The following aspects must be considered in the selection of anticorrosion materials for wet flue gas desulfurization absorption tower and chimney inner cylinder:
(1) meets the anti-corrosion requirements under complex chemical conditions: the chemical environment in the chimney is complex, the acid content in the flue gas is high, and the condensate formed on the surface of the lining is highly corrosive to most building materials, which requires the lining materials to have strong acid corrosion resistance;
(2) Temperature resistance requirements: the flue gas temperature changes greatly, and the flue gas temperature after wet desulfurization is between 40℃ and 80℃. The flue gas temperature in the chimney is between 130℃~ 150℃ when the desulfurization system is overhauled or not in operation and the unit is in operation. It is required that the lining has the ability to resist temperature difference change, does not crack in the environment with frequent temperature changes and is durable.
(3) Good wear resistance: the flue gas contains a lot of dust, and the actual wear may be obvious under the action of corrosive media, so the anticorrosive material is required to have good wear resistance;
(4) It has certain bending performance: due to the high-altitude characteristics of some chimneys, including the earth's own movement, earthquake, wind, etc., the chimneys, especially the high-altitude parts, may be inclined or deviated, and some uncontrollable mechanical effects may occur during the installation and transportation of the chimneys, so the anticorrosive materials are required to have certain bending performance;
(5) Good adhesion: anticorrosive materials must have strong adhesion strength, which not only means high adhesion strength of the material itself, but also means high adhesion strength between the material and the substrate. At the same time, it is required that the material is not easy to crack, delaminate and peel, and has good adhesion and impact strength, thus ensuring good corrosion resistance. Usually, we require the adhesion between primer and steel structure foundation to reach at least 10MPa. Desulfurization slurry circulating pump is a large equipment behind relay heat exchanger and booster fan in desulfurization system. Usually, centrifugal pump is used to pump slurry directly from the bottom of the tower for circulation. It is the pump with the largest flow rate and the harshest use conditions in desulfurization process. Corrosion and wear often lead to its failure. Its characteristics mainly include:
(1) Strong abrasiveness
The slurry at the bottom of desulfurization tower contains a large number of solid particles, mainly fly ash and desulfurization medium particles, and the particle size is generally 0-400 & micro; M, more than 90% is 20 ~ 60 & microm, and the concentration is 5% ~ 28% (mass ratio). These solid particles (especially Al2O3 and SiO2 particles) have strong abrasiveness.
(2) Strong corrosiveness
In a typical limestone (lime)-gypsum desulfurization process, the pH value of the slurry at the bottom of the tower is generally 5 ~ 6, and it can reach 6 ~ 8.5 after adding desulfurizer (the pH value of the slurry in the circulating pump is related to the operating conditions of the desulfurization tower and the adding point of desulfurizer); Cl- can be enriched to more than 80000mg/L, which will produce strong corrosiveness at low pH value.
(3) Cavitation phenomenon
In desulfurization system, the slurry delivered by circulating pump often contains a certain amount of gas. The slurry delivered by centrifugal circulating pump is actually gas-solid-liquid multiphase flow, and the influence of solid phase on pump performance is continuous and uniform, while the influence of gas phase on pump is far more complicated and difficult to predict than that of solid phase. When the liquid conveyed by the pump contains gas, the flow rate, lift and efficiency of the pump all decrease, and the greater the gas content, the faster the efficiency decreases. With the increase of gas content, additional noise and vibration will appear in the pump, which may lead to the damage of pump shaft, bearing and seal. The gas accumulated in the suction port of the pump and the back of the blade will lead to the increase of flow resistance or even cut-off, which will further worsen the working condition. The main reasons for the deterioration of pump working conditions are the increase of cavitation, low gas density, large specific volume, high compressibility, strong rheology, small centrifugal force and poor energy conversion performance. The test shows that when the gas volume ratio in the liquid reaches about 3%, the performance of the pump will suddenly decline, and when the air intake reaches 20% ~ 30%, the pump will be completely cut off. The allowable air content (volume ratio) limit of centrifugal pump is less than 5%.
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