Heat exchanger is the rational use and conservation of energy, develop new energy sources key equipment. With the new technologies, new processes, new materials, applications, plate heat exchangers with small footprint, low investment and high efficiency heat exchanger, and gradually replacing the shell and tube heat exchanger. However, plate heat exchanger flow cross-sectional area is small, after fouling prone to obstruction, is a plate heat exchanger heat exchanger efficiency and reducing the main reason.
    Analysis of a scaling
    1.1, ionic or molecular state of dissolved impurities in water
    a. Calcium categories: the main components in the water are Ca (HCO3) 2, CaCl2, CaSO4, CaSiO3 so. Calcium is the result of the major components of heat exchanger fouling.
    b. Magnesium: The main components in the water are Mg (HCO3) 2, MgCl2, MgSO4 and so on. Magnesium dissolved in water after the heat generated after the decomposition of Mg (OH) 2 precipitation, sludge or scale composition.
    c. Sodium: The main composition of NaCl, Na2SO4, NaH-CO3 and so on. NaCl does not generate the scale, but there is free oxygen in the water exists, will accelerate the corrosion of metal wall; Na2SO4 high levels of salt will affect the safe operation; of NaHCO3 in water temperature and pressure will break down under the action of a NaCO3, NaOH, CO2 , so that metal grains damaged.
    1.2 to the existence of impurities in colloidal state of
    a. Iron compounds: The main ingredient is Fe2O3, it will generate iron fouling.
    b. Microbiology: Because the circulating water temperature, dissolved oxygen and other microorganisms in favor of breeding conditions for microorganisms to thrive. Circulating water temperature is high, such as phosphate in water and pharmaceutical dosing is precisely microbial nutrients, microbial breeding not only obstruction plate channels, sometimes blocked pipes, but also to metal corrosion.
    c. Sludge: cooling circulating water sludge, dust from the air and supplemental water, suspended solids, and gradually deposited in the lower flow heat exchanger.
    d. Viscous scale: mainly micro-organisms in water discharge and sediment, corrosion products, bacteria algae debris bond formed, often attached to the wall on the heat exchanger.
    Two plate heat exchanger fouling cleaning method
    2.1 The choice of cleaning agent
    The choice of cleaning agents are being used for the pickling, which includes organic acids and inorganic acids. Organic acids are: oxalic acid, formic acid and so on. Inorganic acids are: hydrochloric acid, nitric acid and so on.
    Heat exchangers made of nickel-titanium alloy, the use of hydrochloric acid as a cleaning fluid. Easy to produce a strong corrosion of the plate, shortening the service life of heat exchanger. Multi-use of the nitric acid. Nitric acid wash can be used in corrosion inhibitor 0.2% ~ 0.3% of the Wu Luotuo flat, adding 0.15% to 0.2% of aniline and 0.05% ~ 0.1% of the sulfur fluoride acid ammonium. The nitric acid wash and rinse the equipment after the air can be self-passivation.
    Discovered through trial and error, choose the best effect of formic acid as a cleaning fluid. In the acid cleaning solution by adding buffer and surface-active agent, cleaning better and reduces the cleaning solution on the plate corrosion. Through the pilot scale studies have shown that the chemical samples and found that formic acid can be an effective way to remove attached to the plate on the scale, while its heat exchanger plate of the corrosive effect is small.
    2.2 The basic principle of scale removal
    2.2.1 Dissolution: acid solution easily and calcium, magnesium, carbonate scale react to produce soluble compounds, so that scale dissolved.
    2.2.2 Peel role: acid solution can dissolve the metal surface oxide, destruction and scale combination. So attached to the surface of metal oxide scale divestiture. And falling down.
    2.2.3 Gas flip effects: acid solution reacts with the carbonate scale, the produce large amounts of CO2, CO2 gas in the overflow process, for insoluble or dissolved slower scale layer has a certain amount of lifting power, so that scale falling down from the heat exchanger surfaces.
    2.2.4 Loose role: As the calcium, magnesium, carbonate and iron oxide dissolved in acid solution, the residual scale will become loose and can easily be washed off the flow of acid solution.
    2.3 cleansing scale of the technological requirements
    2.3.1 Pickling temperature: raising the temperature conducive to raising the descaling pickling effect. If the temperature is too high would aggravate acid lotion on the corrosion of heat exchanger plate, through trial and error found that pickling temperature controlled at 60 ℃ is appropriate.
    The concentration of acid lotion 2.3.2: According to repeated tests conclude that formic acid lotion should be 81.0%, water 17.0%, buffer 1.2%, 0.8% surfactant concentration of the preparation of cleaning with excellent results.
    2.3.3 pickling method and timing of: pickling methods should be based on static and dynamic cycle of soaking a combination of methods. Pickling time for the first static soak 2h, and then dynamic loop 3 ￣ 4h. In the pickling process should always be sampled for testing the concentration of acid pickling, when the two adjacent test concentrations less than 0.2% of the difference, you can view the end of pickling reaction.
     2.3.4 passivation treatment: pickling after the end of the scale plate heat exchanger surfaces and metal oxides are dissolved in the vast majority off, exposing fresh metal, highly corrosive, so pickling, the right words Heat plate for passivation treatment.
     2.4 cleansing scale concrete steps
     2.4.1 Chong Xian: acid washing prior to the heat exchanger open-washing, so that both increase the effect of pickling, but also can reduce the consumption amount of acid pickling.
     2.4.2 pour cleaning fluid to clean the device, and then into the heat exchanger.
     2.4.3 Acid: The acid solution to fill the heat exchanger a static soak 2h. Then continuous dynamic cycle of 3 ~ 4h. 0.5h carried out during every alternate positive and negative cleaning. After pickling, acid cleaning solution should be diluted and in the rear out.
     2.4.4 Alkali Cleaning: After pickling, with NaOH, Na3PO4, softened water according to a certain percentage of preparation is good, dynamic way loop heat exchanger caustic washing, to acid-base neutralization, so that heat exchangers plate is no longer corrosive.
      2.4.5 Washing: caustic washing after using a clean soft water. Repeated washing of the heat exchanger 0.5h, the heat exchanger inside the residue thoroughly washed clean.
      3 to prevent the plate heat exchanger fouling measures for
      3.1 running strictly quality pass, the need for the system of water and cans of soft water softening strict water quality testing, qualified only after injection pipe network.
      3.2 The new system put into operation, the heat exchanger and heating systems should be separated for a period of time cycles, and then the system heat exchanger and the people in order to avoid impurities into the pipe network in the heat exchanger.