12 replies to this topic

[Sakthi Vel]

Dear Genius,

 

I want explanation about steam turbo blower. We have steam turbine for generating air which is used for raw material of our process. Now days,  our steam turbine efficiency goes down as per turbine design due to that steam turbine consumption is so high and vacuum also not maintained  and we could not find out any leaks and also checked of all the measuring instruments and  parameter  in that turbine.

 

   

                                                                   Design             Actual 2015  

Turbine inlet steam pressure         barg          35 (Nor)            36

Turbine inlet steam temperature   °C            320 (Nor)          343

Exhaust steam pressure                mmhg        670                  430

                                                     torr           80                  320

                                                   bar abs        0.1                 0.42

Steam quantity                             Mt/hr        11.7 (Nor)         14.8

Exhaust hood temperature              ° C          45.5 (Nor)          83

Chilling water quantity                  m3/hr        550                  520

Chilling water inlet temperature     ° C            27                   31

Chilling water outlet temperature   ° C            39                   44

Differential temperature                 ° C            12                   13

Suction air flow rate                      Nm3/hr    120000 (Max)   103490

Discharge air pressure                    barg           0.68                3.1

 

 

So that , can anyone suggest and turbine efficiency  ?

 

Note : This  steam turbine establish in 1996.

 

Thanks .

Edited by Sakthi Vel, 13 October 2015 - 01:23 AM.

[breizh]

Hi ,

You should contact the vendor . When was the last overhaul of the equipment ?

 

http://www4.eere.ene...amo_steam_tool/

 

Good luck.

Breizh

Edited by breizh, 11 October 2015 - 08:15 AM.

[PingPong]

                                                          Design             Actual

Exhaust steam pressure               mmhg    670                 430

                                               torr        80                  320

This cannot be right, because torr simply means mmHg.

 

                                                          Design             Actual

Discharge air pressure                 barg        0.68                3.1

This makes no sense. How is such big difference between design and actual possible?

 

                                                          Design             Actual

Steam quantity                          Mt/hr     11.7 (Nor)        14.8

 

Chilling water quantity               m3/hr     550                 520

Chilling water inlet temperature  ° C         27                    31

Chilling water outlet temperature° C         39                    44

When calculating the duty of the condenser, based on the chilling water data, one finds that design duty is 7.7 MW and actual duty is 7.9 MW, a difference of less than 3 %. However actual steam flow is almost 27 % higher than design. That makes no sense. Something must be wrong with one of these measurements.

 

The actual turbine exhaust temperature seems to indicate that the turbine efficiency is less than design, but because the actual steam flow is 27 % higher than design it operates at a different point on the efficiency curve, maybe well beyond the BEP, so that does not necessarily mean that there is something wrong with the turbine itself. You should try to obtain the efficiency curves of the turbine.

 

My best guess at this point would be that the condenser is the problem. Its U-value seems to be much lower than design, resulting in a much higher condensation pressure and temperature than design. Problem could be fouling. Or maybe part of the tubes is submerged in the condensate, resulting in loss of exchange area A. Check actual condensate level.

Edited by PingPong, 11 October 2015 - 05:37 AM.

[Bobby Strain]

We can only guess without good data. And this data is not sufficient to determine anything.

 

Bobby

[PingPong]

Despite inconsistencies in the data it can be estimated that:

 

1) the actual efficiency of the turbine is not lower than design (in fact I calculate that it is even a few percent higher)

 

2) the actual U^.A of the condensor is a factor 3 to 4 lower than design.

That means that either the U is much lower than design, due to fouling or .......,

or the effective A is much lower than design, due to partial flooding of the condenser due to too high condensate level, or .........

[Sakthi Vel]

Thank You Mr.Ping pong  for your valuable feedback .

[Sakthi Vel]

Dear Mr ping pong,

 

A request to you Sir. Can you send that turbine efficiency calculation to me?. It’s better to understand more for about turbine efficiency.

 

Email : rsakthi789@gmail.com

 

Thanks & regards,

 

Sakthi Vel

[Bobby Strain]

Ping,

     Not to argue, but the design conditions appear to be with some condensation. And the operating data suggests that the exhaust is somewhat superheated. So, I am puzzled how you estimated the effeciency for the design case?  Again, it's hard to draw any conclusion without complete and accurate data, properly presented.

 

Bobby

[PingPong]

Not to argue, but the design conditions appear to be with some condensation. And the operating data suggests that the exhaust is somewhat superheated.

That is right, but I took that into account.

 

To calculate the turbine efficiency one needs a detailed steam table and a Mollier diagram.

 

The design data are theoretical (calculated) data, so those data must be consistent, unless Sakthi made a typing error above.

 

Design case:

Steam flow rate = 11.7 mt/h = 3.25 kg/s

Steam enthalpy at 320 ^oC & 35 barg is 3027 kJ/kg

Steam entropy at 320 ^oC & 35 barg is 6.52 kJ/kg.K

Water enthalpy at 45.5 ^oC & 0.10 bara is 188 kJ/kg

 

Isentropic expansion down to 0.10 bara would result in a mixed phase with an enthalpy of 2065 kJ/kg (and an entropy of 6.52 kJ/kg.K)

 

Design condenser duty can be calculated from the chilling water data:

Q = (550/3.6) kg/s * 4.19 kJ/kg.K * (39 - 27)K = 7682 kW

So the enthalpy drop of the turbine exhaust over the condenser is: 7682 kW / 3.25 kg/s = 2364 kJ/kg

and the enthalpy of the turbine exhaust must be: 188 + 2364 = 2552 kJ/kg (mixed phase)

 

Therefor, in the design case the (isentropic) efficiency of the turbine must be:

(3027 - 2552) / (3027 - 2065) = 0.49 = 49 %

 

Design turbine power (excluding bearing losses) must be:

3.25 kg/s * (3027 - 2552) kJ/kg = 1544 kW

 

----------------------------------------------------------------------------------------------------------------

Actual 2015 Operation:

Steam flow rate = 14.8 mt/h = 4.11 kg/s

Steam enthalpy at 343 ^oC & 36 barg is 3082 kJ/kg

Steam entropy at 343 ^oC & 36 barg is 6.60 kJ/kg.K

 

Isentropic expansion down to 0.42 bara would result in a mixed phase with an enthalpy of 2270 kJ/kg (and an entropy of 6.60 kJ/kg.K)

 

Real expansion is to 83 ^oC at 0.42 bara, so turbine exhaust enthalpy is 2650 kJ/kg (this is steam only, as it is above the dewpoint of 77 ^oC at 0.42 bara).

 

Therefor, in actual operation the (isentropic) efficiency of the turbine must be:

(3082 - 2650) / (3082 - 2270) = 0.53 = 53 %

 

Actual turbine power (excluding bearing losses) must be:

4.11 kg/s * (3082 - 2650) kJ/kg = 1776 kW

---------------------------------------------------------------------------------------------------------------

 

The turbine is not the cause of the high exhaust pressure. If there is no air leakage, as Sakthi seems to be convinced of, then the condenser must be the problem.

 

Note also that the 27 % higher-than-design steam consumption in actual operation is not only caused by the higher-than-design exhaust pressure, but also by the 15 % higher-than-design turbine power. Assuming of course that the steam flow measurement of 14.8 mt/h is correct.

[Bobby Strain]

Pong,

     That was a good demonstration. I hope our friend appreciates your efforts. You have already resolved the issue in Posts #3 and  #5 as being the condenser. But now Sakhti has a good lesson in steam turbine analysis. I believe Harvey Wilson (Katmar) offers a calculator for steam turbines. I got the free copy many years ago. I didn't know anyone used Mollier charts now. Digital steam tables are available for free.

 

Bobby

[katmar]

PingPong has shown very nicely that the turbine is working close to its design condition.  The water flow and the temperature rise through the condenser are very similar to design as well so I do not see anything wrong in the condenser.

 

The only glaringly different factor in the original list of parameters is the discharge pressure on the air blower.  In my opinion, you need to look at the air circuit because the flow rate is down (although not hugely) and the discharge pressure is in a whole new ball park.

 

The theoretical power consumption for the blower duty is also much less than the turbine power PingPong has calculated.  Are the numbers and units correct for the air side?

[PingPong]

The water flow and the temperature rise through the condenser are very similar to design as well so I do not see anything wrong in the condenser.

I based my conclusion on the much smaller-than-design U^.A of the condenser, as follows:

 

 

In the Design case the U^.A of the condenser can be calculated from its duty Q and the LMTD

Q = 7682 kW as calculated above, and LMTD = 8 K

Therefor design U^.A = 7682 / 8 = 960 kW/K

 

Actual 2015 operation: if there is no air leakage, as Sakthi and his coworkers seem to be convinced of, the steam condensing temperature at 0.42 barg is 77 ^oC, while the chilling water warms from 31 to 44 ^oC.

That gives an LMTD of 39 K.

Duty Q = 4.11 kg/s * (2650 - 322) kJ/kg = 9568 kW

Therefor actual U^.A = 9568 / 39 = 245 kW/K which is a factor 4 lower than design.

 

The high turbine outlet pressure of 0.42 barg can only be caused by airleakage or condenser malfunction (fouling, flooding, whatever) or a combination of both.

 

The theoretical power consumption for the blower duty is also much less than the turbine power PingPong has calculated.

In my opinion theoretical blower power is always higher than estimated turbine power.

 

From the given data I estimate that the Design power of the air blower is roughly 2500 kW (@ 80 % eff.), while the design turbine shaft power is roughly 1500 kW as calculated above.

It is possible that there is also an electric motor on the same shaft providing 1000 kW.

Sakthi to clarify.

 

Based on the given discharge pressure of 3.1 barg I estimate that the Actual 2015 power of the air blower would be roughly 7100 kW (@ 80 % eff.), while the design turbine shaft power is roughly 1700 kW as calculated above.

That difference is obviously absurd, even is there is also a 1000 kW electric motor present. Moreover I cannot imagine that a blower that was designed for 0.68 barg discharge can deliver 3.1 barg in actual operation.

Sakthi to verify blower data.

 

EDIT: typo corrected (7100 i/o 5400)

Edited by PingPong, 14 October 2015 - 08:38 AM.

[Bobby Strain]

So, it's back to my initial point.

 

Bobby