OUR SERVICES

ENERGY & ENVIRONMENT SERVICES

ANAEROBIC DIGESTION AND BIOGAS

The Coalition Government is committed to increasing energy from waste through Anaerobic Digestion. The biological core process of ‘Biogas Plants’ is recognised as a technology that can remove organic wastes from landfill sites, reduce greenhouse gases and de-couple the UK from unreliable fossil fuel sources. It also creates green electricity, enables green gas to grid, recovers green fertilisers, supports jobs and rewards investors. In 2009/10 government support for the industry included over £40million in equipment grants, an £850 million budget allocation for Renewable Heat Incentives in addition to almost £100 per MWh as carbon incentives for green electricity production from biogas plants. The potential scale of the technology is 100 Million Tonnes of farm and food waste in the UK each year being converted in Anaerobic Digestion processing plants that could generate almost half of the current total domestic gas requirement.

This industry is rapidly moving from laboratory scale to full chemical industry scale, and requires all of the chemical industry disciplines appropriate to this scale of operation.

Anaerobic Digestion (AD) is the bacterial fermentation of organic matter, in the absence of air, that replicates the conditions in the digestive system of a cow. The AD process can receive pre-treated organic matter (replicating the cow chewing grass) or any individual or combination of animal manures, food waste or energy crops which are turned into either a shredded woody mass for dry digestion or a pumpable ‘soup’ in a wet digestion system.

The pre-treated organic material is fed into an air tight digester vessel where several groups of bacteria reduce the organic matter into ever shorter chain chemicals until the simplest forms of carbon, Methane (CH4) and Carbon Dioxide (CO2) are formed, which then leave the fermentation chamber or digester as biogas.

Biogas characteristically has a calorific value mid-way between coal gas (used throughout the early 19th and 20th Century as domestic gas in the UK) and natural gas derived from gas fields in the North Sea. Natural gas is composed mainly of methane and the established presence of the UK’s gas pipeline grid enhances the attractiveness of AD with the real potential of generating around half the domestic consumption of gas as biogas from anaerobic digesters.

The Biogas produced via AD can be injected direct into the gas grid once it has been appropriately cleaned of CO2 and other impurities like Hydrogen Sulphide (H2S), and water. The cleaned and compressed biogas is referred to as biomethane and this process of Gas to Grid (GTG) is probably the most efficient way of moving energy around the country. It has the lowest carbon footprint in global warming terms, of any fuel production system available.

Other markets for biomethane include compressing the gas to the pressures used by SCUBA divers for air bottles. It is also known that cars fitted with Compressed Natural Gas (CNG) are cheap to run, pollute much less than diesel and petrol vehicles, and have a range of several hundred miles on a couple of bottles of compressed biomethane.

In early 2011 there are about 60 “new model” biogas plants in the UK - excluding those on sewage works and landfill biogas collection systems. Most of the gas currently produced on these sites is used in industrial grade engines which generate electricity and also produce hot water - half of which is used to heat the digester and half is available for other uses such as district heating or district cooling. The more advanced plants are now planning to use the hot water for further electrical production via Organic Rankine Cycle systems. These operate in basic terms like a fridge in reverse where the hot side fluid flow is forced through a rotary expander (a compressor driven by the fluid) and this generates the power. The working fluid is normally a refrigerant and the condenser still produces warm to hot water for further use in a district heating scheme.

On the farm, energy crops are normally grown as a break crop to kill weeds and diseases in arable land after a year growing a grain crop. There is a growing market for “purpose designed” crops for this purpose to remove any political/social impacts.

The liquid digestate from the plant is a highly desired fertiliser with a deserved reputation for transforming farm enterprises. If the inputs and process meet the requirements of a quality standard (PAS110), then the soil association accepts them as organic fertilisers and thus the biogas process is the gateway to large scale organic farming.

For over 30 years PROjEN has been involved in the design and build of a variety of complex process plants and the PROjEN AD/Biogas team consists of a number of individuals who have been involved in some of the UK’s most iconic AD and Biogas installations. The team is headed by BioEnergy Divisional Manager Shane Pugh and the technical team is headed by Dr Les Gornall – probably the best known and most respected member of the AD community. PROjEN’s reputation and presence has grown significantly as many realise that PROjEN’s design and build experience coupled with its expertise in health, safety and legislation matters make it an ideal partner for AD/Biogas builders. Significantly the company is also technology agnostic – not tied to any particular technology or supplier to ensure the customer gets the best fit solution every time.