Air ejector troubleshooting

[Jordan-111]

We are experiencing "sudden loss of vacuum" or "pressure spike" on our air ejector system (2-3 times a day). The vacuum unit is a two-stage ejector with a direct contact inter-condenser. The unit is fairly new.
Design data: Operational data (when broken sonic wave): When running good:
1st stage suction: 1.3 inHgA 1.95inHgA
No 1st stage design discharge pressure 11 inHgA 9.8inHgA
2nd stage suction: 6.7 inHgA 7.88 inHgA 5.9inHgA
2nd stage discharge: 29.9 inHgA Constant backpressure(discharge to atmosphere) Constant backpressure
Cooling water flow: 80 USGPM 80 USGPM 80 USGPM
Inlet temperature: 67F 62 F 61F
Outlet temperature: 98F 94.5F 93.8F
Motive steam temperature: 500F 450F 450F
Motive steam pressure: 165PSIG 166PSIG 166 PSIG

We tried shutoff pressure test 3 times, they all generated different 1st stage suction pressure. (it could be that our instrument is broken)
I think the 2nd stage was broken due to excessive non-condensable loading, either from cooling water or there might be a leak somewhere in the system that causes the 2nd stage break operation.
Thanks in advance for the responses.
Regards.

 

[Jordan-111]

Thank you guys!
The Ryznar and Langelier are really useful.
We do have another source of water that is better quality, the LSI number for this water is -0.53, we will try it for 24 hours and see if there is any difference.

Thanks again,
Jordan

 

[Jordan-111]

Guys,
Just another quick question, with a two stage steam ejector system + direct contact inter-condenser, what is the maximum discharge pressure on 1st stage? Or what is the normal pressure drop on the inter-condenser?
Also, our temperature profile on the inter-condenser is at the bottom just a couple inches above the vapor inlet to the inter-condenser. Is there any reason for this? Considering we have the design cooling water flow rate.
Thanks,
Jordan

 

[pierreick]

H,
Refer to the specification sheet given by Graham. You may need to call them for more information.

https://fliphtml5.com/okzt/vchs/basic

Good luck
Pierre

 

[georgeverghese]

This intercondensor is operating in countercurrent flow mode. Vapor flow up from the bottom, direct contact quench water flow down from the top. Looking at the top section, with CW at approx 65degF, equilibrium vapor pressure would be approx 0.3psia. But you have 3.8psia at condensor top, which has an equilibrium temp of approx 150degF. So the driving temp differential at condensor top is 150-65 = 85degF. This seems huge, you should be able to operate at a much lower MTD ie. lower condensor pressure. Is this typical normal operation of these barometric condensors? This seems very inefficient.

This tells me the cooling water isnt contacting the rising vapor well enough. Either (a) interphase contact is poor or (b) interphase contact time is inadequate or (c) the biological growth is getting in the way of good contact or it may be a combination of the preceding. In a heat exchanger type condensor, one should be able to get much a much closer temperature approach.

On the the other hand, this operating data may be what is expected of a partial condensor with noncondensibles in the feed. So in this case, interstage pressure will be related to the mole ratio of condensible motive steam to noncondensible air.

Its not clear what you mean here, especially the bit about the "temp profile" :

"Also, our temperature profile on the inter-condenser is at the bottom just a couple inches above the vapor inlet to the inter-condenser. Is there any reason for this? Considering we have the design cooling water flow rate.

 

[Jordan-111]

Guys,

I tried to contact Graham, however, there is no response yet.
George:
I agree with your comment. When I tried to do shut off test, the 1st stage discharge is usually around 3.7 inHgA and the 2nd stage suction is about 2.8 inHgA. 2nd stage suction seems a bit high, but there are also some non-condensable releasing from the cooling water.
"Temp profile" is the surface temperature on the inter-condenser. I attached a video below and I believe the hot and cold temperature change should be around the middle of the condenser.

Thanks,
Jordan

 

[georgeverghese]

Ok, saw the video clip.
Strange why the temp is dropping as you move down the leg. This must be the liquid seal leg section and not the contact section. Cooling water may be auto cooling itself within this seal leg due to the reduced pressure in this condensor - outside metal temp is dropping from 70degF to about 62degF as you go down the seal leg.

 

[pierreick]

Hi,
Did you open the condenser to check the condition of the spray nozzles? I suspect some being damaged to explain the temperature profile.
Pierre

 

[Jordan-111]

Sorry for the late reply.
We opened the inter-condenser 2 months ago and it looked ok (not sure if there is any internal damage).
As for the temperature profile, at the end of the video, the surface temperature jumped from 62F back to 72F around the area of vapor inlet. From what I have been told that this interface should be around the middle of the inter-condenser.

Jordan

 

[Jordan-111]

I attached a new trend of the steam ejector system, do you guys think the cause is still due to the scale/fouling of the inter-condenser?
Unfortunately, our water wells are not able to provide the designed cooling water flow rate, we might be able to mix well water and lake water after some piping modifications.
Do you think there might be some blockage on the inter-condenser tail pipe?
Thanks,
Jordan

 

[pierreick]

Hi,
As I said previously this is not too bad.
Can you consider asking operators to perform a preventive cleaning which should be systematic, once per shift, mid shift?
Did you check the condition of the direct condenser?
Any feedback from Graham?
In the future you may consider an indirect condenser or a Vaccuum pump if this is too much trouble for your operation guys.
Pierre

 

[Jordan-111]

Hi Pierre,
No feedback from Graham yet.
Our annual shutdown is in 2 weeks, we will open up the inter-condenser and take a look inside.
Thanks,
Jordan

 

[Jordan-111]

We are performing our annual shutdown this week and I just took some pictures on the steam ejector. Do you see anything that is abnormal?

Thanks,
Jordan

 

[Jordan-111]

Another picture.

 

[Jordan-111]

Another picture.

 

[Jordan-111]

Another picture.

 

[Jordan-111]

Tailpipe arrangement from inter-condenser.

Jordan

 

[pierreick]

Hi Jordan,
Thanks for sharing!

Now, what about the spray nozzles? Are they in good conditions?
Pierre

 

[Jordan-111]

Please see attached picture.

 

[Jordan-111]

Please see attached picture.

 

[Jordan-111]

Please see attached picture.