Chemical Reaction Hazards

Hazards Arise from Pressure

The greatest hazard that threatens process vessels is pressure. It is rare that temperature alone will cause a vessel to fail. Therefore it is critical to identify, and then mitigate or prevent the potential for overpressurization of your vessels.

There are many potential sources of pressure:

Chemical over-pressurization chart

Desired Process

Raw Material Desired Reaction Product (Heat / Vapor / Gas)

Undesired Process

Raw Material Desired Reaction Product + Heat Undesired Reaction Undesired Product (Heat / Vapor / Gas)

OR

Raw Material Upset Scenario Undesired Product (Heat / Vapor / Gas)
  • Heat from the desired reaction leading to a secondary reaction or decomposition reaction at elevated temperatures (generating non-condensable gas and/or vapor)
  • Upset conditions (e.g. loss of cooling, excess catalyst, incorrect raw material added etc.) lead to greater or uncontrollable rates of reaction or alternative reactions (generating non-condensable gas and/or vapor)
  • Self-heating or self-reactive substances during shipping or storage that over time can accumulate heat (generating non-condensable gas and/or vapor)
Identifying and Assessing Sources of Overpressure

There are three key steps to take to avoid or appropriately protect against an overpressure situation:

What aspects of my process should I focus my evaluation on?
  • IDENTIFY HAZARDS
  • Thermal Screening: quantify heat associated with process chemistry and the thermochemistry of materials involved with the process

How do I run my process safely?
  • DESIGN OR CONFIRM PROCESS EQUIPMENT
  • Reaction Calorimetry: determine heat and gas removal requirements to control the desired process chemistry

How do I avoid or mitigate the effects of a runaway reaction?
  • DESIGN OR CONFIRM CONTROL AND SAFETY SYSTEMS
  • Adiabatic Calorimetry: determine the consequences of potential upset scenarios such as failed equipment or improper procedures, and mitigate the consequences by determining appropriate control or safety systems (SIS, SIL, pressure relief, etc.)

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Understanding chemical safety instruments gives an introduction to some of our calorimeters as well as practical uses.

Thermal Screening

In addition to the evaluation of literature data and performing theoretical calculations, small-scale instruments such as the Differential Scanning Calorimeter (DSC) or Advanced Reactive System Screening Tool (ARSST) can be used to quickly thermally screen starting materials, process streams, and products to identify the existence of hazards.

  • Thermal ScreeningIs there thermal decomposition of raw materials, intermediates, products, etc.?
  • Are there exothermic reactions that should be studied more closely?
  • How should this material be stored or shipped?

Reaction Calorimetry

Reaction calorimetry is a tool that is used to understand the equipment or process requirements to perform a chemical process safely. Typical instruments are the RC1 (Mettler Toledo) and the CPA202 (ChemiSens).

  • How much heat does my cooling system need to remove?
  • How large of a scrubber do I need, and what rate of gas generation does it need to handle?
  • What are the temperature dependent kinetics of my reaction?
  • What is my heat of reaction or instantaneous heat flow for a step in my process?
Reaction Calorimetry

Adiabatic Calorimetry

Adiabatic calorimetry is a tool that can simulate large-scale vessels to determine the consequences of a runaway reaction. This can be performed in instruments such as the Vent Sizing Package 2 (VSP2), ARSST, or Accelerating Rate Calorimeter (ARC).

  • Are there secondary or decomposition reactions that begin within the maximum temperature of synthetic reaction (MTSR)?
  • How much non-condensable gas would be generated if I had a runaway reaction?
  • How do I protect my vessel if an upset scenario occurs?
Adiabatic Calorimetry

Relief System Sizing gives introductory guidance to chemically reactive vent sizing using either VSP2 or ARSST data.

FAI is a world leader in chemical process safety.