The pump manufacturer Dickow has developed a new pump line NKX for circulation of thermal oil. The pump casing is designed for 16 bar and 350 °C. The new pump line extends the application limit of the previous NKLs-type. The new NKX will replace the series NKLs with exactly the same dimensions in future.
The NKX is used as a circulation pump for hot oils in industrial heating plants/units. The performance range covers capacities up to 400 m3/h and differential heads up to 90 m in 50 Hz services; and capacities up to 2,500 US-gpm and differential heads up to 400 ft in 60 Hz services. The dimensions and performance range of these centrifugal pumps are according to DIN EN 733, that means range is subdivided into different pump sizes in order to achieve best efficiency for all service conditions inside the envelope.
The NKX are a single stage, single flow volute casing pumps in horizontal back-pull-out design with end suction and top discharge flanges. The back-pull-out design allows disassembly of the bearing bracket unit, complete with impeller, mechanical seal and cooler after removing the casing bolt nuts, without removing the volute casing from the piping system (Fig. 1). If spacer couplings are used the drive motor can remain bolted to the base plate when removing the bearing bracket unit.
The mechanical seal of the new design is located in an area with lower temperature and there is only a minimum exchange of heat energy between pump casing and mechanical seal area. An integrated cooling and venting system provides a self-venting pump, patent is pending (Fig. 2).
The start of the drive motor activates the internal venting mechanism. This mechanism builds up a constant pressure and therefore a permanent circulation flow around the mechanical seal in order to dissipate the frictional heat via the connected cooling coil. The coil dissipates the heat to the atmosphere, a cooling fan mounted to the pump shaft guarantees sufficient air exchange. The constant venting of the mechanical seal chamber respectively the evacuation of gaseous low-boiling hydrocarbon components (Fig. 3) is done via an integrated gas separator immediately after the inlet into the cooling coil. The separated gas is transported through an internal pumping ring inside of the bearing bracket towards the volute casing. The sleeve bearing located directly behind the impeller has a top venting bore that feeds the gas into the rear chamber of the volute casing. The normal pumping flow absorbs the gas and carries it away.
A standard mechanical seal can be used for these extreme operating conditions up to 350 °C. The maximum allowable operating pressure at the mechanical seal is 10 bar. Advantages of the new design:
- the pump is self-venting,
- the mechanical seal chamber does not require manual, external filling and venting,
- no need to collect and dispose any spilled oil,
- no operating personal may be harmed or injured during venting of the hot pump,
- the cooling coil allows operation of the pump up to 3500 rpm.
Since the volute casing dimensions have not changed, the NKX rotating units will fit into the existing NKLs volute casings. Because of the cooling fan however a new, larger, perforated coupling guard is required in this case.
The pumps have closed casted impellers, hydraulically balanced by throttle gap and relief bores to keep occuring axial loads to a minimum. All impellers are dynamically balanced acc. to DIN ISO 1940 part 1, at a balance grade of G 6.3, that grants a smooth and vibration free run of the pump.