Wet desulfurization sewage conveying equipment must be able to withstand some erosion and corrosion. This article describes how the company through the special material selection, so NEMO NEMO? Pump (single screw pump) in the power plant desulfurization wastewater transfer to be successfully used to the peer Recommend a new desulfurization sewage transport equipment. China is a big coal-fired power country. Its energy production and consumption are dominated by coal. The proportion of coal in China's energy consumption remains at around 70%, a rate that is hard to change in the short term. 80% of coal consumption is for combustion, and coal combustion is also the main source of SO2, nitrogen oxides and soot in the atmospheric environment. SO2 and soot emission caused by coal combustion can account for 80% -90% of the total emission. China's SO2 emissions have exceeded 20 million tons for many years in a row and have become the largest SO2 emission country in the world. The 11th Five-Year Plan clearly sets forth two hard targets for environmental protection: 1) a 20% reduction in energy consumption per unit of GDP; and 2) a 10% reduction in SO2 emissions from 2005 levels. In order to meet the policy requirements, many thermal power plants have adopted some measures in succession to reduce the direct emission of SO2. Many of these large-scale thermal power plants use the more mature limestone / gypsum wet FGD process abroad. As far as the desulfurization process itself is concerned, its own characteristics determine that the process is extremely corrosive to both the overcurrent components and the equipment in contact with the electrolyte, in particular carbon steel parts. Carbon steel components in the desulfurization dust easily corroded process is due to acidic electrolytes caused by electrochemical corrosion in humid environments. The other non-metallic materials because of micro-cell electrolyte composition is low, its corrosion resistance better than carbon steel. In order to make the equipment suitable for the desulfurization sewage conveying in the desulfurization process of the power plant, Ni-Chi (Lanzhou) Pump Co., Ltd. has summed up some successful experiences in the manufacture of single-screw pump for desulfurization sewage conveying (NEMO ® pump). Nemo pump material special optimization options ◆ pump parts Naimo pump body parts made of cast iron lined rubber process. Pump components of the NAMO pump generally refer to the pump suction chamber (Figure 1) and the discharge body (Figure 2), Figure 1. Pump suction chamber 1/4 section These two components belong to all parts of the NAMO pump Pressure parts. In limestone wet desulfurization equipment commonly used anti-corrosion wear-resistant materials are: nickel-based corrosion resistant alloy, rubber lining (especially soft rubber lining) and synthetic resin coating (especially glass flake resin lining). For the anti-corrosion treatment of the two parts of the suction chamber and the discharge body, Ni-Chi company usually adopts the method of soft rubber lining. When the metal material as a pressure-bearing parts, it is non-metallic materials as anti-corrosion parts, should take full account of the non-metallic materials and metal bonding strength. At the same time, the design of pressure-bearing components ensures that non-metallic materials can be stably adhered to metal pressure-bearing components over a long period of time. In the use of lined with soft rubber lining process, resistant to the company has a mature process to ensure that are summarized as follows: First HT250 castings of the pump suction chamber and exhaust the inner surface of the cleaning process to remove the inner surface of the casting On the oil, sand, and then use a similar method of rotational molding process butyl rubber can be uniformly lining the workpiece's inner surface. Because there are many micro-pits on the inner surface of the casting, the non-metallic coating material can be deposited into these pits after being softened to form countless micro-necks for good mechanical bonding. In general, there are three types of rubber materials that can be used as linings: butyl rubber, EPDM rubber, and fluoroelastomers, depending on the concentration of chlorine particles in the desulfurized wastewater and the temperature of the desulfurization wastewater. The specific construction process is slightly different. Figure 2. Pump Discharge Body 1/4 Sectional Diagram ◆ Flow Components and Rotors All flow components and rotors are bi-directional stainless steel 1.4462 Spray CrC process. Wet Desulfurization System, the main corrosion of pump equipment Wet desulfurization system within the working environment is very complex: solid, liquid, gas mixed with each other, acid-base blend, alternating hot and cold, the flue gas in the solid and gaseous components, flue gas flow rate , Temperature and slurry pH, F-, Cl- and erosion of sediment and sediment particles and many other influencing factors. General thermal power plant exhaust contains SO2, NOx, HCl, HF and other gases, the absorption tower and the flue gas containing CaCO3, Ca (OH) 2 and other substances in the absorbent fully contact, the pollutants are absorbent in the slurry In order to achieve the separation of flue gas, and therefore the desulfurization washing solution contains H2SO4, HCl, HF and other acid and Cl-, and contains about 15% -20% suspended solids. All of these wash slurries are ultimately delivered through the Naimo pump via the recovery system. Due to the large amount of Cl-, F-, SO32-, and SO42- in the limestone slurry and gypsum slurry in the wastewater and the recycle of the wash water in the desulfurization system, these ions are gradually enriched in the slurry and corrode the metal components serious. In particular, Cl-, which is the main cause of metal pitting, crevice corrosion, stress corrosion and selective corrosion, accelerates the corrosion damage of metal parts in a single screw pump. Experience shows that when the content of Cl- reaches 20000 × 10-6, the stainless steel can not be used any more, but the lining of non-metal material should be used. This is the reason why Nike's desulfurization sewage pump's suction chamber and discharge body should use rubber lined. Normally under normal conditions, single screw pumps deliver sewage under these conditions, with corrosion rates of up to 1.25 mm / a on metal parts and up to 5 mm / a on individual parts. Niu Chi's choice of metal materials In view of the above reasons, Ni-Chi in the choice of single-screw pump over-current components and the rotor, the general use of iron - molybdenum - nickel - chromium stainless steel production. Although from a cost point of view, in the thermal power plant wet flue gas desulfurization system, the selection of anti-corrosion materials should be based on the principle of economic and applicable to meet the requirements of desulfurization process, that is, try to choose a longer life of the metal or Non-metallic materials, metal surfaces may be exposed to corrosive media in different parts should be lined with non-corrosive and wear-resistant non-metallic materials, but when these measures difficult to meet the process requirements, you can only use nickel-based materials Based stainless steel to produce single screw pump flow components and rotors. Ni-Chi companies generally choose the DIN standard, grade 1.4462 duplex stainless steel to produce over-current components and rotors, the main chemical composition of this material is as follows: C ≤ 0.03, Si ≤ 1.00, Mn ≤ 2.00, P ≤ 0.030 , S≤0.020, Cr≤21.00-23.00, Ni≤4.50-6.50, Mo≤2.50-3.50, N≤0.05-0.20. This material is now more recognized in the field of desulfurization, the use of better performance of stainless steel, the past five years we have more than a dozen well-known domestic sewage treatment equipment company for the country more than 10 power plant flue gas desulfurization project provided about 150 units For the delivery of desulfurization sewage Naimo single screw pump, according to the use of on-site feedback, the effect is ideal. International manufacturers of the same industry with the choice of metal anti-corrosion materials, the data show that the United States in the power plant desulfurization wastewater is mainly selected high-nickel-based alloy or carbon steel wrapped high-nickel-based alloy plate, which has superior performance, good temperature resistance, Good corrosion resistance, resistance to medium permeability, and can ensure good construction quality, but its expensive, processing and manufacturing needs special technology and equipment, construction site difficult, not suitable for China's national conditions; Germany and Europe and other countries more The use of FRP and carbon steel lined rubber plates, especially in the desulfurization of sewage conveying equipment, these countries mainly use carbon steel lined rubber process or choose duplex stainless steel. Ni-Chi (Lanzhou) Co., Ltd. as the pump resistance Germany Nimo pump company in China's wholly-owned company, fully using Germany's advanced machining technology and some high-end new technologies to meet the ever-changing market needs. For example, the company's NM series single screw pump, desulfurization wastewater treatment plant in the delivery of anti-corrosion technology, the use of the above-mentioned technology, and the use of the effect is indeed good. At present, our country in the field of equipment used in anti-corrosion materials, mainly metal parts coated or lined with butyl rubber and vinyl ester resin glass flake, these two non-metallic materials with good heat resistance and chemical stability, Construction is simple, cheap, has been used in the country for many years, is commonly used in domestic wet FGD process materials. However, their low abrasion resistance and stress corrosion resistance (vinyl ester resin glass flake), anti-scaling poor, and the construction period is long, the efficiency is low. At the same time, many of the equipment due to its own design and manufacturing characteristics of the decision of the coating or lining process can not be used to meet the design requirements of certain equipment components, in this case, resistance Chi (Lanzhou) Pump Co., Ltd. used to fill the technical The domestic industry equipment manufacturers with a blank product. According to Ni-Chi company's analogy test, as long as the desulfurization sewage chloride ion concentration ≤ 60000 mg / l, the pH of the sewage between 3-6, can be made of duplex stainless steel corrosion parts. If the chloride ion concentration is higher, the corrosion resistance of the metal part is improved by spraying the CrC coating on the surface of the duplex stainless steel part. According to the use of resistant Chi experience, this metal parts suitable for a variety of common acids and chlorine compounds such as the transport of abrasive media. ◆ pump shaft seal pump seal with a special mechanical seal, and with flushing water device. Sewage slurry generally contain 20% -40% of the solid limestone and gypsum, solid particles in the tens of microns to hundreds of microns, while the sewage slurry contains highly corrosive H2SO4, HCl, HF and other strong acidic waste liquid, The pH of the sewage is basically between 4.5-6.5. Because the sewage contains solid particles and other abrasive media, but also contains acidic corrosive media, so select pump body seal, we must carefully select the seal material and seal form. Under normal circumstances, you can choose the most commonly used mechanical seal and packing seal, but the use of these two seal forms have their own advantages and disadvantages, for example, the choice of mechanical seal, without the corresponding flushing device, the use of mechanical seal is relatively poor, repair The cost is too high, and the stoppage processing time caused by it is longer. Meanwhile, the medium in the sewage like Ca (OH) 2 is easy to crystallize or precipitate after being exposed to the CO2 in the air, and adheres between the moving ring and the stationary ring Of the sealing surface, resulting in seal damage and failure. The choice of packing with a simple flushing device seal, if the contact with the filler shaft section hardness and roughness of less than certain requirements, the filler section is often worn out a deep groove
