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Figure 3, Ec~ipmen[ Se[ Up for Mashing <br />Floating String Technique <br />The Floating String method utilizes tuo concentric circulation pipe strings, a stationary out- <br />let string and a movable or floating inlet string. The distinguishing characteristic is that the float- <br />ing string is always positioned so that the point of water injection coincides very close]} with the <br />position of the blan}:et-water interface. The outlet string remains bottomed at total depth through- <br />out the process. Figure 4 depicts the method of operation and progression of a cavity washed by <br />this technique. Close control requires that [he cavity be µashed in a number of stages. The num- <br />ber of pipe manipulations increases with the complexity of the desired shape. However, the num- <br />ber of pipe manipulations can sometimes be reduced by using a number of concentric floating <br />liners, as shown in Fig. 5. <br />As leaching progresses, any point on the surface of the exposed salt section proceeds along <br />a path normal to the surface at [hat point. The rate at which that point progresses is proportional <br />to the salinity of the water opposite tha[ point. A prediction of progressive confi; rations is [hen <br />possible by extrapolating from one washing stage to the next, as illustrated. <br />One of the complexities of this proved ire arises from the fact that the final cavity configura- <br />tion is the result of the alteration of each washing stage by every successive state. Therefore, <br />cavity shape is greatly affected by the uniformity of the salt, flow rate and pipe setting. This ren- <br />ders precise control very difficult. <br />300 <br />• <br />