Heavy duty pumps enable eco-friendly solution for cement slurry
26 Feb 2019
You need tough pumps to handle the abrasive cement slurry that European materials specialist Xella produces at its site. Watson-Marlow took up the gauntlet…
Boasting 6000 employees, 91 plants in 20 countries and sales organisations in more than 30 countries, Xella has a significant global presence.
The materials company’s commercial clout comes with a commitment to sustainability both in manufacture and use. Not only with regards to bringing energy-efficient and environmentally compatible products to market; but also about production, management, human resources, compliance and research.
Through its Ytong, Silka and Hebel brands, Xella is one of the world's largest manufacturers of autoclaved aerated concrete (AAC).
AAC offers high thermal insulation and, thanks to its porous structure, can undertake both structural and physical building functions, normally without additional measures or supplementary building materials.
The reuse of waste slurry streams is a part of the company’s manufacturing process, the. The raw materials for AAC include quartz sand, calcined gypsum and lime (mineral), which are mixed with water to an aqueous suspension.
The aerating agent is aluminium powder, which is added at the end of the process to a concentration of 0.05-0.08% by volume, depending on the pre-specified density. Finally, the mix is poured into moulds. When the forms are removed from the material, it is solid but still soft. The material is then cut into blocks or panels before being placed in an autoclave chamber for 12 hours.
Bubble trouble
Both Xella’s sites in Rotenburg in Germany and Meppel in the Netherlands process slurry. However, at the German planr, the application involves the circulation and transfer of cement slurry‘ or ‘schlamm’,
At Rotenburg, centrifugal pump technology was deployed but ongoing problems were experienced, largely due to various additives in the cement slurry.
Ongoing problems were experienced, largely due to various additives in the cement slurry
By circulating the slurry, the particles become smaller and smaller and, at a certain size, air bubbles are created. Unfortunately, the air bubbles led to the formation of air pockets in the centrifugal pumps, causing them to fail.
Meppel by contrast had been an early adopter of Watson-Marlow Fluid Technology Group’s Bredel pumps, after its previously-used progressive cavity (PC) pumps produced high maintenance costs and long downtime periods.
Two Bredel 80 pumps and one Bredel 100 were installed there several years ago, with the site operating a four-shift system running 144 continuous hours, for six days per week.
This type of pump has no valves or seals to leak, clog or replace, and provides flow rates to 108,000 l/h and pressures to 16 bar. Bredel pumps can also handle viscous and abrasive slurries, pastes and sludge, with up to 80% solids in suspension. In the past, the Dutch plant used
At Meppel, one of Bredel 80 pumps runs 90% of the time, circulating the slurry in the tank underneath the cutting machine at a rate of 14.5 m3/hr. The slurry in this tank overflows into a back-up tank, which is where the other Bredel 80 is deployed, pumping the slurry to a bulk storage tank.
Meanwhile, the Bredel 100 is used to pump slurry from the bulk storage tank to the mixer at flow rates of between 13.8 and 18 m3/hr, along several long-sweep elbow bends in the system.
Xella’s solution for its German plant was to adopt two Bredel pumps for circulation and transfer of the waste return stream but exclusively using the higher-flow Bredel 100.
As a result, says the firm, it is able to meet its sustainability goals without compromising on process efficiency or commercial goals.
