Overview of the Technical Principles of Flameless Combustion

Overview of the Technical Principles of Flameless Combustion
1、 The method for determining the state of flameless combustion.
There is no clear international standard for the definition of flameless combustion state. Currently, most people agree with the research of Yunning and his son. They have obtained a large number of experiments on the relationship between the internal circulation rate of flue gas and temperature under the diffusion combustion mode, where mixing and combustion are carried out simultaneously.
The axial evolution and radial diffusion of fuel jet and oxidizer jet lead to surrounding air entrainment, gradually diluting the combustion products and non reactive gases in the center area of the jet, achieving a "low oxygen" combustion state.
In addition to these, there are other methods of judgment. For example, temperature rise is used to determine whether combustion is in a flameless state. Kumar et al. believe that after normalization of the combustion process, a temperature change of about 15% in the reactor can be defined as flameless combustion. Antonio Lavaliere et al. used inlet temperature and temperature rise to describe the combustion situation, and the study also concluded that the process where the inlet temperature is lower than the self ignition temperature and the temperature rise is greater than the inlet temperature is called feedback combustion, the process where the inlet temperature is higher than its inlet temperature is called high-temperature combustion, and the process where the inlet temperature is higher than its inlet temperature is also called flameless combustion.
2、 Flameless combustion system.
In the absence of an external heat source, the reactants are heated to above 1000 ℃ by recovering and utilizing the waste heat from combustion flue gas or high-temperature waste heat. The flue gas regulation process in the furnace controls the mixing of fuel, air, and flue gas, and the volume fraction of oxygen in the combustion area of the furnace is 2% -5%. The fire boundary extends to the entire furnace, resulting in a uniform temperature distribution and a significant improvement in combustion efficiency and utilization, forming a new combustion method that is different from traditional luminous flames.
3、 Flameless combustion characteristics.
1. High temperature and low oxygen are the basic conditions for achieving flameless combustion. Before the reaction, the oxidant should be preheated to reach a certain high temperature or sufficient preheating, so that the temperature at any position of the furnace during combustion is greater than the self ignition point of the fuel;
2. By using methods such as entrainment through high-speed jets or backflow through special burner structures, as well as filling with diluted gas, the fuel and oxidizer are fully diluted, and the oxygen concentration in the combustion reaction zone is kept between 2% and 15% as much as possible;
In flameless combustion mode, the combustion is "soft" and there is no combustion noise. The combustion space spreads over a large range, making the temperature distribution of the entire space uniform and reducing pollutant emissions.
4、 Realize flameless combustion pathway.
1. Fill with nitrogen gas.
2. High speed jet.
3. Special combustion chamber structure.