Lyu Junfu

Characterization of Pressure Signals in Fluidized Beds Loaded with Large Particles Using Wigner Distribution Analysis: Feasibility of Diagnosis of Agglomeration

Abstract An experimental verification is reported on the early predicting index of agglomeration in bubbling fluidized bed. Coarse quartz sand, which has the same density but larger diameter than the bed material, was used to simulate the initial agglomerated particle. Wigner distribution was used to analyze the pressure fluctuation of the tested bed, and the average amplitude of local domain frequency (LDF) and local peak weighted average frequency (LPWA) under different operating conditions were measured and compared. The results showed that the LDF is sensitive to the agglomeration phenomena and had quick response to the incipient agglomeration in fluidized beds. It can be concluded from the results that these two parameters could be taken as the characteristic indexes to the agglomeration in fluidized beds.

Numerical Simulation of Oxy-coal Combustion for a Swirl Burner with EDC Model *

The characteristics of oxy-coal combustion for a swirl burner with a specially designed preheating chamber are studied numerically. In order to increase the accuracy in the prediction of flame temperature and igni- tion position, eddy dissipation concept (EDC) model with a skeletal chemical reaction mechanism was adopted to describe the combustion of volatile matter. Simulation was conducted under six oxidant stream conditions with dif- ferent O2/N2/CO2 molar ratios: 21/79/0, 30/70/0, 50/50/0, 21/0/79, 30/0/70 and 50/0/50. Results showed that O2 en- richment in the primary oxidant stream is in favor of combustion stabilization, acceleration of ignition and increase of maximum flame temperature, while the full substitution of N2 by CO2 in the oxidant stream delays ignition and decreases the maximum flame temperature. However, the overall flow field and flame shapes in these cases are very similar at the same flow rate of the primary oxidant stream. Combustion characteristics of the air-coal is similar to that of the oxy-coal with 30% O2 and 70% CO2 in the oxidant stream, indicating that the rear condition is suitable for retrofitting an air-coal fired boiler to an oxy-coal one. The swirl burner with a specially designed preheating chamber can increase flame temperature, accelerate ignition and enhance burning intensity of pulverized coal under oxy-coal combustion. Also, qualitative experimental validation indicated the burner can reduce the overall NOx emission under certain O2 enrichment and oxy-coal combustion conditions against the air-coal combustion. Keywords oxy-coal, eddy dissipation concept model, coal, swirl burner

Effects of the Secondary Oxygen Injection on the Performance of a Staged-Entrained Flow Coal Gasifier

In a staged entrained flow coal-slurry gasifier, the secondary oxygen was injected into the gasifier in order to protect the refractory in the dome region, to improve the mixing process as well as gasification performance. Based on a proposed 3-D numerical model, simulations were conducted for the staged gasifier at different mass flow rates of the secondary oxidizer. The characteristics of the gasification flames were analyzed as well as the influence of the secondary flow on the flow field of the staged gasifier. As the mass flow rate of the secondary oxidizer decreases, the secondary gasification flame curves up according to the backflow region and wall temperature increases. When the mass flow rate of the secondary oxidizer is less than 10% of the total oxidizer mass flow rate, there is an obvious change of the turbulent mixing in the staged gasifier.