September 20, 2007

Ask the Questions and Continue the Hot Topic Discussions

Several weeks ago we conducted a Mercury CEMS Hot Topic Hour. Subsequently Juan Ramirez of Seminole Electric e-mailed us explaining that Seminole had been using Appendix K sorbent traps on a wet stack and would like to know how many days they could extend their runs. Jim Wright of Clean Air Engineering volunteered that nine days was achievable but that one had to consider the quality of the data when the runs were extended too far. This week Juan replied as follows:

“Thanks! That is exactly what we are seeing. We are trying for 11 days right now on a scrubbed stack.”

This sequence of questions and answers was published in the E-Alert and summarized in the Monitoring and Sampling Newsletter. This newsletter in turn is accessed from the Mercury Decision Tree search engine.

McIlvaine is willing to do the work to achieve the best value of a chat room with the least amount of effort on the part of the participants. So if you have questions or comments about the subject matter in the “Hot Topic Hours” or in the material appearing in any branch of any of the Decision Trees, just send us an email to Bob McIlvaine at rmcilvaine@mcilvainecompany.com

pH Control and Air Flow Monitors were the Hot Topics

FGD slurry pH control is important and difficult. The efficiency of the scrubber system and the consumption of expensive reagents depend on accurate measurement. It is no easy task to design sensors which will withstand the combination of abrasion and corrosion. Fortunately, suppliers have developed reliable sensors and techniques to maintain their reliability. In the Hot Topic Hour on September 20 these techniques were discussed by the experts.

The mass air flow monitor in the stack is critical to the compliance needs of the utility. It is also important in determining trading allowances. With the recent addition of mercury and the potential for CO_2, it is even more critical to obtain accurate mass flow measurements. This subject was also covered in depth yesterday.

Emerson, Yokogawa, and Invensys are major suppliers of pH sensors to the power plant air quality market. ABB (TBI) has provided an extensive analysis of the requirements. This is found under their product branch of the FGD Decision Tree. Pfaudlers'  more expensive ($5,000 instead of $1,000) pH sensors which are used where the temperature is elevated and the corrosion high. So they are not active in this market where abrasion is the biggest problem.

Steve Rupert of Emerson discussed the PERph-x pH sensor which is designed for long life in the harshest applications. Evolution to meet the demands of FGD slurry applications include a porous Teflon junction, fumed silica gel reference electrolyte and double junction design.

The scaling resistant solution kit stops sulfates from forming on the junction. Accurate and stable measurements are obtained with the evolved features.

Details on pH sensors are found in the FGD Decision Tree as follows

There are three major options to measure the mass of flue gas exiting the stack. They are pressure differential, thermal, and ultrasonic. Each principle has its advantages and disadvantages. Each has advantages under certain conditions, e.g., wet stack or varying load. To take advantage of best features of each, there are sometimes redundant monitors of a different type. So in one case where the unit cycles there are pressure differential monitors used as the primary monitor, but ultrasonic as the back up for low load measurement.

In the U.S. EMRC has about 30 percent of the coal-fired market with their pressure differential monitor. Kurz is the leading supplier of the thermal monitors. GE Panametrics and ThermoFisher offer ultrasonic monitors.

Ed Wadington of EMRC says that minimization of stack components is important in terms of maintenance minimization. The pressure differential system that EMRC supplies requires so little maintenance that no service contracts are needed. S type pitot tube with optional back purge has proved capable of continuous operation without plugging. The ability to function well in a wet stack is another advantage. References include Duke, Nebraska Power, TVA, Dominion, Basin Electric and others.

Jed Matson of GE Panametrics introduced participants to a wide array of sensing solutions for the power industry. The ultrasonic flowmeters are just one of a number of products in this group which includes flow, gas analysis, moisture, pressure level and calibration. The ultrasonic flowmeters are used in gas turbine installations for the stack but also to determine gas flow.

For coal-fired boilers the ultrasonic flowmeters measure the pulverizer flow, boiler feedwater, and even the condensate. The maintenance is low in the coal-fired stack application because only the buffer is subjected to the actual stack gases.

Details on mass flow monitors are found in the FGD Decision Tree as follows: