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Structure And Classification Of Dual Fuel Burner

At present, there are two main combustion modes of natural gas boilers. One is the special combustion mode, that is, the combination of boiler and gas, which can fully reflect its advantages in equipment investment and operation economy; The other is the mixed combustion mode, which is equipped with two combustion systems: gas oil and gas coal. The boiler can burn gas alone or burn another or two fuels separately, which is also called dual fuel burner at this time.

A dual fuel burner is a kind of burner in which both burners have gas and fuel nozzles at the same time. The air conditioner, combustion stabilizer, ignition device, and flame monitoring device in the control room of the dual fuel burner must meet the requirements of both fuels at the same time.

1、 Design
Although there are many forms of dual fuel burners, and high-power boilers, it is mainly a multi-gun combustion mode formed by the mixed combustion of pulverized coal pipe or oil gun and pulverized coal or heavy oil. The mixing and combustion are further strengthened by the role of rotating airflow in the central gas pipe; In order to improve the low load performance, the air adopts a three-way structure, and each air volume is adjusted by setting a separate regulating baffle, so the burner is relatively complex.

2、 Constituent Body
The dual burner is mainly composed of three parts: the common part, fuel oil part, and gas part.

1. Common parts
It includes an air pipe, deflector used to control the direction of airflow, air branch pipe, and fire-resistant fire passage. In addition, there is a small fire igniter, whose position should be able to reliably place fuel and gas. The position of the fire detector shall be able to detect small fire, the main flame of gas, fuel (or coal) flame. When a large gas supply system is installed in the fuel burner, it may interfere with the mixing mode of fuel combustion. The solution is to arrange the fuel gas inlet outward on the periphery of the burner.

2. Fuel components
It is mainly an oil atomizer, which is used to separate the oil and evenly distribute the oil mist into the airflow in a controllable way. The following types of atomizers are usually used:

(1) Jet atomizer
The oil enters the swirl chamber from the air hole at the corner, ejects from the ring nozzle in a conical form, and disperses into droplets. The pressure of oil is generally between 0.35 and 1.4 MPa, up to 7.5 MPa. The viscosity of the oil during operation is about 15 × 1030 m2 / s. The simple jet atomizer has a certain impact on the load regulation rate of the burner, but the load regulation rate can be improved by overflow and backflow. Because too much oil can flow back, the amount of oil entering the swirl chamber is certain regardless of the flow rate: a good swirl can be formed when the flow rate is large, and a certain thickness of oil mist flow can be maintained at the water outlet.

(2) Steam-assisted atomizer
This kind of atomizer was used in the early stage. The water vapor was guided into the oil stream and broke into the oil stream to form fog. In the process of use, due to the large consumption of steam, the use of jet atomizer has a certain impact on it. In recent years, this model has made major reforms, and steam consumption has been greatly reduced.

3. Gas components
The fuel gas components of the double burner adopt the nozzle mouth mixing type. Since the oil atomizer occupies the central position of the burner stability area, the gas components are limited to a certain extent. The removable nozzle or ring cavity heating can make it reach the central position; However, if the rotating cup oil mist is used at the same time, this cannot be achieved, and in other design styles, when the load increases, the central air supply becomes difficult. Therefore, gas usually enters through a ring tube or nozzle arranged between the atomizer and the housing.

3、 Classification
Dual fuel burners can be divided into two types: assembled burners (including fans and control devices, which are assembled by the manufacturer before leaving the factory) and field assembled burners (both burners and controllers are assembled on site, with additional fans). The former type is mainly used in fire tube boilers, while the latter is mainly used in water tube boilers. Generally speaking, the dual fuel burner is formed around the existing fuel burner. The fuel injector has been installed in the center of the burner, and the gas must be introduced from the opening of the oil atomizer and the shell.