Zhang Shu-ting

Rate-based modelling of SO2 absorption into aqueous Na2SO3 in packed column

A rate-based model of a counter-current reactive absorption process has been developed for the absorption of SO2 into Na2SO3 in a packed column. The model adopts the film theory, includes diffusion and reaction processes, and assumes that thermodynamic equilibrium among the reacting species exists in the bulk liquid. For the calculation of the absorption rate of SO2 into Na2SO3 solution, it is important to take into account all reversible reactions simultaneously. The model was used to calculate concentration profiles in the liquid film, partial pressure, mass transfer rate, pH profiles, enhancement factor along the column. Model predictions were compared to experimental data and a good agreement was achieved. The study provided a basic study for theoretical analysis and engineering design of the process of SO2 absorption in flue gas by sodium alkali solution and other wet FGD process.

Studies on Characteristics of Producer Gas from Sewage Sludge Pyrolysis

The pyrolysis experiments of sewage sludge at low and middle temperature range from 250°C to 700°C were carried out in a φ 200mm laboratory fixed bed external-heat reactor. The influence of final pyrolysis temperature on product yield of gases was studied. It was found that the gases yield increased with increasing the final pyrolysis temperature. But the productive rate increased above 450°C. The results indicated the secondary pyrolysis of intermediate product occurred about 450°C. According to the analysis of NCG, the yield of CO2 was maximum at lower pyrolysis temperature but the yields of H2, CO, CH4 were higher at elevated pyrolysis temperature and the maximum caloric value of gaseous emissions were 16712 kJ/m3. According the TG-DTA curves the decomposition of sewage sludge had three stages. The first stage was deprivation of interstitial moisture (100°C-110°C), the second stage was the depolymerization reactions of lipid and the generation of large molecular intermediate fragments (110°C-325°C), the last stage was cracking of the large molecular and the decomposition of protein and saccharide (325°C-600°C). All the results can offer reliable base data for the application of pyrolysis technique of sewage sludge.