Study On Combustion Characteristics Of Modified Sludge In Ca-L Process Regeneration Reactor And Its Effect On Calcium Carbonate Decomposition

Calcium-looping technology is one of the effective techniques for capturing CO₂in electric power plant.Calcium carbonate decomposed in the calcination reactor and it needs to the outside heat from the oxygen-rich combustion of coal.This increases the energy cost,and the SO₂ emission from the combustion will mix with the concentrated gas,which is not conducive to purify CO₂.Meanwhile,it also reacts with CaO,and inactivates the regenerated calcium-based absorbent.In this study,the dried municipal sludge with low-sulfur content was used as an alternative fuel,and the hydrothermal treatment was used to reduce nitrogen content of sludge.The sewage sludge in China with high yield and lower sulfur content can be used as the replaced fuel in Ca-L process to realize its resource utilization.The following three aspects were studied by using the macro thermogravimetric experimental equipment,vertical reactor and chemical adsorption instrument:?1?Thermochemical reaction of dried sludge under different O₂/CO₂ atmospheres were studied and the combustion characteristics of the dried sludge was analyzed;?2?The nitrogen content in fuel and the NOx emissions characteristic in modified sludge wans studied.?3?The calcium carbonate decomposed characterisctics under the effect of sludge combustion was investigated.The combustion characteristics of sludge under O₂/N₂ and O₂/CO₂ atmospheres were studied on self-built macro thermogravimetric analyzer.The results show that the combustion of sludge was promoted in O₂/CO₂ atmosphere.When the combustion atmosphere of sludge is O₂/CO₂=30%/70%,which combustion characteristic temperature is lower,and the maximum value of combustion characteristic index S is18.78×10^-10(min^-2·^oC^-3).Sludge was hydrothermally treated using a reaction kettle,and the denitrification effect of the modified sludge was studied in a vertical fixed bed reactor.The macro thermogravimetry and thermogravimetric analyzer experimental results were used to compare low nitrogen treatment and combustion characteristics of hydrothermal-treated sludge?HTS?.Results showed that with the increase of hydrothermal temperature,the nitrogen content of sludge gradually decreases.Comparing the combustion index and kinetic analysis of the two thermogravimetric analysis results,the combustion characteristic index S of the sludge showed a downward trend with the increase of the hydrothermal temperature,which indicates that the hydrothermal reaction reduced the combustion characteristics of the sludge.Results showed that the hydrothermal treatment was an effective way to reduce the NOx emissions from sludge combustion in O₂/CO₂ atmosphere.The NOx reduction ratio significantly increases from 6.05%to 40.46%as the hydrothermal temperature increases from 200 to 280 ^oC.Calcium carbonate was decomposed with sludge combustion on a horizontal tube furnace.The samples were analyzed by chemical adsorption instrument and pyrolysis-mass spectrometer.Results showed that the good pore structure is formed during the CaCO₃ decomposition process.This promotes the adsorption of organic matter released during the DSS combustion,and decreases the relative decomposition ratio of CaCO₃.However,the relative decomposition ratio under the effect of the HTS combustion is improved due to the smaller volatile content in HTS.