The VSP is a state of the art laboratory tool which
allows a hazards assessor to collect precise "off-normal" process design data.
Using the VSP calorimeter experiments can be performed
to model upset scenarios such as loss of cooling, loss of stirring, mischarge
of reagents, mass-loaded upset, batch contamination and fire exposure heating.
As these experiments are performed prior to taking a
chemical process from the small lab scale onto the pilot plant and
manufacturing scales the data needs to replicate the cooling properties of a
large scale vessel. This is achieved as the calorimeter centers around a 120ml
thin walled metal test cell which is kept truly adiabatic. A set of fast acting
heaters prevent heat loss from the system. Due to the low mass of the test cell
relative to the reactive mass, the system has a low Phi factor which allows the
direct collection of quality data that does not need to be manipulated after
the experiment to correct for the heat energy that is adsorbed by the cell
walls.
As the metal test cell is made with thin walls the
pressure that is developed inside will eventually bulge the cell. However this
issue is overcome by compensating for the pressure inside the vessel cell by
applying an equal pressure to the outside of the can thus keeping the ?P across
the cell wall to an acceptable level. This ingenious design first implemented
by FAI in adiabatic calorimetry allows a system with a high pressure rise rate
to be studied without the test cell rupturing.
It is these three crucial factors (truly adiabatic, low
phi and high pressure rise rate) that make the VSP a perfect apparatus for
modeling upset scenarios on the large scale. Tests can be run in a "closed" or
"open" test cell mode, allowing for direct venting simulation.
The data that is directly collected from the reactive
system is
- Adiabatic rate of temperature rise
- Adiabatic rate of pressure change
This data then allows the calculation of
- " Heat of reaction or mixing (DELTAHr)
- Total adiabatic temperature rise
(DELTATadibatic)
- Onset temperature
- Vapor pressure - temperature relationship
- Self-accelerating decomposition temperature
- Time to maximum rate (TMR)
Some of these parameters are then used to allow the
direct calculation of process scale relief vent sizes, quench tank designs and
other relief system design parameters related to process safety management.
The VSP2 is a true adiabatic safety calorimeter for
process hazard characterization.
| ARSST |
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See also the information
about the ARSST from Fauske |
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