EvapCo Operation

[gladkenn]

Dear All,

How do we operate Evaporative Condenser? My colleages insists in operating all the circulating pumps of 5 evapCo units even though the a couple of Evapcos are on standby, meaning the fans aren't operating. They argue that scaling would occur if the tubes (ammonia inside) are allowed to dry up. Whats your take on this?


Gladkenn

 

[imok2]

The condenser tubes will build up scaling if the system in operation and the water is high in precipatates and the water quality is poor, so you will need to chemically treat the tower water and have a large enough bleed to keep the solids down, however if the condenser is not in operation then I don't see where you will have a problem It takes heat in the condenser tubes to promote the scaling on them

 

[quark]

It is not the case with scaling but corrosion with stagnated water. For evaporative condensers, either of it is not a problem.

 

[SAK9]

The argument that keeping the tubes wet will reduce scaling does not make sense.When you allow the tubes to get dry,the biofilm will die off.

Turn the pumps off and see what happens over a week or so.

 

[sterl]

This is not such a simple question...Its not extraordinary to set condensing capacity sequencers such that the pumps on all condensers are the first thing engaged; whether its the smartest way to operate depends on a lot of plant specific factors.

If your climate and your duty cycle is such that 1) you have a remote sump some distance from the condensers and 2) your capacity requirement increases to near-100% very quickly, you may run into discharge pressure problems and compressor jackedet or thermosyphon oil cooling problems if you try to operate without the water "already at" the condensers.

Paralleled evap condensers are always going to have some minimum refrigerant flow. So, if you shut water flow off frequently on a particular condenser, you will tend to "soft scale" the coil. If you happen to be in a season where there is a lot of airborne debris (maple keys or poplar bolls or even sawdust) keeping the water flowing may prevent plugging the nozzle deck or the underside of the eliminators.

You can also encounter strange water treatment scenarios as well as de-passivation of the galvanizing on your coils by letting a single condenser's coil alternately go from wet to dry....That dependent to a large degree on your makeup water content as well as bleed rates and water treatment intensities.

The accepted generality is: if you can live without the water flow for an extended period, like days, take it out of the sequence; if its going to start today, you might as well start it this morning.