Pump selection problem 5

[gilden]

We have a small reactor with a filter element in the bottom. The reactor is working at atmospheric pressure. The reaction mixture is a suspension. During reaction the liquid part of the suspension is pumped by a gear pump from the filter (reactor) outlet back to the top of the reactor. The flow at which the liquid is passing the filter is dependent of the pressure difference over the filter. Now I want to speed up the recirculation flow as high as possible without cavitating the pump. To increase the pump flow, the flow through the filter has to be increased, which can be achieved by increasing the pump flow. Viscious circle? If the pump flow is much higher than the flow through the filter, the pump will cavitate. At the one hand the pumpflow is needed to create a depression under the filter and to create a pressure difference resulting in a higher flow through the filterelement. However if the pumpflow is too high, the pump will cavitate. How do I select the best pump to increase the recirculation flow to a maximum without cavitating the pump? Which specification is the most important? The pump suction capacity? Other? And how do I best control such a system? Is a gear pump the best type of pump for such an application? Who can help me?

 

[gilden]

To 25362:
the solid particles are the product (reactions on solid supports).

 

[25362]

To gilden, if so, a continued reaction would only worsen the filter's resistance to flow, and compositepro's proposition of relocating the filter after the pump appears to be eminently logical.

Two downstream filters in parallel may be considered, one in operation, the other cleaned and ready for use, suitably valved, may serve to keep the process running for as long as required w/o creating excessive back pressure on the selected pump.

Otherwise, if continuity of operation is not an important factor, a simple valved-up filter by-pass, could be opened while the filter is cleaned for reuse.

 

[gilden]

To 25362 and others:

I measured the pressure at the suction side of the gear pump: -60 mbar. Reactor was at atmospheric pressure. The reactor (diam. 102mm) contained 30 cm of water. The flow was 50L/h (measured during pumping). The filter (in the bottom of the reactor)has a pressure drop of 2.5 mbar for flow of 50L/h. The reactor outlet is a 1/4" SS line with a length of 0.6". What will be the available NPSH? Or is NPSH not applicable to gear pumps?