Bredel hose pumps have been installed as part of a landmark abrasives handling project at the combined heat and power (CHP) plant of Dong Energy in Studstrup, Denmark.
The project has seen the facility switch from coal to biomass fuel in line with its ambition to supply sustainable energy. Bredel peristaltic hose pumps were selected by the lead contractor, Eurocon, after trials demonstrated how specific challenges such as high density, inhomogeneous mass, abrasive particles and high pressure, could be overcome in a superior manner to competing progressive cavity pumps.
In converting from coal to biomass (wood pellets), Dong Energy required the construction of a plant facility for firing ash from coal combustion to achieve the optimum binding of alkali in the flue gas. This would also serve to spare the boiler walls from scale/slag accumulation, corrosion as well as reduce poisoning of the deNOx catalyst.
For this purpose, fly ash is mixed with 35% water, fed to the dosing tanks (each with a recirculation line) through a 650m-long pipeline and finally injected to the pellet mills. Inside, to avoid settlement, four Bredel 80 hose pumps are deployed to circulate the fly ash slurry, which is then dosed from the recirculation line into a Babcock boiler.
The ash slurry is dosed via four wood pellet mills, each mounted with a Bredel 40 pump. In total, the installation involves 21 Bredel pumps of mixed sizes, some of which run continuously.
Extending hose life to enable maximum uptime
It was evident at an early stage in the project that the potential for hose wear was high. Here, project co-operation between WMFTG, Eurocon and Dong Energy saw the delivery of an optimised solution that would potentially result in huge financial savings – fly ash is traditionally handled by large double-acting hydraulic pumps costing circa £500,000 each.
By making subtle changes to the process, it was found that the life of the natural rubber hose elements in use at Dong Energy could be maximised. With good engineering support from WMFTG, the system back pressure versus shimming was optimised, reducing mechanical stress on the pump hoses.
“To summarise, the effect of abrasiveness on hose life is low; the effect of factors such as dry solid content and pump speed is much higher,” says Mr van der Meulen, Bredel Hose Pumps Training & Application Manager. “At Studstrup, the dry solids content of the fly ash entering the system is controlled automatically – when it exceeds the limit at which the slurry can be successfully pumped, a Bredel 40 is activated to add water until the B100 [used to transfer the prepared slurry from a buffer tank to the storage tanks] is able to pump again. As for pump speed, this has an almost linear effect on hose life: half the speed is double the hose life.”