Temperature control circulating type

The introduction of forced air circulation in an oven allowed the control up to 300 - 400°C and the air bath is the main type of column oven available today for laboratory gas chromatographs. Several types of temperature controllers are used to control the temperature of these ovens. They basically differ in terms of cost, accuracy, and flexibility. They are usually advertised as isothermal or temperature-programming controllers but all, in general, use the following basic types of control ... 

Isoteniscope. (a) Schematic diagram of the apparatus, which must be connected to the ballast bulb and manometer shown in Fig. 2. A temperature controller is also needed, or a commercial circulating-type temperature control bath can be used. 

Figure 5 illustrates the simplicity of the Dimersol Process. Dried feedstock, which may vary widely in propylene composition, is charged to the reactor where soluble catalyst is added in low concentration. Close reactor temperature control is obtained by circulation of the reaction mix through a cooler which may be of the air or water type. The reaction occurs at essentially ambient temperature, allowing for the exothermic heat of reaction, and at a pressure sufficiently high to maintain a liquid phase. 

The filter housing is placed inside a Carbolitc PF30 forced air circulation oven. A Carbolite type 201 Temperature Controller is supplied as an integral part of the control section of the oven. It is a digital instrument with PID control algorithm. 

Conveying-screen dryers are fabricated with conveyor widths from 0.3- to 4.4-m sections 1.6 to 2.5 m long. Each section consists of a sheet-metal enclosure, insulated sidewalls and roof, heating coils, a circulating fan, inlet air distributor baffles, a fines catch pan under the conveyor, and a conveyor screen (Fig. 12-51). Table 12-23 gives approximate purchase costs for equipment with type 304 staimess-steel hinged conveyor screens and includes steam-coil heaters, fans, motors, and a variable-speed conveyor drive. Cabinet and auxiliary equipment fabrication is of aluminized steel or stainless-steel materials. Prices do not include temperature controllers, motor starters, preform equipment, or auxiliary feed and discharge conveyors. These may add 75,000 to 160,000 to the dryer purchase cost (2005 costs). 

Commonly used types of grinding media are carbon steel, stainless steel, chrome steel, tungsten carbide, ceramic, or zirconia. Ball mills produce up to 50 ton/hr of powder substantially passing a 200-mesh screen. Temperature control can be achieved by the use of jacketed ball mills through which a heat transfer fluid is circulated. 

Chem Systems Inc. has been developing a three phase reaction system for methanol synthesis since the mid 1970 s (ref. 28). The original concept incorporated a liquid-fluidized-bed reactor. This research, which was funded by the Electric Power Research Institute, used particles of a heterogeneous catalyst, obtained by crushing pellets of a commercial Cu-ZnO-AljO type catalyst, which was fluidized by a circulating inert hydrocarbon liquid such as a mineral oil. One of the major benefits of the process over conventional synthesis is claimed (ref. 28) to be excellent temperature control of the reactions so that higher per pass conversions can be achieved, thereby reducing... 

Figure 5.26 Cells for liquid samples, showing just a few of the wide variety of types and sizes available. From left to right, top row standard 1 cm spectrophotometer cuvet with two optical faces and two frosted faces semimicro 0.7 mL cuvet 10 p,L submicro cell constant temperature cell with a jacket for circulating a temperature-controlling fluid. From left to right, bottom row 5 mm fluorometer cuvet (all four faces are optically clear) in-line continuous flow cell for process monitoring (sample flow is from bottom to top) 10 mm flow cell cylindrical cell. [Courtesy of Starna Cells, Inc., Atascadero, CA (www.starna.com).]...

Prevention of hot spots and efficient removal of the heat of reaction are very important because of the thermal instability of hypochlorites. The continuing reaction of hypochlorite to form unwanted byproducts is part of the discussion of emergency vent scrubbers (Section 9.1.10.3A), where it is more of an issue. Here, we note that the production of high-quality bleach depends on a consistent supply of chlorine in the tail gas and on adequate temperature control. The absorbing solution is therefore circulated by titanium centrifugal pumps around the reactor(s) through titanium coolers, usually of the plate-and-frame type. The recirculation of liquor in itself provides turbulence in the reaction zone, and the volume of circulation determines the maximum temperature possible in the reactor. A gas feed or the vaporization of a liquid chlorine supply may also be used to promote turbulence. 

Dryer. A shelf-type dryer with hot air circulation with a temperature control range of 392°F (200°C) or more is recommended. 

When using certain gases, it is desirable to maintain them at a set temperature for reasons related to the process and for safety. To do this, there are a number of different types of chillers and heaters. Circulating temperature controllers, use a temperature controlled liquid that is circulated through clam shell t)q)e jackets or coils placed around the cylinder. This type of system can have the actual control unit in a remote location and can easily be used in areas classified as hazardous. Another t5q)e controls the temperature of the air that is circulated through the cabinet. The air either transfers to or absorbs heat from the cylinder. Also available to heat cylinders are electrical resistance t5q)e devices. Some of these electrical devices cannot be installed into areas classified as hazardous. 

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