Document k6EXyxrG3X3zDRDN970LVVeoB

PLAINTIFF'S EXHIBIT THE DOW CHEMICAL COMPANY restricted FOR USE OF DOW EMPLOYEES ONLY t-O -=r OMrion cr TEXAS i AllttlOfS V. H. MAUDLIN OlpWlWIt CHL0R-ALKALI DEVELOPMENT Titta Evaluation of a Thickener in Removal of Asbestos Fibers from the Chlorine Cathode Washing System 730753 R-______ Lob coda tetfan and raport nombar TCL-446 Data February 5, 1973 Prablam Numbar . 1*93 CORP. RES. AND DEV. LAB. NO. oK u S p p Infocmtlwa aanmary wWi wmMom PATENT DISCLOSURE NO.. DISCLOSURE PLANNED?___ The purpose of this study vas to evaluate the use of a thickener to concentrate the effluent from a chlorine cell cathode washer. The area necessary to concentrate 1500 gpm of O.ljf by veight asbestos in vater slurry to a concentrate of 0.5J> solids vas found to be: 3720 square feet if acidizing is used in the washing process, 2800 square feet if no acidizing is used. In either case a flocculant, Purifloe A-23, should be used. fB0 8$73 ,0i UN 621*636 ISs OeMnM TEXAS W. H. Caines S. F. Edquist L. J. Fourrier H. H. McClure D. A. Rikard 0. F. Schumm J. A. Vanvestenburg E. J. Williams Attantion of ISSUED TO MIDLAND A. C. Wilcox SARNIA S. Bolt A. Knight J. Waite LOUISIANA S. R. Pearson Attantlon of DOW IMP. SERVICE L. Little C.R-1- MiDLANP^CJLl. TEXAS. *C.R.I. WESTERN. fC.R.I. LOUISIANA. *DEPARTMENT FILE. CORP. RES. S DEV., 3030 BLDG.. MIDLAND 2US0 3/71 TABLE OF CONTENTS Page I. Purpose ........................................................................................................... 1 II. Summary............................................................................................................. 1 III. Conclusions ............................................................................................ 1 IV. Introduction ............................................................................................. 2 V. Experimental ..........................................................................................^ VI. Results .....................................................................................................5 VII. Discussion of Results..............................................................................10 VIII. Appendices................................................................................................ 13 *121182611 ST0284125 I. PURPOSE The purpose of this study vas to evaluate the use of a thickener In removal of asbestos fibers from the chlorine cathode washing system used by Dow Industrial Service. II. SUMMARY The area of a continuous thickener to concentrate a dilute slurry of asbestos from a chlorine cathode washer was determined. III. CONCLUSIONS To concentrate 1500 gpm of a 0.1 percent by weight asbestos in vater slurry to a concentration of Q.5f solids: 1. A flocculant, Purifloc A-23, should be used in the concentration of 2 - 3 ppm. 2. An area of 2800 square feet.is adequate if the cathodes are not acidized. 3. If the cathodes are acidized, 3720 square feet will be necessary. * 21* 18301$ * -2' IV. IHTRODUCTIOH The object of this study vu to determine the diameter of a continuous thickener operating on an asbestos-vater slurry of approximately 0.1% by veigbt concentration of solids. The cathode washing operation performed by Dow Industrial Service generates a flow of approximately 1500 gpm of 0.1% asbestos slurry. These fibers must not be allowed to enter any waste water discharge for ecological reasons, making landfill the most practical method of disposal. It is desirable to transport the asbestos fibers to the landfill area in as concentrated form as possible. An_experimental rotary drum vacuum filter vas tried by L. Little, a D.I.S. employee and a Konline-Sanderson representative on the asbestos slurry at D.I.S. They found that the feed slurry must be at least 0.5? by weight solids for the solids to be discharged from the filter. They also report a flow rate of approximately 25 - 30 gph per square foot of filter area. This data was confirmed by Bird Machine Company*on a sample sent to their lab. The problem of thickening the dilute slurry to a concentration suitable for filtration vas thought to be best solved using a continuous thickener of the "Dorr Pond" type. Three methods of sizing a thickener using settling tests in graduated cylinders vere used; Coe and Clevenger* Talmage and Fitch3, and Faust". The results of the methods resulted in the respective diameters of: 1*2.8', 31*.!*', and 19*3'. In an article published by Chemical Engineering and written by Bryant Fitch, he states, "However, if underflow concentration ia of critical importance, you should not rely too heavily on the batch procedure particularly where . Indicated underflow concentrations are lov. Say less than 23% by volume. . Indicated compression times are long. Say over 2k hours. . There is no clearly defined "compression point." . Strong channeling is not eveldent in "compression" regime. "In such cases, continuous piloting or the semi continuous procedure to be described later should be used." A continuous experiment thickener vas devised and used to try and determine which if any of the diameters would be correct. The apparatus consisted of a U" Plexiglas tube six feet long with a cone and discharge nozzle in the bottom. A fifteen-gallon sample of the slurry was pumped to the tube and the overflow and underflow collected and recycled to the feed pipe. -3- Data5from this teat indicated a diameter of 30 feet vould be suitable for the problem. It vaa felt, however, that further atudy va3 needed in a larger teat apparatus that contained a solids removal system. A three-foot diameter "laboratory thickener" was bought from the Denver Equipment Company and installed at the D.I.S. facilities. The results of this study are reported here. 1Letter from Bird Machine Company to Dow Chemical Company dated November 14, 1972 -- See appendix. 2Coe, H. S., Clevenger, G. H., "Methods for Determining the Capacities of Slime-Settling Tanks," trana. AIMS, 55, 356 (1916) 3Talmage, V. P., Fitch, E. B., "Determining Thickener Unit Area," Industrial and Engineering Chemistry, Volume UM, No.l, p.38 (1955) **Faust, A. S. et al, "Principles of Unit Operation" page **67. sChlor-Alkali Status Summary, January-March, 1972. See Appendix 821 n a z o i**. -k- V. EXPERIMENTAL A. Materials 1. Asbestos slurry. The asbestos slurry used was obtained directly from the cathode vasher in use at the Dov Industrial Services facilities. 2. Flocculant Purifloc A-23 vas used as a flocculant. 3. Apparatus The thickener vas a 3'0" diameter Denver Equipment Company Laboratory thickener complete vith rake assembly and underflow pump. The feed slurry vas directly from the cathode vasher sump pump through a tvo-inch rubber hose and a one-inch ball valve and feed pipe. The Purifloc vas injected into the feed piping vith a controlled volume pump and mixed in a series of 90 ells before entering the thickener. Tvo 55-gallon drums served as check tanks to measure the volume of the overflow and a smaller 15-gallon drum vas used to collect the underflow for measuring and sampling. A variable speed transmission vas added to the rake drive train to allow various rake and underflow pump speeds. It vas determined during the runs that the pump vould plug when running at very slow rates and a recycle line vas added allowing the underflow to continuously recycle through the sump in the bottom of the thickener. B. Procedure The dilute slurry vas flov-controlled to the thickener at a maximum rate that produced a clear overflow vhile a measured amount of Purifloc vas being added. The overflow vas collected in one of the tvo check tanks and timed. When this tank vas filled, the overflow vas diverted to the other tank and the first tank emptied. This switching of tanks continued throughout the entire run. The underflow vas continuously recycled through the collection sump of the thickener and periodically diverted to the small holding tank vhere the volume vas measured. Samples were taken of the feed and underflow and analyzed for solids concentration. This procedure vas repeated using various amounts of Purifloc to determine the optimum amount to be used. -5- VI. RESULTS The data from the experimental runs on the Denver Lab thickener calculated to the area needed to process 1500 gpm are shown in Table I. TABLE I Purifloc pm 0.6 1.0 1.9 2.3 2.4 2.9 3.1 4.6 6.4* 7.7* 9.1* 13.7* 17.0* 17.1* Feed Concen. Wt. i 0.05 0.l4 0.15 0.03 0.07 0.05 0.07 0.l4 0.12 0.08 0.19 0.09 0.10 0.04 Underflow Concen. Vt. % 0.4l 0.54 0.52 0.97 1.56 0.34 0.8l 0.46 1.06 0.89 1.27 0.69 0.38 0.57 Area for Sq.Ft 4l4o 2390 2140 2100 2410 2060 2800 2600 3060 2550 2860 2650 3420 3720 Runs made when D.I.S. vas acidizing every cathode. 624*t82SiS Graph I is a plot of Purifloc A-23 addition versus area required for 1500 gpm. Graph II is a plot of Purifloc A-23 addition versus the weight percent solids in the underflow. Table II is the results of settling test performed in a graduated cylinder using various flocculating agents. Included is the settling test using Purifloc A-23 of 3 and 15 ppm concentrations in the slurry from the cathode washer when every cathode vas acidized. Table III is the results of settling test performed in a graduated cylinder on the row unthickened asbestos slurry with the pH adjusted to various levels. The slurry sample vas taken at the time every cathode vas being acidized. -to- P V R / FLOc. P P m o & ttm ifa r u r c c fc P P flf i einszois -8- TABLE II SETTLIHO RATES OF ASBESTOS SLURRIES Time in Minutes Flocculant (Cone.) Inches Settled 0.71 1.42 2.12 2.83 3.54 4.25 4.96 5.66 6.37 7.08 7.79 8.50 9.20 9.91 10.62 11.33 Rone .22 .46 .70 .85 .97 1.10 1.28 1.46 1.65 1.80 2.00 2.10 2.20 2.35 Polyhall 402 Polyhall 295 Polymer JB Jaguar + A-23 A-23* A-23* (5 PPm - (S.JPP___ (5 PP) 2ptan 3 ppm 15ppm .12 .09 .11 .15 .27 .29 .38 .42 .25 .35 .49 .56 .56 .57 .68 .38 .65 65 .75 79 .80 .84 55 91 .92 .92 1.10 1.10 1.02 1.15 1.20 1.15 .81 1.28 1.30 1.25 1.40 1.50 1.36 1.50 1.70 1.40 1.65 1.52 .10 0.30 0.50 0.50 TABLE III SETTLING RATES OF ASBESTOS AT VARIOUS ADJUSTED pH 2* 2.1 3.9* 7.2 10.0 12.0 Rate of Settling (Interface) In./Min. 4.72 4.22 1.91 1.79 1.30 Raw, unthickened slurry without pH adjusted. -9- VII. DISCUSSION OF RESULTS A. Flocculant Addition B. Thickener Area with Minima Acidizing C. Thickener Area vith Maximum Acidizing D. Settling Rates at Various pH's E. Proposed Process Page No. 10 10 10 10 11 cm szo iS t iC I * 1 8 2 0 1 8 * -10 VII. DISCUSSION 07 RESULTS A. Flocculant The flocculant, Purifloe A-23, vas recommended by the Organic Product Research Department to Dov Industrial Services. This recommendation vas determined valid after a series of tests vas made comparing A-23 to several flocculants produced by Stein, Hall and Company. The area necessary for 1500 gpm vhen up to 1.0 ppm Purifloe vas added vas over U0O0 square feet. Vhen the concentration vas increased above the 1 ppm range up to 3 ppm, the area decreased to 2800 square feet. Above the 3 ppm addition little benefit vas realized. The data appears that the larger addition of Purifloe hindered the settling. It must be noted, however, that the last six runs vere performed three months after the first eight and D.I.S. bad changed their vash procedure to acidizing every cathode. The acidizing apparently has same effect on the settling rate. The settling test in a graduate vas repeated using the slurry that had been acidized and a 3 and 15 ppm Purifloe addition. No difference vas found betveen the tvo, however, the rate is different than the test done before acidizing vas begun. B. Thickener Area with Minimum Acidizing The first eight runs of this study vere made prior to June, 1972, vhen D.I.S. vas using a nHMimm of cathode acidizing in the vash procedure. The first set of data vas taken vlth a low Purifloe addition, 0.6 ppm, and resulted in poor settling. If this run is Ignored because of the low flocculant level, the largest area of the remaining seven is 2800 square feet. The thickener diameter for this area vould be 60 feet to handle 1500 gpm of unthickened slurry. C. Thickener Area with Maximum Acidizing The last six runs vere made after D.I.S. had started acidizing every cathode. Prom these six runs, 3720 square feet vas found to be the largest area needed for 1500 gpm of unthickened slurry. The diameter of a thickener of this area vould be 69 feet. D. Settling Rates at Various pH's It vas anticipated that by increasing the pH of the slurry, the ferric chloride in the slurry vould form a flocculant and make the addition of Purifloe unnecessary. This vas not the case as the settling rate actually decreased as the pH vas increased. The supernatant liquid vas less turbid at a pH above 7.0 than belov. The problem of this study is removing asbestos fibers and not clarification, so it is concluded that pH adjustment has no value in settling of asbestos. -11- 0. Proposed Process The 0.5 percent thickened slurry will have to be further devatered for disposal. A rotary drum vacuus filter seems to be suitable for this service. There has been no actual study done on the use of such equipment by this department. A preliminary study vas performed by D.I.S. personnel in conjunction with the Komline-Sanderson Co. They found that a feed slurry of 0.5% solids would produce a filtrate rate of 30 gph per square foot of filter area. Based on this, a filter of 600 square feet would be necessary. The solids removed by calculation should be 750 pounds per hour, however, in actual practice, it is closer to 500 pounds per hour. The difference could be the time necessary to place and remove the cathodes in the washer. Figure 1 is a flow sheet of the proposed process. ST028M 35 d 3 SOd 0 d 981*18261** VIII. APPEHDICES Appendix A Appendix B Appendix C -13- Results of Tests Done by Bird Machine Company on Sample of Asbestos Slurry Methods of Determining Thickener Areas B-l Taln&ge and Fitch B-2 Fitch, Batch Test Chlor-Alkall Status Summary January-March, 1972 { . 1*18281$