Environmental Impact of Fossil Fuels

Keywords: environmental impacts of fossil fuels, fossil fuel impact

The pollution of large combustion plants comes from fossil fuel such as: coal, oil (petroleum) and natural gas

Fossil fuel: have been formed from the remains of organisms which lived hundred of millions of years a go.

There are three main types of fossil fuel: Coil, oil (petroleum) and natural gas.

Coil – was formed from the remains of tree and plants which grew in swamps.

Oil – it is formed from the sea, the sea contains many tiny animals and plants called plankton, they get their energy to live and multiply from sunlight. When they die they sink to the bottom of the sea. Those that died millions of years ago, form oil and gas which are the main sources of fuel.

Natural gas – is mainly made up of methane, which is given off by anaerobic bacteria breaking down some of the organic matter which formed oil and coal.

Fossil fuels are burned to producing energy,

Pollution is defined as the contamination of air, water or soil by materials that interfere with human health, the quality of life, or the natural functioning of ecosystems. Air pollution is the pollution of the atmosphere by emissions from industrial plants, incinerators, internal combustion engines and other sources.

Pollutants can be classified as either primary or secondary. Primary pollutants are substances directly produced by a process, such as ash from a volcanic eruption or the carbon monoxide gas from a motor vehicle exhaust.

Secondary pollutants are not emitted. Rather, they form in the air when primary pollutants react or interact. An important example of a secondary pollutant is ozone-one of the many secondary pollutants that make up photochemical smog.

(Pepper, I.L & C.P Gerba & M. L Brusseau. 1996)

Source

Large combustion Plants refers to the coal power station, Oil refinery, natural gas

processing plant and others

Coal power plant

Coal is composed of carbon, sulphur, hydrogen, oxygen and nitrogen.

In a coal power station pollutants are formed by the burning of the fossil fuel coal. Burning coal at high temperature will produce oxides of nitrogen. Inside the coal are compounds of sulphur and nitrogen. These originate from the dead organisms that make up the coal. When the coal is burnt the Sulphur and Nitrogen is oxidised producing SOX and NOX, which are released into the atmosphere as primary pollutants. The NOX produced from combusting the Nitrogen in the coal is called fuel NOX. There is also NOX produced by the combustion of Oxygen and Nitrogen in the air. This is known as thermal NOX. (Peirce, J.F & R.F.Weiner & P.A. Vesilind.1998)

When a fuel burns, it reacts with oxygen to form oxides.  If the fuel burns completely, then all the carbon in it is turned into carbon dioxide which is slightly acidic.  If there is not much air available, the carbon may be turned into carbon monoxide, which is a very poisonous gas.

The main primary pollutants created by a coal fired power station are NOx, SOx and VOC’s. Sulphur oxides are created from the burning of the coal. Coal naturally contains sulphur, the amount of which varies depending on which organisms created the coal. When the coal is burnt, so also is the sulphur.

When a fuel burns, it reacts with oxygen to form oxides. If the fuel burns completely, then all the carbon in it is turned into carbon dioxide which is slightly acidic.  If there is not much air available, the carbon may be turned into carbon monoxide, which is a very poisonous gas.

The carbon dioxide released by the coal power plant causes climate change and global warming, coal fire power plants are the main contributor to co2 in the air.

Proteins in living organisms contain nitrogen. When coal burns, Nox is formed in the following ways:

When nitrogen bound in the coal is released and combines with oxygen to form fuel Nox.

    When high combustion temperatures break apart stable nitrogen molecules in the air which then recombine with oxygen to form “thermal NOx.”

 

Primary pollutants formed in a coal fired power plants are:

Nox – formed at high temperature and pressure of the combustion causes the atmospheric nitrogen and oxygen to react.

VOCs (Volatile Organic Compounds) – produced when unburnt hydrocarbons are released through the chimney of the furnace.

Carbon monoxide is a gas formed as a by-product during the incomplete combustion of all fossil fuels. Exposure to carbon monoxide can cause headaches and place additional stress on people with heart disease.

 Sulphur dioxide mostly comes from the burning of coal or oil in power plants. Sulphur dioxide reacts in the atmosphere to form acid rain and particles. And is also a major contributor to photochemical smog.

Nitrogen oxides and sulphur oxides are important constituents of acid rain. These gases combine with water vapour in clouds to form sulphuric and nitric acids, which become part of rain and snow. As the acids accumulate, lakes and rivers become too acidic for plant and animal life.

(Peirce, J.F & R.F.Weiner & P.A. Vesilind.1998)

 

 

 

 

Impact

Coal Fired Power Stations

Coal-fired power stations are major sources of pollution. The extensive use of coal is because there is a lot of it around. Although it produces pollutants coal is an important fuel for some considerable time to come.  A coal-fired power station has three main inputs: coal, cooling water pure water to use in steam turbines. The main outputs are electricity, waste heat, CO2, SOx, NOx and ash.

Fossil fuels are also linked to the decrease of air quality. Clean air is essential to life and good health. Several important pollutants are produced by fossil fuel combustion: carbon monoxide, nitrogen oxides, sulphur oxides, and hydrocarbons. In addition, total suspended particulates contribute to air pollution, and nitrogen oxides and hydrocarbons can combine in the atmosphere to form tropospheric ozone, the major constituent of smog.

Coal-fired power stations are responsible for the diffusion of greenhouse gases such as carbon dioxide. The amount of carbon dioxide in the atmosphere must be carefully balanced to maintain the greenhouse effect, which is what keeps the surface of the earth warm enough to support life. Like all things in nature a change in one part of the environment can result in changes in another.

 

The effect of increased greenhouse gases in the environment is that the temperature of the atmosphere is expected to increase. It is predicted by some scientists that this temperature increase could result in the following:

The destruction of ecosystems such as the Great Barrier Reef.

A change in the world’s weather patterns, resulting in an increase in both intensity and frequency of storms, cyclones, floods and droughts.

The melting of glaciers and polar ice.

Rising sea levels resulting in the permanent flooding of vast areas.

Economies may be affected by the destruction of crops and industry.

 The effect of releasing gaseous acids into the atmosphere, as a result of modern lifestyles, results in Acid Rain and more serious Global Warming.

The effects of global warming is of such great concern that many nations agreed to reduce greenhouse gas emissions.

 Mining the coal that is to be used in the generation of electricity results in the destruction of the environment. Water systems can be threatened from the run-off as a result of the washing of coal.

The pollution that is caused by the means of acid rain can have a variety of effects on the environment that are mostly negative such as; acid rain being a form of chemical weathering on buildings that are constructed from limestone or marble.  Acid rain can also contaminate water supplies by dissolving the lead and copper pipes which transport the water to houses and other buildings. Another effect of acid rain is the pollution that is caused on lakes and reservoirs killing most of the wildlife, this includes trees plants and animal habitats  

Acid rain also affects rivers and lakes, as the acidity levels go up, the pH level falls. With the pH of water below 4.5 most fish will die, this will have a detrimental effect on wildlife as if the fish die the birds that feed on the fish will also die.

SOx emissions

All living organisms contain compounds of sulphur which are the origin of the sulphur found in coal. When coal burns, the sulphur compounds are converted to oxides of sulphur.

Sulphur Dioxide exposure can affect people who suffer from asthma or emphysema by making it more difficult to breathe. It can also irritate people’s eyes, noses, and throats. Sulphur dioxide can harm trees and crops, damage buildings, and make it harder for people to see long distance.

NOx Emissions

The flue gases in the power station contain oxides of nitrogen (NOx). This is because fuels contain compounds of nitrogen formed from the proteins contained in organisms. When the fuel is burnt, these nitrogen compounds are oxidised to form fuel NOx .At the high temperature of combustion, atmospheric nitrogen and oxygen combine to form thermal  NOx

High levels of nitrogen dioxide exposure can give people cough and can make them fell short of breath. People who are exposed to nitrogen dioxide for long time have a higher chance of getting respiration infection. Acid rain can hurt plants and animals, and can make lakes dangerous to swim or fish in

Nitrogen dioxide also reacts with the oxygen or hydrocarbons in the presence of sunlight to form an irritating photochemical.

Carbon monoxide – carbon monoxide makes it hard for body parts to get the oxygen they need to run correctly. Exposure to carbon monoxide makes people fell dizzy and tired and gives them headaches.

Ozone near the ground can cause a number of health problems. Ozone can lead to more frequent asthma attacks in people who have asthma and can cause sore throats, cough breathing difficult. It may even lead to premature death. Ozone can also hurt plants and crops.

When the ozone in the stratosphere is destroyed, people are exposed to more radiation from the sun (ultraviolet radiation). This can lead to skin cancer and eye problems. Higher ultraviolet radiation can also harm plants and animals

 

Volatile Organic Compounds (VOCs): causes eye irritation, respiratory irritation, some are carcinogenic, and decreased visibility due to blue-brown haze

Advantages

Very large amounts of electricity can be generated in one place using coal, fairly cheaply.

Transporting oil and gas to the power stations is easy.

Gas-fired power stations are very efficient.

A fossil-fuelled power station can be built almost anywhere, so long as you can get large quantities of fuel to it. Didcot power station, in Oxfordshire, has its own rail link to supply the coal.

Disadvantages

Coal is not a renewable resource.

Coal-fire power stations create pollution.

Mining coal damages the environment.

During the production of electricity carbon dioxide is released, increasing the amount of greenhouse gases in the atmosphere.

The main drawback of fossil fuel is pollution. Burning any fossil fuel produces carbon dioxide, which contributes to the greenhouse effect warming the Earth.

Burning coal produces more carbon dioxide than burning oil or gas. It also produces sulphur dioxide, a gas that contributes to acid rain. this can be reduced before releasing the waste gases into atmosphere.

Mining coal can be difficult and dangerous. Strip mining destroy large areas of the landscape.

Coal-power stations need huge amounts of fuel, which means train-loads of coal almost constantly. In order to cope with changing demands for power, the station needs reserves. This means covering a large area of countryside next to the power station with piles of coal

Sulphur dioxide, nitrogen oxide and nitrogen dioxide are also produced in these emissions and can produce acid rain.

(Peirce, J.F & R.F.Weiner & P.A. Vesilind.1998)

Monitoring Pollution

Pollution is measured to ensure that the air quality are not exceeded

Monitoring air pollution

When monitoring air pollution it is important to know or decide what pollutants are to be monitored, where they should be monitored, what instruments are to be used for that purpose and what kind of weather base needs to be collected, and it is also important to figure out how many stations are necessary to meet this goal.

Carbon monoxide – is typically measured by using an infrared gas analyzer. With this instrument the absorption of infrared radiation by carbon monoxide in the sample air stream is compared with absorption in a reference gas of known carbon monoxide concentration. This method allows continuous non-destructive measurement of carbon monoxide in the sampled air

Sulphur dioxide – is generally measured by ultraviolet emission spectrometers. This approach is based on the principle that sulphur dioxide emits a measurable flux of radiation when irradiated with intense UV from a light source in the spectrometer.

Nitrogen oxides – are measured by chemiluminescence. Tow sequential chemical reactions involving ozone are used. First, NO is measured, then NO2. Infrared radiation is emitted during oxidation of NO to NO2 by ozone introduced into the instrument. The amount of radiation produced is proportional to the NO concentration in the air stream. To measure NO2, a catalyst is used to reduce all NO2 in the air stream to NO, whose subsequence reaction with ozone permits the indirect determination of NO2

Ozone – concentration are generally measured by using a UV absorption spectrophotometer, although chemiluminescent-type instruments are also used.

Various no-methane hydrocarbons – are measured using such instruments as a gas chromatograph. Hydrocarbons are generally more difficult to measure than most other pollutants, and often require greater operator involvement in the measurement process

(Pepper, I.L & C.P Gerba & M. L Brusseau. 1996)

Monitoring of air quality has been undertaken by scientists for several years.

The air taken into the sampler is drawn first through a white filter paper, on which any smoke present leaves a deposit as a stain a; greater or lesser blackness. It then passes through a reagent solution which traps any sulphur dioxide present and converts it to sulphuric acid. After a week’s sampling the seven sets of smoke stain and reagent bottle are brought to the laboratory for analysis.

The smoke is determined by measuring instrumentally the loss of reflectance of the once-white filter papers, the reflectance values being convened into equivalent smoke concentrations from a standard calibration graph. The sulphur dioxide is measured by careful titration of the very weak acid solutions, followed by calculation of the results.

They also monitor air quality throughout the district, using diffusion tubes and the air quality monitoring station. Contaminated land is a key project for the service, with the production of a contaminated land strategy.

Monitoring gaseous emissions from soil and land fill

Soils play an important role in controlling back ground concentrations of most air pollutants. Soil can either emit or take up from the atmosphere many trace gases, including NOx, N2O, CO2, and CH4. In general there are three different approaches to measure gas fluxes between soil, and the atmosphere and these are:

Chamber approaches, micrometeorological approaches, and soil profile approaches.

Monitoring of tropospheric pollutants

 

When monitoring tropospheric pollutants, an important step is to know which pollutants are present in the troposphere and how their concentrations vary.

Chemists monitor the concentrations of tropospheric pollutants, to study patterns and learn about the rate at which certain reactions will take place in certain conditions

 

Studying individual reactions in the laboratory

 To make predictions about pollution, chemists need to know what reactions take place and how quickly they occur. Many of these reactions involve broken down fragments of molecules called radicals. Reactions with radicals happen very quickly but other reactions happen very slowly. Chemists measure the length of time of these reactions to predict the rate at which a reaction will proceed for any set of conditions.

 

Modelling Studies

 

 The information on rates of reactions is used in computer simulation studies to reproduce and predict the behaviour of pollutants during a smog episode. The more accurate the information used, the more closely the model simulates the observed behaviour.

 

Smog Chamber Solutions

 These are laboratory experiments on a large scale. Primary pollutants are mixed in a huge clear plastic bag called a smog chamber and exposed to sunlight under carefully controlled conditions. Probes monitor the concentrations of various species as the photochemical smog builds up. The chamber has to be big to minimise any ‘surface effects’ where the reactions take place on the walls of the container instead of the gas phase.

Chemists monitor pollutants to find out exactly what pollutants are involved in smog formation, and how they vary in concentration. These changes in concentration can show changes in the atmosphere, for example the presence of sunlight.

 

Chemists study reactions to see which pollutants react with which. Most importantly, to see which radicals are formed where, because they are very reactive, and cause a lot of atmospheric reactions. The speed of these reactions needs to be measured to understand how fast substances are being made and destroyed.

 

Chemists can makes models of situations, to predict what will happen in the future. One such model is smog chamber simulations. These are huge plastic bags which are exposed to sunlight under controlled conditions. Analytical probes monitor the concentrations of different gases as the photochemical smog forms.

Control

One of the Methods for controlling air pollution include removing the hazardous material before it is used, removing the pollutant after it is formed, or altering the process so that the pollutant is not formed or occurs only at very low levels. Industrially emitted particulates may be trapped in cyclones, electrostatic precipitators, and filters. Pollutant gases can be collected in liquids or on solids, or incinerated into harmless substances.

 The best way to control pollution is to control level of carbon emissions released into the atmosphere

Using coal with low sulphur content

  Power plants can use coal with low sulphur content.  As a result, less sulphur dioxide will be produced and the amount of sulphur dioxide in the flue gas will be significantly reduced.

 

Install scrubbers in power plants

  Power plants can install scrubbers to reduce the amount of sulphur dioxide in the flue gas.  The principle of how scrubbers can remove sulphur dioxide are given below:

 

  Dry Scrubber

     Calcium oxide reacts with sulphur dioxide in the flue gas, forming insoluble calcium sulphite which is then filtered out in the flue gas.

    

      CaO(s) + SO2(g)  CaSO3(s)

 

  Wet Scrubber

     Calcium oxide is first allowed to react with water, forming calcium hydroxide.

       CaO(s) + H2O(1)  Ca(OH)2(aq)

 Calcium hydroxide then reacts with sulphur dioxide in the flue gas, forming water and calcium sulphite.  Calcium sulphite is then filtered out.

 

      Ca(OH)2(aq) + SO2(g)  CaSO3(s) + H2O(1)

( Barret.R and F. Feates. 1994)

Install electrostatic precipitator in power plants:

Power plants can install electrostatic precipitator to reduce the amount of particulates in the flue gas.  Flue gas passes through the electrostatic precipitator.  The particulates in the flue gas are attracted by the electric field and then removed from the electrode.

 

Control the temperature in the combustion chamber:

The amount of nitrogen oxides released can be reduced by reducing flame temperature and availability of oxygen in the combustion zone.  But the flame temperature cannot be too low, which would cause incomplete combustion and produce carbon monoxide.

 

The limestone process

The other main way of reducing SOx emissions is to react them with calcium carbonate to produce gypsum for the building trade. This is a hassle as it has to compete with other brands, and be marketed.

NOx emissions

Coal fired power stations used to get the flames as hot as possible to increase the yield, but as the rate of reaction increases as temperature increases, the amount of thermal NOx (produced from the nitrogen and oxygen combining), increases to get the flames hottest the coal was powdered and mixed with an excess of air.

Low NOx burners

There is this type of burner, where the injection of air is controlled, so the flames are not as hot.

This significantly lowers the production of NOx.

Gas reburns

The injection of ethane and methane (natural gas) reacts with NOx to produce nitrogen, carbon dioxide and water vapour.

CH4 (g) + 4NO2 (g) à 2N2 (g) + CO2 (g) + 2H2O(g)

Some of the alkanes will not react, and carbon monoxide is produced as a result of incomplete combustion.

CH4 à CO + H2O

The alkanes and CO are then reacted with air to combust them completely. This oxidation is exothermic and so produces heat that contributes to the generation of electricity.

(Barret.R and F. Feates. 1994)

Conclusion

Fossil fuels, like coal, oil, and natural gas, provide the energy that powers our lifestyles and our economy. One of the main uses of fossil fuels is: to generate electricity, fuel cars, and to heat or cool buildings

Fossil fuel is one of humanity’s most important sources of energy. Fossil fuel plays a major role in our economy and many of our current technology have been developed with fossil fuel in mind. However burning fossil fuel is damaging the Earth’s environment with the release of pollution to the atmosphere. In addition ecosystems are becoming damaged by the extraction of fossil fuel.

Fossil fuels impact the environment greatly; carbon dioxide emissions contribute to harmful global warming and climate change.

Inefficient burning of fossil fuels results in the production of carbon monoxide, which is a very harmful and poisonous gas.  Inhalation of this gas is likely to cause death as it interferes with the transport of oxygen in the blood stream

Combustion of fossil fuels such as coal, oil and natural gas produces gases such as nitrogen oxides, which cause acid rain.