable gases that our company recovers and pipes to one of our clean, environmentally-friendly cogeneration or trigeneration energy systems. Our company provides economic and ecological solutions for cities and municipalities and provide a new cash flow simultaneously. We offer turn-key solutions for cities that includes the preliminary feasibility analysis, engineering and design, project management, permitting and commissioning. We provide very attractive financing packages for cities that does not add to a city's liability, yet provides a valuable new revenue stream. And, we are also able to offer a turn-key solution for qualified municipalities that includes our company owning, operating and maintaining the onsite power and energy plant. At
the heart of the system is a (Bio) Methane Gas Recovery system similar
those used in Flare Gas Recovery or Vapor Recovery Units. Methane
Gas Recovery, Flare Gas Recovery, Vapor Recovery, Waste to Energy and
Vapor Recovery Units all recover valuable "waste" or vented
fuels that can be used to provide fuel for an onsite power generation
plant. Our waste-to-energy and waste to fuel systems significantly
or entirely, reduces your facility's emissions (such as Methane
Gas Recovery and vapor recovery units can be located in hundreds of
applications and locations. At a landfill, Wastewaster Treatment
System (or Publicly Owned Treatment Works - "POTW") gases from
the facility can be captured from the anaerobic digesters, and manifolded/piped
to one of our onsite power generation plants, and make, essentially,
"free" electricity for your facility's use. These
associated "biogases" that are generated from municipally
owned landfills or wastewater treatment plants have low btu content or
heating values, ranging around 550-650 btu's.
This makes them Additionally, if heat (steam and/or hot water) is required, we will incorporate our cogeneration or trigeneration system into the project and provide some, or all, of your hot water/steam requirements. Similarly, at crude oil refineries, gas processing plants, exploration and production sites, and gasoline storage/tank farm site, we convert your facility's "waste fuel" and environmental liabilities into profitable, environmentally-friendly solutions. Our
Methane Gas Recovery systems are designed and engineered for these
specific applications. It is important to note that there are many
internal combustion engines or combustion turbines that are NOT suited for
these applications. Our systems are engineered precisely for your
facility's application, and our engineers know the engines and turbines
that will work as well as those that don't. More importantly, we are
vendor and supplier neutral! Our only concerns are for the optimum
system solution Our turn-key systems includes design, engineering, permitting, project management, commissioning, as well as financing for our qualified customers. Additionally, we may be interested in owning and operating the flare gas recovery or vapor recovery units. For these applications, there is no investment required from the customer. For more information, please provide us with the following information about the flare gas or vapor:
What is an Anaerobic Digester? An
Anaerobic Digester is a device for optimizing the anaerobic digestion of
biomass and/or animal manure, and possibly to recover biogas also referred
to as BioMethane for energy production.
Digester types include batch, complete mix, continuous flow (horizontal or
plug-flow, multiple-tank, and vertical tank), and covered lagoon. Anaerobic
digestion is a biological process that produces a gas principally composed
of methane (CH4) and carbon dioxide (CO2) otherwise known as biogas. These
gases are produced from organic wastes such as livestock manure, food
processing waste, etc. The
The
U.S. EPA AgSTAR is an outreach program designed to reduce methane
emissions from livestock waste management operations by promoting the use
of biogas recovery systems. A biogas recovery system is an anaerobic
digester with biogas capture and combustion to produce electricity, heat
or hot water. Biogas recovery systems are effective at confined livestock
facilities that handle manure as liquids and slurries, typically swine and
dairy farms. Anaerobic digester technologies provide enhanced
environmental and financial performance when compared to traditional waste
management systems such as manure storages and lagoons. Anaerobic
digesters are particularly effective in reducing methane emissions but
also provide other air and water pollution control opportunities. AgSTAR
provides an array of information and tools designed to assist producers in
the evaluation and implementation these systems, including:
Methane
(and Biomethane) Emissions from Animal Waste Management Methane
emissions occur whenever animal waste is managed in anaerobic conditions.
Liquid manure management systems, such as ponds, anaerobic lagoons, and
holding tanks create oxygen free environments that promote methane
production. Manure deposited on fields and pastures, or otherwise handled
in a dry form, produces insignificant amounts of methane. Currently,
livestock waste contributes about 8 percent of human-related methane
emissions in the Biomethane from Anaerobic Digesters Methane (and Biomethane) is a gas that contains molecules of methane with one atom of carbon and four atoms of hydrogen (CH4 ). It is the major component of the "natural" gas used in many homes for cooking and heating. It is odorless, colorless, and yields about 1,000 British Thermal Units (Btu) [252 kilocalories (kcal)] of heat energy per cubic foot (0.028 cubic meters) when burned. Natural gas is a fossil fuel that was created eons ago by the anaerobic decomposition of organic materials. It is often found in association with oil and coal. The same types of anaerobic bacteria that produced natural gas also produce methane today. Anaerobic bacteria are some of the oldest forms of life on earth. They evolved before the photosynthesis of green plants released large quantities of oxygen into the atmosphere. Anaerobic bacteria break down or "digest" organic material in the absence of oxygen and produce "biogas" as a waste product. (Aerobic decomposition, or composting, requires large amounts of oxygen and produces heat.) Anaerobic decomposition occurs naturally in swamps, water-logged soils and rice fields, deep bodies of water, and in the digestive systems of termites and large animals. Anaerobic processes can be managed in a "digester" (an airtight tank) or a covered lagoon (a pond used to store manure) for waste treatment. The primary benefits of anaerobic digestion are nutrient recycling, waste treatment, and odor control. Except in very large systems, biogas production is a highly useful but secondary benefit. Biogas produced in anaerobic digesters consists of methane (50%-80%), carbon dioxide (20%-50%), and trace levels of other gases such as hydrogen, carbon monoxide, nitrogen, oxygen, and hydrogen sulfide. The relative percentage of these gases in biogas depends on the feed material and management of the process. When burned, a cubic foot (0.028 cubic meters) of biogas yields about 10 Btu (2.52 kcal) of heat energy per percentage of methane composition. For example, biogas composed of 65% methane yields 650 Btu per cubic foot (5,857 kcal/cubic meter). Anaerobic Digester DesignsAnaerobic digesters are made out of concrete, steel, brick, or plastic. They are shaped like silos, troughs, basins or ponds, and may be placed underground or on the surface. All designs incorporate the same basic components: a pre-mixing area or tank, a digester vessel(s), a system for using the biogas, and a system for distributing or spreading the effluent (the remaining digested material). There are two basic types of digesters: batch and continuous. Batch-type digesters are the simplest to build. Their operation consists of loading the digester with organic materials and allowing it to digest. The retention time depends on temperature and other factors. Once the digestion is complete, the effluent is removed and the process is repeated. In a continuous digester, organic material is constantly or regularly fed into the digester. The material moves through the digester either mechanically or by the force of the new feed pushing out digested material. Unlike batch-type digesters, continuous digesters produce biogas without the interruption of loading material and unloading effluent. They may be better suited for large-scale operations. There are three types of continuous digesters: vertical tank systems, horizontal tank or plug-flow systems, and multiple tank systems. Proper design, operation, and maintenance of continuous digesters produce a steady and predictable supply of usable biogas. Many livestock operations store the manure they produce in waste lagoons, or ponds. A growing number of these operations are placing floating covers on their lagoons to capture the biogas. They use it to run an engine/generator to produce electricity. The Digestion ProcessAnaerobic decomposition is a complex process. It occurs in three basic stages as the result of the activity of a variety of microorganisms. Initially, a group of microorganisms converts organic material to a form that a second group of organisms utilizes to form organic acids. Methane-producing (methanogenic) anaerobic bacteria utilize these acids and complete the decomposition process. A variety of factors affect the rate of digestion and biogas production. The most important is temperature. Anaerobic bacteria communities can endure temperatures ranging from below freezing to above 135° Fahrenheit (F) (57.2° Centigrade [C]), but they thrive best at temperatures of about 98°F (36.7°C) (mesophilic) and 130°F (54.4°C) (thermophilic). Bacteria activity, and thus biogas production, falls off significantly between about 103° and 125°F (39.4° and 51.7°C) and gradually from 95° to 32°F (35° to 0°C). In the thermophilic range, decomposition and biogas production occur more rapidly than in the mesophilic range. However, the process is highly sensitive to disturbances such as changes in feed materials or temperature. While all anaerobic digesters reduce the viability of weed seeds and disease-producing (pathogenic) organisms, the higher temperatures of thermophilic digestion result in more complete destruction. Although digesters operated in the mesophilic range must be larger (to accommodate a longer period of decomposition within the tank [residence time]), the process is less sensitive to upset or change in operating regimen. To optimize the digestion process, the digester must be kept at a consistent temperature, as rapid changes will upset bacterial activity. In most areas of the United States, digestion vessels require some level of insulation and/or heating. Some installations circulate the coolant from their biogas-powered engines in or around the digester to keep it warm, while others burn part of the biogas to heat the digester. In a properly designed system, heating generally results in an increase in biogas production during colder periods. The trade-offs in maintaining optimum digester temperatures to maximize gas production while minimizing expenses are somewhat complex. Studies on digesters in the north-central areas of the country indicate that maximum net biogas production can occur in digesters maintained at temperatures as low as 72°F (22.2°C). Other factors affect the rate and amount of biogas output. These include pH, water/solids ratio, carbon/nitrogen ratio, mixing of the digesting material, the particle size of the material being digested, and retention time. Pre-sizing and mixing of the feed material for a uniform consistency allows the bacteria to work more quickly. The pH is self-regulating in most cases. Bicarbonate of soda can be added to maintain a consistent pH, for example when too much "green" or material high in nitrogen content is added. It may be necessary to add water to the feed material if it is too dry, or if the nitrogen content is very high. A carbon/nitrogen ratio of 20/1 to 30/1 is best. Occasional mixing or agitation of the digesting material can aid the digestion process. Antibiotics in livestock feed have been known to kill the anaerobic bacteria in digesters. Complete digestion, and retention times, depend on all of the above factors. Producing and Using BiomethaneAs long as proper conditions are present, anaerobic bacteria will continuously produce biogas. Minor fluctuations may occur that reflect the loading routine. Biogas can be used for heating, cooking, and to operate an internal combustion engine for mechanical and electric power. For engine applications, it may be advisable to scrub out hydrogen sulfide (a highly corrosive and toxic gas). Very large-scale systems/producers may be able to sell the gas to natural gas companies, but this may require scrubbing out the carbon dioxide. Using the EffluentThe material drawn from the digester is called sludge, or effluent. It is rich in nutrients (ammonia, phosphorus, potassium, and more than a dozen trace elements) and is an excellent soil conditioner. It can also be used as a livestock feed additive when dried. Any toxic compounds (pesticides, etc.) that are in the digester feedstock material may become concentrated in the effluent. Therefore, it is important to test the effluent before using it on a large scale. EconomicsAnaerobic digester system costs vary widely. Systems can be put together using off-the-shelf materials. There are also a few companies that build system components. Sophisticated systems have been designed by professionals whose major focus is research, not low cost. Factors to consider when building a digester are cost, size, the local climate, and the availability and type of organic feedstock material. In the United States, the availability of inexpensive fossil fuels has limited the use of digesters solely for biogas production. However, the waste treatment and odor reduction benefits of controlled anaerobic digestion are receiving increasing interest, especially for large-scale livestock operations such as dairies, feedlots, and slaughterhouses. Where costs are high for sewage, agricultural, or animal waste disposal, and the effluent has economic value, anaerobic digestion and biogas production can reduce overall operating costs. Biogas production for generating cost effective electricity requires manure from more than 150 large animals. Below-ground, concrete anaerobic digesters have proven to be especially useful to agricultural communities in parts of the world such as China, where fossil fuels and electricity are expensive or unavailable. The primary purpose of these anaerobic digesters is waste (sewage) treatment and fertilizer production. Biogas production is secondary. Accomplishments
The AgSTAR Program has been very successful in encouraging the development
and adoption of anaerobic digestion technology. Since the establishment of
the program in 1994, the number of operational digester systems has
doubled. This has produced significant environmental and energy benefits,
including methane emission reductions of approximately 124,000 metric tons
of carbon equivalent and annual energy generation of about 30 million kWh.
The graph below shows the historical use of biogas recovery technology for
animal waste management.
The
development of anaerobic digesters for livestock manure treatment and
energy production has accelerated at a very fast pace over the past few
years. Factors influencing this market demand include: increased technical
reliability of anaerobic digesters through the deployment of successful
operating systems over the past five years; growing concern of farm owners
about environmental quality; an increasing number of state and federal
programs designed to cost share in the development of these systems; and
the emergence of new state energy policies (such as net metering
legislation) designed to expand growth in reliable renewable energy and
green power markets. In
the past 2 years alone, the number of operational digester systems has
increased by 30%. For more detailed information on anaerobic digester use
in the The
process of anaerobic digestion consists of three steps. This
section describes the anaerobic digestion (AD) process, outlines
guidelines for assessing the feasibility of AD and biogas usage at a swine
facility and provides summary information on AD system performance and
reliability. Anaerobic
Digestion Technology Description AD
promotes the bacterial decomposition of the volatile solids (VS) in animal
wastes to biogas, thereby reducing lagoon loading rates and odor. The
primary component of an AD system is the anaerobic digester, a waste
vessel containing bacteria that digest the organic matter in waste streams
under controlled conditions to produce biogas. As an effluent, AD yields
nearly all of the liquid that is fed to the digester. This remaining fluid
consists of mostly water and is allowed to evaporate from a secondary
lagoon, land-applied for irrigation and fertilizer value or recycled to
flush manure from the swine building to the digester. The
benefits of AD include:
AD
takes place in three steps: hydrolysis, acid formation, and methane
generation. During the first step, hydrolysis, bacterial enzymes break
down proteins, fats and sugars in the waste to simple sugars. During acid
formation, bacteria convert the sugars to acetic acid, carbon dioxide and
hydrogen. Then the bacteria convert the acetic acid to methane and carbon
dioxide, and combine carbon dioxide and hydrogen to form methane and
water. Digester
technologies that can be used to collect biogas from swine facilities
include:
Although
a sequencing batch reactor has been used for AD at one swine facility in
the Appendix
B provides contact information that can help producers find AD system
designers/installers, odor control technologies, generators, heating and
cooling equipment, and other information to help manage air and water
quality at hog facilities. Covered
lagoon digesters are the simplest AD system. These systems typically
consist of an anaerobic combined storage and treatment lagoon, an
anaerobic lagoon cover, an evaporative pond for the digester effluent, and
a gas treatment and/or energy conversion system. Figure 1 shows a typical
schematic for a floating covered anaerobic lagoon.
Figure
1 . Covered anaerobic lagoon digester Covered
lagoon digesters typically have a hydraulic retention time (HRT) of 40 to
60 days. The HRT is the amount of time a given volume of waste remains in
the treatment lagoon. A collection pipe leading from the digester carries
the biogas to either a gas treatment system such as a combustion flare, or
to an engine/generator or boiler that uses the biogas to produce
electricity and heat. Following treatment, the digester effluent is often
transferred to an evaporative pond or to a storage lagoon prior to land
application. Climate
affects the feasibility of using covered lagoon digesters to generate
electricity. Engine/generator systems typically do not produce sufficient
waste heat to maintain temperatures high enough in covered lagoon
digesters in the winter to sustain consistently high biogas production
rates. Using propane or natural gas to provide additional heat for the
lagoon contents is typically not an economically viable option. Without
that additional heat, most covered lagoon digesters produce less biogas in
colder temperatures, and little or no gas below 39 FACE=
"Symbol">° F. As a result, covered lagoon digesters are most
appropriate for use in warm climates if the biogas is to be used for
energy or heating purposes. Complete
mix digester systems consist of a mix tank, a complete mix digester and a
secondary storage or evaporative pond. The mix tank is either an
aboveground tank or concrete in-ground tank that is fed regularly from
underfloor waste storage below the animal feedlot. Waste is stirred in the
mix tank to prevent solids from settling in the waste prior to being fed
to the digester. The complete mix digester is essentially a
constant-volume aboveground tank or in-ground covered lagoon that is fed
daily from the mix tank. Complete mix digesters with in-ground lagoons
often employ covers similar to those used in covered lagoon digesters. In
the digester, a mix pump circulates waste material slowly around the
heater to maintain a uniform temperature. Hot water from an
engine/generator cogeneration water jacket or boiler is used to heat the
digester. A cylindrical aboveground tank, such as that shown in Figure 2,
optimizes biogas production, but is more capital intensive than in-ground
tanks. The only operating AD system in Source:
EPA. (February 1997). AgStar Technical Series: Complete Mix Digesters –
A Methane Recovery Figure
2 . Complete mix digester schematic Complete
mix digesters have an HRT of 15 to 20 days, which means that complete mix
digesters can reduce the overall lagoon volume required for waste storage
and treatment. This makes complete mix digesters comparable to covered
lagoon digesters in cost, despite the increased complexity of stirring,
mixing and plumbing components. In addition, biogas production rates, and
therefore heat and electricity production, are greater and more consistent
than for covered lagoons. This can help reduce system payback periods
compared to covered lagoon systems. Like covered lagoon systems, digester
effluent from complete mix digesters is frequently stored in evaporative
ponds or storage lagoons. System
Requirements This
section provides guidelines for conducting a preliminary assessment of the
feasibility of using AD at a swine facility. Although AD system
requirements will vary depending on the application and system design,
there are some rule-of-thumb measures that should be noted when assessing
the feasibility of AD at a given location. For AD to potentially be
technically feasible and cost-effective, a swine facility should:
If
the above characteristics are present, the facility is a possible
candidate for AD. Many pre-existing waste storage and treatment lagoons
are too large to practically or cost-effectively employ covers over
their entire area. Partial covers may be an option to recover methane
from these older systems, as an alternative to installing a completely
new storage and treatment lagoon system. If
energy recovery is to be employed, methane production and gas quality
should be considered and compared to energy requirements at the
facility. Daily biogas production at installed farm-based anaerobic
digesters in the Facilities
that are located south of the line of climate limitation in Figure 3 are
usually warm enough for cost-effective energy recovery from covered
lagoon digesters. In most cases, facilities north of the climate line in
Figure 3 are too cold for cost-effective energy recovery from covered
lagoon digesters. Complete mix digesters can be used in cold or warm
climates. If odor control is the only objective, either covered lagoon
or complete mix digesters may be used, but odor control will be less
effective in the winter for covered lagoon digesters south of the line
of climate limitation in Figure 3. In general, complete mix digesters
are the most appropriate choice for use in Colorado.
Figure
3 . Line of climate limitation for biogas energy recovery Table
2 shows which digesters are appropriate for the waste collection
strategies at covered swine facilities. Complete mix digesters can
operate with a waste total solids (TS) percentage between 3 and 10
percent, while covered lagoon digesters can use waste with a TS
percentage less than 2 percent. Table
2 . Matching a digester to existing waste collection practices
Source
– Adapted from: EPA. (July 1997). AgStar Handbook: A Manual for
Developing Biogas Systems at Commercial Appendix
C describes each of the various waste collection technologies listed in
Table 2. Biogas Utilization Systems This
section discusses some of the biogas utilization options that are
available for use with AD. Electricity generation with waste heat recovery
(cogeneration) and direct combustion and use in equipment that normally
uses propane or natural gas are the two primary options for biogas
utilization. Electricity generated using biogas can be generated for
on-farm use or for sale to the electric power grid if an economically
attractive power purchase agreement can be negotiated through the local
utility or rural electric cooperative. Direct combustion allows the gas to
be used in existing equipment that normally uses propane or natural gas
such as boilers or forced air furnaces with minor equipment modifications.
Combustion is usually a seasonal use for biogas, as most boiler and
furnace applications are only required during the winter. The EPA FarmWare
manual describes some characteristics of engine/generator and direct
combustion systems that can be used with biogas. The following subsections
draw from the FarmWare manual to provide some basic information about the
use of these systems at covered swine facilities and other farm
applications. Electricity Generation Commercial
electricity generation systems that use biogas typically consist of an
internal combustion (IC) engine, a generator, a control system and an
optional heat recovery system. IC
engines designed to burn propane or natural gas are easily converted to
burn biogas by adjusting carburation and ignition systems. Such engines
are available in nearly any capacity, but the most successful varieties
are industrial engines that are designed to work with wellhead natural
gas. A biogas-fueled engine will normally convert 18 to 25 percent of the
biogas Btu value to electricity. Two
types of generators are used on farms: induction generators and
synchronous generators. Induction generators operate in parallel with the
utility and cannot operate as a stand-alone power source. Induction
generators derive their phase, frequency and voltage from the utility.
Synchronous generators operate as an isolated system or in parallel to the
utility, and require more sophisticated intertie systems to match output
to utility phase, frequency and voltage. Control
systems are required to protect the engine and the utility. Control
packages are available that can shut the engine off due to mechanical
problems, utility power outage or utility voltage and frequency
fluctuations, or in the event that excess power is generated that the
utility will not accept. Generators that operate in parallel with the
utility system, such as induction generators, require an intertie system
with safety relays to shut off the engine and disconnect from the utility
in the event of a problem. Intertie negotiations with a utility for
induction generators are typically much easier than for a synchronous
generator, due to the level of control the utility has over the
characteristics of power entering the grid from an induction generator.
The primary advantage of a synchronous generator is its ability to act as
a stand-alone power source. However, if operated as an isolated system, a
synchronous generator must be oversized to meet the highest electrical
demand, while operating less efficiently at average or partial loads. Due
to the system size and more complicated control requirements, a
synchronous generator operating as an isolated system is typically more
expensive than an induction generator. Biogas
engines reject approximately 75 to 82 percent of the energy input as waste
heat. This waste heat can be used to heat the digester and/or provide
water or space heat to the facility. Commercial heat exchangers can
recover waste heat from the engine water cooling system and the engine
exhaust, recovering up to 7,000 Btu/hour for each kW of generator load.
Waste heat recovery increases the energy efficiency of the system to 40 to
50 percent. Ongoing
research and development is focusing on the use of microturbines and fuel
cells for converting biogas to electricity. Microturbines are high-speed,
small-scale (typically less than 100 kW) gas-driven turbine systems that
produce electricity efficiently, have low emissions and require little
maintenance. Reflective Energies in The
Department of Energy’s WRBEP funded a project in fiscal year 2000 in Direct
combustion of biogas on-site in a boiler or forced air furnace can provide
seasonal heat to nurseries, farrowing rooms and other facilities at a
swine facility. A cast iron natural gas boiler can be used for most farm
boiler applications. The air-fuel mixture will require adjustment and
burner jets will need to be enlarged for use with low-Btu gas. Cast iron
boilers are available in many sizes, from 45,000 Btu/hour and up.
Untreated biogas may be used, but all metal surfaces of the boiler housing
should be painted to prevent corrosion. Flame tube boilers with heavy
gauge flame tubes may be used if the exhaust temperature is maintained
above 300 FACE= "Symbol">° F to prevent condensation. Forced
air furnaces can be used in place of direct fire room heaters, but biogas
must be treated to remove hydrogen sulfide because of potential corrosion
problems in metal ductwork. System
Performance and Benefits of AD There
are several measures of waste management system performance that are
relevant for producers considering the use of AD. These include:
AD
is the only waste management strategy available that provides the option
to recover methane for energy production. The
APCD has determined that the minimum standard for compliance with odor
control regulations for waste vessels and impoundments is an 80 percent
reduction in all odor-causing gases, including hydrogen sulfide, ammonia
and volatile organic compounds from waste vessels or impoundments. Table 3
compares the effectiveness of some of the odor control methods being
implemented at covered swine facilities in Table
3 . Odor control effectiveness of management strategies for
anaerobic lagoons
Source:
Iversen, Kirk and Jessica Davis. (February 1999). Innovations in odor
management technology. In
addition to regulating odors from waste lagoons, the new odor control
regulations have requirements for waste that is applied to agricultural
land. The new regulations for waste treatment at covered swine facilities
require that waste applied to agricultural land and not injected be
treated to remove at least 65 percent of the TS and over 90 percent of the
total volatile fatty acids or 60 percent of total VS. If not treated,
waste applied to agricultural land must be injected or knifed into the
soil upon application. Land application is not permitted between November
1 and February 28. Of the waste management strategies in Table 3, four
will help reduce the TS and VS content prior to land application.
Wet
feeding can reduce the TS and VS by a value equal to the dilution rate
of the feed (i.e., 3:1 ratio of water to feed). However, introducing
this type of feeding system increases water requirements and may
increase required anaerobic lagoon volumes. Solids separation can reduce
TS by 30 to 45 percent. Solids separation methods include screen
separators, mechanical presses, settling tanks, settling basins, vacuum
filters and many other means. An efficient AD installation will reduce
the TS percentage by up to 76 percent and VS by up to 90 percent. Of the
above technologies, AD with covered anaerobic lagoons is the only one
the APCD considers a proven technology because of their odor control
effectiveness. Therefore, unlike the other options above, covered
anaerobic digesters do not have to meet the additional testing
requirements for technologies that the APCD considers experimental. Composting
may or may not meet the TS requirement because it often involves the
addition of a bulking agent to increase TS to optimize waste
decomposition. However, composting can be effective at controlling odors
and reducing pathogens. The APCD is presently reviewing the compliance
status of one facility that uses composting. Composting has applications
besides manure treatment for livestock facilities. The Colorado
Governor’s Office of Energy Management and Conservation is currently
supporting the demonstration of composting technology for hog mortality
disposal at a hog farm in In
an AD system, most of the organic nitrogen (N) from the digester is
converted to ammonium, an easily manageable fertilizer with slow release
properties when compared to mineralized fertilizers. This is an
advantage over anaerobic lagoons alone. Organic N in the form of protein
and urea is mineralized in soil solution after land application. This
mineralized N can pose a groundwater problem when land-applied because
mineralized N can be converted to nitrates and leach into groundwater in
the spring and fall when plant uptake of N is low. A
disadvantage of reducing the nutrient content of lagoon effluent via AD
is the loss of the value of nutrients. Reducing the use of lagoon
effluent as fertilizer increases the need for industrial fertilizers,
the manufacture and transportation of which uses significant quantities
of petroleum. However, this loss is balanced by the benefits of
increased control farmers have over the nutrient content of effluent
used for irrigation purposes. System
reliability is a key concern for swine producers that are considering AD
with energy recovery as an objective. AD systems first began to be used
extensively after World War II in A
recent survey of anaerobic digesters yielded mixed results for system
reliability (Table 4). At farms across the Table
4 . Status of farm-based digesters at swine facilities in the
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