Chemical pump selection
All the time, corrosion is one of the most headaches harm of chemical equipments, carelessly, lightness is damage equipment, serious will cause accident and even the disaster. According to the statistics, about 60% of chemical equipment damage is due to corrosion, so when in chemical pump selection, firstly notice material selection of scientificity. Usually we have a kind of error, think stainless steel is "universal material", no matter what media and environmental conditions are carrying out stainless steel, this is very dangerous. Belows are main points for selecting materials in some commonly used chemical media:
1. Sulfuric acid As one of strong corrosive media, sulfuric acid is one of the important industrial raw materials that widely used. Different concentrations and temperatures sulfuric acid corrode material difference is also bigger, to concentration more than 80%, temperature less than 80 ℃ concentrated sulfuric acid, carbon steel and cast iron have good corrosion resistance, but it doesn't suit for high-speed flow sulfuric acid, is uncomfortable for pump<valve materials; Ordinary stainless steel such as 304 ( 0Cr18Ni9), 316 (0Cr18Ni12Mo2Ti) also is limited to sulfuric acid medium. Therefore conveying sulfuric acid pump&valve usually adopts high silicon cast iron (casting and machining difficulty is large), high alloy steel (20# alloy)
manufacturing. Fluorine plastic has good sulfuric acid resistant performance, using fluorine lined pump (F46) is a more economical choice.
2. Hydrochloric acid many metal materials are not hydrochloric acid corrosion resistant (including various stainless steel material), containing molybdenum high ferrosilicon only can be used for 50 ℃, below 30% hydrochloric acid. Opposite to metal materials, most non-metal materials have good corrosion resistance to hydrochloric acid, so lining rubber pump and plastic pump (e.g., polypropylene, fluorine plastic, etc) is the best choice of conveying hydrochloric acid.
3. Nitric acid general metal mostly is quickly corroded and damaged in the nitric acid, stainless steel is the most widely applied nitric acid resistant material, has good corrosion resistance under normal temperature to all concentration nitric acid, mentionable containing molybdenum stainless steel (e.g., 316, 316L) corrosion resistant to nitric acid is not only better than the ordinary stainless steel (such as 304, 321), sometimes even worse. For high temperature nitric acid, usually adopting titanium and titanium alloy material.
4. Acetic acid it is one of the strongest corrosive substance in organic acid, ordinary steel will severely corrosive in all concentration and temperature acetic acid, stainless steel is an excellent acetic acid resistant material, SS316 containing molybdenum, can also be used for high temperature and dilute acetic acid steam. For high temperature and high concentrated acetic acid or containing other corrosive medium etc strict requirements, can choose high alloy stainless steel or fluorine plastic pump.
5. Alkali (sodium hydroxide) steel is widely applied in below 80 ℃, within 30% concentration sodium hydroxide solution, many factories still use ordinary steel in 100 ℃, below 75%,
although corrosion increased, but economical efficiency is good. Ordinary stainless steel corrosion resistance to alkali has no obvious advantage compared with cast iron, as long as the medium allows small amounts of iron mixed, not recommended adopting stainless steel. For high temperature lye more used titanium and titanium alloy or high alloy stainless steel.
6. ammonia (aqua ammonia) most metallic and nonmetallic corrosion is very slight in liquid ammonia, aqua ammonia, only copper and copper alloy is unfavorable used.
7. Brine (sea water) ordinary steel in sodium chloride solution and sea water, salt water erosion rate is not too high, generally should use coating protection; All kinds of stainless steel also have very low uniform corrosion rate, but may be because of chloride ion and cause localised corrosion, usually adopting SS 316 is better.
8. Alcohols, ketone, esters, ethers commonly alcohols medium has methanol, ethanol, glycol, propanol, etc. ketone media are acetone, butyl ketone, ester media are various methyl, ethyl ester etc, ethers media are armour ether, butyl ether, etc., which basically no corrosive, commonly used materials are applicable, when specific choosing, according to media property and related requirement to make reasonable selection. In addition it is worth noting ketone, esters, ether to many kinds of rubber has solubility, when choosing sealing materials, avoid making mistakes.
There are many other media cannot be detail introduced, anyhow when selecting material, must not optional and blind, should look up relevant information or refer to ripe experience.
cooling problem
High temperature medium convey requires higher requirements to pump's structure, material and auxiliary system, the following we talk about different temperature changes on the cooling requirements and company applicable pump type:
1. For temperature below 120 ℃ medium, usually not establish special cooling system, we adopt medium itself to lubricate and cooling. Like DFL (W) H chemical pump, DFL (W) PH shielding chemical pump (when more than 90 ℃, canned motor protection level should adopt H level), while DFCZ ordinary type and IH chemical pump because using suspension structures which makes temperature limit to 140 ℃ ~ 160 ℃; IHF fluorine lined pump highest using temperature can reach 200 ℃; Only CQB common magnetic pump use temperature does not exceed 100 ℃. Well worth mentioning is for easily crystallized or containing particles media should be equipped with sealing flushing pipe (leave interface when designing).
2. For above 120 ℃, within 300 ℃ medium, generally set cooling chamber on the pump cover, sealing chamber should also be connected to cooling fluid (must match double end mechanical seals), when not allow cooling fluid infiltrates mediums, should adopt after cooling medium itself and access (can be realized through the simple heat exchangers).
3. To more than 300 ℃ high temperature medium, not only pump head required cooling, suspension bearing room also should have the cooling system, pump structure is commonly center supporting form, mechanical seal is better to use metal bellows type, but the price is high (price is 10 times of ordinary mechical sealing).
sealing problem
No leakage is chemical equipment pursuit forever, this request contributed to magnetic pump and shielding pump application expanding. Yet truly without leakage still has a long way to go, such as magnetic pump isolation and shielding pump shielding sleeve service life problem, material pitting corrosion problems, static sealing reliability problem, etc. Now make a simple introduction of basic situation of sealing aspects as follows:
1. Sealing form To static sealing, usually only has sealing gasket and sealing ring two forms, while sealing ring mostly as o-rings wide application, to dynamic seals, chemical pump rarely uses packing seal, mechanical seal is given priority, mechanical seal has single end and double end, balanced type and non-equilibrium type, balanced type is applicable to high pressure
medium sealing (usually refers to the pressure higher than 1.0 MPa), double end mechanical sealing is mainly used for high temperature, easy crystallization, high viscosity, including particle and toxic volatile medium, double end mechanical sealing should inject isolated liquid to sealing chamber, its pressure generally higher than the liquid medium pressure of 0.07 ~ 0.1 MPa.
2. Sealing material chemical pump static sealing materials general use fluororubber, special circumstance adopts PTFE; Mechanical seal dynamic and static ring material configuration is the key, not carbide on cemented carbide is the best, high price is one hand, it is not reasonable if there is no hardness difference, so best according to medium characteristics tomake a difference.
Viscosity problem
Medium viscosity has a great influence to pump's performance, when the viscosity increases, pump head curve declines, the best conditions head and flow also decreases, while power is subsequently rising, so efficiency reduced. Generally parameters on samples are conveying water performance, when conveying adhesive medium should undertake conversion (different viscosity modified coefficients can consult relevant conversion chart). For high viscosity pulp, cream and viscous fluid transmission, the proposal is selecting screw pump.
