2 replies to this topic

[murk954]

I'm trying to figure out how to clean out carbon build up in HX tubes that run axial along the heat exchanger. The entire inside is a series of graphite blocks with radial and axial hollowed out tubular holes. The radial tubes (shell side) have water flow and the axial tubes have a xylene condensate that deposits loose black carbon buildup over time. The heat transfer occurs through the graphite medium.

My first attempt was to simply run a brush tipped wire through, however, the multiple graphite blocks are stacked inside and the axial tubes don't line up from block to block (there are about seven blocks). I don't want to have to take the Hx apart so if anyone has a chemical alternative that will eat away at the carbon build up and not the teflon gaskets/graphite heat-exchange medium, that would be great!

By the way, these types of Carbone Poly-Bloc brand heat exchangers are meant to withstand very corrosive fluids, hence the use of graphite.

[kkala]

I remember the case of a graphite heat exchanger (by Carbon Lorraine) placed at discharge of the circulating pump in a phosphoric acid evaporator (~1979). Heating medium was steam; wet process phosphoric acid (containing F) was in tube side. Main scales were due to gypsum deposits. Only long brushes were used by maintenance people to clean the exchanger tubes, which were first washed with hot water.
Since in the present case brush is not applicable, one could try to pass a "hard" slurry through the circulating pump (if any) to replace the brush (e.g. fine sand in water). Continuous recirculation is what can be imagined (if possible), with possible erosion consequences on the impeller of recirculating pump.
For chemical cleaning, hot concentrated HNO3 attacks carbon; but graphite is also crystal carbon; you could ask advise from the supplier of exchanger. Teflon seems to have a resistance to HNO3. You can see at http://books.google....ic acid&f=false

[breizh]

I would advise to talk to the vendor !

A few years ago I was using this type of equipment to concentrate rare earth chlorides ( carbone loraine )

Hope this helps
breizh