Steam Boiler

Fire-Tube Steam Boilers

Fire-tube steam boilers are cylindrical vessels that hold water that surrounds a set of tubes conducting hot gases produced by a furnace. Consequently, the heat in the tubes transfers to the water surrounding them, producing steam. 

Advantages of Fire-Tube Steam Boilers

  • Fire-tube steam boilers are widely available as “packaged” systems. Thus, their transportation and relocation are rather easy. 
  • Their installation is rather simple, if previously an adequate foundation and the connections to water, electricity, fuel, and steam systems are in their place by the time of arrival.
  • The maintenance and cleaning operations of a fire-tube steam boiler relatively simple. They have easy access to its firesides, allowing the change of the fire tubes without further repair of the boiler. 
  • The control systems are less complicated than the ones on water tube boilers.
  • The accessories required by a fire-tube boiler are available at economical prices, due to the relatively low pressures that they have to stand.
  • They are not only easy to operate, but they are also fuel-efficient. Their range of operation is between 600,000 BTU/hr to 50,000,000 BTU/hr.
  • They are used for space heating and diversity of industrial operations.

Disadvantages

  • Although fire-tube boilers are smaller in design, they have a larger water volume than similar size water-tube boilers, causing them to take longer to bring up to operating temperature from a cold start. 
  • Generally, this type of steam boilers generates a maximum output of 27,000 kg/h. Most commercial and industrial users that demand a higher output install multiple fire-tube boilers in tandem.
  • Fire-tube boilers can’t work with applications that require high pressure, beyond 250psig.
  • The cause is the large diameter that the cylindrical bodies of fire-tube boilers have.

Water Tube Steam Boilers

Water-tube boilers have a furnace that burns gas or another type of fuel, whose combustion heats water-containing tubes. As a result, the tubes produce steam by transferring the heat received to the water circulating inside them. Next, the resulting vapor reenters the furnace through a superheater to generate extra pressure. In particular, this device heats the saturated steam above the boiling point at very high pressure, turning it into superheated dry steam, which leaves the boiler with pressure high enough to drive large turbines. They are used by industries and utilities that demand high-pressure steam for their processes.

Advantages of Water-Tube Steam Boilers

  • They contain minimal amounts of water; therefore, they have a high capacity to respond to fluctuations in load and heat supply.
  • Their design containing small diameter tubes and steam drum, allows for the toleration of very high steam pressures, up to 160 bar. 
  • Water-tube boilers are highly efficient because they economize fuel by the use of an induced draft that feeds the furnace fire. Also by the recirculation water for preheating purposes, and for their capacity to produce superheat.
  • They can produce high steam pressures, up to 5,000 psi.  

Disadvantages

  • The degree of pressure that they produce limits their availability as preassembled “packaged” boilers, up to 1,500 psi.
  • The assembly and installation process of the boilers at the site where they are going to work can be comparatively difficult and time-consuming.
  • Their cost, including the installation, happens to be higher than fire-tube boilers.
  • The difficulty of the cleaning process makes the maintenance process a complicated task that requires highly skilled personnel.
  • It is not possible to replace the tubes, because there is not a common standard of fabrication.

Conclusion 

Fire-tube boilers are widely available in packaged form, allowing smooth relocation and installation. They are also easy to operate, control, and maintain. However, they take longer to respond to fluctuations in the pressure demand. Their uses are for space heating and diversity of industrial operations that do not require high pressure.

Water-tube boilers are highly efficient, produce very high pressures, and for their low water content, respond fast to fluctuations in demand for steam. The degree of steam pressure limits its availability as ‘packages” because as the pressure generated increases, so does the size of the boiler.

There is a point beyond which they have to be custom assembled and installed in their working location. They have big sizes, are challenging to maintain, and the cost of acquisition and installation is higher than fire-tube boilers.

If you require information or assistance for buying, renting, installing, and operating Fire-tube or Water-tube steam boilers, contact us here.

Sources: Superior Boilers

Like all industrial equipment, steam boilers require periodic maintenance and inspections to ensure their correct, safe, and efficient operation.

However, boilers are machines that compromise the continuity of production in many industries. This means that shutting them down can come at a high price, not only because of the maintenance cost but also on lost production.

It is for this reason that we establish an annual maintenance plan in which we perform important inspection tasks to detect most breakdowns preemptively.

What is the maintenance plan for a steam boiler?

    • Internal inspection of the pressure body, plates, household, and tubular beam to control the formation of incrustations or corrosion of building materials.
    • Hydro-washing of sludge deposited at the bottom of the body if it exists. This is important for optimal operation.
    • Change inspection door gaskets, always install new gasket materials and check cover seats. This will avoid many accidents within the company.
    • Measurement of plate thicknesses, and cylindrical body by ultrasound, we also record these values. It may be necessary to recalculate the maximum working pressure if these thicknesses are reduced over time.

Important aspects for your steam boilers

    • Disassembly of security elements. In the case of electromagnetic level controls, check floats, bottles, verify play in mechanisms, check the integrity of the mercury ampoules and check that the insulation of the cables is not damaged.

For the electrodes, the task is cleaning parts that are in contact with water, alignment check, caulking, and seals.

    • Hydraulic test of the work pressure equipment. Performed in order to verify that there are no leaks before and after maintenance (inspection of door seals, flanges, threads, etc.). After that, the container must remain pressurized for at least 15 minutes.
    • Verification of opening of safety valves at a regulated pressure. If possible, remove them for stamping on a test bench.
    • Inspection of refractory status in a burner or dry bottoms. Fill cracks if there are any or replace damaged parts with the appropriate materials.
    • Verification of the internal state of the burner and its cleanliness. Check the condition of cables and connection cards.
    • Start-up of the equipment where the operation of the control and safety elements will be checked.
    • Gas analysis and combustion regulation. Through this process, the percentage of the following gases will be determined: O2, CO2, and CO.

Also, the temperature of the gases in the chimney, and the thermal efficiency of the boiler will be measured.

    • Preparation of a technical report with the results obtained in the measurement of combustion efficiency and the general condition of the equipment, maintaining a history.

The steps for maintaining a steam boiler are quite specific, so you should entrust it to skilled professionals. In conclusion, if you need this type of service or any other related to preventive maintenance in your facilities, let us help you.