Landfill gas to energy statistics

Here are some quick statistics on the number of landfill gas to energy plants by state. California has 77 operational plants, Illinois has 32, Texas has 27, and Colorado has 1.  Granted we have a much smaller population than all of these other states, but with over 30 landfills in the state of Colorado there should be more of these plants in operation.  The only landfill gas to energy plant in operation is located at the Lowery Landfill in Aurora.  The gas gathering system consists of 218 wells and collects LFG from both the Lowery Landfill and the Denver Arapahoe Disposal Site (DADS).  Between the two landfills, Lowery being closed and DADS still in operation, they collect enough gas to produce 3.2 megawatts of electricity.  This is enough electricity to power nearly 3,000 homes.  In April of last year, a new LFG to energy plant broke ground at the Larimer County Landfill, located in Fort Collins.  This plant is expected to produce 1.6 megawatts of electricity.  Both the Lowery Landfill/DADS and Larimer County Landfill have plant sized below the average size of simlilar plants in the United States, which is 3.4 megawatts.  The largest LFG to energy  plant is located in Puente Hills, CA and produces 50 megawatts.  

How much methane does a landfill produce?

I have been doing a lot of research to try to determine how much methane or LFG an actual landfill can produce.  Many factors go into the production of the LFG and include, age of garbage, temperature, moisture level, and type of garbage.  In general the more organic the garbage the more methane and carbon dioxide that is produced.  Also, the warmer the better and the higher the moisture content the better. As for the age of the garbage there are wide ranges of time periods where many experts say the LFG production is at its peak.  Gas production normally starts around the 1 to 3 tears after the garbage has been covered, and after 5-10 years gas production is at its peak.  There are many different suggestions to when the landfill stops producing gas ranging from 10 - 40 years.  And many times the life of gas production varies depending on the conditions of the landfill and its contents.  Here is a quick video that show LFG being emitted from a bore hole drilled into a garbage layer.  Sure does seem like a lot of LFG being produced!

Landfill Gas, does this sound familiar

Making the shift from anaerobic digestion to other types of waste to energy technologies will be easier if we look into a process that is nearly the same.  This type of technology is known as landfill gas.  Landfill gas is produced in almost all landfills and many times the landfill gas that is produced is lost to the atmosphere.  Landfill gas is made up of 50% methane(CH4) and 50% carbon dioxide(CO2).  Sound familiar, this is the nearly the same composition of biogas.  Landfill gas (LFG) is also produced in the same way.  Microbes deep under the layers of trash in landfills eat away at the trash and transform the garbage into it most basic form, which happens to be both methane and carbon dioxide.  One major difference in this process is that while nothing special needs to be done for the LFG to be produced, such as buying a digester and then agitating and heating it (as in anaerobic digestion), but collecting the :LFG is more difficult.  In order for LFG to be captured the garbage is first covered with a layer of soil that both contains the garbage but also helps create an environment suitable for the naturally occurring microbes to begin their work.  Once the LFG is produced it slowly makes it way up through the layers of garbage until it is emitted to the atmosphere.  When the LFG is lost to the atmosphere, it is known as fugitive emissions.  Collecting the LFG to use in productive ways is accomplished by drilling wells into the garbage.  Lining these wells with PVC pipe gives the LFG a path to take to get to the surface.  Just like most things in this world, the LFG will take the path of least resistance and that is the PVC pipe.  An array of these wells are drilled and connected to a central LFG collection line.  This raw LFG also contains some other gases that are non desirable such as ammonia (NH3) and hydrogen sulfide (H2S).  Therefore, the LFG is treated to remove these gases.  Once the LFG has been cleaned up, it can be used just as biogas or even natural gas would be used.  Here is a diagram that may help you visualize what a LFG system looks like.

Back to the Future!

How long has the idea of using trash for energy been around?  At least since the the movie "Back to the Future" came out in 1985.  In "Back to the Future," Doc fills his time machine with garbage to power a trip back to the future.  Mr. Fusion, the name given to this garbage to energy generator, may have seemed like some science fiction idea that may never become reality, but it has.  A larger scale Mr, Fusion has been created and has proven to turn everyday garbage into energy.  This technology consists of a tank that contains plasma arcs that reach almost 6000 degrees Fahrenheit.  Simply put a plasma arc is a  lightning strike.  The high temperatures of the plasma arc cause anything within the tank to break apart into smaller and smaller particles until a gas is produced, that can be burnt just as natural gas is burnt, to create mechanical energy.  This mechanical energy can be used to power a car, or to make electricity.  So if this type of technology can convert any type of garbage into energy why did Doc pick through the trash and then pour a beer into Mr. Fusion?  I'm sure it was done that way just to make the scene more interesting and to grab the attention of the audience.  By the way pouring liquids into a fusion gasifier ( the technical name of this "lightning tank") would cause big problems. But isn't it great when seeming out of this world ideas in movies become reality.

  

DIY Anaerobic Digester

Whos more wasteful? -- or -- Who releases more waste energy streams to the environment? A Cow or a Human?

So after doing my last post I became curious of who is more wasteful releases more energy to the environment, a cow or a American citizen.  As in who throws away more  Garbage being the assumed largest waste stream for the human and manure being the largest waste stream for the cow (garbage being manure for the cow).  Off the top of their head I'm sure most people would say that humans are the most wasteful out of all species and release a lot of wasteful energy to the environment.  But after noticing that the average cow produces 14.4 pounds of manure per day and the average American citizen produces 4.4 pounds of garbage, I began to think that a cow may release more energy to the environment be more wasteful.  To the compare the two candidates I will calculate how much energy can be recovered from the manure and the garbage.  Garbage has an energy content of 10,000 BTU/lb totaling 44,000 BTU per person per day.  Manure has an average energy content of 8,500 BTU/lb totaling 122,000 BTU per cow per day. Using this simple procedure, an average cow essentially releases wastes (poops out) 277% more energy than an average American throws in the garbage can.  Now we will just need to determine the best way to utilize this wasted energy.

The cow is victorious in release the most energy to the environment being more wasteful.

 

Shifting from cow manure to garbage

Throughout my blog I have focused on anaerobic digestion of cow manure.  While this has been proven to be a valuable source of energy not everyone or every city is near a large population of cattle.  Take for instance here is Colorado, northeast Colorado has a large population of dairy farms and cattle feedlots, however, Denver and the other front range cities are farther away.  What do these large cities have instead of cows and there energy rich manure....TRASH.  According to the EPA, the average person produces 4.4 pounds of trash per day.  Multiply this by the population of Denver and the surrounding area of 2.5 million people and that totals 11 million pounds of trash per day.  The average energy content of wood/paper is typically 5-7,000 BTU/lb, while plastics typically have an energy content of 15-20,000 BTU/lb. Using this data we are able to assume an average energy content of garbage as 10,000 BTU/lb.  Multiply this by the 11 million pounds of trash produced in the Denver area to get 110 billion BTU's of energy.  That is enough energy to power almost 360,000 homes that use on average 300,000 BTU/day.  

How can this energy be collected and transfered into a useable form of energy?  First, the trash can be burned or incinerated to produce heat that is then used to produce steam and finally electricity.  Or the trash can be gasified to produce syngas that can be burned to produce energy.  Or how about just let natural decomposition of the trash take its course in landfills to produce landfill gas.  Landfill gas consists of methane and CO2, the two main gasses that make up biogas from anaerobic digestion of cow manure.  Of course there are efficiency losses in all of these processes, but why not use this energy, as it is just sitting there in the landfills waiting to be used.