How Does a Fire Tube Boiler Work & What Does it Do?

| Edward McKellar

The commercial boiler used in your facilities provides various functions. It may provide hot water or steam for workstations, processes, HVAC, heating systems, and other applications. Without the boiler, you will not have the hot water or steam needed on demand. Unfortunately, you are now dealing with hot water issues. Maintenance and repairs on the boiler have become a constant occurrence, as the equipment is on its last legs. It is only a matter of time before the boiler stops completely, which may cause unnecessary emergency downtimes to your commercial operations. With the rising costs of performing repairs and the increased chances of the boiler eventually stopping altogether, you are now in the market for purchasing or renting a new one.

Power Mechanical Inc. offers new and used boilers for sale or rent worldwide. We offer a wide range of boiler types including trailer mounted, mobile boiler rooms, and many others. When the constant costs of repairing your old boiler are more expensive than what it would be to purchase or rent a new one, we provide you with the boiler models that fit your applications and budget. When looking at the different types of boilers available, you may notice that some are fire tube boilers. Read about what a fire tube boiler is and how one works in a commercial setting. Then contact Power Mechanical to see how our boilers for rent and sale will benefit your operations.

What Are the Benefits of a Fire Tube Boiler?

A basic boiler design for hot water and steam generation consists of a sealed tank chamber that pumps cold water into the chamber and high-temperature water or steam to the desired application. Near the chamber will consist of a heating mechanism that also has piping that directs a heat source into the chamber. Using thermal conduction and heat transfer, the heat passes through the walls of the piping and raises the temperature of the nearby water to the desired controlled point for boiler efficiency.

A boiler may operate using natural gas, propane, electric, wood, or oil. For a fire tube boiler, the main heat source is fire generated from a furnace. The boiler tank is only filled halfway with water leaving about a 1/5 gap of empty space at the top. In the water portion of the tank is a large cylinder. Inside the large cylinder is a main center cylinder called a Morrison tube and smaller hollow cylinders around it. A large fire plume becomes sent down the Morrison tube that creates both heat and gasses. These gasses go down the boiler’s entire length as the entire surface becomes superheated. The heat transfers through the metal and into the water surrounding the cylinders until turning into steam.

The generated gases travel to the end of the boiler and then enter the smaller hollow cylinder tubes. The gases now move back up the tank chamber as it continues heating the water in this secondary passing phase. For some fire tube boiler designs, the gases and heat may travel a third time back down the boiler. Once the heat becomes fully transferred into the water through thermal conduction, the flue gases leave the chamber through an exhaust stack.

The main benefit of a fire tube boiler is that they are more economical than other types of boilers. They come in smaller compact designs while holding a larger water volume when compared to similar heat exchanger boilers. The numerous tubes and large center flue provide more heating surfaces for the flame and gasses to perform the heat transfer process. Fire boilers come in various configurations including horizontal return tubulars (HRT), vertical boilers, scotch marine boilers, and fireboxes.

A one-pass HRT has the horizontal boiler mounted on top of the furnace. The boiler has tube sheets connected at each end that are connected by tubes. The generated heat and gases enter the tubes and exit through the chimney or stack at the other end. They are considered one-pass boilers.

Vertical boilers are also one-pass systems that have a similar design to HRT boilers. The vertical tank has the furnace at the bottom and tubes running from the lower tube sheet to the upper tube sheet. Scotch marine boilers have the furnace itself as a large tube inside the boiler. These boilers may pass the heat and gases two times, three times, or four times through the boiler chamber with the use of bafflers or tubes.

Firebox boilers have the furnace partially inside the tank chamber. The furnace is water cooled along the large surface area. These boilers may be one-pass, two-pass, three-pass, or four-pass boilers. Firebox boilers may be categorized as locomotive boilers and firetube firebox boilers.

The Differences Between a Water Tube Boiler and a Fire Tube Boiler and How They Work

Water tube boilers and fire tube boilers have some key differences. A fire tube boiler relies on having one tube (for one-pass boilers) or several tubes (for two-pass, three-pass, or four-pass designs) to push heated gas from one end of the chamber to the other. The sealed chamber of water pulls the heat through the metal sides of the tubes’ walls using thermal conduction as the heated water creates steam. The fire tube boiler has the water around the heated cylinders and gases.

Water tube boiler design works in the opposite manner where the heated gases inside the chamber surround the water. The firebox generates hot gas that moves into the main rectangular chamber tube of the boiler that runs along its entire length. The hot gases surround the water and create a superheater effect in the steam boiler to heat the water externally. The water tubes are completely sealed as the tubes can withstand higher water pressures. Water boiler systems are safer than fire tube boilers and can help lower how much fuel is used to create the generated heat at the desired level. However, they are less cost-efficient than a high-efficiency fire tube boiler.

What Should You Expect with a Fire Boiler?

A fire tube boiler is considered a high-pressure vessel. It requires safety features that can prevent mechanical failures to prevent extreme steam pressures that could cause the tubes to warp or the tank to explode. A fire boiler should never exceed pressures of 350 PSIG (pounds per square inch gauge). You will need to have safety valves along the chamber that will release the built-up steam when reaching a dangerous level as you want to keep it at a low pressure.

There should also be fusible plugs to monitor the water levels. If the water level in the boiler is too low, the fusible plug melts from the firebox and causes the steam to escape. The noise from the steam warns the boiler operator about the low water level.

Another safety feature includes stays or ties that connect the casing to the firebox to prevent both from warping. The stays may also have longitudinal holes that leak when there is corrosion, telling the operator about possible safety issues with them.

What is the Cost for a Fire Tube Boiler?

The cost of the fire tube boiler depends on different factors. You have to base the costs on the size of the boiler and the design type of the industrial boiler, such as whether it is a single-pass boiler or a multiple-pass boiler. It also depends on whether you plan to purchase a boiler upfront, which will have a larger initial cost, or you plan to rent one. Renting a fire boiler can lower the initial cost by spreading out the payments. It is always advisable to get an online quote on our website to have a closer cost estimate for the price of the boiler as well as installation costs.

Should You Get a Boiler Rental or Buy a Boiler?

You may find different advantages and disadvantages for both renting or buying a boiler. It will always depend on your specific situation and the needs of the application.

Renting a boiler allows you to better space your payments over a long-term or short-term period. This situation is ideal when you need a temporary boiler while your existing boiler is undergoing repairs, or you plan to upgrade to a larger boiler in the near future. You may also try out different boilers to see how they work in the application until you find the one that best fits your needs. Rental contracts also usually offer a service team to provide maintenance and repairs to the rental boiler.

However, keep in mind that renting a boiler does not cut down on the overall downtime of operations. You will have to wait for the rental to arrive and become installed, then uninstall the rental after repairing the old boiler or purchasing a new one. Also, rental boilers can come in various conditions as you are unable to know whether the previous customer maintained the rental.

Purchasing a boiler gives you greater control of the make, model, design, and size of the boiler that you are able to get instead of selecting whatever rental boiler is available. You only deal with the one downtime to uninstall the old boiler and install the new one rather than multiple downtimes needed for a rental boiler. When it comes to maintenance, you are able to set the schedule based on your operations and how often the boiler is used versus relying on the maintenance terms of the rental contract.

However, the initial costs of purchasing a boiler will always be higher than renting one. Also, if you select the wrong boiler for the application, you will spend twice as much swapping it out to get a new one.

Are You in Need of a New Boiler? Rent or Buy One with Us!

Here at Power Mechanical, we offer boilers for rent and purchase. We offer new and used boilers for various companies across the east coast. Our company also provides boiler installation, repair, and safety testing services for your boiler. If you are interested in getting a new or used boiler, call 1-866-455-0460. You can also complete our online contact form. A member of the Power Mechanical team will get in touch with you today.

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