CAKE HANDLING SYSTEMS

Why New Cake Handling Systems Reduce Costs by 75%

The 20th European Biosolids & Organic Resources Conference is Europe’s foremost conference for the biosolids and biowaste industries and this year as well as reviewing sludge developments to date, will be exploring future solutions.

Due to my work with Utilities and Contractors in the Water Industry I was asked to demonstrate at the event some of the cost benefits Anglian and United Utilities are seeing from their innovative truck loading silos and sludge reception technology for digestion satellite and hubs, which is contributing to their overall gas generation model.

By MARK NEAL

Innovative water companies are trying to be more efficient and cost effective and reduce their carbon emissions. Some are already changing their focus from water supply / waste treatment to energy generating. They are looking at the potential of sludge in a new way – as a possible source of profit rather than a cost. Why?

Instead of thinking of sludge as a cost centre and something to be disposed of, many water companies are deciding that generating gas from sludge at large water treatment sites (hubs) and transporting sludge from smaller treatment works (satellites) to hubs will be the model of the future. As part of sludge treatment improvement facilities, forward thinking water companies have Anaerobic Digestion and Thermal Hydrolysis infrastructure such as these already in operation:

Davy Hulme being fed by 7 satellites (Wigan, Preston, Hyndburn etc.) by United Utilities Colchester, Cliff Quay and Pyewipe being fed by more satellites (ie Thetford, Bedford, Marston, Dovercourt, Canwick) by Anglian Water’s

With UK population predicted to reach 71 million by 2030, there will inevitably be more sludge to deal with in large cities and towns. By treating this as an opportunity to generate energy rather than a problem, companies are building Anaerobic Digestion Plants and Thermal Hydrolysis infrastructure near large population centres and creating smaller satellite stations to store the sludge.

This pioneering method collects the sludge from the satellites, dewaters it and delivers it to the hubs for processing. Not only is the storage solution more efficient in construction, but in operation and efficiency also.

BENEFITS

  • Energy creation instead of waste sludge disposal
  • No container rental costs
  • No requirement to regularly swap full containers
  • Fewer staff needed at all times, including bank holidays
  • By storing the sludge in new innovative ways, the plants become more flexible and the satellites capture more fuel (sludge). The solutions demonstrated focussed on the storage and discharge of Sludge, these included Truck Loading Silos, Truck Receptions Silos and Process Silos for Advanced Anaerobic Digestion.

To reduce costs further, Anglian and United Utilities chose to dewater the sludge to reduce the cost of transporting water so choosing “trailered cake @ 22%” Dry Solids instead of “tankered wet @ 6% solids.” This choice means they use 1 truck instead of 4, so saving costs of up to 75%.

ADDITONAL BENEFITS

  • Reducing haulage costs by 75%
  • Have more sludge available to process
  • Not hauling sludge borne water between locations
  • Saving fuel
  • Up to 4 fold reduction in CO2

How it works

Each storage unit is discharged by the same technology and features the same benefits. In each case, a Saxlund Sliding Frame mechanism is used to undercut the full section of the contents of the silo to prime a screw trough. Materials are discharged on a “first-in, first out” basis – important in handling materials with a shelf-life. Since the whole section is undercut, the pile section discharge is termed “mass-flow” (like laminar flow in a pipe) from the silo. This gives a homogenous discharge to the next process.

Where there is some dewatering requirement for the dilution of the sludge prior to the next process, the most efficient mix is controlled via the injection of final effluent in the pressure cavity of the Progressive Pump. Since the Progressive Cavity pump auger has already been primed by the action of the Sliding Frame and Saxlund Discharge Screw, a volumetric mix ratio between the Sludge and Final Effluent can be measured by comparison of revolutions between the Dilution and PC Pumps. This can otherwise be more random with the method of filling the inlet hopper of the PC pump with final effluent and expecting the PC Pump Auger to prime the PC Pump.

With 60 years’ experience in delivering BioEnergy projects across Europe, Saxlund holds patents on key technologies to improve feed and combustion efficiency which in turn reduce fuel costs and carbon emissions.

With its UK engineering and project management office based in Southampton, we are currently collaborating with Tier One and Tier Two water companies, consultants, contractors and investors, to deliver truck reception systems as Saxlund’s sliding frame technology, tested in hundreds of successful applications, is the only real solution for discharging sewage sludge silos at this size.

To learn how Saxlund technology could help you, please contact Mark Neal – info@saxlund.co.uk

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