Modular, multi-stage, integral sealed motor pump with integrally-cooled motors and independently controlled rotor speeds

Abstract

An integral motor pump module directs at least 90% of its rotor discharge over at least 50% of its motor housing surface, thereby cooling the motor with little or no need for a separate flow path. The discharge can flow through an annulus formed between the motor and pump housings, and can extend over substantially all of the sides and rear of the motor housing. The rotor can be fixed to a rotating shaft, or rotate about a fixed shaft, which can be threaded into the motor and / or module housing. A plurality of the modules can be combined into a multi-stage pump, with rotor speeds independently controlled by corresponding variable frequency drives. The motor can be a radial or axial permanent magnet or induction motor. A separate cooling flow can provide additional cooling e.g. when pumping heated process fluids. Embodiments include guide vanes and / or diffusers.

Description

FIELD OF THE INVENTION[0001]The invention relates to pumps, and more particularly, to integral sealed motor pumps.BACKGROUND OF THE INVENTION[0002]In a conventional rotodynamic pump design, fluid flow and pressure are generated by an impeller rotating inside a stationary pump casing. The torque required to drive the rotor is provided by an external driver and transmitted through a rotating shaft to the impeller. Higher pressures can be achieved by adding multiple impeller stages in series and using a larger driver to provide torque to all stages through the same shaft. The shaft must get larger in diameter and longer in length to accommodate the combined torque and axial length of all rotor stages. Pumps with high stage counts or a vertical arrangement can use very long shafts that lead to various rotordynamic issues related to shaft deflections and critical speeds. Furthermore, dynamic seals are required to maintain the pressure boundary at the locations where the rotating shaft pe...

AI Technical Summary

Benefits of technology

The patent describes a pump module that eliminates the need for a separate motor cooling flow path by directing the discharge of process fluid over the motor housing. The pump module includes a rotor with individual bearings for each stage, which allows for higher performance limits and greater power density in the overall pump. The motor is also cooled using the working fluid, which further improves performance. The pump module also includes a plurality of variable frequency drives, which allows for independent control of each stage and accommodates low net positive suction head and off-peak conditions. The use of thrust bearings simplifies assembly and maintenance, and reduces the instrumentation required on each stage. Overall, the patent describes a more efficient, effective, and easy-to-use pump module for process fluid handling.

Problems solved by technology

Pumps with high stage counts or a vertical arrangement can use very long shafts that lead to various rotordynamic issues related to shaft deflections and critical speeds.

These seals are a source of leakage and other failure modes.

Even with rigid baseplates, nozzle loads on the pump can cause alignment problems between the driving motor and mechanical seals.

However, these designs still suffer from issues arising from the use of a single, long shaft to drive all of the pump stages, and they still require careful alignment of the motor with the pump housing so as to couple the motor and pump shafts as efficiently as possible.

Even then, significant energy is lost due to the lack of a physical coupling between the motor and the pump shaft.

Also, the components used for magnetic coupling and product lubricated bearings add complexity to the design.

Also, it can be difficult to cool a motor of a canned motor pump, because the motor is inside of the pump housing.

This exposure to fluid in the vapor phase can result in overheating and / or bearing failure.

Furthermore, the requirement of diverting a certain fraction of the pump output into a cooling flow necessarily reduces the efficiency of the pump.

Head generation and flow delivery for disk motor pumps is limited by the amount of torque which the motor, at a given diameter, can develop.

The speed of rotation is limited by both the frequency limitations of the inverter used to drive the motor and the NPSH (Net Positive Suction Head) available at the inlet of the impeller.

However, for integral disk motor designs, smaller diameter impellers provide smaller available disk areas to house the permanent-magnet disk motor, thereby limiting the torque that can be developed by the motor.

Another limitation is the relative unavailability of disk motor designs (magnetic rotors and stators) that can deliver a range of pressures and flow rates.

However, due in large part to the added complexities associated with integrated motors, most canned motor pump designs are either single-stage pumps, or include only one motor that drives several rotors fixed to a common shaft.

However, multi-stage pumps are limited due to the requirement that all of the rotors must turn at the same rate.

Furthermore, a failure of any one stage will cause an immediate and total failure of the entire pump.

However, this approach is, by its nature, limited to only two stages.

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