Viridor Cuts Costs and Downtime by Switching to SlurryPro Pumps
Project Overview
The Glasgow Recycling & Renewable Energy Centre (GRREC) is a £154m flag-ship AD plant, now run by Viridor.
Viridor was able to radically improve uptime and wear life by switching from rotary lobe pumps to SlurryPro centrifugal pumps on their digestor recirculation lines. The result was a significant saving in replacement parts, engineer time, and the cost of downtime.
Challenge
Like many early AD plants in the UK waste-to-energy sector, the original contractor specified pumps that were ill-suited to the diversity of energy-from-waste (EFW) digestate streams. Much of the technology used was a copy and paste from Danish or German systems, pioneer countries in farm-based AD plants. The pumps installed had a record of success in dedicated farm slurry and energy crop AD plants, and have a lower capital cost than other alternatives.
However, the precise meshing of the lobes in these pumps is a major disadvantage in household and industrial waste-to-energy schemes, which typically have highly abrasive content. This immediately starts to wear the internal lobes and casing, leading to a rapid reduction in efficiency. This meant increasing the speed (and power consumption) to maintain flow, as well as frequent downtime and costly intervention to replace worn parts.
The new owners, Viridor, needed to turn things around and deliver the results that were originally envisaged.
Solution
Viridor approached Atlantic Pumps, the specialists in pumps for abrasive applications. Following a study which looked at alternative positive displacement and centrifugal pumps, it was recommended that SlurryPro centrifugal slurry pumps would be the best solution.
6×4 SlurryPro pumps, optimised for the duty with open 2-vane impellers and double mechanical seals were proposed. On paper, these appear to have a lower efficiency new-for-new than lobe pumps, but it is important to remember that pump curve charts and performance data are based on clear water.
When comparing capital purchase costs, it is key for long-term profitability to forecast lifetime cost of ownership. Slurry pumps, when properly specified for abrasive sludges, solids passage, and flow/pressure requirements of the duty, are often more expensive than pumps made for smooth pastes and clean water. However, the operational savings can soon compensate as shown in the demonstration example right:
| Positive Displacement Pump | Centrifugal Slurry Pump | |
| Initial purchase price | £20,000 | £30,000 |
| Energy costs (per year) – rated, based on clear water | £25,000 | £50,000 |
| Energy costs (per year) – actual, due to wear | £50,000 | £50,000 |
| Spare parts (per year) | £50,000 | £5,000 |
| Cost of downtime (£1,000/day) | £20,000 | £2,000 |
| Total pumping costs first year | £140,000 | £87,000 |
| Total pumping costs subsequent years | £120,000 | £57,000 |
Results
From the bare cost savings on spare parts alone, it was clear within months that the move to SlurryPro had repaid for itself and would continue to improve the financial stability of the plant.
The reduction in wear-rate now means the energy consumption is both predictable and steady, and the length of time between maintenance (MTBM) has been improved by 3 to 4 times. This, in turn, has reduced H&S risk incident exposure, increased energy yields and recycling capacity, and reduced unplanned downtime and disruption.
After years of constant operation, the original SlurryPro pumps continue to provide the required pressure and flow. The success has seen Viridor repeat this in other similar high-wear duties and now operate multiple SlurryPro, and other pumps from Atlantic.
From the bare cost savings on spare parts alone, it was clear within months that the move to SlurryPro had repaid for itself and would continue to improve the financial stability of the plant.
