Purge gas flow

Minimum purge gas flow rate required to prevent tip degradation when operating at mm down condition, even under maximum wind velocity,... 

Velocity seals are more recent developments in air seal design. They use conical baffles to redirect and focus the purge gas flow field just below the flare tip to sweep air from the flare stack. Some velocity seal designs can reduce the purge gas flow rate requirement to about 1/10 of the rate needed without the seal. Also, some velocity seal designs reportedly require only about 25 to 33 percent of the purge gas used in diffusion seals (AICliE-CCPS, 1998). More details about air (purge reduction) seals may be found in API RP 521 (2007). 

If, as illustrated in figure 12.6, the isothermal starting lines of the various curves do not coincide, then A< >o, A< cai, and Aheat transfer change between runs, for example, due to a variation in the purge gas flow or the fact that it is virtually impossible to relocate the crucible containing the sample exactly in the position used for the calibrant run (normally the reference crucible remains in place throughout a series of runs). Note that a similar correction should have been used in the computation of heat flow or area quantities if, in the example of figure 12.4, the isothermal baselines of the main experiment and the zero line were not coincident. 

Figure 3. Recoveries of selected compounds as a function of purge gas flow rate...

It is clear from experimental data that the rate of removal of the analyte can exceed the rate of supply. Hence there is an advantage to be obtained in rapid heating (e g. 1000 K s ) and stopping the purge-gas flow during atomization. 

Figure 15. Time evolution of cell HFR at different cell temperatures and for various purge gases. The purge gas flow rate was 4.5 L/min. (reproduced with permission from Tajiri et at.33)...

The tips of the test swabs were cut off and placed in labeled plastic vials. One ml of 1M HNO was added, the samples were agitated and allowed to leach for 15 min. A 10 yul aliquot was placed on the tantalum strip and the purge gas flow was started (At alone for Sb and Ar H2 for barium). The atomizer unit was automatically cycled through preset time for drying, ashing and atomization (at 2500°C). Absorbance values were recorded on the chart recorder and results were obtained by comparison with a standard curve prepared for each tantalum strip. 

An example of an actual physical activation procedure is as follows [176] the dried raw material is crushed, and sieved then the furnace temperature is increased at a rate of 10 [°C/min] up to 600°C for about 3 h, under inert purge gas flow. The resulting chars are then activated at 500°C-900°C for 10-60 min under purified C02 flush. In Figure 3.16 [175], a flow chart of the physical activation method is shown. 

If it is desired to carry out a chlorination, the apparatus is modified by replacing the dropping funnel and trap with a simple Y inlet tube attached directly to the reactor. One side of the Y is attached to the purge gas and the other to the chlorine source. If there is any question about the purity of the chlorine, it can be passed through a sulfuric acid wash. The chlorine flow rate during the reaction is about 300 ml./min. with no purge-gas flow. At the end of the reaction, the chlorine is purged from the system, and the product is removed as before. 

Significant temperature gradients in the furnace chamber will cause gaseous flow from hot to cold, which may apply a spurious force to the specimen pan. This is a more severe effect for chambers under moderate vacuum ( thermomolecular flow [3]). Purge gas flow direction may be an important consideration, in order to avoid condensation of gaseous products on the hangdown wire, or along the balance beam, as the gas flows out of the hot zone of the furnace. 

Figure Conversion Shift at T=721 K and 70 std cc/nain Purge Gas Flow Rate...

For PQ-USY and EX20P, the larger the purge gas flow rate, the higher the purity was obtained and the lower the yield was observed. 

---