A new concept known as “hydraulic fracturing “ to enhance the recovery of land fill gas from new and existing land fill sites have been tested jointly by a Dutch and Canadian companies. They claim it is now possible to recover such gas economically and liquefy them into Bio-LNG to be used as a fuel for vehicles and to generate power.
Most biofuels around the world are now made from energy crops like wheat, maize, palm oil, rapeseed oil etc and only a minor part is made from waste. But such a practice in not sustainable in the long run considering the anticipated food shortage due to climate changes. The EU wants to ban biofuels that use too much agricultural land and encourage production of biofuels that do not use food material but waste materials. Therefore there is a need to collect methane gas that is emitted by land fill sites more efficiently and economically and to compete with fossil fuels.
There are about 150,000 landfills in Europe with about 3–5 trillion cubic meters of waste (Haskoning 2011). All landfills emit landfill gas; the contribution of methane emissions from landfills is estimated to be between 30 and 70 million tons each year. Landfills contributed an estimated 450 to 650 billion cubic feet of methane per year (in 2000) in the USA. One can either flare landfill gas or make electricity with landfill gas. But it is prudent to produce the cleanest and cheapest liquid biofuel namely “Bio-LNG”.
Landfill gas generation: how do these bugs do their work?
Researchers had a hard time figuring out why landfills do not start out as a friendly environment for the organisms that produce methane. Now new research from North Carolina State University points to one species of microbe that is paving the way for other methane producers. The starting bug has been found. That opens the door to engineer better landfills with better production management. One can imagine a landfill with real economic prospects other than getting the trash out of sight. The NCSU researchers found that an anaerobic bacterium called Methanosarcina barkeri appears to be the key microbe. The following steps are involved in the formation of landfill gas is shown in the diagram
Phase 1: oxygen disappears, and nitrogen
Phase 2: hydrogen is produced and CO2 production increases rapidly.
Phase 3: methane production rises and CO2 production decreases.
Phase 4: methane production can rise till 60%.
Phases 1-3 typically last for 5-7 years.
Phase 4 can continue for decades, rate of decline depending on content.
Installation of landfill gas collection system
A quantity of wells is drilled; the wells are (inter) connected with a pipeline system. Gas is guided from the wells to a facility, where it is flared or burnt to generate electricity. A biogas engine exhibits 30-40% efficiency. Landfills often lack access to the grid and there is usually no use for the heat.
The alternative: make bio-LNG instead and transport the bio-LNG for use in heavy-duty vehicles and ships or applications where you can use all electricity and heat.
Bio-LNG: what is it?
Bio-LNG is liquid bio-methane (also: LBM). It is made from biogas. Biogas is produced by anaerobic digestion. All organic waste can rot and can produce biogas, the bacteria does the work. Therefore biogas is the cheapest and cleanest biofuel that can be generated without competing with food or land use. For the first time there is a biofuel, bio-LNG, a better quality fuel than fossil fuel.
The bio-LNG production process
Landfill gas is produced by anaerobic fermentation in the landfill. The aim is to produce a constant flow of biogas with high methane content. The biogas must be upgraded, i.e. removal of H2S, CO2 and trace elements;
In landfills also siloxanes, nitrogen and Cl/F gases. The bio-methane must be purified (maximum 25/50ppm CO2, no water) to prepare for liquefaction. The cold box liquefies pure biomethane to bio-LNG
Small scale bio-LNG production using smarter methods.
•Use upgrading modules that do not cost much energy.
•Membranes which can upgrade to 98-99.5 % methane are suitable.
•Use a method for advanced upgrading that is low on energy demand.
•Use a fluid / solid that is allowed to be dumped at the site.
•Use cold boxes that are easy to install and low on power demand.
•Use LNG tank trucks as storage and distribution units.
•See if co-produced CO2 can be sold and used in greenhouses or elsewhere.
•Look carefully at the history and present status of the landfill.
What was holding back more projects?
Most flows of landfill gas are small (hundreds of Nm3/hour), so economy of scale is generally not favorable. Technology in upgrading and liquefaction has evolved, but the investments for small flows during decades cannot be paid back.
Now there is a solution: enhanced gas recovery by hydraulic fracturing. Holland Innovation Team and Fracrite Environmental Ltd. (Canada) has developed a method to increase gas extraction from landfill 3-5 times.
Hydraulic fracturing increases landfill gas yield and therefore economy of scale for bio-LNG production
The method consists of a set of drilling from which at certain dept the landfill is hydraulically broken. This means a set of circular horizontal fractures are created from the well at preferred depths. Sand or other materials are injected into the fractures. Gas gathers from below in the created interlayer and flows into the drilled well. In this way a “guiding” circuit for landfill gas is created. With a 3-5 fold quantity of gas, economy of scale for bio-LNG production will be reached rapidly. Considering the multitude of landfills worldwide this hydraulic fracturing method in combination with containerized upgrading and liquefaction units offers huge potential. The method is cost effective, especially at virgin landfills, but also at landfill with decreasing amounts of landfill gas.
Landfill gas fracturing pilot (2009).
• Landfill operational from 1961-2005
• 3 gas turbines, only 1 or 2 in operation at any time due to low gas extraction rates
• Only 12 of 60 landfill gas extraction wells still producing methane
• Objective of pilot was to assess whether fracturing would enhance methane extraction rates
Field program and preliminary result
Two new wells drilled into municipal wastes and fractured (FW60, FW61). Sand Fractures at 6, 8, 10, 12 m depth in wastes with a fracture radius of 6 m. Balance gases believed to be due to oxygenation effects during leachate and
Note: this is entirely different from deep fracking in case of shale gas!
Conceptual Bioreactor Design
The conceptual design is shown in the figures.There are anaerobic conditions below the groundwater table, but permeability decreases because of compaction of the waste. Permeability increases after fracking and so does the quantity of landfill gas and leachate.
Using the leachate by injecting this above the groundwater table will introduce anaerobic conditions in an area where up till then oxygen prevailed and so prevented landfill gas formation
It can also be done in such a systematic way, that all leachate which is extracted, will be disposed off in the shallow surrounding wells above the groundwater table.
One well below the groundwater table is fracked, the leachate is injected at the corners of a square around the deeper well. Sewage sludge and bacteria can be added to increase yield further
Improving the business case further
A 3-5 fold increased biogas flow will improve the business case due to increasing
Economy of scale. The method will also improve landfill quality and prepare the landfill for other uses.
When the landfill gas stream dries up after 5 years or so, the next landfill can be served by relocating the containerized modules (cold boxes and upgrading modules). The company is upgrading with a new method developed in-house, and improving landfill gas yield by fracking with smart materials. EC recommendations to count land fill gas quadrupled for renewable fuels target and the superior footprint of bio-LNG production from landfills are beneficial for immediate start-ups
Conclusions and recommendations
Landfills emit landfill gas. Landfill gas is a good source for production of bio-LNG. Upgrading and liquefaction techniques are developing fast and decreasing in price. Hydraulic fracturing can improve landfill gas yield such that economy of scale is reached sooner. Hydraulic fracturing can also introduce anaerobic conditions by injecting leachate, sewage sludge and bacteria above the groundwater table. The concept is optimized to extract most of the landfill gas in a period of five years and upgrade and liquefy this to bio-LNG in containerized modules.
Holland Innovation Team and Fracrite aim at a production price of less than €0.40 per kilo (€400/ton) of bio-LNG, which is now equivalent to LNG fossil prices in Europe and considerably lower than LNG prices in Asia, with a payback time of only a few years.
(Source:Holland Innovation Team)