Carbohydrazide (CHD) , as a derivative of hydrazine, has a strong reducing agent and is widely used in industry. It can be used as an intermediate for the manufacture of energetic materials, and can also be directly used as a component of rockets and propellants, and as a deoxidizer for boiler feed water.
Chemical properties of carbohydrazide
Carbohydrazide is a nearly neutral white crystalline powder that is highly soluble in water. It can be regarded as a derivative of hydrazine and carbon dioxide. The latest method is to react hydrazine with dimethyl carbonate. It is a low-toxic substance with stable chemical properties and is easy to transport and store.
Application of carbohydrazide in power plant chemistry
Boiler feed water deaerator
Deoxygenation is an important part of the boiler feed water treatment process in thermal power plants. Excessive dissolved oxygen in feed water will cause pitting corrosion in the feed water pipeline and economizer in the short term, increase roughness, increase flow resistance, and easily accumulate sediments, accelerating under-scale corrosion. Corrosion products are deposited on the heating surface of the boiler, which not only affects the heat transfer of the heating surface, but also brings the risk of tube burst, seriously affecting the economic and safe operation of the heating surface. Removing dissolved oxygen in feed water is an effective means to inhibit oxygen corrosion. Power plants use a combination of physical degassing and chemical deoxygenation to remove dissolved oxygen in boiler water. As a chemical deoxygenator, hydrazine hydrate is currently the most widely used choice, with high deoxygenation efficiency and high-temperature volatile decomposition in the furnace. However, the oral LD50 of hydrazine hydrate for rats is as high as 57 mg/kg. As a carcinogen, it has been banned in the United States and the European Union and other regions, and it is exposed to heat or encounters gaseous substances during storage and transportation, which is explosive.
Neutral corrosion inhibitor
During the hydraulic pressure test and shutdown protection of boilers in many thermal power plants, hydrazine hydrate is added to reduce the corrosion of equipment. As a neutral strong reducing substance, carbohydrazide also has excellent corrosion inhibition effect. Through comparative tests, it can be seen that carbohydrazide can greatly reduce the Fe2+ concentration in the solution under the same concentration as hydrazine hydrate. The lower the Fe2+ concentration, the better its corrosion inhibition effect. Carbohydrazide is a neutral, safe, and eco-friendly corrosion inhibitor, so it should see more use in building green power plants. Some studies suggest carbohydrazide stops corrosion by sticking to the metal surface and creating a protective film.
Chemical cleaning reducing agent
Currently, EDTA has been widely used in chemical cleaning of power station boilers. During the cleaning process, a large amount of Fe2+ is produced in the solution due to the dissolution of scale. Fe3+ can react with the metal matrix, increasing the corrosion during the cleaning process: 2Fe3++Fe=3Fe2+. In order to reduce Fe3+ to Fe2+ and reduce corrosion, hydrazine hydrate is widely used as a reducing agent in the chemical cleaning process. However, the toxicity and carcinogenicity of hydrazine hydrate bring great safety risks to operators, and the residue in the waste liquid after cleaning also brings great environmental risks. Carbohydrazide derived from hydrazine hydrate has become a good substitute because of its stable chemical properties and low toxicity.
Conclusion
Carbohydrazide, as a new chemical product derived from hydrazine hydrate, has been widely used in various fields such as the defense industry. At present, its application as a reducing agent and corrosion inhibitor in thermal power plants has not been promoted, but its stable chemical properties and low toxicity have obvious advantages over hydrazine hydrate commonly used in power plant chemistry.
