Refinery Pump Selection Requirements
1 Selection points
1.1 Main pump types and features
According to different process routes, the main equipment of the refinery is generally atmospheric distillation, vacuum distillation, catalytic cracking, hydrocracking, delayed coking, etc.
According to the above process flow, the more important pumps in the refinery are generally the initial distillation column bottom pump, the atmospheric column bottom pump, the vacuum column bottom pump, the oil slurry pump, the hydrogenation feed pump, the coke discharge pump (decoking pump), etc., These pumps mainly transport dangerous liquids such as flammable, explosive or toxic, some of the medium temperatures is as high as 400 ℃ or more, and some also contain solid particles, so the material is required to have good corrosion resistance and wear resistance, and the pump must also have High reliability and long-term safe operation.
1.2 Selection steps
1.2.1 Determination of pump type
In the refinery design process, most of the required main pump types have been specified, such as OH (cantilever type), BB (both ends support type), VS (vertical suspension type), etc. in the API610 standard. Therefore, generally not The pump type needs to be selected again.
Flow and head are the main basis for selecting pumps. In the inquiry form, three flows of minimum continuous flow, normal flow, and rated flow are generally proposed. When selecting a pump according to the API610 standard, the rated operating point of the pump should be selected on the right side of the best efficiency point (BEP) of the pump, and the normal operating point should be on the left side of the optimal efficiency (BEP), and the actual minimum flow rate of the pump should be selected. Should not be greater than the minimum continuous flow required. The head should be selected according to the rated operating point, that is, the head required in the purchase order is the head corresponding to the rated flow point, and there is no margin for the head during model selection.
Inquiries generally require that the pump should have a flat and continuously rising performance curve, no hump, and the lift from the rated operating point to the dead point should not rise more than 20%.
Some engineering companies require that the rated operating point of the pump should be selected on the left side of the best efficiency point (BEP) of the pump when selecting a pump, and it should be satisfied according to different requirements during model selection.
1.2.3 Cavitation allowance (NPSHr)
NPSHr is an important performance index of the pump, and there are specific numerical requirements for this in the purchase order, and sometimes the requirements from small continuous flow to rated flow area (public number: pump housekeeper),.NPSHa-NPSHr≥0.8 meters and other requirements, The purpose is to ensure that the pump does not cavitate during operation, and special attention should be paid to the selection. Measures to reduce NPSHr, such as reducing speed, selecting impeller with good NPSHr performance, increasing inducer, etc.
However, in actual projects, sometimes the NPSHr value proposed by the design unit is very harsh, and several manufacturers participating in the bidding cannot meet the NPSHr requirements.
The pump flow parts used in refineries are generally made of standard materials, as long as they are selected according to the requirements of the design inquiry and the material series listed in the API610 specification. There are no special requirements for the material of the constant bottom pump, the initial bottom pump, the reduced bottom pump, the feed pump, and the coke discharge pump. Generally, the S series or the C series in the APl610 standard can be used. More special is the oil slurry pump in the catalytic cracking process. In addition to meeting the performance requirements, it is also necessary to solve the problem of wear resistance under high-temperature conditions. Anti-wear materials can be selected or certain wear-resistant parts of the pump can be used. measures to improve sex.
For the pressure-bearing pump body of the high-pressure pump, such as the outer cylinder of the feed pump, the selected shell material must meet the change requirements of the temperature-pressure relationship of the pump. The domestically designed pumps often lack this information, so special attention should be paid to this. . In addition, for shafts of different materials, special attention should be paid to the maximum motor power allowed by the shaft. Generally, foreign pumps are given the maximum allowable value of P (kW)/n (r/min) for shafts of different materials. The value can determine the maximum power of the motor that can be equipped with each material shaft.
1.2.5 Sealing and auxiliary systems
Sealing and auxiliary systems are an important part of the pump and play a decisive role in the reliable operation of the pump. The API682 standard selects the sealing scheme.
The design institute generally does not make specific requirements for sealing in the purchase order but requires the pump manufacturer to determine the detailed sealing scheme according to the requirements of the working conditions. The determination of the sealing scheme depends on many experiences. For complex working conditions, the schemes selected by each company may be very different.