A European cardboard mill producing 240 000 t/y of cardboard from wastepaper required a solution to overcome regular pump breakdowns in the fibre line effluent sump.

The main effluents from the fibre line process of the mill are collected in a large, 2.5-m-deep sump prior to being pumped further through rotary drum screens and sent to the wastewater treatment plant. The liquids in the sump have varying characteristics and can be highly polluted with all kinds of solid particles, such as fibres, clips, tapes and ropes.

The original sump pumps failed frequently and the two original submersible pumps were regularly clogged, interrupting the process and leading to high repair costs.

Sulzer replaced the two existing submersible pumps with one non-clogging AHLSTAR NPP42-150 pump equipped with a Sulzer Ejector.

The solution included one dry-installed process pump with a complete priming system. An AHLSTAR NPP42-150 non-clogging pump unit with ejector replaced the failing submersible pumps.

The NPP42-150 pump unit is located above the liquid level in the sump. At each pump start, a fully automated priming is completed in a few seconds with the Sulzer Ejector package. One of the initial submersible pumps was removed from the sump and the other one is kept as standby, to be used from time to time in parallel with the NPP42-150, when a maximum drainage flow is required.

Sulzer asserts that its AHLSTAR non-clogging NPP42-150 with vortex impeller is the right pump for sump applications where liquids are heavily polluted with debris and other big solid particles. 

The previously installed submersible pumps were cast iron, whereas all the wetted parts of the NPP42-150 pump are of duplex stainless steel, said to be ideal for liquids which can be both corrosive and abrasive, ensuring a longer pump service life with minimum wear of parts. 

The NPP42-150 pump unit is above the sump liquid level, allowing for safe and rapid maintenance operations. Several other AHLSTAR process pumps are installed in the cardboard mill, ensuring efficient inventory control of spares.

Sulzer explains that its ejector is an inexpensive and simple device that is powered by compressed air from the mill network. It allows full priming of the inlet pipe and pump in a few seconds. After priming, the ejector is stopped, and the NPP42-150 pump starts running. No compressed air is required during normal pumping operation. 

The complete Sulzer Ejector package includes an ejector, valves with actuators for motive air and ejection suction pipe, a level control switch and a control box with logic.