How do we calculate the efficiency of a combined cycle power plant? Please explain with an example. (a 2 (GTs) 1 (ST) module.)

 

Sunny,

Based on your past questions and the volume of questions since you have found this site, I think two very good resources for you are Google and Wikipedia.

By Googling 'combined cycle power plant efficiency', I came up with a very nice wikipedia article at the top of the Google results page describing combined cycle plants and discussing efficiency and many other parameters. From that article, "The thermal efficiency of a combined cycle power plant is the net power output of the plant divided by the heating value of the fuel." That's a very simple calculation--if you know the heating value of the fuel (not an assumption based on old fuel analyses). As an example, take the net power output of the three turbine generators and divide it by the heating value of the fuel being burned (you need to know the fuel flow-rate as well as the heating value per unit). But, it is a simple calculation. Lots of other factors can be used to fine-tune the calculation to make it very precise, and the more precise the more valuable the information for troubleshooting and improvement activities.

There are many companies which sell programs, some very sophisticated, and some as simple as a spreadsheet, to calculate power plant efficiencies. Many consulting engineering companies also do this, for a fee. To do a proper calculation, you need a lot of very detailed data. You can make a rough calculation using some assumptions (we don't know how much data and how detailed the data is that's available at your site), but that would be an approximation. To be very accurate, you'd need to understand all the "house" loads and the fuel characteristics of what's being burned, as well as air flow data and exhaust flow data and condenser efficiencies; the list can get very large very fast depending on how accurate you want to be. To be even remotely accurate, you'd probably have to install some instrumentation, either temporary for a "snapshot" of operating parameters, or permanent, if you want an ongoing analysis.

Having said that, I'm a firm believer in trending. If you can begin gathering data, accurately, and continue to gather that same data, accurately, over time, you can develop a trend of power plant performance and efficiency even if it's based on some assumptions and ignores a lot of detailed data. You would need to be very cognizant of changes in plant operating characteristics if you see large changes in the trend to negate changes in parameters which aren't being monitored. But, you can develop a pretty good trend by using the same information, accurately obtained, and plotting that data over time.