At a glance

In our today’s blog we will discuss How steam power plant works, also the different circuits of operation such as fuel and ash circuit, air and fuel gas circuit, feedwater and steam circuit, cooling water circuit.

Introduction

Steam power plant basically operates on Rankin cycle. The Rankin cycle is a vapor cycle in which fuel is used to produce heat in the boiler, which converts water into steam; this steam later expands on a turbine to generate mechanical energy to rotate the alternator for obtaining electrical output.

While studying the working of the steam power plant, we are doing to divide that process into four circuits

• Fuel and ash circuit
• Air and fuel gas circuit
• Feedwater and steam circuit
• cooling water circuit

fuel and ash circuit of steam power plant

Coal is used as a fuel for steam power plants, so in this circuit, we are going to discuss coal handling and ash handling of the power plant

In our previous blog, we discussed the site selection of steam power plant. Still, as we know, it is impossible to select a site near the coal mines, so we need to import the coal from the supply site to a storage place by rail, road, or water.

For small size power stations, coal is transported by road with the help of trucks. And for such a power plant, inland transportation is sufficient. However, if the power plant is near the waterways such as rivers, cannel, lakes, or seas, transportation by ship or boat is quite effective. For most of the power plant transportation of coal is done by using railways, road.

Manual uploading of coal from rail cars is used where the size of a plant is small, as the requirement of coal is also less. But for larger plants, manual unloading is not possible, so the coal is unloaded using wagon tipplers with the help of wagon tipplers coal conveyed to the coal handling plant.

So we have transported the coal to a coal handling plant now next step is to transport this coal to the boiler to burn it. This process is done with the help of conveyors. Basically, these conveyors are sliding belts with wheels that can carry tons of coal.

The coal is not directly burnt in the boiler. Instead, it is first stored in the bunkers from where it falls into hoppers (in the hoppers, pulverized coal is stored) by gravity.

This coal is burnt in the boiler. Any unburnt coal particles in the middle of the grate are collected in a pipe and again refired.

The ash resulting after complete combustion of fuel collects at the back of the boiler. It is removed from the ash storage with the help of scrap conveyors.

air and fuel gas circuit of steam power plant

The fuel gas circuit is all about the wastage of flue gases from the boiler and superheater and the air taken from the atmosphere for the combustion process.

The air is drawn from the atmosphere with the help of a forced draught fan or natural draught fan through the air- preheater. In air preheaters, this air is getting heated by wastage flue gases in their way to exhaust from the chimney. This heated air then enters the boiler furnace.

After passing through boiler tubes and superheater, the gases are drawn by induced draught fan through dust collector, economizer, and air preheater and finally get exhausted through the chimney in the atmosphere.

feedwater and steam circuit

We all know that after fuel combustion in the boiler, water is converted into steam to rotate the turbine blades, so in this circuit, we will discuss feed water cycles and how the steam cycle works.

For a steam power plant, almost a close loop cycle is preferred to reduce the losses and increase the efficiency of the power plant.

After the seam expansion on a turbine, the remaining steam is condensate in the condenser; this condensed steam is extracted using a condensate extraction pump and then forced to low-pressure feedwater heaters. The temperature is raised by heat extracted from the turbine.

The feed water is now pumped into the deaerator. First, it reduces the oxygen content in the condensate. Next, it gets passed towards the high-pressure feedwater heaters, increasing its temperature again by using flue gases.

This feed water is pumped into a boiler through an economizer where it is gets heated again by wastage flue gases which are going toward their way out form chimney.

In the boiler, water is converted into a steam of high pressure, wet steam. This wet steam is passed through the superheater. The superheater heats the steam to remove the possible water contents. This steam then expands on the blades of the turbine to rotate the turbine.

After giving out its heat energy to the turbine, this steam is condensed in the condenser, which is converted into feed water. Still, not all the steam expanded is converted into the water because some get waste during the process. So we need to take the fresh feed water from the water source passing through the makeup water treatment. So this makeup water for a boiler is first passed to economizer to heat up by low-pressure steam.

cooling water circuit of steam power plant

Cooling water is needed for the condensation process and many more applications.

Cooling water is supplied from the natural water source such as a river, lake, sea canal, or cooling towers thorough screening process to remove the contents from water that can damage condenser tubes.

This cooling water is circulated through the condenser for the condensation process and later discharged to the water source.

Cooling water circulation is a close loop process. Water gets cooled down every time before passing through the condenser. This circulation helps to reduce the pressure of condenser water.