If you’ve ever visited a coal-fired power plant, you may have noticed large white billowing clouds coming from the plant’s smoke stack.

These clouds are flue gas created when coal is burned in a boiler to create steam. But where does flue gas come from, and what is its purpose?

In this blog post, we will explore the surprising origins of flue gas and its role in a steam power plant. Stay tuned!

What Is Flue Gas and Where Does It Come From in a Steam Power Plant?

Flue gas is any gas produced as a result of burning fuel.

First, fuel is combusted in a boiler to create steam. The heat from the boiler is transferred to a turbine in a power plant.

The steam expands in the turbine and drives the turbine shaft to turn the generator. The steam exits the turbine and enters the condenser, cooled by water.

This cooled steam is then converted into water vapour, and this vapour exits the power plant through a flue pipe.

How Did Flue Gas Originate and Why Is It Used in Steam Power Plants Today?

The exhaust gas released into the atmosphere via a flue, a pipe or channel is referred to as flue gas.

It comes from a fireplace, oven, furnace, boiler, or steam generator. Flue gas is the byproduct of combustion plants that contains carbon monoxide, sulphur oxides, nitrogen oxides, particulate matter (dust), and any remaining compounds from the combustion of fuel and air (also known as exhaust gas or stack gas).

Flue gas is the gas exiting the atmosphere via a flue, a pipe or channel for conveying exhaust gases from a fireplace, oven, furnace, boiler, or steam generator.

“Flue gas” is frequently used to describe the combustion exhaust gas generated in power plants. This gas is preheated by the heat recovered from the flue gas stream in the steam power plants.

As a result, the steam flow through the low-pressure (LP) turbine increases, increasing the steam turbine’s power output. Carbon dioxide (CO2) and carbon monoxide (CO) concentrations in flue gases are typically higher than in ambient air.

Carbon monoxide causes a chemical reaction with the haemoglobin in the red blood cells of humans to form carboxyhemoglobin (COHb), thus decreasing the amount of oxygen that can be transported in the blood. Carbon monoxide is also toxic to living organisms.

Flue gases also produce nitrogen oxides (NOx), sulphur dioxide (SO2), and other pollutants. The efficiency of a combustion power plant can be increased by using enthalpy in the flue gas stream.

The enthalpy is the energy content from the introduction of heat at one or more temperatures. Energy recovery can be achieved by burning various fuels in the furnace of a power plant or by installing heat exchangers in the flue gas path of a power plant.

Energy recovery is typically made to meet environmental standards, lower fuel costs, and reduce operating costs for the power plant. Steam power plants using Flue Gas Recovery (FGR) systems are an environmentally friendly source of electricity that efficiently delivers thermal and electrical energy to the power grid.

Energy recovery in power plants can be classified into two types: dry cooling and wet cooling. Dry cooling is the recovery of sensible heat from the flue gas stream.

In this type, the heat from the flue gas is transferred to fresh air through air-to-air heat exchangers, which use air as the medium to transfer heat.

What Are the Benefits of Using Flue Gas in a Steam Power Plant and How Does It Improve Efficiency and Emissions Control Systems?

Flue gas is used in power plants to improve the efficiency of the power plants.

Flue gas is also used in power plant emissions control systems. Flue gas recovery systems in combined cycle power plants use heat in the flue gas streams to heat the combustion gases in the boilers.

This increases the power output of the power plant and reduces the fuel consumption by almost 50% compared to using air to combust the coal in the boilers. It can improve efficiency and emission control systems.

Flue gas is also used in power plant emissions control systems. Various gases are produced by burning fuel in a furnace, such as coal, in a power plant.

The gases produced are generally harmful; they pollute the environment and contribute to global warming. Flue Gas Desulfurisation Systems (FGD) help reduce emissions by burning the sulphur in the flue gases.

The sulphur is removed by injecting limestone into the flue gas stream. The limestone reacts with the sulphur to form calcium carbonate that precipitates and can easily be separated from the flue gas stream.

The calcium carbonate can then be disposed of or used as fertiliser.

Is There a Disadvantage to Using Flue Gas in a Steam Power Plant? If so, What Are They?

Are there any drawbacks to using flue gas in a steam power plant, and if there are, what are they?

First, flue gas is dirty and smelly. Flue gas contains a lot of sulphur dioxide and nitrous oxide, both harmful pollutants. Second, flue gas is very corrosive. Flue gas contains a lot of carbon dioxide, which is very corrosive at high temperatures. A power generator can have a long life if maintained properly, but an improperly maintained power plant can break down and fail.

Flue gas is a by-product of combustion and thus contains many pollutants, such as sulphur dioxide and nitrous oxides. These pollutants need to be removed before being released into the atmosphere. Fortunately, the flue gas can be cleaned using various pollution abatement systems.

How Will the Use of Flue Gas Continue to Evolve as We Seek to Improve the Efficiency and Reduce the Environmental Impact of Our Energy Production Systems?

As fossil fuels, such as coal, continue to dominate energy production worldwide, the need to reduce the effects of greenhouse gas emissions becomes increasingly important.

Using flue gas in power plants can help reduce carbon emissions by generating more electricity from each unit of coal than if the air is used instead of flue gas in a power plant. This is achieved by recovering the energy content of the flue gas.

A power plant using flue gas to recover energy will emit fewer greenhouse gases than one using air to combust the fuel in the furnace. If the flue gas is combusted with air in a boiler, more greenhouse gases will be released than if the flue gas is combusted over a heat recovery steam cycle (HRSC). Therefore, GHG emissions can be reduced by using flue gas in the boiler of a combined-cycle power plant.

FGD is a wet flue gas desulphurisation process that removes sulphur dioxide from flue gas produced by fossil fuel-fired power plants. FGD is an efficient, dry process that involves injecting limestone into the flue gas stream.

Limestone reacts with sulphur dioxide to form calcium sulphite, which precipitates and can be easily removed from the boiler stream. In many countries, including the United States, FGD is used to reduce the amount of sulphur dioxide (SO2) emissions to below the Environmental Protection Agency’s (EPA) health-based emissions standards.

Sulphur dioxide can be removed using several processes. Lime absorption, scrubbers, sprays, and absorption are the most commonly used processes. Several FGD systems are commercially available.

The History of Steam Power Plants and Their Development Over Time

The aeolipile, which Hero of Alexandria proposed in the first century CE, is the first machine that may be classified as a reaction steam turbine. In this apparatus, a hollow spinning sphere received steam through a hollow, rotating shaft. It came out of two opposing curved tubes, much like a spinning lawn sprinkler releases water. The lack of productive labour generated by the device reduced it to little more than a toy. Another steam-powered machine, described in 1629 in Italy, was designed so that a stream of steam impinged on blades protruding from a wheel, causing it to rotate by the impulse principle.

Beginning with a 1784 patent by James Watt, the steam engine inventor, a variety of reaction and impulse turbines were presented, all of which were adaptations of comparable water-powered systems. Unfortunately, none were very successful, at least not until William Avery of the United States built the units after 1837. One Avery turbine had a hollow shaft through which steam was delivered and two hollow arms, each measuring about 75 centimetres in length. At the ends of the arms, they had nozzles that let steam escape in a tangential direction, causing a reaction that turned the wheel. About 50 of these turbines were made for sawmills, cotton gins, and carpentry businesses, and at least one of them was tested on a locomotive. They were abandoned despite having efficiency on par with contemporary steam engines because of their extreme noise levels, difficulties managing speed, and the necessity for repairs.

There were no additional developments until the end of the nineteenth century, when numerous inventors built the framework for the current steam turbine, or until Thomas Savery introduced steam power to the industry in 1698. He built and patented the first engine in London, which he called the “Miner’s Friend” since it was designed to pump water from mines. A soldered copper boiler, used in earlier models, readily bursts at low steam pressures.

As time went on, a steam turbine turned thermal energy from pressurised steam into mechanical energy to perform mechanical work on a rotating output shaft. Charles Parsons, a British engineer, created the contemporary version in 1884 after realising the benefit of gradually using many stages connected in series to extract steam’s thermal energy. Parsons also created the reaction-stage principle, which states that the stationary and moving blade passages experience almost equal pressure drops and energy releases. He also created the first usable huge maritime steam turbines after that.

Soon after, a Swedish man named Carl G.P. De Laval built tiny reaction turbines that revolved at 40,000 revolutions per minute to power cream separators in the 1880s. However, because of their great speed, they weren’t appropriate for other commercial uses. So Carl G.P. De Laval concentrated on single-stage impulse turbines with convergent-divergent nozzles. Laval later built other turbines with horsepower capacities ranging from 15 to hundreds of thousands. He created the initial 15-horsepower marine turbines in 1892.

The first multistage impulse turbines were created in the 1890s by C.E.A. Rateau of France and Charles G. Curtis of America simultaneously. Curtis also created the velocity-compounded impulse stage. By 1900, the largest steam turbine-generator unit generated 1,200 kilowatts, and ten years later, similar devices were capable of producing more than 30,000 kilowatts. After the first decade of the twentieth century, steam turbines became the leading prime movers in central power plants since this was far more than even the most potent steam engines could produce. After successfully being installed in many 68,000-horsepower turbines on the transatlantic passenger liners Lusitania and Mauretania, launched in 1906, steam turbines became widely used in large-scale marine applications.

Later, steam turbines were also used in nuclear-powered ships. Pressures in steam generators increased from around 1,000 kilopascals gauge in 1895 to 1,380 kilopascals gauge by 1919, and finally to 9,300 kilopascals gauge by 1940. During the same time, steam temperatures soared from about 180 °C (saturated steam) to 315 °C (superheated steam), and then to 510 °C, but heat rates decreased from over 38,000 to under 10,000 Btu per kilowatt-hour.

By 1940, it was common to find single-turbine installations that could generate 100,000 kW. The cost of fossil fuels has been steadily growing for the better part of the last century, which has led to the construction of larger, more efficient turbines. To achieve this, steam generator pressures and temperatures must be greatly increased.

Before 1970, a few supercritical steam-operating units that could function at pressures of up to 34,500 kilopascals and temperatures of up to 650 °C were built. Reheat turbines that operate between 540 °C and 565 °C and at lower pressures are now routinely installed to ensure high dependability. To operate within the constraints of reactors, steam turbines in nuclear power plants, which are still being developed in several nations outside of the United States, normally run at roughly 7,580 kilopascals and temperatures as high as 295 °C. Large, highly alloyed steel blades are necessary for turbines with low-pressure end outputs of over one million kilowatts. The temperature restrictions of the materials used in steam generators, pipes, and high-pressure turbine components, as well as the demand for exceptionally high reliability, make it unlikely that there will be any significant breakthroughs over the next few decades.

In the future, somewhat more effective units with a power capacity of over 1.3 million kilowatts might be created. When steam is required for other processes like chemical processing, to power other machinery (such as the compressors of big central air conditioning systems serving lots of buildings), or to drive big pumps and fans in power plants or refineries, smaller units may be utilised for cogeneration, although the use of big steam turbines is connected to the generation of electric power and naval propulsion. Because a full steam plant, which includes steam generators, pumps, and accessories, is needed, the steam turbine is not a desirable power source for tiny sites. And that gets us to the present when steam power plants were created thanks to the development of turbines.

How Flue Gas Is Created and Its Effects on the Environment?

Let’s discuss the gases and their effects on the environment.

Flue gas emissions, called chimney emissions or stack emissions, are gases released by a thermal power plant’s chimney or a factory’s stack. These gases also contain heavy metals like cadmium and lead, carbon dioxide, carbon monoxide, nitrogen oxides, sulphur dioxide, mercury, hydrogen chloride, hydrogen fluoride, hydrogen cyanide, and hydrogen sulphide.

These gases are produced by burning fossil fuels such as coal, oil, natural gas, and biomass (wood, crop waste, and animal waste). These gases are emitted into the atmosphere with the help of chimneys.

These gases are discharged into the atmosphere and adversely affect our living world. These gases are termed greenhouse gases as they absorb heat energy emitted from the earth and trap it in the atmosphere.

These gases cause global warming and are responsible for other environmental problems like acid rain, smog, and ozone depletion.

Are There Ways to Reduce Flue Gas Emissions From Steam Power Plants?

Not all gases emitted while burning fuel in a power plant are harmful to the environment.

The government and the environmental authorities have to protect the environment. The government should regulate the emission of harmful gases from power plants and industries.

This can be done by controlling the fuel consumption of plants and by using clean fuels like natural gas. The pollution control equipment installed in the power plant should be regularly maintained and cleaned.

The only use of clean fuels can decrease the emission of harmful gases.

The burning of non-renewable fuels is not a sustainable solution. The consumption of fossil fuels can be reduced by using existing renewable energy sources like geothermal energy, wind energy, and solar energy.

By altering fuel consumption, pollution can be controlled to a certain extent. The industries producing harmful gases should be held accountable for their pollution and should pay a fine for the emissions they cause to the environment.


Steam power plants have been around for centuries, and their development has evolved to become more efficient and environmentally friendly.

Flue gas is an essential part of the steam power plant process, and its use helps improve emissions control systems while reducing environmental impact. Although flue gas has some drawbacks in a steam power plant, the benefits far outweigh them.

As we seek ways to improve efficiency and reduce emissions from our energy production systems, flue gas will play an increasingly important role in the future of steam power plants. If you’re interested in learning more about how flue gas can benefit your business, don’t hesitate to contact us today.