Refinery pump selection requirements
In recent years, with the increase of new construction and expansion projects of large-scale refineries with annual output of 10 million tons or more and many small and medium-sized refineries in China, the demand for petrochemical pumps is expanding day by day. To meet the new market demand, chemical pump manufacturers are actively improving product design and production technology to expand production capacity. However, there are some technical details to note along the way.
Key points of pump selection for refinery project
1. Main pump types and features
According to different process routes, the main installations of the refinery are atmospheric distillation, vacuum distillation, catalytic cracking, hydrocracking, delayed coking and so on.
According to the above process, refinery of the more important pump is commonly forerunning atmospheric pressure bottom bottom pump, pump, vacuum bottom pump, slurry pump, hydrogenation feed pump, coke water pump (decoking pump), etc., these pumps are mainly transport inflammable, explosive or toxic and other dangerous liquid, some medium temperature as high as 400 ℃ above, some still containing solid particles, so the material has good corrosion resistance, abrasion resistance ability, the pump must also has a high reliability and long-term safe operation.
Pump selection procedure of refinery project
1.1 determination of pump type
In the process of refinery design, most of the required pump types have been specified, such as OH (cantilever type), BB(two-end support type) and VS(vertical suspension type) coded in API610, so it is generally unnecessary to choose pump types.
1.2 flow – head
Flow rate and head are the main basis of selecting pump. The minimum continuous flow rate, normal flow rate and rated flow rate are usually put forward in the requisition. When the pump is selected according to API610 standard, the rated working point of the pump shall be at the right side of the optimal efficiency point (BEP) of the pump, and the normal working point shall be at the optimal efficiency point (BEP), and the actual minimum flow rate of the pump shall not be greater than the required minimum continuous flow rate. The head should be selected according to the rated operating point, that is, the head required in the requisition is the head corresponding to the rated flow point, and there is no margin for the head in the selection.
It is generally required in the enquiry form that the pump should have a flat continuous ascending performance curve, without hump, and the lift from the rated working point to the closing dead point should not rise by more than 20%.
Some engineering companies require that the rated operating point of the pump should be chosen in the best efficiency point of the pump (BEP), and the selection should be satisfied according to different requirements.
1.3 cavitation margin (NPSHr)
NPSHr is an important performance index of the pump, in the inquiry purchase order has specific numerical requirements, and sometimes proposed small continuous flow to rated flow area, npsha-npshr ≥0.8 meters requirements, the purpose is to ensure that the pump in operation does not occur cavitation, in the selection of special attention. Measures to reduce NPSHr, such as reducing the speed, choose the NPSHr impeller with good performance, increase the induction wheel and so on. But on the actual project
In, sometimes the design unit put forward the NPSHr value is very harsh, participate in the bidding several manufacturers can not meet the requirements of NPSHr, at this time should seek things to the design unit to explain, take measures to re-type or adjust the design.
Pump flow components used in refineries are generally made of standard materials, as long as they are selected according to the requirements of the design requisition and the API610 specification. Normal bottom pump, priming pump, reducing bottom pump, feeding pump, coke pump, etc., have no special requirements on material, generally S series or C series can be used in APl610 standard. Special is the oil slurry pump in the catalytic cracking process, which not only meets the requirements of performance, but also needs to solve the problem of wear resistance under high temperature working conditions.
For the pressure pump body of the high-pressure pump, such as the external barrel of the feed pump, the shell material selected must meet the requirements of the temperature – pressure relationship of the pump. Figure 3 shows the temperature – pressure curve of a pump. Domestic design of the pump is often lack of this information, so we should pay special attention. In addition, for shafts of different materials, special attention should be paid to the maximum motor power allowed to be equipped with the shaft. Foreign pumps are generally given the maximum allowable P (kW)/n(r/min) value of shafts of different materials. According to this value, the maximum motor power that can be equipped with each material shaft can be determined.
1.5 sealing and auxiliary system
The sealing and auxiliary system is an important part of the pump, which plays a decisive role in the reliable operation of the pump. Generally, the design institute will not make specific requirements for sealing in the requisition, but requires the pump manufacturer to determine the detailed sealing scheme according to the working conditions. Sealing scheme determination, need to rely on the experience of many places, for complex working conditions, the company’s choice of the scheme may be very different. In order to ensure safety, some companies choose the sealing scheme to have too many functions, and as a result, offer higher prices, which may put them at a disadvantage in commercial bidding. My opinion is to avoid excessive function of shaft sealing system under the premise of ensuring safety and reliability. In addition, the world’s well-known sealing manufacturers, such as BURGMANN company of Germany, the British JOHN CRANE company, for different media conditions of the selection of machine sealing and system, there are many mature experience, when the choice of sealing scheme can fully solicit the opinions of sealing manufacturers, and strive to choose a more reasonable sealing scheme.
1.6 motor, steam turbine and other driving machines
Motor selection is also very important, in the design of the purchase order has often selected the required motor power, voltage, explosion protection, protection level. Therefore, the efficiency of the pump is required, if the pump efficiency is low, the specified motor power may not be enough.
In order to save energy and recycle energy, some pumps are driven by hydraulic turbine or steam turbine. At present, the domestic petrochemical factory of hydraulic turbine was chosen as the pump drive is more, while the use of steam turbine to drive the pump is very few, the main reason is that the current domestic small steam turbine (below 2000 kw) market is basically a blank, and the price is quite expensive imported from abroad, to some extent, affected the small steam turbine pump driven machinery promotion role. But petrochemical companies generally hope to promote the use of small steam turbine in petrochemical companies to replace part of the pump motor, because petrochemical plants generally have their own power plants, there are rich various pressure levels of hot steam resources.
2. Suggestions on data sheets
Each engineering company, patent business (such as UOP- United States universal oil company) generally have the company’s special pump data sheet, pump manufacturer or seller had better use the data sheet provided in the inquiry order. Now each pump manufacturer after obtaining the inquiry purchase order often USES own company’s pump data sheet to make a fresh copy, in addition to the trouble and the content error, when the technical exchange is very inconvenient. Because different company’s pump data sheet format, sequence, content and so on are not completely the same. On the contrary, if the data sheet in the inquiry order is directly used, during the technical review or technical exchange, it will be very intuitive and clear for the design institute to confirm the pump manufacturer’s response to the requirements of the technical inquiry order, so as to facilitate the technical exchange and confirmation of both parties.
3. Standards of API610
API610 is the most authoritative technical standard for design and acceptance of oil refinery pumps, which is widely used in China. Pump designed and manufactured according to API610 specification is usually called API pump. Most of China’s petrochemical design and manufacturing reference to this standard. Large APl pump manufacturers in China have many imported technology products with perfect performance. Therefore, when participating in the project, they can choose the type directly according to the requirements without redesign, but sometimes they need to make some local improvements to meet the needs.
The API610 standard is constantly being revised and improved. It is usually updated every 7-8 years or so, and some contents of different versions may change. Therefore, it should be applied flexibly in the application of APl610 specification, and some non-principled provisions may not be completely copied.
As the pump manufacturer of the refinery project, it is not necessary to pursue the latest version of APl610 too much in the design publicity. Don’t always claim that their products are in full compliance with APl610 standards, so as to avoid the technical exchange or acceptance of their own trouble. In fact, no pump manufacturer can make the so-called 100 percent APl610 pump.
Pump selection seems simple, but it is not. Want to make a good selection, is not an easy thing, often need to be on the basis of a lot of practical experience, involving pump, seal and auxiliary system, high-speed system, lubrication system, cooling system, the material, motor, even the cardo, electrical, instrumentation, process and other aspects of knowledge, sometimes need to design unit, pump manufacturers and users get together to discuss communication consultation, determine the final selection of the pump.