Nitrogen trichloride accumulation

The next two sections discuss protection against process hazards that are peculiar to chlorine processing. Section 9.1.10 covers emergency pressure relief both before and after the compressors. An important part of the discussion covers the design and operation of vent scrubbers to prevent the release of chlorine to the environment. Section 9.1.11 is dedicated to the explosion hazards presented by hydrogen and nitrogen trichloride. The sources of NCI3 are discussed, as well as its fate in the process. This includes the mechanisms of accumulation and safe decomposition. 

One of the hazards encountered in the operation of a vaporizer is the possible accumulation of nitrogen trichloride in the liquid phase. The hazards of nitrogen trichloride in general and the particular hazards associated with vaporizers are discussed in Section 9.1.11.2. 

F. Abraham and J. F. Knoop, Maximum Accumulation of Nitrogen Trichloride in a Continuous-Feed Chlorine Vaporizer, The Chlorine Institute Nitrogen Trichloride Workshop, New Orleans, LA (1998). Ya. J. Apin, Acta Physiochim. URSS 13,405 (1940). 

This is useful in estimating the accumulation of the hazardous compound nitrogen trichloride when a batch of chlorine is allowed to vaporize. 

NCI3 is much less volatile than chlorine, and so it tends to accumulate in suction chiller bottoms (Section 9.1.6.4A) and in chlorine vaporizers (Section 9.1.8.7) or other vessels from which chlorine is withdrawn as vapor. One method for its removal as a waste from suction chillers has been the dilution of the bottoms with a chlorinated organic. The standard choice for this duty has been carbon tetrachloride. With the use of this solvent restricted under the Montreal protocol, other materials have been suggested as replacements. Chloroform is one possibility, but it is important to note that it (b.p. 61 °C) is more volatile than nitrogen trichloride. Section 17.4.2 outlines problems that can arise with replacement solvents. Section 9.1.11.2E discusses alternative proeesses for the safe destruction of NCI3. 

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