Limestone stir rate

Since water is the reactant in equation (1), the diffusion should be important only in removing the products from the reaction zone. The measurements presented in the Experimental Results Section were designed to determine the relative effects of the surface reaction rate and the diffusion of products on the overall dissolution rate. The variables in these tests were temperature, pH, stirring rate, and type of limestone. 

The difficulty with applying equation (4) is the uncertainty as to whether the RS value measured in the bulk liquor (which can be measured) is the same as the RS in the boundary layer surrounding the limestone particles (which cannot be measured). Test conditions employing high stirring rates and relative large particles ( 100 ym) have been chosen to minimize the differences in these two RS values. 

The next day the filtered solution is then used as the initial charge to the reactor. In this way, the initial reactor composition will be approximately the same in the beginning as during the run. The pH controller is then set to the desired value. The pH controller is used to meter scrubber feed liquor (pH 2) into the reactor to maintain a constant reactor pH. After the stirring rate has been set and the desired temperature reached, 10.00 g of sized limestone are added to the reactor. 

Fifteen runs using three limestones are reported for various reactor conditions. A base case experiment was performed for each of three limestones 1) Fredonia, 2) Brassfield, and 3) Pfizer (see Tables II and III). Operating conditions were then varied to show the effect of stir rate, temperature, and pH as well as reactor feed composition. 

Figure 4. Fredonia limestone dissolution rate vs. stirring rate, (50°C pH 5.8).

Stirring rate appeared to have little effect on the CaC03 and MgC03 dissolution rates for the Fredonia limestone at pH 5.8. 

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