Tough pumps bear fruit for lime treatments

In order to stay within strict emissions thresholds, coal-fired and energy-from-waste (EfW), steel plants and oil and gas refineries use lime to remove sulphur dioxide (SO2) from their flue gas output. An added  benefit of flue gas desulphurisation (FGD) is the creation of high grade by-products, such as gypsum.

The British Lime Association cites efficiencies in the range of 95-99% – mineral lime reagents are used in abatement techniques at more than 85% of UK sites that treat flue gas. Its abrasive nature means facilities using centrifugal pumps have experienced recurring problems with seal failures, leading to excessive maintenance and repair costs. This has implications for the flue gas desulphurisation (FGD) process.

During a site visit to a major European EfW plant, running a 15-hour wet scrubbing operation, Watson-Marlow Fluid Technology Group contracters noted that centrifugal pumps were experiencing frequent failure when transferring abrasive lime slurry reagent. 

In such cases, the principal problem is that slurry entering the scrubbers is both high in temperature and contains up to 25% dry solid content. Also, the slurry crystallises as it cools.

Emissions from incinerators are under scrutiny, so they need to perform without any unpredictable downtime. Realising the requirement to change its pumps in the wet scrubbing process to meet stringent industry demands, the European EfW plant trialled WMFTG Bredel hose pumps.

In Bredel hose pumps, which are both dry running and self-priming, the actual pumping principle is based on alternating compression and relaxation of the , drawing content in and propelling product away from the pump. As a result, the fluid being transported is only in contact with the hose, making itideal for handling aggressive or abrasive chemicals, such as lime.

Unlike centrifugal pumps or progressive cavity pumps that may be found in FGD processes, Bredel pumps are virtually maintenance-free as there are no expensive seals, valves, diaphragms, glands, rotors, stators or pistons to leak, clog, corrode or replace, leading to a much more controlled process and lower OPEX costs.

To be noted that the Bredel pumps include a unique rotor design which does not rely on the gearbox shaft. This protects the bearings of the gearbox from overloads which might occur in other hose pumps. With such a design, Bredel provides the guarantee of trouble-free and long lasting operation, even in heavy duty operations.

In addition, despite the lime slurry being both high in temperature and solid content, Bredel pump hose life is repeatable, and is not impacted by abrasion or crystallisation. 

Following the change from centrifugal pumps to peristaltic hose pumps, the EfW plant reported a more controlled operation and much improved OPEX costs.

On a typical basis, some 255,000 tonnes of waste are incinerated at the facility from a total of 1 million tonnes collected. This process leads to the generation of 139,000 MWh of electricity, around 35,000 MWh of which is used by the plant, with the remaining 104,000 MWh sent to the grid.

Ultimately, the success of the Bredel pumps is helping the plant continue these operations while maintaining its commitment to the environment.