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Future Energy Sources 4.2 Methane & Biogas from Waste & Garbage

Posted August 26, 2007 4:42 AM by masu

Last week we looked at ways of extracting the energy in the waste stream from cities and towns by burning it in environmentally friendly ways and then using the heat as an energy source.

However, in the past much of the waste stream for population centres has jut been buried in landfill and left to decompose naturally. As the biological material in this rubbish is broken down by anaerobic bacteria considerable amounts of methane CH4 and other green house gasses are released and percolate up through the filling ultimately dispersing in the atmosphere.

Another problem is what is often referred to as sewer gas which is the byproduct of anaerobic decomposition of biological material in sewerage and contains toxins like hydrogen sulfide H2S, ammonia NH3 as well as the green house gasses methane CH4, carbon dioxide CO2 and nitrous oxides NOx.

Not only is this a waste of an energy resource, but the gasses being released into the atmosphere are far more detrimental to the atmosphere and cause considerably more green house heating than carbon dioxide CO2 and H2O which are the major byproducts of burning the gasses that come from the decomposition.

So, what can be done to both prevent the release of green house gasses into the atmosphere and utilize this wasted energy resource. There are several methods curently being used throughout the world:

  1. Electricity Generation: Landfill and Sewer gasses can be used to generate electricity that can either be used directly at the point of generation or distributed using the existing electricity grid. There are a number of technologies being used and under development including internal and external combustion engines as well as fuel cells. The main limiting factor is the level of contamination in the Sewer and Landfill gas. Internal combustion engines are generally more compact and efficient but they are not very tolerant to impurities in the fuel and as a result usually require the raw gas to be refined in some way prior to being used. On the other hand external combustion engines are less critical and can tolerate greater levels of fuel contamination and can usually use the raw gas without complex refining, however, they are usually less efficient. Fuel cells are the most critical technology when it comes to impurities and can be severely damaged if contaminants are not kept to a minimum. Fuel cells therefore require the greatest processing of raw fuel but can be highly efficient.
  2. Direct Use of Heat: This is the simplest way to use landfill and sewer gas and involves the burning of the gas and use of the resultant heat locally in things like kilns, boilers etcetera. It is however dependent on having a use for that head near the landfill or sewerage treatment facility.
  3. Combined Heat and Power: This is a combination of the previous two systems where the waste heat from the power generating process it utilized locally. This normally requires a mixture of complex technologies but it is the most energy efficient overall.
  4. Fossil Fuel Replacement or Substitution: This involves reefing the sewer or landfill gas to the point that it can be used as a direct substitute for natural gas. This inevitably requires complex technology and usually requires some sort of direct use of the raw sewerage or landfill gas to run the refining facility. It is a costly process and requires a considerable steady supply of raw materials that can be sustained over several years to make it economically viable.

You can read more on the use of landfill and sewer gas from the following links:

What's happening to both the current and past waste in your area? Is it just being buried in landfill or dumped in the ocean or rivers or are the resultant land fill and sewer gasses being used constructively. If land fill and sewer gas is being used what technologies have been developed and how is the resultant energy used? What about all those rubbish dumps that have been just left to rot, can we afford to just forget about them and allow the landfill gas percolate to up and be distributed in the atmosphere where it compounds the global warming problem?

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#1

Re: Future Energy Sources 4.2 Methane & Biogas from Waste & Garbage

08/26/2007 1:36 PM

Masu's description of the problems of using "sewer gas" is quite correct, the gas(es) do have to be refined to remove from the gas stream before it can be used, even the "direct use of heat" method. It is important to know that hydrogen sulfide (H2S) is the rotten egg smell (along with sulfur dioxide) one gets when sulfur is present in rotting waste. However, H2S is deadly poison and when it reaches its deadly concentration in the air, you will not smell it and you will die within seconds.

It is also to be noted that in refining crude oil, natural gas, or coal products, that all of it must have sulfur removed. Also, the other impurities must also be removed, which includes nitrous oxides, ammonia, carbon dioxide, carbon monoxide, water, sand, and heavy metals. This must be done before the crude, natural gas, or coal can be distributed as the products we use today. Naturally, all fuels, regardless of the source, must be safe for use, errr, let's say safer to use. no fuel is ever 100% safe, except, perhaps, hydrogen which is actually safer than natural gas.

Note, too, that the ammonia and nitrous oxides that are recovered from crude oil, natural gas or coal refining can go directly into the manufacturing of fertilizer. Ammonium Nitrate is a very powerful fertilizer as well is the primary ingredient in a powerful explosive.

As for the fuel cells, most all need hydrogen and oxygen for their fuel. One, however, the solid oxide fuel cell can operate with any gaseous at 850°C fuel, hydrocarbon or carbohydrate (alcohol). The solid oxide fuel cell will "reform" the fuel by its natural solid electrolyte and operating temperature and at an efficiency of 55% to 90%. Steam turbines, external combustion and internal combustion engines operate at best at 35% efficiency and thus waste two thirds of the heat energy generated. All heat engines that burn carbon fuels and air, except for the SOFC, do produce nitrogen oxides.

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#2

Re: Future Energy Sources 4.2 Methane & Biogas from Waste & Garbage

08/27/2007 9:06 AM

Hi Masu. Interesting articles.

"Not only is this a waste of an energy resource, but the gasses being released into the atmosphere are far more detrimental to the atmosphere and cause considerably more green house heating than carbon dioxide..."

Question: Doesn't anaerobic decomposition of biological products occur continuously in nature? If so, is our household contribution really a major contributor?

Jorrie

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#3
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Re: Future Energy Sources 4.2 Methane & Biogas from Waste & Garbage

08/27/2007 10:29 AM

Atmospheric methane CH4 has around 25 times the green house effect as carbon dioxide CO2 but it is not as simple as that. Unlike CO2 methane is not stable and will combine with oxygen to form water H2O and CO2. As a result methane has a large short term heating effect around 25 times as CO2 but as the time base increases the effect tend to decrease.

None the less, when looked at in a geological and climatology time frame we are facing what can only be described as extremely rapid warming and CH4 is definitely one of the contributing factors.

In the very distant past and I am talking about 3.5 Gyr ago, atmospheric methane levels were considerably higher, however, until recently the level was considerably lower and relatively stable. That is until the start of the industrial revolution and since then the levels of atmospheric CH4 have increased by around 150%.

There is much debate over the sources of atmospheric CH4 and the cattle belching hypothesis is not accepted by the majority of scientists, but our actions are directly and indirectly responsible for around 55% or around 330 Tg yr-1 of the CH4 released into the atmosphere. The other worrying thing is that the natural methane sinks are only removing around 80% of all the methane that ends up in the atmosphere.

So in answer to you question

  • Doesn't anaerobic decomposition of biological products occur continuously in nature? If so, is our household contribution really a major contributor?

Yes it does, but regardless of the actual source our actions are producing around 55% of the total amount of CH4 that enters the atmosphere and if we can reduce this it is at least in the short term, equivalent to reducing or CO2 output by around 25 times as much.

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#4
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Re: Future Energy Sources 4.2 Methane & Biogas from Waste & Garbage

08/27/2007 10:47 AM

When one reads his civil engineering text book chapters for waste disposal one finds that each human on earth produces waste that can digest to ±50 cubic feet of methane gas per day. This is a rule of thumb, of course, not an exact figure. I do believe that masu is speaking of using our wastefulness, not stopping any natural processes that has been going on since life began on earth. What he is trying to show is that we do 'plow under' enough energy to supply our needs for centuries to come. On the earlier blog posting, I did give the link(s) to one company that is actively contributing to solutions for recovering our wasted energy. Please see the links within the Siemens web site and you will learn what is and can be done today. Siemens is a major player in the energy field, however, they are far from being the only player. I recommend them for their foresight and ingenuity, and is a very good source of information. As for this particular chapter in Masu's work, you might want to look at Siemens Fuel Gasifiers link.

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#5

Re: Future Energy Sources 4.2 Methane & Biogas from Waste & Garbage

08/28/2007 11:34 AM

'Sewer gas', a.k.a. 'biogas', is an important fuel source at major municipal wastewater treatment works [WwTW]. The gas is extracted by gently heating sludge that is separated from the incoming stream and confined in large tanks often known as 'digesters'. The biogas driven off is dewatered and used as a fuel to heat the digester contents; that not needed for heating is used to generate electricity to run all the other aspects of the works. Biogas contains methane, ammonia and hydrogen sulphide, all of which have a calorific value.

A well-run major WwTW should be a net exporter of electricity, adding (bio)mass to the expression that is popular in Yorkshire, "where there's muck, there's brass" (loosely translated as: 'where there is dirt there is money to be made').

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#6

Re: Future Energy Sources 4.2 Methane & Biogas from Waste & Garbage

08/29/2007 12:18 AM

Masu,

I've subscribed to most of these threads but may have missed a few, so this may not be the most appropriate place to respond. Anyway here goes. The stuff we discard is so energy rich you would think we would mine it. I'm hoping technologies such as pyrolysis and robotic sorting can go close to eliminating the landfill issue altogether and soon. Not only is the energy too valuable to waste and the CO2 loading unconscionable but the land itself being put to poor use in this way just beggers belief.

As they say, "They aren't making any more land."

Catalyst on the ABC (Australian Broadcasting Corporation, like the BBC) showed a segment on the use of Pyrolysis to recover energy from biomass (garden waste) with the char reserved as fertiliser called agrichar. There was a link on CR4 as well a few weeks ago. The linked article seemed like an over unity plug in the headline so I didn't go any further. The Catalyst item was well reported without any attention grabber rubbish (after seeing how it sent you blue in the face I'm over the free energy crowd).

It is a topic I will watch with interest and possibly experiment with (charcoal in the odd garden bed to compare).

Why it is of particular importance to Australia (and Brazil, Cuba etc.) is the sugar industry use of Bagasse is still geared largely to disposal and harvesting whatever energy is left rather than the efficient use of the bagasse as a fuel stock. The situation is getting better with bagasse stored for slack season generation, especially in the refinery and distillery situation. The underlying problem is the age of the infrastructure. There is probably a case for investment incentives under carbon trading.

While on carbon trading did you see how Aborigines in the NT are being paid carbon credits for traditional land management practices. Considering that the traditional "cool burn" methodology leaves fine char instead of just ash, the management of the Tropical Savannah by traditional methods could well provide back up data for the research on the man made soils of South American antiquity and current crop trials.

There is a lot happening on many fronts and much of it goes back to the traditional, seems like a lot has been forgotten in the rush to progress.

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#7
In reply to #6

Re: Future Energy Sources 4.2 Methane & Biogas from Waste & Garbage

08/29/2007 6:51 AM

Hi Emjay4119,

I believe I saw the programs you referred to in your post. Until recently I lived south of Adelaide and when we were at the local dump I noticed that they had installed a gas recovery system and several generator sets. I did try but was unfortunately unable to locate any information on the project so I don't know anything about the technology being used or the sort of energy they are recovering, but clearly it was worthwhile doing.

On the subject of controlled burn offs of the bush, it has been going on in Arnhem land and the Northern Territory for quiet some time but it is good to see that the benefits are being rewarded.

There is however an interesting point that was explained to me some time back but I have been unable to confirm it. When the Australian aborigines arrived in Australia between 50,000 and 70,000 years ago much of Australia was far more densely forested. They did however employ setting fire to the countryside as a tool for hunting and as a result of the increased frequency of fire the flora and fauna have survived according to their tolerance of frequent exposure to fire. After many millennia of selective survival much of the Australian flora is now highly tolerant to fire and even require periodic fires to be able to reproduce.

The point is, no matter what we do our actions will have an effect on the environment and that we as humans have a long history of altering our environment to suit our needs. The thing that needs to change is our awareness of the consequences of our actions and the development and adoption of technologies, techniques, actions and attitudes that will minimize the impact our actions are having on the complete global environment. We can no longer do what ever suits or local needs and only look at local consequences.

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Re: Future Energy Sources 4.2 Methane & Biogas from Waste & Garbage

08/29/2007 7:37 PM

Masu,

Undoubtably true re the extended burning, but these days "politically incorrect".

One company that does garbage dump energy recovery is called Synergen (or close). A sparky I was doing some project work with works for them when they get a contract. Last I heard they use modified Cat Diesel engines for the prime mover. Apparently they also do sewage plants too.

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Re: Future Energy Sources 4.2 Methane & Biogas from Waste & Garbage

08/29/2007 8:21 PM

Emjay4119,

Why not try this on for size; Fuel Gasifiers! If the Germans can do it for 30 years, why not Australians? You Blokes don't seem to stand on your heads like we Yanks.

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Re: Future Energy Sources 4.2 Methane & Biogas from Waste & Garbage

08/29/2007 9:26 PM

Chtank,

Like you said the technology exists, the need exists. The only "new" aspect is using the char to "sequester" carbon and enhance soil fertility. New except for the fact it was practiced for thousands of years in parts of South America (according to the docos anyway).

The other thing about fuel gassification I don't understand is how the process is not used to to process reject coal in the Bowen Basin. The low rank waste spont coms anyway, so why not use it. There are stories I can't yet verify about water resourses and other political interferance.

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Re: Future Energy Sources 4.2 Methane & Biogas from Waste & Garbage

08/30/2007 9:13 AM

I do believe that greed, both political and corporate, are the main roadblocks to the adoption of much of our technology. For the most part, the public is so sold on fast cars and electric power that they fear the new technologies might deprive them of some comforts. One look are the controversy created when schools ban cell phones and the states ban the cell phones while driving. I still use the hand held wired to the wall telephone and am the laughing stock of my peers in Houston. However, the same people are amazed that I am active on the Internet at age 74, most think that I am too old to be allowed on the Internet without adult supervision.

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#12

Re: Future Energy Sources 4.2 Methane & Biogas from Waste & Garbage

08/30/2007 1:27 PM

The most effective way of handling landfill biogas is by far to purify the methane up to the level where it is usable as natural gas. The technology is out there and is actively designed and manufactured (custom) by Air Liquide. Their membrane separation process aims essentially at seperating the carbon dioxide from the biogas. Considering that carbon dioxide is roughly 45% of the biogas, the membrane process does a great job at rendering the biogas to a very nearly "pipeline quality" finished product. When required, a final polishing step can be installed such a PSA (pressure swing adsorption) to remove very small amounts of nitrogen, oxygen and carbon dioxyde that still remains in the product gas.

This process, especially AIr Liquide's membrane technology has been installed at various landfill sites in the US, mainly in Pennsylvania. Please trust me when I write that this process is getting implemented at an evergrowing rate in the US. I should know because I work as an engineer in a landfill site and I am going to implement what I have wrote about above. It is an extremely lucrative investment that has "win-win" implications for all involved, especially environmentalists such as myself.

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Re: Future Energy Sources 4.2 Methane & Biogas from Waste & Garbage

08/30/2007 2:13 PM

the object is to end the use of landfills altogether, that is why the Siemen gasification process was suggested. It would behoove Air Liquide to investigate this process, too. I do believe the process would easily fit well within Air Liquide's system and could also reduce their costs by providing electrical power through the use of the methane off gas to operate a SOFC. Thus, Air Liquide would be able to provide lower cost liquid gases such as oxygen, nitrogen, and CO2. This way, it becomes one corporation helping another. When I was working in the petrochemical industry, we often use Air Liquide and Air Products gases, either in high pressure containers or in liquid.

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Re: Future Energy Sources 4.2 Methane & Biogas from Waste & Garbage

09/06/2007 9:46 AM

I just came across this article while doing my daily science readings: http://www.sciencedaily.com/releases/2007/08/070830163124.htm. I am a subscriber to Science Daily and to Google alerts for Nanotechnology, Nanomaterials, solar cells, and fuel cells. There are more science related newsletter I receive as well, but these are my primary newsletters. I am sure you will find this one article of a real benefit and I hope you can take the time to read it.

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Re: Future Energy Sources 4.2 Methane & Biogas from Waste & Garbage

09/07/2007 6:58 AM

Chtank,

Thanks for the link. The article really goes to the heart of the Biomass issue doesn't it. Nutrient recycling seems to be so essential. If the recycling is effective and if the use of char as per one of my earlier posts comes to fruition and if the energy output stacks up as a sensible multiple of the energy input, then we have a winner.

If it was easy it would already be in place.

The topic of this thread "Waste and Garbage" is I feel quite important for the reuse of resources to prevent loss of fertility etc. I know I'm probably preaching to the converted here, but I see no single magic bullet. Several evolving technologies along the line of the sum of Masu's threads, now that is a different matter.

A joke I was sent the other day reminded me that if humans didn't work so hard the environment would be a lot better off. Now that we have as a race worked so hard we will have to keep working hard (and thinking hard) just to repair the damage.

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Re: Future Energy Sources 4.2 Methane & Biogas from Waste & Garbage

09/07/2007 9:04 AM

I disagree with you completely. The most effective way to handle landfill, including its inherent biogases, is to not use landfills at all. I suggest that Air Liquide should take a long, hard look at landfill produced biogas and make arrangements to work with Siemens to use their biomass Gas generators. Siemens also uses the gas refining technologies to remove the CO2 and the sulfur compounds. Air Liquide's primary uses is to bottle or liquefy numerous gases for industrial purposes. The use of your membrane technology is fine for landfill gases, however, it is far more efficient to gasify the trash before it is in the landfill. This is easily done with steam and a little oxygen and some help from Siemens. You may, also, like to read a little about biomass gasification and what EPA andDoE have to say about the problem.

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Re: Future Energy Sources 4.2 Methane & Biogas from Waste & Garbage

07/06/2008 1:06 PM

"H2S is deadly poison and when it reaches its deadly concentration in the air, you will not smell it and you will die within seconds..."

Actually, H2S is a mild poison, albeit still a poison. H2S is unsafe above concentrations (in air) of only 13 parts per million. It can be detected via nostril power at about 1 part in 10 million.

H2S poisoning affects the nervous system. Its powerful smell can often be a warning, but its continued presence can paralyze the olfactory nerve, and when this happens it can no longer be smelled. It can still be detected by noticing the early symptoms of H2S poisoning— slight headache, burning eyes, and clouded vision. If, at any time, when working with or near biogas, these symptoms are noticed, go immediately to wherever there is fresh air. Another person who has not been exposed to the biogas will be able to smell the H2S if it is present. (Information from The Biogas Handbook.) David House

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