Introduction

This is a 3D model of a Turbine Driven Centrifugal Pump.

3D Model Annotations

Steam Turbine

Steam turbines are used as prime movers where the conversion of heat energy into mechanical rotary motion is required. Applications of steam turbines include large power station generators, ship propulsion, compressors and pumps. This 3D model shows a centrifugal pump driven by a steam turbine.

Rotor

Rotors consist of a series of blades mounted to the turbine shaft. As the name implies, the ‘rotor’, rotates. The type of blades used depend upon if the turbine is an impulse or reaction turbine. Despite reaction turbines being classified as ‘reaction’, there is always a small degree of force imparted due to impulse. For this reason, they are also called impulse reaction blades.

Rotor Blades

Rotor blades are normally attached to the rotor discs by the Fir Tree method (there are other methods, but the fir tree is most common). The blades are forged and then machined from billets of alloy steels containing chrome, nickel and titanium. The blades must be particularly strong because they transmit the energy from the steam to the rotor; they also need to be able to resist creep due to the turbine’s high rotational speeds (high resulting centrifugal force), high temperatures, and potential erosion damage from water.

Diaphragm

The diaphragms are disc shaped pieces attached to the turbine casings, which hold the stationary blades between stages. These are constructed from carbon steel or in some cases cast iron, which are machined and welded in place. In older designs the diaphragms sit inside machined recesses to reduce steam leakage across the stage and to accurately hold them in place (movement would allow blade contact with the casing or other turbine parts).

Shaft

The turbine shaft is a straight solid piece installed along the centre axis of the turbine. Turbine rotor blades are attached to the rotor, and the entire assembly rotates. The weight of the shaft (radial load) is supported at both ends by plain bearings, whilst a thrust bearing is used to handle axial loads.

Casing

The turbine casing houses the shaft, bearings, rotor and diaphragm. High pressure and intermediate pressure turbine casings are made from cast chrome molybdenum steel in order to withstand the effects of the high temperatures and pressures at which they operate. The casing forms a large pressure boundary around a turbine’s internal components. Due to the high pressures present within the HP and IP turbine casings, the casing walls are considerably thick. Low pressure turbine casings are normally constructed from carbon steel because it is cheaper than other suitable alloys. Casings are installed in two parts (upper and lower casing); this allows for the removal of a turbine’s internal components.

High Pressure Steam Inlet

High pressure steam enters through this connection.

High Pressure Steam Discharge

High pressure steam is discharged through this connection.

Intermediate Pressure Steam Inlet

Intermediate pressure steam enters through this connection.

Intermediate Pressure Steam Discharge

Intermediate pressure steam is discharged through this connection.

Centrifugal Pump

This 3D model represents a double suction, single stage, between bearings, centrifugal pump. ‘Double suction’ refers to the liquid entering on both sides of the impeller. ‘Single stage’ refers to the number of impellers (one impeller = single stage, two impellers = two stages). Centrifugal pumps are further classified as ‘overhung’ or ‘between bearings’. An overhung pump has an impeller shaft supported by bearings on only one side. A between bearings pump has an impeller shaft supported by bearings on both sides.

Discharge/Outlet

Fluid is discharged from the pump through this connection.

Suction/Inlet

Fluid is drawn into the pump through this connection.

Wear Ring

An impeller wear ring is installed to reduce the clearance between the casing and impeller. Reducing the clearance reduces the amount of leakage from the discharge to suction side of the impeller; this ultimately improves the efficiency of the pump. Wear rings may be installed on the impeller, casing, or both.

Impeller

Fluid flows into the eye of the impeller and then outwards radially. As the fluid moves outwards through the impeller vanes, its kinetic energy is converted to pressure energy. There are three types of centrifugal impeller, these are the closed, partially closed, and open types; the type used depends upon what fluid is being pumped. The impeller type shown on this 3D model is a closed (fully shrouded) type impeller.

Volute Casing

Centrifugal pump casings are of the diffuser or volute type. Single stage pumps (one impeller) almost always utilise volute casings, whilst multistage pumps (>1 impeller) usually utilise diffuser casings. Irrespective of if a diffuser or volute casing is used, their purpose is to convert kinetic energy (flow) to pressure energy (head).

Compression Packing

Compression packing seals the space between the shaft and casing. Compression packing is usually referred to simply as ‘packing’. An alternative to compression packing is the mechanical seal.

Stuffing Box

The area where the packing and lantern ring are installed is known as the ‘stuffing box’. The packing is literally ‘stuffed’ into this space. On this model, the annotation marker has been placed above the stuffing box.

Lantern Ring

Lantern rings are used to distribute cooling liquid to the packing. Cooling liquid cools and lubricates the packing, which reduces the likelihood of it overheating (overheated packing does not seal correctly). Typical cooling liquids include oil, emulsions, and water.

Bearings

Bearings carry the axial and radial loads generated by the pump when it is stationary and in service. The type of bearing used depends upon many factors, including load, load direction, and rotational speed. Ball bearings are considered a suitable bearing for many service applications, although they are less favoured for heavier loads. Ball bearings and roller bearings are types of anti-friction bearing.

Impeller Inlet

Fluid is drawn into the impeller through this inlet.

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