Challenges for Air Heaters and Big Potential for Heat Exchangers to meet New Power Plant Parameters - Hot Topic Hour Yesterday
Participants agreed yesterday that there is a big potential to optimize both air heaters and supplemental heat exchangers to meet new parameters for power plants.
John Guffre of Paragon Air Heater discussed the effects of using the air heater for SO3 removal. He reviewed
1. The physical effects on the air heater.
2. The balance between air heater efficiency and the amount of SO3 removed.
3. The downstream effects of SO3 removal on other APC equipment.
4. What the plant needs to add (equipment, CEMS) to properly remove SO3.
The new parameters for boiler performance are creating complexities for the air heater. The quest for improved boiler efficiencies dictates lower air heater outlet temperatures. Lower outlet temperatures can result in greater corrosion. The addition of activated carbon upstream of the air heater is also a cause of air heater corrosion when brominated carbons are used.
One of the parameters affecting the impact of SO3 is the rotational speed of the air heater. Another is the proper location of soot blowers. Operational variations are another. John cited the ability to slow down the air heater at night or at off peak conditions and increase the metal temperature. This can eliminate the ammonium bisulfate buildup.
Paragon Air Heater is looking beyond just the supply of seals and baskets to help guide the power plant in decisions which can impact precipitator efficiency, mercury removal, corrosion, scaling and SO3 emissions. Corrosion of the air heater due to corrosion underneath brominated activated carbon deposits had been documented. Air heater chucks fell off within six months. John believes that adding bromine with the coal rather than with the activated carbon may reduce the corrosion problem.
Jon Lehmkuhler of Chemtura explained that their bromine is normally added as calcium bromide as a slurry with the coal. In the boiler a number of gaseous compounds are formed. It would seem that the gaseous form is less likely to be concentrated on the surface and cause corrosion.
Ed Levy of Lehigh Energy Research Center reviewed the latest status of the work on condensing heat exchangers. Pilot work has shown that the benefits on pollutant removal are significant. Furthermore the flue gas contains 6 percent to 17 percent water. So capture and use of this water is significant. Amine and ammonia CO2 capture units need flue gas cooled to 100°F. So a plant equipped with condensing heat exchangers would be carbon capture ready.
The efficiency improvements from heat capture are significant but McIlvaine speculates they could even be greater when considering the opportunities created. For example the I.D. fan downstream of the condensing heat exchanger could be axial rather than centrifugal. It could operate at very high efficiency on a smaller volume.
Charlie Bullinger of Great Rivers Energy updated us on their very progressive approach to capture the waste heat from power plants. He reported that the co-located Blue Flint ethanol plant which does not have a boiler but instead uses steam supplied by the Coal Creek Station is running at capacity. Despite high corn prices, the plant is competitive due to its cheap energy supply. He reported that the Spiritwood plant is being restarted and is now looking for an additional user of steam in addition the Cargill Malt plant. Great Rivers is continuing to look at coal drying as a way to improve efficiency. Great Rivers has success in drying North Dakota lignite and providing a 2.8 to 5 percent efficiency improvement.
There was some discussion over the new Moxie Liberty 936 MW gas turbine plant in Pennsylvania which will use shale gas. It will also use air cooled condensers. Ed Levy was asked whether Lehigh had looked at condensing heat exchangers for gas turbines. He replied that there has been some investigation and the application is promising.
One impact on air heaters could be the development of ceramic filters for power plant applications. Clear Edge has TopKatŪ which removes both particulate and NOx at 850°F. It can also remove SO2 by the dry injection mode. The use of this device ahead of the air heater would eliminate particulate and reduce the potential for SO3 deposition. John Guffre was asked whether this mode would allow more efficient air heater design. He replied that leakage and efficiency could be significantly improved under such conditions.
A number of other subjects were reviewed including the gas-to-gas heat exchangers employed by Hitachi and Mitsubshi ahead of precipitators to greatly improve particulate capture. The use of sonic horns in addition or in place of soot blowers was briefly discussed. Use of waste heat to beneficiate flyash included removal and reuse of ammonia and extraction of rare earths and metals.
The Bio and Photo of John Guffre, Paragon Air Heater Technologies can be seen at:
BIO AND PHOTO, JOHN GUFFRE - OCTOBER 18, 2012.htm
The individual presentation is as follows: