The following article is intended to provide to all interested people the visual information about how the equipment of a thermal power station is arranged inside. This article describes a relatively new type of power unit PGU-450, that uses in its work the combined cycle (most of heat stations still have only the steam cycle). Pictures presented here were made during the power unit construction, that allows to capture some equipment devices disassembled. Several of the following photos may be used by students and teachers of energetic professions as a methodological material.
The source of energy for this power unit is natural gas. While gas combusts, thermal energy releases, which is then used for the work of all unit equipment. The unit scheme has three power machines: two gas turbines and one steam turbine. Each of three machines is designed for the nominal output electric power of 150 MW. Gas turbines have the similar operating principle as jet aircrafts.
Two components are required for gas turbines: gas and air. The air from the street passes through air vents. Air intakes are closed with lattices to protect the gas turbine unit from birds or litter. They also have the anti-ice system that prevents from freezing in winter.
Then the air goes through air ducts to the compressor inlet of a gas turbine (of the axial type). After that, the compressed air falls into a combustion chamber with natural gas. Two combustion chambers are installed in every gas-turbine unit. They are located on each side.
Each combustion chamber is equipped with 8 gas burners.
The process of burning of the gas and air mixture and the release of thermal energy occur in combustion chambers. Here is a combustion chamber inside. Walls of such machines are covered with the fireproof lining.
At the bottom of the combustion chamber there is a small viewing window, that allows to control the process. This video shows the burning process of the gas-air mixture in the combustion chamber of the gas turbine unit at the time of its launch and at work for 30% of nominal power.
Then heated combustion products get to the gas turbine and rotate it.
The turbine produces more work than it is needed for the compressor, and an excess of this work is used to drive the “payload”. An electrical generator with the power of 150 MW serves as such load. So here electricity is generated. A “gray barn” in the photo is exactly the generator. The generator is located on the same shaft with the compressor and turbine. Taken together, they rotate with the frequency of 3000 rev/min.
While going through the gas turbine, combustion products give it some of their heat, but not all the energy of combustion products is used to rotate the gas turbine. Much of this energy can not be used by the gas turbine, so combustion gases at the outlet of the gas turbine (exhaust gases) carry with them lot of heat (the gas temperature at the outlet of the gas turbine is about 500 °C). In aircraft engines this heat is wastefully released into the environment, but at this power unit it is used further in the steam-power cycle. For this purpose, exhaust gases from the output of the gas turbine are “blown” from below into so-called “recovery boilers” ( boiler-utilizers). One such boiler works in each gas turbine. Every boiler looks like a high-rise building.
In these boilers heat energy of exhaust gases is used for heating of water and turning it into steam. Subsequently, this steam is exploited for the work in the steam turbine.
For the heating and evaporation, water flows inside tubes with a diameter of about 30mm, that are placed horizontally, and exhaust gases from the gas turbine “wash” these tubes on the outside. So that is how a transfer of heat from gases to water (steam) takes place.
Having given most of the heat energy to steam and water, exhaust gases occur at the top of the recovery boiler and are removed through a flue.
On the external side of the building, chimneys of two heat-recovery boilers coincide into a single vertical pipe.
The following photos allow to estimate the size of chimneys.
Let’s go back to the construction of recovery boilers. Tubes through which water passes inside the boiler are divided into many sections – tube bundles, which form several areas: the single-phase preboiling range, evaporation area and the superheater. The first one is used to heat the water from the temperature of 40 °C till a temperature close to the boiling one. Then water enters a deaerator, that is a steel tank where water parameters are supported in such a way so that gases dissolved in water begin to intensively vaporize.
After going through the deaerator, water becomes potable and goes to the input of feed pumps. Here are 3 new waterfeed pumps.
Feedwater pumps have the electric drive. Between pumps and the electric motor there is a fluid flywheel – a unit, allowing to gradually change rotation frequency of the shaft in a wide range.
A feed pump itself is centrifugal and multistage. This pump develops a complete vapor pressure of the steam turbine, and even exceeds it.
Parts of an old feeding pump with a similar design. The pump consists of alternating rotating centrifugal wheels and fixed guide discs.
A fixed guide disc.
After feed pumps, feed water is put into the so-called “drums-separators” – horizontal steel tanks designed to separate water and steam.
Each recovery boiler has two separators ( 4 at the power unit). Taken together with tubes of evaporator sections of heat-recovery boilers, they form contours of the circulation of the steam-water mixture. It works as follows. Water with a temperature close to the boiling point comes into tubes of evaporator sections, reheating to the boiling temperature and then partially converts into steam. At the output of the evaporation section, we have the steam-water mixture, which enters drum-separators. Inside the drum-separators special devices are installed, they help to separate steam from water. Then steam is fed to the superheater, where its temperature increases even more, and separated water is mixed with feed water and then it enters the evaporation section of the recovery boiler.
A steam turbine has a 2 cylinders – the cylinder with high-pressure and a low-pressure cylinder.
A new low-pressure rotor.
A high-pressure rotor at a closer look. It has 20 steps. Note a massive steel turbine body consisted of two parts and pins with which these halves are connected to each other.
Nozzle arrays serve to send to steam the right speed and direction. They are fixed sections with fixed blades, placed between rotating discs of rotors. Nozzle arrays do not rotate – they are immobile and serve only to guide and accelerate steam in the right direction.
Parts of nozzle arrays prepared for mounting.
The lower part of the turbine body with installed halves of nozzle arrays.
Then a rotor is put in the body, upper halves of nozzle arrays are assembled. The upper body, various pipes, heat insulation and a shroud go after.
After passing through the turbine, steam enters the condenser.
When the steam turbine body is fully assembled, at the outputs of the low pressure cylinder a space appears, here the pressure during the work of the steam turbine is about 20 times lower than atmospheric one, so the low pressure cylinder body is designed not to resist the pressure from inside, but to resist the pressure from the outside.
The condenser has a similar arrangement with the waste-heat boiler. If we open one of two covers and look inside, we will see “tube boards”.
Cooling water, which is called process ( industrial) water, flows through these tubes.
At the output of condensate pumps, water (condensate) is again fed to the input of recovery boilers, and so the steam power cycle is closed.
Process water, heated in tubes of steam turbine condensers, is taken out through underground pipelines of the technical water supply and it occurs in a water colling tower. Here is its foundation.
Below the cooling tower there is a catchment basin, where water drops fall.
The space above and below quenches is filled with a special padding of plastic shutters.
Impressions of being inside the tower.
Steel shutters at the bottom of the cooling tower are designed to regulate the flow of cold air and prevent from surfusion of industrial water in winter.
The video shows how the tower cools industrial water.
As process water is in a direct contact with the surrounding air, it gets dust, sand, grass and other dirt. Therefore, at the entrance of this water into the shop, there is a self-cleaning filter. It consists of several sections, mounted on a rotating wheel. Such filter inside.
The assembly of all technological equipment in the turbine shop is made by means of two bridge cranes. Each of them has three separate winches intended to work with loads of different weights.
Electricity is generated by three generators, driven in rotation by two gas and one steam turbine. The railway is laid right in the turbine hall, in order to deliver oversized equipment.
The process of delivering of one stator.
Due to a big weight, the installation of electric motor stators were carried out using both overhead cranes.
The interior view of generator stators.
The installation of rotors of electric generators.
The output voltage of generators is about 20 kV. The output current is equal to thousands of amperes. This electricity is derived from the turbine hall and goes to the step-up transformers, located outside the building.
Such pipelines are used for the transmission of electricity from generators to step-up transformers.
These current transformers serve to measure the current.
A step-up transformer with the output voltage of 220 kW.
Besides electric power, thermal power plants also produce thermal energy used for the heating and hot water supply of nearby regions. Having heated surrounding buildings and given them its heat, heating-system water returns to the station in order to be heated again.
The work of all power unit is controlled by the system “Ovation” of the American corporation “Emerson”.