A 21st Century Vision of Steam Traction

Why a Coal Fired Steam Turbine in a Power Station and an Electric Locomotive are Better than a Steam Locomotive

by Ojiugo C Ndukwe & Oloruntobi E Babalola

In this section we will compare coal powered stations and electric locomotives to steam train considering economical and technical issues. The basis for one argument is that the power supply in both electric and steam trains are essentially the same, that is from the burning of coal. At first glance, it could be assumed that if the power was generated on the train it would be cheaper, more efficient, and convenient! From our research and analysis, we disproved such assumptions and found out why the steam locomotive was replaced by other technologies.

 

The Production of Electricity to Drive Electric Locomotives

As the name suggests this locomotive is powered by electric motors which draws current from cables overhead, a third rail (an electrified rail down next to the tracks) mounted alongside the running rail. The locomotive is therefore not self sufficient. The main reason for their introduction was the problem of smoke, (especially in tunnels) caused by steam locomotives.

To produce electricity in large quantities, the most reliable and efficient method is with a turbine. Steam turbines (coal fired or nuclear powered), internal-combustion engines, gas combustion turbines, water turbines, and wind turbines are the most common methods to generate electricity. Apart from coal-fired turbines, we will be looking at various sources of electricity which drive electric locomotives. These alternatives generally provide cleaner ways of producing electricity.

The pie chart below shows approximately the percentages of electricity produced in the world in 2000. From the pie chart it can be seen that about two-thirds of electricity is generated from fossil fuels.

Pie chart showing world sources of electricity in 2000

We will now explore the different sources of power that can be used to produce electricity to drive steam locomotives.

Coal-fired Steam Turbines

Coal is burnt in large furnaces and the heat generated is used to evaporate water located in boilers, creating steam. This steam expands exerting increasing pressure in the boiler. The steam turbine at the outlet of the boiler converts the energy from the moving steam into mechanical energy. The rotation of the turbine spins a magnet inside a power generator producing electricity. The main problem with this process is pollution the effects of which will be explained and explored later in this section.

Nuclear Power

The fission (splitting) of the nucleus of an atom releases heat and light energy. Fission of uranium occurs in a nuclear reactor (controlled environment) to generate heat. The heat is then used to produce steam that powers turbines and generators to generate electricity. Nuclear power however had several disadvantages:

The radioactive material generated during fission could be toxic if it is released into the environment. The nuclear waste is stored on the power plant site also raises health and safety concerns.

When all the costs associated with nuclear power are considered, it is currently more expensive than generating electricity from fossil fuels or with many renewable energy technologies. It is therefore not suitable at the moment for driving electric locomotives.

Renewable Sources

Renewable energy resources include the sun, wind, water and biomass (plants and other organic material). Renewable sources are inexhaustible and produce no air pollutants. They therefore provide security and economic advantages. However, they are more financially expensive than using fossil fuels. There is also some difficulty to site and permit wind turbines and other renewable sources. In addition, some renewable energy technologies (from the sun and wind) only generate electricity intermittently.

In summary, though renewable sources provide better economic advantages, at the moment mostly fossil fuels are used in power stations. In the future the goal of alternative energy sources is to replace fossil fuels as energy sources. Judging from the present rate of consumption of fossil fuels, the supplies will eventually run out and the so called alternative energy sources are likely to be the single way of produce electricity.

 

Analysis of the Limitations of Steam Locomotives Compared with Coal Fired Steam Turbines and Electric Locomotives

Efficiency

For a steam locomotive, the working fluid of the steam engine is water. Thus a tender, an attached car to the steam locomotive that can carry the fuel and water, is needed. A lot of power therefore is needed to pull the tender along with the storage structures and water processing equipment. Also, solid fuel requires more storage space, which further adds to the power wastage. The large mechanical transmission system causes the mechanical efficiency of the steam locomotive to be low. Additional inefficiencies present were due to poor combustion and engine losses. In practice, a steam engine exhausting the steam to atmosphere will have an efficiency of 5%, but with the addition of a condenser the efficiency is greatly improved to 25% or better.

The electric locomotive on the other hand uses energy the most efficiently due to the low friction of steel wheels on rails, the efficiency and regenerative abilities of electric motors, and the use of a weightless fuel (electricity), provided transmission losses are kept low through the use of high voltage lines.

Comparison of locomotive efficiencies:

  • Steam locomotive: 8% thermal efficiency of locomotive, 1.35 tkm/MJ transport efficiency of energy
  • Electric locomotive: 25% thermal efficiency of locomotive, 5.25 tkm/MJ transport efficiency of energy

The transmission efficiency of electric energy from the plants to the location of use is an important consideration in this respect. Today transmission losses between central power plant and end user are roughly 6%. In the US, thus transmission efficiencies are reckoned to be as high as 94% as of 1998. According to official statistics, transmission losses were 12.1% in 1917, corresponding to an average transmission efficiency of 88%. This means that the amount of useful energy transferred from plant to electric locomotives is comparable to that on steam locomotives and even far better. Furthermore several prototype superconducting systems are now being tested in the US and Europe which will lead to an improvement in the transmission efficiency.

Let us now consider efficiencies at power stations. For instance, in a combined cycle power plant, a gas turbine generator is combined with a steam turbine generator to maximise the efficiency of electricity generation. The burning material is first used to drive a gas turbine can produce 60% efficiency. Capturing the waste heat it can then be reused in the steam turbine. This process is known as cogeneration, which is a process in which the residual steam is used for heating. It is therefore possible to use about 90% of the energy produced by burning fuel, wasting only 10% of the energy produced by the combustion.

Coupled with the measures taken to improve efficiency in the stations electric locomotives are by far more efficient than steam locomotives making them the better alternative.

Maintenance

The steam locomotive was subject to high maintenance and thus needed a lot of manpower to operate and service. British Rail Figures showed the cost of crewing and maintaining a steam locomotive was twice that of an electric locomotive, and the daily mileage achievable was far lower. As labour costs rose, particularly after the Second World War, non-steam technologies became much more cost-efficient. Traditionally, steam locomotives need careful nurture before and after each journey. It takes a lot of time to light the fire and heat the boilers. Electric locomotives on the other hand can be started and halted by the push of a button.

Environmental Issues

A major criticism of the traditional steam engine was the negative impact on the environment. When the coal burns, it gives off sulphur dioxide, nitrogen oxide and carbon dioxide, among other gases. These gases have the following negative effects:

  • Sulphur dioxide (SO2) is the main cause of acid rain, which damages forests, lakes and buildings.
  • Nitrogen dioxide (NO2) is a major cause of smog, and also a cause of acid rain.
  • Carbon dioxide (CO2) is the main greenhouse gas, and is the leading cause of global warming.
  • Small particulates are a health hazard, causing lung damage.
  • Carbon monoxide (CO) is a poisonous gas and contributor to global warming.

As mentioned earlier, excess smoke was common in steam locomotives. At full output, about 50% of un-burnt carbon was passed into the atmosphere, resulting in a rain of cinders and particulates. Furthermore, water polluted with expelled cylinder lubricant and boiler treatment chemicals was released as steam to the atmosphere and as water from boiler blowdown (blowdown protects boiler surfaces from severe scaling or corrosion problems that can result otherwise).

About 80% of global Carbon dioxide emissions come from power plants. Thus power plants are estimated to be responsible for at least half of Global warming. However, it is important to note that due to cleaner coal technologies, there has been a decrease in emissions from Coal fired turbines. The Figure below shows a decrease from 1980 to 2002 in the United States:

 Decrease in emissions from electricity in the US

 

Clean Coal Technologies (CCT)

Some of the processes employed in clean coal technology (CCT) are outlined below:

Coal Washing

Coal contains mineral content that needs to be removed before it is burnt. Removing the unwanted elements, make the coal burn more efficiently. Coal washing involves grinding the coal into smaller pieces and passing it through a process called gravity separation. The coal is then pulverised and prepared for burning.

Gasification

In Integrated Gasification Combined Cycle (IGCC) systems, coal is not combusted directly but reacts with oxygen and steam to form a “syngas”. This product gas is cleaned and burned in a gas turbine to generate electricity and to produce steam to power a steam turbine. IGCC’s are able to convert coal to electricity at high efficiencies and with low emissions.

Removing Pollutants

  1. Sulphur (IV) oxide: Flue gas desulphurisation (FGD) systems are used to remove sulphur (IV) oxide. Wet scrubbers are the most popular FGD system used. This is because they are cheaper and more available than other FGD technologies. A chemical reaction occurs between S02 and limestone to form gypsum (a calcium sulphate):
    SO2 + CaCO3 + 1/2O2 + 2H2O = CaSO4.2H2O + CO2
  2. Nitrogen oxides: The use of ‘low nitrogen oxides burners’ is one of the methods to reduce Nitrogen oxides. They restrict the amount of oxygen available in the hottest part of the combustion chamber where the coal is burned hence minimising the formation of the Nitrogen oxides. Low nitrogen oxides burners can be used with other methods like overfire air, reburning or flue gas recirculation. These combinations can achieve up to 74% Nitrogen oxides removal efficiency.

Carbon Capture and Storage (CCS)

This involves capturing the carbon dioxide and storing it deep underground. CO2 can be pumped into disused coal fields where it gives off methane which can be used as fuel. It can also be pumped into and stored safely in saline aquifers or into oil fields to maintain pressure, making extraction easier.

Due to the scale of the technologies involved steam locomotives cannot benefit from clean coal technologies and are therefore less environmentally friendly.

Locomotives in China

To further compare steam locomotives with electric locomotives, we will consider China where at present both technologies are in use. In China, a system has been setup based on the operating costs and opportunity costs presented by the electric, diesel and steam locomotives. It was concluded that the most economical and rational rail transport structure should be Steam locomotives, for remote inland areas with low transport level. Diesel locomotives for medium level lines and Electric locomotives should be generally adopted for rail lines involving huge volume.

China’s present price structure, for transporting equivalent loads, shows that the lowest cost is generated by steam locomotives. Steam locomotives, having smaller traction power, are a technically inferior type of traction but prevent the full use of the railway lines due to limited tonnage, which means that it reduces the operational costs. However, in heavy traffic sections, the opportunity cost related to the affected railway transport capacity exceeds the operating cost saved by steam locomotives, providing a reason for fazing them out.

 

Conclusion

It would seem, given the areas of comparison, that electric locomotives are the better choice of railway transportation today. The steam engine appears be of inferior technology and has no solid grounds on which it is the better option. The use of electricity in transportation has aided the realisation of the Tube railways of cities, and has contributed largely to the successful operation tunnels, such as the (London-Paris) Euro-tunnel. They also have the advantage of being easier to run, much quieter, and very fast. The issue of pollution has also been considered and owing to “Clean coal technology” electric traction is the superior alternative.

The electric locomotive and electric motor coach may be regarded as natural developments that have followed steam traction. However, the question still remains whether or not this would be the case if 21st century technology was adopted and incorporated in the design of a steam locomotive today.

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1 Comment

  1. […] other demonstrates the valve working. Find out about the engine mechanisme of the steam locomotive. Which is Better? The power supply in both electric and steam trains are essentially the same, that is from the […]

    Pingback by Welcome « A 21st Century Vision of Steam Traction — 25 June 2008 @ 5:10 pm


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