Boiler Categories

Steam Boiler

In the first half of the 18th century, steam engines used in British coal mines, including Watt's early steam engines, operated at steam pressures equal to atmospheric pressure. By the latter half of the 18th century, steam pressures exceeding atmospheric pressure were employed. In the 19th century, the common steam pressure was raised to approximately 0.8 MPa. Correspondingly, the earliest steam boiler was a large-diameter vertical cylindrical shell for containing water, which was later replaced by a horizontal shell, with fires burning beneath the shell in a brick-lined furnace.

Double Fire Tube Boiler

As boilers grew larger, to increase the heating surface, fire tubes were added to the boiler shell. Fire was burned at the front end of the tubes, with flue gases exiting from the back and being channeled through brick flues to the chimney, thereby heating the external surface of the boiler shell. This type of boiler is known as a fire tube boiler. Initially, only one fire tube was installed, referred to as a single fire tube boiler or Cornish boiler. Later, two fire tubes were added, known as a double fire tube boiler or Lancashire boiler.

Horizontal External Combustion Reheat Pipe Boiler

Around 1830, after mastering the production and expansion techniques of high-quality steel pipes, fire-tube boilers emerged. Some fire tubes were installed inside the boiler shell, forming the main heating surface, with the flame (flue gas) flowing through the tubes. A large number of fire tubes were installed below the water line in the boiler shell, known as horizontal external combustion return flue-tube boilers. They have a lower metal consumption but require substantial masonry.

Pot drum

In the mid-19th century, the water-tube boiler emerged. The heating surface of the boiler was the water pipes outside the boiler shell, replacing the boiler shell itself and the fire-tubes inside. The increase in the heating surface area and steam pressure of the boiler was no longer limited by the diameter of the boiler shell, which was beneficial for enhancing the evaporation capacity and steam pressure of the boiler. The cylindrical boiler shell in such boilers was then renamed to a drum, or called a steam drum. Early water-tube boilers only used straight pipes, and the pressure and capacity of straight-pipe boilers were limited.

In the early 20th century, the development of steam turbines necessitated boilers with higher capacity and steam parameters. The straight tube boilers were no longer sufficient. With advancements in manufacturing processes and water treatment technology, bent tube boilers emerged. Initially, multi-drum designs were used. As water-cooled walls, superheaters, and economizers were adopted, and improvements were made to the steam-water separation elements within the drums, the number of drums gradually decreased, saving metal and also benefiting the boiler's pressure, temperature, capacity, and efficiency.

Safety

Gas boilers differ from other gas appliances due to their unique installation location, high gas consumption, and higher safety requirements. Therefore, in North America, all gas fireplace products must pass stringent safety and environmental protection standards before being launched into the market. These standards are continuously updated as the products evolve. Each type of fireplace product has specific safety testing standards. For example, the testing standards for balanced gas fireplaces and flue gas fireplaces differ, as do those for decorative gas fireplaces and heating gas fireplaces. Consequently, North American balanced gas fireplace products should have certifications such as Ansi Z21.88 or CSA2.33, indicating that the product's safety and environmental protection meet the standards, and users can use them with confidence.

Auxiliary Boiler

The earlier fire-tube boilers, water-tube boilers, and firebox boilers were all types of natural circulation boilers. Due to varying heating conditions in the rising and descending pipes, density differences were created, resulting in natural flow. While developing natural circulation boilers, the use of once-through boilers began in the 1930s, and auxiliary circulation boilers were introduced in the 1940s.

Forced-circulation boiler

The auxiliary recirculating boiler, also known as a forced circulation boiler, is an evolution of the natural circulation boiler. A recirculation pump is added to the downcomer system to enhance the water circulation of the evaporative heating surface. In a once-through boiler, there is no drum. The feedwater is supplied to the economizer by the feedwater pump, passes through the evaporative heating surfaces such as the water wall and superheater, and becomes superheated steam before being sent to the steam turbine. The entire flow resistance of all parts is overcome by the feedwater pump.

Composite circulating boiler

After World War II, these two types of boilers experienced rapid development due to the demand for high-temperature, high-pressure, and large-capacity power generation units at the time. The aim of developing these boilers was to minimize or eliminate the need for drums, allowing the use of small-diameter tubes as heating surfaces and providing greater flexibility in their arrangement. With advancements in automatic control and water treatment technologies, they gradually matured. At supercritical pressure, once-through boilers were the only viable option. In the 1970s, the largest single unit capacity was a 27 MPa pressure with a 1300 MW power generation unit. Later, composite circulating boilers were developed, combining auxiliary circulation boilers with once-through boilers.

Steps and Standards for Water Quality Testing in Gas Boilers

Determination of Chloride Ion Content

Measure 100ml of boiler water into a 250ml conical flask, add 2-3 drops of phenolphthalein indicator, which should turn pink. Then titrate with sulfuric acid until colorless. Add 2-3 drops of potassium ferricyanide indicator and titrate with silver nitrate standard solution until a chestnut red color appears. Record the volume of silver nitrate consumed, multiply by 35.5 to obtain the standard for chloride ions: chloride ions ≤ 400.

Determination of Alkalinity

Pipette 100ml of furnace water into a 250ml conical flask, add 2-3 drops of phenolphthalein indicator, the solution turns pink. Titrate with the standard sulfuric acid solution until just colorless, then add 2-3 drops of methyl orange indicator, continue to titrate with sulfuric acid until orange-red, record the volume of sulfuric acid consumed; this value is equivalent to the alkalinity value.

Measurement of 3 Hardness

Measure 100ml of boiler water into a 250ml conical flask, add a few grains of Loheng T indicator, then add 2-3 drops of ammonia-ammonium chloride buffer solution. Titrate with EDTA standard solution until the solution changes from wine red to blue. Record the volume of EDTA solution consumed. This volume is equivalent to the boiler water's hardness value.

Standard: Hardness: Steam oven less than or equal to 0.03 mmol per liter

Water heater 0.6 mmol per liter

pH Measurement

Determine using pH test strips

Standard: pH level: 10-12

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