jjv2006 -
How are you coming along with this? I have a similar project for a permanent install. I'm looking for clarifier/thickener installations here in the U.S. for proof of principle. My client will want to visit an installation if they go forward with the design. You do have to take into account where you're going to pump the ash that you settle out of your flow. My initial flow is 8100 gpm (12 mgd) and @2% solids. You can determine your solids density if you know the higher heating value and ash content of the coal burned, the heat rate of the plant, as well as the load they are running the plant. For example, I have a 1350 MW plant with a heat rate of 10,000 btu/kwh; This gives me a heat input of 13500 MBH/hr at full capacity. My coal is assumed to have a HHV of 11,000 btu/lb. From this I calculate the tons of coal per hour that I'm burning. Now, the client told me that the coal has an ash content of 7.13% and that 90% of the ash is fly ash. My fly ash production rate is, therefore, 39 tons per hour at full load, or about 61 gpm (dry volume).
If you're dealing with hydroveyors like I am, then the water flow rate will remain constant (8000 gpm for my example), but the ash content will vary based on load. Toyo pumps has a picture of a treatment facility in New Mexico that uses clarifiers to thicken ash. I'm trying to track it down so I can track down the thickener manufacturer. My design to get 2% up to about 5-7% uses two 100 ft. diameter clarifiers. To go from 20% to 50% solids (another option we're looking at) it takes the same size clarifiers. The number I've been getting is something like 0.3 to 0.5 gallons per square foot of clarifier area for sizing. But as you've probably determined from your internet searches is that it's all a guess until you get the rheology report for your particular plant. The amount of carbon left in the ash as well as the condition of the ash (are the spheres broken and jagged) as well as the calcium content all have an effect on the performance of the fly ash. If you're burning PRB, you can run into cementitious problems. You might contact Dorr-Oliver Eimco for more assistance. They have an example of a facility they installed overseas (Gale Common, British Energy). You'll probably end up with a polymer additive so you get agglomeration and quick settling, which would not be that much more expensive or complicated for a temporary installation. I have to steer clear of complexity on my job. But you are talking a lot of expensive equipment to handle that flow rate to create a sludge that you can handle. The estimate I got for my two 100 ft. diameter clarifiers was between 1.5 to 1.7 million...just for the clarifiers; no pumps, nothing else. Just parts and installation of the clarifiers (metal aboveground tanks). I imagine you'll have to solidify to at least 60% so it can be stacked somewhere for drying prior to loading for landfilling? I'm just guessing. I hope you're still monitoring this thread b/c I think we may be able to help each other out.