3 Pass Fire Tube Boiler | Special Industrial Boiler

3 Pass Fire Tube Boiler – All You Need To Know

Introduction

Is your boiler’s thermal efficiency low and costs you more fuel? There is an easy solution. Introducing a 3 pass fire tube boiler that can maximize your boiler’s thermal efficiency. Plus, it will lower your boiler’s fuel consumption and raise your profits on products. However, it would be best to have the basic know-how to get most of these boilers. So, read the whole easy-to-understand guide of 3 pass fire tube boiler.

What Is A 3 Pass Fire Tube Boiler?

As the name suggests, the 3 pass fire tube package boiler is any boiler that has three passes for the flue gas to move through. After the fuel burns, it produces flue gases that move back and forth through the whole boiler shell three times. One pass means that the flue gases have once covered the boiler shell.

Likewise, the flue gases cover the whole boiler shell three times in a 3 pass boiler. The three passes of boilers ensure full utilization of flue gases’ heat. As a result, the 3 pass fire tube boilers have more efficiency than the water tube boilers.

The 3 pass boiler comes in different designs. Here are multiple ways you can alter its design.

Designs Of Fire Tube Steam Boilers

The following are the various designs:

• Dry Back – The furnace’s backside has a dry sheet cover only.
• Wet Back – The furnace’s backside has a water jacket cover.
• Multiple Furnaces – A boiler’s furnace may range from one to three. It may variate their prices.
• Design Of Furnace – Two types of furnace cylinders are available: corrugated and non-corrugated. The corrugated furnace has groves on its cylinder, or you can say, it isn’t straight. On the other hand, the non-corrugated furnace is straight.

• Multiple Passes – Generally, a smoke tube boiler has one to four passes. The 1 and 2 pass fire tube boilers are common. However, the 3 pass and 4 pass boilers are a bit rare and more efficient.
• Steam Dome – The steam dome supports steam liberation. It is installed on top of the boiler shell.

So, the following were the various designs of fire tube steam boilers. Choose that best suits your industrial requirements. Now, let’s understand whether the 3 pass boiler is beneficial or not.

Advantages Of 3 Pass Boilers

Following are the characteristics of a fire tube boiler (3 passes):

• It has the simplest design and cheaper maintenance.
• Does not require highly skilled operators. Basic know-how is sufficient to run this fire tube burner.
• Compatible with large and small industries.
• Higher thermal efficiency than one-pass and two-pass smoke tube boilers. Sometimes, even more than 4 pass boilers.
• Less refractory is required because the flue gases don’t necessarily need to be at high temperatures to generate steam.
• It has a larger cylinder volume and heats more water than a two-pass smoke tube boiler, so it generates more steam.
• Water treatment is not extremely important, but it is better to use treated water.
• Does not need 100% pure water. Therefore, cheaper than water tube boilers.
• The 3-pass fire tube boiler has a lower operating cost for the same capacity and power output as water tube boilers.

3-Pass VS 4-Pass Boiler

A four-pass boiler does not automatically have a higher heat transfer area than a three-pass boiler, nor does it burn less fuel. The number of passes a fire tube boiler has no intrinsic benefit and indicates how the tubes are arranged inside the boiler design.

A 3-pass boiler is a steam boiler that uses three separate furnaces to heat the steam. The steam then passes through a condenser, where it is cooled into the water and reused. A four-pass boiler is similar, but it uses four furnaces instead of three.

The first furnace heats the water to near-boiling temperature, while the second raises it to a full boil. This process takes place in two separate coils or tubes within the same furnace, so it’s called a “2-pass” system. The third pass takes place in a different furnace, where a small amount of feed water is added to the boiler to help cool and condense the steam before it travels through pipes to your home’s radiators or other heating devices.

A 3-pass system is cheaper and more efficient than a 4-pass system because it requires less energy for heating and fewer parts for cooling. A 4-pass system has more capacity and can produce more steam, so if you have bigger needs for hot water then this might be the better option for you。

What Are The Different Types Of Fire Tube Boiler?

Due to smoke tube boilers dominating the industrial market for decades, massive improvements have been seen. Currently, there are eight different types of fire tube boilers. Each has a perfect design and suits specific requirements. So, let’s delve into it and tell you which firetube boiler type suits your industry requirements.

1.     Cornish Steam Boiler

It is the earliest form smoke tube boiler designed by a scientist named, Trevithich a Cornish. This design has a plain cylindrical shell and a small flue pipe. The hot flue gases pass through this pipe to convert water into steam. It is used in industries like sugar mills, small hydropower plants, chemical industries, etc.

2.     Cochran Steam Boiler

Cornish steam boilers are vertically designed and produce a low amount of steam. In other words, they are the smaller version of vertical steam boilers. They are best suited for small power stations and industries.

3.     Lancashire Steam Boiler

The Lancashire steam boiler is a copy of the Cornish boiler. However, it has two flue pipes instead of one. The remaining structure is entirely identical. It isn’t compatible with large-scale industries.

4.     Locomotive Steam Boiler

The locomotive steam boiler comes in a horizontal design with numerous tubes. It has been designed for train engines because it can produce steam while moving. Moreover, it is famous for cheap construction, low-cost installation, and high steam-generating capacity. It has the best application in small-rated plants.

5.     Scotch Marine Steam Boiler

The Scotch marine steam boiler is a large-scale industrial boiler, which means it can produce a high amount of steam. It has innumerable tubes and has a large heating region. The waste exhaust gases leave the boiler through a pre-installed chimney.

6.     Horizontal Return Tubular Boiler

It has a horizontal design, with a large steam drum lying horizontally. A number of tubes connect the furnace to the horizontally aligned drum. The tubes submerge as the drum fills with water, and heat transfer starts. It is best suited for small and large industries.

7.     Immersion Fired Boiler

The immersion-fired boiler is a single-flow boiler. It is a two-in-one model, used as a boiler and burning chamber. Numerous burners with needle-type tubes supply the air-fuel mixture for combustion.

8.     Vertical Smoke Tube Boiler

The name suggests a small vertical design and a medium heat generator capacity. It requires low space and has the cheapest operation cost. Plus, it is super easy to install and has a simple operation. If bought from the right manufacturer, it can fulfill your industrial requirements. However, in general, it is suitable for medium-sized industries.

What Are The 3 Pass Fire Tube Boiler Parts And Functions?

The three-pass fire tube boiler, also known as the smoke tube boiler, has numerous parts that function together to generate steam. Here are the parts contributing to steam generation and their functions.

Furnace

A furnace is a boiler part where the combustion takes place. It has a robust design capable of enduring high temperatures and pressures. For more strength, you should go for a corrugated furnace design. However, it is not rare to see non-corrugated furnaces.

Shell

Shell is a long cylindrical space for boiler parts and acts as a pressure vessel. It has a high-pressure tolerating ability and gets full of water with a space left at the top for steam liberation.

Tube Sheets

A 3 pass fire tube boiler will have tube sheets to cover the shell. It acts as a seal to limit the water flowing outside. Moreover, it has a space for mounting fire tubes and is often connected to the shell by stay bars.

Fire Tubes

Fire tubes reside inside the shell either horizontally or vertically. They may pass one or multiple times, called multiple-pass smoke tube boilers. The tubes will have unique thick tubes, known as stay tubes. Their function is to minimize mechanical stresses on the tube sheets in the case of high pressures.

Fire Tube Burner

A fire tube burner supplies the products for combustion. Put simply, it is an air-fuel mixture with an ignitor that mixes air and fuel and ignites them. No heat can be produced without the function of fire tube burners.

Smokebox

A 3 pass boiler design has a smokebox. It is connected to the boiler chimney and helps take the waste exhaust gases out of the system.

Reversal Chambers

Depending on the type of smoke tube boiler, it may have one or multiple reversal chambers. Its function is changing the direction of exhaust gases from one pass to another. Generally, this boiler has two reversal chambers:

• Front Reversal Chamber – Located closest to the burner.
• Back Reversal Chamber – Located far from the burner.

How to a Fire Tube Boiler Work?

A 3 pass boiler has four main processes: feeding fuel, combustion, heat transfer, and taking exhaust gases out of the system. To understand better, let’s divide the working principle of the fire tube boiler (3 passes) into steps.

·       Feeding Fuel

A 3 pass fire tube boiler feeds the air-fuel mixture through a burner. To ignite the fuel, an ignitor starts the combustion process.

·       Combustion

As the air-fuel mixture reaches the furnace, it ignites through an ignitor, and the combustion process starts in the furnace. The burning of fuel produces hot flue gases, which are transferred to the furnace wall or shell.

·       Heat Transfer

The boiler shell has fire tubes surrounded by water. It is connected to the furnace wall and has paths for flue gases to move (fire tubes). When hot flue gases flow through the tubes, the water surrounding them absorbs all the heat. As a result, the heat transfers from flue gases to water, and steam is produced.

The 3 pass fire tube boiler has 3 passes for the hot flue gasses to move through. Due to the 3 passes, the water absorbs maximum heat from the fire tubes.

·       Venting Out Exhaust Gases

After the hot flue gases lose their heat to the water, the boiler needs to evacuate waste exhaust gases. Therefore, a three-pass boiler uses a chimney to remove waste gases from the system.

And that’s it. It is all that a smoke tube boiler does to produce steam.

Best 3 Pass Fire Tube Boiler Brand

Undoubtedly, a three-pass boiler boosts your boiler’s thermal efficiency and lowers fuel consumption. However, it is uncommon for people to complain that the three-pass steam boiler is inefficient. It has only one reason: low-quality products. Sometimes, even a four-pass firetube boiler costs industrialists more fuel.

Multiple problems, one solution: Yongxing boiler. We have state-of-the-art manufacturing departments where the 3 pass boilers are manufactured under the supervision of world-class engineers.

Plus, we provide the latest technology adopted by firetube boilers with each aspect tested several times. So, check out our products and contact our support team with any queries about 3-pass boilers.

Fire Tube Boiler Parts Diagram

Follow us our 3-D fire tube boiler parts diagram.

Parts of the fire tube boiler like follows:

Fire Tube System Figure

3 Pass Firetube Boiler Design

Three-pass fire tube boilers are the most common type of boiler used in industrial and commercial applications. These boilers have three separate passageways for the combustion air, flue gas, and water within the furnace area. This design provides more surface area for heat transfer than other boilers.

The water tubes in a three-pass boiler are arranged in two groups: one group contains tubes that carry water through the furnace area, while the other group contains tubes that carry steam out of the furnace area. The steam passes through its separate passageway within the furnace.

The two groups of fire-tube tubes can be arranged either vertically or horizontally (in what is known as a return tube). Most boilers use vertical arrangements, but horizontal arrangements are joint on larger units with multiple furnaces or high-pressure steam turbines.

The arrangement of these passageways is vital because it affects how well heat travels throughout the furnace area and how efficiently it transfers from one section to another.

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