Pumping hot liquid

[wfn217]

I want to circulate a solids suspension in water through an external heat exchanger and back into the tank. The temperature will gradually increase from 190 F to 340 F with a final pressure of 103 psig in the tank. How can I pump (circulate) the suspension at it's boiling point and high pressure?

 

[GL431]

340°F is the boiling point at 103 psig. What is the purpose here? To evaporate water and concentrate the slurry? Or to soak the solids at 340°F with little evaporation of the water?

For pumping at the boiling point, you have to ensure that you have sufficient NPSHA. I.e. the level control in the tank must be good or the tank must be high enough. It appears that at the inlet to the tank, you will have a three phase mixture (solids, liquid water and steam). That is an environment which favours erosion/corrosion. So, the heat exchanger, outlet piping, valves, tank inlet nozzle and impact areas on the tank walls should be designed for this. The heat exchanger will probably be designed for non-boiling operation. I.e. it will operate at a pressure above 103 psig. That means you would need a valve between it and the tank across which the mixture would flash.

In other words, it appears as if you have an interesting design problem on your hands. You have given us very little information to start off from. It is also not clear whether you are asking about the pump or also about the whole system including the pump.

 

[wfn217]

GL,

The purpose is to soak the solids at 340 F. You have answered my question.

 

[dcasto]

Your pump will be operating at 190 F. As long as you have NPSH, there will be no problems. You can get a water cooled packing to increase life. The pump should be capable of handling the solids and the head required. Looks routine to me once you check the above.

 

[itdepends]

Pump the discharge of the heat exchanger back into the bottom of the tank and use a high flow/low temp increase per pass to make sure the discharge from the HX doesn't flash.

The use of some overpressure such as air or nitrogen in teh tank will make your life easier too.

 

[moltenmetal]

Select the right pump and exchanger and design the recirculating loop such that there's enough NPSH. What's the particular problem?

 

[mbeychok]

wfn217:

Pumping a suspension of solids in water (or a slurry) through an external heat exchanger is going to be tricky because of the possibility of heat exchanger tube blockage with the solids.

Have you considered the alternative of:

(1) Using an internal heating coil inside the tank or a bayonet heater inserted through the side of the tank.
(2) Plus an agitator or stirrer within the tank to keep the solids in suspension.

That would seem to be a simpler, more reliable method.


Milton Beychok
(Visit me at www.air-dispersion.com)
.

 

[moltenmetal]

There's a semantics problem here. To me, a suspension implies solids readily suspended by fluid movement. A slurry implies solids that settle readily, or at high concentration. One is relatively easy to pump and exchange heat with, the other not so. So wfn217- which one is it?

 

[wfn217]

A suspension. We will probably heat the suspension by sparging with steam. Although this adds water to the batch, we will just use less water initially.