Vent Size Package VSP

The original Vent Size Package (VSP) became available first in the United States, and is currently distributed by Fauske and Associates. A very similar type of equipment, called PHI-TEC, is available in Europe. 

The primary application of the VSP is to obtain data necessary to calculate the vent design (size and relief setting) for emergency venting of nonvolatile and reactive runaway systems. The calculated vent design is to limit the maximum pressures at the point of emergency venting to acceptable levels. A secondary application is to provide thermal stability data for reactive systems. 

The data required for the emergency vent design includes [191] (1) the thermokinetic and pressure history monitored under near adiabatic conditions, (2) the character of the type of vented system (vapor, gassy, or hybrid), (3) the phase of the vented material (vapor, liquid, or two-phase), and (4) the degree of two-phase disengagement (turbulent, bubbly, or homogeneous). To determine these characteristics, the VSP defines the system as viscous (100 cp) or nonviscous, and also whether or not it has a foaming tendency. 

A disadvantage is that the maximum sample size is only 100 cm3 which may not, then, be fully representative. Extrapolation of test results to plant facilities must therefore be carried out with good judgment [193]. 

The pressure control system can equilibrate pressure change rates up to 20 bar/s. The outside guard heater can cope with temperature changes up to 100°C/min. A heat loss rate of less than 0.1°C/min can usually be achieved below 350°C and 25 bar [194]. The tests are run with either open or closed test cells in a closed outer bomb, which can be vented under specified conditions. The containment vessel can withstand pressures up to 100 bar. The use of a closed test cell results in the most severe pressure and temperature changes. 

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Vent Sizing Package (VSP) The VSP is an extension of ARC technology. The VSP is a bench-scale apparatus for characterizing runaway chemical reactions. It makes possible the sizing of pressure relief systems with less engineering expertise than is required with the ARC or other methods. 

The vent sizing package (VSP) was developed by Fauskes Associates, Inc. The VSP and its latest version VSP2 employ the low thermal mass test cell stainless steel 304 and Hastelloy test cell with a volume of 120 ml contained in a 4-1, high-pressure vessel as shown in Figure 12-13. The typical ([t-factor is 1.05-1.08 for a test cell wall thickness of 0.127-0.178 mm. Measurements consist of sample temperature Tj and pressure Pj, and external guard temperature Tj and... 

Figure 12-13. Vent sizing package (VSP) apparatus. (Source Fauskes Associates Inc.)...

Several commercial calorimeters are available to characterize runaway reactions. These include the accelerating rate calorimeter (ARC), the reactive system screening tool (RSST), the automatic pressure-tracking adiabatic calorimeter (APTAC), and the vent sizing package (VSP). Each calorimeter has a different sample size, container design, data acquisition hardware, and data sensitivity. 

Figure 8-9 Runaway reaction temperature data acquired using the vent sizing package (VSP).

When a runaway reaction occurs within a reactor vessel, two-phase flow should be expected during the relief process. The vent sizing package (VSP) laboratory apparatus described in chapter 8 provides the much needed temperature and pressure rise data for relief area sizing. 

Experimental data can be obtained from the DSC and from reaction calorimeters for the conditions of the desired reactions, and from the DSC, the ARC, the Reactive System Screening Test (RSST—Fauske and Associates) and from the Vent Size Package (VSP) for conditions allowing undesired reactions. The pressure effect can be studied using the ARC or DIERS methods. From the results of these tests, the rate of temperature rise and the maximum acceptable conditions for specific equipment can be calculated. The same holds for the pressure rise rate. 

FIGURE 3.15. Vent Size Package (VSP) Test Cell. 

The Reactive System Screening Tool (RSST) was described in Section 33.2.7. This apparatus is a relatively recent development. Therefore, only limited literature data are available regarding the application of results from this equipment for direct scale-up of reactor systems. The Vent Size Package (VSP) is discussed further in Section 3.3.2.6. 

The Vent Size Package (VSP) apparatus was described in Section 3.3.2.6. The relatively small 100-cm3 test cell size implies that the samples tested may not be fully representative of commercial scale systems in some cases. The contents of the test vessel may be stirred, although the stirring facilities are not... 

Testing includes screening (e.g., literature research, mixing calorimetiy, thermodynamic calculations, estimation of heats of reaction, DSC, flash point calculations), quantitative assessment (e g., accelerated rate calorimetry, specialized calorimetry), and scaleup (vent size packaging [VSP], modeling, reaction calorimetry). 

FIGURE 3.4 (See color insert following page 40). The vent sizing package (VSP) test of cyclopentadiene reveals a slow exotherm upon reaching 25°C that accelerates to a violent decomposition after 80 min. The decomposition caused the test cell to rupture. These data show that the consequences of a runaway reaction would be severe. 

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