Bioenergy: A Sleeping GIANT
Bioenergy covers a multitude of different technologies--each with its own fit into the energy market
By Joyce Laird
There is no single technology when it comes to biomass energy generation. There are closed-loop, open-loop, biodigester, thermal digester and cogeneration processes. There are waste-to-energy (WTE) and landfill gas energy (LGE) technologies. All process a feedstock in a specific way to generate energy or combined heat/energy output.
A closed-loop system burns material that has been planted and harvested specifically for that purpose, while an open-loop system uses material that was not originally intended as a fuel source, such as wood scraps from a lumber mill or even municipal solid waste/sludge.
For utility-level biomass energy production co-firing and direct firing are most commonly used. Biodigesters and thermal digesters tend to fit into smaller power generation scenarios. Direct firing means that only biomass material is burned. Co-firing is using biomass material to supplement an existing technology such as coal or natural gas, reducing the need for the primary fuel and making the process greener.
Cogeneration/combined heat and power (CHP) generates both heat and power. A CHP system consists of an engine, a generator unit and heat exchangers that collect waste heat. Power plant electrical switch and control systems distribute the electricity and manage the engine, while hydraulic equipment ensures efficient heat distribution.
William P. Ewing is a partner in the Atlanta office of Barnes & Thornburg LLP, where he is co-chair of the firm’s Renewable Energy Practice Group. "We do a lot of work for utilities and developers in the renewables area," he says. "Many projects are not economical on their own and they rely on tax incentives to make them economical."
Ewing notes that biomass offers the most potential in regions of the US such as Georgia where there is a lot of timber and a timber management system in place and where solar and wind are not as viable. "However, biomass can be anywhere because it can use waste sitting on a forest floor or municipal solid waste from landfills. Also, it generates energy on demand, 24/7, the same as natural gas or coal—only in a clean manner. Solar and wind can’t do that."
Biomass power projects are typically funded by relying on significant federal and state tax incentives. These can easily fund over 60% of project cost. Developers typically partner with "tax equity investors" to obtain funding. Tax equity investors receive return based not only on cash flow but also federal and state tax benefits associated with the project. Investors are generally large taxpaying entities, such as banks, insurance companies and utilities. Tax benefits generally arise from two broad categories: tax credits and tax deductions."We structure the deals to be able to take advantage of all that is being offered," Ewing says.
The EPRI (Electric Power Research Institute) is a not-for-profit, funded by electricity producers and other energy sources. "We are predominantly only interested in biomass for electric energy generation," Dave O’Connor, project manager, says. "I break it down into two areas: building up the supply chain for sustainability, and finding the best way to take that supply and convert it into electricity. The best for one company is not necessarily best for another company.
"If looking at new generation, that’s one thing. If looking at being very efficient, that’s another. If looking to use existing assets then you may have two or three choices. We’ve got research going on in both the supply and technology side of the issue.
"In the US a lot of the drivers tend to come from the EPA," O’Connor continues. "There are critical things: the industrial boiler MACT—maximum achievable control technology—which says what your air emissions must be if you are biomass-fired only. The electric generation Unit A MACT has to do with coal-fired units, but it applies to biomass plants in that if you want to use an existing asset—for example, for co-firing—you want to know what your coal plant looks like."
As for WTE, O’Connor says that globally the capacity has expanded significantly in recent years, driven largely by policy considerations: "Many nations have banned landfills as inefficient and environmentally undesirable, leading to a steady increase in the annual tonnage of MSW—municipal solid waste—subjected to energy recovery. This has led to a proliferation of smaller-scale LFG and digester gas systems."
Biomass—A good example of changing a polluter into a clean energy source is what the DOE and Ameresco Inc. have done by creating a 34-acre (13.76-hectare) Biomass Cogeneration Facility at the Savannah River Site in South Carolina, once a coal power plant. The clean biomass fuel stock will consist of local forest residue and wood chips and bio-derived fuels. The plant has the capacity to combust 385,000 tons (349,272 t) of forest residue into 20 MW of clean power annually.
In Canada they are doing the same thing. Tim Christie, senior advisor for Energy Supply Transmission & Distribution Policy for The Ontario Ministry of Energy, says that by the end of 2014 Ontario is going to cease all use of coal for electricity generation. "One of the plants at Atikokan in northern Ontario will be converted to burn 100% wood pellets. It will generate about 200 MW.
"We are expanding bioenergy through two avenues: first through a feed-in tariff program that offers fixed rates for anybody who generates renewable energy. We’ve issued many contracts for bioenergy, mainly in the biogas sector. These are typically farm projects and treatment of sewage and municipal waste that produce biogas."
A total of four plants have the potential to be converted to biomass electricity production. Christie says that they are starting with this first project and will look at the results from this conversion.
"Biomass is a familiar technology as far as how it works so utilities are comfortable with it. It also has a benefit that most other renewable technologies don’t have in that it can be turned off and on to meet demand. As we get rid of coal, biomass can provide flexible, renewable power generation."
Biodigester—Biodigester biomass energy systems are not going to crank out the 100 MW needed for a utility, but they do great putting out 1 or 2 MW, which is plenty to power a large working farm.
Two years ago, Fiscalini Farms (Modesto, CA) installed a full biomass digester system for $3,750,000. The digester itself consists of two circular above-ground insulated concrete tanks. Each tank is 86' (26.2 m) in diameter, and 26' (7.9 m) in height. Heating tubes thoroughly heat waste to 100°F (38°C). Each of the two tanks was constructed according to California seismic regulations, using 500 cubic yards (126 m3) of concrete, and 50 tons (45.4 t) of reinforcing steel per tank. Inside each tank are four agitators, which stir the mixture to a homogenous combination. Each tank holds approximately 860,000 gal (3.26 million l) of effluent.
"Once the methane is produced by the bacteria," John Fiscalini, the farm owner says, "it rises to the top of the tank, and is trapped inside an expandable rubber bladder. A series of sensors within the system keep the exhaust levels within EPA regulation. It is then piped outside of the tanks, cooled and dried, and moved by blowers through a pipeline to our CHP unit. The CHP unit makes both electricity and hot water. It produces about 500 kW of electricity. The farm only uses 200 kW, so we sell 250 kW back to the grid and power a lot of homes in the area. It also produces enough heat for the system itself, the barns and cheese plant—and we still have heat left over."
This year Fiscalini is installing new off-site waste tanks to process FOG (fat, oil, grease) pumped out of local restaurant grease traps. It will be brought in by tanker truck. The sources already pay a tipping fee to landfills to collect the waste, so Fiscalini plans to charge the same or a lower fee.
"When we bring in this off-site waste, we can run the engine at a greater speed to get more gas out of the digesters, which in turn produces more electricity to sell to the utilities."
Pyrolysis—An extremely exciting biomass energy project is in progress at the Milwaukee School of Engineering (MSOE). Matthew J. Traum, an assistant professor in the Mechanical Engineering Department is heading this up. MSOE’s processor can handle a variety of organic materials.
"We can measure and control internal temperatures. The biomass processor changes the feed rate and heating of the material, depending on what the temperatures are. Instead of a digestion process, we use pyrolysis," Traum explains. "Because it is a thermochemical processor it can convert both cellulose and lignin to syngas leaving only bio-char [a fertilizer] as a product stream."
Standard aerodynamic microturbine blades can’t stand up to particulate matter or a two-phase flow. Traum’s undergraduate project team is working on a new disk turbine that can. "Disk turbines process two-phase flow without any damage," he says. "The hope is that our system will be able to take the syngas right from our biomass processor, feed it directly into a combustor where it will be heated through the combustion process, and then run the hot gasses through our disk turbine to produce electricity. This type of turbine is not only more robust, but much less expensive to manufacture than aerodynamic bladed turbines."
Another big difference in this system is that it is modular, with each unit about the size of two chest freezers, a big difference from the huge biodigesters that need to be put underground. "The idea is, if you are a small farmer," Traum says, "you would buy one, and if you have an industrial-scale farm, you could buy as many as you needed to produce electricity and heat. A key to our design is also the type of gas the system produces. A digester system produces methane gas and some larger hydrocarbons. Our system produces mostly carbon monoxide and hydrogen during the heating process that drives all of the volatile gasses from the biomass."
Engine Fuel & Emissions Engineering Inc. (EFEE; Rancho Cordova, CA) manufactures selective catalytic reduction (SCR) systems. "It’s the same basic principle that has been used for many years in power plants to reduce unwanted nitrogen emissions. You put the energy exhaust through the SCR similarly to the three-way catalytic converter on a car," Christopher Weaver, president, says.
"We’ve taken mobile SCR technology and adapted that to cogeneration and biomass digester systems. The key problem we had was the emissions from biogas are highly variable. We have to adjust the amount of reductant we are injecting to match the amount of oxygen and nitrites coming down the pipe. We put in solid state NOx sensors both upstream and downstream, adapted to this type of emission. It became a self-tuning unit that allows the system to find the level that always produces the minimum NOx emissions. Our latest system has the ability to control the exhaust temperature as it gets into the catalyst. This allows us to achieve even lower NOx emissions."
Waste-to-Energy—In Sydney, Australia, all household waste is sent to alternative waste treatment facilities using technology that includes anaerobic digestion. New York City wants to duplicate that effort by developing a state-of-the-art facility to convert that waste to clean energy as part of PlaNYC, the city’s ambitious sustainability agenda. The goal is to locate the facility within 80 miles (130 km) of the city and begin by processing a maximum of 450 tons (408 t) of waste per day. The city is seeking only the cleanest and latest waste-to-energy technologies, and the Request for Proposals specifically excludes conventional incineration proposals.
Jim Gittinger is the business development manager for the Babcock & Wilcox Power Generation Group's (B&W) waste-to-energy area. He says that small distributors and independent power producers have entered this market in the US by establishing biomass power facilities near waste sites and landfills. "They make money by selling power to the utilities who then distribute it. But there are issues with emissions and the permitting process can be very difficult."
B&W provides two boiler options when using refuse as a combustion fuel. The first, known as mass burning of MSW, uses the refuse in its as-received, unprepared state. The second technique uses refuse-derived fuel (RDF), where the as-received refuse is first separated, classified, and reclaimed in various ways to yield salable or otherwise recyclable products. The remaining material is prepared for firing in the boiler furnace.
"There is a fundamental difference," Gittinger says, "between basic biomass and waste-to-energy. In biomass you have to buy the fuel. With waste-to-energy, you are paid to take it. You have to be in a part of the country where the tipping fee is high enough—that is where the source pays the power facility to take the garbage rather than paying a landfill to take the garbage."
Mixed Technologies—Headquartered in France, AREVA is the global nuclear industry leader, but AREVA’s Renewables group is quickly expanding into wind, solar, bioenergies, hydrogen and storage.
Burning biomass is a carbon-neutral way of producing energy, since the CO2 released during combustion is the same CO2 that the organic fuel sources captured as they were growing. Every year, between 20,000 and 500,000 t of organic matter are recycled by AREVA’s bioenergy plants, which can burn all types of residues including wood, sugarcane, bagasse, industrial effluents and straw.
Because fuel supply, constraints, and envisaged profitability are specific to each project, AREVA’s design architects and construction engineers explore all the alternatives and opt for the most appropriate technology: combustion, anaerobic digestion or heat recovery. They select the most advanced components and services from around the world, taking charge of purchasing, optimization, and assembly.
Most importantly, no project can be successful without solid financing. AREVA provides a comprehensive package for the development of carbon assets throughout the life of the project, from the feasibility study to the acquisition and sale of credits.
In the US, AREVA has joined forces with Duke Energy (Charlotte, NC) in the joint venture ADAGE to create a project development and financing structure dedicated to the rollout of biomass energy solutions for this market.
B&W is involved in all energy areas; fossil, nuclear and renewables. "We’re an OEM and we basically supply boilers and pollution control equipment. We also have a division that operates and maintains power facilities," Phil McKenzie, business development manager for biomass, Power Generation Group, says. "We manufacture boilers for combusting biomass. We also make gasifiers for the gasification of biomass. Essentially if it is any energy conversion process we have a product line associated with it."
Some of B&W’s biomass technologies include bubbling fluidized-bed boilers, circulating fluidized-bed boilers, stoker-fired boilers and black liquor recovery boilers (process recovery). All fit specific combustion technologies and all units are custom designed to meet specific requirements. But the design is done within a framework of pre-engineered components to minimize engineering costs and delivery time.
"Our customers run from small projects to major utilities," McKenzie says. "They may want to construct a 100% biomass energy generation plant or co-fire an older one. We have many options. We also have systems that scrub the gas to remove all NOx emissions such as NOx, SO2, SO3, mercury and particulates, and we have sensor emissions monitoring systems that meet the needs of each type of biomass fuel to ensure emissions meet any current regulations."
McKenzie notes that globally the biomass energy area is growing rapidly, but in the US it has slowed down quite a bit. "It was moving ahead until the 1603 tax credits program expired in December 2011," he says. "Another issue has been market dynamics. With the recent recession, overall power demand is down. This affects power purchase agreements (PPAs), the cornerstone of plants. PPAs became harder to come by because there is already a surplus of electricity production.
"As we move out of the recession, we’re seeing increased manufacturing activity which increases power demand, and the creation of municipal waste. We are hoping to see a renewed demand for municipal solid WTE energy plants and also breathe life into the more standard forms of utility-scale biomass power generation in the US."
This article was first published in the 2012 edition of the Energy Manufacturing Yearbook.