SACHE Faculty Workshop - September 20031

Inherently Safer Design Example

Dennis C. Hendershot

Rohm and Haas Company

Engineering Division

Croydon, PA

Dhendershot@rohmhaas.com

2003 SACHE Faculty Workshop

Baton Rouge, LA

September, 2003

SACHE Faculty Workshop - September 20032

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).

SACHE Faculty Workshop - September 20033

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?

SACHE Faculty Workshop - September 20034

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