Inherently Safer Design Example

1
Inherently Safer Design Example

• Dennis C. Hendershot
• Rohm and Haas Company
• Engineering Division
• Croydon, PA
• Dhendershot_at_rohmhaas.com
• 2003 SACHE Faculty Workshop
• Baton Rouge, LA
• September, 2003

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Scenario

• You are the chief engineer for a municipal water
  and sewer department. You are asked to identify
  inherently safer technologies for treatment of
  drinking water and also for disinfection of
  effluent from the municipal sewage treatment
  plant prior to discharge to a stream. You are
  chartered to investigate options from the basic
  treatment technology through options to improve
  the inherent safety of the existing chlorination
  facility (chlorine usage is one 90 ton rail car
  every month, both for the drinking water and
  sewage treatment plant).

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Basic technology

• Options for municipal drinking water
• Identify options to eliminate or significantly
  reduce chlorine usage
• New hazards for the options?
• Options for waste water effluent disinfection
• Identify options to eliminate or significantly
  reduce chlorine usage
• New hazards for the options?

4
Existing water treatment process options

• Objective drinking water and sewage plant
  effluent chlorinated to the concentration
  required by public health and environmental
  authorities
• Both existing plants use 90 ton chlorine rail
  cars with liquid chlorine transferred with
  pressure (say 125 psig, from the chlorine vapor
  pressure and a nitrogen blanket) about 200 feet
  across a site road in a 2 inch pipe to a 50 psig
  steam heated vaporizer, then gaseous chlorine is
  injected into the water
• Identify design alternatives and discuss inherent
  safety advantages and disadvantages