ACWA Boosts Naburn's Carbon Credentials
18 May 2010, News release from ACWA Services
Leading process technology solutions provider ACWA is constructing an additional sludge digester which will feed the existing renewable energy systems that will help to ensure Yorkshire Water can minimise the carbon footprint of its Naburn wastewater treatment works.
Main contractor on the environmentally-friendly £4 million project is Mott MacDonald Bentley (MMB). The company subcontracted ACWA to undertake specialist work for the new digester and biogas system at Naburn's sludge treatment facility, which is co-located with the wastewater treatment works to the south of the city of York.
The works upgrade is required because Yorkshire Water is increasing the sludge processing capacity at Naburn. The overall project includes constructing an imported sludge cake reception and rewetting facility, additional digestion, dewatering and return liquor pumping capacity, a sludge conditioning process area and works to fully integrate the additional treatment processes into the site's existing operations.
ACWA's £1 million subcontract comprises a number of key elements within the upgrade, starting with conversion of an old liquid sludge import tank into a digester feed tank that will work in parallel with a nearby existing digester feed tank. This will provide an additional two days of storage for the screened sludge imports, which will be thickened in twin sludge thickeners.
The company is also providing a biogas mixing facility for the new fourth sludge digester. The three existing digesters use traditional paddle mixing systems, but Yorkshire Water requested a modern biogas mixing system for the additional unit. This will involve extracting biogas from the top of the digester, which will be fed through a compressor to nozzles mounted on the bottom of the tank to enable thorough mixing. Excess biogas will be piped to the existing boilers and combined heat and power (CHP) units.
The sludge will be passed through a heat exchanger, provided by ACWA, to ensure it is kept at the correct temperature for digestion. The company will also supply the monitoring and control instrumentation that enable temperature and level control data for the new digester to be collected.
In addition, ACWA is supplying the pipework that feeds the digester and conveys digested sludge to storage tanks as well as dedicated sludge recirculation pumps, pressure relief valves and pipework to circulate the sludge through the new heat exchanger.
The company will also provide new gas transfer pipework from the digester, replacing the inadequate existing gas transfer pipework without disrupting treatment operations. The company is also undertaking a condition survey of the carbon steel transfer pipework to the existing gas holder tank and flare stack.
The remaining elements of ACWA's contract include provision of all measuring devices needed to monitor the performance of the gas production process, as well as condensate removal for the gas production system, a new gas holder and a new flare stack. The contract began in September 2009 and has just completed its design phase. It is scheduled for completion in September 2010.
ACWA Proposals Manager Gary Harris said: 'The additional capacity that ACWA is helping to create will enable Yorkshire Water to meet its need for extra sludge treatment capacity and increase existing energy generation at Naburn. This will ensure that the works is generating green, renewable energy and also potentially additional power for supply to the national grid.'
For further information please email ACWA Services