Practice of cleaning complex and insoluble scale with sulfamic acid
Keywords: cooling system; sulfamic acid; chemical cleaning; insoluble scale
The heat exchange system usually works with water as the medium. Because there are many kinds of salts in the water, after a period of operation, the system will scale, which affects the working efficiency of the system. Generally, chemical cleaning is used to remove the scale. Some scales are mixed with multiple components, such as sulfates, silicates, phosphates, etc. The scales composed of these salts are difficult to clean completely with strong acids such as hydrochloric acid and sulfuric acid. Sulfamic acid has a strong ability to dissolve these complex and insoluble scales.
1 The nature of sulfamic acid
Sulfamic acid  English name: sulfamic acid.
1.1 Physical properties
Colorless or white orthorhombic crystals, soluble in water, water solubility: 146.8 g/L (20 ℃), melting point: 205 ℃, good stability at room temperature, decomposes at 260 ℃, industrial product purity is greater than 98%.
1.2 Chemical properties
It can be understood that a hydrogen ion in the sulfuric acid molecule is replaced by an amine group. It is a medium-strong acid with acidic properties. Its salts are easily soluble in water. A 1% aqueous solution has a pH of 1.18 at 25 ℃, a molecular weight of 97.09, and a molecular formula. It is NH2SO3H, which is produced by the reaction of fuming sulfuric acid and urea in industry.
2 The mechanism of sulfamic acid fouling
The scale-dissolving reaction of sulfamic acid is carried out in aqueous solution.
2.1 The chemical reaction of sulfamic acid with weak acid salts and metal oxides
 Most of them are metathesis reactions, which are fast and produce salt and water. CaCO3+NH2SO3H→(NH2SO3)2Ca+H2O+CO2↑Fe2O3+NH2SO3H→(NH2SO3)3Fe+2(NH2SO3)2 Fe+H2O
2.2 Reaction of sulfamic acid with insoluble salt MpRq
It is mainly accomplished by the movement of chemical equilibrium and the greater solubility of sulfamate. MpRq + NH2SO3H→M (NH2SO3) p+ HqR When the concentration of sulfamic acid is large enough, the balance shifts to the right, that is, the insoluble salt MpRq is dissolved, generating sulfamate and the acid HqR corresponding to MpRq. Due to the high solubility of sulfamate, the generated sulfamate is soluble in water, and the scale is gradually dissolved, while MpRq will decompose or dissolve in water. CaP04+NH2SO3H→(NH2SO32Ca+H3P04CaSO4+NH2SO3H→(NH2SO3)2Ca+H2SO4Ca(SiO3)2+ NH2SO3H→(NH2SO3)2Ca+SiO2+ H2O Aminosulfonic acid cleaning insoluble scale engineering practice An oxygen plant cooling system consists of cooling tower and circulation Composed of pumps and pipelines. After a long time of operation, the system fouled more and the cooling efficiency decreased, which affected normal production, so it was decided to clean and descale.
3.1 Analysis of scale components
When the scale sample collected from the cooling system of the oxygen plant was immersed in hydrochloric acid, it was found that 10% hydrochloric acid had no response at 60 ℃. After considering that the scale sample may be composed of complex insoluble salts such as sulfate, silicate, phosphate, etc., qualitative and quantitative analysis of its composition was carried out, and the results confirmed that the scale sample was indeed the case. The content of its ingredients is shown in Table 1.
This kind of scale can't be dissolved with hydrochloric acid or sulfuric acid. I have tried a variety of cleaning media and found that only sulfamic acid and ethylene diamine tetraacetic acid (EDTA) can dissolve scale samples well. Comparing these two cleaning media, the most suitable one is sulfamic acid. Its economic advantages, operating conditions and safety are better than EDTA.
The items include sulfamic acid concentration, temperature, time, corrosion inhibitors and additives. Then, on the basis of the static small-scale test, a dynamic simulation test is performed to simulate the process of pickling, washing, neutralization, passivation and so on.
There is a certain technical difficulty in cleaning the complex and insoluble scale, and the key is to choose an appropriate cleaning agent. Sulfamic acid is a good chemical cleaning agent, which can dissolve various scales that are difficult to dissolve with hydrochloric acid under normal conditions.
Cleaning effect inspection and evaluation of cooling system pipes, various parts of the cooling tower and the plastic multi-faceted hollow spherical packing inside the cooling tower, cleaned, no residual scale, no overwashing. The cleaning effect is good.
Public announcement of the environmental protection acceptance report for the completion of the project of Tangshan Sanding Chemical Co., Ltd. with an annual output of 2,000 tons of ammonium sulfamate, 1,500 tons of guanidine sulfamate
Committed to the deep processing of sulfamic acid and the production, development and sales of other new products. The company introduces international advanced technology and equipment, with an honest style, a rigorous work attitude, and a production philosophy of excellence, it continues to grow and develop