Experimental Study On The Catalysis Of Mineral Matter For NO_x And SO₂ Reduction In Advanced Reburning With Pulverized Coal

In China, the NO_x and SO₂ emitted from the coal combustion contribute significantly to the total emission, and there are 35%⁴0% NO_x from electric power plants. As a result of the environmental problem in the worldwide getting worse and worse, the request of the emission of the main atmosphere pollutants such as NO_x and SO₂ is becoming stricter and stricter. So there need some new technique with a higher NO_x reduction efficiency or SO₂ reduciton efficiency strongly, and it is more cost-efficient to improve the reduction efficiency in the exist equipments for NO_x and SO₂ reduction. There are more and more attention paid to the combining reduction of NO_x and SO₂. At present, there are some studies on the catalysis of mineral matters in the coal ash for NO_x reduction in coal reburing, but only the catalysis for the heterogenous reduction of C-NO is considered. In the text, the catalysis of the mineral matters for the NO_x and SO₂ reduction in the reburning and advanced reburning with pulverized coal is studied, and their catalyses for the homogenous reduction of CHi-NO, NHi-NO and CO-NO are analyzed in order to find out the catalytic paths and reaction mechanism of mineral matters. It can provide a theoretic gist for the improvement of NO_x reduction in the advanced reburning, and it can also supervise the realization of combining reduction of NO_x and SO₂ in the furnace.In the text, all the experiments are carried out on a two staged drop flow reactor. There contains two kinds experiments: one is on the catalyses for NO_x reduction in the advanced reburning of NaOH, KOH, FeCl3 and Ca(OH)₂, and the other is on the catalysis for the combining reduction in the advanced reburning of calcium carbide residue (CCR). The effects of the category and load of mineral matters and the original fraction of oxgen (OFO) in the reburning zone on the catalysis of NO_x and SO₂ reduction are studied with the same reaction temperature, the smae fuel ratio, the same NH3/NO ratio and the same resident time.Through comparing and analyzing the catalyses for NO_x reduction of mineral matters in the reburning, SNCR process and the advanced reburning get their catalytic capabilities and the catalytic paths. It indicates that: the mineral matters can catalyze the denitrification process of the reburning and advanced reburning in different degrees, and the catalysis for the advanced reburning is more obvious, and the catalytic capabilities of mineral matters are ranked as NaOH> KOH> FeCl₃- Ca(OH)₂; the catalyses for the advanced reburning of mineral matters are realized by their catalyses for the SNCR process contained in the advanced reburning. From the effects on the conversions of some main gas matters in the reburning, SNCR process and advanced reburning by mineral matters, the results can be concluded as following: NaOH and KOH can restrain the oxygenation of NH₃ with oxygen, then promote the reduction of NH₃ with NO, at the same time, they can increase the concentration of CH4 and CO which can catalyze the homogenous reduction of CHi-NO, NHi-NO, CO-NO etc.; however FeCl3 and Ca(OH)₂ have little effects on the two aspects. So NaOH and KOH have a higher catalytic capability on NO_x reduction in the advanced reburning than FeCl3 and Ca(OH)₂.Through comparing and analyzing the catalyses for NO_x reduction and SO₂ reduction of calcium carbide residue (CCR), it indicates that: calcium carbide residue (CCR) can improve the desulfurization and denitrification process of the reburning and advanced reburning a little, but it works only when the original fraction of oxygen (OFO) in the reburning zone is low, and its catalysis for the reburning is more obvious than the advanced reburning. From the effects on the conversions of some main gas matters in the reburning and advanced reburning by calcium carbide residue (CCR), the results can be concluded as following: calcium carbide residue (CCR) has a little effect on the NO_x reduction and SO₂ reduction in the reburning and advanced reburning like Ca(OH)₂, due to its few effect on the conversions of the main gas matters in the reaction. The CaO contained in the calcium carbide residue (CCR) can absorb SO₂ in fuel poor or fuel rich in different ways, so it improves the SO₂ reduction. When the Ca/S ratio is larger than 2.52, calcium carbide residue (CCR) can increase the SO₂ reduction efficiency in the advanced reburning when the original fraction of oxygen (OFO) in the reburning zone is high.