Adsorption characteristics of SO₂ and NO in a simulated flue gas over the steam activated biomass chars

Biomass chars were prepared under different pyrolysis temperatures, pyrolysis rates (rapid and slow pyrolysis) and steam activation temperatures from wheat straw and rice husk; their surface area and pore structure parameters were measured by nitrogen sorption at 77 K. The effects of pyrolysis temperature, pyrolysis rate, steam activation temperature as well as the concentration of SO₂ and NO in a simulated flue gas on the adsorption characteristics of SO₂ and NO over the biomass chars were carried out in a fixed-bed adsorber. The results indicated that the steam activation can significantly increase the surface area, micropore volume and total pore volume of biomass chars, while decrease their average pore sizes; as a result, the breakthrough time and adsorption capacities of SO₂ and NO over the activated biomass chars are increased. Moreover, rapid pyrolysis gives the biomass chars better adsorption characteristics than slow pyrolysis. A pyrolysis temperature of 873 K is superior to 673 and 1 073 K to get biomass chars of high adsorption performance for SO₂ and NO. Similarly, there also exists an optimum steam activation temperature between 973 and 1 173 K to prepare activated biomass chars of high adsorption performance. The breakthrough time increases but the adsorption capacities of SO₂ and NO decrease with the decrease of the concentration of SO₂ and NO in the simulated flue gas. The wheat straw char prepared under the conditions of rapid pyrolysis, pyrolysis temperature of 873 K, and steam activation temperature of 1 073 K performs best for the adsorption of SO₂ and NO; over it, the adsorption capacities of SO₂ and NO reach 109.02 and 21.77 mg/g, respectively.