Steam Boiler

The steam boiler is a high-pressure tank that heats water through combustion to produce steam used in various industries. In the following, specifications, working pressure, brands, and how to select steam boilers are presented.

Steam Boiler Review, Selection, and Pricing

Steam boilers are one of the essential heating equipment in industries and some heating systems.

Steam boilers can be divided into water tubes and fire tubes primarily based on their sketch, regardless of their capacity, size, and working temperature. Fire-tube steam boilers come in two types: wet back and dry back.

In dry back boilers, the end of tubes in 2 pass and 3 pass are connected to a network. Due to the temperature difference between the past two (1000℃) and past three (250℃), the network may experience thermal stress and start leaking.

Dry back boilers require insulation and maintenance on fire-resistant materials from time to time to separate 2-pass and 3-pass, which increases maintenance costs. Therefore, considering the significance of heat transfer surfaces and the use of the back shell of the boiler for heat exchange, wet-back boilers are more common.

Types of Steam Boilers

There are two main and common types of boilers, known as water tube boilers and fire tube boilers. These two types have important differences in structure and function.

Water Tube Boiler

In water tube boilers, flow tubes are parallel and connected and consist of a large amount of other tubes. These pipes are exposed to the gases from the furnace. The feed water flows through these pipes and is heated by the hot gases around them.

These types of boilers are used for industrial and large applications due to their more specific design and ability to withstand higher pressures.

Fire Tube Boiler

In fire tube boilers, fuel such as oil, gas, or coal is ignited in a horizontal furnace, and the heat is transferred to the filler tubes.

Inside the tank, the water turns into steam, and the steam produced is collected in the boiler. This steam can be used to provide energy or generate electricity. These types of boilers are generally used in smaller applications and home uses.

Comparison table of specifications of water tube boilers and fire tube boilers

Note: These specifications are only general comparisons of fire tube and water tube boilers, and for more detailed information about your specific needs, refer to relevant sources and standards.

Steam Boiler Classification Based on Combustion Gas Passes

This classification is based on the number of gas passes in the boiler.

• 1-Pass Boiler: In this type of boiler, the combustion gases go through the boiler once and then are transferred to the chimney. These types of boilers were often used in the first generation of coal-fired boilers and steam-powered machinery.
  
  
• 2-Pass Boiler: In two-pass boilers, the flue gases first travel through a boiler, then go back and pass through the boiler again, and finally transfer to the chimney. These types of boilers are usually used to produce hot water.
  
  
• 3-Pass Boiler: In three-pass boilers, flue gases pass through the boiler three times and are finally transferred to the chimney. These types of boilers are used to produce hot water and steam.
  
  
• 4-Pass Boiler: In four-pass boilers, flue gases pass through the boiler four times and are finally transferred to the chimney. These types of boilers are usually used in high tonnages and for steam production.
  
  
• Return Furnace Boiler: In this type of boiler, the combustion gases first pass through the furnace twice, and then they are transferred to the pass pipes and move towards the chimney. These types of boilers are usually more efficient than double-pass boilers.
  
  

These categories indicate the differences in performance and application between different types of boilers and refer to the number of passes or paths that flue gases take.

Steam Boiler Components

The main components of a boiler are:

Steam Boiler Burner

The boiler burner is the part of the boiler that combines fuel (usually gas or oil) with air and ignites it in the combustion chamber. This action produces heat and thermal energy, which is used to convert water into steam.

Steam Boiler Combustion Chamber

The combustion chamber is the place where fuel and air mix and the ignition takes place. The energy from combustion provides the heat needed to convert water into steam.

Steam Boiler Heat Exchanger

The heat exchangers used in steam boilers transfer heat from the hot gases resulting from combustion to the water inside the pipes. This process turns water into steam, which produces thermal energy.

The heat exchanger acts as a medium that allows the heat produced by the burner to be transferred to the water. To exchange heat between hot gas and water, a system of tubes or bent pipes is used.

Hot gas (usually from burner combustion) passes through the tubes and transfers its heat to the tube wall. In other words, the heat of the gas is transferred to the water inside the pipes through the pipe wall, but the gas and water themselves do not come into direct contact with each other.

Steam Boiler Thermostat

The thermostat is used to control the temperature of the produced steam and maintain the desired temperature as well as control the temperature of the environment or the working fluid (such as water or steam).

When the temperature reaches the value set by the user, the thermostat sends a signal to the corresponding control device to stop the heat production process (for example, the combustion of the burner in the boiler).

This control is optimized by the thermostat, which means that the thermostat, by detecting the desired temperature when the heat is no longer needed, automatically reduces the heat production process.

Note: Usually, 2 or 3 thermostats are used to ensure the performance and safety of steam boilers.

Steam Boiler Check Valve

The check valve is a type of control valve that is used to limit the flow of fluid in a specific direction in a pipeline.

This valve also acts as a safety unit and prevents reverse fluid flow. A backflow valve automatically causes fluid to flow in a specific direction, usually the direction of normal flow, and prevents reverse flow.

This feature contributes to the safety of the system because preventing reverse flow can prevent potential hazards such as equipment failure, reducing system efficiency, or causing problems.

These valves are used in various cases, including in water, gas, and oil piping and heating/cooling systems. Using check valves (backflow valves) to control fluid direction and prevent reverse flow in these systems is very important.

Steam Boiler Safety Valve

Safety valves play an important role in pressure control and boiler safety. Sometimes, due to the existence of many problems, the pressure gauges in the boiler cannot measure the internal pressure of the boiler correctly.

For this reason, the pressure inside the boiler increases suddenly. In these cases, these valves operate automatically. If the pressure inside the boiler rises to a level that threatens safety, the safety valves open and release the pressure in a controlled manner.

This action reduces the pressure in the boiler and maintains the safety of the system. As mentioned in the case of boiler thermostats, in the case of boiler safety valves, to maintain 100% safety in the operation of the boiler, more than one safety valve is always installed on the boilers.

Steam Boiler Pressure Gauge

Pressure gauges are responsible for measuring the steam pressure in the system. If the steam pressure inside the boiler exceeds the virtual limit that has been determined, the pressure switch sends the information resulting from the pressure increase to the control circuit.

The control circuit also compares the information it receives from the pressure gauges with the limit set by the operator. If this pressure is higher than the limit, it sends an order to shut down all the components of the boiler.


In general, depending on the type and capacity of the boiler, usually two or three pressure gauges are considered, including the following:

• Burner pressure gauge
• Burner flame pressure gauge
• Reliable pressure gauge
  
  

Fully-Corrugated Furnace and Pipe Effect on Steam Boiler Efficiency

Nowadays, due to the importance of convection heat transfer in increasing the efficiency of steam and hot water boilers, the use of techniques that can increase heat transfer has also increased.

Based on complete studies on increasing heat transfer from the heat transfer method known as V.H.T.E. (Vortex Heat Transfer Enhancement) and as the name suggests, the basis of work in these methods is based on the creation of a vortex.

The application of the V.H.T.E. method is to use Corrugated Furnaces and Corrugated Tubes (Spiral), which causes an increase in displacement heat transfer as well as the efficiency of the boiler by producing more turbulence in the fluid flow.

Recent research has shown that the heat transfer inside the fully corrugated furnace and tubes has a very complex pattern, to the extent that the convection heat transfer in the fully corrugated furnace and tubes at the ridged spots is approximately five times the heat transfer in the plain (regular) furnace and tubes.

Radiative heat transfer in the corrugated furnace and tubes increases due to their vast surface area created by the corrugated pattern which greatly increases the efficiency of the steam boiler.

Factors to Keep in Mind When Choosing a Steam Boiler

When choosing firetube boilers, in addition to the capacity and working pressure of the boiler, you should also pay attention to other important parameters such as the pass number in the combustion chamber of the boiler, whether the boiler is wet back or dry back, and the type of fuel and burner (Always note that the nominal capacity of the burner should be considered 20% more than the capacity of the boiler).

Also, The quality of peripheral equipment such as feed water pump, safety valve, discharge valve, pressure switches, level controls, one-way feed valve, main steam outlet valve, electrical panel, consumable electrode, and even the way of making and assembling other tubes are important factors to guarantee its stable performance.

According to generally accepted international standards, in the construction of steel boilers, the body (shell), furnace or combustion chamber, and grids must be made of special alloy steels for the construction of tanks under heat and pressure according to DIN 17MN4 or ASMEA516/G70 and pipes or tubes, they should be made of DIN ST 35.8 seamless refractory pipes with the bendable ability.

One of the most important points in the design and production of boilers is the conformity of all parts of construction, execution, control, access, testing, etc., with documented standards, as well as the implementation plans for the construction and design of boilers from approved brands.

In other words, only the use of high-quality alloy steels and those, as mentioned earlier, standard refractory tubes alone cannot guarantee the performance, efficiency, and longevity of the boiler. Still, it is necessary to build the boiler using approved plans and methods.

Defined and accepted by international standards. This point is so important that the construction of a boiler without documented and approved plans cannot be justified in any way.

Another important point regarding the construction and production of standard boilers is the way to connect the fire tubes to the tube plates of the boiler.

This connection must be done by the expand (waltz) method, except for the resistant pipes inside the sub-furnace, which must be done according to the standard by the expand welding method and using special I.S.A.B. devices to weld the network for the hot water or steam boiler.

Note: All boilers are usually built according to the pressure level regulations by the "American Society of Mechanical Engineers" because they are generally greater than 15 pascals.

Factors to Keep in Mind When Installing a Steam Boiler

When buying and installing a steam boiler, you should pay attention to the following points:

• The ability to access various parts of the boiler and the presence of headhole-handhole-manhole valves in different parts for periodic services and even the possible replacement of defective tubes.
  
  
• Pay attention to the full dimensions of the steam boiler with accessories and their weight for entering the engine room and installing it at the inspection site.
  
  
• In engine rooms where steam boilers are used, water softeners and descalers must be used in the way of boiler feed water. The maximum water hardness allowed for steam boilers is 20 P.P.M.
  
  

How to Increase the Longevity of a Steam Boiler

Important factors to increase the life of the boiler are as follows:

• Boiler design and construction should be based on approved construction plans and also according to accepted methods provided by international standards.
  
  
• The use of alloy steels and standard refractory tubes, the sufficient heat level of the tubes, the number of passes of the boilers, and the waltzing of the tubes and plates instead of welding.
  
  
• Choosing a burner with a calculated capacity suitable for boiler heating (maximum 20% more than the boiler capacity).
  
  
• Adjusting the burner flame (blue burning and direct longitudinal flow of the burner flame in steam boilers).
  
  
• If a diesel fuel burner is used, the type and angle of the fuel injector from the diesel burner nozzle are determined based on the diameter and length of the combustion chamber of the boiler and according to the suggestion of the boiler manufacturer.
  
  
• Accurate calculation and implementation of the chimney in terms of diameter and height of smoke suction according to the volume of combustion air.
  
  
• Carrying out periodic inspections and services, especially about how the burner ignites as well as the correct functioning of controls, safety valves, thermostats, etc.
  
  

Presented by Damatajhiz HVAC Group

Buying a Steam Boiler

To buy a steam boiler easily, you must first determine the required capacity and working pressure.

The selection of steam boilers is based on the combination of loads (load of steam-consuming processes and equipment, steam required for hot water production, pipe waste, and initial start-up).

On this website, technical information on dozens of models of steam boilers from reliable brands with original warranties has been presented for you to enjoy the good feeling of an optimal and smart purchase.

Steam Boiler Price

You can browse and compare our steam boiler selection for the best choice and keep in mind that Damatajhiz HVAC steam boilers are all at the very best price in the market today.

However, the price of steam boilers varies according to the variety of models, capacities, and brands available in the market.

It should be noted that the prices presented on the Damatajhiz HVAC website are up-to-date, and the discounts desired by consumers are already included in these prices.

Dear user:

While thanking you for the trust you have in the technical opinions of DamaTajhiz HVAC sales experts, it should be noted that the determination and selection of the desired product brand based on history, brand strength, service, and product price is ultimately determined by the buyer.

But in steam boilers, most of the users and buyers choose and buy best-selling brands such as Hararat Gostar due to their quality, price, and after-sales service.

If, after reading the above material, you have more questions about deciding on the type of steam boiler you need, you can ask your questions from the heating equipment and engine room sales experts after contacting DamaTajhiz HVAC by the extension numbers 107-108-121-122.

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