Feed system, fast-response

In this paper we will first describe a fast-response infrared reactor system which is capable of operating at high temperatures and pressures. We will discuss the reactor cell, the feed system which allows concentration step changes or cycling, and the modifications necessary for converting a commercial infrared spectrophotometer to a high-speed instrument. This modified infrared spectroscopic reactor system was then used to study the dynamics of CO adsorption and desorption over a Pt-alumina catalyst at 723 K (450°C). The measured step responses were analyzed using a transient model which accounts for the kinetics of CO adsorption and desorption, extra- and intrapellet diffusion resistances, surface accumulation of CO, and the dynamics of the infrared cell. Finally, we will briefly discuss some of the transient response (i.e., step and cycled) characteristics of the catalyst under reaction conditions (i.e.,... 

Stanton and Bremer (378) demonstrated the superiority of the response of the analyzer/temperature control system over both a temperature control and a direct analyzer control in a 72-tray deisobutanizer. A temperature control alone produced a product purity offset due to variations in nonkeys an analyzer-only control had a long lineout time and was sensitive to feed flow changes. An analyzer/temperature control gave a fast response and eliminated all these ill effects. Other favorable experiences with analyzer/temperature control have also been reported (25, 89, 203, 287, 379). Two references (25, 379) contain in-depth descriptions of tuning considerations and of other accessories that can improve system operation, particularly if the analyzer control is performed through a computer system. 

During periodic operation, the system is forced to follow changes in the input. So-called cycling of the feed is the case where oscillations are applied to the concentrations of the reactor feed. Whether the input is followed perfectly depends on the dynamic behavior of the system. The most important parameter describing the dynamic behavior is the characteristic response time A small value of corresponds to a fast-responding system. Based on the period of the forced oscillation and characteristic response time of the system three different periodic operations can be distinguished [27,45] ... 

In the front-end or gas section of the plant, i.e. the Feed Gas Preparation (FGP) and Gas-to-Liquids (GTL) units, the system dynamics are fast, typically less than a few minutes. The steam system, although with a very high design capacity, has even faster system dynamics, in the order of one minute. These fast proeess response dynamies mean that special attention needs to be given to the design of the regulatory eontrol. 

If a fast-acting temperature-measuring device is available, which has a gain of 0.2 psi/°C, select the gains for various kinds of pneumatic controllers that use air pressure for the input and output signals. Then, calculate the response of the closed-loop systems to a 20°C step change in the feed temperature. 

Al-Haj Ali et al. [5,6] developed different types of linear time invariant models by system identification, which adequately represent the fluidized-bed drying dynamics. MBC techniques such as IMC and model predictive control (MPC) were used for the designing of the control system. Simulations with multivariable MPC strategy provided robust, fast, stable, and non-oscillatory closed loop responses. A stationary form of Kalman filter was designed to estimate the particle moisture content (state observer). Performance studies showed that the Kalman filter provided satisfactory estimates even in the presence of significant noise levels and inaccurate initial states feed to the observer. 

---