BLOG: Power Perspectives

[#1]

Did you know that methane gas is 21 times more harmful than carbon dioxide when it comes to global warming?

Those of you in the landfill business are aware of the need to mitigate the methane. While flaring or running pipes to tap into existing natural gas lines offers a solution, what if someone told you that methane could fuel a generator set, offsetting your electricity costs and even bring in cash? What if that positive return could continue for up to twenty years?

Getting started:

• One of the first important steps – you need to analyze the quality of your gas. What is the concentration of methane? This is vital to the success of your project.
• Based on the sample, you can determine what other elements could cause harm to an engine, dictating how you want to design your gas cleaning system.
• It also helps you size the power system that you'll need to convert it to electricity.

Several technologies can do this – my background is in reciprocating generator sets. I like recips because they have a long life, are efficient and offer a pretty short payback cycle.

If you come to the conclusion that the project makes economic sense, you'll need a collection system. In general, gas is extracted by using a series of wells and a vacuum system. Pipes are inserted deep into the landfill to provide a point of release for the gas. A slight vacuum is then applied in the pipe to draw the gases to a central point where they can be processed and treated for use in generating electricity.

Rules of thumb:

• Landfill gas develops in landfills in approximately one to three years, depending on the type of waste.
• A landfill must be at least 40 feet (12 meters) deep and have at least one million tons of waste in place for landfill gas collection and power production to be technically feasible.

There are several financial benefits to utilizing landfill gas for power generation:

• Support your own energy needs
• Sell excess to a utility
• Earn carbon credits

In addition, you are offsetting emissions that would be released had the energy been generated by traditional coal-burning methods. It also helps you establish yourself as a good community partner – taking advantage of "green" technology.

There are obvious benefits but what are the road blocks?

• Getting management buy-in?
• Choosing a developer?
• Financing the project?
• Determining which government grants/incentives apply to you? Can your stimulus plan help?

Which of these do you see as the biggest challenge? What strategies do you have to overcome them? Please post your comments below.

Message Edited by woodag on 06-12-2009 12:37 PM

[#2]

I have been very involved in this Landfill Gas Cogeneration business. In fact, Operations people from Waste Management told me at one site visit that the Electricity Generation business unit was the most profitable in the company. They exclusively use Cat engines. 

[#3]

The power generation from Landfill gas is very attractive for all stake holders. As the waste is managed by Government normally, therefore, their involvement makes less feasible in Pakistan due to volatile government policies and priorities. All stake holders try to be safe to avoid risk involved in investment. So, in my opinion Financing the project is more critical to think about the project. If government grants locally / internationally are available then a pilot project can be worked out on win win situation to attract and develop more similar sites. The involvement of Caterpillar upfront can be more attractive to Local Government to involve in this project.

I have visited some Landfill sites outside Pakistan and workedout some basic calculations. 

Sadat Hussain Qurashe

Six Sigma Blak Belt

[#4]

Thouhg I have little experience on the subject, I found it very interesting as the technology seems to be quite environment friendly.

Sumanta

[#5]

Great post Dick! There is another factor to take into account with energy generated by landfill gas - emissions control technology. Although there is no particulate matter generated, stationary engines burning landfill gas still need to reduce emissions of NOx, CO, and VOCs. For lean-burn engines, this may require  oxidation converters and/or SCR. Another issue that often comes into play with landfill gas is the possible presence of siloxanes which can "mask" a catalyst and prevent it from functioning. Special filters upstream from the emissions control technology are needed to remove the siloxanes if they are present in the landfill gas.

LR

www.cleanairsys.com

[#6]

Basically we need the trash to be bio-degradable. If the landfill consist mainly plastic, there's no bio-breakdown & thus, no methane gas to collect. The concept can be applied in agricultural waste disposal system.

[#7]

I was involved in a large Landfill Gas project, as a Build-Own-Operate installation, 18 years ago. It was sized at 8.6MW, based on the landfill owner's gas energy flow rate advice (which they obtained from a Consultant). We only managed to produce full power for 30 minutes!

Legal proceedings resulted, and a lot of experimentation to develop legal positions and defences. To make a long story short, we learned a lot about landfill gas field operation, and it is critical to developing any landfill gas generating plant.

The first major error, by the consultant, was that they drilled each well in the landfill, individually, and pumped it almost immediately to determine the gas production rate. Then they moved on to another well location, and did the same, repeating this process until they had covered the landfill area. What they didn't cater for was the effect that pumping one well has on adjacent wells, and they were over-simplistic in totalling up the individual well gas flow rates. So, lesson 1 is to drill the well field, pipe the system up, and pump the whole well field from the common piping to determine the whole gas flow/energy rate as one entity. Allow time for the production to establish, and trim each well's flow to minimise any oxygen being drawn in because oxygen kills the methane production rates.

This will enable determination of the size of the landfill gas generating plant to be employed.

Over time, the landfill well flow rates need to be continually monitored and flow rates (via the small vacuum applied) controlled to keep air ingress at the minimum possible. Sometimes this can be hard to manage if the topsoil over the landfill dries out, making it easier to suck air into the fill. There was some debate about returning condensate collected from the gas back into the landfill, to maintain moisture levels, but environmental authorites were not keen on this.

The methane content can vary from a best of 70% (which doesn't last for long, if you start pumping the gas) to below 50%. The balance is usually carbon dioxide, with small traces of other materials. The gas is always wet, so some drying is necessary, and even scrubbing, if the halenogenic acids are high. Use care to design your gas processing plant to allow for the dew point of the condensate, at the pressures that you will be operating in. We had a relatively high gas pressure, which resulted in the dew point being close to normal ambient air temperatures, and so we had a lot of problems with fouling of gas train piping with condensate.

Landfill gas projects are very widespread in Australia, and they can be quite profitable.

[#8]

I am currently in the permitting phase of a 1.6 MW lfg project, and have been for the last year and a half! MPCA is giving my permit engineer fits! They have required me to do a AERA as well as model all fugitive dust and vehical emissions. Waste management was able to put in a plant 42 miles away with out these problems, Maybe I hould get the Roseitti brothers to help me???

[#9]

I have been handling repairs & maintenance of 2nos. 900kva fully automatice with load sharing at katunayake International Air port Sri Lanaka for the last fefteen years. during this period I have noticed the large amount of food wast removed from passanger flights are collected by the local authorites. can this wast be converted to usefull gas to use on this two plants. if anyone is interested in a joint venture the proposals are well come.

[#10]

That's a big Airport. What are they doing for waste water treatment? If you have a waste water digester system you could potentialy add the food waste to that to increase methane production to the point that it supplies enough fuel to run an ICE........Good luck...

[#11]

Hi Setti,

If you have a need to dispose of biodegradable wastes and are seeking a JV you might contact David Murphy [david.murphy@aerobicbiotech.com] of Aerobic Biotech Corp who is planning a composting facility in Colombo.

[#12]

I see a recurring theme in the various posts above: the LFG quality is extremely variable in different areas of the same landfill, is subject to flow disruptions and can be extremely fugitive. So it is extremely difficult to predict a given outcome even after extensive sampling and testing. (So the process is a bit like chasing moonbeams)

The answer of course is to separate MSW, remove and recycle all non-combustibles, and to then convert the combustible material into a refuse derived fuel for gasification into a syngas that can be fired in either turbines or reciprocating engines.

The technology exists, but the apparently the initiative does not. If anyone cares to contact me at pmason at telus.net (substitute 'at' with @), I would be happy to send them data on how an effective conversion of waste can be accomplished.

[#13]

I am writing to comment on t300dle's June 30th posting specifically in regards to the issue of gas volumes.

My company is the largest biogas power plant (landfill and digester) building in Canada. Of all the many projects we've constructed over the years only one project has ever had a good match between biogas volumes and the installed generation capacity. In all other cases the generation capacity installed has exceeded the actual volumes of gas available.

The fundamental reason for the mismatch has been gross over-estimation of biogas quantity and quality. This has consistantly been the case for both landfill and digester systems.

I explain to my customers that biogas volume projections are, typically, peak production numbers and have a huge tolerance band. Biogas, by the nature of how it's produced, is highly variable over time and the design of any gas utilization system, i.e. power plant, should be based on a conservative biogas estimate and not on a peak biogas estimate. I tell tham that gas volume projections are the same as automotive engineers designing their vehicle's speedometer to peg out at 200 MPH. Yes, in theory, the vehicle, under the right set of conditions, could go that fast. The reality is that it's not sustainable and disappointment is guaranteed for anyone owing an average car.

To maximize investment LFG and DG power plants should be designed to operate at 100% ouput for 100% of the time. That starts by right-sizing the plant to the amount & quality of biogas that is available all of time. You do that by taking  a very conservative view of any biogas projections. Alternatively the approach which I like best is having the person providing the projections agree to pay the difference in underutilized capacity resulting from biogas limitations. It's amazing how quickly those flow/quality estimates will start to shrink once their skin is in the game.