Peisheng Li

Investigation of sulfur forms and transformation during the co-combustion of sewage sludge and coal using X-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy was used to investigate the characteristics and evolution of sulfur (S) in mixtures of bituminous coal and sewage sludge (SS) and their chars during isothermal combustion. Five groups of mixtures with SS content of 0%, 10%, 20%, 30% and 100%, were examined at different burn-off ratios (beta) of 0, 30%, 50%, 70% and 100%. The S in the coal mainly exist as the forms of mercaptan (S1), sulfide (S2), thiophene (S3), sulfoxide (S4), sulfone (S5) and sulfate (S6). During the coal combustion process, the content of S1 and S2 decreased, while that of S3 and S5 increased in the early stage and decreased in the late stage. The S4 content increased throughout the entire process of combustion. Small amount of S6 was detected, showing a fluctuated pattern. The trend of S1, S2, S5 and S6 in SS was alike with that in coal, whereas S4 decreased at the end of combustion. The changing process of S3 in SS was opposite to that of coal, while the composition of S in the mixtures resulted from the mixing of coal and SS. The transformation of each functional group during co-combustion were correlated with their transformation characteristics during the mono-combustion of coal and SS, and no obvious interaction was observed, which demonstrated that the coal-origin and SS-origin sulfur in mixtures kept their own characteristics in the combustion. SS may accumulate on the solid surface as alpha increase, resulting its significant influence on the evolution of each form of S. When alpha was low, most of the S-contained functional groups presented the characteristics of coal. The percentage of coal-origin functional groups declined as alpha increased. The transforming trends of most functional groups were similar with that of SS when alpha reached 30%.

Nonisothermal TGA Study on the Combustion Reaction Kinetics of Biomass

The combustion reaction kinetics of two Chinese straws were investigated by a differential thermal balance , volume fraction of reactive gas was N2: O2 = 80:20 and heating rate was 30degC/min. Reaction of samples were mainly composed volatile and fixed carbon combustion phase, ranges of them were 425 K - 650 K and 650 K - 810 K in round numbers according to TG, DTG and DTA curves. Reaction kinetic parameters were calculated with Coats-Redfern method. Ranges of activation energy in volatile combustion phase were 20 kJ.min -1 or so, fixed carbon combustion phase were different, they were 145 kJ.min -1 and 66 kJ.min -1 . Results showed that the order of reaction of volatile combustion phase and fixed carbon combustion phase were zero and second, respectively. The reaction initial temperatures of two samples ranged from 420 K - 460 K and reaction final temperatures ranged from 780 K - 810 K.

Sewage Sludge Drying Based on Heat Pump

A suit of low temperature test dryer for sewage sludge drying based on heat pump was put forward in this paper. Principle and characteristic of this equipment was introduced. Sewage sludge drying mechanism were briefly summaried from literatures. Factors such as drying air temperature and flow speed that effect sewage sludge drying process were discussed. Drying temperature and flow speed both contribute positively to drying speed in initial drying section while contributing little in the evening section of drying process. Change of superficial morphology during the drying process was analyzed. Economy of this low temperature dryer based on heat pump was discussed. Results show that the operation cost is equal to the operation cost of the dryer with coal as heat source, while is less than half of the dryer with electricity or natural gas as heat source.

Mathematical Modeling of Drying Characteristics of Sewage Sludge

Drying characteristics of sewage sludge were investigated using hot air of a temperature range of 50~80degC and an air velocity range of 0.60~1.48 m/s at a laboratory scale dryer. Several mathematical models available in the literatures were fitted to the experimental data by multiple nonlinear regression analysis. Four statistical parameters: coefficient of determination (R 2 ), reduced chi-square (chi 2 ), root mean square error (RMSE) and mean relative deviation modulus (P) were used to evaluate the fitting of these models to experimental data. The Page model gave the better predictions than others. Then a modified model based on Page model was developed and the new model could fit the drying characteristics of sewage sludge well with R 2 over 0.9993 at widely drying conditions.

Removal of Vapor-Phase Elemental Mercury by Novel Chemically Promoted Noncarbon Sorbents

Adsorption experiments of vapor-phase elemental mercury were carried out using bromine and iodine modified Kaolin, Zeolite, Bentonite and Chitosan in a laboratory-scale fixed-bed reactor. VM3000 online mercury analyzer was applied to detect the inlet and outlet Hg 0 concentrations. The characterizations of the sorbents were analyzed using Fourier transform infra-red spectroscopy. The results indicated the iodine was found in the inlayer of Bentonite, and the chemical reactions of iodine and sulfate ion with the amide of Chitosan were occurred. Fixed-bed absorber tests showed that compared to Kaolin and Zeolite, the modified Bentonite exhibited excellent mercury capture because of its unique structure. Mercury removal efficiency of Chitosan sorbent could be promoted from 50% to 100% when added appropriate amount of H 2 SO 4 . The iodine-modified sorbents demonstrated higher mercury capture efficiency than that of bromine-modified sorbents. Moisture presence can decrease the Bentonites capacity for mercury uptake, while that of chitosan sorbents exhibited opposite tendency due to their unique physicochemical properties.

Characteristic and Evolution of Sulfur Functionalities in Coal and Sewage Sludge during Combustion

X-ray photoelectron spectroscopy was used to investigate the forms and the evolution of sulfur in a bituminous coal, a sewage sludge(SS) and their chars at different burn off ratio (0, 30%, 50%, 70% and 100%) during isothermal combustion. Samples were dried at 105°C and ground into fine powder, and passed through a 120 mesh screen. Chars were prepared at the temperature of 850°C under the environment of N2 and O2 (N2:O2=80:20) in a tube furnace reactor. Important conclusions were obtained from experiment as follows: The sulfur in the coal mainly existed in the forms of mercaptan(S1), sulfide(S2), thiophene(S3),sulfoxide(S4), sulfone(S5) and sulfate(S6). With the process of combustion, the contents of S1 and S2 decreased while that of S3 and S5 presented in the tendency of increasing in early stage and decreasing in terminal stage. S4 ascended in whole combustion period. Small amount of S6 was detected and the fluctuant characteristic of it was observed. The tendency of SI, S2, S5 and S6 in sewage sludge was consistent with that in coal, however, S4 decreased in the end of combustion. The evolution of S3 in sewage sludge was opposite to that of coal.

Detection of ash fusion temperatures based on the image processing

The detection of ash fusion temperatures is important in the research of coal characteristics. The prevalent method is to build up ash cone with some dimension and detect the characteristic temperatures according to the morphological change. However, conditional detection work is not accurate and brings high intensity of labor as a result of both visualization and real-time observation. According to the insufficiency of conventional method, a new method to determine ash fusion temperatures with image processing techniques is introduced in this paper. Seven techniques (image cutting, image sharpening, edge picking, open operation, dilate operation, close operation, geometrical property extraction) are used in image processing program. The processing results show that image sharpening can intensify the outline of ash cone; Prewitt operator may extract the edge well among many operators; mathematical morphology of image can filter noise effectively while filling up the crack brought by filtration, which is useful for further disposal; characteristic temperatures of ash fusion temperatures can be measured by depth-to-width ratio. Ash fusion temperatures derived from this method match normal values well, which proves that this method is feasible in detection of ash fusion temperatures.