Zhigang Cui

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.

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.