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r~ <br />u <br />The most promising technique is an empirical relationship derived in the laboratory that has <br />proved qui[e successful in laboratory specimens. Basically, the technique is simply an experi- <br />mental relationship between blanket height and total mass removed which can be compared with the <br />theoretical blanket space curve with any errors corrected as they occur. <br />In practice, the best available empirical wash curve is followed in removing salt, and blan- <br />ket additions are made according [o the following relation: <br />Vb = a f R_H (R2 - 1'Z) aY = ,r (RHZ - H3/3) <br />which rela[es the blanket volume Vb to the <br />blanket height, H, for any given sphere of ra- <br />dius R. See Fig. ll. <br />The cumulative additions of blanket ma- <br />terial made during the leaching process must <br />equal the blanket volume Vb calculated at any <br />given heigh[. H. If less blanket additions were <br />necessary, the segment under consideration <br />was underwashed, and if more blanket volume <br />was necessary, the segment was overwashed. <br />In this manner, it is possible to forma spher- <br />ical cavity in which [he volumetric differences <br />between [he projected diameter and [he over- <br />washed section represents a maximum error <br />equal to [he sum of the overwashed segments <br />which cannot be retrieved. Underwashed seg- <br />ments can be rewashed to leach addi[ional sal[ <br />as required. Figure 12 illustrates [his prin- <br />ciple graphically. The top curve is an empir- <br />ical wash curve which is used only as a guide. <br />The bo[[om curve is [he theoretical blanket <br />space curve which is used to control cavity <br />shape. The cavity shown in Fig. 13 was <br />leached according to this technique and the re- <br />sult was a fairly uniform spherical cavity <br />which, except for [he hidden crack, might have <br />been 100% successful. <br />The procedure followed when using the <br />material balance equa[ion is given below: <br />1. By manipula[ing the blanket, find the <br />greatest value of h such [ha[ Vb (cal- <br />culated) is equal to Vy (from curve, <br />Fig. 11). <br />Figure 11. Posi[ion oC Blanke[-l: ater Cor.~au <br />as a fwaion of Gviry Volu^e occupied by <br />blanker material <br />4.0 <br />2. Wash with blanke[ in this posi[ion for a cer[ain time in[erval (based on experience). <br />3. Lower blanke[ by incremen[ and again find greatest value of h such that Vb (calculated) is <br />equal to Vb. <br />4. Repeat 2 and 3 throughoutthe process. <br />Figure 14 shows relation benaeen specific gravity of brine solutions and weight per cubic <br />foot. <br />By a similar technique. [he water inlet can be closed and water displaced from the cavity by <br />air. The amoun[ of water displaced is measured and the change in water level is determined by <br />[he use of electric probes. 1`taking the same assume[ion as above, the diameter of the blanke[- <br />water con[act can be determined. <br />305 <br />2.0 <br />1.6 <br />0 <br />z 1.2 <br />0 <br />U <br />a <br />LL 0.8 <br />t <br />0.4 <br />0 <br />R <br />V=lt ~ (RZ -Y210Y'1ft Rn2-h3/3) <br />R-h <br />0 I.0 2.0 3.0 <br />Vb,R=I <br />i <br />