Pump motor sizing

[John wells]

I was approached by an employee working at an industrial plant with a question/problem with a pump on site. The plant is a Molasses Plant
and during the colder months they have a 25 HP centrifical pump that continually goes out on overload due to the colder temperature of product. If motor
is feathered and product is bled until molasses pipe between holding tank and motor (about 250?) frees up, pump is fine and runs without a problem. The
owner has asked us if installing a larger HP motor?a 40 or 50 would take care of it or is asking us for information/solutions to the tripping issue. I?m
not sure if any type of VFD would be an option here for the high torque starting due to the temperature of product. Heat trace tape was declined as apparently it has not worked in other instances.

 

[Volta]

Molassas in January

Molassas in January

Cliche for a reason!

A couple other way to heat pipelines too, induction / hysteresis or impedeance.
Depending on the layout, might be cheaper to rework (only?) a section of the pipe for such heating.
Welcome.

 

[weressl]

Cliche for a reason!

A couple other way to heat pipelines too, induction / hysteresis or impedeance.
Depending on the layout, might be cheaper to rework (only?) a section of the pipe for such heating.
Welcome.

Heating up product and providing heat tracing are two different issues. Heat tracing is usually to prevent heat loss from a material already at a certain temperature. The heat tracing depends on insulation as without insulation the heat loss will be much greater (40W/ft versus 4W/ft). Heating up a product also requires a much greater amount of heat AND time than simple heat tracing. If you have only heat tracing it may take days to heat up the product and then you only heat up the product that is in the pipe and as soon as the flow starts it will be followed by unheated product, so it practically got you nowhere. Electric heat is usually not the most cost efficient method of product heat. Molasses are often heated with steam, and then the transfer pipe is electric traced.

Should you have this pump close to the storage tank there may be a unique solution available without needing major modification such as installing steam heater and agitator. This will work if the pump is not used for transfer all the times.

Install a recirculation line with a restrictive orifice. You would run the recirculation line and control it by temperature. All the mechanical energy from the pumping converts to heat, so when you recirculate you actually heat the product up. The heat tracing will keep the pipes warm, so the molasses don't cool/thicken up when it is just standing in the line.