biogas

With processing, biogas can be a renewable substitute for natural gas and is suitable for use in homes and businesses for cooking, heating purposes and electricity generation and of course transport. It has many benefits including being carbon neutral and since it can be produced locally, create jobs and improve energy security.

Biogas is commonly produced by anaerobic digestion as part of the treatment of wet organic waste.  This occurs in municipal wastewater and sewage treatment plants, industrial operations that have liquid wastes containing organic material, and on types of farms where animals are kept or held in a small area, such as pig or poultry farms.

Biogas is a mixture of mainly methane and carbon dioxide with very small amounts of hydrogen sulphide and other impurities.  The methane content can range from 50% to 80% (on a volumetric basis).

The high amounts of carbon dioxide in biogas typically reduce the heating value to between 18 and 26 MJ/m 3 (GCV) compared with natural gas typically around 40 MJ/m 3 (GCV).

Sewage treatment plants are methane generators by the nature of the process.  The gas can be used on site to produce electricity for local consumption or exported from the site.  Plants at Christchurch and Auckland are good examples where both methane and natural gas supplies are used in generators at each site.

In many industrial and farming cases treatment of the waste to produce biogas is not economical in itself but is carried out for other reasons such as waste management.  Also, small-scale generation of biogas is rarely economic because of the high labour requirements and dilute nature of the effluent being treated.

Biogas from anaerobic digestion can be used to produce heat for the digestion process itself, or for process heat and electricity in other parts of the plant.  It can be upgraded to “natural gas” quality and fed into a local utility network. It can also be used directly as a fuel in a number of different types of plant such as reciprocating gas engines, mini-gas turbines, Stirling engines, and fuel cells or by direct combustion in boilers or other CHP heat plant.

Anaerobic digestion is a mature technology and is used worldwide, particularly for municipal waste water treatment.  Here the scale of treatment can justify the costs of installing and operating the equipment needed.  If the organic content of wet waste stream is too dilute, recovery of the energy content will be made more expensive.  Excess moisture may cause handling problems for gasification processes.

Anaerobic digestion is essentially a continuous process so it requires a reliable continuous feed of material.

1. Biogas is carbon neutral and has associated environmental benefits.
2. Biogas is locally produced / utilised, supports the domestic economy and reduces dependency from international markets.
3. Biogas is a potential substitute for natural gas and imported mineral fuels.
4. The most common utilisation of biogas is currently the direct combustion in a gas engine driven generator. The power is usually fed into the local grid. Generators are often containerised for modular installation, with standard 40 foot containers housing generators with ratings upto 1 MW.
5. Biogas can be used in boilers for industrial or communal energy plants, e.g. hospitals or swimming pools, for space for process heating.
6. Biogas can be used as a transport fuel.
7. Biogas can be upgraded to "natural gas specification" by extracting the CO2. This is similar to the process used at the Kapuni Gas Treatment Plant, where high concentrations of CO2 have been removed from natural gas for the past 40 years. Smaller scale plants are now used in Europe to treat biogas for the utilisation in local distribution networks as a supplement for natural gas. Biogas treatment plants are also made in New Zealand and exported overseas.
8. The capture and combustion of biogas from existing, natural or man-made sources reduces emissions of methane, which is a potent greenhouse gas.
9. Biogas can be produced from most organic waste streams from agricultural or industrial food processing including waste streams from liquid biofuels processes.
10. Mainly in Europe, high yielding energy crops such as maize have been purposely grown for the production of biogas. Intensive farming achieves biogas yields of more than 200 GJ per year per ha.
11. Biogas achieves two to three times higher energy yields per ha compared with liquid biofuels.
12. Biogas crops can be grown as rotational crops and be harvested within 8 months. Biogas crops can be stock piled in the form of silage.
13. Treated biogas can be distributed through the existing, national gas transmission system and be stored in depleted gas fields for seasonal load management.
14. Biogas technology is readily available and has reached a level of maturity that suits the application and operation by farmers.
15. The mineral/organic waste from the biogas process can be fully recycled on the farms and would minimise the demand for imported fertiliser.
16. Anaerobic digestion improves the environmental acceptance of rural waste streams where used as fertiliser.

Most biogas is produced from landfill, sewage / wastewater generated gas and gas from farm or food waste.

Landfill - Biogas is generated in landfill sites since organic matter such as domestic food and garden waste is buried and compressed in a dark oxygen free environment. For decades after a landfill site is filled biogas continues to be generated and released into the atmosphere.

Sewage / wastewater biogas generation - Sewage treatment plants are methane generators by the nature of the process. The gas can be used on site to produce electricity for local consumption or exported from the site. Plants at Christchurch and Auckland are good examples where both methane and natural gas supplies are used in generators at each site.

Farm and food waste biogas generation - In many industrial and farming cases treatment of the waste to produce biogas is not economical in itself but is carried out for other reasons such as waste management. Also small-scale generation of biogas is rarely economic becauseof the high labour requirements and dilute nature of the effluent being treated.

Energy crops - In Europe, thousands of farmers now produce biogas from purposely grown energy crops like maize, often in co-digestion with animal manure. These plants fuel power generators with ratings between 0.5 to 10 MW and some inject treated biogas into the natural gas distribution systems. The driving forces behind this rapid industry development have been political will and national feed-in tariffs.

Biogas - a brief synopsis

more to come...

Biogas - the transport potential

The potential for biogas use in transport in New Zealand is significant. Biogas has the potential to substitute for significant amounts of petrol and diesel. To minimise refuelling cycle with biogas, the CO2 needs to be extracted, the same as if biogas was to be injected into the distribution systems. New Zealand has had experience with compressed natural gas (CNG) since the 1980s, when about 10% of the national vehicle fleet was running on CNG.

Useful New Zealand focused reports on biogas potential

1. An overview of New Zealand's biogas potential, Waste Solutions (2008)
2. New Zealand Energy Strategy to 2050, Biogas as an alternative to natural gas, Maunsell/AECOM (2007)
3. Biogas opportunities - An overview of biogas potential in New Zealand, East Harbour Management Services (2004)

For a snap shot of how some European Countries are investigating and maximising the potential of biogas use in transport see the following links:

Europe / European Commission Initiatives on biogas and transport

• 'BIOGAS MAX - A DRIVING FORCE' - The European Biogasmax project creates a network of biogas-related demonstrations on the European territory with the aim of sharing experiences in terms of best practices in managing urban transportation. Web-site here
• Biogas in Captive Fleets - A NICHES Consortium Publication

UK

• 'Biogas as a Road Transport Fuel' - An Assessment of the potential role of biogas as a renewable transport - Research undertaken for the UK's National Society for Clean Air and Environmental Protection.
• National Farmers Union - Information on biogas potential

Sweden

Since the 1990s, an increasing number of Swedish cars run on biogas, natural gas or a mixture of the two. 1 m3 of biogas is equivalent to approximately 1.1 litres of gasoline and in Sweden was in 2007 sold more than 28mio. m3 of biogas for transportation.

• Sweden tests first biogas train (2005)
• Biogas as a Transportation Fuel - FVS Fachtagung 2003 (Swedish Gas Centre)
• Biogas upgrading and use as transport fuel 2004 (Swedish Gas Centre)

The table below sets out some brief details of the key biogas generation sites in New Zealand and the party that owns/operates them. They are listed in terms of the type of biogas, i.e., landfill, rural waste (farm of food waste), wastewater, co-digestion, etc.

Project Name (and location)	Type of Biogas	Application	Owner	Power Rating kW	Gas Rating kW	Year of Commissioning
PNCC digester upgrade	Co-digestion	Co-generation	Palmerston North CC	750	--	2008/10
HCC Digester upgrade (Hamilton)	Co-digestion	Co-generation	Hamilton CC	1000	--	projected
Beef feedlot manure (Waikato)	Feedlot waste	Study	Industry	1000	--	2008
Piggery feedlot manure (Waikato)	Feedlot waste	Study	Industry	2000	--	2008
Chicken Waste (Waikato)	Industrial	Study / Research	Inghams	--	500	2008
Tirau Dairy (Tirau)	Industrial waste	Boilers	Fonterra	--	4000	1990
Southern Landfill, Happy Valley	Landfill	Power generation	Todd Energy	1000	--	2008
Silverstream (Lower Hutt)	Landfill	Power generation	EDC	2,700	--	1994
Greenmount	Landfill	Power generation	Envirowaste	5,400	--	1992
Rosedale	Landfill	Power generation	Envirowaste	2,700	--	1994
Horotiu Landfill	Landfill	Power generation	WEL Green Energy Joint Venture	900	--	2004
Spicer Landfill (Porirua/Wellington)	Landfill	Flaring	Porirua CC	--	1000	2009
Awapuni (Palmerston North)	Landfill	Boilers / Co-generation	--	--	--	--
Burwood Landfill (Stage 1)	Landfill	Co-generation	Christchurch CC	230	4,000 (est'd)	2007
Burwood Landfill(Stage 2)	Landfill	Co-generation	Christchurch CC	475	--	2007 (in construction)
Tirohia Landfill	Landfill	Power generation	HG Leach	1,000	--	2008
Hampton Downs Landfill	Landfill	Power generation	Envirowaste	4,000	--	2009
Palmerston North Landfill	Landfill	Power generation	Palmerston North CC	1,000	--	?
Landcorp (Waimakariri/Rangiora)	Manure biosolids	Co-generation	LandCorp	15	--	2007/08
Kiwifruit Waste (Tauranga)	Rural waste	Study	Zespri	500	--	2008
Piggery Waste (Canterbury)	Rural waste	Study	PIC	--	500	2008
Piggery Waste (Waikato)	Rural waste	Research	NIWA (?)	20	--	2008
Piggery Waste (Canterbury)	Rural waste	Study	Dept of Corrections	--	?	2009
Mangere WWTP I(Auckland)	Sewage	Co-generation	Watercare	7400	--	2004
Hamilton WWTP (Hamilton )	Sewage	Co-generation	Hamilton CC	1000	--	2005
Bromley WWTP	Sewage	Co-generation	CCC	1,500	--	1996
Tauranga WWTP	Sewage	Co-generation	Tauranga CC	230	--	1996
CCC digester upgrade (Christchurch)	Thermophilic / biosolids	Co-generation	Christchurch CC	1500	--	projected
GI digester (Dunedin)	Thermophilic / biosolids	Boilers	Dunedin CC	--	375	2001
FORTEX Silverstream (Mosgiel)	Wastewater biosolids	--	--	?	--	?
Rosedale Road wastewater treatment plant	Wastewater biosolids	Co-generation	North Shore CC	?	--	1984
Total Capacity in MW				37	11

Current estimate of total capacity in New Zealand is around 50 MW. The majority of this is used for electricity generation.

If you have a project planned or an operation that is not represented in this table – we would be keen to hear from you. Please contact Connie Crookshanks.

coming soon...

1. Landfill gas potential:
   It is estimated that about 50% of the gas potential is captured for energy generation. Typical trends are:
   • increased recycling of waste;
   • closure of small landfills and operation of larger regional landfills;
   • improved capture of landfill gas through better lining and extraction techniques.
     
2. Sewage gas potential:
   Wastewater treatment plants are relatively mature with regard to the chosen treatment processes and may not grow substantially beyond the growth rate of population. Future upgrades may include anaerobic digesters.

3. Biogas from rural and industrial waste streams:
   Significant growth is expected for environmental reasons.
   New Zealand could be extracting over 6 PJ/a biogas from the organic wastes.

4. Energy crops:
   In the long-term, this is the area with the highest potential and will be driven by domestic natural gas reserves and prices, international prices for mineral fuels and the economic cost of greenhouse gas emissions.
   Biogas cropping in good farming areas such as the Waikato can yield up to 300 GJ/ha/yr

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