Study On Sulfer Dioxide Emmitsion Characteristics During Power Coal And Blended Coal Combustion

It is well known that coal is the primary energy resource in China. Meanwhile, SO₂ produced by coal combustion has always had serious effects on the economic development and production and life. coal combustion in power plants has always been a dominant contributor to the release of sulfur dioxide, in so saying, investigations on the rule of sulfur released from power coal and the technology of control technology of SO₂ have important significance. In recent years, due to short supply of power coals in China, many power plants are able to apply with fixed coal as combustion use. So it is universal for power plants to use blended coals. At present, there are scarce investigations on the rule of sulfur dioxide released from blended coals. As result, investigation on the characteristics of combustion of blended coals and the rule of the release of sulfur dioxide from blended coal is of great signification in realistic and theoretical meaning.Firstly, the characteristic of combustion process of eight primary power coals from Shandong province and their blended samples have been studied using the thermo-gravimetric analysis (TGA) method respectively, their burning performance parameters are in turn gained . The relationship and difference between single and blended coals are studied comparatively. As coal ranks increase, ignition temperatures and temperatures at largest weight loss accelerate, flammability index of coals have a trend of decrease. The combustion characteristic of blended coal lies between the two single coals, the ignition temperature of blended coal is close to that of component coal which is easier to catch fire, and the flammability index of blended coal is more influenced by component coal of poor combustibility. When blended coal is mixed with two component coals of similar rank, the combustion characteristic of the blended coal is similar to the two single components. When the ranks of two component coals are largely different, the combustion characteristic of the blended coal is similar to the two single components by stage. In the phase of precipitation and combustion of volatile, the combustion process is similar to that of low rank coal; in the phase of combustion of the coke, the combustion process is similar to that of high rank coal. The flammability index of blended coal becomes less when the combustion characteristics of component coals are largely different.Secondly, dynamic characteristics of SO₂ released from different coals are studied by high temperature pipe furnace, the relationship between coal qualities and the characteristic of SO₂ released from different coals is studied, the influence of combustion conditions on the characteristic of SO₂ released from different coals is studied too. The characteristic of SO₂ released from different coals presents obvious double-peak structure by which the sulfur in the coal falls into low sulfur coal and high sulfur coal. Although low sulfur coal and high sulfur coal can not is divided into organic sulfur and pyritic sulfur, the release characteristic of low sulfur coal and high sulfur coal can be judged by the composition of organic sulfur and pyritic sulfur. As the sulphur content increases, the releasing rate and the release total quantity are higher, however, there is little regularity between the sulphur content and the release rate of sulfur. The relationship between coal rank and the release characteristic of SO₂ is showed as followed: coal samples with different ranks have different combustion characteristic and sulfur forms, which has great effects on the characteristic of release of SO₂. It is significant that increasing temperature is able to increase the release rate of sulfur dioxide. Furthermore, this effect is more obvious at the stage of the release of high temperature sulphur. However, the influence is little after 1200℃. As the oxygen density increases, coarsening rate of SO₂ is higher; the release rate of sulfur is higher too.Thirdly , the characteristic of SO₂ released from blended coals is studied by high temperature pipe furnace, the release characteristic of SO₂ during the combustion of blended coals with different mixing ways is analyzed , moreover, the influence of combustion conditions on the characteristic of SO₂ released from blended coals is studied. The release characteristic of SO₂ from blended coal lies between that from the two component coals and is close to the characteristic of the component coal with larger proportion. When coals with different ranks to a large extent are blended, the time when SO₂ reach to the peak delays as the proportion of the coal with high rank increases. When coals with different sulfur contents are blended, coarsening rate of SO₂ and the release quantity of sulfur decrease as the proportion of the low sulfur coal increases. However, there is little effect on the release rate of sulfur. The influence of combustion condition on the release characteristic of SO₂ from blended coals is similar to that from single coals.Moreover, the release characteristic of SO₂ from blended coals is forecasted by BP neural network model. In this study , coal property parameters (volatile content,fixed carbon content\ organic sulfur content\pyrite sulfur content) and combustion condition parameters (temperature\ oxygen density) are used as input variable , meanwhile, the release rate of sulfur is used as output variable. 54 groups of sample data are applied to be exercised, and 10 groups of test data are used to inspect the model. The result is shown that the neural network model exercised meets the experimental error and has relatively high accuracy. as such , the BP neural network model set by this study can be used to forecast the release rate of SO₂ from blended coals.