Chemical centrifugal pumps are designed to work with liquid chemicals. Their design allows you to pump even the most aggressive substances, which may include explosive or toxic components. There are many types of centrifugal units, but the most popular in the chemical industry has become a sealed device.
Product Description
Hermetic chemical centrifugal pumps are designed to avoid the smallest fluid leakage during pumping, and also to avoid 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 separation of pumping equipment, then it is classified according to such signs as:
- design features;
- purpose of use;
- type of circulating fluid;
- technical specifications;
- type of material from which the flow parts are made;
- difference in isolation methods;
- device power;
- pump cooling method;
- options and material for sealing.
General description of chemical aggregates
It is worth saying that there is a wide variety of this type of equipment. All of them differ among themselves 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 conjunction with liquids that are very different from water in composition. The main difference, of course, is the chemical composition, as well as the varying degrees of aggressiveness of this substance. In addition, it is worth adding here that a wide variety of classification and design of centrifugal pumps allows them to be used also for working with neutral media that are pumped with high pressure, with vacuum pressure, with different temperatures. To date, such devices are actively used to move the following substances:
- caustic compounds;
- liquefied gas and gas containing substances;
- alkaline and acid solutions;
- petroleum products and various solvents;
- suspensions and liquids having a high viscosity;
- mixtures and solutions containing abrasives, fibers and solids.
Types of instrument
So there is a wide variety of pumps. To correctly select them for the type of liquid and for other parameters, there is a special marking.
The device category marked X includes centrifugal chemical pumps with a magnetic coupling of a sealed type. Their main difference is precisely in the presence of a coupling. In other words, the principle of operation is not based on the mechanical interaction of parts, but on magnetic fields. Also in this group are equipment options such as horizontal, vertical, submersible, semi-submersible, etc. This category is considered the most common, and is used for distillation of either neutral or aggressive substances.
The next group is labeled as AX, AXO. Such pumps are intended for distillation of liquids with abrasive inclusions up to 1 mm. The density of the substance should also not exceed 1850 kg / m 3 .
There is a small group of pumps of the XO brand, which 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, 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 abrasive inclusions of large diameter.
There is a separate group of pumps, which is labeled as CG. This equipment is vertical, explosion-proof and is used for pumping acid, and is also suitable for working with more than 500 types of different aggressive environments. It is also a chemical centrifugal pump of a sealed type, but with a different design, unlike X and XE.
The last group worth highlighting is HCM. This includes centrifugal sealless, used for the distillation of substances with a density of up to 1400 kg / m 3 , a temperature of 0 to +80 degrees Celsius and a concentration of suspended particles of not more than 1.25 mg / cm 3 .
Varieties of hydraulic equipment
Centrifugal pumps and units based on them can differ not only in their own design, but also in the physicochemical properties of the fluids for which they are intended to be pumped. The following types of devices are available:
- A horizontal pump is one of the fairly common and standard. It is made of a variety of insulating material, and also has a high level of performance.
- Vertical centrifugal chemical pumps are stationary equipment used with tanks in which hazardous substances are stored. In order to ensure high productivity, it is necessary to maintain sufficient head for pumping. For this reason, almost all appliances are equipped with electric motors.
- There is a small group of apparatus that removes vapors or gases from a closed system to create a vacuum. Such devices are called self-priming vacuum pumps.
- The cantilever centrifugal chemical pump has such a structural difference as a rigid or elastic coupling. It is used for pumping oil, as well as for other liquids whose temperature does not exceed 400 degrees Celsius.
- The membrane type of installations is most suitable if the liquid substance includes mechanical particles.
- A rather common category are circulating 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 Materials for assembly
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 tightness and tightness. In the manufacture of centrifugal pumps, only high-quality materials are used that are able to withstand wear and tear, and hence the failure of equipment that belongs to the process chain. In this case, the most attention is usually paid to such parts of a centrifugal pump for chemical liquids, such as the flow part and working elements, which will be in direct contact with the aggressive medium.
Very rarely, the flow part is made of a material such as gray cast iron. As practice shows, this material has poor resistance to aggressive environments, due to which there is a rapid destruction of the material. Moreover, such a material cannot maintain high pressure during operation. The principle of operation, the device of a centrifugal pump are some of the fairly simple, but it is important here to choose the right structural material. The flow part is best made from the following materials:
- siliceous or chromium cast iron of a highly alloyed group;
- titanium based alloys;
- chromium-nickel steel with additives from molybdenum or copper;
- PTFE or propylene.
Why are the devices made
The description begins 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 wider operating temperature regime, in higher chemical resistance, which is a key parameter. However, the cost of alloys based on this inclusion does not allow the manufacture of whole pumps.
As for a material such as polypropylene, it also has good resistance to the chemical environment, it is easy to process, and its price is much lower. The practicality of this material is highly appreciated, which allows you to confidently displace metallic materials. However, a significant minus 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 ability to accumulate electricity of a static type. Because of this, it is very dangerous when used in explosive industrial enterprises.
Next are the fluoroplastics. This material is considered better than polypropylene. Its resistance to the chemical effects of aggressive media is at a higher level, and it is also able to work in a larger temperature range. If it is a fluoroplastic like PVDF, 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 is worth adding that in practice these indicators are usually somewhat lower than in theory.
Further, it is worth paying attention to the fact that quality is determined not only by the material of which the pump is made, but also by the type of seal used in its design. There are two types - face or stuffing box seals. An exception is only horizontal units in which magnetic couplings play the role of a sealant. The tightness of the unit is important not only because the leak is dangerous to human health, and can also be explosive, but also because the mixtures themselves are expensive, and complete tightness will help to accurately determine the flow rate of the pumped medium. As for stuffing box seals, now they are practically not used, but end-face seals cannot provide one hundred percent tightness. Magnetic couplings are very demanding on alignment, although the motor itself can easily be replaced by another. To date, all sealed units are available with sleeve motors, which ensures complete tightness.
Key Work Elements
Any type of centrifugal pump, whether chemical or any other, is an impeller with blades mounted on a shaft, as well as a housing with a flow part. In addition, the design includes various valves, nozzles, manometers and other details. The classic version of the unit is horizontal, when the working position of the shaft will correspond to the horizon.
The principle of operation of a centrifugal pump
The pumped liquid enters the housing through the suction pipe, and then immediately enters the center of the rotating wheel. Here, centrifugal forces act on it, because of which the liquid will be thrown onto the walls of the housing or the walls of the flow part. After that, it will slowly move towards the pressure pipeline. During the operation of the pump, sections appear inside it where high and low pressure acts. It is because of this that part of the liquid medium will be thrown out, and the other part will occupy the vacant space.
In order to pump and discharge pressure, the device has convex shaped blades. When installing the wheel in the pump, it is important to ensure that each blade is positioned so that when the wheel rotates, the concave part is on the back side of the direction of travel. It is worth noting here that this type of equipment is not designed to work "dry." The housing must always be filled with some kind of liquid. The presence of water is not necessary only for self-priming pumps. It is worth noting that the design, the principle of operation of centrifugal pumps for water is almost no different for the same devices, but with aggressive environments instead of water. The only significant difference between them is that different materials are used to make the case or the flow part. This statement also applies to all other surfaces that may come into contact with an aggressive environment 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 device of a centrifugal pump for water is almost no different from a pump for chemicals, this statement will be true for them.
Among the advantages, the following qualities stand out:
- simple adjustment;
- relatively inexpensive equipment;
- simplicity in operation;
- compactness;
- reliability and profitability;
- due to the light weight and dimensions do not require pouring the foundation.
The equipment itself works quite smoothly, which protects it from water hammer. As for the maintenance of such units, then most often it is only a replacement for sealing elements or bearings. Such devices are capable of pumping liquids in which there are solid inclusions 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 performance, then slurry pumps will have to be operated .
It is worth mentioning here about adjusting the power of the pump. It is quite simple, which is a plus, but there is one component that is controversial. If you reduce the number of revolutions of the pumping equipment, then the pressure head will 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 unchanged, but at the same time increase the pressure head. The centrifugal pump copes with this task quite poorly, unlike, for example, volumetric devices.
Accessories and group marking
It should be noted that hermetic pumps can be equipped with special additional devices if necessary. These include the following elements:
- Indusers. 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 fluid leakage through the gland.
- Heat-resistant shirts used to heat or cool the appliance.
- Additional special engine insulation.
- Integrated heat exchangers and optional flange valves.
- Separate remote terminal box.
There is also a small labeling of the pump groups for their use. The letter "P" designates vertical submersible pumps to which the categories of HP and AHPO belong. The letter "G" means a sealed category of devices, "P" is a reversible device, for example, category XP. The last large group is marked with the letter "A". It means that the pump can be used for pumping liquids with abrasive inclusions.
The price of a centrifugal chemical pump starts at 5,000 rubles and can exceed 600,000 thousand rubles.