Xiumin Jiang

Pyrolysis treatment of oil sludge and model-free kinetics analysis

Pyrolysis of tank bottom oil sludge was investigated to summarize the pyrolysis characteristics through analyzing the change of mass loss, pyrolysis gas compositions in heating process. For this propose, various approaches including thermogravimetric analysis (TGA), CNHS/O elemental analysis, electrically heated fixed bed quartz reactor coupled with Vario Plus emission monitoring system, and oil-gas evaluation workstation (OGE-II) equipped with a flame ionization detector (FID) were used. The pyrolysis reaction is significant in the range of 473-773 K where multi-peak DTG curves can be gained. Higher heating rate increases the carbon (C) and sulfur (S) contents but decreases hydrogen (H) content in solid residues. The major gaseous products excluding N(2) are CHs (Hydrocarbons), CO(2), H(2), CO. The yield of CHs is significant in the range of 600-723 K. Higher heating rate causes the peak intensity of CHs evolution to increase and the CHs evolution to move towards a high-temperature region. Around 80% of total organic carbon content (TOC) in oil sludge can be converted into CHs in pyrolysis process. The CHs data were used for kinetic analysis by Vyazovkin model-free iso-conversion approach. Dependences of the activation energy on the degree of conversion obtained from different methods were compared.

Co-firing of oil sludge with coal-water slurry in an industrial internal circulating fluidized bed boiler.

Incineration has been proven to be an alternative for disposal of sludge with its unique characteristics to minimize the volume and recover energy. In this paper, a new fluidized bed (FB) incineration system for treating oil sludge is presented. Co-firing of oil sludge with coal-water slurry (CWS) was investigated in the new incineration system to study combustion characteristics, gaseous pollutant emissions and ash management. The study results show the co-firing of oil sludge with CWS in FB has good operating characteristic. CWS as an auxiliary fuel can flexibly control the dense bed temperatures by adjusting its feeding rate. All emissions met the local environmental requirements. The CO emission was less than 1 ppm or essentially zero; the emissions of SO(2) and NO(x) were 120-220 and 120-160 mg/Nm(3), respectively. The heavy metal analyses of the bottom ash and the fly ash by ICP/AES show that the combustion ashes could be recycled as soil for farming.

Characteristics of oily sludge combustion in circulating fluidized beds

Incineration of oily sludge in circulating fluidized beds may be an effective way for its management in some cases. The objective of the present paper is to investigate combustion characteristics of oily sludge, which would be helpful and useful for the design and simulation of a circulating fluidized bed. Firstly, the pyrolysis and combustion of oily sludge were studied through some thermal analyses, which included the thermogravimetric (TG) analysis and the differential thermal analytical (DTA) analysis. It was found that the combustion of oily sludge might be the combustion of its pyrolysis products. Secondly, an experiment for measuring of main components of the volatile from oily sludge pyrolysis was carried out. Some mathematic correlations about the compositions of volatile from oily sludge devolatilization were achieved from the experimental results. Finally, the combustion characteristics of oily sludge was studied in a lab-scale circulating fluidized bed, which could obtain some information about the location of release and combustion of the volatiles.

Devolatilization of oil sludge in a lab-scale bubbling fluidized bed.

Devolatilization of oil sludge pellets was investigated in nitrogen and air atmosphere in a lab-scale bubbling fluidized bed (BFB). Devolatilization times were measured by the degree of completion of the evolution of the volatiles for individual oil sludge pellets in the 5-15 mm diameter range. The influences of pellet size, bed temperature and superficial fluidization velocity on devolatilization time were evaluated. The variation of devolatilization time with particle diameter was expressed by the correlation, τ(d) = Ad(p)(N). The devolatilization time to pellet diameter curve shows nearly a linear increase in nitrogen, whereas an exponential increase in air. No noticeable effect of superficial fluidization velocity on devolatilization time in air atmosphere was observed. The behavior of the sludge pellets in the BFB was also focused during combustion experiments, primary fragmentation (a micro-explosive combustion phenomenon) was observed for bigger pellets (>10mm) at high bed temperatures (>700 °C), which occurred towards the end of combustion and remarkably reduce the devolatilization time of the oil sludge pellet. The size analysis of bed materials and fly ash showed that entire ash particle was entrained or elutriated out of the BFB furnace due to the fragile structure of oil sludge ash particles.

Interaction of elemental mercury with defective carbonaceous cluster.

The interaction of elemental mercury with defective carbonaceous clusters is investigated by the density-functional theory calculation. The defective carbonaceous cluster is represented by seven-fused benzene ring and single atomic vacancy at the surface. Also, the non-defective carbonaceous surface is employed for comparison. The defective carbonaceous cluster with chlorine is carried out to evaluate the effect of the statured carbon at the neighboring sites of vacancy on mercury adsorption. The results indicate that vacancy can promote the activity of its neighboring sites, and the defective carbonaceous cluster has much larger mercury adsorption energy than the non-defective carbonaceous cluster with and without chlorine. Cl atom can improve the activity of its neighboring sites on the non-defective carbonaceous surface, but the effect of Cl atom on mercury adsorption of vacancy is very complex, which depends on the Cl concentration. High concentration of Cl decreases the mercury adsorption because Cl competes for the active sites with mercury. Hence, we find that vacancy can be regarded as a potential functional group to improve the mercury adsorption on carbonaceous surface, but the saturated carbon at the neighboring sites of vacancy can rapidly decrease the mercury capture capacity.

Effects of retorting factors on combustion properties of shale char. 3. Distribution of residual organic matters

Shale char, formed in retort furnaces of oil shale, is classified as a dangerous waste containing several toxic compounds. In order to retort oil shale to produce shale oil as well as treat shale char efficiently and in an environmentally friendly way, a novel kind of comprehensive utilization system was developed to use oil shale for shale oil production, electricity generation (shale char fired) and the extensive application of oil shale ash. For exploring the combustion properties of shale char further, in this paper organic matters within shale chars obtained under different retorting conditions were extracted and identified using a gas chromatography-mass spectrometry (GC-MS) method. Subsequently, the effects of retorting factors, including retorting temperature, residence time, particle size and heating rate, were analyzed in detail. As a result, a retorting condition with a retorting temperature of 460-490 degrees C, residence time of <40 min and a middle particle size was recommended for both keeping nitrogenous organic matters and aromatic hydrocarbons in shale char and improving the yield and quality of shale oil. In addition, shale char obtained under such retorting condition can also be treated efficiently using a circulating fluidized bed technology with fractional combustion.

Mathematical model of oil shale particle combustion

At first this paper simply introduces the ignition mechanism and combustion characteristics of Huadian oil shale. Combustion behaviour was found to be homogeneous at the beginning of combustion, shifting to heterogeneous combustion in the high-temperature stage; combustible matter was noted to be volatile in the low-temperature stage, but in the high-temperature stage combustible matter included fixed carbon and residual volatile. On the basis of the combustion characteristics of Huadian oil shale, homogeneous and heterogeneous combustion processes of Huadian oil shale are modelled. In the mathematical models, conductive, convective and radiative heat transfer between particles and the surrounding atmosphere, pyrolytic heat and also the heat value of the volatiles are all included in the energy equations; inference of volatile release to particle density is also considered in the models. Thermogravimetric experimental data are used to validate the described models.

Combustion mathematical simulation of single seaweed particle in a bench-scale fluidized bed

In this study, combustion experiments of green algae granulations (Enteromorpha clathrata) (EN) were carried out in a bench-scale fluidized bed. The particle diameter was kept constant during the combustion process and combustion model was described as a shrinking core model. Model was divided into water ball, volatile-matter ball, and carbon ball. Ash ball radius was assumed to be the same during the combustion and carbon ball was burned layer by layer. Simulation of single-particle combustion process consists of process of water evaporation, release of volatile matters and combustion, and the process of char combustion. Finally, a mathematical model was established for the combustion of EN single particle in the fluidized bed, validated by the experiment data. The model can be applied for the design of the combustion devices for the combustion of seaweed particles with high content of ash.

A TGA-MS INVESTIGATION OF THE EFFECT OF HEATING RATE AND MINERAL MATRIX ON THE PYROLYSIS OF KEROGEN IN OIL SHALE

A demineralized Dachengzi oil shale sample, p-kerogen, is obtained through hydrochloric & hydrofluoric (HCl&HF) treatment. Themogravimetric analysis combined with on-line mass spectrometry (TGAMS) tests on original oil shale and p-kerogen were carried out at two heating rates, 5 °C/min and 15 °C/min, to study the effect of heating rate and mineral matrix on the pyrolysis of kerogen in oil shale. In the pyrolysis products, the amounts of both the organic and inorganic gases generated are significant with the evolution of oil in the temperature range of 370–570 °C. Increasing the heating rate from 5 °C/min to 15 °C/min leads to the decrease of most of the small molecule products of interest in this research, which indicates that in the oil shale pyrolysis the secondary cracking reactions may be inhibited by such increase. With increasing heating rate the thermogravimetric (TG) curves shift to a higher temperature region with an increase of about 10 °C due to the temperature difference between the surface and the center of the sample particles. The amount of alkenes generated is higher than that of alkanes and the alkene/alkane ratio increases with heating rate. At the same heating rate, the amounts of both the inorganic and organic compounds generated in the oil shale pyrolysis are higher than those produced in the pkerogen pyrolysis, suggesting that mineral matrix has an obvious catalytic effect on the pyrolysis of kerogen. Hydrogen release is markedly strengthened in the oil evolution process because of the resultant effect of mineral matter which promotes the cracking reactions in the pyrolysis of kerogen. Compared with oil shale, the TG curves of p-kerogen shift to a lower temperature zone with a decrease of about 10 °C because the pore channels formed in the demineralization treatment intensify the heat and mass transfer in the sample particles.

Prediction of gaseous products from Dachengzi oil shale pyrolysis through combined kinetic and thermodynamic simulations

The characteristics of gas evolution from Dachengzi oil shale pyrolysis under different temperatures were experimentally investigated using a fixed bed reactor and then were evaluated by integrating thermodynamic equilibrium simulation employing HSC Chemistry program and Sandia PSR kinetics simulation in this paper. The experiment results indicate that the non-condensable gases contain much higher CO2, CH4 and H2 and lower CO and C2–C4 hydrocarbons in terms of volume percentages, and mainly consist of CO2 and CH4 as well as some minor gases in terms of mass distribution. CO2, CO and H2 are firstly produced followed by the generation of light hydrocarbons. The HSC calculation results present that some C2 and C2+ hydrocarbons disappear in the predicted gaseous products thermodynamically, and the nitrogen- and sulfur-containing gases mainly are N2 and H2S, respectively. Then, the normalized HSC species are inputted into the Sandia PSR code by three methods, i.e., the CHO input method, the regional input method and the individual input method, considering the potential kinetic constraints. Some C2 and C2+ hydrocarbons appear in the predicted gaseous products based on the three methods. The regional input method demonstrates that more H2 and CO are produced at higher temperature, which agrees with the experimental results. And more C2H4 and C2H2 release at higher temperature depending on the enhanced secondary gas cracking reactions. The peak concentration of every gas product is obtained at higher temperature with lower value compared to the experimental results possibly due to ignoring the effect of the shale ash. The individual input method indicates that C2 and C3 hydrocarbons are generated after the formation of CH4, CO, CO2 and H2. The change trends of CO2, CO and H2 obtained from the experiment and simulation with rising temperature are very similar, but those for CH4 are different, due to most likely certain limitations of a fixed bed reactor as a reaction system. Combining the HSC and PSR calculations, the obtained gas products are closer to the realistic situation.