Pneumatic controllers, configuration

Various configurations have been developed for muitistaging of fluidized beds using the pneumatically controlled downcomer, as shown in Fig. 38. Figure 38A shows the fundamental concept of multistaging of fluidized beds, with a downcomer between two adjacent beds, each downcomer being supplied with a separate stream of control gas. Consequently, there are as many control gas streams as there are stages. 

Fig. 38. Configurations for multistage fluidized beds using the pneumatically controlled downcomer. [After Kwauk, 1974 Liu and Kwauk, 1980 Liu et al., 1981.]...

Gas supplies are required for the carrier gas, and depending on the instrument configuration, perhaps also for the detector, for operating pneumatic controls such as... 

Finally a pneumatic active control device may be an interesting example of active control. The schematic diagram of control configuration is shown in Fig. 8.61. 

Another common interlock configuration is to locate a solenoid switch between a controller and a control valve. When an alarm is actuated, the solenoid trips and causes the air pressure in the pneumatic control valve to be vented consequently, the control valve reverts to either its fail-open or fail-close position. Interlocks have traditionally been implemented as hard-wired systems that are independent of the control hardware. But, for most applications, software implementation of the interlock logic via a digital computer or a programmable logic controller is a viable alternative. Programmable logic controllers (PLCs) used for batch processes are considered in Chapter 22 and Appendix A. 

Pneumatic nozzles prevail, but the spray pattern is somewhat different than found in a fluidized bed. In air suspension systems, the spray is usually a comparatively narrow, but solid cone of droplets. In a nozzle configured for perforated pan coating equipment, the initial spray pattern is also a solid cone. However, this pattern is flattened to an elliptical. shape by the u.se of. secondary atomizing air, delivered from openings adjacent to and angled slightly toward the primary atomized droplet stream (Fig. 10). In most nozzles, this secondary air is adjusted and controlled independently. The nozzle is... 

The screw-crammer system uses a conical hopper with a screw that is driven by a separate gear reducer and variable-speed drive motor. The output and effectiveness of the crammer are determined by the screw configuration and the available speed. The ram-type system, on the other hand, uses a pneumatic ram to stuff material into the screw. The ram is a piston-driven unit with the stroke timing adjustable by setting a series of timers located in the control panel. The feed section used by the ram system has an opening that is 12-14 times larger than that of a standard screw extruder. This allows low-bulk-density material to flow freely into the feed throat where the ram can compress it into the screw. Depending on the extruder size, the ram can compact materials with a force of 2000-9000 psi. 

The possibility of executing some statements is permanently determined by the hardware configuration. For example, execution of some switch-case statement is based on a control variable indicating deviation of the centre hall sensor installation position from the actual centre position of the pump. Such deviation never occurs unless one performs physical reconstruction of the pneumatic pump. 

Although there is no need to use a complementary controller on simple processes, it is nevertheless interesting to speculate on its configuration. If the process is a first-order lag, its complementary controller turns out to be proportional-plus-reset. In fact, pneumatic two-mode controllers are made this way, as shown in Fig. 4.13. 

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