The Sulzer Pumps standardised helico-axial multiphase pump range consists of twelve frame sizes covering total volumetric flowrates (oil, water & gas) at suction conditions (actual flow at pump inlet) from 22,000 bbl/day (146 m3/h) up to 600,000 bbl/day (4,000 m3/h). It is based on the latest second generation helico-axial hydraulics (Poseidon license) developed by the Poseidon group (Institut Français du Pétrole, Total & Statoil).
Two mechanical designs are available: high speed (up to 6800 rpm) and low speed (below 4000 rpm).The pump is an inline multistage pump with a horizontally split inner case in a barrel (cartridge pull-out design).
Each compression stage comprises a rotating helico-axial impeller and a stationary diffuser.
The main advantages of the helico-axial hydraulic are :
- Ability to pump any GVF from 0 (100% liquid) to 1.0 (100% gas).
- Mechanical simplicity and reliability (one single shaft, rotodynamic principle).
- Compactness.
- Self-adaptation to flow changes
- Very tolerant to solid particles (open type axial impeller, without tight clearances).
Performance Range
Pressure 150 bar / 2175 psi
Temperature 175 ° C / 350 ° F
Hydraulic Design
Each compression stage consists of an impeller, mounted on a single rotating shaft, followed by a fixed diffuser. The impeller blades have a typical helical shape. The profile of the open type impeller and diffuser blading arrangement is specifically designed to prevent the separation of the gas-liquid mixture during the compression process. The hydraulic passages accommodate solid particles in suspension, and special care has been taken in the design to prevent their accumulation in the pump casing.
Due to the compression process the gas volumetric flow rate decreases as it goes through the pump. Therefore the pump is generally equipped with different series of hydraulics, i.e. different series of geometries, whereby one series would have identical compression stages. The changing geometry from one series to the next provides adjustment for the decreasing volumetric flow rate.
An important feature of this design is the hydraulic flexibility which it affords and the wide range of duties that can be met by a single pump. This means that the multistage pump can be easily retrofitted to take account of changing reservoir characteristics during the production life of the field; in particular, the oil flowrate may be maintained longer.
Mechanical Design
Based on Sulzers’ experience with injection pumps and centrifugal compressors a modular design for the multiphase pump range has been developed. The design is in general accordance with API 610.
The selected layout is a multistage barrel in-line pump with axially split inner casing. The in-line layout is required to allow the transport of the solid particles contained in the pumped fluid. The impeller tip clearance is in accordance with API 610 requirements.
The diffusers are of split design and located in an axially split inner case. The axially split design allows an easy inspection of the rotating parts. In addition the rotor does not have to be dismantled during the pump assembly allowing low residual rotor unbalance to be achieved guaranteeing a low level of vibration.
For ease of maintenance, the hydraulic parts (complete rotor with impellers, diffusers, inner case and suction casing) are designed as a pull-out block.
The shaft sealing is achieved with mechanical seals. In order to avoid gas or solid particles contaminating the faces and also to allow for dry running conditions, a pressurised external fluid is injected into the seal. Between the seal fluid circuit and the suction/discharge nozzle an overpressure of 5 bar is continuously maintained (even when not running).
A seal fluid reservoir is located on the skid. One combined seal and lube oil system is used for both lubrication and cooling.
Operating conditions often dictate the need for materials that possess excellent corrosion and erosion resistance:
- Corrosion: effluent may contain hydrogen sulphides with water and chlorides, sometimes combined with high temperatures.
- Erosion : sand may be entrained by the effluent.
Therefore, in order to cater for aggressive effluents of this nature, all wetted parts would usually be in duplex stainless steel or super duplex stainless steel (pitting resistance equivalent number ³ 40). The pump may also be equipped with exchangeable wear rings in front of the impellers and diffusers.
MPP Pump Range
The Sulzer MPP modular range of pumps consists of standardized frames with a total nominal capacity of up to 600,000 BPD (4’000 m3/h) at the pump suction flange. The standard range id designed to boost up to 60 bar with an extended design available up to 85 bar.
The approximate achievable ratio between discharge pressure (p2) and absolute suction pressure (p1) with a Sulzer multiphase pump as a function of the gas volume fraction at pump suction conditions.
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