Effect Of Additives On Flow Characteristics And Na Capture Efficiency Of Zhundong High Alkali Coal Ash Slag

At present,coal is still the main fuel in China's energy consumption,of which the Zhundong coalfield in Xinjiang is the largest integrated coalfield in China.However,Zhundong coal has relatively high alkali metal content and is easy slagging,which cannot guarantee the safe and efficient operation of the boiler.The combustion technology of wet bottom boiler can overcome the shortcomings of slagging of water wall and serious fouling/ash accumulation/slagging of heating surface when dry bottom boiler burns slagging-prone coal,which is especially suitable for slagging-prone coal.Therefore,it is of great significance to carry out experimental research on the flow characteristics of coal ash slag and the capture effect of alkali metal at high temperature.In this paper,a typical Zhundong high alkali coal in Xinjiang was selected as the research object.Based on the coal quality characteristics of high alkali metal content,the experimental study on the flow characteristics of coal ash slag and the sodium capture efficiency of different additives was carried out.The research contents are as follows.Firstly,the flow characteristics of Zhudong high alkali coal with four additives were studied in detail by using horizontal tube furnace.The results show that the mixing of SiO₂ and Fe₂O₃ promotes the melting of coal ash,and the addition of 10 wt.%can also change the type of coal ash slag from crystalline slag to vitreous slag,thus promoting the fluidity of coal ash slag,while CaO and MgO can inhibit the melting of coal ash and reduce the fluidity.In addition,with the increase of SiO₂ addition ratio,the sodium capture efficiency of liquid slag increases gradually,while that of Fe₂O₃ is the opposite.Secondly,the effect of?NH₄?₂SO₄ additive on the sodium capture efficiency of Zhundong high alkali coal was studied in a vertical tube furnace under different atmospheres.The results show that?NH₄?₂SO₄ increases the concentration of NO_x and SO₂ in flue gas,while the diffraction intensity of NaCl in the ash decreases and the diffraction intensity of CaSO₄ increases.When the proportion of?NH₄?₂SO₄ reaches10 wt.%,Na₂SO₄ begins to be produced,and increases with the increasing proportion of?NH₄?₂SO₄.Lastly,by comparing the sodium capture efficiency,it can be seen that with the increase of?NH₄?₂SO₄ addition ratio,the sodium capture efficiency increases continuously,and at the same?NH₄?₂SO₄ addition ratio,the sodium capture efficiency in oxygen-rich atmosphere is generally higher than that in air atmosphere.Finally,Factsage software was used to simulate the possible precipitation forms and content of alkali metals when adding different proportion of?NH₄?₂SO₄ and SiO₂.NaCl?s?in coal ash gradually transforms into NaCl?g?,Na₂O?slag?and Na₂SO₄?liq?with the increase of temperature in the temperature range of 600¹500?.Na₂SO₄?liq?is easily decomposed at high temperature,so Na₂O?slag?is the main form of Na element in ash at high temperature.In addition,by comparing the proportion of Na₂O?slag?under different working conditions of the two additives,it can be seen that the highest proportion of Na₂O?slag?is 20%SiO₂,20%?NH₄?₂SO₄ and 10%SiO₂ at1500?.