Dry Wash Tank
While there are several designs used for resin exchange resin tanks/beds ours has been simplified to water purification tanks. These are what are called reverse flow tanks, and work essentially the same way a canister type filter does, with the fuel entering in one side and then passing down into the tank to then filter through the resin media and come back up a center tube to the center of the cap where it leaves the tank.
The tanks come with a center tube in place complete with a basket type strainer cut to fit. These will have to be removed and discarded as they are too porous for the resin and eventually the resin will find itself migrating up that center tube and wanting to transfer to the other tank. This is not a good idea. We have modified ours so that this will not happen.
The replacement tube is a 1/2″ black iron pipe that scews into the T fitting which has it’s ends capped with 70 mesh stainless steel screen. This is lowered into the tank and then measured off so that the fit will duplicate the original.
The 70 mesh screen is held in place using common hose clamps. Not very pretty, but effective. The top of the 1/2″ pipe must be beveled so that it is not too tight a fit into the cap risking spliting it. It has to be just snug enough to allow it to fit very snugly but still be removable by hand. Be sure to taper the lip of the pipe so it does not cut into the cap.
The tanks used here are water purifying tanks. They can be acquired through any company that deals with water purifying. The recommended resin depth is 24″, although with keeping in mind that resin will double in size the tanks we have would not accomodate this, so we have opted for 19″ of media per tank, which still gives 38″ total, above the minimum recommended by Purolite. Our tanks are 44″ at the lip, 42″ at the shoulder, so we have pretty much maximised bed allowance.
While filling the tanks for the first time it is very important to cover the pipe’s opening so that no media get in it. Initial loading should be with finished biodiesel (if available) enough to cover the resin, but not fill the tank.
When using metal drums as a wood chip filter there is some advance preparation that must also be done. Unlike the resin tanks the chip drums are filled to capacity and hand packed. For more on this see our interview with RolfQuo Biodiesel.