9 replies to this topic

[gopal.panjwani]

What is the best way to select the steam pressure for a turbine of certain megawatts if we have steam available at HP & MP pressure both. Is there a guideline which defines that above certain power we should select HP steam instead of MP steam.  Also what are the CAPEX vs OPEX relations with respect to selected steam grid for a given turbine. Please suggest.

[Erwin APRIANDI]

Hi gopal.panjwani,

 

Simple answer is to see what is other use of your steam (HP and/or MP), if it is solely for the use of steam turbine you can go for MP pressure, But if you have other user of steam (HP or MP steam) it is better to use HP steam and to take the steam outlet of the turbine to be used for other.

 

There are two types of steam turbines, First is Non-Condensing (Back-Pressure Steam Turbine) and Others is Extraction Steam Turbines. You will mostly use the Extraction type if you are using it for other purpose in the plant (This is what I have experience on)

 

 Non-Condensing.bmp   511.58KB   44 downloads

 

 Extraction.bmp   510.92KB   43 downloads

 

For CAPEX & OPEX relation it is dependant to a lot of factors, such selected steam pressure, numbers of consumers and heating requirement, source of fuel for the boilers, and etc.

 

For this one, from my experience usually there will be a study just to get the comparison

Edited by erwin.apriandi, 28 March 2013 - 03:26 AM.

[ramsingh_mech]

Gopal,

 

There is a variation in steam pressures with respect to the project requirements , for example in my project , we supply steam for utilities with three pressure ranges as High Pressure steam(HP) @ 58 barg, Mediium pressure steam(MP) @12 barg, Low pressure steam(LP) @6 Barg.These pressure shall serve the purpose for different type of operations like Heat exchanging, Pegging , Heat Tracing..etc.

 

And coming to the Main steam or Super heated steam ,it is used to run the Steam turbine to generate the power.

 

How could you fix the pressure to generate the megawatt?

 

Well, once you decided to built ,this much MW power plant, first step you need to find out the Quantity of steam required to generate the MW.( There is standard thumbrule , to produce 1MW of steam  you need 4 tons of Steam) Hence , you need to decide the Boiler first ..

for Example In stepwise:

1.If you need 60 MW Power Plant , the Steam required is 60X4 = 240 Tons.

2. Approach the boiler vendor for 240T Capacity boiler.Then Boiler vendor shall decide the Steam pressure and outlet parameters as per standards Suppose for 24 Tons boiler the parameters are Pressure- 110kg/cm2 , Temperature- 540-550Degc.

3.Then Steam turbine pressure to be fixed by considering all the pressure drop factors .

 

Regards

RAM.

[thorium90]

Ram, I dont know where you got such a thumb rule, but the amount of power one can generate from steam depends on its pressure and the amount of superheat and whether it is a backpressure or condensing turbine. Even efficiency is not considered. To use this thumb rule to select the size of a boiler and the pressure is to be frank, pretty dangerous.

 

A quick calculation on my part shows your thumb rule for a backpressure turbine to be pretty off. Although I had to make quite a number of assumptions so perhaps your thumb rule is based on something else.

Edited by thorium90, 28 March 2013 - 07:51 AM.

[shan]

First thing first, you have to consider steam balance to determine back pressure turbine or condensing turbine by using HP or MP or both HP & MP steam for additional power generation in a brown field plant. 

[gopal.panjwani]

Thanks all for replies to my query.

May be I should elaborate more on my query.

In my case as I have to select a condensing type turbine for a Syngas compressor ( 11.0 MW), I have available steam at 88 bar &  45 bar pressure and as such there is no such limitation of steam from client.  Which one should I choose considering fixed cost, operating, efficiency etc. Which is best choice n why?

[shan]

Use 88 bar steam for more power per kg of steam.

[ramsingh_mech]

Gopal ,

 

Now your question is clear,Obviously you may go for High Pressure Steam 88barg, 

Considerations:

 

1. Fixed cost: May be more as compared to other option(45 barg) ,due to metallurgical considerations.and change in other physical parameters of turbine.

2.Operation & efficiency are much better as compared to other option(45 barg) bcoz your Steamrate will comedown as enthalpy levels are higher side.

 

RAM.

[Bobby Strain]

If you want the best return on investment, you need to do a lot more work if you have steam consumers at 45 bar(g) or lower pressure. You may find an extraction turbine to be the best solution. You won't get another chance to get the most from your investment.

 

Bobby

[breizh]

http://www1.eere.ene...ment/steam.html

 

Consider this resource , a lot of great information are available there !

 

Breizh