FEATURE PUMPS, VALVES & ACTUATORS
OPTIMISING OPERATION IN NET ZERO QUEST Intensive techniques like
Efficient sludge pumping has an important role to play in achieving zero carbon goals, says Mick Dawson, consultancy director, BHR Group, who urges operators to better understand their sludge systems
M
ore efficient pumping of sludge could help water companies in
England reach their goal of net zero carbon emissions by 2030, along with meeting the regulator’s requirement to reduce capital expenditure and cut bills for customers. However, most utilities have not yet acted to reduce the carbon and financial cost of transporting sludge. For decades the industry standard
calculation technique for sludge pumping system pressure losses has been WRc’s ‘TR 185 How to design sewage sludge pumping systems’ document, which dates back to 1983 and has served the industry well. It suited a pre-digital era when water companies could afford to build in a wide safety margin because energy was less costly, carbon went unquantified and budgets were bigger. Other recent factors impacting directly
on sludge processing are population growth, which is increasing volumes, and legislation restricting disposal to land. This means utilities are using intensive techniques like thermohydrolysis, which result in sludges with higher dry solids content. In summary, existing equipment now
has to work harder, moving thicker, more concentrated sludges that are more difficult to pump. As with any application, accurate selection and sizing of pumps used for the transport of sewage sludge has important cost implications, along with operational risk management considerations. Under-sizing can mean failure to achieve
the required throughput, whilst oversizing leads to excessive capital cost and energy consumption. This challenge means operators need to get to know their assets and process streams better. The need for leaner pump systems
means more variables need to be taken into account, which can be challenging where the data is not readily available. At the heart of making sludge pumping more efficient is a better understanding of sludge rheology – how it flows. Variables include pipe size, length,
roughness, fittings and elevation as well as the viscosity and temperature of the sludge and the flow rate desired by the operator. To ensure efficient pumping systems, design engineers estimate total pressure losses across the range of variables at a given site. If these estimates
14 APRIL 2020 | PROCESS & CONTROL
The system losses tool can be used to accurately size pumps and pipes used in sludge processing
SLOT 2.0, which was launched in January
2020, enables pump system operators to understand where each pump should be operating on its pump and efficiency curves, matching against the particular system pressure curve to find the operating point. This makes it possible to determine optimum pump-operating points and identify the most effective pumps to use on a given system – selecting the optimal size, type, quantity and configuration, right down to the manufacturer. Potential blockages can also be identified by monitoring the actual versus the predicted pump performance. The software shows what is actually
happening in the network and can be used to generate scenarios in advance of anticipated changes to the system or the sludge rheology. This means it is now possible to specify pumps more precisely
BHR’s SLOT 2.0 software helps pump system operators find the operating point of their equipment
are inaccurate this can result in oversized pumps and higher frictional losses, adding considerable capital and operational cost to any system. The good news is that engineers can
now predict sludge rheology and assess and interpret the impact and interaction of these variables through a systems losses tool developed by BHR Group.
than ever before and the capital cost and optimum energy consumption can be calculated well ahead of installation. It is realistic to envision pump system
designers using SLOT 2.0 to digitally twin the sludge pipe network. Being able to accurately compare pressure and flow in the real network with SLOT’s predictions, it is possible to see, for example, what would happen to pump operation in the event of a struvite blockage; or how the system would respond if a sludge stream was thickened by 8 per cent. For new-build sludge processing
projects, SLOT 2.0 enables accurate sizing of pumps and pipes. It is underpinned by BHR Group’s sludge rheology database, and makes it much easier to characterise new sludge types that cannot be predicted using existing rheology data. Ultimately, SLOT 2.0 makes it possible
for utilities to make investment decisions based on the most comprehensive assessment possible of both capital and whole-life cost of assets, bringing down the total expenditure (totex) required. BHR is also looking beyond the existing assets as more sensors will be installed in sludge networks, with the uptake of real- time monitoring. Fifteen utility and contracting companies
Mick Dawson, consultancy director, BHR Group
in the UK have already trialled sludge management operations with SLOT 2.0 and feedback to date has been positive. Indications are that the value of being able to predict and manage sludge network performance at the desktop, before going out on site, will prove powerful going into AMP 7 – the regulatory asset management period 2020-2025. Meanwhile, BHR Group is continually
improving SLOT, with further advancements anticipated as users relay their experiences and requirements. The long-term outlook heralds greater capacity sludge systems with higher velocity throughput and solids content, which means the need for close attention to the whole performance envelope is only going to grow.
BHR Group
www.bhrgroup.com
thermohydrolysis produce sludges with higher dry solids content which are more difficult to pump. Image: Severn Trent
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