Has anyone injected SBS sodi8um bisulfate for SO3 reduction? 2

[jayboz]

Just curious if anyone has dealt with this, and what results you got with reductions of SO3 on a COAL fired power plant. And the affects on the equipment at the plant , if any.

Thanks

Jack

 

[wtflippin]

Jayboz,

I am looking for information on the same subject, but for an oil-fired boiler (2.5% sulfur). See my thread July 24, 2003 in this forum. We are investigating alkaline injection alternatives to control opacity and backend corrosion caused by the conversion of SO3 to H2SO4.

I have received some information on SBS injection at three coal-fired sites, including system descriptions, results, costs, etc. I am interested in learning more though, including reagent availability, costs, and deposition issues. If you are interested in an information exchange, please let me know. I will check this thread for a response.

 

[orenda1168]

Magnesium oxide as an oil dispersion, or magnesium hydroxide as an aqueous dispersion, both injected in the boiler's radiant zone, have been successfully used to reduce SO2-->SO3 conversion (catalytic) and provide a neutralizing medium in heat recovery areas to minimize/eliminate H2SO4-induced corrosion. The process has been applied to both coal and oil-fired boilers up to and including 800MW units.

Dick Kersey
Orenda Technologies, Inc.

 

[JEB66]

Get a copy of the EPRI report 1004167. The stuff will remove SO3 and helps maintain precipitator performance.

But there are other considerations to think about in the EPRI report. The duct pluggage is one. Nozzle pluggage is another item, especially if the SBS is injected ahead of the air heater. A sputtering nozzle will plug the air heater. The nozzles will need a lot of cleaning to keep the spray pattern right.

Since this is a slurry, there is pump maintenance. So there is additional costs to think about besides the annual license fee.

Also you will want to find alternate sources for the material. If you get locked into one supplier, they will control you.

 

[cub3bead]

Haven't used sodium bisulfite for this application but have used elemental sulfur to achieve similar results. The S is fed along with the limestone to the ball mill. Where it starts reacting with the water (usually scrubber reclaim water) to form sodium thiosulfate. Na2S2O3 inhibits oxidation of the CaSO3 to CaSO4 in the scrubbing loop which helps prevent CaSO4 scaling in the scrubber.

Elemental S can be used in conjunction with feed of dibasic acid (DBA) to enhance scrubber performance.

You do have to be careful to avoid overfeed of the elemental sulfur because it changes the settling characteristics of the CaSO3 hemihydrate in the waste treatment system so that it settles more like CaSO4 dihydrate which can result in damage to the rakes in the primary clarifer and the thickner by torque overload if your operators aren't on top of the situation.

 

[25362]

Since the gas residence time in the scrubber would be a few seconds, cub3bead kindly explain the mechanisms by which sodium thiosulfate first forms and then inhibits the oxidation of calcium sulfite to calcium sulfate (by the combustion excess air) in the scrubber. What would be the scrubber operating temperature ? Thanks.

 

[cub3bead]

Agreed the gas side residence time is short but this is a liquid side chemical raction where the residence time is long in comparison. Absorption of oxygen from the combustion gases is limited by the solubility of O2 in H2O. The absorber operates at the adiabatic saturation temperature which if I recall is in the area of 135-140 deg F.

FGD systems that are not inhibited or forced oxidized will have about 25% of the CaSO3 oxidized to CaSO4 which causes the scaling problem. If you can keep the CaSO4 below 15% in the scrubbing liquor you can minimize CaSO4 scaling in the absorber vessels. Another plus is the CaSO3 crystals grow larger and improved settling and dewatering has been observed in the FGD waste treatment system.

The S reaction efficiency depends on the residence time in the mill storage tank, absorber vessels and FGD waste treatment system. Any unreacted sulfur will leave with the solids.

Unfornately, I have not been able to readily lay my hands on the papers that were published. They are buried in my files and I have not found them today. This was first described in the late 1980's as the building boom was winding down on large coal fired power projects. As soon as I locate them I will post the chemical reaction equations here. My brain has purged the chemical reaction equations since FGD technology is not my primary area of practice.

 

[25362]

To cub3bead, thanks.

The working temperature could be considered a drawback, because it takes away plume buoyancy and brings the remaining pollutants to ground more easily if not reheated.

I was under the impression that both calcium salts are problematic in the final separation stage. CaSO3 would tend to form crystals that are small and flat plates, good at trapping and retaining water; if the cake consistency is that of a toothpaste it wouldn't be acceptable for landfills. Whilst CaSO4 forms larger and rounder crystals much easier to settle and filter.

 

[LjungstromGuy]

Just a quick note on using SBS injection with Ljungstrom air preheaters. If injection is ahead of the air preheater considerations have to be made to the design of the air preheater heat transfer surface to allow for improved cleaning.