Continuous Emissions Monitoring Systems
Why does a plant have CEMS? Because they have to........... Of course we all want to live in a world where we can breath the air and drink the water without fear of toxins. So here comes a couple of agencies to make sure that the plants follow strict rules or face fines and possibly being shut down.
TCEQ -Texas Commission on Environmental Quality
EPA - Environmental Protection Agency
So how does this interaction affect us as analyzer techs and the plant as a whole?
Example - We are a refinery and have three boilers in operation. We petition the state for a permit on each and in this permit the state and us agree that we are only allowed to emit so much CO & NOx per year. We will also be measuring for O2 and we will get to that later. Lets say that the permit only allows us to emit 100,000 lbs of NOx a quarter. That's 400,000 lbs of NOx a year. Everyone understands that there are 4 quarters in a year?
To arrive at a number of how much we are emitting at this second is a calculation of our flow of gas into the boiler to create our fire to boil the water and what NOx level we are reading at that second. If are running 4 ppm of NOx with a flow of 49 PPH then that along with some other variables will give us our current lbs/hr. That number will just steadily add up all day and at the end of the day we will have a total of how much NOx we emitted that day.
Now imagine we are having problems with the boiler and issues are causing us to run high NOx at 75 ppm today with the same flow as yesterday. It would not take a whole lot of days running at this level to be in trouble of busting our permit. We bust the permit we pay a fine.
CEMS must pass a daily validation. A validation is a self check on calibration gas. Do not confuse this with calibration. A validation is a check and a calibration is where we adjust the analyzer to read correctly. If the analyzer reads correctly on it's mornign validation then nothing else has to be done. If it fails the morning validation then the technician must fix/calibrate the analyzer ASAP. We are only allowed a certain amount of downtime and must keep track of any and all maintenance time on each analyzer.
(Analyzer must have 95% uptime per quarter)
We began discussing different pieces of equipment in plants which will require a CEMS such as boilers, furnaces, fuel gas to be burned, scrubber off a FCCU, and basically any combustion type device.
We have a choice in whether we want to go with Insitu or Extractive.
Insitu is an analyzer that is mounted directly into the process and takes the reading and transmits the data right there. Examples of these are a zirconium oxide O2, FTIR, or tuneable diode laser. Each of these is mounted into the process and taking an immediate reading. Thats fine, till it breaks....... Now you will have to fix this analyzer while the process is going, so you will literally pull a long probe off a stack and repair there at the job. This normally doesnt sit well with techs or management so that's a pretty bad downside to them.
Extractive on the other hand is the route most plants are going and for many reasons. Safety is just one but you can easily analyze and fix issues. You can expand the system if needed. As we discussed about this system you will have a heated sample probe, heated sample bundle, chiller, sample pump, water slip relay, filters and a distribution panel sending the sample to our analyzers. This panel will also have our relays for sending cal gas to the probe.
Either way we go, all the data will be sent to a DAS. The data aquisition system will compile reports for our environmental engineer to submit to the state. These reports will not only include how much of each pollutant we have emitted but an analyzer uptime report and a calibration/validation report.
One of the worst things you can do as a technician is forget to check your CEMS in the morning and get busy and then the next day find out that it failed yesterday. Why, because your cal bottle went empty. First you're an idiot for not checking the report and second you're fired because the bottle went empty!!!!
This is a typical boiler situation. Our sample probes are inside those white boxes mounted up there on the stacks. Where does the power come from to heat the sample probe housing?