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design and evaluation

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Powermaster >Home > Technical Guide > Design and Evaluation

types, design, evaluation, reliability, ease of use, maintenance and service.

Types of Boilers

Types of Boilers
Generally speaking, there are two types of industrial boiler designs:

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

The majority of industrial steam boilers are fire tube boilers.

Powermaster manufactures fire tube boilers, which have been the mainstay of the industrial steam boiler generation, to a maximum capacity of 2000 boiler horse power (BHP) and a maximum operating pressure of 300 lbs/in² (PSI).

If a larger boiler size is required, we recommend 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. 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 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 safety.

• Horizontal boiler's 80-2000hp tube sheets are 30% thicker than the ASME stress requirement , thus guaranteeing a longer useful life.
• 11 gauge boiler tubes are significantly thicker than the ASME requirement , thus guaranteeing a longer useful life.
• Controls 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 stamped 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 less developed countries that do not have their own codes, to require imported boilers to bear the ASME stamp.

Design and Evaluation

The first fire-tube boilers manufactured in the early 19th century used large amounts of refractory, burned coal, and had inefficient heat transfer. As a result, heat transfer surfaces of 10 ft² per BHP were required to meet the required steam generation. In the 1960s, fire-tube boiler manufacturers had greatly improved their designs and technologies. They typically burned liquid or gaseous fuels, which allowed for higher heat transfer and lower emissions. The design criteria for these boilers evolved, requiring only 5 ft² of heat transfer surface per BHP to achieve reliable and efficient boilers, but they were typically limited to 700 BHP.

With the technological advancements of the 20th century and the development of engineering expertise and computerized techniques, the design criteria for fire-tube boilers have continued to evolve. Today, most manufacturers worldwide can design boilers with higher power outputs using less heat transfer surface, sometimes as low as 3 ft² per BHP, while maintaining reliability and safety standards.

The criteria governing the design and manufacture of fire-tube boilers today are no longer based on 5 ft²/BHP. Instead, greater emphasis is placed on:

•Operating efficiency
•Low levels of pollutant emissions
•Compliance with manufacturing codes (ASME for North America)
•Compliance with the requirements of the National Board of Boiler and Pressure Vessel Inspectors
•Ease of maintenance
•Long lifespan and reliability

Powermaster, under the leadership of Eng. Herman B.E. Notholt, has developed its boiler designs with advanced technologies while maintaining the highest standards of safety and reliability for their customers. All its SWB, WB-A2-3P, and WB-A2-4P series boilers have a heat transfer surface of 5 ft² per BHP up to 700 BHP.

Las primeras calderas de tubos de humo que se fabricaron a principios del siglo 19, utilizaban cantidades muy grandes de refractario, quemaban carbón y realizaban la transferencia de calor de una manera poco eficiente. Como resultado de esto, se requerían superficies de transferencia de calor de 10 pies² por BHP para poder cumplir con la generación de vapor requerida. En la década de los 1960´s, los fabricantes de calderas de tubos de humo habían mejorado mucho sus diseños y tecnologías. Se quemaban normalmente combustibles líquidos o gaseosos que permitían tener una mayor transferencia de calor y menores emisiones a la atmósfera. El criterio del diseño de estas calderas evolucionó, requiriendo únicamente superficies de transferencia de calor de 5 pies² por BHP para obtener calderas confiables y de buena eficiencia, pero se fabricaban calderas de tubos de humo de máximo 700 BHP. Con los avances tecnológicos del siglo 20 y el desarrollo de la ingeniería, experiencia y técnicas computarizadas, el criterio de diseño de calderas de tubos de humo ha seguido evolucionando. Hoy en día la mayoría de los fabricantes en el mundo, logran diseñar calderas de más potencia utilizando menos superficie de transferencia de calor en ocasiones tan bajas como 3 pies² por BHP, manteniendo los estándares de confiabilidad y seguridad.

Los criterios que gobiernan en el diseño en la fabricación de calderas de tubos de humo actualmente, no norman los 5 pies²/BHP, dándole mayor interés en la fabricación de este tipo de calderas a:

• Eficiencia de operación.
• Bajos niveles de emisiones contaminantes.
• Cumplimiento con los códigos de fabricación (ASME para Norteamérica).
• Cumplimiento con los requerimientos del National Board of Boiler and Pressure Vessel Inspectors.
• Facilidad de mantenimiento.
• Larga vida útil y confiabilidad.

Powermasterunder the leadership of Ing. Herman B. E., Notholt, has developed its designs of boilers with the advancing technologies while maintaining the highest standards of safety and reliability to their customers. All boilers of the series SWB, WB-A2-3P and WB-A2-4P, have a surface area of heat transfer 5 piés2 by BHP up to 600 BHP. In larger capacities, the excess heat transfer surface results in a deterioration of the efficiency and performance of the boiler, so that out of 700 BHP onwards it gradually reduces the heat transfer surface to maintain the guaranteed efficiencies higher of the market.

Todos los diseños de Powermaster garantizan una larga vida útil, seguridad y confiabilidad en su operación, pero prestan especial atención y énfasis a la eficiencia.

Minimum 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 condensate return, is sufficient.urned 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.

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 3-5 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 3-5 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.

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 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 environmentally 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.