There's Gas in Them Thar Hills

Landfill operators in North Carolina and Rhode Island realize many benefits by recovering landfill gas for energy

By Joe Constance

When Bill Rowland passes the Wilder's Grove Landfill near Raleigh, North Carolina, he smells money. Why? He's president of Raleigh-based Natural Power, Inc., which extracts 4.5 million cubic feet of gas a day from the dump. And the gas fuels a nearby steam boiler owned by Natural Power that, in turn, generates $450,000 to $500,000 in annual gross revenue from steam sales.

Across the U.S., landfill owners are collecting the landfill gas (LFG) produced by decomposing organic matter and using it to heat homes and power local businesses, even major production facilities. "It's rewarding," says Eric Peterson, vice president of SCS Engineers in Reston, Virginia, a firm that specializes in landfills. "Anytime you collect the gas and use it for energy purposes, you're controlling migration of methane, you're controlling emissions, and you're recovering energy, which offsets other fuels that might be used for the same purpose."

Rowland is a pioneer when it comes to mining landfill gas in the East. In the 1970s, he operated a municipal solid waste landfill, but government regulators restricted his operation so much they forced him to close. A couple years later, he noticed steam coming out of the closed landfill. "Curiosity got the best of him," recalls his daughter Cynthia McCoy, vice president at Natural Power. "He checked it out and found it was landfill gas, and he figured he could stick a pipe in it and suck it out like water." After talking with several people in California who had developed landfill gas operations, "One thing led to another, and there was our first plant, making electricity and selling it to Carolina Power and Light." That was 1983, and it was first one on the east coast.

Rowland was onto something. Each person in the United States generates approximately 4.5 pounds of waste a day, or almost a ton yearly, most of which is deposited in municipal solid waste landfills. Each pound of this refuse produces approximately .1 cubic foot of gas annually. When you multiply this by the millions of pounds of refuse buried in U.S. landfills, you end up with enough LFG to supply 5 percent of the nation's natural gas needs.

Profiting From Pollution Prevention
People started paying attention when LFG, which is about 50 percent methane, became well-known as a potent greenhouse gas and an explosion hazard if left uncontrolled. Restrictions were placed on LFG emissions from landfills in the late 1970s, forcing owners and operators of landfills to capture the gas and flare it (burn it off) or recover it as energy.

LFG is generated continuously at landfills as waste decomposes. Therefore, a gas collection system at a landfill must operate round-the-clock. Typically, a blower creates a vacuum that sucks the methane gas from a series of wells dug into the landfill. Once collected, the gas goes to a central processing facility where it is compressed and treated to remove moisture and other contaminants. Processing ranges from minimal to extensive depending on the intended use. If the LFG is sold to a utility, the provider must eliminate all contaminants to supply pure pipeline-grade methane. Alternatively, the gas could be sold to a production plant, which often can accept gas streams containing only 50 percent methane.

LFG is typically a medium-Btu gas with a number of energy applications. The most prevalent use is in the production of electricity for sale to a local utility. Other options include direct use of the gas as boiler fuel and production of compressed natural gas for vehicle fuel. It burns cleaner than natural gas in terms of nitrous oxide emissions.

EPA officials estimate that more than 700 landfills across the country could install economically-viable landfill gas energy recovery systems, yet only about 200 energy recovery facilities are in place. In most instances, the LFG is burned off.

Generally, a prospective LFG-to-energy landfill needs to contain at least 1 million tons of refuse to be economically viable. As each pound of waste decomposes (a process that may take 30 years or more), it will produce a total of about 4.5 cubic feet of gas. The economics of operating a gas-conversion facility are based on the minimum amount of time a landfill will produce gas. Potential operators must determine if this operating lifetime is long enough for them to turn a profit.

The depth and shape of a landfill also are important factors. A landfill must be at least 40 feet deep so air won't be pulled into it by the vacuum used to withdraw the gas; air impedes the anaerobic environment in which the gas is produced. And a landfill should be made up of one large mound, as opposed to many small ones.

Another factor motivating the development of gas recovery operations is federal tax credits, which are available to owners and operators of LFG recovery facilities through 2007. Following the introduction of the tax credit, many landfills started recovering their methane gas. McCoy says Landfill gas plants also can be lucrative if you have a non-profit organization supplying grant money.

Success Stories
Natural Power, Inc. teamed with Raleigh Landfill Gas Corporation on the project to capture LFG from the Wilder's Grove Landfill. The recovered gas fuels a boiler at the Ajinomoto pharmaceutical plant, about a mile from the dump. During normal operation, the boiler uses about 1.27 million cubic feet of LFG each day to generate 24,000 pounds of steam an hour. Natural Power owns the boiler and sells the steam to Ajinomoto, which uses it to run a chiller that cools water for amino acid production. The arrangement has allowed the pharmaceutical plant to save about $140,000 annually in energy costs.

The gas collection system at Wilder's Grove consists of 80 wells drilled to depths of between 40 and 80 feet. The recovered LFG contains from 50 percent to 55 percent methane as well as carbon dioxide and organic carbons; it needs no purification for use in the boiler. Upon its closing in December 1997, the Wilder's Grove Landfill contained an estimated 5 million tons of refuse, which should provide methane gas for an estimated 15 to 20 years.

Ajinomoto uses 1.5 to 2 million cubic feet of gas a day. The rest is burned out the flare. 'We've been looking into different ways to use the gas that are cost-effective without tax credits or grant money," McCoy says. "We're looking at separating the gas into carbon dioxide and methane and making dry ice out of the carbon dioxide and putting the methane through a methanol plant to make methanol. It looks promising."

In 1996, Natural Power also began operating an LFG recovery facility at the White Street landfill in Greensboro, North Carolina. This landfill is owned by the city of Greensboro and contained about 5.5 million tons of refuse when it closed in 1997. Gas extracted from over 100 wells fuels a large steam boiler at Cone Mills, a textiles plant three miles from the recovery facility, by means of a 3-mile-long, 16-inch-diameter transmission pipeline. On average, 2 million cubic feet of LFG flow daily from the landfill.

Meanwhile, the extraction of LFG from a Rhode Island landfill also has met with success. In the early 1980s, residents in Johnston, Rhode Island began complaining about odors coming from the nearby 150-acre Central Landfill, managed by the Rhode Island Resource Recovery Corporation. In 1989, a local developer, Northeast Landfill Power Joint Venture, completed construction of an LFG-to-electricity facility. Now, the facility turns captured landfill gas into as much as 13.5 megawatts of electrical power an hour, enough to serve 17,000 households. The company sells the electricity to Narragansett Electric, the local utility, and pays Rhode Island Resource Recovery about $75,000 in monthly royalties.

"There's no reason to have a landfill and not recover the gas," says Dennis LaRusso, an engineer with Rhode Island Resource Recovery. It's a huge advantage."
By recovering energy from LFG, landfill owners and operators turn a liability into an asset. And who can turn up their nose to that?

Engineering a Landfill Gas Plant
Like a modern landfill, designing and building a plant to recover landfill gas for energy poses many technical challenges. As Eric Peterson, vice president of SCS Engineers in Reston, Virginia, says, "There's many levels of involvement in this type of work from initial concept and evaluating a project through design and construction and consulting during operations."

Many LFG project owners hire outside consulting firms to do the engineering work. Natural Power in Raleigh originally used SCS Engineers for the Wilder's Grove and White Street landfills, and now they use Engineering and Environmental Science Company, which has an office in Raleigh.

According to Peterson, the first step is an investigation to assess how much gas will be generated by the landfill over time. Evaluation involves reviewing information such as the landfill's size, the amount of waste in place, how long it's been filling, and how long it will keep taking waste or if it's closed. Engineers evaluate payback costs and assess various options if the owner plans to to sell electricity or steam to a utility or other user.

This can turn into a long, drawn-out process. As McCoy says, "Before you can even do one, you have to have permits on the flare, and there's all kinds of calculations involved. Then you have to size your equipment and piping. There's a lot of calculations you have to do to make sure you have a blower and a flare and the piping big enough to handle what gas is supposed to come out of the landfill."

The project's complexity depends on several factors such as local ozone sensitivity and air regulations, houses and creeks nearby, and hydrogeological concerns. "Everything has to be on grade because the gas is wet," McCoy explains. "Not only have you got gas moving, but you have condensate moving as well in these pipes, and that's a whole different ballgame -- you have to get rid of that." Engineers have to design tanks for it and figure out whether it can go down the sewer or if they have to hire someone to treat it.

If the project moves ahead, engineers design a gas collection system consisting of a network of polyethylene pipes and a blower. If it goes out for bid, they prepare bid documents, construction drawings, and specifications, and they provide construction engineering services and system startup. During operation, they provide operation and maintenance services as well as engineering for expanding and permitting.

As an environmental engineering firm, SCS Engineers makes a living in the landfill gas conversion field. "Landfill gas is about 40% of our business, which is very unusual. It's a real specialty niche for us," Peterson says. Headquartered in Long Beach, California, they deal nationally with 10 offices around the country. The firm uses mostly civil engineers, but some mechanical and chemical engineers as well as biologists get in on the fun.

Joe Constance is a freelance writer in Wyckoff, New Jersey.