Steam turbine exhaust enthalpy determination

[freefallingbody]

Dears,

The steam turbine + generator is designed for 6 MW power generation. Thsi is an extraction-condensing type turbine. Inlet steam pressure 44 bar, inlet steam flow is about 25 tons/hour. After first stage, pressure is 15 bar and temperature is 370 Deg.C. Condensing pressure is 0.06 bar absolute and temperature is 45 deg.C.

Due to the possibility of wet steam at the first stage extraction, I am finding it difficult to find out the enthalpy. I refered to ASME PTC on Steam turbines and finding it extremely difficult to understand the iterative procedure.

Assuming 0% wetness in exhaust steam, I got the enthalpy of steam based on temperature and pressure and then I got 1st stage efficiency of 84.8% and condensing stage efficiency of 60%.

My question is: How important is the need of an iterative calculation suggested by ASME? Will the error be significant?

Regards

Dinesh

 

[davefitz]

The only way to determine the error is to iterate. The difference between each iteration is a measure of the error.

Modern blades should have stage efficiencies on the order of 90+ %, not including throttling losses , pressure losses thru extraction nozzles ( at the pressure measuring point if extraction flows are in service), and exhaust losses. I think you will need to make at least one more iteration just to see the order of magnitude of the error.

 

[toothless]

What is the inlet temperature? Knowing that and the given figures for the 1st stage temp and pressure, you can figure out the efficiency. At 15 bar (217.5 psia) and 370 C (698 F), you definitely have superheated steam at that point (after the 1st stage).

Given the outlet conditions, looks like that is superheated as well.

 

[norzul]

Yes at 15bar+370C it is superheated. The saturated temp at this 15bar is about 198 C.

The thermal efficiency:

((Extracted Enery at 15bar& 370C)+ (Electrical Energy at Generator Terminal)) / (Input Energy at 44bar&??C)

Thanks

norzul

 

[freefallingbody]

Looks like my estimation of 1st stage efficiency is correct at 84.8%. I think at condensing stage, the steam is wet hence an iterative calculation may be required.

Thank u all for your replies.