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Depressurizing a 2% slurry line

Depressurizing a 2% slurry line

Depressurizing a 2% slurry line

(OP)
I have a 2% slurry service (the medium is:  2% sulfuric acid + 98% water in mass fraction) in 17 bar and 204 C. I have to reduce the lines pressure to an atmospheric level to feed it to the downstream facility. I also have to cool it to 50C. I think of a restriction orifice and a self actuated valve for the pressure reducing part. And as long the service contains solids a basket strainer is considered before the exchanger (after the RO). I am not so sure about that whether this configuration would work. I can alter the configuration if you think it is not appropriate.
-    Shall I first cool the fluid and then reduce its pressure or vice versa? ( I know the exchanger would be more expensive)
-    If I first depressurize it, is it possible to use a strainer in a two phase flow before feeding the fluid to the heat exchanger?
-    I have a stand by strainer in case the operating one is plugged. How should I replace and clean them when line  is 17 bar and 204C .(it would not be safe for the operator to clean the strainer unless some safety measures were taken)
-    If I introduce two phase flow to the exchanger shall I put it in the shell side?
I don't know I had any success describing the situation. But any recommendations would be highly appreciated. Depressurizing
 

RE: Depressurizing a 2% slurry line

You neglected to mention whether this was continuous or batch operation.  Answers below are based on continuous, since doing this in batch would be easy.

The conventional solution for pressure acid leach equipment is to throttle the slurry into a flash vessel using a ceramic-lined "choke" control valve (look up "Survivor valve" on the Flowserve website as one example).  The flash will get you down to a reasonable temperature and generate steam that might be useful, but will also concentrate your slurry and acid.  Cooling from that point to 50 C is easy.

If heat recovery and concentration of the slurry is not desired for some reason, you can remove much of the destructive energy of the stream by cooling below the boiling point.  This will make throttling easier.  However, depending on your flowrate and what's in your slurry, your exchanger could easily be fouled beyond usefulness in a very short period of time.

RE: Depressurizing a 2% slurry line

(OP)
Dear moltenmetal,

Thank you for your reply

This is a continuous process.
I was thinking of a basket strainer before the exchanger and putting the choke valve after the exchanger.
frankly I don`t think my client would agree with a new vessel and a set of necessary instruments. and besides this is a pilot plant which heat recovery is not important.
but what makes me concern is reliving the strainer which seem a little odd in that operating conditions(water in 17 bar and 204C)
 

RE: Depressurizing a 2% slurry line

If the intention of the strainer is to strain large chunks out of the slurry to protect the orifice from plugging, that's one thing.  If the intention is to remove the 2% solids that make this stream a slurry, or to prevent the exchanger from fouling, the strainer will be a failure.

If it's a pilot plant, you won't mind changing orifices frequently when they wear out.  But if (when) you calculate the orifice size required for continuous pilot operation, you may find that it's smaller in diameter than two or three SLURRY particles abreast...

I'm not going to solve this one for you completely.  I can recommend a good pilot plant design/build company (www.zeton.com) if you're interested.  They've done this sort of thing many times.

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