ANALYSIS OF THERMAL STRESS AND OPTIMIZATION OF ALCOHOL WASH PROCEDURES FOR REMOVAL OF NOX GUMS/SALTS IN BAHX(COLD BOXES)

摘要

NO_x gums/salts are potentially unstable compounds that ethylene productionfacilities should include in their safety program. These compounds can form at cryogenictemperatures and high pressures, and can form deposits in equipment. NO_x gums/salts areunstable at elevated temperatures, with certain species being unstable at ambienttemperatures and colder. Experimental analysis has shown that NO_x gums/salts candecompose with an energy density similar to TNT. Operators can conduct precautionaryprocedures to remove NO_x gums/salts from production equipment and minimize the risk ofexplosion. This is often achieved by flushing internal passages of equipment where NO_xgums/salts are suspected of accumulating with alcohol. This serves a dual purpose to dissolvethe compounds and provide a heat-sink before the equipment temperature rises above thetemperature where NO_x compounds can become unstable.Brazed aluminum plate-fin heat exchangers (BAHX, commonly installed in 'cold boxes')are susceptible to NO_x gum/salt accumulation due to equipment operating at coldtemperatures and high pressures that favor their formation. Flushing cryogenic temperatureequipment with ambient temperature alcohol raises concern about potentially thermallyshocking and damaging the BAHX. To address this issue, Chart Energy and Chemicals (amanufacturer of cold boxes) and a close industry partner investigated an in-field BAHXundergoing an alcohol wash event. This paper details methods used including a dynamic 3-Danalysis for thermal and structural simulation. Tips are provided on practices to avoid. Finally,a set of general guidelines applicable to general alcohol wash procedures is offered thatmitigates NO_x gums/salts hazards and does not damage a BAHX.