Experimental Study On The Combustion And Acidic Gas Emission Characteristics Of Paper Mill Sludge/coal Mixtures

With the fast development of the paper industry, total volume of paper wastewater treated has gradually growed every year, total volume of paper mill sludge has also increased dramatically. Use of incineration to deal with sludge and show their "Reducing the volume and weight. Eliminating the hazard and Recycling", the unique advantages, and has become an important approach. This paper takes the dewatered sludge which through the belt press filter from certain paper mill in Machong Town, Dongguan City as research subject, and experiment study on combustion and acidic gas emission characteristics of paper mill sludge/coal mixtures were investigated.Firstly, this paper obtained the test results of ultimate analysis, primary analysis and value of sludge under different samples which showed that, paper mill sludge had characteristics of high devolatilization, low fixed carbon and heating value, and pulverized coal had characteristics of low devolatilization, high fixed carbon and heating value. Moreover, the content of N element in sludge were higher than coal and the content of S element varied slightly with coal.Secondly, the combustion characteristics of paper mill sludge, coal and blends of them with different proportions were studied by thermogravimetric analysis (TG-DTG) at different heating rates. Three obvious temperature zones existed in the paper mill sludge combustion curves, which corresponded to two stages of devolatilization and fixed carbon combustion, where the weight of sludge was lost promptly. During combustion of blended samples, the paper mill sludge and coal basically maintained their own devolatilization characteristics. The combustion curve of sludge-coal blends exhibited a transitional behavior from that of sludge to that of coal. The DTG curve of the blends was closer to that of the material in larger proportion. The comprehensive combustion characteristic index S of the sludge-coal blends declined, which demonstrated that samples with higher volatility had better combustion characteristics. The burnout index Cb increased with the heating rate and the proportion of coal. Thirdly, both the combustion reaction equation during the different combustion periods and the corresponding kinetic parameters were calculated by the Coats-Redfern equation. Before the peak of combusted devolatilization in the first phase, activation energy decreased with the increasing proportion of pulverized coal, and it was appropriate to describe the combustion mechanisms of paper mill sludge and sludge-coal blends by the equation f(α)= (1-α)0.5-Due to the influence of the heating rate and different components, the reaction coefficient of after the peak of combusted devolatilization and the peak of fixed carbon combustion is not constant. Activation energy of paper mill sludge, coal and blends of them is higher than others in the phase of fixed carbon combustion. The value of activation energy corresponded to the phase of sludge combustion.Fourthly, in the current study, facilitated with the tubular furnace combustion system, acidic gas emission rule of the sludge combustion, due to different combustion temperatures, and different peat ratios, were recorded and explored. As the result of the experiment shown, under the constant temperature combustion conditions of different proportions of peat mixture, the distribution of NOX release is "bimodal". In the first peak which was generated in the early stage of the reaction, the concentration of NOx is relatively high, and the duration time is relatively short; while the second peak in the latter stage is wide and flat. According to the data, only a peak was marked down in the release process of SO2. The "first peak" of NOX and the peak of SO2 appeared in advance as the reaction temperature rose. Moreover, the peak values increased as the reaction temperature rose. The emission load of NOX and SO2 increased with the temperature increase, In the whole temperature period, the emission load of NOX in the pure is higher than any other reactant. With the increase ofω, the emission load of NOx reduced. In the same reaction temperature, the emission load of SO2 is slightly higher than other samples when the coal combustion. Overall, the emission load of SO2 is not very different from each other.At last, general summary of this paper and further research was presented. It has benefit for the further studying.