Chemical pump correct selection should pay attention to those
Petroleum and chemical industry in the national economy occupy a very important position, the chemical process pump is the key equipment is also more and more get the attention of people, how to choose the right chemical pump models is the user's attention is heavy. Because the chemical characteristics of the medium perplexing, together with user requirements continue to increase, as the manufacturer, how to choose, should which aspect to pay attention to? Is very important. This article from the chemical pump selection, transmission medium, the sealing problem of three big aspects to make a summary. The conveying medium and medium type and medium viscosity two aspects, in the hope that customers in the chemical pump selection can help.
The following chemical pump common problems and gives some selection methods: corrosion problem all the time since, chemical equipment corrosion is most headache problem, has slightly carelessly, light damage to the device, it caused heavy accident and disaster. According to relevant statistics, chemical equipment damage is approximately 60% due to corrosion, in the chemical pump selection should first pay attention to material science. There is usually a kind of misunderstanding, think of stainless steel is" universal", no matter what the medium and environment conditions are held out of stainless steel, which is very dangerous. Because medium on chemical pump material requirements, a lot of corrosion-resistant chemical pumps, corrosion resistant stainless steel centrifugal pump are done on material corrosion resistance.
Chemical pump correct selection should pay attention to the three aspects:
One, material elements
1 organic acid acetic acid it is the most corrosive substances, ordinary steel in all the concentration and temperature of the acetic acid will be serious corrosion, stainless steel is an excellent resistance to acetic acid materials, molybdenum stainless steel chemical pump can be applied to high temperature and dilute acetic acid vapor. For the high temperature and high concentration of acetic acid or contain other corrosive media such stringent requirements, can use of high alloy stainless steel chemical pump or fluorine plastic pump.
2 alkali ( NaOH ) steel is widely used in 80 DEG C, 30% within the concentration of sodium hydroxide solution, there are many factories in the 100 C, 75% still used the ordinary steel, although the increase of corrosion, but the economy is good. Ordinary stainless steel on the corrosion resistance of cast iron caustic and there was no obvious advantages, as long as the medium to allow a small amount of iron incorporation does not recommend using stainless steel. Lye for the use of high-temperature titanium and titanium alloy or high alloy stainless steel. The company generally cast iron chemical pumps can be used for low concentration of alkali at room temperature, special requirements can be all kinds of stainless steel pumps or fluorine plastic pump.
3 ammonia (ammonium hydroxide ) the majority of metals and non-metallic liquid ammonia and ammonia (ammonium hydroxide ) in the corrosion is very slight, only copper and copper alloy unfit for use. Most of the company's products for the transportation of ammonia and ammonia.
4 brine (salt water) ordinary steel in sodium chloride solution and sea water, salt water corrosion rate is not too high, generally to be used to protect paint; all kinds of stainless steel also has a very low uniform corrosion rate, but may be caused by localized chloride corrosion, usually made of 316 stainless steel is better.
5 alcohols, ketones, esters, ethers common alcohol medium with methanol, ethanol, ethylene glycol, isopropanol, acetone, methyl ethyl ketone ketone medium, medium has a variety of methyl ester, ethyl ester, ether, ethyl ether, medium having ether ether, they basically has no corrosion, materials can be applied, specific selection should be based on dielectric property and related requirements to make a reasonable choice. Also of note is a ketone, ester, ether on a variety of rubber is dissolved, the seal material selection to avoid making mistakes. There are many other media can not in this one one introduction,
6 sulphuric acid as the strong corrosive medium, sulfuric acid is very extensive use of important industrial raw materials. Different concentration and temperature of sulfuric acid on corrosion difference is bigger, the concentration of more than 80% in the temperature less than 80 DEG C, concentrated sulfuric acid, carbon steel and cast iron has better corrosion resistance, but it is not suitable for high-speed flow of sulfuric acid, not suitable for a valve materials; ordinary stainless steel such as 304 ( 0Cr18Ni9 ), 316 ( 0Cr18Ni12Mo2Ti ) on sulphuric acid medium are also of limited use. So the transport of sulfuric acid chemical pump usually high silicon cast iron ( casting and processing is very difficult ), high alloy stainless steel ( alloy No. 20 ) manufacturing. Fluorine plastic has good resistance to sulfuric acid properties, using fluorine pump ( F46 ) is a more economical choice. Applicable to products: IHF fluorine pump, corrosion-resistant centrifugal pumps, fluorine plastic magnetic pump.
7 of most metal materials are not hydrochloric acid ( including stainless steel), molybdenum containing high silicon iron also can only be used for 50 degrees, 30% hydrochloric acid. Metal material and instead, the vast majority of non-metallic materials for hydrochloric acid has good corrosion resistance, so the rubber lined pump and plastic pump ( such as polypropylene, fluorine plastic ) is the best choice for transporting hydrochloric acid. Applicable to products: IHF fluorine pump, corrosion-resistant centrifugal pumps, magnetic pumps ( CQ polypropylene or fluorine plastic magnetic pump ).
The 8 most general metal nitrate in nitric acid was rapidly corrosion, stainless steel is the most widely used material for room temperature resistant nitrate, all concentrations of nitric acid has good corrosion resistance, it is worth mentioning that molybdenum stainless steel (316, 316L ) on nitric acid corrosion resistance is superior to the common stainless steel ( such as 304, 321), sometimes even better. As for high-temperature nitric acid, usually the use of titanium and titanium alloy material. The company products are: chemical pumps, shielding pumps, corrosion-resistant centrifugal pumps, self-priming pump, chemical pump, magnetic pump, IH.
Two, medium problem
1, the temperature of the medium
We all know that in pump selection in the conveying medium just how important this. First from the transmission medium temperature. High temperature medium conveying of chemical pump structure, materials and auxiliary system put forward higher requirements, the following talk about different temperature variation of cooling requirements and the company for pump type:
1). For temperatures below 120 degrees C. medium, usually do not set special cooling system, the lubricating and cooling medium to itself. Like DFL ( W ) H chemical pump, DFL (W ) PH shielding chemical pump ( over 90 degrees C shielding motor protection grade should be used in class H); and DFCZ and IH chemical pump adopts the suspension structure can make the temperature reached 140 degrees to 160 degrees; IHF fluorine chemical pump maximum use the temperature can reach 200 DEG c;
2). For more than 120 DEG C, 300 C within the medium, in general chemical pump pump cover shall be provid, ed with a cooling chamber, a sealed chamber should also be connected to the cooling liquid ( must be equipped with double mechanical seal ), while not allowing the coolant into the medium, the medium itself should be taken after cooling access ( via simple heat exchangers to achieve ).
3). For more than 300 DEG C high temperature medium, not only the pump head needs to be cooled, suspension bearing chamber can also be provided with cooling systems, chemical pump center supporting structure is generally form, preferably using a metal bellows mechanical seal type, but the price is high ( the price of an ordinary mechanical seal 10 times ).
The viscosity of the medium of the chemical pump performance influence is very large, when the viscosity increase, chemical pump lift curve, the best working head and flow were decreased, while the power increases, thus reducing efficiency. On the general parameters of samples of water are delivery performance, when the transportation of viscous medium should be converted into ( different viscosity correction factor can be found in the relevant conversion chart ). The higher viscosity of the paste, paste and the delivery of viscous fluid, and suggested the use of screw pump, the pump G type screw pump which is the biggest characteristic of medium strong adaptability, smooth flow, pressure pulsation is small, since the energy absorption of honesty, it is any type of pump can not be substituted by.
In three, the sealing problem
No leakage is always the pursuit of chemical equipment, it is such a demand has led to shield pump magnetic pump and expanding the application. However it is truly no leakage is still a long way to go, such as the insulation shell of magnet pump and shielding pump life issue, pitting corrosion, material problem in static sealing reliability problems. Now in a chemical pump seal with respect to some basic situations are introduced briefly as follows:
The 1 seal
For the static seal, usually in a chemical pump only sealing gasket and the sealing ring two kinds of forms, and the sealing ring and O ring is the most widely used; for dynamic sealing, chemical pump is rarely used for packing seal, mechanical seal mechanical seal to give priority to, and single side and double face, balanced and unbalanced cent, balance type suitable for high pressure sealing medium (usually a pressure greater than 1.0MPa ), a double end mechanical seal for high temperature, easy to crystallize, viscosity, containing particles as well as the toxic volatile medium, a double end mechanical seal to seal cavity implantation isolation fluid, the pressure is generally higher than the medium pressure is 0.07 ~ 0.1MPa.
The 2 sealing material
Chemical pump static sealing material in general use of fluorine rubber, using special circumstances-tetrafluoroethane; mechanical seal ring is more critical of the material configuration, and not on the hard alloy of cemented carbide, high prices are on the one hand, there is no hardness difference is unreasonable, so the best choice according to the medium characteristic of the chemical pump sealing material.