No one has to tell the manager of any plant how stringent the regulations for emissions monitoring are, and this goes double in power plants. The Clean Air Act of the 1990s requires power plants and other industrial combustion related operations to monitor flue gas and comply with Title 40 CFR sub-chapter C parts 50-97. A standard Continuous Emissions Monitoring system (CEMS) designed to meet these regulations consists of a sample probe, filter, sample line (umbilical), gas conditioning system, calibration gas system, and a series of gas analyzers. For one large Southeastern power facility serving about 10 million customers, meeting these requirements was, of course, a top priority, but the problem they kept facing was managing calibration gas.
To meet environmental requirements, it’s critical that a constant supply of calibration gas is available to the CEM sample analyzers. The calibration gases are required in order to obtain accurate data regarding NOx, CO2 and other harmful gases that are a part of the combustion process. The calibration gas cylinders commonly range from 2,000 to 3,000 psi on average. The power facility was replacing the cylinders when cylinder pressure approached 300 psi. They utilized 12 installed cylinders per unit, or 36 total, for the plant.
The problem arose because they were attempting to manage the 36 cylinders with a manual recording that was being conducted every twelve hours (each shift) with each of the nine CEMS shacks (located 50 yards apart at an outside base of HRSG stacks). The plant outside operator manually recorded the cylinders’ pressures on each shift and captured them in the shift operator log. If the pressure was lower than 300 psi, the operator replaced the cylinder with the full one located at the shack and moved another full one from the central location to the specific shack.
As can be imagined, the method was fraught with challenges and compromise. Since the cylinders typically lasted two to four weeks, the operators were often doing nothing, wasting valuable time when they could be performing other tasks. Hand-entering data was open to illegibility and human error, and the often rainy or stormy weather made trips into the field difficult. The manual recording required a minimum of three manhours per day, and if the operator was required for an emergency, might not get done at all. This last possibility put the plant in danger of a CEMS failure due to calibration gas not being available, which could incur fines.
In fact, the plant already had the basis for a successful solution to their problem. Having previously installed a wireless network which included a wireless gateway and control valve DVCs with wireless adapters, the facility could take advantage of a wireless pressure gauge to replace the manual operation.
Installing the wireless pressure gauge as part of the network, the data update rate frequency was set to once a minute to maximize the battery lifespan. That was once a minute versus once a day! The gas pressure low alarms were set in the digital control system at 300 psi and the DCS alarms were used to trigger the replacement of the gas cylinders. This prevents CEMS calibration failures due to calibration gas not available and eliminates the need for any trips to the field until a low alarm is given. The plant is so confident in their system, they may reduce the low alarm to less than 300 psi, which will further save calibration gas and personnel time.
Are there tasks you’re still performing manually that might be easily automated?
Read more information on the Rosemount wireless pressure gauge here.