QUESTION FROM PREVIOUS PUZZLER
|To save cost, three waste heat boilers share a common steam drum. One boiler was damaged beyond repair when it was taken offline for cleaning. The boiler was starved of water and overheated when the wrong valve was closed (D3 instead of C2). What is the best way to avoid this situation in the future?|
Rearrange the valves to prevent errors
You could install three separate steam drums or rearrange the valves in a more logical fashion. Either of these options probably would be too expensive for the existing plant, but should be considered for future plants despite the increased cost.
You could add interlocks and/or high temperature alarms on the boilers, but the simplest solution might be to color-code the valves or adjoining pipes.
Trevor Kletz, safety consultant
Install relief valves
At the very least, you should have relief valves in the piping between the various boilers and the steam drum. Each should be sized for the pertinent boiler. Note that ASME Section I doesn’t allow block valves between the boiler and the relief valve.
Where multiple boilers have common feeds, they should have double block and bleeds for the water and steam. It’s impossible to open a valve for maintenance to any degree of safety unless the multiple boilers on a common steam drum have double block and bleeds.
Dave Gray, senior reliability engineer
Augusta Service Co.
Add new steam drums
The best way to avoid this would be to redesign your process, shutdown procedures or safety interlocks, or to add new steam drums. By doing the latter, you would only have one set of valves per drum. This way, the unit could be shut down if a valve were shut.
Andrew K. Schwartz Jr., chairman
Keeshan & Bost Chemical Co., Manvel, Texas
Monitor positions with a PLC
Install proximity sensors and/or automate the valves and then tie them into a programmable logic controller (PLC) or alarm system to monitor and send valve position data. The PLC can be configured to alarm when a valve is closed by adding an input block from the motor starter of the pump to tell the PLC which pump or boiler is running.
Tony Williams, maintenance manager
MFM Building Products, Coshocton, Ohio
Color-code the valves
Paint the corresponding inlet and outlet valves the same color – any color paint will work. Operators should be trained to open or close both valves of the same color.
Paul Rupprecht, manager, maintenance and utilities
Pfizer Inc., Terre Haute, Ind.
One possible solution is to interlock the boiler operation to the valve positions.
Nick Ludovic, plant engineer
Degussa Corp., Chester, Pa.
At our coatings plants, we produce many types of synthetic resins, and for each type we have several recipes. Is there an easier, more reliable way to monitor the product viscosity and determine the end of the reaction other than the classical manual sampling and laboratory testing?
At our coating plants, we produce various types of synthetic resins, and we have several recipes for each one. Is there an easier, more reliable way to monitor the product viscosity to determine the end of the reaction other than the classical method of manual sampling and laboratory testing?