Experimental Study On Occurrence Forms And Transformation Of Alkali Metal K During Biomass Pyrolysis

As a kind of clean renewable energy, biomass has drawn more and more attention. The alkali metal in the biomass will cause ash deposition, slagging, agglomeration and corrosion during biomass thermochemistry utilization process. Therefore, the occurrence forms of alkali metal and its transformation behavior has important scientific significance for promoting the development of biomass thermochemistry conversion technology.Adopting rice husk, straw and buttonwood leather as samples, this paper studied the occurrence forms and content of potassium in biomass by means of chemical fractionation experiments. It shows that the most occurrence forms of potassium in biomass samples is water-soluble substances, the second is remaining parts in insoluble residues, ion exchange parts is less, and acid soluble parts is the least. The content of different occurrence forms of potassium in biomass is different according to the species of biomass sample.The pyrolysis experiment on buttonwood leather and straw under different temperature(400℃, 500℃, 600℃, 700℃, 800℃) was carried, and the potassium content of pyrolysis residual solid was discussed in this paper. It is concluded that with the increase of temperature,the content of pyrolytic residue decreases gradually. Between 400 ℃ to 500 ℃, the potassium content decreases sharply; Between 500 ℃ to 600 ℃, the downward trend of potassium content decrease; After 600 ℃, with the increase of temperature, the content of potassium became stable; The buttonwood leather is more easily influenced by temperature than straw.Analyzing the volatilization of potassium in proportion to the total potassium content shows that: between 400 ℃ to 600 ℃, potassium volatilization of buttonwood leather increase from15% to 60%, potassium volatilization of straw increase from 30% to 45%; At the temperature range from 400℃ to 800℃, the buttonwood leather influenced by temperature more easily than straw in the process of pyrolysis experiment.The pyrolysis experiment on buttonwood leather with different heat preservation time(0min, 15 min, 30 min, 45 min, 60 min), under the condition of 400℃ and 800℃ was carried,and the potassium content of pyrolysis residual solid was discussed in this paper. It is concluded that with the increase of heat preservation time, the potassium content in pyrolysis residue decrease gradually, and when the heat preservation time increase to 30 min, the potassium content became stable; When the pyrolysis experiment in a lower temperature, the heat preservation time influence the pyrolysis reaction more observably. As the heat preservation time increases gradually, the change of ion exchange parts, acid soluble parts and remaining parts in insoluble residues is not obvious, and the change trend of water-soluble parts keep same with total content of potassium. It shows that when we increase the heat preservation time in the process of pyrolysis, some water-soluble potassium evaporated with the release of volatile matter, and the inertia of other forms potassium is stronger, especially the acid soluble potassium and the potassium in insoluble residues, it is not easy to release with the increase of heat preservation time, and it has a little influence on the release of potassium in the pyrolysis process. Analyzing the volatilization of potassium in proportion to the total potassium content shows that: with the heat preservation time from 0 min to 30 min,the potassium volatilization of buttonwood leather increase from 15% to 50%, under the condition of 400 ℃; With the heat preservation time from 0 min to 30 min, the potassium volatilization of buttonwood leather increase from 55% to 70%,under the condition of 800 ℃.The influence factors of buttonwood leather pyrolysis was analyzed through orthogonal experiment. It shows that the main factor is temperature, the second is heat preservation time, and the particle size has little influence on the whole pyrolysis experiment;The optimal pyrolysis temperature is 800 ℃, the optimal heat preservation time is 30 min, and the optimal particle size is 60 mesh.