Proceedings

Thames Water owns and operates two Sludge Powered Generators (SPG), Crossness and Beckton, which have respective annual throughputs of 87 and 180TDS/day (2012/2013). Both units combined employ five fluidised bed combustors with steam recovery and electrical power generation (62GWhe pa in 2012/2013). The SPGs performance is limited by the water content of the sludge and so, substantial amount of natural gas is required to support the combustion. Additionally, the implementation of Thermal Hydrolysis Process (THP) plants at Crossness and Beckton in the next few years will challenge the sludge strategy in EastLondon. THP will be the preferred route for sludge treatment as it is economically more attractive than the SPGs. Unfortunately; a reduced throughput to the combustors will reduce their performance further. A series of trials were undertaken using two different alternative sludge based fuels (1 a mix of dried sludge (95%DS) and indigenous cake and 2 a mix of THP digested cake with indigenous cake) which are believed to be suitable options to displace the use of natural gas in the SPGs. During both trials, natural gas consumption was reduced\removed, bed and freeboard temperatures improved, combustion air preheating could be reduced and the cake throughput increased. The more recent trials using the THP digested cake (40-45%DS) dewatered using the new Bucher press recently employed by Thames Water is the more significant alternative because this has the potential to sustainably displace part of the land disposal of sludge from the two urban STWs in East London. More trials and data collection are now required in order to assess better the full potential of this alternative fuel.

Keywords: Fluidised Bed Incineration, Combustion Optimisation, THP Sludge Cake.

Optimising trials within Thames Water sludge powered generators