hydrogen plant deaerator

[skvishwa]

hi all,
this question concerns the hydrogen plant deaerator.
whenever we take the process condensate in the deaerator of our unit the conductivity goes very high i.e. 5-6.with only dmin water coming to the deaerator it is about 2.
and though all other parameters are within limits this we have not been able to control.we increased the blow down rate to its' maximum but did'nt help.
and one more thing ,we have hydrazine and morpholine dosing for oxygen scavenging and ph control in our deaerator.
what is the preferred location for the dosing of these chemicals?
currently we are dosing morpholine in the deaerator vessel and hydrazine in the bfw pump suction i.e. vessel outlet.
santosh

 

[rmw]

Are you putting the process condensate through the trays, or sprays, depending upon which type deaerator you have, or are you just putting it straight into the storage tank. Perhaps you are not "deaerating" the condensate, just adding it to the system. Some condensate returns assume that the condensate is saturated and that it needs no further deaeration, which might be valid if the condensate is coming in at a temperature higher than the saturation pressure of the deaerator, but not a good assumption if the condensate is subcooled, and needs heating as well as deaerating.

RMW

 

[skvishwa]

the condensate we are putting into the deaerator through two packed beds which are provided for deaeration of that condensate.this condensate enters the deaerator vessel at the atmospheric temperature.
just below the packings lp steam connetion for deaeration has been provided which remains always on due known reasons.
santosh

 

[rmw]

You say it enters the deaerator vessel, but you did not tell me where. Does it enter where the make up water enters, so that it goes completely through the deaeration process, like the make up water does, or does it just enter into the deaerator vessel below the trays or sprays, or packings???

Some deaerators are designed with the thought in mind that condensate will return at an elevated temperature such that the condensate will release flash steam upon its entry into the deaerator vesses, thereby contributing to the deaerating steam, so it is brought in below the trays, sprays, packings, etc, so that the steam can move counter flow to the water flow.

Condensate at a temperature sufficient to provide flash steam to the deaeration process is hot enough that its oxygen soluability is as low as the deaerator is going to get it anyway.

Since your condensate is entering at atmospheric temperature, this tells me that its oxygen soluability is high, and it must be treated like make up water, and go through the complete deaeration process.

It is unclear to me how you get from two packed beds with steam provided for deaeration to entering the deaerator at ambient temperature. Is the condensate stored after it is deaerated?? Or, is the deaerating steam supply to the packed beds woefully inadequate??

 

[skvishwa]

the deaerator that we have is like typical deaerator in a boiler which is used for dmin water deaeration.
in this deaerator we have two packed bed sections ,one for the dmin water which comes at a temp of about 95-100 deg c.
another packed bed section is there which is independently for the process condensate .the process condensate enters at the top of this packed bed section.
we have steam injection into the deaerator at two points.one is direactly into vessel hold up water entering near the bottom and another near the top of the vessel below the process condensate stripper .both the steam are fully open.we maintain the pressure inside the deaerator at about 1.2 to 1.3 kg/cm2 by injecting steam(LP steam 3-4 kg/cm2).
santosh

 

[skvishwa]

in continuation of the last post, this condensate is not steam condensate, it is process condensate which comes after cooling and condensing the process gas( gas coming out of LT shift reactor).it is not heated before entering into the deaerator and atleast four hydrgen generation plants i have i did not see the reheating facility for this condensate before it enters in the deaerator stripping section.
santosh