Knoll Maschinenbau GmbG

Archiv for: waste water technology

Application of the KNOLL progressing cavity pump in the wastewater industry

A new application for the MX is the loading of chamber filter presses in the wastewater treatment sector.

A so-called feed pump feeds the sludge or suspensions into the cavities of the filter chamber, initially at zero pressure and at a high delivery rate. The pressure inside the filter chambers begins to rise when the solids form a layer upstream of the filter cloth. The speed of the feed pump, i.e. the delivery rate, decreases with rising pressure. The process medium is fed into the chambers at pressures of up to the set maximum of approx. 16 to 20 bar. The adjustment range of the feed pump should, because of the time factor, be as large as possible, i.e. the initially pressureless filling process requires a very high delivery rate compared to the low delivery rate during the pressure holding cycle at maximum pressure.

This is why two pumps are normally used for the filtration process. A larger single-stage pump fills the filter press until a medium pressure of 4 – 6 bar is achieved. A small 4-stage pump is used for the high-pressure process until dewatering has been completed and a sufficiently dry filter cake has formed. A further reason for using two pumps is the poor efficiency of conventional progressing cavity pumps at very low speeds. A strong backflow, which also decreases the lifetime of the equipment, occurs in conventional stators at low speeds and high pressures.   

KNOLL Maschinenbau requires only one progressing cavity pump for the entire filtration process. This pump operates both as a filling pump and as a high-pressure pump. The MX handles the process in a two-stage configuration and can cover the full control range with a high level of efficiency. Thanks to the stator with EvenWall® geometry, the MX pump has a very linear characteristic and reliably provides the required pressure at a very low frequency. The KNOLL technology saves the investment in a second pump and minimises the cost of process control. It also cuts energy costs by approx. 50 %.

The two-stage MX pump can deliver pressures of up to 24 bar and is ideally suited to this application as a filling and high-pressure pump.