Gas boilers include gas water boiler, gas hot water boiler, gas steam boiler, etc. The gas hot water boiler is also known as gas heating boiler and gas bathing boiler. Gas boilers, as the name implies, refer to boilers that use gas as fuel. Compared to oil boilers and electric boilers, gas boilers are the most economical choice, so most people opt for gas boilers as steam, heating, and bathing equipment.

Gas boilers include models such as the KS-Q Gas Water Boiler, CLHS (CWNS) Gas Hot Water Boiler, and LHS (WNS) Gas Steam Boiler. Among them, gas hot water boilers encompass both gas heating boilers and gas bathing boilers. With the completion of the national "West Gas to East" project, gas boilers have gradually become the top choice for consumers.

The "Special Equipment Safety Supervision Regulations" define boilers as equipment that uses various fuels, electricity, or other energy sources to heat the contained liquid to certain parameters and output thermal energy. The scope includes pressure steam boilers with a volume of 30L or more; pressure hot water boilers with an outlet water pressure of 0.1MPa or more (gauge pressure), and a rated power of 0.1Mw or more; and organic heat carrier boilers. [1]

Burner

The construction of the gas burner consists of the following 5 systems:

1. Air Distribution System

The function of the air supply system is to deliver air of a certain wind speed and volume into the combustion chamber, its main components include: housing, fan motor,

Blade wheel for fans, fire tube for air guns, air door controller, air door dampers, cam adjustment mechanism, diffuser plate.

2. Ignition System

The function of the ignition system is to ignite the mixture of air and fuel, with main components including: an ignition transformer, ignition electrodes, and high-voltage ignition cables. A safer type of ignition system is the electronic pulse igniter, widely used by manufacturers like Zhuoyi Energy-Saving for gas boilers. It is convenient and time-saving, requiring only a finger press, and boasts high safety. It prevents accidents caused by accidental extinguishing. In case of a flameout, the control system can promptly close the solenoid valve and shut off the gas supply.

3. Monitoring System

The function of the monitoring system is to ensure the safe and stable operation of the burner, with main components including flame sensors, pressure sensors, and temperature sensors (as shown in the figure below).

4. Fuel System

The function of the fuel system is to ensure the fuel required for the burner to burn. The fuel system of oil-burning burners mainly includes: fuel lines and connectors, fuel pumps, solenoid valves, nozzles, heavy oil preheaters. Gas-burning burners mainly consist of filters, regulators, solenoid valve groups, ignition solenoid groups, and fuel butterfly valves.

5. Electric Control System

The electrical control system serves as the command and coordination center for all the aforementioned systems. The main control components are programmable controllers, which vary depending on the type of burner. Common programmable controllers include the LFL series, LAL series, LOA series, and LGB series. The primary distinction among them lies in the different timing of the program steps.

Boiler Types

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 above atmospheric pressure were employed. In the 19th century, the common steam pressure was raised to about 0.8 MPa. Correspondingly, the earliest steam boiler was a large-diameter vertical cylindrical vessel for holding water, which was later replaced by a horizontal vessel, with a fire burning in a brick-lined furnace beneath it.

Double-flue boiler

As boilers grew larger, fire tubes were added within the shell to increase the heating surface. Fire is burned at the front of the tubes, with flue gases exiting from the back and passing through brick-lined flues to the chimney, thereby heating the exterior of the 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-fired reheating tube 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 fire-tube boilers. They have a lower metal consumption but require significant 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 both the 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 shell, which was beneficial for enhancing the boiler's evaporation capacity and steam pressure. The cylindrical shell in such boilers was then renamed to a drum or a steam drum. Early water-tube boilers used only straight pipes, and both the pressure and capacity of these straight-pipe boilers were limited.

In the early 20th century, the development of steam turbines necessitated larger 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 enhancing the boiler's pressure, temperature, capacity, and efficiency.

Safety

Gas boilers differ from other gas appliances in that they have a unique installation location, high gas consumption, and are safety-critical products. Therefore, in North America, all gas fireplace products must pass stringent safety and environmental standards before being launched into the market. These standards are continuously updated as products evolve. Each type of fireplace product has specific safety testing standards. For instance, the testing standards for balanced flue gas fireplaces and chimney gas fireplaces are different, as are those for decorative gas fireplaces and heating gas fireplaces. Hence, North American balanced flue gas fireplace products should have certifications such as Ansi Z21.88 or CSA2.33, indicating that the product's safety and environmental standards have been met, and users can use them with confidence.

Auxiliary Boiler

Historically, fire-tube boilers, water-tube boilers, and firebox boilers were all types of natural circulation boilers. Due to varying heating conditions in the ascending 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

Auxiliary circulation boilers, also known as forced circulation boilers, are developed based on natural circulation boilers. A circulation pump is installed in the downcomer system to enhance the water circulation in the heating surface for evaporation. In once-through boilers, there is no drum; feedwater is sent to the economizer by the feedwater pump, passes through the water-cooled walls and superheater, etc., and becomes superheated steam before being sent to the steam turbine. All the flow resistances in each part are 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 for 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, a hybrid once-through boiler was developed, combining an auxiliary circulation boiler with a once-through boiler.