Reaction intermediates and products characterisation of NH3 in desulphurisation with activated coke

Abstract

The sulphate is an important factor restricting the efficient and stable operation of the activated coke (AC) flue gas purification system. The simulation experiments and in situ infrared tests of AC taken from desorption tower of the AC flue gas purification system were carried out to first calibrate the thermal desorption characteristics of adsorbed NH₃ and sulphate and explore the reaction behaviour of NH₃ with SO₂ and H₂SO₄. On this basis, some advice for optimising the sulphate generation was put forward to improve the purification efficiency of the AC system. The results show that the temperatures of the desorption of adsorbed NH₃, the decomposition of (NH₄)₂SO₄ and NH₄HSO₄ are 224, 276 and 319 °C, respectively, which lays the foundation for the quantitative analysis of sulphate on AC. Regardless of the NH₃ amount, only a small portion of H₂SO₄ is converted to sulphate, as the H₂SO₄ deposited in AC pores or agglomerated together could not come into contact with NH₃. The final reaction product of NH₃ and SO₂ is mainly (NH₄)₂SO₄ which is continuously generated because the newly generated H₂SO₄ is continually exposed to NH₃, if NH₃ is enough. The reaction of NH₃ with H₂SO₄ takes precedence over with NH₄HSO₄. In the initial stages in which H₂SO₄ is exposed to NH₃, the product is essentially all NH₄HSO₄ as intermediate. Then, it is further converted to (NH₄)₂SO₄ whose amount reaches equilibrium when the accessible H₂SO₄ is exhausted. All the NH₃ adsorbed on AC entering the desulphurisation tower generates NH₄HSO₄, but the amount is limited. The remaining SO₂ entering the denitrification tower mainly generates (NH₄)₂SO₄; thus, limiting the remaining SO₂ amount is necessary to guarantee denitrification efficiency. When the NH₃ injection is changed to the desulphurisation tower, the initial NH₃ injection rate can be increased to complete the conversion of accessible H₂SO₄ as soon as possible in order to obtain higher denitrification efficiency.