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Types, Design, Evaluation, Reliability, Ease of Use, Maintenance, and Service

  • Types of Boilers

    There are two types of industrial boiler designs:

    • Fire Tube: In fire tube boilers, hot combustion gases flow through tubes and heat the water that surrounds them.
    • Water Tube: In water tube boilers, water flows through tubes and is heated by the flame and combustion gases that surrounds it.

    The large majority of industrial steam boilers are fire tube boilers.

    Calderas Powermaster manufactures fire tube boilers, which have been the mainstay of the industrial steam boiler generation, to a maximum capacity of 1500 boiler horse power (BHP ) and a maximum operating pressure of 300 lbs/in² (PSI).

    If a larger boiler size is required, it is convenient, when possible, to divide the boiler capacity requirement into two or more fire tube boilers. Barring that, a water tube boiler would be necessary.

    A water tube boiler would also be required to achieve a higher maximum operating pressure.

    Calderas Powermaster does not manufacture water tube boilers.

  • Safety

    Boilers use an incredible amount of pressure to generate an equally impressive amount of energy. A deficiency of strength in any part of the boiler caused by poor materials, inferior workmanship, or a failure of the safety controls or other critical components of the boiler to function properly can cause tremendous damage. Because of this, understanding the safety features of your boiler is critical.

    Powermaster boilers are designed to be among the safest in the market. From the quality and thickness of the materials, to the safety controls and devices, Calderas Powermaster always exceeds the standard safety requirements in order to guarantee a top-tier boiler in terms of both performance and security.

    • Horizontal boiler's 80-1500hp tube sheets are 30% thicker than the ASME requirement , thus guaranteeing a longer useful life.
    • 11 gauge flux tubes are 100% thicker than the ASME requirement , thus guaranteeing a longer useful life.
    • Control measures exceed the minimum requirement to such a degree that there will always be a redundant control to regulate the water level or working pressure, thus greatly reducing the possibility of an accident.
    • Safety features also exceed the minimum requirements with combustion gas relief valves at the exit of the second pass coming standard on most horizontal boilers, thus mitigating any type of explosion or potential accident.

  • Manufacturing Standard

    In the US, boilers are designed and manufactured in strict accordance with the Boiler and Pressure Vessel Code (the “Code”) set forth by the American Society of Mechanical Engineers (“ASME” or “the Society”); only then can the boilers be embossed with the corresponding ASME stamp. The ASME Code is a product of the compilation of all the Society´s engineering knowledge base gathered over the years. The goal of the Code is simple: to protect boiler users, by demanding minimum quality, design, calculation, and manufacturing requirements, and thus ensuring that the end user receives a safe and reliable boiler with a long useful life.

    The requirements regarding materials are much stricter, demanding greater thicknesses, than both the European and Asian codes. Because of this, it is very common, especially in more developed countries where they do not manufacture their own boilers, to require imported boilers to bear the ASME stamp.

  • Minimum Water Quality Requirements

    As previously described, in fire tube boilers, water surrounds tubes containing combustion gases. If the tubes, from the outside, become encrusted with scale, the heat transfer will be reduced, resulting in a less efficient boiler and increasing the exit temperature of the combustion gases. Nevertheless, this type of scaling is easily removed, and if done correctly the boiler can be returned to its original working order without critical repercussions.

    In water tube boilers, not only does scaling of the tubes from within reduce the heat transfer (and therefore efficiency) of the boiler and increase the exit temperature of the combustion gases that surround the water-containing tubes, but it also diminishes the flow of water required inside the tubes. This, in turn, causes damage to the tubes and may even burn them out completely.

    For this reason, water tube boilers require an incredibly precise water treatment system – one that cannot fail. The requirements, therefore, for the reliable operation of a water tube boiler demand stricter and more costly controls, such as the 100% elimination of dissolved oxygen via a pressurized deaerator (a device used for the removal of oxygen and other dissolved gases from the feedwater of steam boilers). This is completely unnecessary in a fire tube boiler for which a simple, non-pressurized atmospheric deaerator or even a system that provides for a high percentage of returned condensates, is sufficient.

    Water tube boilers also require an exact control of salts, a buildup of which can considerably reduce the efficiency of the boiler. To do this, continuous surface blowdowns are required. Once again, such a measure is not normally required for the fire tube boiler, making it a simpler, and more reliable and economical option.

  • Heat Transfer Surface Area Requirements

    In the early 1940’s, it was discovered that the greatest percentage of heat absorption in a boiler occurs by means of radiation, with approximately 70% of a boiler’s heat transfer occurring within the walls of the furnace. (The remaining 30% of the transfer takes place in the convective section, an area which does not come in direct contact with the flame.)

    The fundamental component in the design of the pressure parts of a boiler is therefore the flame furnace. The immense quantity of heat transferred within its walls necessitates the provision of an ample heat transfer surface area made of heat resistant steel in order to alleviate the force of such an immense heat transfer and prolong the useful life of the boiler.

    American ASME-stamped boiler users, since the beginning of the 20th century, have been accustomed to demanding that boiler manufacturers provide, as a minimum, a heat transfer surface area in the pressure parts of the boiler of 5 ft² /BHP in boilers up to 700 BHP. By doing so, they guarantee themselves a minimum installed heat transfer surface area, which results in lower fatigue and flame release coefficients. The lower the coefficients, the less material fatigue will be experienced over time and the greater the heat absorption distribution, resulting in a more reliable, efficient, and ecologically-friendly boiler with a longer useful life.

    Having this minimum heat transfer surface area requirement also provides for ease in the comparison and evaluation of boilers. A boiler with a smaller heat transfer surface area will cost less but will have higher fatigue and flame release coefficients . It may operate efficiently, but it will not have as long a useful life, nor will it function with the same level of safety and reliability.

  • Useful Life of the Boiler

    One of the most relevant factors in selecting a boiler is evaluating its useful life.

    The useful life of a fire tube boiler meeting the following criteria can easily reach 20 years:

    • Designed and manufactured in strict accordance with the ASME Code, and if possible, bearing the ASME stamp
    • Heat transfer surface area of 5 ft²/BHP
    • Acceptable fatigue and flame release coefficients

    Water tube boiler meeting the following criteria may similarly achieve a useful life of 20 years:

    • Designed and manufactured in strict accordance with the ASME Code, and if possible, bearing the ASME stamp
    • Built as a two dome construction with natural circulation and a large furnace
    • Heat transfer surface area of 5 ft²/BHP
    • Acceptable fatigue and flame release coefficients
    • Supported by an excellent (and generally very costly) water treatment system

    Boilers not meeting the above-mentioned criteria will have a significantly shorter expected useful life.

    Understanding the factors that contribute to the optimal performance and safe operation of your boiler is critical. From confirming the quality of the materials and craftsmanship of the boiler to understanding key elements of boiler design and the particular maintenance requirements of the various types of boilers, the more knowledge you have, the better able you will be to select the ideal boiler to meet your specific operational goals.

    Calderas Powermaster is dedicated to ensuring our clients receive the information they need to make the right decision concerning their boiler needs. For more information about the topics addressed above or to speak with a qualified Calderas Powermaster team member about your particular boiler requirements, please contact us directly.