Adiabatic Calorimetry & Relief Vent Sizing

Fauske & Associates, LLC (FAI) was the principal research contractor for the Design Institute for Emergency Relief Systems (DIERS), an extensive R&D program sponsored by 29 companies under the auspices of AIChE and completed in 1985.  Company founder, Dr. Hans K. Fauske served as the principal investigator and overall leader of the DIERS research project.  A primary purpose of that effort was evaluation of emergency relief vent requirements, including energy and gas release rates for systems under upset conditions and the effect of two phase flow on the emergency discharge process.

The DIERS program resulted in the development of a bench scale low thermal inertia adiabatic calorimeter, which was first commercialized as the Vent Sizing Package (VSP^TM). Later improvements led to the VSP2^TM. The Reactive System Screening Tool (RSST ^TM) was introduced by FAI in 1989 to provide an easy, inexpensive approach to the DIERS testing method. Recent enhancements led to the Advanced RSST (ARSST^TM) in 1999. FAI uses the DIERS-based VSP2^TM and ARSST^TM calorimeters to characterize chemical systems and design emergency pressure relief systems. Both instruments provide vent sizing data that are directly applicable to the process scale.

Background

Fauske & Associates, LLC's (FAI) Advanced Reactive System Screening Tool^TM (ARSST) is a low thermal inertia calorimeter used to obtain critical upset process design data.  FAI offers the ARSST along with options for customization such as a high-pressure vessel and flow regime detector, as well as commonly used items such as test cells, heaters, glands and thermocouples. At FAI, we not only utilize the ARSST^TM in our fully equipped hazards laboratory but we also manufacture and sell the calorimeter for use by our clients.

The ARSST^TM is based on DIERS two-phase methodology which is recognized by OSHA as an example of good engineering practice. This easy-to-use device is also capable of generating low phi-factor data for DIERS vent sizing and is an excellent tool for industry as well as any university engineering lab for research or unit operation studies.

ARSST^TM tests are used to model such upset scenarios as loss of cooling, loss of stirring, mischarge of reagents, mass-loaded upset, batch contamination and fire exposure heating.  This easy to use and cost-effective calorimeter can quickly and safely identify potential reactive chemical hazards in the process industry.  ARSST^TM data yields critical experimental knowledge of the rates of temperature and pressure rise during a runaway reaction, thereby providing reliable energy and gas release rates which can be applied directly to full scale process conditions. 

The ARSST^TM typically utilizes a sample size of 5-10 grams in a lightweight glass test cell with a volume of approximately 10 ml.  The test cell is outfitted with a belt heater (used to heat the sample through a preprogrammed temperature scan) and then installed in 350 ml containment vessel.  Tests are typically run using open test cell methodology.  In this test configuration, the test cell is vented to the containment vessel.  Volatilization of the test sample is prevented by imposing an inert  backpressure on the containment vessel.

Benefits

The ARSST^TM enables users to quickly obtain reliable adiabatic data which can be used for a variety of safety applications including characterization of material compatibility, thermal stability and reaction chemistry.  Test data includes adiabatic rates of temperature and pressure change which, due to the low thermal inertia, can be directly applied to process scale to determine relief vent sizes, quench tank designs and other relief system design parameters related to process safety management.

Features

• User friendly
• Easy setup for fast test turnaround
• Quickly screen new and existing processes for thermal hazards
• Scanning and isothermal modes
• Reliable results for thermal hazard assessment
• Open or closed cell testing (obtain vapor pressure data from closed cell testing)
• Small sample size
• Lightweight glass test cell with good mixing
• Compatible with Flow Regime Detector (FRED) equipment for vent sizing applications (FRED distinguishes between foamy and non-foamy behavior)

Applications

• Obtain complete chemical systems data:
  -    Critical temperature
  -    Kinetic parameters

• Estimate process safety parameters including:
  -    Onset temperature
  -    Temperature & pressure rise rates
  -    Adiabatic temperature rise
  -    Heat of reaction and mixing
  -    Tempering temperature
  -    Time to maximum rate (t_mr)
  -    Self-accelerating decomposition temperature (SADT)

• Vent sizing
• Emergency relief system design
• Accommodates handling of energetics and pyrotechnics

Background

Fauske & Associates, LLC's (FAI) Vent Sizing Package 2™ (VSP2™) is a low thermal inertia adiabatic calorimeter used for process hazard characterization that utilizes state-of-the-art DIERS technology to obtain critical upset process design data.  It is the commercial version of the original DIERS bench scale apparatus. At FAI, we not only utilize the VSP2^TM in our fully equipped hazards laboratory but we also manufacture and sell the calorimeter for use by our clients.

Its versatile and innovative design allows the VSP2^TM to simulate upset (abnormal) conditions which might lead to a runaway chemical reaction (e.g. loss of cooling, loss of stirring, mischarge of reagents, mass-loaded upset, batch contamination, fire exposure heating, etc).  Resulting temperature and pressure rise rates are directly scalable since it is a low thermal inertia (phi-factor) apparatus. 

Benefit

The VSP2^TM utilizes established DIERS technology to identify and quantify process safety hazards so they can be prevented or accommodated by process design.  

Test data includes adiabatic rates of temperature and pressure change which, due to the low thermal inertia, can be directly applied to process scale to determine relief vent sizes, quench tank designs and other relief system design parameters related to process safety management.  Adiabatic data obtained with the VSP2^TM can be used to characterize reactive chemical and consequences that could occur due to process upset conditions.

Features

The versatile configurations offered by the VSP2^TM design directly simulates process conditions including:

• Loss of cooling or agitation
• Accumulation or mischarge of reactants
• Contamination of batch
• Thermally initiated decomposition
• Resident incubation time
• In-situ liquid/gas dosing or sampling

Applications

Use of the VSP2^TM can help users obtain complete chemical system data such as:

• Low thermal inertia testing allows data to be directly applied to process scale
• Temperature and pressure rise rates applicable to relief system design "Based on DIERS two-phase flow technology, recognized by OSHA as an example of “good engineering practice”
• Many testing configurations
  -    Solids, liquids or two phase mixtures
  -    Closed or open (vented) tests
  -    Scaled blowdown simulation
  -    Test cells are available in 304 & 316 SS, Hastelloy C, Titanium and glass

• Accurate adiabatic data 
  -    Onset temperature
  -    Total adiabatic temperature rise (ΔT_ad)
  -    Heat of reaction or mixing
  -    Vapor pressure data
  -    Time to maximum rate (t_mr)
  -    Self-accelerating decomposition temperature (SADT)

• Relief valve sizing
• Quench tank design
• Effluent handling
• Critical temperature
• Effect of two-phase flow

FAI has also created the PrEVent software to allow users to implement practical emergency vent sizing using industry recognized methodology.  It applies DIERs methodology (including the Leung-Omega and Fauske methods) for reactive chemistry and API 520/2000 or NFPA 30 for non-reactive systems.

Background

Knowledge of the prevailing flow regime during emergency venting of a runaway chemical reaction is essential in order to estimate a realistic but safe relief system design.  It is not possible to predict the foaming behavior from physical properties alone. Since flow regime characterization methods for actual runaway conditions are not available, the general DIERS practice has been to design for “foamy” conditions, i.e. homogeneous vessel conditions, which is a conservative assumption.  Considering that the occurrence of “foamy” versus “non-foamy” conditions is very sensitive to impurities, minute changes in concentration levels and other factors, the flow regime characterization needs to be performed under actual runaway conditions coinciding with the relief venting process. 

The Flow Regime Detector sensor is comprised of a small immersion heater and an attached thermocouple that is positioned in the upper free board space of the test cell.  (For Flow Regime determination tests, the test cell is only about 1/3 full).

Prior to externally heating the chemical sample itself, power is supplied via an auxiliary control box to the internal heating coil to establish an elevated (baseline) sensor temperature.  This baseline temperature should be well above the anticipated boiling (tempering) temperature of the sample.  The detector operates on the principle that if the flow regime following the onset of boiling is non-foamy, then the detector thermocouple (TC2) will continue to measure a temperature well in excess of the sample temperature (TC1). 

Benefits

Fauske & Associates, LLC (FAI) offers a Flow Regime Detector (FRED™) for use in conjunction with the ARSST^TM and VSP2^TM  calorimeters to distinguish between foamy and on-foamy runaway reactions.  Relief systems for non-foamy systems may be more realistically designed by treating the two-phase discharge flow as churn-turbulent rather than homogeneous.

Features

• Easy to use and interpret results
• Compatible with ARSST^TM and VSP2^TM

Fauske & Associates, LLC (FAI) has been the industry leader in adiabatic calorimetry since the concept of DIERS testing was first introduced in 1985. 

Our team is happy to help train your staff in the understanding of technical issues, process safety programs or audits, regulations and more.  We perform process safety audits as part of a comprehensive hazards analysis and can work with you to make sure your staff is supplied with skills training needs in many ways including: 

Level I - Gap Analysis
Level II - training & consulting
Level III - Program Development and Implementation

Partial List of Services Offered:
• Reviews and upgrades of all your safety process systems and regulatory requirements
• VPP Consulting
• Audits, reviews, and upgrades of all your Operating, Safety, and Maintenance Procedures
• Training program evaluations for both completeness and effectiveness (from technical skills to professional development) and upgrades where
needed
• Reviews and upgrades of your program elements such as Employee Participation and Process Safety Information for effectiveness and completeness
• Work process effectiveness evaluations and upgrades
• Overall organizational development (e.g., motivation, work processes)
• Stress reduction
• Evaluations of the effectiveness of communication

We design, custom develop and deliver any site specific training materials needed by your organization. Our Consultants, Engineers and Technical Specialists are available to deliver the classroom, lab or on-the-job training your staff needs. In addition, we will assist with the identification and procurement of commercially available training materials where available.

ARSST^TM (Advanced Reactive System Screening Tool)

DIERS (Design Institute for Emergency Relief Systems)  Technology

FRED™ (FLOW REGIME DETECTOR)

PrEVent™ (Practical Emergency Vent Sizing Software) 

RSST ^TM   (Reactive System Screening Tool) 

VSP^TM (Vent Sizing Package) 

VSP2^TM (Vent Sizing Package 2)