1, the nature of dimethyl ketone oxime
(1) Physical properties
Di Methyl Ketoxime, the English abbreviation DMKO, chemical name is Acetone oxime, molecular formula: (CH3) 2C = N-OH, molecular weight 73.09, density 0.901g / cm3, boiling point 136 ° C, Melting point 61 ° C, flash point 47.2 ° C, PH (25% aqueous solution): 6.6, LD50: 5500mg / kg, the appearance of white prismatic crystals, has a strong reducibility, volatile in the air quickly, neutral The reaction has a solubility in water of 320 g/L (21 ° C), is easily soluble in an organic solvent such as an alcohol, a ketone or an ether, and is easily hydrolyzed in a dilute acid, and has a strong reducibility.
(2) Reducing
Because DMKO has strong reducibility, it is easy to react with oxygen in the feed water, thereby reducing the dissolved oxygen content of the feed water, and the reaction speed is fast and the oxygen removal is complete. The chemical equation for the reaction of DMKO with oxygen is as follows:
4(CH3)2C=N-OH + O2 → 4(CH3)2C= O + 2N2 + 2H2O
2(CH3)2C=N-OH + O2 → 2(CH3)2C= O + N2O + H2O
(3) Effect of decomposition products on water vapor system at high temperature
The decomposition products of DMKO include formic acid, acetic acid and nitrogen oxides. Under the premise of ensuring the oxygen scavenging effect, formic acid, acetic acid, CL-, SO42- None of the tested water vapor samples were detected. At the same time, the NO2- and NO3- contents of some samples were detected and none were detected. Therefore, the use of DMKO for oxygen removal has no good effect on the water vapor system.
(4) Corrosion inhibition and passivation of metals
Due to its strong reducing properties, DMKO can form a good magnetic oxide film on the surface of the steel, which can effectively delay the corrosion of the thermal equipment. The chemical equation for the magnetic oxide film is:
2(CH3)2C=N-OH + 6Fe2O3 → 2(CH3)2C= O + 4Fe3O4 + N2O + H2O
The wet protection of the thermal equipment with the solution containing DMKO can obviously obtain the corrosion inhibition effect, the concentration of the protective agent is 350-400 mg/L (soft water preparation), and the pH is ≥10.5 (ammonia adjustment). In addition, DMKO also has a good passivation effect on metals, and has the advantages of low dosage, non-toxicity, and no pollution.
(5) It can prevent the deposition of oxides such as iron and copper.
DMKO can reduce the iron content of feed water, prevent the boiler from overheating and corrosion damage caused by the formation of iron oxide deposits. At the same time, DMKO has a cleaning effect on the corrosion products of copper deposited in pipelines, economizers, etc. The reason why the copper content of the furnace water will increase significantly in the initial stage of DMKO use.
(6) low toxicity
The toxicity of DMKO is much lower than that of hydrazine. The LD50 is 5500mg/kg, and the toxicity is only 1/20 of hydrazine, which will not cause human injury and environmental pollution.
Article 7.2.2 of the Code for Design of Labor Safety and Industrial Hygiene of Thermal Power Plants (DL 5053-1996) states: The addition of hydrazine vapor is not suitable for domestic use. In 1985, the new US Occupational Protection and Health Care Act. Hydrazine has been officially listed as a dangerous drug, and hydrazine is a suspected carcinogen. It is prohibited to use hydrazine as an auxiliary drug within the occupational scope of citizens' normal life (such as power supply for power plants). According to the operation of domestic power plants, hydrazine is not completely decomposed in steam, and there are residual amounts. Therefore, it is recommended to use a new oxygen scavenger such as dimethyl ketone oxime instead of hydrazine when steam is used for domestic steam.
2. Application in boiler water deoxidation
(1) Water quality
Boiler water only controls two indicators: one is dissolved oxygen <7.0μg / L; the second is PH value 8.5-9.2 (25 ° C). The water supply is deoxidized by heat to reduce the amount of DMKO used in further deoxidation. The residual oxygen remaining in the dehydrated water is only 10-40μg/L. In addition, the temperature of the feed water is raised by thermal deaeration. The activation temperature required for DMKO to remove oxygen can be achieved. Therefore, as long as a small amount of oxygen scavenger is added thereto, the oxygen content of the feed water is reduced to less than 7 μg/L, thereby achieving the feed water quality standard.
(2) DMKO pharmaceutical dosage method
Adding DMKO, the original equipment for adding hydrazine can be used. Without adding any equipment and investment, 0.5kg DMKO is first added to the tank to prepare a solution with a concentration of 0.1% (wt), and then added.
(3) DMKO dosage
The dosage of DMKO can be calculated according to the following formula
Q×(na + ΔA)
G = ────────
10× ε
For example, when the boiler feed water flow rate is 100 m3/h and the dissolved oxygen content is 25 μg/L, the excess amount of DMKO is 20 μg/L, the addition ratio of DMKO is 4.5, and when the purity of DMKO is 99.5%, it is calculated to be added to the water. The amount of DMKO was 13.32 g/h, that is, 133.2 μg/kg, and the amount per month was 8.888 kg. For a 200MW generator set, the DMKO usage is 66kg at full load for one month.
(4) Precautions when adding
First, control the water supply system PH value of 8.5 ~ 9.2, to avoid the pH value of the feed water due to the low ammonia content; second, DMKO should be dissolved evenly when dissolved, to avoid unevenness and affect the oxygen removal effect.
(5) Influence of DMKO on water vapor system
Since DMKO is directly added to the furnace by the water supply system, the iron ions and various anions in the water vapor system of the boiler are analyzed:
System iron ions: During the test, the water vapor of each furnace was analyzed and analyzed, and the content of iron ions was all zero, so DMKO was used to prevent any corrosion of the system metal.
System anion: After analysis, the addition of DMKO and the addition of hydrazine, the content of CL- and SO42- in the water vapor system are all zero.
(6) ease of operation
Adding DMKO saves labor, reduces labor intensity, increases labor intensity, greatly reduces the toxicity of oxygen scavengers, improves the oxygen scavenging effect, and reduces the amount of oxygen scavengers. Save money.
3. Application in shutdown protection
DMKO has a good protective effect on the metal surface, and its effect is better than ammonia and hydrazine, which is suitable for long-term deactivation protection of boilers. In the boiler wet shutdown protection, DMKO first removes dissolved oxygen from the water and then passivates the metal surface to form a magnetic iron oxide protective film for protection.
Process conditions for furnace protection:
(1) Selection of PH value: Research and practice have proved that the pH of the solution should be greater than 10.5. When the pH is less than 10.5, the corrosion of the metal will increase with time, and the pH of the solution is adjusted with ammonia.
(2) Concentration and sealing state: The initial sealing performance of the system is very important. The initial concentration of DMKO is 300-400mg/L, the protection period is not less than 200mg/L, and the PH value is 10.5~10.8. Under stricter conditions, corrosion will not occur. In the case, once the protective film is formed, the metal corrosion can be controlled to be small under unsealed conditions, that is, the post-sealing requirement can be relaxed.
(3) Usage: The pH value of DMKO liquid is adjusted with ammonia water. After mixing well, the prepared protective liquid can be added to the boiler through the metering pump or hydraulic ejector until the economizer, superheater and boiler body are filled with protective liquid. The upper protective fluid balance tank of the steam drum overflows.
(4) The chemical monitoring items during the protection period are DMKO concentration, pH value, dissolved oxygen, Fe, Cu, etc.
Proof of on-site use:
(1) In the first two weeks, the content of Fe and Cu in the feed water increased, and then gradually decreased, and stabilized after 2 months.
(2) If the boiler is deactivated for one year, a good effect can be obtained by using a protective liquid with a DMKO concentration of 300 to 400 mg/L.
(3) The boiler is deactivated for more than half a year, and the DMKO protection is better than hydrazine.
