Sludge system pumping losses: UK industry standard is flawed
Dawson, M.K., Heywood, N. I., Alderman, N.J., Papachristou, C. and Ioannou, P., BHR Group Ltd, UK
(free)
Pump selection and sizing for transport of sewage sludge and other non-Newtonian biosolid slurries has important capital and operating cost implications. Under-sizing results in an inability to achieve required process throughput whilst over-sizing leads to excessive capital cost and energy consumption. Selection and sizing are dependent on the system losses, which comprise static head losses and frictional losses through straight pipe, fittings and equipment on the suction and discharge sides of a pump.
This paper provides a critique of the UK water industry standard calculation technique for sewage sludge pumping system pressure losses (based on WRc Report TR185 ‘How to Design Sewage Sludge Pumping Systems’). The approach described in TR 185 is a pragmatic and simplified one which enabled design calculations when there were no PCs, spreadsheets or programmable calculators. However, this approach is fundamentally flawed and more reliable methods for predicting friction pressure losses for pipeline flows of sludges exhibiting yield-shear thinning behaviour have been added to the literature since the 1980s.
The implications of the shortcomings in TR185 are illustrated using a series of case studies. The outputs from the TR185 approach are compared with those from a fully rigorous up-to-date calculation technique embedded in BHR Groups System Losses Tool (SLOT). The magnitude of errors resulting from the TR185 approximations and how the errors are influenced by system and sludge characteristics are discussed.
The BHR Group System Losses Tool has been developed as part of the WWM research programme, funded by the water industry, in order to replace TR185 based calculation methods.
