Bioplant points to efficient future

Renescience Northwhich will be the world's first commercial full-scale bioplant of its kind when it opens next year in Cheshire. Thomas Dalsgaard reports on how enzymes and warm water will help turn household waste into energy

An artist's impression of the facility
An artist's impression of the facility

Wind and waste can both be used to generate the electricity that supplies power to businesses and light and warmth to homes.

Although Dong Energy is mostly associated with providing energy from offshore wind, it is now entering the waste and resource market to help the UK move towards greener waste management.

The company has recently committed to build the world’s first commercial full-scale bioplant in Northwich, which secured unanimous planning approval from Cheshire West and Chester Council’s planning committee in February.

The plant will receive unsorted household waste, which – through enzyme treatment – will be converted into biogas as well as recyclable plastics and metals. The company will finance, build and operate the plant, which should be operational in 2017.

There will be about 150 people involved during the peak phase of construction, with an average of 75 at any given time. The plant will also require approximately 24 full-time local employees to operate it.  

New technology

The site will be using Renescience technology which has been in operation since 2009 at a demonstration plant in Copenhagen. It does not involve incineration, pyrolysis, gasification or advanced thermal treatment.

Renescience Northwich will have an annual capacity of 120,000 tonnes of waste, which is roughly equivalent to the waste produced by 110,000 UK households.

Waste will be supplied by waste management firm FCC Environment, which already collects household waste in the Northwich region.

When the residual waste arrives at the Northwich plant it will, without pre-sorting, be treated with enzymes and warm water so teams can extract more of the recyclable material and other resources.

Enzymes are mixed with the warm water and the waste inside a sealed vessel, where they are able to reach and break down all the organic matter. This means the organic matter can be efficiently extracted from the other waste so there is no need for separate shredding or incinerating at the facility.

Cleaned metals and solid plastics will be recovered separately for recycling, together with another stream of clean, solid recovered fuel for onward use elsewhere. Inert materials, such as sand, gravel and glass, will also be recovered for reuse as aggregates. Tand these processes are all carried out inside the building.

The separated organic material is recovered as a thin bioliquid, which is digested by bacteria within a sealed anaerobic digestion vessel to produce biogas. The biogas is then captured and used as a renewable energy source for electricity.  

Waste elimination

When compared with most traditional waste treatment processes, Renescience is capable of a higher capture rate of organic materials. Importantly, it almost entirely eliminates the amount of waste that eventually goes to landfill.

The refuse derived fuel or solid recovered fuel produced by Renescience at the Northwich plant will have a high calorific value making it suitable for use elsewhere in energy recovery plants or cement kilns, which require high temperatures to operate.

Meanwhile, digestate, which is a compost-like output remaining after the anaerobic digestion stage, will be suitable for use in land restoration. The biogas will be fuel gas engines on site, generating renewable electricity and heat.  

Electricity generation

The gas engines will each have an electrical generator, and together will produce between five and six megawatts of electricity. A small amount of this will be used to power the facility itself, but about 5MW, which is enough to power approximately 9,500 households, will flow into the national electricity grid for use by consumers and industrial users.

Generating the same amount of electricity in a modern gas-fired power station, for example, would release 15,000 tonnes of carbon dioxide equivalent per year.  

Heat from the gas engines will also be used on site to maintain the required temperature for the bioreactors and to heat the buildings on site where needed. This will help to make the facility more energy efficient, because it will use the heat from the engines rather than using fresh fuel to create heat. 

This plant is not only an example of cutting-edge green engineering at its best, but it also demonstrates once again that the UK is leading the way in renewable energy.  

Thomas Dalsgaard is executive vice-president for Dong Energy 

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