What Are the Different Types of Combustion Systems?

Combustion system refers to the combination of equipment and corresponding smoke, wind, and coal (pulverized coal) pipes required to fully burn the fuel in the furnace of the boiler and exhaust the flue gas generated by the combustion into the atmosphere. The combustion system should be based on the type of fuel used, such as solid, liquid or gaseous fuel, the type and combustion method of the power plant boiler, and reasonably select the process flow, determine the specifications and quantity of equipment and pipelines, and fully consider the necessary margins so that The combustion system operates under the safest and most economical conditions. ^[1] The function of the fuel system is to ensure the fuel required for the burner to burn. The task of the combustion system is to release the chemical energy contained in the fuel through combustion and convert it into heat energy that can be absorbed by soda and water. Therefore, the quality of the combustion system will directly affect the thermal efficiency of the boiler. ^[2]

Industrial combustion systems are generally provided by the burner air supply system,

In conventional open-cycle gas turbines, combustion is a continuous process in which fuel is burned in the air supplied by the compressor; electrical sparks are required only during the initial combustion process, after which the flame must be maintained by itself. Designers have many choices in the structure of the combustion chamber, because the different requirements of aircraft and ground installations in weight, volume and windward area may make the solution very different. In recent years, severe restrictions on nitrogen oxide (NOx) emissions have had a significant impact on the combustion design of both industrial and aviation gas turbines.

The earliest aircraft engines used single-tube combustion chambers, as shown in Figure 6-1.

Single tube combustion chamber

After flowing out of the machine, it is divided into several independent airflows and enters the respective combustion chambers. These combustion chambers surround the shaft that connects the compressor and the turbine. Each combustion chamber has its own fuel nozzle connected to a common fuel manifold. This arrangement is particularly suitable for engines equipped with centrifugal compressors, as the fluid is divided into separate streams in the diffuser. An example of this is the Rotter Dart engine shown in Figure 1-10. The biggest advantage of a single-tube combustion chamber is that only one of the single-tube combustion chambers needs to be studied, and its air flow and fuel flow only account for a small part of the entire combustion chamber. For aviation installations, single-tube combustion chambers are not ideal in terms of weight, volume, and windward area, so today's aircraft engine designs no longer use such combustion chambers. Small gas turbines, such as auxiliary power units (APUs) and automotive devices, are often designed as single-tube combustion chambers.

Single-tube combustion chambers are still widely used in industrial engines, but the latest design uses a ring-tube system with each flame tube evenly wrapped around a ring-shaped casing. It is exactly this kind of system that Siemens "Typhoon" adopts; The layout of industrial gas turbines of GE and Westin House also adopts this kind of layout. The air flow will return after flowing out of the diffuser downstream of the axial compressor; using this phenomenon, the total length of the compressor-turbine connecting shaft can be greatly shortened, and the fuel nozzle and the flame can be easily maintained.

As far as layout is concerned, the most compact is the annular combustion chamber. This layout helps to maximize the use of space in a specific diameter range; it can reduce pressure loss and minimize the diameter of the engine. There are several shortcomings in the annular combustion chamber, so the annular tube combustion chamber was first developed.

First, although many fuel nozzles can be used, it is difficult to obtain a uniform oil and gas distribution and outlet temperature distribution.

Second, the structure of the annular combustion chamber is not strong, and it is difficult to avoid warping of the hot flame tube wall.

Third, compared with single-tube combustion chambers where only a single tube in multiple groups of flame tubes is required for testing, most research work on annular combustion chambers must be conducted for the entire combustion chamber, which requires test equipment to provide Total air flow. ^[4]