Analysis of the Salt Deposition in the Inlet Pipeline of Waste Chlorine Absorption Tower in Chemical Plant
During the waste chlorine treatment process, the accidental chlorine gas is drawn into the waste chlorine absorption tower through a titanium draft fan. Hydroxide sodium solution is sprayed into the tower using an alkali circulation pump, and chlorine gas and hydroxide sodium solution undergo full contact and reaction within the tower. The chlorine gas in the waste chlorine is absorbed by the alkali solution, and the alkali solution continuously circulates to produce a sodium hypochlorite solution. This process not only produces the sodium hypochlorite solution required for acetylene purification but also prevents chlorine gas from entering the atmosphere and causing environmental pollution, which is of great significance in the chloralkali industry.
Analysis of the Causes of Blockage in the Inlet Pipe of the Waste Chlorine Absorption Tower
1 Reaction Mechanism of Accidental Chlorine Process
Reaction Equation: Cl2 + 2NaOH = NaCl + NaClO + H2O. In the process of hydroxide sodium absorption of chlorine gas, the raw materials are liquid alkali and chlorine gas. In the reaction process, 1 mol of chlorine gas can generate 1 mol of sodium hypochlorite and 1 mol of sodium chloride. At a certain temperature, the solubility of sodium chloride in water is constant, and sodium chloride exceeding the solubility range will crystallize and precipitate. If the conditions are not controlled properly, the sodium hypochlorite produced by the reaction will decompose to produce oxygen and sodium chloride. When the concentration of sodium chloride in the solution reaches saturation, sodium chloride will crystallize and precipitate, causing pipe blockage.
2 Poor Stability of Sodium Hypochlorite
Sodium hypochlorite solution is unstable and easily decomposes. The instability of sodium hypochlorite is due to the high asymmetry of the spatial configuration of the valence electron pairs of the anion and the large ion potential of the central atom chlorine.
2.1 Decomposition Under Heating
Sodium hypochlorite undergoes hydrolysis to form sodium hypochlorite: ClO – + H2O → HClO + OH – Sodium hypochlorite is unstable and decomposes: 2HClO → 2HCl + O2 The final reaction produces sodium chloride: HCl + NaOH → NaCl + H2O In summary, 2NaClO 2NaCl + O2 Its degree of decomposition increases with the temperature, producing more sodium chloride and causing supersaturation and crystallization.
2.2 Catalytic Decomposition by Heavy Metal Ions
In the process of preparing alkali, production water is used to dilute high-concentration alkali. The production water contains impurities of heavy metals, and heavy metal cations catalyze the decomposition of sodium hypochlorite, accelerating the decomposition of sodium hypochlorite and leading to the generation of more sodium chloride and supersaturation precipitation, causing pipe blockage.
3 Precipitation from Other Weak Reactions
Sodium hypochlorite solution is weakly alkaline. In terms of its alkalinity, it can cause the precipitation of Ca2+, Mg2+, Fe3+, and CO2-3 in water. Moreover, due to the strong oxidation of sodium hypochlorite, it can decompose certain organic substances dissolved in water, resulting in the precipitation of oxide precipitates. These weak reactions also contribute to precipitation and blockage to some extent.
In summary, the blockage in the inlet pipeline of the waste chlorine absorption tower is not caused by sodium hypochlorite, but mainly by crystalline substances composed mainly of sodium chloride. The reaction between chlorine gas and hydroxide sodium solution generates sodium hypochlorite and sodium chloride. Under certain conditions, sodium hypochlorite decomposition generates sodium chloride. When the concentration of sodium chloride in the solution becomes too high and reaches saturation, sodium chloride crystallizes and precipitates. As the reaction continues, sodium chloride crystals continuously precipitate and accumulate, and the weak reactions of impurity ions in the water also contribute to precipitation and crystallization, ultimately leading to blockage.