Your opacity analyzer normally runs fine, but then cold weather sets in and now the opacity readings are a bit flakey, spiky, noisy, weird, unusual, annoying, etc. Well, you should initially rule out the opacity analyzer … it’s not its fault! It’s probably physics! Or earth sciences! But it’s not sunspot activity.
What is most likely happening is:
- Your stack has significant moisture in its effluent
- Your purge air system for the opacity monitor draws makeup air from the very cold ambient air
- When the very cold ambient air meets the very hot, moist stack effluent, the effluent temperature drops significantly
- forces the relative humidity to approach 100%
- then forces steam (water) molecules to coalesce (condense) … a phase change
- then creates visible (water) vapor (some say ‘steam’ but it is really vapor)
- if you can see it, so can the opacity analyzer’s stack light beam
So, how would you prove this before investing any money in the solution? How about a very simple test:
1. Somehow stop the purge gas flow temporarily
> block or partially block the blower’s (or blowers’) suction(s)
> turn off the blower(s)
> remove the feeder hose(s) to the injection ports
2. Observe your opacity readings for five to 30 minutes
- did the spiking go away?
3. Re-employ the blower system
- did the problem return?
If answers to questions 2 and 3 are “yes” then you have “Phase Change”
So, how do you fix it? Here are a few ideas:
- if it only occurs once in a Blue Moon, just declare it on your quarterly reports and take it as “down time”
- if it happens too often, your Regional EPA won’t enjoy seeing a high down time number
- install ducting so that the opacity analyzer draws makeup air from a warmed room
- install purge air preheaters (1500 watts per side minimum; 3000 watts per side for extreme conditions)
Call us at 877-616-0600 to discuss this in greater detail.