Steam Boilers 101

A steam boiler is a pressurized vessel that transfers heat to water to produce steam for a variety of applications.

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This guide will provide a comprehensive and straightforward overview of what boilers do, how boilers function, and how to choose a safe, reliable and efficient steam boiler.

Table of contents

• How do boilers work?
  • Anatomy of a Boiler System
  • Firetube vs. Watertube
• Common boiler applications
  • Boilers vs. Hot Water Heaters vs. Furnaces
• Boiler Efficiency
  • Fuel-to-Steam vs. In-Service
  • Boiler Turndown
  • NOx Ratings
• Boiler Safety
• Maintenance and Monitoring

How Do Boilers Work?

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.

The Anatomy of a Boiler System

• Pressure Vessel: A pressure vessel contains gases or liquids at high temperatures, usually under high pressure. In a boiler, the pressure vessel is constructed from a high-strength material, often steel.
• Burner: The burner provides heat to the boiler by combusting fuel and oxygen. Fuel sources include natural gas, low-pressure propane, No. 2 oil, coal and other fuels.
• Tubes: In watertube boilers, the metal tubes situated inside the boiler contain water and are externally heated. In firetube boilers, heated gas passes through one or more tubes, heating water surrounding the tubes.
• Economizer: An economizer is a heat exchange mechanism that transfers heat energy otherwise lost in exhaust gasses and uses that energy to heat the water entering the boiler. Consequently, less additional energy is required to heat the incoming water, making the boiler more efficient.
• Deaerator Tank: Deaerators are pressurized feedwater tanks that use pressure and heat to remove oxygen and other dissolved gases (notably, carbon dioxide) from the water fed into the boiler. Dissolved oxygen and carbon dioxide could otherwise cause serious corrosion to the boiler.
• Heat Exchanger: A heat exchanger transfers heat from one substance to another without those substances directly interacting. In a boiler, the hot gas’ heat is transferred to the water via a heat exchanger.
• Control Panel: The control panel enables operators to control boiler settings such as temperature and pressure. Commercial and industrial boiler control panels include detailed analytics.
• Feedwater Tank: The feedwater tank is a collection tank that supplies the water used by the boiler to create steam. The feedwater tank is where the treated water is collected and then pumped into the boiler. Boiler chemicals that remove oxygen and protect the metals within the boiler are injected and mixed within the feedwater tank. Facilities with condensate return lines can collect condensate water from steam that drops below the boiler point and fed back into the system to recapture the treated water.
• Combustion System: The combustion system works by combining air and fuel then igniting the mixture to produce heat. Ensuring the correct balance of air to fuel is an important component of the boiler combustion system.
• Reverse Osmosis System: Reverse Osmosis works by using a high-pressure pump to increase the pressure on the raw water side of the RO and force the water across the semi-permeable RO membrane, leaving almost all (around 95% to 99%) of dissolved impurities behind in the reject stream.
• Chemical Monitoring Systems: The carefully controlled addition of chemicals can enhance a boiler’s operations. Chemical monitoring systems precisely monitor chemical levels and provide ongoing analysis.
• Fuel Types: Combusting fuel is the ultimate source of the boiler’s heat. Gas, oil, and coal are common sources of fuel. When coal is used, it is often crushed and heated to improve efficiency. Less commonly, biomass such as wood chips or other natural materials may be used.
• Water Treatment: Water used by the boilers needs to be treated before entering the boiler to prolong the life of the boiler. Water softeners and Reverse Osmosis systems help to prepare the water by removing dissolved solids like calcium and magnesium to reduce the potential for scale build-up within the boiler. Feedwater tanks are also a part of the water treatment as they use heat to reduce the number of dissolved gases within the water that can contribute to oxidation and corrosion within the boiler.

Firetube vs. Watertube Boilers

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.

Firetube Boilers

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.

Watertube Boilers

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.

Common Boiler Applications

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 vs. Hot Water Heaters vs. Furnaces

Boilers, hot water heaters, and furnaces all produce heat, but they vary in their design and function. Let’s uncover the differences:

• Boilers heat water in a pressurized container to create steam. Many facilities will set a steam pressure, that has a direct correlation to steam temperature which can be adjusted for a wide range of commercial and industrial applications. When used domestically for central heating, the steam can be efficiently distributed to radiators to heat the house. Boilers vary in complexity and design, depending on their specific purpose.
• Compared to boilers, hot water heaters are more basic. Their single function is to heat water. Commonly, water is stored in a tank and heated with heating rods. Alternatively, instant water heaters rapidly warm water without the need for a storage tank.
• Rather than heating water, furnaces heat air that circulates through a home or building. Fuel burns to warm a heat exchanger, which heats the air before it distributes through a series of vents. The furnace temperature is controlled with a thermostat.

Boiler Efficiency

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.

Fuel-to-Steam Efficiency vs. In-Service Efficiency

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.

Boiler Turndown Ratios

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 Ratings

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.

The Most Efficient Boilers

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:

• Each module starts up in less than five minutes, making the system more flexible and heat efficient.
• Smaller modular boiler units take up less floor space.
• You can rotate the use of individual units to reduce wear and tear.
• Operators can turn off individual boilers when not needed to save fuel.
• If one unit stops working, the rest continue to function. There’s less chance of downtime.
• The system is completely scalable. You can add more units as needed.

Boiler Safety

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.

Boiler Safety Through the Decades

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 . 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 . Those state laws would eventually inform a national safety code.

The ASME’s first Boiler and Pressure Vessel Code was published in . 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.

So, What’s the Safest Boiler on the Market?

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.

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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.

Boiler Maintenance & Monitoring

Effectively monitoring and maintaining boilers before any problems arise will help ensure your facility stays safe and productive.

Chemical Water Treatment

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

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.

Controllers and Monitoring Systems

Modern boiler controllers include sophisticated diagnostics to help users identify potential issues before they become serious problems. Comprehensive monitoring systems can provide analytics on everything from current steam pressure to water hardness.

Learn More About Steam Boilers

Managing Low Water in a Steam Boiler

Understanding common steam boiler issues like low water conditions can better equip you and your team to handle concerns that arise. Adequate water levels are vital to boiler operation and safety. Low water conditions in your boiler occur when it fails to replace the water as it evaporates. 

Managing low water in a steam boiler is an important element of boiler maintenance that impacts everything from safety and wear to boiler effectiveness.

Why Is Low Water a Dangerous Condition for a Boiler?

The primary purpose of water in a boiler is to protect metal components from the high temperatures produced in the unit. While metal surfaces like steel can withstand high temperatures, boiler temperatures highly exceed steel’s limits. When water levels get too low, the metal components are exposed to extreme heat, which can cause them to melt and warp. In addition to melting metal components, boiler low water conditions can also crack or loosen tubing, leading to water leaks.

Low water is especially dangerous because it creates conditions where the boiler vessel can overheat and potentially explode. Adding cool water to overheated components will create steam, which expands significantly and creates too much pressure inside the boiler, causing the vessel to burst. A boiler explosion is a risk to lives, property and operations, and will cost you and your company significant time and money to recover from. Maintaining adequate water levels in your boiler is essential to safe operations.

Common Causes of Low Boiler Water

Low water levels in your boiler can happen for several reasons, some of which may be out of your control in some ways. Many of the common causes of low boiler water can be prevented with proper maintenance and adequate monitoring. Understanding these common causes can also help you understand how to fix and prevent low water issues:

• Failed feed pump and water level controls: Sometimes, your boiler components fail. Components like the feed pump or water level controls are more likely to fail without proper maintenance, though failures can also occur randomly. Your boiler’s feed pump and water level controls communicate to refill the boiler as water evaporates. If either of these components fails, the boiler may not get enough water.
• Low water levels in the feed tank: The feed pump pulls water from a feed tank. This water reservoir exists to refill your boiler when water levels get low. However, if water levels in the feed tank get too low, there will be nothing for the pump to pull into the boiler, resulting in low water levels. 
• Lack of monitoring: Boilers require constant monitoring to maintain adequate water levels and efficient operation. Whether your water levels are monitored manually or via systems like low water cutoffs, a lack of monitoring increases the risk of missing when water levels get low.

How to Fix Low Water in a Boiler

Water levels within your boiler will fluctuate as it evaporates and is refilled. When it gets low, water needs to be added to the boiler through feed pumps or similar operations, depending on the boiler. As the controls sense low water levels, the pumps will kick in and feed water into the boiler until it reaches normal levels. When these systems fail to replenish low water, you’ll be at high risk of boiler damage. Fixing and maintaining low water levels is relatively simple with the right features. 

Depending on your boiler, you may use low water lights or low water cutoffs to monitor your water levels. 

Regularly Check the Low Water Light on the Boiler

Some boilers have indicator lights that can visually tell you when your boiler’s water level is too low. If your boiler has a low water light, check it regularly. Make this part of your daily or pre-shift checklists to ensure your team monitors it. If you notice the light come on, you know water needs to be added to the boiler immediately. 

Older boilers may not have a low water light — instead, your boiler may have a sight glass that allows you to see into the boiler and determine where the water level sits. The sight glass offers another way to visually gauge the water level, so check it regularly. You and your team should be familiar with what the normal water level looks like through the sight glass so it’s easy to tell when it falls. 

Use Low Water Cutoffs

A typical low water cutoff (LWCO) is a floating system within the boiler that rises and falls with the water levels. When the water level falls too low, LWCOs will automatically shut the boiler off to prevent damage. LWCOs are typically triggered when the water level falls within a few inches of the boiler’s tubes, as exposure can lead to several tubing issues. 

LWCO systems may also use probes or a combination of floaters and probes. The probes sit in the water and shut off the boiler when the water reaches a certain level. While most boilers today come standard with LWCOs, your older boilers may not have them. In this case, you should have a professional install them for peace of mind. 

The repairs you’d need after low water damage can be costly, sometimes requiring a new boiler altogether. LWCOs are a simple preventive measure that can save you money in the long run.

Steam Boiler Maintenance

Boilers can fail even with LWCO systems in place, so maintaining your boiler is essential to further helping prevent damage and keeping the boiler in efficient condition. Consistent steam boiler maintenance can extend your unit’s life and keep it working effectively for a long time. Here are a few maintenance tips to keep your steam boiler in optimal condition and prevent low water damage. 

Create a Maintenance Schedule and Checklist

Timely maintenance can make a huge difference in your boiler’s performance. Create a boiler maintenance schedule and checklist to stay on track and ensure maintenance tasks are done consistently. Some tasks should be done before and after each shift — like checking water levels — while others can be done daily or weekly. Indicate which tasks should be completed and when, and keep a log that tracks completed maintenance so you know for sure when tasks were completed and what’s needed next.

The key to steam boiler maintenance is being consistent, and a scheduled checklist can help you do just that.

Conduct Blowdowns

Blowdown is a process that involves emptying your boiler’s water tank and refilling it. This process helps you determine a few things, including:

• The boiler’s ability to refill adequately: After blowing down, you can watch the speed at which the boiler refills. Water should fill the tank quickly, meaning the valves are working properly. A slow refill could indicate several problems, including blockages.
• Whether the LWCOs work: A blowdown is also a perfect chance to check the performance of your LWCOs. As the boiler drains, you’ll be testing the LWCOs — if they shut it down, you’ll know it’s working properly. If not, you’ve identified an issue with your LWCOs and should address it promptly. 
• Potential blockages: Blowdowns are an effective way to identify and potentially fix blockages in the water lines. Sludge, scale and sediment in the water can build up in your boiler, causing obstructions. These obstructions can cause the water to refill slower than is ideal. Depending on the severity, blowdowns can help push blockages through the lines to clear them. If they’re not resolved after blowing down, the issue should be addressed after shutting down and cooling the boiler.

Maintain Water Treatment

Boiler water must be treated to remove minerals that can cause buildup, encourage overheating or cause other damage. For example, oxygen in the water can cause corrosion like pitting and rusting on your boiler’s metal components. As the metal corrodes, it will become weak, thin and more susceptible to breakage. Various chemicals and treatments can be added to the boiler water to remove oxygen and other elements or particles so the water has fewer impurities.

Keep in mind that your boiler water can be contaminated with other particles like oil. High concentrations of contaminants can lead to water carrying over into the steam lines. Maintaining consistent water treatments helps prevent boiler issues related to water impurities and contaminants.

Schedule Regular Inspections

Like any machine, boilers require professional inspections to operate properly. While your team should conduct visual inspections daily, professional inspections should be scheduled annually. Professionals can identify weaknesses in the boiler system and areas that pose potential threats before they become major problems. Professional inspection also ensures every aspect of your boiler is inspected, even the hard-to-reach or see components.

Regularly scheduling professional steam boiler inspections is the best way to catch potential issues before they become major setbacks.

Factors to Consider When Replacing Your Industrial Steam Boiler

Even with the best preventive care and maintenance, boilers don’t last forever, and a time may come when you need a replacement. Look for signs that your boiler may need to be replaced, including odd or loud noises, decreased efficiency or expensive upkeep. Whether your boiler simply aged out or there’s a sudden break, knowing when to replace it and what to consider when doing so is essential.

Here are a few factors to consider when replacing your boiler.

Safety Ratings

Safety should be a top priority when working with any industrial equipment, including boilers. Since boilers involve chemicals, high temperatures, high pressure, combustion, moving parts and other safety hazards, you should use a boiler with high safety ratings. Choosing a boiler that’s been designed and built with safety standards in mind can help reduce risks while working with the boiler. 

For example, consider if a boiler has any safety features or components that help reduce the likelihood or severity of common boiler issues. Some boilers won’t start if you try to bypass their built-in safety measures, reducing the risk of small issues becoming major problems. Also, consider whether certain components like tubing are designed to withstand high temperatures and pressure. Most are, though this is a necessity, so you wouldn’t want to sacrifice this.

Advanced Controls and Monitoring

While you should only have trained individuals monitor and service your boiler, even the most knowledgeable people can overlook potential concerns. Some modern boilers feature advanced controls and monitoring capabilities that can help you effectively monitor and address boiler issues. Boilers with monitoring and smart controls are beneficial because they can help your team catch issues that may be difficult to identify. Boiler monitoring can also send alerts when potential issues are detected, notifying you and your team before the problem escalates. 

Look for important low-water features that will help you monitor water levels. Boilers with built-in LWCOs help reduce the risks of low boiler water immediately upon installation, saving you time and resources to install them later. Many boilers also feature blowdown systems, allowing you to conveniently perform this necessary maintenance routine.

Rent or Buy

You also have the option to rent or buy a replacement boiler depending on your needs and budget. Both choices have pros and cons, so weighing your options will help you make the best decision for your facility. 

Purchasing a new or refurbished steam boiler may make sense for your facility if you already own a boiler or have consistently high needs for it. For example, if your production line always needs the boiler, you may be better off owning one — or multiple depending on the size of your operation. 

When deciding whether to buy a boiler, be sure to consider price as a major deciding factor. While you may be able to cover the purchase, be sure to also consider the price of installation, maintenance and operational costs. Investing in maintenance for your boiler may be most cost-efficient than another replacement, though you should be prepared to cover those costs.

Renting can be a more convenient option for some facilities. Boiler rentals are ideal for emergency situations. Let’s say your primary boiler is undergoing extensive maintenance or repairs and must be shut down for a week. Rather than pause operations and lose money, you could temporarily rent a boiler to continue operations while your boiler is out of commission. Boiler rentals also offer more flexibility and lower costs, allowing you to plan for the long term and save money, all while continuing operations.

Choose Steam Boilers From Smith Hughes

Whether you need a cost-effective boiler option or a temporary fix in an emergency, boilers from Smith Hughes are your most reliable option. Our comprehensive packages can include everything from installations and start-ups to boiler training and more. Our team will work closely with you to find a solution for your time and space needs. We also offer numerous boiler service packages, including 24-hour emergency boiler room services.

Contact our team for more information or to get a quote.

Sources:

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