Advanced Materials Research Vols. 614-615

Abstract: Wetness is one of the important parameters of the relationship with the turbine operating efficiency and safety. Wetness is determined by the number of small water droplets in the steam, and the nucleation rate on the formation of small droplets has a direct relationship.The nucleation rate is difficult to through experiments measured. This article through numerical simulation obtained the distribution of the nucleation rate and supercooling degree.

Abstract: Co-combustion experiment of oil shale semi-coke and corn stalk at different blend ratios was performed using thermogravimetric analyzer. The influence of different blend ratios has been studied. The combustion characteristics are obtained under the heating rates of 20oC/min and the experimental temperature range of 40-850oC. The combustion process of the blends is divided into three stages: low-temperature stage, transition stage and high-temperature stage. With the increasing of corn stalk in the blends, the reaction of combustion mainly shifts from high-temperature stage to low-temperature stage, and there is no obvious change for the ignition temperature, but the burn out temperature comes down. The combustion kinetics parameters of the blends were analyzed using Flynn-Wall-Ozawa model. The result shows that the activation energy of the volatile matter stage increases and the activation energy of semi-coke combustion stage decreases. The combustion characteristics of the oil shale semi-coke get improved significantly with the mixture of corn stalk.

Abstract: The combustion experiments of oil shale semi-coke and corn stalk mixtures were conducted using thermogravimetric analyzer. The results show that the advance ignition and burnout can be achieved when semi-coke is mixed with corn stalk. The influence of different blend ratios has been studied, and the combustion characteristics were obtained. Comprehensive combustion characteristics get improved with the increase of corn stalk proportion in the mixture. The interaction of mixture in the combustion process occurs mainly in 400-600oC. It can be explained that the combustion of fixed carbon in corn stalk is delayed. What is more, TG curves were simulated by Johnson-Mehl-Avrami equation. The result shows the feasibility of using Weibull distribution to simulate the TG curves of co-combustion.

Abstract: Three oil sand samples from Indonesia have been non-isothermally pyrolysed on thermogravimetric analyzer (TGA). The analyses were performed at different heating rates (5, 15 and 25oC/min) up to 850oC with nitrogen as purge gas. The weight loss curve shows that the main pyrolysis of oil sand takes place in the range of 200~600oC. On the basis of experimental data, a pyrolysis kinetic model was proposed. The kinetic parameters of activation energy (E) and frequency factor (A) were obtained by Integral Method. There is no clear relationship between activation energy and heating rate.

Abstract: Fuel control is the major part during the FCB control process of the unit, especially the fuel used by W-shape of flame boiler is inferior coal which has the character of low-volatile and low heating value. The switching way, procedures and speed of the fuel during the FCB process will directly determine whether the boiler can have a stable combustion after the fuel amount is greatly reduced for the unit. In this article, the strategy for quick switching of new type of fuel amount for W-shape of boiler and quick stabilization control for boiler combustion is proposed. And in this article, we also take an example of an engineering concerning foreign affairs which has successfully implemented FCB. the boiler fuel control technology which realized the function of FCB for W-type flame boiler unit is deep analyzed. It leaves a very good reference value for the test of FCB for other similar units.

Abstract: Pulverized coal ignition time is one of crucial parameters in coal ignition process. Based on a general heat absorption equation without chemical reaction, this study was focused on some crucial factors which influence pulverized coal ignition time to theoretically explain the mechanism of heat absorption of pulverized coal. The influences of recirculated flue gas (RFG) temperature, flame temperature, primary air temperature, and coal particle diameter on ignition time were discussed. The importance of radiation heat and convection heat was analyzed. The results show that the higher temperatures of RFG, flame, and primary air can lead to the shorter ignition time respectively. The increase of the coal particle diameter greatly increases the ignition time, and as the diameter goes up, the amount of the ignition delay becomes greater. For high accuracy of ignition time calculation, both radiation heat and convection heat should be taken into account. When flame temperature is very high and RFG temperature is very low, radiation is the dominant factor, otherwise convection is more crucial.

Abstract: The products of coal under fast pyrolysis experiments were carried to study the mechanism of coal products under the fast heat effects of deflagration. Several coal were studied here, such as young lignite, old lignite, long flame coal, coke and young anthracite. The experiments temperature is between 588~1313K, experiments heating velocity is 5000K/s, and with normal pressure, experiments time are 1s, 2s, 5s, 10s. Through fast pyrolysis experiments, products separated out from coal was got. There are CH4, CO, CO2, C2H4, C2H6, C4, C5, C3H6, C3H8. This mixed gas is flammable. The results could be used to study the combustion efficiency and mechanism of this special combustion course of different rank coal. This work is useful for study the coal using in the field of energy using and combustion. It may provide one new method to protect our environment tomorrow.

Abstract: In recent years, a combined cooling and power system (CCPS) with NH3-H2O absorption cycle has been aroused great interests. The previous researches on CCPS have been reviewed to summarize the properties of working pair and the experimental apparatus and demonstration devices firstly. Then, a new CCPS driven by solar energy has been developed and discussed.

Abstract: In this paper, we focus on the relationship between oxygen-enriched combustion efficiency and oxygen content of primary air under N₂ /O₂ atmosphere combustion on CFB boiler. Firstly, an entirely possible of CFB boiler oxygen-enriched combustion model was proposed. Secondly, a platform was built for simulation of CFB combustion process on XD-APC configuration software. Finally, industrial simulation with industrial data was going on to prove the platform was reasonable. The simulation results were consistent of industrial data. It shows the simulation platform reliability, and the model accuracy. On this basis, coal combustion efficiency was simulated. It shows that the combustion efficiency increases following by oxygen content increasing. It’s economic for real process when oxygen content chooses from 25% to 30%.

Abstract: Homogeneous charge compression ignition (HCCI) offers high efficiency and ultra-low NOx and SOOT emissions which raises world-wide attention. A 3-dimensional CFD HCCI model has been established using STAR-CD code for combustion characteristics studies under negative valve overlap (NVO) strategy via an early closure of exhaust valve. The combustion characteristics of HCCI were investigated. Simulation results were in good agreement with the available experimental data. Studies on in-cylinder temperature and OH radical concentration showed almost the same spatial distribution when auto-ignition occurred, OH radical had higher concentration in the field of higher temperature. The φ-T maps showed extraordinarily low NO emissions and no soot emissions under HCCI combustion. It was found that OH concentration rapidly increased after the start of the combustion at 356°CA and NO emissions were formed when the temperature was high enough at 358°CA. Most of CO emissions were converted to CO2 through the main combustion.