Powering ahead with gas and electricity ′Power from Poo′

11.05.2015

Northumbrian Water’s ‘power from poo’ production is now cooking on gas too.

After three years of generating electricity from sewage treatment it is also being used to create gas for the national grid.
The water company already leads the way as the only wastewater company in the UK to use all its sludge remaining after sewage treatment to produce renewable electricity.

It captures the methane released by bacteria digesting the sludge and uses it to drive engines to create electricity.
Now Northumbrian Water also has the biggest gas to grid plant of its kind in the industry. It cleans and purifies the methane which is then injected into the grid.

The pioneering £8m gas to grid plant is in the final stages of commissioning at Howdon at the mouth of the Tyne.
It has been built alongside Northumbrian Water’s advanced anaerobic digestion (AAD) electricity generation process which has already saved multi-millions of pounds in operating costs and delivered a 20% cut in the water company’s carbon footprint.

Northumbrian Water has two AAD plants, one at Howdon on Tyneside and the other at Bran Sands, Tees Port, Middlesbrough – a previous combined £70m investment in leading green technology.

When fully commissioned the gas to grid plant at Howdon will produce up to 88 million kilowatt hours (kWh) of renewable energy per year - enough to supply the gas requirements of about 5,000 domestic homes. The plant will also deliver a £3m annual efficiency which helps Northumbrian Water have some of the cheapest bills in the industry.

Once the methane has been produced by the AAD plant it is cleaned in water towers in the gas to grid process to remove impurities and propane is added before it is injected so that it matches the existing gas in the grid.

As with natural gas the artificial odour chemical Butyl Mercaptan is also added giving it the characteristic gas smell so it can be detected for safety.

The gas to grid process is more efficient than electricity production as energy is lost as heat and noise from the gas engines used to create electricity.

Richard Warneford, Northumbrian Water’s Wastewater Director, said: “We are now able to produce both gas and electricity. More than 20% of our total power use is now from renewable energy sources including hydro power at our treatment works and reservoirs like Kielder Water.

“Our customers can now be reassured that we are doing all we can to use the waste they flush down the toilet as a fuel and turn it into electricity and gas to add to the national grids which people use to light their homes and cook their meals.
”We are leading the industry in pushing the bounds of technology and learning from the challenges of integrating the new gas plant with our existing advanced sewage treatment and electricity generation processes.”

The advanced anaerobic digestion (AAD) thermal hydrolysis process involves pre-treating the sludge┬áremaining after sewage treatment, heating it to 165 degrees Celsius under six bars of pressure – a bit like putting it in giant pressure cookers.

This destroys any pathogens and breaks down the cell structure, which makes it better to be fed to billions of bacteria in giant digester tanks – and easier for them to digest.

The resulting methane released by the bacteria is collected in 11-metre diameter biogas storage bags before being burned in gas engines capable of producing nearly 10 megawatts of electricity (the equivalent of about 35 million kWh per year) or being fed into the gas into grid process.

Waste heat and steam generated from the process are also captured and recycled for use elsewhere at the works.
The two AAD plants on Tyneside and Teesside reduce about 300,000 tonnes of wet sludge, resulting from the treatment of domestic sewage and biodegradable industrial effluent from a population equivalent of about four million, to about 100,000 tonnes.

And that 100,000 tonnes of processed pasteurised sludge is an excellent enhanced biosolid fertiliser used by farmers.
Northumbrian Water is also monitoring the gas to grid plant with a view to possible future installation of further plant alongside its second AAD plant at Bran Sands on Teesside.

For further media information contact Alistair Baker, PR & Media Manager 0191-3016851 / 07711 793493

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