Xiaojiang Wu

Experimental Study on Ash Melting Behavior of Xinjiang High-Alkali Coal Blended with Low-Alkali Coal During Coal Combustion

In this study, one typical Xinjiang high-alkali coal (HA coal) and another low-alkali coal (LA coal) have been mixed to study the ash melting behavior as a function of coal blending ratio, through the use of AFTs, XRF tests of samples. Moreover, the thermodynamic equilibrium calculation and ternary phase diagram CaO–SiO2–Al2O3 analysis were also used to clarify the mechanism of blended coal ash melting behavior and to optimize the coal blending ratio. The results indicate that the trend of AFTs is not linearly related to the blending ratio of coal mixtures. Instead, it is highly linked with the changes on the liquidus temperature from the ternary phase diagram systems. The initial melting temperature of HA coal ash is approximately 275 °C lower than that of LA coal ash due to the existence of alkali and alkaline metals, although it has relative higher ash fusion temperature. The mixing of LA coal is not only beneficial to reduce the amount of vaporized sodium, but also increases the initial melting temperature of blended ash due to the physical and chemical reactions between alkali and silica particles.

Experimental study on low NOx emission using blast furnace gas reburning and industrial application in stoker boiler

In order to get some useful information on reforming one stoker boiler with the capacity of 75t/h by using gas reburning technology, the effect of some key factors such as stoichiometric coefficient, residence time, reburning temperature and reburning gas - coal heat ratio on NOx emission characteristics was studied in a one-dimensional experimental system. The results showed that the longer residence time of flue gas in reburning zone of furnace will get lower NOx emission, there exists an optimum residence time of flue gas in reburning zone, the optimum residence time is around 0.8s. There also exists an optimum stoichiometric ratio of air in reburning zone of furnace, the value of that is around 1.0. The removing rate of NOx increases with both increasing feeding rate of reburning gas and increasing reburning temperature. The gas reburning technology has been successfully used during reforming an stoker boiler with the capacity of 75t/h, the NOx removing efficiency was over than 50%.

Experimental Study on Low NOx Emission Using Blast Furnace Gas Reburning and Industrial Application in Stoker Boiler

To get the modification method of blast furnace gas reburning technology on one 75t/h stoker boiler, the effect of some key factors such as stoichiometric coefficient, residence time, temperature and heat ratio input on NOx formation regulation was studied on a one-dimensional test system with fuel reburning. The results showed that prolonging the reburn zone residence time can help to lower the NOx emission and the best time was 0.8s. There existed an optimum value 1.0 for reburn zone stoichiometric coefficient. The NOx reduction efficient increased with the increase of the reburn heat input and the reburn zone temperature. The use of blast furnace gas reburning technology has been successfully implemented during the modification of stoker boiler, the NOx reduction rate was over 50%.

Study on the effect of flame offset on water wall tube temperature in 600°C and 700°C ultra-supercritical boiler

ABSTRACT The distribution of water wall temperature in the ultra-supercritical (USC) boilers was obtained by establishing a coupled heat transfer model. The reliability of this model has been validated through the comparisons of simulated and measured water wall temperatures along different dimensions in the furnace of reference USC boiler. Then, the effect of flame offset on water wall tube temperature in 600°C and 700°C USC boilers was investigated by importing the flame offset variables into the coupled model. The water wall temperature distribution is significantly influenced by flame offset, and both the fluctuation and growth rate of temperature are increased with the ascent of flame offset distance, especially on the furnace walls that flame deviates toward. The radiative and convective heat flux to water walls is strengthened simultaneously during the flame offset process, resulting in the local overheating of water wall. In the 600°C USC boilers, when the distance of flame offset exceeds 5 m, multiple peak distribution of wall temperatures appears, which can increase the burst risk of water wall tubes because of shear stress inside the tube material. The maximal distance of flame offset should be limited to 3 m to avoid the tube burst accidents. In the 700°C USC unit, the variation tendency of water wall temperature is resemble with that in 600°C USC unit, but the fluctuation of wall temperature is larger. As the flame offset distance approaches 3 m, the maximal water wall temperature reaches 595°C, which greatly exceeds the material allowable temperature in the 600°C USC unit. The material of water wall tubes with allowable temperature of 605°C is recommended for the 700°C USC unit. Based on the thermal security of metal material, the maximal distance of flame offset should be yielded to 2 m.

Analysis of sensitivity and optimization potential for oxy-fuel plant system

A sensitivity analysis of net electric efficiency has been conducted to assess the performance of a purpose-designed 600 MWe supercritical oxy-fuel bituminous coal-fired power plant system with three recirculation models of flue gas using commercial software THERMOFLEX 23. To compare in a direct way, a new definition of “efficiency sensitivity” was introduced. The assessment was performed for 7 major operating parameters. It is suggested that air leakage acts as the most important impact factor on the performance of oxy-fuel system. The other factors are also influential including oxygen concentration from ASU, oxygen excess ratio, and gas leakage in gas preheater. Optimization, i.e., thermal integration, was also considered to minimize the energy loss of the oxy-fuel process. For the purpose of optimizing, the improvement of turbine system which utilizes the thermal energy of hot flue gas through heating feed water is also very important for oxy-fuel process. By heating the feed water at the outlet of the secondary feed water heater upstream of the deaerator, the rise of net efficiency of an oxy-fuel process can narrow the energy penalty relative to the air-firing system. With the proposed optimization potential ratio, \( \frac{B}{W} \) or \( \frac{B \cdot Q}{W} \), it was concluded that the power plant system of 600 MWe has lower optimization potential ratio than that of 300 MWe, which means that the power plant with higher capacity has lower improvement potential of net electric efficiency.