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Direct simulation of a malfunction using VSP2 (Vent Sizing Package 2)

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Direct simulation of a malfunction using VSP2 (Vent Sizing Package 2)

The VSP was introduced in 1985 by DIERS for the characterization of runaway reactions.  The advantages of the VSP are the lightweight test cell and the resulting small Phi factor (low thermal inertia), the adiabatic pressure tracking and the heat-wait-search. The adiabatic operation allows the temperature and pressure data to be applied directly to large scale vessels.

In the adiabatic reaction calorimeter VSP2, experiments for worst-case scenarios, such as a cooling-failure, can be simulated.  The runaway of the exothermic reaction under adiabatic conditions is allowed in order to determine the maximum temperature and pressure, the corresponding rise rates of temperature, pressure and gas production.

  • Known cases for “runaway” reactions are:
  • Overheating
  • Incorrect dosing
  • Unknown exotherms or decomposition reactions
  • Impurities
  • Incorrect mixing
  • Incorrect batch temperatures or pressure control

Knowledge of the temperature and gas production rates in such a failure scenario can be used to safeguard a process, develop contingency measures, or design a pressure relief device.

Other use cases outside of the design of pressure relief devices:

  • Determining a suitable temperature or pressure for a safety shutdown.
  • Determining suitable stoppers for catalytic or radical reactions.
  • Optimizing a process by varying the quantities used.

The experiment set-up consists of a pressure vessel with a volume of approx. 4 liters. A stainless steel vessel with a wall thickness of 0.2 mm and a free internal volume determined by gauging (to allow for internals and stirrer) of 110 ml is inserted into this as the measuring cell. This stainless steel vessel is thermally insulated from the environment. The system is brought to the storage temperature by means of an electric heater at the bottom of the measuring cell. Subsequently, the immediate environment of the system is brought up to the internal temperature of the measuring cell by means of another electric heater surrounding the container. In case of an exothermic decomposition reaction, the jacket heater continuously adjusts the temperature of the measuring cell to the sample temperature. Due to the insulation, as well as the low temperature difference between the measuring cell and the environment, almost adiabatic conditions can maintained. The measuring system can be operated either open or closed to the environment. When the system is closed, the pressure in the pressure vessel is adjusted to the internal pressure of the measuring cell by adding or discharging nitrogen. By maintaining a small pressure difference between the measuring cell and the pressure vessel, the thin-walled measuring cell is protected against deformation. Temperature and pressure in the test cell and in the pressure vessel are recorded during the reaction.

Sources:

1. Process Safety News Fall 2011.

2. Askonas, Burelbach, Leung, Fauske and Associates, 2000, THE VERSATILE VSP2: A TOOL FOR  ADIABATIC THERMAL ANALYSIS AND VENT SIZING APPLICATIONS, North American Thermal Analysis Society, 28th Annual Conference.

3. Fauske.com

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