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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

Groundwater pumping.

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)

 

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Biogas is fast becoming a fuel of the choice for rural economy in many parts of the world because large number of agriculture and farming communities lives in rural area. Most of these countries depend on imported   Diesel, LPG and Gasoline for their industries, agriculture, transportation and cooking. Countries like India with large population spends a huge amount of foreign currency towards import of petroleum products, making it more vulnerable to the fluctuating oil and gas prices in the international market. However, there is an increasing awareness in India recently about the importance of generating biogas as an alternative energy source to fossil fuel because 70% of the Indian population lives in rural areas. With an estimated cattle population of 280 million (National Dairy development Board 2010) there is a potential to generate biogas at 19,500 Mw.

The following calculation is based on the costing details provided by successful case studies of community based Biogas plants in India. One community based biogas plant has 121 families consisting of 5 members per family as stake holders. They supply cow dung at the rate of 4.50 Mt/day for 365days in a year and generate biogas by an anaerobic digester, designed and constructed locally. Biogas is supplied to all the stakeholders every day for 2 hrs in the morning and for about 2 hrs in the evening for cooking. This is equal to burning 3025 kgs of wood/day (121 families x 5members/family x 5kg wood per member= 3025 x 4000 kcal/kg= 12.10 mil Kcal/day= 48.40 mmBtu/day).The piped natural gas in India is supplied now at the rate of $16/mm Btu, which means the plant is able to generate revenue worth $774.40 per day. But each family of 5 members are charged only Rs.150 per month or 121 families are charged 121 x Rs.150= Rs.18, 150/month ($363/month). The family members also supply milk to co-operative dairy farm which has also contributed to set up the biogas plant. Total cost of the project is $43,000 of which Government subsidy is $20,000, Dairy farm contribution $ 16,000 and the stake holders $7000.The economic and social benefit of this project is enormous. The economic benefit by way of fuel savings, revenue from the sale of vermin compose and by way of Carbon credit amounts to Rs.48,94,326 ($97,926/yr).(source:SUMUL).

The above case study clearly shows how successfully India can adopt bioenergy as an alternative to fossil fuel in rural areas. We have already seen how biogas can be enriched to increase its methane content and to remove other impurities by way of water scrubbing as shown in the figure. The purified and dried biogas with Methane content 97% and above can be liquefied using cryogenic process by chilling to -162C.The liquefaction of biogas is energy intensive but it is worth doing  in countries like India especially when there is no natural gas pipeline network.BLG (liquefied biogas)  is an ideal fuel for industries with CHP (combined heat and power) applications with energy efficiency exceeding 80% compared to conventional diesel engine efficiency at 30%.By installing LBG service station and catering to transport industry, India can cut their import of crude oil while reducing the greenhouse gas emissions.

Producing LBG also leads to a renewable fuel available for heavier vehicles. The fuel can be stored as LBG on the vehicle, which increase the driving distance per tank. The need is that the vehicle is running frequently, otherwise LBG will vaporize and CH4 will be vented to the atmosphere. LBG is in liquid form only when the gas is stored on the vehicle. When it gets to the engine it is in its gas phase. When LBG is delivered to remote fuel stations or storages it is transported in vacuum insulated pressure vessels. One such manufacture of these semi-trailers is Cryo AB and the dimensions of a standard equipped semi-trailer, suitable for Nordic logistic conditions, is shown in Figure 13.

This trailer is optimized for the transportation of LNG/LBG and has a tank capacity of 56,000 liters (~33,000 Nm3 LBG). It is vacuum insulated and the heat in-leakage is less than 0.9 % of maximum payload LBG per 24 hour. The maximum payload is 83.7 % filling rate at 0 bar (g) (=19,730 kg). The source of heat is the surrounding air and the heat in-leakage raises the pressure of the LBG. The maximum working pressure is 7.0 bar (g). If this pressure is exceeded gas is vented to the atmosphere through a safety valve. (Cryo AB, 2008)

Fuel station technology:

There are three different types of fuel station available, using LBG as a feed stock:

– LBG refueling station

– LCBG refueling station

– Multi-purpose refueling station

LBG stations fuel LBG to vehicles equipped with a cryogenic tank while LCBG stations refuel CBG. LCBG stands for liquid to compressed biogas and LBG is transformed to CBG at the refueling station. Multi-purpose refueling stations are able to fuel both LBG and CBG, and consist of one LBG part and one LCBG part. (Vanzetti Engineering, 2008a) There are a number of companies in the LNG business working with the development of fuel stations using LBG as a feedstock. The presented data in this text is based on information from three different companies; Cryostat, Nexgen fuels and Vanzetti Engineering.

This article will focus on the multi-purpose station and since the three companies’ designs are very similar, only a general description will be presented.

The reason why the multi-purpose station is chosen is because LBG could be a good alternative for heavier vehicles. Here it is assumed that these vehicles already are available and in use on a large extent. The refueling station assumes to be situated in conjunction with one of the frequent roads in India, not in vicinity with the gas network. The following requirements lie as a background for the design:

– Possibility to fuel both LBG and CBG

– One double dispenser for CBG; one nozzle for vehicles (NGV-1) and one nozzle for busses (NGV-2)

– One single nozzle for LBG

– Expected volume of sale: 3000 Nm3/day

– Pressure on CBG: up to 230 bar (200 bars at 15°C)

The standard equipment on the multi-purpose station consists of a storage tank for LBG, cryogenic pumps, ambient vaporizer, odorant injection system and dispensers. (Cryostat, 2008a)

There are three types of cryogenic pumps:

– Reciprocating

– Centrifugal

– Submerged

Reciprocating pumps are able to function at very high pressures and are used for the filling of buffer tanks and gas cylinders. Centrifugal pumps are able to produce high flow rates and are used for the transfer of cryogenic liquids between reservoir tanks or road tankers. (Cryostat, 2008b) A submerged pump is a centrifugal pump installed inside a vacuum insulated cryogenic tank. This tank is totally submerged in the cryogenic liquid, which makes it stay in permanently cold conditions. (Vanzetti Engineering, 2008b)

A sketch over a multi-purpose station can be seen in Figure 14. LBG is stored in a vacuum insulated cryogenic vessel and LBG is delivered with semi-trailers. The volume of the storage tank is usually designed to match refilling on a weekly basis. The transfer from trailer is either done by gravity or by transfer pumps, the latter significantly reducing transfer time. (Vanzetti Engineering, 2008a) From the LBG storage tank the station is divided into two; the LBG part and the LCBG part.

The LCBG part consists of a reciprocating pump, an ambient vaporizer and buffer storage. The reciprocating pump sucks LBG from the storage tank and raises the pressure to around 300 bars, before sending it to the ambient high pressure vaporizer. CBG is then odorized before going to the CBG storage and the dispenser. The buffer unit is gas vessel storage, with a maximum working pressure of 300 bar, enabling fast filling of vehicles. (Nexgen Fueling, 2008)

The LBG part only consists of a centrifugal pump that transfers LBG from the storage tank, through vacuum insulated lines, to the LBG dispenser that dispense LBG at a pressure of 5-8 bar. (Nexgen Fueling, 2008) Some LBG dispensers are supplied with a system for the recovery of the vehicle boil of gas. (Cryostar, 2008a) To reduce methane losses all venting lines are collected and sent back to the higher parts of the storage tank, to be reliquaries by the cold LBG. (Heisch, 2008) (Ref: Nina Johanssan, Lunds Universitet)

Economics of LBG: The LNG trucks averages about 2.8 miles per gallon of LNG, equating to about 4.7 miles per DEG. Table 5 compares the energy content, fuel economy and DEG fuel economy. The greenhouse emission is completely eliminated by using LBG.

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