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STIG PROJECT -- EVALUATION OF WATER FOR INJECTION -- 28 March 1994 9 Multiplier for Overall Concentration of Waste Water The sub-systems described above each operate to increase the concentration of their liquid input streams and the concentration in waste represents the average concentration effect of the sub-systems. Whether or not the final, mixed waste fluid is injectable depends jointly on the average concentration effect and on the concentrations in initial liquid. Since initial liquid concentrations are substantially variable (Figure 2, Table 1), it is useful to view the collection of sub-systems in a mechanical way.The objective is to derive a numerical factor which accounts for concentration effects that can be used irrespective of details about the initial liquid9. At nominal conditions, the ultrafilter yields different concentrations in product and waste, respectively about 0.92 and 1.3 times the concentration of input fluid10. The RO unit receives ultrafilter product and about 10 percentll of that dissolved load exits in the RO product stream. The net concentration multiplier 12 for the RO is 2.68. Cooling tower opearation is aimed at a concentration factor of 2.0 due entirely to evapo-concentration.Losses of dissolved materials from the tower water are considered negligible, so the concentration factor of 2.0 requires no modification 13. Boiler discharge, when at low rate, contributes negligibly to the volume and dissolved load of the waste mixture. During high-rate blowdown, it contributes a dilution effect. Its effective concentration multiplier 14 is approximately 0.0094. Applying those concentration factors to the corresponding liquid volume rates and summing, then dividing the result by the sum of volume rates yields the effective concentration multiplier (m) for the system. Equation (1) is explicit, wherein R, C, U, and B refer to volume rates of waste discharge from RO, cooling tower, ultrafilter and boiler, respectively. (2.68R + 2.00 + 1.3U + 0.0094B)/(R + C + U + B) = m (1) At nominal conditions,m= 1.86.For summer conditions C and U are smaller than nominal and this yields a larger multiplier,m=2.02.Descriptions of alternative flow rate combinations and resulting concentraton multipliers are shown in the legend of Figure 1. III. MINERAL SOLUBILITY ESTIMATES Applying eq. (1) to the average concentration of Si02 in input fluid yields 59.5(1.86) _ 110.7, a predicted average concentration in injectate.Silica is considered a critical component and evaluation of its potential for deposition is relatively simple. This is because the form which deposits is well known and the effect of other dissolved materials, normally electrically charged, do not appreciably interact with dissolved silica, which is mostly electrically neutral. Other mineral forms, involving ionic components, are potential deposits and descriptions of them are worthwhile.Evaluating complete water compositions for potential mineral depositions can be done by classical methods which allocate analyzed components among the many ionic and molecular forms that are significant to mineral saturation. Mathematical requirements involve solving several tens of simultaneous equations which can be practical by computerized methods. WATEQ4F15 was applied to the WSWPCF fluid based on the average concentrations, increased according to multipliers derived above and shown in Table 1. They represent the plausible range to expect in operation of STIG. WATEQ4F contains data for more than 600 DON MICHELS ASSOCIATES -Missoula,Montana USA