Semester

Summer

Date of Graduation

2008

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Lane Department of Computer Science and Electrical Engineering

Committee Chair

Brian D Woerner

Abstract

Circulating fluidized bed (CFB) is used extensively in petrochemical industries especially for fluid catalytic cracking, coal combustion or gasification and various other chemical processes. In this work, data are used to identify cold flow circulating fluidized bed's (CFCFB) multiple sub models and to combine them into a single nonlinear model such that solids circulation rate can be estimated from the move air flow and riser aeration fed to the device, and the total pressure drop developed across the riser at extremely different experimental conditions.;The present work begins with a complete black box model of a state-space description arising from the system identification and converts it into a model without any fictitious variable such that the interaction among the variables under consideration can be analyzed. Furthermore, this concept separates a state into stochastic and deterministic components which gives the nature of noise acting on the measurement device and rationalizes if there exists a certain relationship between independent and dependent variable. In this thesis, the state is a solids circulation rate. Independent parameters that comprise of aerations flow rates including move air flow, riser aeration and loop seal fluidization air are used to obtain deterministic component of a measured solids circulation rate. On the other hand, easily measurable dependent variables like the pressure drops across various sections of the machine are used to predict its stochastic counterpart.;A real time pressure drop model based on the Recursive Prediction Error Method (RPEM) is built to predict the split of move air flow between the standpipe and L-valve. The split estimate is of paramount importance while simulating the phenomenological model of the standpipe or in other applications, if required. Additional aeration fed across the various sections of standpipe act as the fluidization bias and their routes determination within the component may help to maintain their required level to assist in solids movement during operation while minimizing excessive flows. The path determination is also predicted using RPEM on a discrete time pressure drop model such that the user can operate them at the desired intensity according to their operating requirements.;Generally, a PID controller is not "portable", i.e., a controller designed for one plant is usually not applicable to another plant. To resolve this long-standing issue of portable controllable design, the controller scaling method can be used to control similar plants that are different only in gain and frequency scales, thus avoiding tedious control redesign. The adaptive PID control algorithm is then tested on the benchmark NETL CFCFB plant by controlling solids circulation rate according to the reference solids flow rate obtained from the Knowlton's correlation utilizing average voidage in a moving bed condition and the move air flow.;The optimal control of solids circulation rate affecting the heat and mass transfer characteristics which in turn impacts the efficiency of various chemical processes is necessary in CFB units. An example might be the catalytic systems that recirculate catalyst in a reaction/recirculation cycle. In the case of such units in which the addition of catalyst is small and need not be steady, the main solids flow-control problem is to maintain balanced inventories of catalyst in and controlled flow from and to the reactor and regenerator. This flow of solids from an oxidizing atmosphere to a reducing one, or vice versa, usually necessitates stripping gases from the interstices of the solids as well as gases absorbed by the particles. Steam is usually used for this purpose. The point of removal of the solids from the fluidized bed is usually under a lower pressure than the point of feed introduction into the carrier gas. The pressure is higher at the bottom of the solids draw-off pipe due to the relative flow of gas counter to the solids flow. The gas may either be flowing downward more slowly than the solids or upward. The standpipe may be fluidized, or the solids may be in moving packed bed flow with no expansion. Gas is introduced at the bottom (best for group B) or at about 3-m intervals along the standpipe (best for group A). The increasing pressure causes gas inside and between the particles to be compressed. Unless aeration gas is added, the solids could defluidize and become a moving fixed bed with a lower pressure head than that of fluidized solids. Thus, this observation leads to the fact that the gas velocity in the standpipe might be the main parameter to control the solids circulation rate. (Abstract shortened by UMI.).

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