Getting Started Converting Landfill Gas to Energy


Getting Started Converting Landfill Gas to Energy

Interview with Michael Michels - April 9, 2008


How does the interaction of consultant and landfill begin?
Usually, the landfill owner has an issue at the facility they need help with. They get in touch with a consultant they have worked with before, or meet new consultants at conferences or conventions. The waste management field is a small group of individuals, so a lot of relationships develop through word-of-mouth references.

Is gas-to-energy development a significant part of your business?
Cornerstone is a solid waste consulting firm so we deal with all things solid waste. Cornerstone is not an energy developer but that of a design engineer. About one third of our business is landfill gas and air services consulting. We also design new landfills or close old ones and we design transfer stations and material recycling facilities.

How many landfills have gas-to-energy facilities in place?

In general EPA's Landfill Methane Outreach Program (LMOP) reports that, there are about 400 landfill facilities that are converting their gas to energy. There are probably another 500 or so good candidates to run the same type of program. There are many landfills in the United States which do not have these facilities in place and there are thousands of landfills still flaring their gas.

What parameters does a landfill need to meet to make gas-to-energy conversion efficient and economical?

To pinpoint the parameters, we do what's called a feasibility study. We look at things like how much gas is being generated from the landfill, today and in the future, for sustainable purposes. We need to know how big the landfill is, how many tons of waste are accepted per year, and how wet the waste is. Also, what is the potential revenue from gas to energy and how much are the potential gas to energy operating expenses?

Many times landfills send their gas to a direct gas user or a facility that has a boiler for direct use of the gas. Landfill owners are trying to sell this gas as a replacement to natural gas or fuel oil at about 5 to 20% less than the cost of natural gas fuels. The landfill gains income from this sale and the customer reduces their expense. Another good way to create revenue is converting the landfill gas to electricity; the landfill can sell the gas to utility companies or to large users of electricity for them to then convert to electricity. With landfill gas being a renewable resource, there is usually preferred pricing from the utility companies that stem from the renewable attributes of this fuel.

There are also economic incentives for private companies that will have to pay federal income tax on the landfill. One of the biggest incentives is Section 45 of the IRS code, this program generates about a penny per kilowatt hour tax write-off on federal taxes. To take advantage of this, a project must be installed by December 31, 2008. We and The Solid Waste Association of North America (SWANA) and others are working with Congress to get this credit extended for another year or two, it’s a balancing act for Congress between reducing our dependency on coal power by using green renewable fuels and controlling federal taxes.

How long can a landfill generate sustainable levels of gas?
It varies depending on where the landfill is in the country and the moisture content of the waste. In the Midwest, where there is a lot of rainfall, a landfill will start generating gas after about a year or two when it becomes anaerobic, meaning methagens are being formed producing methane gas. In the Midwest, if just natural rain falls on the trash and no water is added to it, the landfill will generate methane gas for about 40 to 50 years. The lifecycle of a landfill has a gas generating period similar to a bell curve, with peak gas generation occurring a year or two after the landfill ceases accepting waste periods and then a slow decline over the remaining years. In places like Phoenix, Arizona, where there is more evaporation than rainfall the landfill waste isn't very wet, it may take five years before a landfill will start to generate methane and over a hundred years before it is fully decomposed. The amount of moisture in the trash is very important to the cycle. There's a push in some US States to have our trash decomposed during our lifetime. Some states have adopted a plan called organic stability, where landfill operators are encouraged to add water to their trash to get it to decompose within 40 years. Getting trash to decompose while the liners are at their strongest, eliminates a lot of potential mistakes that future generations will not have to pay for with their tax dollars.


What is the relationship between the size of a landfill and its ability to generate gas that can be converted to kilowatt hours?
It depends on where the landfill is on its bell curve for creating methane gas and the performance is based on every year of the landfill lifecycle. We create a financial model, which shows year by year the amount of gas production and the amount of electricity and the amount of revenue. The same is done for year two, three and so on, through the entire lifecycle of the project.

In general, 1000 scfm of LFG will produce about 2.7 MW of electricity or in other words, 1,000,000 tons of trash would power roughly 3000 homes. Brown County East Landfill (Green Bay, Wisconsin) for example, has about 5 million tons of waste in place, was closed in Year 2002 and is planning to install 2 engines to generate 1.8 megawatts of electricity.

Is that because of where they are on the curve?
Brown County has been closed for several years, so they are on the backside of the curve. Usually a project will run until the engines have burned all the gas or it does not have enough LFG to operate economically, then the project shuts down and flaring resumes. Brown County was planned as a 10-year operational project. In year 2009, they will have extra gas that the engines can not process, which will be flared off. But later, when the curve meets the exact capacity of the engines, the flares will be shut off. As time goes on, and the engines aren't running at full capacity the project will go back to flaring. See attached graphic.

How do you maximize gas collection and keep landfills at peak gas-generated capacity?
Every landfill's waste composition varies on a day-to-day basis. There might be an area within the landfill that is very dry and just 400 feet away it's soaking wet. So it is necessary to pump out liquid from some of the gas wells. A field technician will check the liquid levels in every gas well, usually within a year of initial operation and again after 5 years, to see trends in the water levels. Sometimes a pump will remove liquid from an area in the landfill and the liquid may never return. But in other areas, gas wells can have a pump running 24 hours a day and it still won't keep up with all the liquid rushing in. It can really vary, a landfill is a very dynamic, ever-changing environment. To maximize gas generation the waste must be watered, but if you're putting water in you've got to have a way to get it out, so the need for pumps is very important. The trend in America is to get trash to decompose faster, especially because the liners are strongest for the first 40 to 50 years of the landfill.

Are there different economics for landfills of different sizes, and different uses for the energy?
There are infinite ways to use the landfill gas - I read one about creating dry ice and another developed a glass blowing facility using methane gas. Depending on where the landfill is in the decline curve, there are opportunities everywhere for usage of the gas, even for small landfills, but they are not always economical. Take a small landfill, located in the middle of nowhere, because no one wanted it near any homes. Now the site is closing and it produces 300-500 scfm of gas, that could be put to good use but you can't pipe that gas 5 to 6 miles away, because it costs way too much. But if a greenhouse or an asphalt plant was interested in relocating their operation near this facility, it would be very economical to attach a low-flow system to a local company like that since their operations may not need a lot of energy. There are some industries actively seeking to locate plants near landfills. General Motors and BMW have plants that have supplemented their energy consumption through landfill gas. This is allowing smaller landfills to do something other than flare off the gas. We have a lot of landfills, thousands of them, that are just flaring off gas right now. It's a huge market but you have to have the right ingredients to make it economical: the correct waste moisture and an end-user nearby. Another example, landfill gas has methane and carbon dioxide; the carbon dioxide was typically wasted but could used for the carbonation in soda or possibly for welding gas. Today the industry does not beneficially utilize much of our CO2 from landfills, most of it gets burned off in flares. There are opportunities, it just takes an industry that it is interested.

How does the purity of the landfill gas affect how it is used?
Usually in a landfill decomposition process, methane and CO2 are the primary byproducts; about 50% each, or 60% methane and 40% CO2. They form together, they come out of the landfill together, and they can be burned together in an engine or flare. They don't have to be separated to produce power, but some facilities try to make compressed natural gas from landfill gas, so the CO2 has to be separated out to leave a higher concentration of methane. This CO2 can be used as a sellable product, but in most cases it's not. Using landfill CO2 in the food industry is probably still a little taboo, but there are other things it can be used for. At facilities that refine the landfill gas for methane it is critical to have low amounts of air in the gas in order to meet the natural gas specification.


Years since initial waste placement

Are their regulations, based on the size of a landfill, requiring them to have a gas-to-energy facility?

The federal government states that any landfill over 2.75 million tons has to determine if they need a gas collection system. At minimum, they have to test the landfill and possibly that means flare the gas. Most states discourage just direct venting. For example, Wisconsin has a state law that requires any landfill over 500,000 tons to have a gas collection system and at least flare. All regulations vary from state to state and from a consultant standpoint, it's very important for us to understand these regulations. At Cornerstone, we have a dedicated group that makes sure our designs are compliant with state regulations; they also find opportunities for our clients to get a competitive advantage by beneficially using the collected gas. Another example, in some US air districts that have non-attainment air programs, the regulators scrutinize the landfill owners for installing a gas-to-electricity. This scrutiny from the regulators is because of the extra emissions that the engines may cause. To remedy this, some of the landfill owners pump the gas off-site to an end-user, that way the emissions can be put under a seperate air permit instead of the landfills permit.

Places like San Francisco and Los Angeles have very tight air emission requirements that some electrical generation equipment engines just can't meet. Landfills are attempting to a replace coal-fired power, but if the air emission regulations cannot be met the project will be stopped. It is a balance between the environment and energy. We need to find more efficient ways of converting gas to energy, we also need the regulators to think about this engine emission not just as an emission source, but as an alternative to coal-fired power. Generating electricity with gas is a lot better for the environment than generating electricity from pollutant-causing coal. In my opinion, cleaner, gas-powered projects should be allowed to expand so we can have more electrical generation from landfill gas.

It's usually the larger cities that have severe non-attainment. In a large metropolitan area, there is a lot of trash. We are working really hard with these regulators to think of gas energy as a prevention of coal emissions. We are not quite there yet, these are the growing pains of our industry.

How does a site owner characterize the gas at his landfill?
Usually it's an assessment by a consultant. A sample of the landfill gas is taken to a laboratory and tested for methane, oxygen, nitrogen, BTU value, and various other things. It is all documented in a detailed laboratory report.

How do you take a gas sample?
If gas is already being extracted from the landfill and flaring, then somewhere between the blower and the discharges to the flare you tap into the pipe, or you can go to an existing sample port and fill a canister with this gas. If direct venting, drop a hose down the vent, but there will be atmospheric air mixing with this sample. There is portable equipment that can sometimes be used for testing, but generally this is not as accurate as laboratory testing. So, if you're doing a feasibility study, you will want to have laboratory testing done. The laboratory should check for hydrogen sulfide and something called siloxanes, these are silicone byproducts. Things like lipstick, toothpaste and deodorant all contain silicone, we throw them in the trash and they decompose, giving off a silicone gas. When silicone gas burns in an engine or a flare it converts into a sand particle; white, silica sand. These little particles leave deposits in engines creating havoc and requiring a lot of maintenance.

How would you measure for BTUs?
BTUs measures heat content, in British thermal units. BTU's are usually measured at a laboratory.

Michael S. Michels, P.E., is a Vice President of Cornerstone Environmental Group, LLC

Cornerstone Environmental Group, LLC (Cornerstone) is an environmental engineering consulting and field service company providing services to the solid waste industry and commercial and industrial clients throughout the nation. The firm was founded by industry leaders who have helped to develop and shape solid waste and environmental technology over the past 30 years. Although we specialize in solid waste services, our professionals are also well known in commercial and industrial settings, with experience assisting clients in commercial real estate, investment banking, and pulp and paper, to name a few. Cornerstone is a frequent resource advisor to the USEPA's Landfill Methane Outreach Program (LMOP).

You may contact Michael at
Cornerstone Environmental Group, LLC
607 Eastern Avenue
Plymouth, WI 53073
Toll Free: (877) 294-9070
Fax: (920) 893-9430