Centrifugal chemical pumps: types, applications and types

2024 Author: Howard Calhoun | [email protected]. Last modified: 2023-12-17 10:16

Chemical centrifugal pumps are designed to handle liquid chemicals. Their design allows pumping even the most aggressive substances, which may contain explosive or toxic components. There are many types of centrifugal units, but the hermetic device has become the most popular in the chemical industry.

Instrument description

Chemical sealed type centrifugal pumps are designed to avoid the slightest leakage of liquid during pumping, as well as to avoid the leakage of possible vapors. This is very important, since some substances, once in the air, can react with it and thereby form an explosive mixture. If we talk about the general division of pumping equipment, then it is classified according to such criteria as:

• design features;
• purposes of use;
• type of circulating fluid;
• technical parameters;
• type of material from which the flow parts are made;
• difference in methodsinsulation;
• device power;
• pump cooling method;
• options and seal material.

General description of chemical aggregates

It is worth saying that there is a wide variety of this type of equipment. All of them differ from each other by the type of substance with which they can work, technical parameters, structural elements, as well as the type of immersion. However, they are all united in one category by the fact that they are operated in tandem with liquids that are very different from water in their composition. The main difference, of course, lies in the chemical composition, as well as in varying degrees of aggressiveness of this substance. In addition, it is worth adding here that a wide variety of classifications and designs of centrifugal pumps makes it possible to use them also for working with neutral media that are pumped with increased pressure, with a discharge pressure, with different temperatures. To date, such devices are actively used to move the following substances:

• caustic compounds;
• liquefied gas and substances containing gas;
• alkaline and acid solutions;
• petroleum products and miscellaneous solvents;
• suspensions and liquids with high viscosity;
• mixtures and solutions containing abrasives, fibers and solids.

Varieties of the device

So there is a wide variety of pumps. To choose the rightthem under the type of liquid and other parameters, there is a special marking.

The category of devices marked with X includes centrifugal chemical pumps with sealed type magnetic coupling. Their main difference lies precisely in the presence of a coupling. In other words, the principle of operation is based not on the mechanical interaction of parts, but on magnetic fields. This group also includes equipment options such as horizontal, vertical, submersible, semi-submersible, etc. This category is considered the most common, and is used for the distillation of either neutral or aggressive substances.

The next group is marked as AX, AXO. Such pumps are intended for the distillation of liquids with abrasive inclusions up to 1 mm. The density of the substance must also not exceed 1850 kg/m3.

There is a small group of XO brand pumps that are designed to work with chemical compounds whose temperature is not lower than 0 degrees Celsius.

More developed group X and XE. They can pump liquids with temperatures from -40 to +120 degrees Celsius. Most often, in order to ensure an uninterrupted supply of a substance, a chemical centrifugal pump of a sealed type X 50-32-150 is used. It can be used to transport substances that have large diameter abrasive inclusions.

There is a separate group of pumps, which is marked as CH. This equipment is vertical, explosion-proof and used for pumping acid, and is also suitable for working with more than 500 kinds of different corrosive environments. It's also chemicalcentrifugal pumps of sealed type, but with a different design, unlike X and XE.

The last group to highlight is the CCM. This includes centrifugal sealless, used for the distillation of substances with a density of up to 1400 kg/m³, temperatures from 0 to +80 degrees Celsius and a suspended particle concentration of not more than 1.25 mg/cm ^3.

Varieties of hydraulic equipment

Centrifugal pumps and units based on them may differ not only in their own design, but also in the physical and chemical properties of the liquids they are intended to pump. There are the following types of such devices:

1. The horizontal pump is one of the fairly common and standard pumps. It is made of a variety of insulating material and has a high level of performance.
2. Vertical centrifugal chemical pumps are stationary equipment used with tanks that store hazardous substances. In order to ensure high performance, it is necessary to maintain sufficient head for pumping. For this reason, almost all appliances are equipped with electric motors.
3. There is a small group of machines that remove vapors or gases from a closed system to create a vacuum. Such devices are called vacuum self-priming pumps.
4. The cantilever centrifugal chemical pump has such a structural difference as a rigid or flexible coupling. It is applied forpumping oil, as well as for other liquids whose temperature does not exceed 400 degrees Celsius.
5. The membrane type of installation is the most suitable if the liquid substance includes mechanical particles.
6. A fairly common category are circulation mechanisms, the main task of which is pumping liquid in a closed circuit.

As you can see, today there is a wide variety of centrifugal chemical pumps by type and application.

Features. Assembly Materials

The classification of centrifugal pumps is extensive, but they all have a common design feature - the presence of a sealing system or couplings to create maximum impermeability and tightness. In the manufacture of centrifugal pumps, only high-quality materials are used that are able to withstand wear for a long time, and hence the failure of equipment that belongs to the technological chain. The greatest attention in this case is usually given to such parts of a centrifugal pump for chemical liquids as the wet end and working elements, which will be in direct contact with the corrosive medium.

Very seldom is a wet end made of a material such as gray cast iron. As practice shows, this material has poor resistance to aggressive environments, which causes rapid destruction of the material. In addition, such a material cannot maintain high pressure during operation. Principlework, the device of a centrifugal pump is one of the fairly simple, but it is important to choose the right construction material. The flow part is best made from the following materials:

• silicon or chromium cast iron of the high alloy group;
• titanium-based alloys;
• chromium-nickel type steel with additions of molybdenum or copper;
• PTFE or propylene.

What appliances are made of

It is worth starting the description with metal alloys, as they are used quite often. It is important to note here that nickel alloys have better properties than ordinary stainless steel. The difference lies in a more extensive operating temperature range, in higher chemical resistance, which is a key parameter. However, the cost of alloys based on this inclusion does not allow the manufacture of complete pumps.

As for material such as polypropylene, it also has good resistance to chemical environment, it is easy to process, and its price is much lower. The practicality of this material is highly valued, which allows you to confidently displace metal materials. However, a significant disadvantage of polypropylene is that it cannot be operated at low temperatures, as well as at rates above +80 degrees Celsius. In addition, it has the property of accumulating static electricity. Because of this, it is very dangerous when used in explosive industrial plants.

Next gofluoroplasts. This material is considered to be of higher quality than polypropylene. Its resistance to chemical attack in aggressive environments is at a higher level, and it is also capable of operating in a larger temperature range. If it is a PVDF type fluoroplastic, then the range will be from -30 to +100 degrees Celsius. And if you use Teflon (PTFE), then the range will expand even more, from -60 to +260 degrees Celsius. However, it should be added that in practice these figures are usually somewhat lower than in theory.

Further, you should pay attention to the fact that the quality is determined not only by the material from which the pump is made, but also by the type of seal used in its design. There are two types - these are mechanical or stuffing box seals. The only exceptions are horizontal units, in which magnetic couplings play the role of a seal. The tightness of the unit is important not only because a leak is dangerous to human he alth and can also be explosive, but also because the mixtures themselves are expensive, and complete tightness will help to accurately determine the flow of the pumped medium. As for stuffing box seals, now they are practically not used, while end seals cannot provide one hundred percent tightness. Magnetic couplings are very demanding on alignment, although the motor itself can be easily replaced with another one. To date, all sealed units are produced with sleeved engines, which ensures complete tightness.

Main work items

Any type of centrifugal pump, both chemical and any other, is an impeller with blades mounted on a shaft, as well as a casing with a flow part. In addition, the design includes various valves, pipes, pressure gauges and other parts. The classic version of the unit is horizontal, when the working position of the shaft corresponds to the horizon line.

The principle of operation of a centrifugal pump

The pumped liquid enters the body through the suction pipe, and then immediately enters the center of the rotating wheel. Here, centrifugal forces act on it, due to which the liquid will be thrown onto the walls of the housing or the walls of the flow path. After that, it will slowly move out towards the pressure pipeline. During the operation of the pump, areas appear inside it where high and discharged pressure acts. It is because of this that part of the liquid medium will be thrown out, and the other part will occupy the vacated space.

In order to build up and discharge pressure, the device has convex blades. When installing the wheel in the pump, it is important to ensure that each vane is positioned in such a way that when the wheel rotates, the concave part is on the opposite side of the direction of movement. It is worth noting here that equipment of this type is not designed to work "dry". The housing must always be filled with some kind of liquid. The presence of water is optional only for self-priming pumps. It should be noted that the designThe operation of centrifugal pumps for water is almost the same for the same devices, but with aggressive media instead of water. The only significant difference between them is that different materials are used for the manufacture of the body or the flow part. This statement also applies to all other surfaces that may come into contact with aggressive media during operation.

Positive and negative qualities of equipment

It should be said right away that the number of advantages is greater than the disadvantages, which ensured the wide distribution of such devices. And since the design of a centrifugal pump for water is almost the same as a pump for chemicals, this statement will also be true for them.

Among the pluses, the following qualities stand out:

• easy adjustment;
• relatively inexpensive equipment;
• easy to operate;
• compact;
• reliability and economy;
• due to the low weight and dimensions, they do not require pouring the foundation.

The equipment itself runs quite smoothly, which protects it from water hammer. As for the maintenance of such units, most often it is only the replacement of sealing elements or bearings. Such devices are capable of pumping liquids containing solids up to 2 mm in diameter, and their total mass of the entire flow should not exceed 15%. If the environment is characterized by worse indicators, then slurry pumps will have to be operated.

Here it is worth mentioning the adjustmentpump power. It is quite simple, which is a plus, but there is one component that is controversial. If you reduce the number of revolutions of pumping equipment, then the pressure power will also decrease, which, on the one hand, is also considered a positive quality. However, there are situations when you need to leave the number of revolutions the same, but at the same time increase the power of the pressure. The centrifugal pump copes with this task rather poorly, unlike, for example, volumetric devices.

Additional accessories and group markings

Note that canned pumps can be fitted with special accessories if required. These include the following elements:

• Inducers. This is a part that allows you to reduce the cavitation index, which will allow you to operate a low-power pump at high speed.
• Impellers. Additional elements that prevent leakage of fluid through the stuffing box.
• Heat-resistant jackets used to heat or cool the appliance.
• Additional special motor insulation.
• Integrated heat exchangers and additional flanged valves.
• Detached terminal box.

There is also a small marking of pump groups according to their application. The letter "P" denotes vertical submersible pumps, to which the KhP and AHPO categories belong. The letter "G" means the hermetic category of devices, "R" are reversible devices, for example, category XP. The last large group is marked with the letter"BUT". It means that the pump can be used for pumping liquids with abrasive inclusions.

The price of a centrifugal chemical pump starts from 5,000 rubles and can exceed 600,000 rubles.