Variable-pressure/variable-rate expression of semisolid materials

In a batchwise variable-pressure/variable-rate expression process, the expression pressure is increased to a predetermined maximum pressure and then held constant until final equilibrium compression is obtained. For analyzing the variable-pressure/variable-rate expression process, the following assumption is made: the internal condition of compressed cake under the instantaneous pressure p in a variable-pressure/variable-rate operation is close to that in a constant-pressure operation under such a pressure p when the same volume of liquid is removed from the same amount of original materials in both operations. Using this assumption, the changes of sample thickness with expression time can be calculated from the analytical equation for the constant-pressure process based on the Terzaghi-Voigt combined model. The match between experiment and theory was satisfactory for the expression of semisolid Korean kaolin.