Adiabatic calorimeter testing provides data for relief system design, safe scale-up of chemical processes, and changes to process recipes. Safe process design requires knowledge of chemical reaction rates, character and energy release - all of which can be obtained from a low phi-factor adiabatic calorimeter such as the VSP2TM (Vent Sizing Package 2) or ARSSTTM (Advanced Reactive System Screening Tool).
The VSP2 TM and the ARSST TM provide thermal data required for safe scale-up of chemical processes and changes to process recipes. A variety of process upset conditions can be tested to quantify hazards identified by a PHA or HAZOP study. The low phi-factor (or thermal inertia) allows the heat and gas generation rates to be measured and directly applied to the process scale, which leads to appropriately designed emergency relief systems.
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 (VSPTM). Later improvements led to the VSP2TM. 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 (ARSSTTM) in 1999. FAI uses the DIERS-based VSP2TM and ARSSTTM 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.
Fauske & Associates, LLC's (FAI) Advanced Reactive System Screening ToolTM (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 ARSSTTM in our fully equipped hazards laboratory but we also manufacture and sell the calorimeter for use by our clients.
The ARSSTTM 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.
ARSSTTM 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. ARSSTTM 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 ARSSTTM 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.
The ARSSTTM 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.
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
Its versatile and innovative design allows the VSP2TM 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.
The VSP2TM 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 VSP2TM can be used to characterize reactive chemical and consequences that could occur due to process upset conditions.
The versatile configurations offered by the VSP2TM design directly
Use of the VSP2TM can help users obtain complete chemical system data such as:
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.
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).
Fauske & Associates, LLC (FAI) offers a Flow Regime Detector (FRED™) for use in conjunction with the ARSSTTM and VSP2TM 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.
Fauske & Associates, LLC (FAI) created its PrEVent™ software to allow users to implement practical emergency vent sizing designs utilizing industry recognized methodology including the Leung Omega method, Fauske Gas/Vapor method and Fauske General Screening method. The software applies DIERS methodology for reactive chemistry and API 520/2000 or NFPA 30 for non-reactive systems. This methodology was designed in conjunction with the VSP2TM and is a great companion to any low phi factor adiabatic calorimeter.
PrEVent™ handles gassy, hybrid and vapor systems for reactive scenarios and can also accommodate deflagration venting as well as fire load sizing. The modern user interface features clear navigation, logical tabs and intuitive drop down menus that take advantage of cutting edge Windows programming techniques for a crisp seamless user experience. It is available as a standalone Windows application, or as a Silverlight 4 based web application supporting a wide-range of platforms including all major browsers on both Mac OS X and Windows – Internet Explorer 6, 7, 8, Firefox 2 and 3, Safari 3 and 4 and Google Chrome.
The streamlined interface allows users to make changes to input values "on the fly" and see the results updated immediately. This is convenient for parametric studies, such as varying the batch size to see how much reactant will "fit" within a particular vessel/relief installation. Input parameters, including vessel geometry, reactant properties and adiabatic reaction rates at venting, are conveniently entered using simple drop down windows and saved for later use.
It is the latest version in a line of vent sizing code solutions designed to be quick and easy to use, requiring many fewer physical properties than other programs.
But, what if your Go/No-Go test result is a "no"? Well, we next look at what temperature it will take make your dust layer ignite. To find the Minimum Autoignition Temperature (MIT) of a dust cloud in the air, the MIT tests the minimum temperature that would cause your dust cloud to ignite. Next, is the LIT Test, which determines the hot-surface ignition temperature of dust layer. Finally, a Burn Rate test is conducted to determine how quickly the dust material will burn.
All of these tests start with the Go/No-Go Test. A comprehensive DHA or Process Hazards Analysis (PHA) can apply your test results to real world scenarios at your facility. Better to know wha t you are dealing with so you can plan safely! In addition, if you have a dust collector and aren't sure what to do next, read: "Combustible Dust Made Easy".
Here are some other tests run for dust explosibility screening:
Unless otherwise instructed, dust testing is performed on the sample as it is received (“as received”) from your facility as mentioned earlier. It may be screened to less than 420 μm (40 mesh) – OSHA’s and NFPA’s demarcation of a “dust” – to facilitate dispersion into a dust cloud. Particle size may vary widely depending on the sample.
Furthermore, please note that per ASTM recommendations (and some NPFA requirements); samples should be tested at a particle size less than 75 μm and less than 5% moisture. Please note that testing materials in a method not complying with the ASTM/EU recommendations may produce explosion severity and explosion sensitivity data that is not considered conservative enough for explosion mitigation design.
Fauske & Associates, LLC (FAI) has been the industry leader in adiabatic calorimetry since the concept of DIERS testing was first introduced in 1985.
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