Silica and Alumina leaching from furnace refractory?
Silica and Alumina leaching from furnace refractory?
(OP)
Has anyone experienced silica, alumina, or sodium leaching or volitizing out of newly installed hot face refractory in a fired furnace? We fouled a downstream waste heat boiler with a very fine, low density, thin ~1/32" coating that analyzes as Fe, Si, Al, Mn, Na, and other trace minerals. We just replaced all the refractory, (hot face and insulating brick)in the reaction furnace prior to restarting this unit. Within 4-6 weeks of startup, we lost approximately 10% duty across the waste heat boiler. The fouling stabilized after about 6 weeks. The reaction furnace is your typical Claus process, burning H2S, NH3, and trace impurities with atmospheric air and 23% O2 enrichment. Normal operating temperatures of the refractory inside the furnace is 2200-2400 deg F. Has anyone else experienced this effect? What can be done to prevent it? Thanks.





RE: Silica and Alumina leaching from furnace refractory?
Things that can affect dusting are temperature swings. gas velocities, and changes in the oxidation state in the firebox.
I would checkout all the parameters on your end like the drying out process, the initial heatup, etc. I would then get with your refractory supplier and discuss it with him as there maybe a better product to use in your case.
Make sure your supplier is well versed in the art and not just cook-booking the whole process.
The best way to mediate the problem is a different refractory material. You can also apply a refractory coating or wash that will also help mediate the problem, but they are very expensive per sq.ft.
RE: Silica and Alumina leaching from furnace refractory?
RE: Silica and Alumina leaching from furnace refractory?
I appreciate the information. Once again I am reminded of how little I really know
RE: Silica and Alumina leaching from furnace refractory?
All his work has been with air bond materials and very little with the chemically bonded materials, specifically the one linked below.
We use a little of all types of air bond but mainly the type linked below. We push it to limit both on temperature and environment. I checked with the people at a onetime sister company that have numerous Sulphur burners and all use an air bond refractory like the 60 Alumina. There has been incidences of dusting but nothing to clog the heat exchanger.
The silica component is a much smaller animal when it get air borne and travels further and sticks to things better.
AS for the O2 enrichment he would have to defer that to the engineering department. Is the O2 raised to 23% or 1% enrichment, or is it 23& O2 added by volume of air?
How does the refractory proper look especially around the burner can? Problems in the front end can create problems down stream due to erosion.
Note any slick area where they might have been some incipient melting of the refractory. This is in reference to the NH3 in the system.
Get a copy of the bake out procedure and the temperature charts.
Sorry I can't get the link from Engineering.com to work, it's me not them. I'll keep trying.
The cut sheet was for a 60% air bond Alumina Silica material
used a lot in sulphur burners.
RE: Silica and Alumina leaching from furnace refractory?
Here is the material that compromises better than 95 of the fireside insulation in the unit. Nearly all of it is rammed. We push this material to the limit as during an upset we make sapphires.
According to Dale Johnson at Plibrico this is the material they use on most of in furnaces such as yours.
htt