Calculating Condenser Backpressure

[PacoCardenas]

Hello all,
I am calculating a condenser clean factor, our condenser is a surface multipressure condenser. I have acces to data of the follwing instrumentation:

CW inlet temp (t1)
CW outlet temp (t2)
CW flow (wg)
Steam temperature (ts)

According to the HEI i have calculated the cleanfactor of the condenser...but i have some doubts about the calculation:

1.- If my condenser is a multipressure, how can I considerate the clean factor? I mean, I have 2 clean factor for each box...for example Lowpress box (B) CF= 84% Highpress box CF=96%...Design CF=90% (titanium tubes) show i take an average real clean factor? =84+96/2? ir is the clean factor specific for each box?

2.- I've read that it is desireable to calculate the steam temperature (backpressure) because instrumentation has not always the real parameters....but i haven't found anything of this on HEI rev.10/11....does someone has any recomendation? I mean...how can i calculate the saturation temperature or backpressure?

3.- Can someone review my calculations?...it would be very helpfull.

Thanks for your support.

 

[EdStainless]

OK, give me the full data sheet.
In addition to what you listed I need all of the data, steam flow, steam enthalpy, and all of the physical design info.

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P.E. Metallurgy, Plymouth Tube

 

[PacoCardenas]

Attached is the condenser datasheet and design information.

(ttp://files.engineering.com/getfile.aspx?folder=2dc78efd-c381-45d9-bd00-9d8e6ac604cb&file=Manual_suplementario_de_condensador_(extrac).pdf)

But what i would like to know, is how can I calculate the real conditions with the parameters that I have. I have made this calculations on a excel file, do you want to review it?

I really appreciate your support EdStainless. Thank you.

 

[EdStainless]

I would rather have the steam load and enthalpy, but I can assume 1000 and and work backwards.
What is the steam load in each pass of the condenser? (It looks like 55%/45% roughly)
I did this quick and dirty (no correction for heavier tubes and such).

The method is to use the HEI and design data to build a model of your condenser.
Then start putting in real operation data.
It will not match, but the offset between the model and actual should be very consistent.
People often just use a linear correction factor.
Then when you performance no longer fits the modified model you know that something is wrong.
And that something is almost always fouling.

Now we need some real data. (and thanks for the translations)

pass 1 pass2
Variable Units Ti Ti
HEI Edition 10th 10th
Tube OD inches 1.000 1.000
Tube Wall inches 0.02 0.02
No. of Tubes 52704 52704
No. of Passes 2 2
Tube Constant,R 262 262
Tube Dia/Ga Const,K 0.116 0.116
Effec.Tube Lengthfeet 38 38
Steam Load lb/hr 2780000 2293000
Water Flow gal/min 440000 440000
Design Cleanliness 0.9 0.9
Load Correction 100 100
Fouling Factor 1 1
Total Correction 0.9 0.9
Enthalpy BTU/lb 1000 1000
Mat'l & Gage,Cmg,Fm 0.951 0.951
Temp Correction,Ct,Fw 1.051 1.085
Inlet Temp deg. F 82 94.64
Flow Constant,FcGPM@1ft/s 2.26 2.26

Velocity Calc ft/sec 7.390 7.390
Heat Trans Coef. BTU/hr F ft2 640.69 661.42
Thermal Effectivns 0.7835 0.7939
Temperature Rise deg F 12.64 10.42
ITD 1 deg. F 16.13 13.13
TTD deg. F 3.49 2.71
ITD 2 deg F 17.64 15.42
TS 2 deg F 99.64 110.06
TS1 deg. F 98.13 107.77
Back Pressure inches Hg 1.829 2.436
Head Loss Feet 17.87 18.45
Lift
Alloy Density lbs/in^3 0.163 0.163
Tube Weight Pounds 241,214 241,214
Water Weight Pounds 628,419 628,419
Total Weight Pounds 869,634 869,634
Weight Difference Pounds 0 0



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P.E. Metallurgy, Plymouth Tube

 

[PacoCardenas]

Attached you can find some data from the last year. On the top of the page there is information about the dates and description (also in english....sorry for the last translation).

I've marked on red the information that might be useful.

There are some signals that were out of service....those one have empty boxes.

What i wanted to know...is how could i calculate the saturation temperature...this is because I am looking for the real clean factor.

CF=Ureal/Udesign
Ureal=Q/LMTD*As

http://files.engineering.com/getfil...-4c2a-adb8-4e124873015b&file=Graficas_U2.xlsx

 

[PacoCardenas]

I've made some calculations according to the plant signals data (see attached). But for the CF how should i consider it? on invidual boxes or should i take an average?

For example, on the sheet named "5 Oct 2001" I have individual CF of:

B-CF%: 98.2440293% A-CF%: 93.4345511%

But if I take the average I have:

A-B-CF%: 95.8392902%

Which should I considere?

An also...can I calculate the Ts? (Saturation temperature)? thanks for your support.

http://files.engineering.com/getfil...b51529ca92&file=operaciones_factor_ensuc.xlsx

 

[EdStainless]

Once you know the cond pressure you just go back to the steam tables.
Using the HEI method you actually calculate the temp, and then use steam tables (or equations) to convert it to backpressure.

What I usually do is find operation data points that are as near to design conditions as possible.
Especially if the data is from recently after the condenser was cleaned.
Then calculate those and see how close to design they are, they should be fairly close.
Make a correction to the std cleanliness to get them closer and call that your baseline.
Then run calculations for other data points and see what cleanliness comes out.

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P.E. Metallurgy, Plymouth Tube

 

[PacoCardenas]

But, how? I mean i can't fondo the way...do you have an example?

 

[EdStainless]

Each box has it own inlet and outlet temps, so each will also have a separate CF.
If you use the HEI method you work in steps. You know total temp rise in the cooling water based on the total heat load steam side. Then using the calculated (and heavily corrected) heat transfer coef you get a thermal effectiveness. From this you get ITD1, TTD, ITD2, and finally TS (saturation temp). I then use the state equations from NIST to turn this into a pressure.
If you contact me, edstainless at earthlink dot net (using punctuation in place of words) I'll send you the file.

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P.E. Metallurgy, Plymouth Tube

 

[PacoCardenas]

Thanks a lot man!

I solve the problem...I really appreciate your help!

 

[PacoCardenas]

EdStainless

Could you review my calculation? (see attached) I did the following calculations:

1.- Calculate TR (TR=(T3-T1)/2) and then i got T2
2.- Calculate Q1 and Q2 (Q=density*Cp*(To-T1))
3.- I make the assumption that Q=Qmax...so Q=(Cp*m (min)*(T hot - T cold)
4.- I got Ts and compare it with the Ts sensed

For Ts of the A box got the same temperature...but for B box i always have 10ºF less.

Thanks.

Your file's link is:

http://files.engineering.com/getfil...1b36660ad7&file=operaciones_factor_ensuc.xlsx

 

[EdStainless]

Before I go into this in detail I really have to question a couple of details.
My biggest concern is the heat load in each zone? How accurate is your measurement of this?
Are your inlet and outlet water temps actual measurements also?
If the area for each is the same, and the inlet water temp to A is 10F higher then I expect the Ts to be higher by about the same. The design data makes sense, and based on the 5F diff that you are really seeing and the water temps I am feeling that the heat load is lower in A than in B by a greater amount.
I would also expect more fouling in A given the higher temps, but that may not be significant.


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P.E. Metallurgy, Plymouth Tube

 

[PacoCardenas]

1.- heat load in each zone? How accurate is your measurement of this?
I calculated it with the CW delta T. The Flow was taken with a radioactive trace and the density and specific heat was taken according to inlet temperatures.
2.- Are your inlet and outlet water temps actual measurements also?
Yes, they are the actual measurements...I took an average temperature during 2 hours (each 5 seconds).
3.- If the area for each is the same
I took different areas, because of the plugged tubes.