III DIERS phase III large-scale intergral tests
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The principal findings of the experimental program and observations based on the results from the program are enumerated below: 1. The venting process is very oscillatory, especially for the top-vented tests. Slugs of liquid and puffs of vapor alternately enter the ventline. Rumbling can be heard and vibrations felt. The models recommended herein attempt to predict only the average behavior during the venting process with no attempt made to account for the oscillations. 2. Despite the oscillatory nature of the emergency relief process, numerous duplicate tests show the experimental results are reproducible. 3. Use of the bubbly (open system, drift flux) vessel model with uniform vapor generation for vessel hydrodynamics coupled with the homogeneous-equilibrium vent flow model will provide a safe design for reacting systems from a volumetric discharge rate perspective. An additi6nal degree of conservatism can be introduced by use of a homogeneous (zero vapor-liquid disengagement) vessel model for vessel hydrodynamics. 4. For pure, single component, nonviscous systems, the churn-turbulent (open system, drift flux) vessel model with uniform vapor generation for vessel hydrodynamics coupled with the homogeneous-equilibrium vent flow model will provide a safe design from a volumetric discharge rate perspective. It should be noted that trace quantities of impurities such as surfactants can drastically alter the vessel hydrodynamic behavior to that of a foamy system. 5. Reacting systems can exhibit churn-turbulent or nonfoamy vessel hydrodynamic behavior; however, it is not possible at present to predict this behavior without testing. In the absence of vessel vapor-liquid disengagement test data under prototypic emergency relief conditions, the conservative bubbly or homogeneous vessel models should be assumed for vessel hydrodynamics. 6. For tall vessels at low vapor generation rates, hydrostatic head effects can lead to top-biased vapor generation. The effect of top-biased vapor generation for systems governed by nonfoamy, nonviscous, churn-turbulent vessel flow hydrodynamics can be significantly increased vapor-liquid disengagement. Use of uniform vapor generation vessel hydrodynamic models for this situation can lead to ultraconservative vent sizes. To avoid this ultraconservatism, use of a nonboiling height vessel model [1, 2] which includes hydrostatic head effects is recommended when appropriate. For systems governed by bubbly vessel flow hydrodynamics, the effect of top-biased vapor generation is minimal. At higher
the DIERS Program, open system drift flux models1 [1,2] were proposed to predict the liquid swell or vapor-liquid disengagement in the vessel. Two distinct flow regimes had been observed: 1. a bubbly or foamy regime characterized by small individual spherical bubbles which were observed at low vapor generation rates and in foamy and viscous systems and 2. a nonfoamy or churn-turbulent regime characterized by coalesced bubbles forming cylindrical vapor pockets rising along their axis which were observed at higher vapor generation rates in nonfoamy and nonviscous systems. For calculating mass discharge rates through the vent line, several conventional models had been selected2 [3, 4]: 1. a homogeneous-nonequilibrium model for short vent nozzles and 2. a slip-equilibrium model for long vent lines. The vessel and vent hydrodynamic models were tied together or coupled by a material balance written at the top of the vessel called the coupling equation [I]. Simultaneous solution of the vessel and vent model equations with the coupling equation allows calculation of the quality, vent mass flux and volumetric discharge rate at any time. The first phase of the DIERS Phase III Large-Scale Integral Tests3 consisted of a series of nonreacting large-scale (32-liter and 2200-liter—8.5-gal and 588-gal) blowdown tests to verify that: 1. bubbly and churn-turbulent (open system, drift flux) vessel models could be used to model closed system hydrodynamic behavior in the vessel, 2. the proper ventline hydrodynamic models were being used, 3. the coupling equation approach was valid, and 4. the effects of scale were being accounted for correctly. The second phase of the DIERS Phase III Large-Scale Integral Tests3 consisted of a series of styrene polymerizations in ethylbenzene solvent which were also run at both 32-liter and 2200-liter (8.5-gal and 588-gal) sizes to verify the applicability of the models for chemically reacting systems.
The principal findings of the experimental program and observations based on the results from the program are enumerated below: 1. The venting process is very oscillatory, especially for the top-vented tests. Slugs of liquid and puffs of vapor alternately enter the ventline. Rumbling can be heard and vibrations felt. The models recommended herein attempt to predict only the average behavior during the venting process with no attempt made to account for the oscillations. 2. Despite the oscillatory nature of the emergency relief process, numerous duplicate tests show the experimental results are reproducible. 3. Use of the bubbly (open system, drift flux) vessel model with uniform vapor generation for vessel hydrodynamics coupled with the homogeneous-equilibrium vent flow model will provide a safe design for reacting systems from a volumetric discharge rate perspective. An additi6nal degree of conservatism can be introduced by use of a homogeneous (zero vapor-liquid disengagement) vessel model for vessel hydrodynamics. 4. For pure, single component, nonviscous systems, the churn-turbulent (open system, drift flux) vessel model with uniform vapor generation for vessel hydrodynamics coupled with the homogeneous-equilibrium vent flow model will provide a safe design from a volumetric discharge rate perspective. It should be noted that trace quantities of impurities such as surfactants can drastically alter the vessel hydrodynamic behavior to that of a foamy system. 5. Reacting systems can exhibit churn-turbulent or nonfoamy vessel hydrodynamic behavior; however, it is not possible at present to predict this behavior without testing. In the absence of vessel vapor-liquid disengagement test data under prototypic emergency relief conditions, the conservative bubbly or homogeneous vessel models should be assumed for vessel hydrodynamics. 6. For tall vessels at low vapor generation rates, hydrostatic head effects can lead to top-biased vapor generation. The effect of top-biased vapor generation for systems governed by nonfoamy, nonviscous, churn-turbulent vessel flow hydrodynamics can be significantly increased vapor-liquid disengagement. Use of uniform vapor generation vessel hydrodynamic models for this situation can lead to ultraconservative vent sizes. To avoid this ultraconservatism, use of a nonboiling height vessel model [1, 2] which includes hydrostatic head effects is recommended when appropriate. For systems governed by bubbly vessel flow hydrodynamics, the effect of top-biased vapor generation is minimal. At higher
the DIERS Program, open system drift flux models1 [1,2] were proposed to predict the liquid swell or vapor-liquid disengagement in the vessel. Two distinct flow regimes had been observed: 1. a bubbly or foamy regime characterized by small individual spherical bubbles which were observed at low vapor generation rates and in foamy and viscous systems and 2. a nonfoamy or churn-turbulent regime characterized by coalesced bubbles forming cylindrical vapor pockets rising along their axis which were observed at higher vapor generation rates in nonfoamy and nonviscous systems. For calculating mass discharge rates through the vent line, several conventional models had been selected2 [3, 4]: 1. a homogeneous-nonequilibrium model for short vent nozzles and 2. a slip-equilibrium model for long vent lines. The vessel and vent hydrodynamic models were tied together or coupled by a material balance written at the top of the vessel called the coupling equation [I]. Simultaneous solution of the vessel and vent model equations with the coupling equation allows calculation of the quality, vent mass flux and volumetric discharge rate at any time. The first phase of the DIERS Phase III Large-Scale Integral Tests3 consisted of a series of nonreacting large-scale (32-liter and 2200-liter—8.5-gal and 588-gal) blowdown tests to verify that: 1. bubbly and churn-turbulent (open system, drift flux) vessel models could be used to model closed system hydrodynamic behavior in the vessel, 2. the proper ventline hydrodynamic models were being used, 3. the coupling equation approach was valid, and 4. the effects of scale were being accounted for correctly. The second phase of the DIERS Phase III Large-Scale Integral Tests3 consisted of a series of styrene polymerizations in ethylbenzene solvent which were also run at both 32-liter and 2200-liter (8.5-gal and 588-gal) sizes to verify the applicability of the models for chemically reacting systems.
