It has been a number of years since I checked out the costs but Na2CO3 was used in several scrubbing system designs, both wet and dry scrubbing.
Reagent cost was the biggest issue, limestone is much cheaper. Secondary concern was the environmental fate of the sodium because it ionizes so easily if it gets wet again. The calcium salts are slower to redissolve and have limited solubility.
The plus side for Na salt scrubbing was the minimal scaling that occurred in the absorbers.
Some of the wet scrubbing designs included a sodium recovery step where lime or limestone was used to precipitate the absorbed SO3 & SO4 from the scrubbing liquor. But these added cost and complication to the design.
If you chase down this path remember to watch your solution temperatures. Glaubers salt has some interesting eutectics that can cause all sorts of havoc.
The trona injection I have seen is in dry powder form and is injected after the air heater outlet. Also have heard of it being feed in with the coal as a dry form also.
Kind of surprised that it would be mixed and fired with the coal. With the extra sodium fractions I would expect that the ash fusion temp would drop and you would have more problems with sticky ash in the SH and RH sections of the boiler.
When it is put on the coal belt it is supposed to have a positive affect on Hg removal. Have seen some testing done with soda ash also. It was feed in with the coal also. Was just wanting a little more info on the trona.
