I know carbon filtration has been discussed (two posts recently) but I wanted to post my experience with it so others can hopefully learn from my failures and not repeat the same mistakes.....or at least make different ones than I did. Here goes a long post:
After much searching, researching, and numerous cold calls I received some answers on the carbon filter set up that I had. Cabot was very helpful, but they only sell carbon by the pallet load, so I had to go with another supplier.
Here is what I learned from Cabot:
They recommended their product called NORIT GAC1240Plus
They stated for best results feed from the top down in my vessel (I thought bottom up would be better)
They actually recommended running two vessels, a lead and lag (no explanation as to why).
They did not recommend cleaning the carbon once it was spent (they suggested disposal and buying new)
I stated I wanted to filter 100 gallons at a time, how long would the carbon last. They responded that 90 days in the "lead" vessel (they assumed I had two vessels). I believe they assumed I was doing 100 gallons per day, which is NOT the case. So I do not really have a good idea how long my carbon will last doing 100 gallons every few weeks or months.
Recommended filtering product at 100 proof
Recommended flow rate in the vessel I have .5 to 1.5 gpm
I purchased three bags from US Water Systems of 600-USW-CARB-SORB US Water Granular Activated Carbon (1 CU/FT per bag). I spoke to one of their techs named Ian and asked what he recommended, this was the product (I am only assuming it is similar to the Cabot product, but for all I know it is completely different).
I put all three bags in the filter housing, and flushed with R.O. water top down. After about 50 gallons of R.O. water it appeared that I had removed all the carbon dust. I then started Vodka through the filter. My pump acted strange, like it was dead heading. Then I had a leak in the bottom portion of the cylinder (where the bottom cone clamps on). What I discovered was that I was dead heading the pump (and forcing Vodka out the seal). I did not clean this carbon enough. The fines that remained formed a plug at the bottom screen.
I then decided to flush again (as any product coming out was black, and it overwhelmed my secondary filter). I drained as much alcohol out as I could (I am going to add it into my next fermenter just before distillation so it will not be a total loss).
I back flushed (bottom up) with 250 gallons of R.O. water. I then forward flushed with 250 gallons of R.O. water. I then back washed with 50 gallons of R.O. water that came out clean. I had to remove the top screen when I back flushed because I again dead headed my pump with a "plug" of carbon dust.
After the second flush I restarted Vodka. Here are the top points:
Even after the second flush the first 2 gallons had a slight tinge to them
I put on a 10 micron filter, this cleared everything up
There is much more water trapped in the system than I thought (I drained it best I could, but I am assuming the water hangs up in the carbon bed). I filtered at 100 proof, I had very low proof for a very long time.
Here is what I would recommend:
Backflush the carbon with R.O. water with the top screen out
When backflushing with no top screen keep rates VERY slow, if you go to fast you will lift the bed and you will lose carbon
Once done with the first back flushing, flush from top down.
Backflush a second time
Be prepared to capture the water/vodka combo for a long time (1 gpm does take a while to purge water out)
I did not have the courage to try this, but MAYBE you could push air through the bed from the top and get all the water out. I was afraid of compacting the bed, making more dust, or creating a channel through the bed, so I opted to just add vodka at around 1 gpm.
Again, sorry for the long post on a topic that has already been covered, but I wanted to share what worked and did not work for me. Hopefully I can save someone reading this some frustration! My best advice is: if you think your carbon is clean, flush it one more time!