Relating gas turbine performance to combined cycle efficiency

Abstract

The gas turbine has been around for over a century, providing power for a
variety of applications. The efficiency, i.e. the amount of power produced per
kilogram of fuel provided, has increased steadily over the years and is today
greater than 44 percent in a state of the art gas turbine. For electricity production
the efficiency can be increased further by combining the gas turbine
with a steam turbine. The energy in the hot exhaust gases can be used to boil
water into steam, which can then be used to drive a steam turbine producing
additional electricity. In a combined cycle the efficiency can reach 63-64 percent
with current technology. These power plants are expensive to operate primarily
due to the fuel prices, which heavily drives the need for even higher efficiency.
This is why companies operating older power plants often consider upgrading
their components.
When an upgrade is considered there is often an information gap between
the OEM (original equipment manufacturer) and the buyer, in this case the
plant owner. If the plant is not delivered as a turnkey by a single OEM, parts
and components are purchased from different OEMs specialized on the specific
equipment, leading to a situation where the OEM have limited knowledge about
the environment in which their equipment operates. Commonly the solution to
this is to create models and apply extensive heat and work balance equations
to calculate the impact on the plant following an upgrade of a component. This
is a time consuming and complicated task which also makes it unnecessarily
expensive since an expert has to be involved to perform the calculations. In this
report a method of predicting the combined cycle efficiency change is presented.
It is a compact formulation which has the potential to speed up the process
considerably. This could provide a tool for the OEM to quickly be able to
provide an answer to the customer, regarding the potential efficiency increase.

Popular Abstract

In this report a method of predicting the combined cycle efficiency of a power plant is
presented. The method consists of a compact equation derived from a formulation of the
thermal efficiency and uses the second law of thermodynamics to capture the changes in plant
behavior when an upgrade of gas turbine performance is implemented. The primary benefits
compared to conventional heat and work balance calculations is the cost reduction related to
the quick and simple approach.
The gas turbine has been around for over a century, providing power for a variety of
applications. It has been used to power aircraft, large ships, helicopters and industrial
machinery. The gas turbine is also commonly used for electric power generation in power plants
around the globe by driving generators that convert the mechanical power into electricity. The
efficiency, i.e. the amount of electrical power produced per kilogram of fuel provided, has
increased steadily over the years and is today closing in on 44 percent in a state of the art gas
turbine. For electricity production the efficiency can be increased further by combining the gas
turbine with a steam turbine. The energy in the hot exhaust gases leaving the gas turbine can
be used to boil water into steam, which can then be used to drive a steam turbine producing
additional electricity without the need for additional fuel. This concept is known as combined
cycle power production since it combines the thermodynamic cycles of the gas turbine and the
steam turbine. In a combined cycle the efficiency can reach 63-64 percent with current
technology. Power plants are expensive to operate primarily due to the fuel prices, which
heavily drives the need for even higher efficiency. This is why companies operating older power
plants often consider upgrading their components.
When an upgrade is considered there is often an information gap between the original
equipment manufacturer (OEM) and the buyer, in this case the plant owner. The OEM rarely
delivers a complete power plant. Parts and components are purchased from different OEM:s
specialized on the specific equipment. Because of this the OEM often have limited knowledge
about the environment in which their equipment operates. Commonly the solution to this is to
create models and apply extensive heat and work balance equations to calculate the impact on
the plant following an upgrade of a component. This is a time consuming task which also makes
it unnecessarily expensive, especially since it requires an expert engineer being involved to
perform the calculations. In this report a method of predicting the combined cycle efficiency
change is presented. It is a compact formulation which has the potential to speed up the
process considerably. This could provide a tool for the OEM to quickly be able to provide an
answer to the customer, regarding the potential efficiency increase.

• author: Frick, Simon
• supervisor: Magnus Genrup
• organization: Department of Energy Sciences
• course: MVKM01 20181
• year: 2018
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: combined cycle efficiency, second law efficiency, exergy, HRSG, irreversibility, heat engine, thermodynamics, T-q diagram
• report number: LUTMDN/TMHP-18/5416-SE
• ISSN: 0282-1990
• language: English
• id: 8947564
• date added to LUP: 2018-06-13 13:20:46
• date last changed: 2018-06-13 13:20:46