Selection requirements for pumps for refineries
Publish Time: 2024-07-11
In recent years, with the increase of new construction and expansion projects of domestic large-scale refineries with an annual capacity of more than 10 million tons and many small and medium-sized refineries, the demand for petrochemical pumps has been increasing. To meet the new market needs, chemical pump manufacturers are actively improving product design and production technology to expand production capacity. However, there are some technical details that need to be paid attention to in this process.1 Selection points1.1 Main pump types and characteristicsAccording to different process routes, the main equipment of refineries 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 primary distillation tower bottom pump, atmospheric tower bottom pump, vacuum tower bottom pump, oil slurry pump, hydrogenation feed pump, coke water pump (decoking pump), etc. These pumps mainly transport flammable, explosive or toxic dangerous liquids. Some of the medium temperatures are as high as 400°C or above, and some also contain solid particles. Therefore, the material is required to have good corrosion resistance and abrasion resistance. The pump must also have high reliability and be able to operate safely for a long time.1.2 Selection steps1.2.1 Determination of pump typeDuring the refinery design process, most of the main pump types required have been specified, such as OH (cantilever type), BB (two-end support type), VS (vertical suspension type) in the API610 standard, so there is generally no need to select the pump type.1.2.2 Flow-headFlow and head are the main basis for pump selection. In the purchase order, three flow rates are generally proposed: minimum continuous flow, normal flow, and rated flow. 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 pump's best efficiency point (BEP), and the normal operating point should be on the left side of the best efficiency (BEP) (Figure 1), and the actual minimum flow of the pump should not be greater than the required minimum continuous flow. 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 the head is not added with margin when selecting.
Purchase orders generally require pumps to have a flat continuous rising performance curve, without humps, and the head rise from the rated operating point to the dead point should not exceed 20%. Some engineering companies require that the rated operating point of the pump should be selected on the left side of the pump's best efficiency point (BEP) (Figure 2) when selecting a pump, and different requirements should be met when selecting a pump.1.2.3 Cavitation head (NPSHr)NPSHr is an important performance indicator of the pump. There are specific numerical requirements for this in the purchase order, and sometimes it is proposed that from the small continuous flow to the rated flow area, .NPSHa-NPSHr ≥ 0.8 meters and other requirements are proposed. The purpose is to ensure that the pump does not cavitation during operation. Special attention should be paid when selecting a pump. Measures to reduce NPSHr, such as reducing the speed, selecting an impeller with good NPSHr performance, and adding an inducer. However, in actual projects, sometimes the NPSHr value proposed by the design unit is very demanding, and several manufacturers participating in the bidding cannot meet the NPSHr requirements. At this time, the design unit should be explained in a realistic manner, and measures should be taken to reselect or adjust the design.1.2.4 MaterialsThe flow-through parts of the pumps used in refineries are generally made of standard materials, and they can be selected according to the requirements of the design inquiry form and the material series listed in the API610 specification. There are no special requirements for the materials of the normal bottom pump, primary bottom pump, reduced bottom pump, feed pump, coke water pump, etc., which are generally S series or C series in the API610 standard. The more special one 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. Wear-resistant materials can be selected or certain wear-resistant measures can be taken at the easily worn parts of the pump to improve performance.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 temperature-pressure relationship change requirements of the pump. Figure 3 is the temperature-pressure change curve of a certain pump. Domestically designed pumps often lack information in this area, so special attention should be paid. In addition, for shafts of different materials, special attention should be paid to the maximum motor power allowed for the shaft. Foreign pumps generally give the maximum allowable P (kW)/n (r/min) value for shafts of different materials. Based on this value, the maximum motor power that can be equipped with each material shaft can be determined.1.2.5 Seals and auxiliary systemsSeals and auxiliary systems are important components of pumps and play a decisive role in the reliable operation of pumps. API682 standard selects sealing solutions. Design institutes generally do not make specific requirements for seals in the purchase order, but require the pump manufacturer's seal factory to determine a detailed sealing solution based on the working conditions. The determination of the sealing solution requires a lot of experience. For complex working conditions, the solutions selected by each company may be very different. In order to ensure safety, some companies make the selected sealing solution redundant, resulting in an increase in the quotation, which may put them at a disadvantage in the commercial bidding. My opinion is to avoid excessive functions of the shaft seal system under the premise of ensuring safety and reliability. In addition, the world's well-known seal manufacturers, such as Germany's BURGMANN and Britain's JOHN CRANE, have many mature experiences in the mechanical seals and systems selected for different media conditions in various industries. When choosing a sealing solution, you can fully seek the opinions of the seal manufacturer and strive to select a more reasonable sealing solution.1.2.6 Motors, steam turbines and other driving machinesThe selection of motors is also very important. The required motor power, voltage, explosion-proof, protection level, etc. are often selected in the design inquiry form. Therefore, there are requirements for the efficiency of the pump. If the pump efficiency is low, the specified motor power may be insufficient.In order to save energy and recycle energy, some pumps in petrochemical plants are driven by hydraulic turbines or steam turbines. At present, domestic petrochemical plants use hydraulic turbines as pump drivers, while few use steam turbines to drive pumps. The main reason is that the domestic small steam turbine market (below 2000kW) is basically blank, and the price of importing from abroad is relatively expensive, which to a certain extent affects the promotion of small steam turbine driving machinery for pumps. However, petrochemical companies generally hope to promote the use of small steam turbines to replace some pump motors in petrochemical companies, because petrochemical plants generally have their own power plants and abundant hot steam resources of various pressure levels.2 Suggestions on data sheetsEach engineering company and patent holder (such as UOP-Universal Oil Products) generally has its own pump data sheet. Pump manufacturers or sellers are better to use the data sheet provided in the purchase order directly. Now, after receiving the purchase order, each pump manufacturer often rewrites the pump data sheet of their own company. In addition to the trouble and errors in the content, it is very inconvenient for technical exchanges. Because the format, sequence, content, etc. of the pump data sheets of different companies are not exactly the same. On the contrary, if the data sheet in the purchase order is used directly, during the technical review or technical exchange, the design institute will confirm the requirements of the pump manufacturer to respond to the technical inquiry book, which will be very intuitive and clear, and it will be easy for both parties to conduct technical exchanges and confirmation.3 About API610 standardAPI610 standard is currently recognized internationally as the most authoritative technical specification for the design and acceptance of refinery pumps, and it is also widely used in China. Pumps designed and manufactured according to API610 specifications are usually called API pumps. Most of my country's petrochemicals are also designed and manufactured with reference to this standard. Large domestic APl pump manufacturers have many series of imported technology products with perfect performance. Therefore, when participating in the project, you only need to directly select the model according to the requirements without redesigning, but sometimes you need to make some local improvements to meet the needs.The API610 standard is also constantly being revised and improved. It is generally updated once every 7-8 years. Some contents of different versions will have some changes. Therefore, in the process of applying the APl610 specification, it should be applied flexibly, and some non-principle clauses may not be completely copied.As a pump manufacturer, you should be realistic in the design and promotion of your products. There is no need to pursue the so-called latest version of APl610 too much. Don't claim that your products are fully in line with the APl610 standard at will, so as not to cause trouble to yourself during technical exchanges or acceptance. In fact, it is difficult for any pump manufacturer to make a so-called 100% APl610 pump.Pump selection seems simple, but it is not. It is not an easy task to make a good selection. It often requires a lot of practical experience, involving knowledge of pumps, seals and auxiliary systems, high-speed systems, lubrication systems, cooling systems, materials, motors, couplings, electrical appliances, instruments, process flows, etc. Sometimes it is necessary for design units, pump manufacturers and users to discuss, exchange and negotiate together to determine the final selection plan for the pump.
