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Chemical Reactivity. Chapter 8: Crowl & Louvar. Chemical Reactive Hazard. Chemical reactivity hazard: situation with potential for an uncontrolled chemical reaction, resulting in harm to people, equipment, or environment. Result could be:

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Chemical Reactivity

Chapter 8: Crowl & Louvar

slide2

Chemical Reactive Hazard

Chemical reactivity hazard: situation with potential for an uncontrolled chemical reaction, resulting in harm to people, equipment, or environment.

  • Result could be:
  • Violent release of heat, toxic or flammable materials
  • Build up of excessive pressure
  • Reaction could be:
  • Self-reacting chemical (i.e., monomer)
  • With other chemicals; intentional or otherwise
  • Catalyzed by contamination, construction materials
  • Exothermic and/or gas producing
  • Due to incompatibility
slide3

Screening for Reactive Hazards

Figure 8-1 Screening flowchart for reactive chemical hazards. An answer of “yes” at any decision point moves more toward reactive chemisty. See Section 8.2 for more details. (Source: R.W. Johnson, S.W. Rudy, and S. D. Unwin, Essential Practices for Managing Chemical Reactivity Hazards (New York: AIChE Center for Chemical Process Safety, 2003.))

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Specific Chemical Reactive Hazard

http://response.restoration.noaa.gov/chemaids/react.html

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Specific Chemical Reactive Hazard

  • Table AF-1: A few pyrophoric and spontaneously combustible categories and chemicals (these materials combust on exposure to air).
  • Table AF-2: Some chemical structures susceptible to peroxide formation (the peroxides formed may become unstable and explode when disturbed).
  • Table AF-3: Chemical categories susceptible to water reactivity.
  • Table AF-4: Common water-reactive chemicals.
  • Table AF-5: Typical oxidizers.
  • Table AF-6: Some polymerizing compounds (these chemicals may polymerize rapidly with release of large amounts of heat).
slide10

Understanding Reactive Systems

Cooling Water

Exothermic Reaction

Why important: Common problem with exothermic reactions.

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Runaway Reactions

How?

1. Loss of coolant.

2. Increased temperature.

3. Increased energy generation.

High pressure due to: Vapor pressure of liquid.

Vapor decomposition products.

Larger vessels respond faster - less heat transfer thru walls!!!

Some chemicals can achieve self heat rates of 100’s deg. C/min! Styrene, Acrylic Acid

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Runaway Reactions

  • Some ways for runaways to occur:
    • Loss of cooling.
    • Overcharge reactant.
    • External fire.
    • Mis-charge reactant.
    • Low reaction temperature in semi-batch reactor. This is called a sleeping reactor.
    • Loss of agitation.

Most reactive runaways result in 2-phase flow thru relief and require a relief area 2 to 10 times larger than single phase relief.

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Application of Calorimeter Data

  • Heat exchanger duty to achieve required reactor cooling
  • Cooling water requirements and cooling water pump size
  • Condenser size in a reactor reflux system
  • Max conc. Of reactants to prevent overpressure in the reactor
  • Reactor vessel size and pressure rating
  • Type of reactor (batch, semi-batch, tubular)
  • Reactor temperature control and sequencing
  • Semi-batch reactor reactant feed rates
  • Catalyst concentrations; max fill for batch and semi-batch reactors
  • Alarm/shutdown setpoints
  • Operating and emergency procedures
  • Relief sizing and effluent treatment systems
  • Solvent concentrations required to control reactor temperature
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In-Class Exercise

A company had a spray painting operation to paint automotive parts. The spray painting was done in a paint booth to reduce worker’s exposure and to collect any paint droplets that might be entrained in the exhaust air. The paint droplets were collected by fibrous filters. At the end of each day, the filters were removed, placed in plastic bags, and stored for disposal in a separate building.

Due to environmental concerns over volatile emissions from paint solvents, the paint supplier reformulated the paint to use a less volatile solvent. This change was done in consultation with the paint company. Several test were done to ensure the reformulated paint worked well with the existing spray equipment and that the quality was satisfactory.

The company switched to the reformulated paint. Several days later the disposal building caught on fire, apparently due to a fire started by the paint filters. Can you explain how this might have happened. Any suggestions for prevention?

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In-Class Exercise

A university lab expansion includes installation of a distribution system to provide gaseous oxygen from manifolded cylinders to a biochemical engineering laboratory. No chemical reactivity hazards have been previously identified for the lab facilities.

Apply the screening method of Figure 8-1 to determine if any chemical reactivity hazards are expected.

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