General Requirements for Boiler Construction

To use the least metal consumption, consume the least fuel to achieve the evaporation of the specified parameters (pressure, temperature), and meet the requirements of safety and reliability in operation.

To ensure the safe and economical operation of the boiler, it is necessary to check the strength of the pressurized parts, control the fuel combustion conditions, and ensure that the safety accessories are sensitive, accurate and the reliability of the automatic device. However, congenital defects must be eliminated first, that is, to ensure a reasonable structure and ensure manufacturing quality.

In terms of structure, specifically, the following requirements should be met:

(1) To ensure that the pressure parts have sufficient strength and stability. The strength of boiler pressure parts refers to the ability of the parts not to fail within a predetermined service life under the action of medium pressure (including additional loads, etc.). The mechanical properties of materials include: tensile strength, yield strength, creep strength, lasting strength, elongation, area shrinkage, impact toughness, etc. The mechanical properties part is the basis for determining the strength. The purpose of determining strength is to ensure safety. Insufficient strength will lead to the rupture or even explosion of the pressurized parts, but it is also necessary to take into account the saving of steel and take into account both. Also, consider its stability.

(2) It is necessary to ensure that each part of the boiler structure can freely expand in the direction predetermined by the design during operation. The pressure parts of the boiler are composed of steel plates or steel pipes, and water is stored inside. The steel plate or steel pipe is a solid, which expands linearly when heated. If the two ends of the pressure parts of the boiler are fixed, the expansion will be blocked after being heated, resulting in thermal stress, which will cause the parts to be bent and deformed, or even damaged, especially when the boiler starts and heats up. In addition to limiting the heating or cooling rate during operation, the thermal expansion should be fully considered in the design of the drum (boiler shell), header, water wall, steel frame, furnace wall, etc.

(3) There must be good water circulation to ensure that the heating surface is reliably cooled. Boiler water circulation means that the water in the boiler flows in a circulation loop. The purpose is to keep the heated surface sufficiently cooled. If the water circulation is not good, it will cause the over temperature of the pipe wall to weaken the strength of the steel and cause damage. In low and medium pressure boilers, natural circulation is generally the main method. Natural circulation boilers are circulated by the difference in specific gravity and density of water vapor to promote the flow of water vapor. Boiler water circulation is generally safe for shell boilers; enough attention should be paid to water tube boilers.

(4) The boiler structure should be selected according to the boiler parameters (pressure, temperature) and the adaptability of the fuel. The combustion equipment and heating area are reasonably arranged according to the boiler structure and applicable fuel to ensure stable combustion conditions and adapt to load changes.

(5) Blowers and induced draft fans should be reasonably configured to keep the fuel and air volume in a corresponding proportion with the change of combustion conditions.

(6) The arrangement of openings and welds of pressure parts should avoid or reduce compound stress or stress concentration as much as possible.

(7) When the boiler steel frame is under load, it should have sufficient strength, rigidity and corrosion resistance.

(8) The boiler structure should be convenient for installation, operation, maintenance and cleaning inside and outside. The arrangement of platform escalators and door holes (manholes, hand holes, cleaning holes, inspection holes, explosion-proof doors, etc.) should be convenient for personnel to pass through and ensure safety.

(9) The reliability of safety accessories and automatic control devices should be considered. Safety accessories and automatic control devices are indispensable components in boilers. Its function is to indicate the operating parameters, prevent timely warnings in the event of abnormal situations or abnormal situations in operation, adjust the combustion conditions in time, and restore the operating parameters to the normal state. Or automatically interlock in abnormal situations to prevent accidents. However, it must also be pointed out that safety accessories and automatic control devices cannot be completely relied on, and operators still need to be on duty.

(10) It is necessary to maintain the furnace wall structure with good heat resistance and sealing, reduce air leakage, reduce heat loss, and maintain stable combustion. In addition, there are environmental requirements.