Document 99eGLGEbpNYox75p2LprdyYZV

UNION CARBIDE INTERNAL CORRESPONDENCE CHEMICALS AND PLASTICS To (n.b) Division locoiion Copy to Mr. R. N. Wheeler Bldg. 189 South Charleston Mr. R. O. Cavender Mr. M. E. Eisenhour Mr. R. J. Lindroth Dr. W. R. Manning Mr. J. R. Matthews Mr. H. L. Robinson Mr. R. W. Sesler Mr. K. L. Topham Mr. J. J. Walker P. O. BOX 8361, SOUTH CHARLESTON, WEST VIRGINIA 25303 Dot* August 4, 1971 RECEIVED Originating opt. Group 1 Safety AUG 061971 Subject Preparing Vinyl d^flutldV/HEELER Cars for Maintenance J -t Dear Nick: In accordance with your request I have examined two proposed methods for preparing the 48, 000 gallon vinyl chloride tank cars for main tenance. The proposed methods are as follows: Method I - 1. Unload car in usual manner by pressuring out contents with vinyl chloride vapor. 2. Strip pressure on car to 0 psig. 3. Pressurize car to 65 psig with nitrogen. 4. Vent pressure on car to atmospheric. Method II - 1. Unload car by pressuring out contents with nitrogen. (Assume 65 psig maintained on car throughout unloading.) 2. Vent pressure on car to atmospheric. Calculations for comparing these two methods were made for two different temperatures, 20* and 30*C. Additionally, two different conditions were assumed for Method II as follows: Condition A - Vinyl chloride exerts its full equilibrium vapor pressure in the car throughout the unloading operation. Condition B - Vinyl chloride exerts only one -half its equilib rium vapor in the car throughout th unloading operation. ucc 024329 Mr. R. N. Wheeler August 4, 1971 Page Two It is felt that these two conditions represent maximum and minimum limits for Method II and that the actual conditions would lie somewhere in between. Results of the calculations are tabulated in the attachments. From these results we may conclude that Method I is superior to Method II for the following reasons: 1. Method I is basically safer because the gas in the car after pressurizing will not form a flammable mixture with any proportion of air. With Method II the gas in the car after unloading will form a flammable mixture with air in the proportion of one volume of gas to about 1/2 to three volumes of air (depending on prevailing conditions). Thus ignition of the gas during venting is not possible with Method I but is possible with Method II. Furthermore, external maintenance around the dome of the vented car should be safer with Method I because of the nonflamma bility of the gas remaining in the car*. 2. The vinyl chloride loss with Method I is considerably less than that with Method II. 3. The vinyl chloride loss is constant for different tempera tures with Method I but is adversely affected by higher temperatures (above 20*C) with Method II. 4. Air pollution.is less with Method I because less vinyl chloride is lost to the air during venting. Please call me if you have any questions. Very truly yours. MESuthe rland/ map Attachments TO- Ucc 024330 RESULTS OF CALCULATIONS Method I Pounds VC1 vapor in car after unloading Pounds VC1 vapor in car after stripping to 0 psig % VC1 in car after pressurizing with Nz to 65 psig % VC1 in car after venting to atmosphere Pounds VC1 lost: Vented to air Left in car Total Volume of gas vented from car, std. cu.ft. ' Volumes of Air/Volume of gas required for flammable mixture Temp, of VC1 in Car 20`C 30*C 3240 1015 18.0 18. 0 4220 1015 18.0 18.0 820 195 1015 820 195 ToTS 29000 29000 Vented gas will not form flammable mixture with air in any proportion Method II - Condition A Pounds VC1 vapor in car after unloading % VC1 in car after unloading % VC1 in car after venting to atmosphere Pounds VC1 lost: Vented to air Left in car Total Volume of gas vented from car, std. cu.ft. Volumes of Air/Volume of gas required for flammable mixture 3240 57. 5 57.5 2660 580 JZ4Q 29000 1.9 4220 75.0 75.0 3460 760 5220 29000 2.8 UCC 024331 2 Method II - Condition B Pounds VCI vapor in car after unloading % VC1 in car after unloading % VCI in car after venting to atmosphere Pounds VCI lost: Vented to air Left in car Total Volume of gas vented from car, std. cu.ft. Volumes of Air/Volume of gas required for flammable mixture TemP- of VCI in Car zo-c 30*C 1620 28.8 28.8 1330 290 TETo 29000 0.4 2110 37. 5 37. 5 1730 380 ITTo 29000 0.9 ucc 024332