Gas turbine power plants
Gas turbine units (GTU) are heat engines in which the thermal energy of the gaseous working fluid is converted into the main components: a compressor, a combustion chamber, and To ensure operation and control, the unit contains a set of interconnected auxiliary systems. GTU in conjunction with an electric generator is called a gas turbine unit. The power output of one device ranges from twenty kilowatts to tens of megawatts. These are classic gas turbine installations. Power generation at a power plant is carried out using one or several GTUs.
Device and Description
Gas turbine plants consist of two main parts, located in the same housing, a gas generator and a power turbine. In the gas generator, which includes a combustion chamber and a turbocharger, a high-temperature gas stream is generated that acts on the blades of the power turbine.With the help of a heat exchanger, exhaust gases are disposed of and heat is simultaneously produced through a hot water or steam boiler. The work of gas turbine installations involves the use of two types of fuel - gaseous and liquid.
In normal mode, the gas turbine operates on gas. In emergency or standby mode, when the gas supply is cut off, an automatic transition to liquid (diesel) fuel is carried out. In the optimal mode, gas-turbine installations produce combined electric and thermal energy. In terms of the amount of thermal energy generated, GTUs significantly outperform gas piston devices. Turbine units are used in power plants both for operation in the base mode and for compensating for peak loads.
History of creation
The idea of using the energy of a hot gas stream has been known since ancient times. The first patent for the device, in which the same basic components were presented as in modern GTU, was issued to the Englishman John Barber in 1791. The gas turbine plant included compressors (air and gas), a combustion chamber and an active turbine wheel, but never received practical application.
In the 19th and early 20th centuries, many scientists and inventors around the world developed a setup suitable for practical application, but all attempts were unsuccessful due to the low development of science and technology of those times. The net power delivered by prototypes did not exceed 14% with low operational reliability and design complexity.
For the first time gas turbine power plants were used in 1939 in Switzerland. A power station with a turbo-generator, made according to the simplest scheme with a power of 5000 kW, was put into operation. In the 1950s, this scheme was refined and complicated, which made it possible to increase the efficiency and power up to 25 MW. The production of gas turbine plants in industrialized countries has formed into a single level and direction of development in terms of capacities and parameters of turbine units. The total capacity of gas turbines manufactured in the Soviet Union and Russia is estimated at millions of kW.
The principle of operation of GTU
Atmospheric air enters the compressor, is compressed and under high pressure through the air preheater and the air distribution valve is sent to the combustion chamber.At the same time through the nozzle into the combustion chamber is supplied gas that is burned in the air stream. The combustion of the gas-air mixture forms a stream of hot gases, which at high speed acts on the blades of the gas turbine, causing them to rotate. The heat energy of the hot gas stream is converted into mechanical energy of rotation of the turbine shaft, which drives the compressor and the electric generator. The electricity from the terminals of the generator through the transformer is sent to the consumer's electrical network.
Hot gases through the regenerator enter the water boiler and then through the heat exchanger into the chimney. Water circulation is organized between the hot water boiler and the central heat point (CHP) using network pumps. The liquid heated in the boiler enters the central heating point to which consumers are connected. The thermodynamic cycle of a gas turbine plant consists of adiabatic air compression in the compressor, isobaric heat supply in the combustion chamber, adiabatic expansion of the working fluid in a gas turbine, isobaric heat removal.
Natural gas is used as a fuel for gas turbines.In the emergency mode, in the event of a gas supply shutdown, the GTU is transferred to partial load, and diesel or liquefied gases (propane-butane) are used as backup fuel. Possible options for the gas turbine installation: electricity supply or combined supply of electricity and thermal energy.
The production of electricity with the simultaneous generation of associated heat energy is called cogeneration. This technology can significantly improve the economic efficiency of fuel use. Depending on the needs, the gas turbine unit can additionally be equipped with water boilers or steam boilers. This makes it possible to get hot water or steam of different pressure.
With optimal use of two types of energy, the maximum economic effect of cogeneration is achieved, and the fuel utilization factor (KIT) reaches 90%. In this case, the heat of the exhaust gases and the thermal energy from the cooling system of the units, which rotate the electric generators (in fact, the waste energy), is used for its intended purpose. If necessary, recyclable heat can be used to produce cold in absorption machines (trigeneration).The cogeneration system consists of four key parts: primary engine (gas turbine), electric generator, heat recovery system, control and monitoring system.
There are two main modes of operation in which gas turbine plants are operated:
- Stationary. In this mode, the turbine operates at a fixed nominal or partial load. Until recently, the stationary mode was the main one for GTU. The turbine was shut down several times a year for scheduled repairs or in case of malfunctions.
- Variable mode provides the ability to change the power of GTU. The need to change the mode of operation of the turbine can be caused by one of two reasons: if the power consumed by the generator has changed due to a change in the consumer load connected to it, and if the atmospheric pressure and temperature of the air drawn in by the compressor changed. Non-stationary modes, with the most difficult ones, include stopping and starting a gas turbine unit. In the latter, the gas turbine engine operator must perform numerous operations before the first rotor thrust.Before the full start of the installation is carried out preliminary promotion of the rotor.
Changing the mode of operation of the installation is carried out by adjusting the supply of fuel to the combustion chamber. The main task of managing a gas turbine is to provide the necessary power. An exception is the gas turbine power plant, for which the main control task is the constancy of the frequency of growth associated with the turbine of an electric generator.
In stationary power engineering, gas turbines are used for various purposes. As the main drive motors of electric generators in thermal power plants, gas turbine installations are used mainly in areas with a sufficient amount of natural gas. Due to the possibility of quick start-up, GTU are widely used to cover peak loads in power systems during periods of maximum energy consumption. Redundant gas turbine units provide internal needs of thermal power plants during the shutdown of the main equipment.
In general, the electrical efficiency of gas turbines is lower than that of other power units. But with the full realization of the thermal potential of the gas turbine unit, the significance of this indicator becomes less relevant.For powerful gas turbine plants, there is an engineering approach that involves the combined use of two types of turbines due to the high temperature of the exhaust gases.
The generated heat energy is used to produce steam for a steam turbine, which is used in parallel with a gas turbine. This increases electrical efficiency up to 59% and significantly increases fuel efficiency. The disadvantage of this approach is the constructive complexity and appreciation of the project. The ratio of electric and thermal energy produced by a gas turbine plant is approximately 1: 2, that is, 20 MW of thermal energy is produced for 10 MW of electricity.
Advantages and disadvantages
The advantages of gas turbines include:
- The simplicity of the device. Due to the lack of a boiler unit, a complex system of pipelines and a variety of auxiliary mechanisms, metal consumption per unit of power of gas turbines is much less.
- The minimum water consumption that is required in the GTU only for cooling the oil supplied to the bearings.
- Fast commissioning. For gas turbine units, the start-up time from the cold state before the load is accepted does not exceed 20 minutes. For steam power plants TPP start-up takes several hours.
- Gas turbine units use gas with a very high initial temperature - more than 550 degrees. This causes difficulties in the practical implementation of gas turbines, since special heat-resistant materials and special cooling systems are required for the most heated parts.
- About half of the power developed by the turbine is spent on the drive of the compressor.
- GTU are limited in fuel, natural gas or high-quality liquid fuel is used.
- The power of one gas turbine plant is limited to 150 MW.
A positive factor in the use of GTU is the minimum content of harmful substances in emissions. By this criterion, gas turbines are ahead of their closest competitor - piston power plants. Due to its environmental friendliness, gas turbine units can easily be placed in close proximity to the places where people live. The low content of harmful emissions during the operation of gas turbines saves money during the construction of chimneys and the acquisition of catalysts.
Economics of GTU
At first glance, the prices for gas turbines are quite high, but with an objective assessment of the capabilities of this power equipment, all aspects fall into place.High capital investments at the start of the energy project are fully compensated by insignificant costs for the subsequent operation. In addition, environmental payments are significantly reduced, costs for the purchase of electricity and heat are reduced, and the impact on the environment and the population is reduced. As a result of the above reasons, hundreds of new gas turbine installations are purchased and installed annually.