Packed thermocouple

Column Diameter 4 mm Column Packing 15% Squalane on 100-120 BS Celite Column Temperature 75°C Thermocouple 10 cm below Injection Point Sample Chloroform Vapor in Air at 125 C... 

The reactor is an 8-mm i.d. quartz tube located in a tube furnace. The quartz tube is packed with 20 by 30 mesh catalyst particles. The catalyst bed is positioned in the tube using quartz wool above and below the bed, with quartz chips filling the remainder of the reactor. The furnace temperature is controlled by a thermocouple inserted into the reactor tube and positioned about 3 mm above the catalyst bed. This allows operation at constant feed temperature into the reactor. 

In this section a short description of a comparison between experimental and simulation results for heat transfer is illustrated (Nijemeisland and Dixon, 2001). The experimental set-up used was a single packed tube with a heated wall as shown in Fig. 8. The packed bed consisted of 44 one-inch diameter spheres. The column (single tube) in which they were packed had an inner diameter of two inches. The column consisted of two main parts. The bottom part was an unheated 6-inch packed nylon tube as a calming section, and the top part of the column was an 18-inch steam-heated section maintained at a constant wall temperature. The 44-sphere packed bed fills the entire calming section and part of the heated section leaving room above the packing for the thermocouple cross (Fig. 8) for measuring gas temperatures above the bed. 

Heat transfer from the shelves to the sublimation front depends on the pressure and the distance between shelf and product (Fig. 1.58). Mass transfer (g/s) increases with the pressure, but also depends on the flow resistance of the already dry product and of the packing of the bones. If the maximum tolerable Tke is defined, the drying time depends only on the two processes mentioned above. It cannot be shortened under a given geometric situation and the chosen Tke. This method of Tkt control does not require thermocouples, and does not contaminate the product. 

The reaction was carried out in a flow system using a fixed-bed reactor made of Pyrex (25 mm x 400 mm) provided with an internal thermocouple well. The catalyst was packed in the reactor and was pretreated in situ with hydrogen at 535°C for 2 hr. The mesh size used was 10-40. 

The pyrolysis apparatus consists of a vertical, electrically-heated Vycor tube (25 mm. I.D.) packed with 6-mm. lengths of Pyrex tubing (10 mm. O.D.) and mounted in an electric furnace about 45 cm. long (Notes 1 and 2). Attached to the top is a 100-ml. dropping funnel with a pressure-equalizing side arm that has an inlet for nitrogen (Note 3). A thermocouple well inside the tube holds a movable thermocouple and extends to the bottom of the heated section (Note 4). The bottom of the reactor is fitted to a 500-ml. side-arm flask packed in ice. The side arm leads to tw o traps in series cooled in ice and to a final trap cooled in a bath of dry ice and acetone (Note 5). 

Figure 5.1-6. Design of single autoclave [13]. a, Connection b, motor c, packing elements d, thermocouple e, bursting disc port f, ethylene and initiator feed g, product outlet.

Figure 17.24. Types of reactors for synthetic fuels [Meyers (Ed.), Handbook of Synfuels Technology, McGraw-Hill, New York, 1984], (a) ICI methanol reactor, showing internal distributors. C, D and E are cold shot nozzles, F = catalyst dropout, L = thermocouple, and O = catalyst input, (b) ICI methanol reactor with internal heat exchange and cold shots, (c) Fixed bed reactor for gasoline from coal synthesis gas dimensions 10 x 42 ft, 2000 2-in. dia tubes packed with promoted iron catalyst, production rate 5 tons/day per reactor, (d) Synthol fluidized bed continuous reactor system for gasoline from coal synthesis gas.

In order to protect the thermocouple against chemical or mechanical damage, it is normally enclosed in a sheath of mineral packing or within a thermowell (Fig. 6.24). Any material which contains the junction should be a good conductor of heat on the one hand, but an electrical insulator on the other. A potentiometric converter is frequently employed to convert the thermocouple signal to the standard 4-20 mA current range prior to further processing and control room presentation. The extension wires which connect the thermocouple element to the control room should have similar thermoelectric properties to those of the thermocouple junction wires. 

The metals were either packed in high-purity graphite and heated in an Ar atmosphere or heated in a pure-nitrogen atmosphere up to 2500 K in a cold-wall autoclave. The temperature was recorded by thermocouples or two-color IR pyrometers. Gas pressures (mbar range up to 40 bar) were measured with piezoelectric gauges. The conditions were recorded on a PC equipped with an A/D converter. Extended heating periods could be maintained without any change in experimental conditions. 

Fig. 3.4. Oxygen scavenger column. The column is packed with Ridox or BTS Catalyst. The heating tape and thermocouple wire are used during regeneration. Water which collects during regeneration can be bled out through the valve at the bottom.

The catalyst was 100 ml of American Cyanamid HDS-3A, a 1/16-inch diameter extrudate of nickel-molybdenum-alumina. It was diluted with inert, granular alpha-alumina to provide a bed depth of 18 inches in the middle section of a 0.96-inch ID vertical reactor with a 5/16-inch OD internal thermocouple well. The catalyst was progressively more dilute toward the top of the bed to minimize exothermic temperature effects, and end sections were packed with alpha-alumina to provide for preheat and cooling zones. 

A cartridge heater is inserted in the cover plate of the packed-bed reactor [277]. The base plate provides conduits to the microreactor. The outlets are standard high-pressure fittings. Thermocouples are inserted into the slurry feed channels. 

Figure 2. Locations of axial and radial measuring devices in reactor. Key , catalyst bed , inert packing 1-23, thermocouples and sampling to gas analyzer and 30, 31, sampling to gas chromatograph.

The thermocouple wires left the reactor radially through the wall. Six such pellets were situated along the axis equidistantly in a reactor with particles of 2.3 mm and 5.2 mm (corresponding D/dp = 10.4 and 4.6). The calculated flow profiles for botn packings are presented in Figure 9, typical measured profiles are plotted in FigureslO and 11 for temperatures. 

Although two reactors are shown in Figure 1, they were not used simultaneously. The reactor shown in the center was the fixed bed reactor which is of primary interest in this contribution. It consisted of a 12.7 mm diameter X 250 mm long steel tube packed with 40/50 mesh catalyst (0.3 mm average particle diameter). The reactor was heated by a nichrome wire coil and was well insulated. The coil spacing was adjusted and was packed in insulation with the intent of making the reactor crudely adiabatic. A variac controlled heater on the reactor inlet and a thermocouple sensor kept the feed to the reactor at the nominal reaction (or feed inlet) temperature of 400°C. The tube of the fixed-bed, reactor was fitted with 12 thermocouples to record the axial temperature profile in the bed (Figure 1). 

Testing. Studies of the catalytic activity and selectivity were conducted in a tubular unit reactor. Since this is a reactor consisting of a catalyst-packed tube of dimensions identical with those of a single tube inside a large-scale reactor, it becomes possible to reproduce the industrial conditions A thermocouple was placed in the catalyst bed, A detailed description of the experimental procedure has been presented elsewhere [4]. The tube was packed with two layers of catalyst (0.6 dm3 each). The total bed length was about 2.65 m. The feed was o-xylene of purity 98.4 wt.%. The air flow rate was 3.5 m3(STP)/h. The calcined catalyst samples were tested under conditions of continuous operation over a period of a couple of weeks during this period the concentration of o-xylene was varied from 20 to 70 g/m3(STP). 

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