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The VSP was developed as part of the DIERS project in the 1980s. The use of VSP in process safety plays a critical role in determining the appropriate sizing of emergency relief systems in industrial processes. The low thermal inertia of this apparatus addresses a common limitation found in other equipment, which is the underestimation of self-heat rate and adiabatic temperature rise. This feature allows laboratory-scale runaway reactions to accurately mimic the severity of those that occur in industrial vessels. This behavior is particularly valuable when validating computerized runaway reaction models, which typically incorporate kinetics, stoichiometry, heats of reaction, physical properties, and vapor-liquid equilibrium constants obtained from diverse sources.

The VSP can be utilized for various purposes, including distinguishing between materials that show homogeneous or non-foamy behavior during emergency relief by measuring the final void fraction in a test cell. It can also determine the impact of viscosity on homogeneous equilibrium flashing flow and measure the necessary parameters for emergency relief device design using graphical or analytical methods. Additionally, it enables direct sizing of emergency relief devices through top- or bottom-vented experiments.

Principle of Operation

VSP is classified as a low phi calorimeter, meaning its thermal inertia factor (Φ-factor) is close to 1, typically ranging from 1.05 to 1.15. To achieve this low thermal inertia factor, a larger volume of reactants, approximately 80 ml, is utilized in a thin-walled metal test cell (can) of 120 ml. However, this design compromises the pressure resistance of the test cell. To compensate for this, the test cell is placed inside an autoclave equipped with a pressure controller. The pressure difference between the test cell contents and the autoclave is kept below a predetermined level by controlling the pressure in the autoclave through nitrogen injections. To maintain adiabatic conditions in the test cell of the calorimeter, a guard heater is employed. This heater ensures that the ambient temperature remains equal to the temperature of the sample. As a result, this calorimeter not only tracks temperature but also pressure. Additionally, the test cell is equipped with a magnetic agitator, enabling operators to conduct reactions that closely resemble conditions found in industrial processes and allowing for experimental simulations of potential runaways.

Test Method

To gather essential data for analytical ERS sizing methods and experimental validation of proposed ERS designs, different test cells/methods are utilized. These cells acquire information including thermal and pressure data related to runaway reactions, data about the onset/disengagement of two-phase flow (foamy versus nonfoamy), viscosity information to distinguish between turbulent and laminar flow, and additional parameters. The test method is accordingly customized to fit various applications, which can potentially be:

  • Closed cell test
  • Open cell test for gas generation rate
  • Open cell test for tempering verification
  • Blowdown-top vent test for vapor-liquid disengagement characterization
  • Blowdown-bottom vent test for viscosity characterization
  • And other customized tests.

Data Interpretation

The rates of temperature and pressure rise, as well as peak reaction temperatures and pressures, are directly obtained from the experimental graphs. The rates of temperature rise can be converted into heat output rates, which can be used to determine the necessary cooling requirements for controlling the reaction at a specific set point. The rates of temperature rise are used in calculating emergency relief systems, while the peak pressures are involved in specifying containment systems. The heat of reaction for the process can be determined by using assumed or measured heat capacity data, as long as the testing cell does not vent before reaching the peak temperature.

In summary, you may obtain:

  • Adiabatic temperature rise and reaction heat.
  • Temperature rise rate and pressure rise rate.
  • Vapor-liquid phase equilibrium data – Antoine plot,
  • Reaction kinetic parameters such as activation energy, reaction order, and preexponential factor.
  • Onset T of the exothermic reaction, but with an appropriate safety factor.
  • Time to maximum rate (TMR) and TD24, i.e., the temperature at which the TMR is 24 hours
  • Temperature of no return (TNR).
  • Self-accelerating decomposition temperature (SADT)
  • Gas generation rate.
  • Tempering capability for an exothermic runaway reaction.
  • Identification of flow regime during vessel venting.
  • Viscosity feature and how it affects flow capacity in relief system.
  • Required data for sizing of ERS.

Why perform VSP test?

Performing vent sizing package tests is essential to ensure the safe design and operation of emergency relief system, especially for gas/vapor-liquid two-phase vent sizing. Vent sizing package tests involve the evaluation of the rate at which gases or vapors are released from containers or process systems during overpressure scenarios. These tests are crucial in determining the sizing and design requirements of pressure relief devices, such as relief valves and rupture discs, to prevent potential overpressure and protect the integrity of the equipment. By conducting vent sizing package tests, process safety professionals can accurately determine the maximum allowable process containment pressure and the recommended venting capacity. This information is necessary for ensuring that pressures within vessels and process systems are controlled within safe limits, minimizing the risks of explosions or structural failures. Vent sizing package tests provide valuable data for the design and installation of pressure relief systems, allowing industries to comply with regulatory requirements and improve overall process safety.

Why use us?

  • Our team of experts has deep knowledge and expertise in performing vent sizing package tests, ensuring accurate and reliable results.
  • We use state-of-the-art equipment and advanced technology to conduct precise measurements and data analysis method, ensuring comprehensive and accurate analysis of your reaction system.
  • Our thorough understanding of vent sizing standards and DIERS technology guidelines for runaway reactions ensures compliance with industry regulations and best practices.
  • Our thorough analysis and reporting provide you with valuable recommendations and insights to optimize your system’s performance and ensure its safe operation.


1. What is a vent sizing package apparatus?

The VSP was introduced in 1985 by DIERS for characterizing runaway reactions. The advantages of the VSP include a lightweight test cell and a resulting small Phi factor (low thermal inertia), as well as adiabatic pressure tracking and heat-wait-search capabilities. Moreover, the adiabatic operation permits direct application of temperature and pressure data in large-scale vessels.

2. How does the vent sizing package apparatus work?

The VSP can be considered as a bench-scale chemical reactor housed within a protective containment vessel. It allows for the addition or withdrawal of liquid or gaseous reactants at any point during an experiment. Tests can be conducted in true adiabatic mode, with capability of external heating or cooling.

3. Why is vent sizing important in process industries?

Proper vent sizing ensures the safety and integrity of vessels and process equipment. It prevents dangerous pressure build-up that could lead to equipment failure or other hazardous incidents. Adhering to vent sizing requirements is essential for mitigating risks and maintaining the overall safety of the operation.

4. Are there any specific regulations or codes governing vent sizing?

Yes, there are various industry codes and standards that provide guidelines for vent sizing, such as API 520 and API 521 in the petrochemical industry. These standards ensure compliance with safety regulations and help engineers design reliable pressure relief systems that meet industry requirements.

5. Can the vent sizing package apparatus be used for different industries?

Yes, the vent sizing package apparatus can be utilized in a wide range of industries, including petrochemical, pharmaceutical, food processing, and energy sectors. It is crucial for any industry that deals with processes involving pressure vessels to ensure proper vent sizing and pressure relief for safe operations.

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