A General Strategy for the Safer Scale-Up of Batch and Semi-Batch Reactions -with Richard Kwasny, Ph.D., Senior Consulting Engineer, Fauske & Associates, LLC
Thermal runaway incidents continue to occur in batch production facilities in the chemical and
This article attempts to provide guidelines that can be used as a basis for developing and designing safer new processes. It can also be used to identify process safety information gaps when existing processes undergo periodic reviews, as required in part by OSHA Process Safety Management 1910.119, Hazard Communication 1910.1200, and the General Duty Clause).
Causes of Thermal Runaway Reactions
Studies have determined that thermal runaway reactions occur due to the following four reasons:
Never assume a chemical is not hazardous because of a low-hazard rating. Many incidents involve materials that have NFPA hazard ratings of 0 and 1. It is best to develop a proper testing program to identify and characterize all reactive materials and reaction mixtures under a variety of process conditions. If your company does not have a testing facility, Fauske & Associates will be pleased to work with you to identify and conduct appropriate tests. Subsequently a process hazard analysis can then be used to assign appropriate controls and safeguards to reduce risk of an adverse event. It is important to remember to update the process safety information, as a process undergoes changes during its lifecycle. The interim process-safety information reports can then serve as a reference for technology-transfer purposes as the process scales from R&D, kilo-lab, pilot plant to commercial-production stage. Once the process has been set, the final process safety report can then be used by a variety of end users either in-house or by outsource facilities. When developing safety documentation, it is important to keep in mind that it must comply with company policies and procedures as well as country and local regulations.
Process Safety Considerations
The following items should be considered in relation to a process safety hazard evaluation.
Preliminary hazard assessment:
Quantification of desired reactions:
Quantification of adverse reactions:
General chemistry and engineering design concepts:
A comprehensive hazard evaluation should be conducted using appropriate estimation and experimental techniques to identify potential reaction hazards in materials, as well as the desired and adverse reactions. We use estimation techniques, differential scanning calorimetry (DSC), Advanced Reactive System Screening Tool (ARSST), and reaction calorimetry (RC), as needed. Identify any adverse or thermal runaway reactions and characterize them using adiabatic calorimetry, such as ARC (accelerating rate calorimetry), or ARSST. If required, the emergency vent size for a specific reactor can be determined using Design Institute for Emergency Relief Systems (DIERS, an AIChE industry alliance) methodology with data generated using an adiabatic Vent Sizing Package 2 (VSP2; a specialized adiabatic calorimeter that uses temperature, pressure, and rate data to allow for sizing emergency vents) or the ARSST.
Sometimes, it is necessary to use specialized equipment or techniques to obtain kinetic information on reaction or decomposition rates under unique or specific plant conditions, i.e., Thermal Activity Monitor (TAM) or AKTS Kinetics. This is an area where expertise is required and Fauske & Associates are able to help you plan and design these types of tests.
It is important to have clear, concise and unambiguous batch directions with appropriate hazards warnings to clearly explain what must be done at each step in the process including the identification of required safeguards. The directions should be reviewed and approved by a team consisting of the chemist, engineer, process safety, operational and environmental personnel including plant management. All operators must be properly trained in the directions, including specific engineering controls, working practices, and personal protective equipment, as needed. Training must be upgraded as the process is revised and it must be documented.
Having a documented process safety strategy or procedure in place allows for a standardized approach to hazard identification and organizing process safety information in a uniform manner. If we conduct hazard assessments for all processes, it develops a safety culture, avoids any confusion about how and why the tests were conducted and what other basic information is needed, allows for proper and consistent interpretation of test results/information, it ensures process safety information is comprehensive and can be used by a wide variety of end users. The reader is encouraged to add plant-specific items or issues to the guidelines in this article, as needed for their particular situation.
To learn more about how to scale-up chemical reactions in a safer manner, Fauske & Associates, LLC conducts training or please contact us at 630-323-8750 or firstname.lastname@example.org for additional information. www.fauske.com