Taking the heat out of biomass for Wessex Water


Following the major redevelopment of its Berry Hill Sewage Treatment Works in Bournemouth, Wessex Water required a cooling solution for its CHP system that could handle increased levels of heat dissipation in a corrosive environment.

The extensive refurbishment of Wessex Water’s Berry Hill Treatment Works delivered a dramatic increase in digestion capacity, in line with the company’s ambitious target of digesting 90% of sewage sludge produced throughout its network of 110 treatment sites.

As part of the site upgrade, the original Combined Heat and Power (CHP) system underwent a full rebuild, enabling it to deliver optimised performance in a modernised biomass process, producing more gas than ever before. Dissipating heat from the CHP plant were two engine coolers, specified approximately six years before the site refurbishment. The performance of this cooling solution was deemed inadequate under the pressure of the site’s new, more efficient and powerful digestion process.

Mark Bean, EM&I Manager North for Wessex Water, comments:

“With a dramatic increase in digestion capacity and therefore gas production, the CHP system was working harder than ever before. As a result, the original coolers were running at higher fan speeds for prolonged periods in order to manage the increased heat dissipation requirement. It was clear the current fan specification simply wasn’t able to maintain the engine and intercooler temperatures required for optimum engine performance.”

Better performance requires more than power

Visiting the site to strategically assess Wessex Water’s cooling requirements, Transtherm’s specialist mechanical engineer, Clayton D’Souza, discovered that due to unavoidable site restrictions, the fans were located close to the back of a building with less than the industry best practice recommended 2m clearance around the air inlet. An installation restraint that would have a detrimental effect on both fan performance and equipment ventilation.

Further investigations revealed that increased exposure to hydrogen sulphide, coupled with the lack of ventilation, had caused corrosive damage to key parts of the finned heat exchanger, considerably reducing the potential lifespan of the product. In addition, due to the presence of wooded areas around the site, there was a considerable amount of pollen into the site during the summer months, which clogged the coolers. Likewise, during the autumn, leaves were drawn into the fans with no effective fan protection in place. To overcome this, the new coolers were fitted with coil inspection panels to aid the cleaning of the coils.

With a specification criterion based around better performance standards, and the additional considerations of anti-corrosion and improved air inlet flow, Transtherm set about providing a data-backed quotation and bespoke product design.

Clayton D’Souza describes the product solution:

“To deliver the power required to dissipate the increased heat from the CHP system, Transtherm recommended the installation of two bespoke engine coolers (1,298 kW and 233 kW), designed in accordance with the multitude of performance hindering variables on site.

“We accommodated space restrictions, whilst improving the air inlet flow of the coolers, by retrofitting the new technology on 2m extended legs, which further improved cooling performance and provided adequate equipment ventilation.

“Lastly, we improved the materials specified for key componentry, including the use of copper tubing and aluminium-magnesium fins which are more durable in a corrosive effluent environment.”

Data-driven specification

With three solutions providers tendering for the project, Transtherm’s data-driven design and quotation service enabled Wessex Water to thoroughly understand the technology they were investing in.

Clayton D’Souza concludes: “Using a combination of climatic weather data, plus independent product and component research we are able to provide customers with an in depth understanding of our technology early on in the specification process.

“This is testament not only to the confidence we hold in our product portfolio, but also to the commitment we have to developing long lasting customer relationships.”

For more information on Transtherm’s data-driven quotation process, or to discuss your cooling requirement, call 024 7647 1120 or live chat with us.