By Tim Daly
What makes the world go round? In your lifetime you’ve probably heard many theories: Angular momentum, gravitational pull, love, money; all popular choices.
In the world of industry however, there is only one true answer: Steam. Steam is the one substance, without which industry could not exist. So, what makes steam go round? In this case, it’s the boiler. In the industrial world, the boiler is the beating heart which circulates steam throughout our system. Without steam, we wouldn’t have industry; And without boilers, we wouldn’t have steam.
How We Got Here
Only a few hundred years ago, water and air were the kings of industry and commerce. Men learned how to harness the wind to move ships across the seas, and water across the land. Similarly, water wheels were used for milling grains, and rivers were tapped for sources of electrical energy.
Then scientists learned that steam could also be contained and used to power pumps and engines, and that these engines could be used to power any number of contraptions.
Steam has the fascinating ability to become more powerful as it’s compressed. Pressure and heat share a common relationship with steam, in that rising steam pressure causes an elevation in steam temperature, and raising steam temperature results in a corresponding increase in pressure. By manipulating these variables, we can use the pressure and temperature of steam to accomplish any number of tasks.
Math being the universal language, men of science and industry settled on the British Thermal Unit (BTU) to measure steam and therefore begin to understand its power.
It takes 1 BTU to heat one pound of water one degree Fahrenheit (sensible heat: heat that raises the temperature in a measurable amount). Once that one pound of water reaches 212°F(at sea level) it takes 970 BTU’s to convert it to steam (latent heat: heat that changes a matter’s phase—solid to liquid, liquid to gas, and vice-versa). Note: it takes 144 BTU’s to convert one pound of ice at 32°f to one pound of water at 32°F.
Moving Right Along
Now that men had figured out the basics of steam, it became paramount to harness and increase its energy. They wanted more pressure, and more temperature; and most importantly more power and more work.
Boilers became bigger and better, economizers and super heaters were added. Efficiency became—and remained—the focus of boiler construction. Condensate systems to reuse water, chemicals to make the water less corrosive, steam traps to streamline system performance, and insulation to reduce energy loss all became important methods to get the most work out of every drop of water used.
Water Tube Boilers And Fire Tube Boilers
While there are many variations of boilers in use today, they all basically fall under one of two categories: Water tube boilers and fire tube boilers.
In a water tube boiler, the fuel is burned in a firebox or furnace; while the boiler water is carried through boiler tubes running along the sides and rear of the firebox.
There is a steam drum at the top of the boiler and a mud drum at the bottom. Since heat rises, the steam is pressurized in the top of the boiler (at the steam drum), and the water goes down through tubes (called down comers) toward the bottom of the boiler (at the mud drum) where the condensate or make-up water is added. As this water is heated, it rises through tubes (called risers) back to the top of the boiler ( at the steam drum).
The real beauty of water tube boilers lies in the ability to take the main steam line coming out of the top of the boiler, and pass is back through the fire box so more heat can be added. This creates what we call super-heated steam. Super-heated steam is very important when the steam is used to generate electricity via steam turbine generators.
Fire tube boilers in essence, work just the opposite of water tube boilers. In a fire tube boiler the water flows into a large chamber that has a series of tubes running through it. Fuel is burned in a chamber at one end of the boiler and the heated exhaust is forced through the tubes. These tubes pass through the boiler chamber a number of times (usually one to four times) adding heat to the water. As the water turns to steam and continues to rise in temperature, it rises to the top of the boiler and exits into the main steam line.
Package Boilers and Field Erected Boilers
Package boilers, while sometimes seemingly quite large, are small enough that they can be manufactured in a factory; and delivered in almost “ready to run” condition to the boiler plant that will be using them.
Field erected boilers, mainly used in power generation, are very large and are erected at the boiler plant. They are too large to be built remotely and transported like package boilers.
Another aspect of steam generation drawing ever increasing consideration by companies involved in the process is co-generation. Simply put, this is the process of using waste heat for other purposes.
A utility company may be using steam for electrical generation, and want to use any excess steam for another process, so they pipe it to a smaller waste heat turbine, or a campus’s heating system.
Or maybe a manufacturing company needs a new boiler. So they consider a gas turbine generator instead of a standard boiler to make a few megawatts of electricity, and attach a heat recovery steam generator to the back end, to generate additional steam for their processes.
Natural Gas and oil are the most common fuels being burned in boilers today. But as the world is learning to recycle, fuels are increasingly becoming more environmentally friendly, and less wasteful. Burning any number of other substances has become fairly commonplace.
Solid fuels like coal, wood, tires, and trash were being shied away from in many parts of the country because of the solid particulates that were being released along with the exhaust. Modern filtration systems and bag houses however, have gone a long way towards removing the pollution causing solids and gases, making these boilers every bit as environmentally friendly as fuel oil and natural gas boilers.
Several factors are considered when choosing a fuel for a particular boiler plant. What fuels are readily available, how will they be delivered, how far must they travel, and at what expense. How much storage space is needed to store fuel, and what sorts of facilities need to be built to protect and store the fuel, as well as prepare the fuel for burning. All of these factors need to be considered when determining the fuel cost for running a boiler.
Steam has become almost extinct in the world of transportation due to the efficiency of diesel, gas and jet engines. Steam now faces competition in the world of electrical generation from gas turbines, nuclear power, as well as more readily available solar and wind turbine power. However, steam is still the lifeblood of manufacturing and processing, and boilers are still the hearts that pump that blood.