Steam

Introduction

The industrial revolution (circa. 1760-1820) may have been fired by coal, but it was powered by steam. Humans have been harnessing the power of steam for thousands of years, but it is only in the past 200 years that we have started to rely on it for countless industrial applications. This course looks at the origins of steam, its theory (thermodynamics), generation and applications.

Fire Tube Boilers

History

The first usage of steam was recorded several thousand years ago. Hero of Alexandria created one of the first steam turbines in the 1st century, but the concept saw little application until much later in the 1800s.

Aeolipile (Hero Engine)

At the start of the industrial revolution, James Watt designed a reciprocating piston engine that was driven by steam; the design was referred to as a steam engine. The steam engine was widely adopted and became one of the most iconic prime movers of the age.

Boulton and Watt Steam Engine Drawing

But James Watt was not the only person to use the power of steam to complete useful work. Other engineers soon realised that steam engines could be used for a wide range of applications. Some applications included powering railway locomotives, tractors and ships.

Steam Powered Automobile

At about the same time as steam’s applications were growing, rapid advances in electrical engineering led to a surge in demand for prime movers that could be used to generate the newest wonder of the age…electricity!

Steam turbines were found to be ideal prime movers for the new power generation industry. Today, over 80% of the world’s electricity is provided from steam turbine prime movers.

Almost all industrial revolution prime movers were powered by steam, and it was boilers that provided that steam. As the applications of steam have grown, so too have the quantity and design variations of steam boilers. Advances in technology and materials have allowed for ever larger prime movers, which has led to a corresponding increase in the size and power of steam boilers.

Steam is used in almost all modern industrial processes, either in the process directly, or for secondary services such as water heating, or space heating. The next lesson discusses the main uses of steam.

Uses of Steam

Steam is used for four main purposes:

• Heating – closed loop. Simple design. Low pressures and temperatures.
• Power Generation – system designs vary from simple to sophisticated. Wide range of pressures and temperatures. May produce medium to very large amounts of steam.
• Industrial Processes – much like power generation steam systems although much tighter tolerances concerning steam quality may exist. Steam systems are often critical for the plant/factory production process i.e. no steam = no production.
• Mechanical Work – steam can -and is- used to drive pumps, compressors and other machinery items that may not be well suited for an electrical drive, or other drive type.

It is rare to visit an industrial plant that does not have a boiler on site. Although the uses of steam are numerous, they generally belong to one of the four categories mentioned above.

Why Steam?

Human civilisation requires energy to function, lots of it. Without energy, it would not be possible to pump water to cities, provide electricity to homes, drive automobiles, or heat buildings. Prior to being used by end consumers, all energy must first be generated and conveyed to the point of use.

Electricity is an example of conveyed energy. Power stations generate electricity by converting heat, pressure, and/or kinetic energy, into electrical current. Converting the original energy source into electrical energy allows it to be conveyed easily across vast distances to the point of use.

Although other energy fluids are available, steam is considered ‘the energy fluid’ and is by far the most common energy fluid in use today. The reasons for steam’s popularity are closely linked to the properties of the water from which it is made. Water is:

• Plentiful.
• Easy to access (geographical location dependent).
• Cheap compared to other energy fluids.
• Non-toxic.
• Easily conveyed i.e. can be pumped.
• Easily controlled i.e. with valves etc.

After water is converted to steam, it becomes an energy fluid with many advantageous properties:

• A given mass of steam can hold five to six times more energy than an equivalent mass of water.
• It can be generated efficiently; many boilers operate with >80% thermal efficiency.
• It can be distributed easily by creating a pressure difference in the steam system.
• It is non-toxic and does not damage the environment.
• It will not spark, ignite, or combust (intrinsically safe).
• The amount of energy within the system can be regulated easily by regulating the steam pressure.
• Steam’s heat transfer properties are high.

Other energy fluids are usually only used if certain variables make the use of steam undesirable. For example, thermal oils (mineral oil) are used to convey large volumes of heat at very high temperatures for which steam may not be suitable. For safety reasons, buildings are often heated via hot water well below its boiling point; the lower pressures and temperatures also place less stress upon system piping and components, which gives them a longer service life.

The Steam System

The purpose of steam is to transport energy from where it is generated, to where it is required, whilst minimising the energy loses associated with conveying. In order to do this, steam systems consist of four main parts.

• Fuel System – provides chemical energy to the boiler (or combustion turbine if a heat recovery steam generator (HRSG) is used).
• Boiler – converts the fuel’s chemical energy to thermal energy.
• Distribution – conveys steam to the point of use.
• Collection/Recovery – recovers condensate (water) from the steam system and returns it to the boiler.

The systems mentioned above form one basic process cycle:

1. Generation
2. Distribution
3. Recovery
4. Repeat

Energy is transferred to the steam during generation. The steam is then distributed to the point of use where some of the energy is transferred from the steam. The loss of energy causes some of the steam to condense and form condensate, which is then recovered, treated, and returned to the boiler. The entire process is designed based upon energy transfer.

1. Generation – chemical energy of the fuel transferred to the water. Boiler water boils then evaporates to form steam.
2. Distribution – energy conveyed to the point of use.
3. Recovery – some of the steam surrenders energy at the point of use and condenses to form water.
4. Repeat – remaining energy within the condensate returned to the boiler.

Note that in power stations, a condenser may be used to change a steam turbine’s exhaust steam to condensate prior to it being returned to the boiler.

Additional Resources

https://en.wikipedia.org/wiki/Steam

https://www.tlv.com/global/ME/steam-theory/principal-applications-for-steam.html

https://www.spiraxsarco.com/learn-about-steam/introduction/steam---the-energy-fluid

https://energyeducation.ca/encyclopedia/Steam