Green energy provider solves scaling problems

Electronic descaling units are saving Southampton Geothermal Heating Company hundreds of pounds worth of salt a day in its CHP scheme.

The UK's first geothermal energy and combined heat and power (CHP) district heating and chilling scheme in Southampton City Centre is ensuring that it maintains its environmental credentials by using state-of-the-art electronic descaling instead of chemicals to remove scale build-up from its chillers and cooling towers.

Launched in 1986, Southampton Geothermal Heating Company's GBP 4 million multisource heating and chilling scheme generates 7MW of electricity per hour to supply 20 major consumers in the city centre as well as the newly opened West Quay Shopping Centre, the largest of its kind in Europe.

Following the dramatic rise of oil prices in the late 1970s, the Department of Energy set up a research programme looking into the potential for alternative energy sources in the UK, particularly wind wave and geothermal energy.

At one such site, located at the Marchwood power station on Southampton Water, the Department of Energy began drilling a well, hoping to test geothermal resources held in the Wessex basin.

Following these initial successful trials, the Department of Energy working with Southampton City Council and the Energy Technology Support Unit drilled a further well in the centre of Southampton.

Within this well, water was found at a depth of nearly 1.8km and at a temperature of 76C.

The size of the resource was deemed too small to develop by the Department of Energy, but the City Council refused to let the project fail and eventually found, Utilicom, a French-owned energy management company as a partner with whom to develop the scheme.

The original well, which currently provides about a fifth of the system's heat input, now operates alongside combined heat and power generators.

These use conventional fuels to make electricity, with the waste heat from this process being recovered for distribution through the 11km mains network.

The district heating scheme in Southampton, which helps reduce its customer's energy bills by 25% and the city's CO2 omissions by 10kt a year, closely resembles a huge domestic central heating system.

Hot, treated water circulates underground from the heat station to a growing number of customers in the city centre and is then returned for reheating.

Power for the "downhole" circulation pumps and plant is generated at the heat station by CHP.

The heat from the CHP generators is fed into the district-heating scheme with surplus power being sold to the National Grid.

Since the pioneering launch of the initial geothermal project in 1986, Southampton's district heating scheme has grown dramatically primarily due to the use of up-to-the-minute technology, which has included the use of a Wartsila 5.7MW multifuelled CHP generator.

In 1994 the company decided to use waste heat from the CHP generators to provide chilled water for air conditioning.

Initially connected to the five-star De Vere Grand Harbour Hotel, the scheme has recently been expanded to include the city's leisure centre, West Quay development and the BBC studios.

Southampton Geothermal Heating Company's success resulted last year in it winning The Queen's Award For Enterprise For Sustainable Development.

Southampton Geothermal Heating Company used a water softener to control scale in the first chilling system installed.

However with the prospect of a tonne of salt a week being used at a cost of GBP 250 if the water softener system was expanded, the company decided to source an alternative means of preventing scale when the chilling scheme was extended four-fold last year.

Following a call to Environmental Treatment Concepts (ETC), a site survey was conducted by one of the company's engineers who suggested fitting Scalewatcher-Enigma electronic descaling units on a rental basis to evaluate their effectiveness.

On 14th May 2001, units were fitted onto all the chillers and two months latter on the newly commissioned cooling towers that had already begun to exhibit heavy scaling.

As the demand for chilled services were still unknown, ETC also installed units on to the condenser's make-up water, pump and existing softener.

After six months of operation, the original chiller was opened for the first time in 12 months and found to be completely scale free.

"We would have expected to see some residual scale on the chillers and inlet pipe, but both were completely clean", said Mike Zorab, Heating Station Supervisor.

Now that the system is stable, and the demand for chilled water can be more accurately calculated, ETC is planning to remove units it believes are no longer required.

"This was an exciting and fascinating project", said John Thompson, Managing Director, Environmental Treatment Concepts.

"We have worked very closely with Southampton Geothermal Heating Company to ensure the Scalewatcher-Enigma worked successfully, visiting the site on a weekly basis to check and monitor unit performance.

Now that the system is functioning correctly, we are able to remove certain units which will substantially reduce the overall cost of the system".

Plans have now been drawn up to increase the district heating and chilling scheme to encompass the redevelopment of Southampton Football Club's old ground at The Dell.

A housing development on at the Polygon in Southampton has already been connected.

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