Acid Reflux To Counter Jacket Leakage

HCl Synthesis Process Overview #

The synthesis of hydrogen chloride from chlorine and hydrogen is an exothermal reaction. For each mol of hydrogen chloride generated, \( 92.05 \ \text{kJ} \) of heat is released. The synthesis furnace is designed with a “3-in-1” graphite jacket to maximize heat recovery through by-product steam generation. The unit is divided into three primary sections: Combustion, Steam Co-generation, and Cooling.

The synthesis is represented by the following thermochemical equation:

\[ \text{H}_2(g) + \text{Cl}_2(g) \rightarrow 2\text{HCl}(g) \quad \Delta H = -184.1 \ \text{kJ/mol} \]

Feed and Ignition #

Hydrogen and chlorine are sourced from the electrolyser and pre-treatment sections. An orifice flowmeter normalizes the flow by accounting for gas pressure and temperature. The gases are then fed into the furnace burner at a controlled molar ratio \( 1.05:1 \) to \( 1.1:1 \). Burner material is typically silica glass or ceramic-based. An automatic electric igniter is used to initiate flame.

Combustion #

The resulting hydrogen chloride gas reaches temperatures between \( 2000 \) and \( 2500 \ ^\circ\text{C} \) as it flows from the combustion chamber.

Steam Generation #

Recirculating pure water absorbs the reaction heat of chlorine and hydrogen synthesis (generally 0.7 ton of by-product steam is generated per ton of 100% HCL, and 60% of the reaction heat is recycled). The steam can be conveyed to caustic soda plant for salt dissolving process or other processes, to save energy and reduce consumption.

Absorption #

It then enters an integral or separate isothermal co-current falling-film absorber. Here, the gas is absorbed in water or weak acid to produce hydrochloric acid at the desired concentration.

Leaking Graphite Block #

This led to cooling water ingress into furnace. The product concentration couldn’t be maintained. Naturally feed water to furnace was lowered; it did bring acid concentration to normal 31% but temperature of tail-gas absorber section increased rapidly. Tail-gas absorber is a vertical packed section which traps HCl fumes, thus reducing the water to it lead to inadequate wetting of packing & HCl fumes loss was experiences. A reflux section was devised & implemented. Calculations were made on the amount of reflux needed for maintaining exit acid concentration. Thia solved elevated temperature problem and HCl fumes loss

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