Steam boilers produce pressurized steam power by heating water to its boiling point using a combustible fuel source.
How the water is heated depends on whether it is a firetube or watertube boiler. The primary differences between the two can be found in their names.
In a firetube boiler, the combustible fuel source is contained within a tube surrounded by a vessel filled with water. The tube gradually heats the water around it, eventually producing steam.
In a watertube boiler, the water is contained within multiple tubes, and heat from the combustible fuel source is applied to the outside of the tubes to produce steam.
As mentioned earlier, the two main types of boilers you will find on the market today are firetube boilers and watertube boilers. Let’s dive deeper into how each type works.
As the name implies, in firetube boilers, a flame passes through an enclosed tube. The flame heats the ambient gas. That heat is transferred through the tube walls, heating the water contained in the vessel to the point that steam is produced.
Firetube boilers have a lot of history. After all, they powered some of the world’s first steam locomotives. Due to the immense stored pressure and inherent inefficiencies, more industrial processes are turning to watertube boilers for greater safety and efficiency.
In watertube boilers, a furnace heats the gas which circulates tubes containing water. The heat is transferred through the tube walls, heating the water inside the tubes until steam is produced. Watertube boilers are typically capable of generating considerably more pressure than firetube boilers.
As watertube boilers do not enclose large volumes of water, their inherent risk is less than firetube boilers. Watertube boilers are also much more efficient, making them a preferred choice for intensive industrial processes.
Steam boilers are used for a wide variety of residential, commercial, and industrial applications.
Boilers intended for residential and commercial use typically have the lowest capacities. They are suitable for use in smaller-scale buildings and facilities that do not require a large amount of steam power.
Industrial boilers can handle a wide array of industrial processes that require greater horsepower. You can find industrial boilers in various settings, including hospitals, university campuses, chemical plants, breweries, food processing facilities, and manufacturing factories. In automotive production plants, steam is used for vulcanizing rubber for tires and other applications.
In food manufacturing and brewing, innumerable processes require steam, both in direct food production and sterilizing equipment and containers. High-temperature steam is also used to ensure food safety through pasteurization.
Boilers, hot water heaters, and furnaces all produce heat, but they vary in their design and function. Let’s uncover the differences:
The efficiency of a boiler will directly affect the cost of running the boiler over its lifetime.
Boiler efficiency improves by optimizing the way boilers are used. Ultimately, however, the design of the boiler system determines much of the efficiency outcomes.
Functionally, boilers can be thought of as heat exchanging mechanisms. A boiler generates heat and ultimately transfers that heat to water — the less heat energy that is lost throughout the process, the more efficient the boiler.
The two industry standards for measuring efficiency are fuel-to-steam efficiency and in-service efficiency. Fuel-to-steam efficiency, also known as Annual Fuel Utilization Efficiency (AFUE), measures combustion efficiency. That is, what percentage of energy is converted to steam. A limitation of fuel-to-steam efficiency is that it only gives you a measurement of efficiency when the boiler runs at full capacity. Practically speaking, most boilers do not constantly run at full capacity. That’s why it’s important to consider in-service efficiency, which refers to the boiler’s total efficiency in its everyday function.
Another important measure of operational efficiency is the boiler turndown ratio. Boilers with a high turndown ratio provide flexibility with the ability to produce lower amounts of steam than the maximum output. This allows facilities to deviate from the maximum steam output and conserve resources by turning down the boiler output to efficiently match the facility’s steam supply demands.
NOx is a blanket term for a group of nitrogen oxides responsible for smog and air pollution (nitric oxide and nitrogen dioxide). Any form of combustion is likely to produce NOx emissions. As boilers combust fuel to produce heat, NOx is produced. NOx emissions are regulated because they can harm human health and damage the environment.
Miura boilers produce less NOx by reducing the flame temperature. As the temperature rises so does NOx creation.
Traditional firetube boilers can take a long time to heat up and begin generating steam — all while consuming large amounts of fuel in the process. In contrast to firetube boilers, watertube boilers are more efficient because the reduced water content means there is less wasted energy used to heat the system when beginning operation.
For greater efficiency, consider a modular boiler system. Instead of a single massive boiler, modular boilers systems are a group of small boilers that work together to meet your steam demands precisely.
Essentially, each boiler in the modular boilers system operates independently. The independent boilers integrate into a single system, with a single master controller switching them ON or OFF as needed to meet demand. All modules may operate simultaneously, or individual modules can be shut down and quickly restarted as needed. This means you’re only producing steam when you need it.
At Miura America, we specialize in modular water tube boiler systems. There are several advantages of using a Miura boiler system:
In the early days of steam power, boilers were volatile and not always securely constructed. Boiler explosions were commonplace, resulting in injury and even death.
Today, boiler design follows rigorous safety guidelines overseeing both the production and use of boilers. Let’s explore a brief history of boiler safety and identify the safest boiler option currently available.
Most early boiler explosions were caused by a breakdown in the parts of the pressure vessel, either through corrosion or poor build quality.
A turning point in the regulation of boilers came about in the wake of the Grover Shoe Factory disaster in 1905. A boiler located at the RB Grover shoe factory in Brockton, Massachusetts exploded, causing widespread injury and loss of life.
There were no reliable boiler operation guidelines in the decades preceding the disaster, and industrial safety inspections were uncommon. As a result, thousands of boiler explosions had occurred.
Following a successful campaign by the American Society of Mechanical Engineers (ASME) to persuade industrialists of the need for regulation, Massachusetts passed a law regulating boiler use in 1907. Those state laws would eventually inform a national safety code.
The ASME’s first Boiler and Pressure Vessel Code was published in 1915. Today, the ASME has issued 28 books, covering a comprehensive range of operational issues, running into tens of thousands of pages.
The safest modern boilers virtually eliminate the possibility of catastrophic failure, creating a much safer work environment.
Modern boilers are robustly built, with additional features to prevent corrosion and damage that might cause safety issues. Effective monitoring and robust safety measures are essential to ensure ongoing safety, particularly for commercial and industrial applications.
In terms of boiler design, the safest type of boiler is a watertube boiler because it is designed to operate with less water volume than a firetube boiler. Additionally, should a watertube boiler fail, that failure would be contained within the tubes rather than exploding outward like a firetube boiler failure.
Boilers should also be designed to minimize the chance of thermal shock or even eliminate it. Thermal shock occurs when cold water enters a boiler and reacts with the extremely hot water already in the boiler. The ensuing rapid contraction and expansion of components could lead to catastrophic failure. Some measures can be taken to reduce the likelihood of thermal shock (such as reducing daily operating cycles). Still, ideally, a boiler should be designed to prevent thermal shock from occurring under any conditions.
Effectively monitoring and maintaining boilers before any problems arise will help ensure your facility stays safe and productive.
Chemical water treatments are used to reduce dissolved oxygen within the water or treat metal surfaces to prevent degradation. Using these treatments allows facilities to control pH, prevent scale, reduce corrosive ions, and ensure the boiler’s reliable function.
Water softeners remove hard metals (notably calcium and magnesium) from the water used in the boiler. Hard water can cause scale build-up and can damage boiler components over time.