Vented tube furnace

A similar process with lower productivity is used for the synthesis of high-purity B4C of controlled stoichiometry. At temperatures of 1600-1800 C, hydroboric acid reacts with acetylene black, high purity sugar, or ethylene glycol in a vented tube furnace ... 

High-purity fine boron carbide powder with an average particle size of 0.5-5 pm has been synthesized by the reaction of boric add with a carbon-containing compound in a vented tube furnace [134]. 

Pyrrolysis of the sample is performed in a tube furnace. A sample of the polymer (ca. 1 g) is placed in a crucible and mounted in the furnace. The ends of the furnace are sealed save for the inlet for the inert gas supply and the gas outlet pipe which must be vented into the fume-hood. The sample is then heated at the required temperature (e.g. 400°C for 3 h) and allowed to cool to room temperature under a nitrogen atmosphere. 

The test specimen is placed in a quartz boat and burnt in a horizontal tube furnace. Combustion gases travel directly into the animal exposure chamber which is a hemispherical PMMA vessel of 4.2 dm mounted on a base of 203 mm dia. A vent bubbler on the top of the chamber serves for discharging the overpressure without any ingress of fresh air. A sampling port permits the chemical analysis of the gas mixture (Fig. 4.25). 

The difference between the improved process and the traditional process is shown in Fig. 9.9. The ammonia is condensed in the separator 3, residual vent gas is heated in the interchanger 1 and is divided into two parts, one of them is sent into the tube furnace to burn, and another is heated by interchanger 4 and the cooler 5, and is then sent into the auxiliary converter 6 to react on Ru catalyst. After the reaction, the gas is cooled by interchanger 4, and is then sent by the blower 7 to mix with vent gas from main converter, where the ammonia is separated by the separator 3. 

FB boilers are similar to SM boiler designs except that, instead of a fully immersed furnace tube, they have a bottom furnace (with a crowned combustion chamber) that sits on a refractory floor. Two-pass fire tubes (smoke tubes) connect the combustion chambers to the gas exit vent (smoke stack). 

After the flue gas leaves the combustion chamber, most furnace designs extract further heat from the flue gas in horizontal banks of tubes in a convection section, before the flue gas is vented to the atmosphere. The temperature of the flue gases at the exit of the radiant section is usually in the range 700 to 900°C. The first few rows of tubes at the exit of the radiant section are plain tubes, known as shock tubes or shield tubes. These tubes need to be robust enough to be able to withstand high temperatures and receive significant radiant heat from the radiant section. Heat transfer to the shock tubes is both by radiation and by convection. After the shock tubes, the hot flue gases flow across banks of tubes that usually have extended surfaces to increase the rate of heat transfer to the flue gas. The heat transferred in the radiant section will usually be between 50 and 70% of the total heat transferred. 

A chromel-alumel thermocouple is used to monitor the temperature of the ceramic boat and also acts as a sensor for the furnace temperature controller. A constant flow of clean, dry N2 gas is maintained through the quartz tube. The metal vapor is carried out of the furnace with N2 and condensed to form a polydisperse aerosol. The primary aerosol is diluted by mixing with a filtered dry air stream. The diluted aerosol is then routed to the chamber as required and the excess aerosol is vented out through a glass fiber filter. 

In the third method, Chiu and Beattie (148) used an interface constructed from a T-shaped glass tube and a constant volume sampler, such as is shown shown in Figure 8.18. One arm of the tee was connected to the furnace tube of the thermobalance, whereas the other was welded to the stopcock of the sampler. The third arm was either vented into the atmosphere or connected to a vacuum pump. The sampler was connected to the heated inlet of the mass spectrometer. A 3-L gas reservoir and a gold leak tube were placed between the inlet and the ion source. To achieve the highest sensitivity, one can directly connect the sampler to the ion source through a direct probe attachment. 

FIGURE 8.1 Pyrolysis unit, Scientific Glass Engineering (SGE) Pyrojector. 1. Sample loading area, 2. Quartz sample tube (reaction zone), 3. Sample loading cover interlock, 4. Valve body, 5. O-ring type seal, 6. Carrier gas inlet, 7. Check valve, 8. Carrier gas vent, 9. Valve spindle, 10. Heat deflectors, 11. Micro furnace,... 

Caution. The exhaust gas from the furnace should be passed through a wash bottle of water (which also serves to monitor the flow rate), and vented outside. In addition, it is advisable to place the gas inlet at the same side of the quartz tube as that used for the introduction of the specimen. This prevents gas which has passed through the tube and may contain Cd and/or Se (or their compounds) from venting into the laboratory. 

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