Ion Exchange Example Assessment cont'd

DOE-HDBK-3010-94

7.0 Application Examples; Liquid Storage and Ion Exchange Examples

either extreme is indicated by a summary of the worst findings allowed for discovery for the

mock ion exchange operation in the original hazard analysis training exercise:

1. With an ion exchange feed temperature of 46 oC, the process is already operating

too close to the 60 oC empirical limit regardless of any claims about the reliability of

the temperature sensors that alarm and secure steam flow to the heat exchanger (Note:

The system has single failure if the steam valve sticks open). The process will

operate at actual feed temperatures without additional heating, although overall

process time will be longer.

2. Based on flowsheet values, the pressure and flowrate of steam through the heat

exchanger compared to the ion exchange feedrate indicates that a major heat

exchanger leak results in sending a very hot liquid/vapor slug (approaching

100 oC) into the ion exchange columns even if the steam valve shuts as it is supposed

to.

3. In the course of discussing the operation of the ion exchange unit, several

operators disagree that the valves on the vent lines leading to the vessel vent system

are supposed to be left open when the process is operating. They state that they shut

the valves when operating and open them when shutdown. Accordingly, another

empirical correlation, that ion exchange columns are supposed to be vented at all

times, is being defeated.

4. Other operators offer the opinion that the valve confusion exists probably because

there are so many valve manipulations required to perform a complete process cycle,

as is obvious from looking at the simple flow diagram of the process provided. It

was further ascertained that procedures refer to each valve by a name because the

valves are not numbered, and no figures are included in the procedures.

5. Upon examining the valve manipulation issue in more detail, the question is raised

about the possibility of partially draining ion exchange columns and thus allowing

some resin to dry. Investigation verifies that relative heights would allow liquid in

the columns to drain into piping if shutdown valve lineups are incorrect.

From just these five summary issues, it is obvious that the example ion exchange system is

not currently safe to operate with regard to an ion exchange exotherm, regardless of how

high or low a source term may have been estimated or how much of the existing equipment

had been designated safety-class or safety-significant. If it were necessary to operate it to

prevent holding process solution in tanks indefinitely, examples of potentially appropriate

compensatory measures include tagging shut valves on the steam line to the heat exchanger,

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