Combined cycle

Help Support Engineer Boards:

Saad85

Member
Joined
Jun 24, 2016
Messages
63
Reaction score
7
What are the advantages and disadvantages of the combined gas and steam cycle?

 

polaz

New member
Joined
Sep 19, 2017
Messages
3
Reaction score
0
Combined cycle with steam using gas turbine exhaust can reach over 60% efficiency but take 30 minutes or more so start up. These are about 1200$ per KW. Several articles talk about more than 250 minutes to a cold start of a combine cycle plant to 100%. 

 

Sheshtawy

Member
Joined
Jul 18, 2017
Messages
68
Reaction score
9
I agree with polaz, and I'd like to add the following

Advantages:
1. Increased efficiency (less fuel costs)
2. Less required cooling water
3. Better adaptability to load fluctuations
4. Although they are slower to start up than stand-alone gas turbine cycles, they're actually much faster than steam turbine cycles

Disadvantages:
1. Higher capital cost in the majority of cases (sometimes it can be actually cheaper to use a combined cycle than to use a steam cycle for the same capacity)
2. Adds more complexity to the system operation
3. Trouble in the first plant (gas turbine part) causes the entire plant to shutdown

 

Philscrimp

Member
Joined
Jun 9, 2017
Messages
13
Reaction score
3
Location
MS
Without going into any details, THANK YOU for posting this...

 

A Random Guy

Member
Joined
May 26, 2017
Messages
20
Reaction score
3
Combined cycle with steam using gas turbine exhaust can reach over 60% efficiency but take 30 minutes or more so start up. These are about 1200$ per KW. Several articles talk about more than 250 minutes to a cold start of a combine cycle plant to 100%. 
$1200 per kW? Not sure where you get that number from. Simple cycle gas turbine (and recips plants) are at that or slightly above. I did development and execution  for a large utility on new CCGTs and we were around $850/kW on the large units (1 GW) and around $1000/kW on units half that size.

 
Top