(274c) Control of a Pressure-Regulated Circulating Riser System for Running a Conversion Process

The pressure-regulated circulating riser (PCR) system provides several significant control and operational capabilities over other generically similar systems. The PCR has the ability to support the operation of up to three different physical and/or chemical reactions in the riser, particle separator, and the counter current moving packed bed sections. The unique capability of independently controlling the pressure drop across and the fluid flow rate through the riser provides a means of optimizing the solids fraction and particle velocity in the riser when running a process there. The design and operation of a PCR is based on a two-fluid model that was previously used to demonstrate how the operation of a riser requires only two independent variables to be specified in order to determine the conditions there. The PCR has a total of three degrees of freedom that define its overall operation, which reduces the complexity of controlling a process. The unique control system provides the basis for ready sizing of PCR systems over a wide range of scales from pilot to that needed for industrial processes.

In this paper, a liquid-solid process is modeled in which a stripping operation takes place in the moving packed bed and a pseudo first order reaction which is dependent on the solids fraction and residence time is run in the riser. Modeling equations are presented that show how the control system is configured to accommodate / optimize a first order reaction in the riser which is dependent on both solids fraction and residence time. The modeling also provides a means of determining whether a system is adsorption or reaction limited and demonstrates how resources can be allocated to the limiting step in the process. This model may be adapted to a variety of chemical separation, conversion and treatment operations.