HRS recently supplied HRS DTI Series heat exchangers to YTL Group to replace ageing heating infrastructure at the anaerobic digestion plant at Wessex Water’s Avonmouth wastewater treatment facility, helping the lead contractor complete the installation within a tight 72-hour window.
As part of its sludge treatment process, the Avonmouth site uses acid phase digestion (APD) to produce biogas and digestate. Heat for the process was previously provided by an ageing carbon steel heat exchanger that had begun to corrode and was starting to fail, allowing sludge to enter the heating water.
HRS Heat Exchangers was initially contacted by YTL Group to provide temporary heat exchangers as an emergency solution. The temporary units proved effective, leading YTL to request a quotation for a complete, permanent replacement.
However, the site’s operations meant that YTL Construction and its engineering partner, Mills Engineering Services, had just 72 hours to install the new heat exchanger in a relatively small, congested area.
The solution comprised a 4.3MW array of HRS DTI Series heat exchangers, which pre-heats incoming sludge before APD. Manufactured from 316L stainless steel, the new heat exchangers offer greater corrosion resistance than the previous carbon steel unit.
The new design also uses stainless steel bellows in place of the previous rubber fittings, helping to extend operational life. For easier inspection and cleaning of the tube side, each unit is fitted with hinged hatches secured with Victaulic connections, requiring the removal of just two bolts.
To accommodate the restricted space and minimise downtime, the heat exchanger was designed to the same footprint as the previous unit, with pipework and connections retained in their existing locations.
The completed unit comprises 60 heat exchangers, each 6m long, giving a total operating length of 360m and a heat transfer surface area of 303 sq m. Sludge passes through all 60 heat exchangers in series, while service water flows through three parallel lines, as in the original system. This enabled rapid installation without modifications to the existing water pipework.
The heat exchanger performs two duties. It heats raw sludge entering the reactor and batch-heats the reactor to maintain the required sludge temperature, with the latter operation controlled by the Avonmouth site.
Despite challenging weather conditions, including high winds and torrential rain, YTL Construction and Mills Engineering Services successfully installed the unit in early Jun 2026. It has since been carrying out both required thermal duties.
All images courtesy of HRS Heat Exchangers.
