in thermal power House Condensing steam Turbine use Condenser/ejector for Vacuum creation at exhaust, and dump heat in condenser and again condensate water of 46 deg C heat up for feed water of boiler through LP & HP Heaters (waste of extraction steam).

my question is ....
1. why not use heat exchanger between Turbine Exhaust and Seconder to warm up feed water up?

are this method save a quantity of energy and what are disadvantage?

 

why not use heat exchanger between Turbine Exhaust and Steam Condenser to warm up feed water up?

 

Ali,

I've worked on my share of steam turbines over many years, and I've never encountered a heat exchanger like the one you have "described"--but I freely admit I haven't seen every configuration that exists.

My guess is you are describing the gland seal steam condenser, and if so, they are usually pretty small. And, since it IS a heat exchanger, it IS already heating up whatever water is flowing through it to condense the gland seal steam, and if that flows back to the closed-loop feedwater system then it is technically improving the heat rate.

Or, are you saying that the turbine at your site was possibly not originally a condensing unit and someone has added a heat exchanger to reduce the load on the condenser? If so, what is the source of the cooling water used for this "intermediate" condenser?

Again, sometimes the cost of designing piping and purchasing valves and such is just too prohibitive at the time of the original installation. If it can be proven (using spreadsheets and formulae) that the heat rate of the plant will be improved sufficiently to recoup the cost of engineering and installation, then many times the decision will be made to make the modification.

Also, since we (me, at least) isn't clear about the heat exchanger you are describing and what the source of cooling water is, it's not possible to say for certain.

Many times when you don't receive an immediate response to a post it's because we don't understand the situation or the request. Help us to help you by describing the situation as best as possible, and you will likely receive a faster and more concise response. For my part, anyway, I can't imagine a heat exchanger between the steam turbine and condenser--it would suggest to me, again, that the turbine was not originally a condensing steam turbine, or that there was originally an extraction line that is no longer in use and so the flow of steam out of the turbine is greater than the condenser can handle. But that's just a SWAG (Scientific Wild-Arsed Guess) on my part.

Hope this helps!

 

The turbine is a heat engine, with the output being considerably affected by the pressure at the turbine exit. A couple of inWC additional pressure at the exit from the last row of blades will knock a couple of % off the turbine output.

Any heat exchanger between the turbine exit and the condenser will act to increase the turbine exit pressure and cut back the power available.

 

Every large steam turbine I have come across has LP (low pressure) heaters above the steam condensing section of the main condenser and below the seal between the condenser and the LP section on the turbine.

 

The reason is because of the Second Law of Thermodynamics which (simply) states that heat MUST be lost for an engine to work. The heat lost here is in cooling the exhaust to condensate. Bruce puts it another way above very well. Suggest you get some info on the Laws of Thermodynamics if you would like to know more

 

I just a engineering question, why not this practice use?

 

> Every large steam turbine I have come across has LP (low pressure) heaters above the steam condensing section of
> the main condenser and below the seal between the condenser and the LP section on the turbine.

but they use steam extracted from the LP cylinder - Bled Steam, no?

they don't use turbine exhaust steam before it enters the condenser.