Document LnG7VopQ5pJ6Xxqgr3VjjkZ5

TOWOLDMON0035710 WATER_PCB-00020179 ttf BATCH SYSTEM Figure 1 COLUMN SYSTEM 'W'Figure 2 Introduction The performance of transformers and capacitors is generally based on the power factor. This quality is dependent upon the removal of adsorbable impurities. For many years Monsanto Company factories, as well as many customers have refined askarel fluids by the simple agitation of a given quantity of Fuller's Earth with the fluid to remove adsorbable matter. The treatment was followed by filtration to separate the adsorbent from the refined fluid. When an adsorbent and fluid con taining adsorbable matter reach equilibrium, the equilibrium gen erally conforms to the Freundlich isotherm -- = lcO 7 where: x = the quantity of adsorbate, y = the quantity of adsorbent used, C -- the concentration of the adsorbate remaining in the fluid at equilibrium, and k, " = constants characteristic for a specific system. The isotherm indicates that on one single equilibrium contact, a high degree of purification cannot be achieved. The equation indi cates further that with a sufficient number of repetitive contacts, the value of C may be made to approach zero (absolute freedom from adsorbable material). Since it is not practical nor possible to carry out sufficient repetitive batch refinements to achieve the maximum quality, one must resort to the next most practical approach; that being a packed bed which achieves these repetitive treatments on a single pass. To accomplish this, it is necessary to select the proper adsorbent and design a system with enough zones, which we shall refer to as equivalent transfer units (ETU), for maximum purifica tion. The sketches show a visual comparison between the batch and the packed bed system: As shown in Figure 1, the batch system reaches only one equi librium, that being dependent on the amount of adsorbable impuri ties in the fluid and the capacity of the adsorbent. The column system. Figure 2, shows the numerous equilibriums reached as the fluid passes through the column. When material passes through successive zones, the adsorbate collects in the bed. In each zone the consistently cleaner askarel contacts fresh adsorbent. In this way maximum purity is obtained. 051052* TOWOLDMON0035711 WATEFLPCB-00020180 Adsorbent Selection and Activation Although Fuller's Earth (Attapulgus clay) has been used for years as the selected adsorbent, it does not function satis factorily in the column system because of its softness. The gran ular material crushes and forms a mud when wetted with the fluid. The mud formation in a packed bed system restricts the flow to the point where the system is inoperative. To overcome the problems presented by the attapulgus clay and to achieve other desired features, Porocel*, after extensive testing, was selected as the proper adsorbent. Porocel, being an activated bauxite, is considerably harder than the attapulgus clay which prevents crushing and even the fine material doesn't form a mud. Additionally, Porocel has about 36% more surface area for effective adsorption than docs the clay. Best perform ance was achieved with 20/60 mesh although 30/60 or even 60/90 mesh material will probably give satisfactory perform ance. The --60 or 200+ mesh is definitely not recommended. At the other extreme, coarser than 20 mesh is not recommended. Before any adsorbent can be used for refinement, it must be thoroughly activated. The "degree of activation" is best deter mined as water content. For Porocel an acceptable moisture level is less than one percent (via Karl Fisher determination). If the adsorbent is packaged and shipped under fairly moisture tight conditions such as polylined bags or steel drums, very little drying is necessary. The adsorbent can be dried in one of several wayB. First, the adsorbent can be heated in shallow drying pans or a rotary kiln to a temperature of 450F to about 900F at atmospheric pressure and then charged to die adsorber. Second, the adsorber can be charged, vacuum applied (5 milli meters of mercury) and the adsorber temperature driven to about 300F. A third method, and probably the most expensive, is to fill the adsorber, heat to about 300F, and purge with dry Ns or dry air until the moisture is driven off. Since most plants handling askarel fluids have steam and vacuum facilities, the combination of heat and vacuum is probably the most econom ical way to dry the adsorbent. After the drying operation, the heal must always be cut back depending on the askarel being refined and the recommended temperature for refinement. Reg. trademark of Minerals & Chemicals Philipp Corporation. TOWOLDMONOQ35712 WATER_PCB-00020181 Design Calculations Equations VS j k,a ^-(where G0 = rp/S) G can be determined by knowing the fluid properties and the size on the adsorber. kx can be calculated from "Transport Phenomena" J,i = 0.91 R*-081 Q, -(k<50) J,, = 0.91 R<r*81 Q, ( Jn = Jn (By definition) G, = cV where c = total molar concentration V = volume ... J. d- kx (Sc)2/8 b (C \2/8 (Substituting J,, = J,,) ----- = 0.91 IV 51 Q, = h - 0.91 R,-0'" Q, G0 (Sc)-2/s a is calculated from physical data on the adsorbents _ 6 (1-E) " ~ Q. D E is calculated from the following Pd =r Dod-Ipl Pa (1-E) =D,, Do(l-Ip) (1-E) =D,, E =T Now G0, kx, and (a) can be calculated. Therefore the HETU can be calculated. Since the total number of ETU is determined experimen tally (depending on the degree of purification desired), the total height can be figured. H = HETU x ETU Typical Scale Vp Example General Data Aroclor Viscosity (/x) of Aroclor 124*2 (a 70C = 6.08 cp or 14.4 Ibs/ft hr Density (p) of Aroclor 1242 (a 70C = 1.35 g/cc or 84.5 Ibs/ft* Porocel Ip I internal porosity) Db (bulk density) Dr (crystalline density) Qs Dr 20/60 mesh Mean Equivalent Particle Diameter 30/80 mesh Mean Equivalent Particle Diameter 0.50 (50%) 56 Ibs/ft" 206 Ibs/ft3 0.50 0.0019 ft 0.0014 ft General Newtonian Constant g = 32.2 lbs (ft)/lbs (sec)2 Diffusion Rate (Dl) = 3.1 X 10~fl ft2/hr Laboratory Conditions for Refinement Treatment temperature C = 70 Bed Packing 20/60 mesh Porocel Dp(ft) = 0.0019 Column diameter (inches) = 1.62 Column Height (inches) = 60 Bed Weight (grams) = 1850 Bed Volume (cc) = 2050 Bed Density (Bp) gm/cc = 0.90 Flow Rate (cc/min) = 30 Go = Fp/S Go = 380 Ibs/hr ft2 R* = --"^--(Reynold's Number) R = 0.053 Dl = 8 X ID-7 cm-/sec or 3.1 X 10-MtVhr Sc = --Schmidt Number pDL Sc = 5.5 X 10* kx = 0.91 Q*G0 lSc)"2/i* kx = 0.485 ** -- p Pa = Dc (1-Ip) Pt-- 206 (1-.5) = 103 r 103 - 56 E =---- 103-- E = 0.456 6(1-E) DpQ. a = 3436 ft' HETU - ^2kx a 380 ~ 0.455 ( 3436) = 0.228 ft Since the total height of the laboratory system was 60 inches or 5 feet then, the total number of transfer units (ETU) is H ETU = HETU _5.0_ 0.228 22.0 Since the laboratory system contained 22 units and refined satisfactorily, any scaled up system must contain this many units or preferably more. Assume we have a column available with the fol lowing physical dimensions that we desire to use. Diameter of the Column (ft! = 2,25 Height (H) ft = 12.5 Area (S) ft 2 = tt(2.25)2/4 or 4 Volume (V) ft8 = (4 ft2) (12.5 ft.) = 50 Aroclor Data Treatment Temperature (C) Viscosity (jx)*t 7("c(lbs/ft hr) =70 =14.4 l 05 10520 TOWOLDMON0035713 WATER_PCB-00020182 Density Mt lire (lbs /ft ) (P) = 84.5 Porocet Data Particle Diameter Dp (ft) 0.0019 Red Charge (lbs ) 2800 R __ Bed Weight _ 2800 lbs ,, D -- Bed Volume "50"ft"~(lb8/,t } 56 Assume we desire to refine 4.5 gpm of fluid Flow(F) = 4 5 gpm X = 36 flVhr G0 = Fp/S = 760 lbs/hr/ft2 R.= G^ ' , t< = 0.100 DL= 3.1 x 10'" (tVbr s --pD,. = 5.5 X 10" k, = 0.91 R,-011 Q,Gq(Sci-2/3 k, = 0.725 E = -^p^ P,, = D.(1-2P) Pfl = 206 (1-.5) P,, = 103 _ 103 - 56 E = " 103... E = .456 _ fi(l-E) b"Q. 6(l-.456) " ~ 0.0319 (0.5) a = 3435 ft2 HETU = kx a 760 " 0.725 (3435) = 0.326 ft ETU = H HETU = 12.5 ft /0.326 ft = 38.3 units Using the existing 12.5 ft. bed column with a fluid flow of 4.5 g.p.m. would do a very adequate refining job, since only 22 units are required to give adequate refining. The actual 38 units would probably give a slightly better quality. However the advantage in an excessive number of ETU's is the gain in operating time between shut downs to change out the bed and the turn up rale available on the column feed. Let's assume we want to double the feed on this unit to 9 gpm. The adsorbent properties remain the same. The only change is G0 which charges kx= 0.91 R*"061 Q.GofS,.)-2'8 Then the HETU would change HETU = A kxa G0 = Fp/S G"=(^r)84-5/4 G0 = 1520 lbs/hr/ft2 R* = GoDp/ft 1520 (0.0019) i\o = i**.* Kx = 0.91 Re-*61 Q6G0(Sc)-2/3 Kx= 1.06 HETU = Go Kxa = 0.41 EUT = H HETU = 31 The answer is yes, the feed can be doubled. The total ETU's (31) is well above the laboratory value of (22) for adequate refinement. One can see from the equations that the adsorptive characteristics of the column are not dependent on the flow. However, by the same reasoning the pressure drop is shown to be highly dependent on the flow rate. Therefore pressure drop becomes a controlling factor in the design of these units. Bed height, the adsorb* ent, packing, and fluid temperature are likewise impor tant factors in the bed operation. N Calculation of Pressure Drop Assuming the 12.5 ft. bed, packed with Porocel at a bulk density of 56 lbs/ft3 and the fluid flowing at 4.5 gpm. According to Leva's equation for predicting pressure drop (AP) 2 fm G02 L(1 -- E)3~N 144Dppg Q,S-N(E)8 where fm = the modified friction factor as determined by the Reynold's Number R L = height of the bed (ft ) same as H g = Newtonian Constant 32.17 lbs (ft )/Lbs force (sec.)2 N = exponent function of the modified Reynold's Number Re G0 = Superficial Mass Velocity in lbs /sec (ft)2 The remainder of the terms are explained in the calcu lation of HETU. 7fi0 \2 (3^00 j (12-5) (1 -- 0.455)3-1 = 144/((k0019f (8475) (32.1-7) (0.5)"-' (0.4557" AP = 18.5 psig 051052 7 TOWOLDMON0035714 WATER_PCB-00020183 Equipment The equipment necessary for an operational packed bed system consists of: 1. Feed System -- a temperature control is needed on the feed for the adsorber. A positive displacement pump to yield sufficient flow at the operating pressure is neces* sary. 2. Adsorber -- The actual adsorber shell must be a suit* able material of construction such as aluminum or stain* less steel to eliminate the possibility of product contain* ination. The surface of a stainless adsorber should be cleaned free of any rust. The top of the adsorber should be removable for ease of loading the adsorber. The bot tom should be equipped with an adequate bed support to retain the granular adsorbent and yet allow the liquid to pass freely. The bottom should contain a dump port large enough to allow for removal of the hed material. The unit should be adequately traced for temperature control. A temperature indicator should be installed in the adsorp tion zone. Vibrators should be installed on the shell of the adsorber large enough to pack the bed to optimum den sity. A No purge should be connected to the bottom of the adsorber and sufficient heat provided to drive off moisture in case the water content of the adsorbent is too high when the column is loaded. The normal recommended height to diameter is about 4-5 to 1 although a shorter unit could possibly be used. Less than 3 H/D is not rec ommended. The normal safety items for a pressurized vessel are also necessary. 3. Filter -- Small in-line polishing filters are needed on the column to catch any residual adsorbent, etc., that may pass through the bed support. The filters should be on a by*pass arrangement to keep the unit on stream at all times. 4. Flow Controller -- A flow controller should be placed on the effluent of the adsorber to control the fluid flow through the adsorbent. 5. Storage System -- A storage tank for the finished prod uct should be provided with sufficient capacity to keep the column on stream. TOWOLDMON0035715 WATER_PCB-00020184 Adsorber Operation The column, after being throughly cleaned, is filled with activated (dry) Porocel. The bed is settled to an optimum density through the use of vibrators. The bed is then flooded with the fluid and allowed to soak into the bed and displace any air which may be trapped in the adsorbent. After the bed has been allowed to soak, pref erably over night at the operating temperature the for ward flow should then be started. Once the quality reaches an optimum level, the bed'will continue to operate at this level until it becomes saturated with adsorbate. When the bed becomes saturated, the quality will show a sharp de crease or breakthrough. At this point the quality will drop to a considerably lower level and hold for a period of time and then drop to a completely unacceptable quality level. Once the breakthrough is obtained, the bed should be changed and the cycle started over. This production model produces the highest quality refined askarel under the most economical condi tions. Because of the efficiency, these units operate continuously for months on a single bed charge. Shown above is a small laboratory model capable of producing up to 50 cc/min. of refined askarel. This unit can be used to produce laboratory quantities or collect scaie-up data to design any size unit up to or larger than the unit shown below. Operating Costs Savings are realized from 1. Manpower reduction 2. More efficient adsorbent utilization 3. Continuous faster refinement 4. Less contamination 5. Less product loss 6. Reduced maintenance The only disadvantage of the porocel column is the higher cost of the adsorbent (about 50%), but this is practically offset by the increased efficiency of the Porocel (40%). TOWOLDMON0035716 WATER_PCB-00020185 Actual Field Experience The Monsanto laboratory tested a small unit collecting scale-up data for a pilot design. After a successful pilot demonstration, a pro duction unit was brought on stream yielding continuous refinement of the Askarel (except for short intervals for changing the bed). Due to the efficiency of the system and the high quality product produced, Monsanto is adopting the system as a production standard world wide. In addition, the system is being disclosed to those customers desiring to use the most efficient and economical method of refine ment. ' Typical Results Achieved 1. Fluid Aroclor 1260 Arocior 1254 Aroclor 1248 Aroclor 1242 Mixture of Aroclor 1260, TTCB, TCB, and dicyclodiepoxy carboxylate Trichlorobenzene Resistivity (ohm cm) 230,000 130,000 40,000 28,000 80,000 18,000 Conventional concentric electrodes. 0.1 inch spacing 500 VDC stress with 1 minute electrification, @ 100* C. Besides the increase in quality, the column adsorber system was found to be 18 to 20 times more efficient than old contact system. The increased efficiency in earth utilization of the column system reduces manpower requirements when compared with the old batch system. 1. Results are reported as resistivity which is the reciprocal of power factor. At these quality levels, unless the new guarded electrode power factor system is used, an accurate measurement cannot be made. 30 COLUMN ADSORBENT EFFICIENCY* ; ' BATCH SYSTEM COLUMN SYSTEM H Compared to batch treatments -- assuming the same quantity of adsorbent <j 8vl @ 20 i EO o K 10 3 9 0 0 100 200 300 400 500 600 700 800 X 1,000 gallons quantity 0510530 | TOWOLDMOIM0035717 WATER_PCB-00020186 A Monsanto Power Factor System constantly monitors on-stream quality through 100 cycle power factor at 100 C. This system requires no external sampling for quality control. Optional Equipment The Monsanto "in line" analyzer is a very useful instrument for monitoring the product quality from the column. The unit was de signed specifically for quality control on the effluent from this system. It provides a continuous monitoring of power factor and has provi sions for recording if necessary. The quality of the refined material is known constantly within three minutes after refinement. The "in line" analyzer is invaluable during start up of the adsorber to deter mine when recycle should be stopped and the forward flow diverted to ihe storage system. The information contained in this bulletin is, to our best knowledge, true and accurate, but all recommendations or suggestions are mads without guarantee, smce the conditions of use are beyond our control. The Monsanto Company disclaims any liability incurred in connection with the use of these data or suggestions. Furthermore nothing con tained herein shall be construed as a recommendation to use any prod uct in conflict with existing patents covering any material or its uss. Monsanto tmo53i | TOWOLDMON0035718 WATER_PCB-00020187 Monsanto "" Monsanto Company / Functional Fluids / 800 North Lindbergh Blvd. / St. Louis, Missouri 63166 TOWOLDMON0035719 WATER_PCB-00020188