• [2013-06-19]

  Professor Jianchun Mi’s team has made progress in their research of MILD combustion

Professor Jianchun Mi, College of Engineering of Peking University, has recently led his team to make an important progress in the understanding of Moderate or Intense Low-oxygen Dilution (MILD) combustion. The results have been published in Combustion and Flame (2013, 160(5), 933-946), (http://www.sciencedirect.com/science/article/pii/S0010218013000394) and Energy & Fuels (DOI: 10.1021/ef400500w), (http://pubs.acs.org/doi/abs/10.1021/ef400500w). The main contributors of the work include Dr. Pengfei Li and Mr. Feifei Wang.

The oxy-fuel combustion technology has attracted increasing attention from the international combustion community due to its advantage of carbon capture and sequestration. The key of the oxy-fuel technology is that pure oxygen or highly-concentrated commercial oxygen is mixed with partial flue gas and then the mixture is treated as the oxidant, instead of air. The major elements of fuel, regardless of natural gas or coal, are carbon and hydrogen, whose theoretic products of combustion are CO₂ and H₂O. Thus, the high concentrated CO₂ can be collected for commercial use or underground sequestration when H₂O is removed. However, there are many problems with this technology in the conventional form such as low combustion stability, large loss due to incomplete combustion, low efficiency and operational safety.

Professor Mi’s team has made efforts in combining the MILD combustion with the oxy-fuel combustion, i.e., realizing the oxy-fuel MILD combustion technology. They found that the oxy-fuel MILD combustion can effectively resolve most of the above problems, reducing NOx emissions mostly, and simplifying the CO₂ enrichment process, regardless of the fuel types (gaseous, liquid and solid fuels) or thermal input.

The paper which appeared in Combustion and Flame reports their significant contribution for realizing the oxy-fuel MILD combustion. They provided the detailed performance and stability characteristics of a parallel jet burner system experimentally burning NG, LPG and C₂H₄ with air or O₂/CO₂ mixture in the MILD combustion mode. Effects of the initial mass fraction of CO₂, equivalence ratio, burner configuration, fuel type, and thermal field are quantified. Moreover, the NOx formation mechanisms are investigated through the computational fluid dynamic simulation. The important contribution of this work to the MILD combustion has been recognized by all the four referees.

For the paper published in Energy & Fuels, a fundamental analysis of combustion regime is provided. Professor Mi’s team has found that the MILD-like combustion, satisfying the mathematic MILD definition, should theoretically occur at any oxygen fraction as long as the preheating temperature prior to their reactions is sufficiently high. This has broken the MILD requirement that is the moderate or intense low-oxygen dilution.

The technology is expected to apply not only to the existing plant improvements but also to the new plant construction.

Figure 1. Images showing the effect of equivalence ratio on the in-furnace appearance of O₂/CO₂ combustion at different initial mass fractions of CO₂ in the oxidant stream.