1. Wet alkali solution method for internal anticorrosion of gas fired central heating boiler
The gas-fired central heating boiler is filled with a certain concentration of lye and the pH value is kept above 10. The specific methods are as follows: remove scale and sediment, ensure that the valves are tight, and install blind plates on the pipeline connected with the operation system. A small lye tank can be installed at the highest position of Gas-fired central heating boiler to ensure the supplement of alkali liquor in case of alkali liquor loss.
The alkali agents used are sodium carbonate, sodium hydroxide, trisodium phosphate or their mixture. Soft water shall be used for preparation, and raw water shall not be used. The dosage of sodium carbonate is 20kg per ton of boiler water, 5-6kg of NaOH and 10-12kg of Na3PO4 per ton of boiler water. The lye is sent into the boiler through a special pump until the water comes out from the air valve, and the water pressure in the pot is greater than the atmospheric pressure. The system tightness inspection should be strengthened at the initial stage of protection, and the alkali liquor concentration should be monitored once a month after normal operation. When the concentration of alkali solution is lower than 5% of injected concentration, alkali should be added.
2. Wet hydrazine method for internal anticorrosion of gas fired central heating boiler
此法是在燃气集中供暖锅炉内充满联氨H2N2和氨NH3的混合液。防腐原理是利用联氨具有的强还性去除水中氧，即N2H4 O2→N2 2H2O，使阴极极化。同时又利用氨在水溶液中呈碱性，提高pH值，使金属表面钝化，造成阳极极化，以达到防腐目的。因联氨具有毒性，使用受到限制。
This method is to fill the gas-fired central heating boiler with the mixture of hydrazine H2N2 and ammonia NH3. The anti-corrosion principle is to use the strong reducibility of hydrazine to remove oxygen in water, that is, n2h4o2 → n22h2o, so as to polarize the cathode. At the same time, the use of ammonia in aqueous solution is alkaline, increase the pH value, make the metal surface passivation, resulting in anodic polarization, in order to achieve the purpose of anti-corrosion. The use of hydrazine is limited because of its toxicity.
3. Wet organic corrosion inhibitor method for internal anticorrosion of gas fired central heating boiler
Organic corrosion and scale inhibitor is a water treatment agent with functions of anti-corrosion, scale prevention and scale removal. The main components are polyphosphate, organic phosphate, BTA copper corrosion inhibitor and inorganic base. The preservative mechanism is that the agent can hydrolyze the negative charged polyphosphate anion and positive cation after dissolving in water, and the polyphosphate anion is in the anode area of metal corrosion cell and Fe2 which loses electron In combination, the iron polyphosphate, which is very difficult to dissolve in water, is formed on the metal surface of the anode area to form anodic polarization. The hydrolyzed reagent cations capture electrons in the cathode area of the metal, and become atoms with strong affinity to the metal and are adsorbed on the metal surface of the cathode area, forming cathodic polarization.
As a result of the above factors, metal corrosion was stopped, which played a role in corrosion prevention. The pH value of organic corrosion and scale inhibitor is more than or equal to 13. When the water is treated with 1L agent, the pH value of the water solution can be guaranteed to be more than 10, which can effectively prevent the acid corrosion caused by CO2 gas, and it also plays an anti-corrosion role. When the organic corrosion and scale inhibitor is used as the maintenance agent, the organic phosphorus in the agent can also dissolve some components in the scale and iron scale of the boiler and steam water system, making the hard scale become porous with loose structure. At the same time, it can make the agent penetrate under the scale to form a protective film, which destroys the combination of the metal surface layer and the scale, and causes the scale to fall off
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