We have recently completed upgrading two NOx/SOx CEMS systems at St Johns River Power Park in Jacksonville, FL. This project was started during the summer of 2006 when I started a series of meetings with the plant staff to review their existing systems piece by piece and ultimately developed a very detailed specification for the upgraded hardware and software. This was an important step in successfully completing the project.
The plant has environmental personnel who are responsible for the reporting and I&C staff who are responsible for maintaining the hardware. During the course of several meetings we discussed many design issues that they wanted to correct with the new design. We also specified in detail the equipment that we wanted to use and the standards that we wanted to follow. The time that we invested at this early stage has paid dividends in the final product. As with all new systems, we have had to track down some annoying bugs and work out a few unexpected issues but the upgrade went about as smoothly as can be expected.
Few things are as intimidating as ripping out a vital power plant system that has been running for about 13 years and committing to installing its replacement. We had a ten day outage for the installation of Unit 1. The goal was to use the lessons learned during the first installation to allow us to upgrade Unit 2 in 3 days. It was not easy but we were able to accomplish this goal.
The guys from Williams Industrial Services stand over the carcass of their recently defeated foe, the old CEMS cabinets. These things were built to last forever and did not give in easily.
Buzzards started to circle the stack about mid way through the outage. No one can remember that happening before. Despite the bad omen we pressed on and were ultimately successful.
A separate crew installed the new cabinets on the duct.
The new cabinets were staged outside the shelter so that they could be installed as soon as the old cabinets were removed.
The new cabinets were put in place.
We swapped the duct and stack analyzer racks after the factory acceptance test so that the new layout matched the old cabinet layout. This ended up requiring a great deal of re-wiring and re-tubing on site. For Unit 1 each cabinet was brought in separately and they were bolted together on site. This required the factory to disconnect all of the wiring between the cabinets. It took much longer than expected to reconnect everything. For Unit 2 we brought the air cleanup train, the duct analyzer cabinet, the stack analyzer cabinet, and the PLC cabinet into the shelter as a complete unit, rolling the cabinets along a few pieces of conduit. This proved to be a much better plan.
This picture shows the new Unit 1 cabinets on the right and the old Unit 2 cabinets on the left. 14 or so years of development makes a huge difference and the I&C techs love the new analyzers. They previously had pre-C series Thermo analyzers. I like to joke that the old analyzers actually had a little bird with a chemistry set who would then tweak a potentiometer to adjust the 4?20mA output like an old Fred Flintstone cartoon. The new i Series analyzers really pay off when you are prepping for linearities. The techs look so much more relaxed as they confidently flow the gas knowing that the analyzers will read as they should. They definitely don?t miss the drama of the old system.
One of our many design improvements was to mount the Teledyne Ultraflow 150 TIE components in a larger NEMA 4 box. This allows more room to work and the cables fold up neatly in the bottom. We don?t expect to have much trouble with the instrument but when they do it will definitely be easier to work on. Another tweak was to add a slow instrument air purge to the cabinet so that it always has clean dry air inside instead of stack gas.
The calibration gas cabinet to the new system has a couple of new tweaks. The CGA bottles have two solenoids in series to insure that a leak in a single solenoid will not cause them to fail a test.
One thing that we did miss in our spec and didn?t catch during the FAT was that the solenoid arrangement in the cabinet does not allow the solenoids to be easily removed. This was one of the few items in the new system that we were not completely happy with. I?m pretty sure that as soon as we wrap up the project the techs will be in here reworking this cabinet.
We upgraded the calibration gas racks. The old system had the regulators mounted to the bottle with Teflon tubing going to the cal gas solenoids. We installed a bulkhead and mounted all of the regulators in fixed positions with SS tubing to the solenoids. A braided SS hose attaches the regulator to the bottle. This makes everything easier to read and the bottles easier to change out. One problem during installation is that we did not have an experienced tube bender available so it ended up looking like an Escher drawing of impossible angles. This still needs to be cleaned up and is a remaining punch list item.
One major improvement in the design of this system was to install accumulator tanks near the probes for blowback. The old system performed blowback through a 1/4? line with the solenoid actuated down in the shelter. The new system uses the accumulator tank mounted at the probe and 3/8? lines. The accumulator pressure is monitored and the solenoid is actuated small PLC?s mounted on the stack and duct. The blowback is much more forceful than the old system?s and the time to perform a blowback was cut to a third of the old time. This means that the blowbacks are more effective and disrupt the system for less time.
We call this the multiplexer box and we have one on the stack and one on the duct. The top left corner has a little AB Micrologix PLC which acts as a MODBUS slave to the PLC in the shelter. The PLC controls the blowbacks and multiplexes other measurements onto a single fiber cable going down to the shelter. The PLC also measures the temperature of the cabinet so that we know how hot the equipment gets during the day. The PLC will easily allow expansion of the system if we need to add anything to the duct or stack in the future and was relatively inexpensive. We also used a larger box to allow for expansion. The box is also purged with instrument air. The old system used a fixed multiplexer that allowed a couple of 4?20mA and a couple of digital signals to be passed. The two blue boxes on the top right corner control the probe and stinger heaters on the new M&C probe.
The new M&C probe on the stack and duct replaced EPM out of stack probes. The M&C has a superior design for the coarse filter that allows it to be easily changed. The coarse filter also has a much larger surface area than the M&C so we expect fewer problems. The probe sits at an angle because the welder who originally installed this flange 20 years ago did not pay attention to the bolt pattern when he attached it to the stack.
This picture shows the Teledyne UF 150 TIE enclosure on the left, the M&C probe in the middle, and the blowback accumulator box on the right.
It seems that as the original Part 75 CEMS systems start to reach the 12?13 year old mark it makes sense to replace them. Old PLC?s, analyzers, and other instruments are much harder to maintain than the newest generation of equipment. Spare parts are becoming harder to locate. Availability suffers and your technicians spend too much time baby sitting temperamental equipment. It ultimately becomes justifiable to replace everything. Many utilities are also realizing as they prepare for new Mercury CEMS that it is a good time to revisit their NOx/SOx CEMS as well. Your techs will have their hands full with these complex new system so upgrading the old systems to free up their time is a good strategy. It is important to do the preliminary legwork and specifiy a system that will fix any problems or design flaws in your old system and insure that your new system will perform reliably.