| Oily sludge is a high volatiles and viscosity organic hazardous wastes in the oilfield and petroleum industry, which is harmful to the environment without being safely disposed. However, there is high content of crude oil in the oily sludge, which is an alternative energy. The utilization of oily sludge can solve the problem of environmental pollution, meanwhile, and also obtain resource recovery. The scientific use of oily sludge is a win-win approach for both the environment and the resource.Oily sludge, consisting of mineral oil, mineral substance, water and slurry, is originally derived from crude oil which is mixed with soil and other solid medium. It has the characteristics of high viscosity and oil content. Traditional pyrolysis has disadvantages such as, viscosity-high oily sludge could be insufficiently processed for coagulation and volatile of oil could go through second-decomposition under low heating rate, which could result in the low pyrolytic oil production. Based on the characteristics of oily sludge and the disadvantages of traditional pyrolysis, this thesis puts forward pyrolysis of oily sludge in the rotary kiln with solid heat carrier. Quartz sand as the solid heat carrier has the advantages of large heat capacity, high heat transfer rate and high transport efficiency, whose heat transfer rate can be several hundred degrees when it is mixed with oily sludge in the pyrolysis. Fast pyrolysis efficiently prevents volatile of oil from second-decomposition, thus raising the production of pyrolytic oil. Moreover, solid heat carrier breaks oily sludge into small fractions in the pyrolysis process, making thermal decomposition more efficient. Rotary kiln is widely used in thermal-chemical processes of drying, pyrolysis and combustion for its good material adaptation and outstanding mixing abilities. Pyrolysis in rotary kiln with solid hear carrier differs from traditional ones in temperature distribution and heat transfer could efficiently increase the production of pyrolytic oil and promote the fuel characters during the process. This treatment is an advanced approach of oily sludge recovery. The following researches are carried out and the conclusions are drawn as follows:(1) The oily sludge thermal chemical processes were studied under the different heating rates and carrier gas using TG analytical instruments. The results indicated that the heating rate was an important parameter effecting the oily sludge pyrolysis. There were two mass losses and two peaks in DTG curve in pyrolysis of oily sludge under different heating rates. The relative two peak temperatures in DTG curve rose at the high heating rate. Moreover, the ranges of the pyrolysis temperature became wider and the curves of TG and DTG both moved to the high temperature zone with the heating rate rising. The corresponding kinetic parameters were obtained by means of model kinetic analysis and distributed activation energy model analysis respectively. The model kinetic analysis results indicated that the activation energy was 68.87-103.83kJ/mol in the first mass loss and it was44.24-81.21kJ/mol in the second ones. The distributed activation energy model analysis results showed that the activation energy first decreased and then raised with the mass loss. Comparison of combustion and pyrolysis of oily sludge, the combustion had a more mass loss in the high temperature zone. And there was a more relative peak in DTG curve in the high temperature zone. The activation energy in combustion was much higher than that in pyrolysis. The Py-GC/MS techniques was employed to investigate the pyrolysis mechanism. The results indicated that there were several possible reactions and mechanisms in the pyrolytic reactions of oily sludge such as, desorption, dealkylation, aromatization, ring opening,carbonylation, isomerization, and so on.(2) The type of sequence batch pyrolysis processes of oily sludge were carried out on a self-designed rotary kiln with solid heat carrier. The different pyrolytic productions of gas, oil and residue and the pyrolysis characteristics were investigated by kinds of analysis approaches. The results indicated that28.87wt%of the pyrolytic oil production was obtained and the oil recovery was63.45wt%when temperature of solid heat carrier was at823K and the blend ratio of oily sludge and solid heat carrier was1:2. With the temperature and blend ratio increase the oil recovery decreased. However, the total conversion rate of petroleum compounds increased, and the top value is89.96wt%. The HHV of pyrolytic oil was about40.38-43.58MJ/kg. The higher saturates content (72.50wt%) and lower asphaltenes (9.80wt%) in the pyrolytic oil was against to the lower saturates content (29.53wt%) and higher asphaltenes (34.72wt%) in the oil obtained from extraction. The qualitative analysis of the pyrolytic oil was carried out using GC/MS. The results showed that the main products were the linear chain hydrocarbons, distributed in the range C13-C25-The production of pyrolysis gas was achieved at33.64wt%at923K. the concentration of H2and CH4increased with the temperature rising. H2raised with the time increase, however, the CH4and CxHy evolution curves were against that of H2.The HHV of gas was in the range of24.62-41.79MJ/Nm3. The HHV of residue was in the range of4.74-12.32MJ/kg under different pyrolysis temperatures. The maximum energy distribution in the liquid product was achieved to52.28%at823K and the maximum one in the gaseous product was about58.87%at923K.(3) A dynamic model of oily sludge pyrolysis in a rotary kiln with solid heat carrier was developed along with presenting PMT model. The validity of the proposed model was justified by our experimental data and literature reports. Using the PMT model, the axial temperature distributions of volatiles, oily sludge and solid heat carrier were predicted. It is convenient to provide the parameters and conditions for the industrial application of oily sludge pyrolysis in a rotary kiln with solid heat carrier. The results indicated that the temperature of volatiles decreased with the axial position in the rotary kiln. There was the main heat transfer between solid heat carrier and oily sludge in the first0.2m along the kiln. The temperatures of volatiles, oily sludge and solid heat carrier reached the dynamic equilibrium at the distance of0.3m away from the entrance of the rotary kiln. The temperature of volatiles was affected by the solid axial velocity obviously. The volatiles yields were also predicted by the PMT model. The results showed that the volatiles yields rose along the rotary kiln. The main volatile product was CxHy. The evolution of CxHy trended to steady at0.5m away from the entrance of kiln. However, the yields of CO, H2and CO2were continuously increasing along the kiln. The pyrolysis volatiles yields had a rise when the solid axial velocity was low, which was affect on the CO2yield evidently.(4) A recovery treatment of oily sludge based on the rotary kiln with solid heat carrier was presented. The pilot-scale rotary kiln with solid heat carrier was successively designed and performed. The study on oily sludge pyrolysis in the pilot rotary kiln was carried out. By mass balance calculation, the yield of pyrolytic oil was about17.76wt%(oil recovery rate achieved44.4wt%) at823K and the one was15.53wt%(oil recovery rate achieved3&83wt%) at923K. With the temperature increasing, the gas energy increased and the energy in the oil and char decreased. However, the total produced energy increased. The net energy output of the system was8.22MJ/kg at the pyrolysis temperature was823K. The energy recovery ratio was55.54%without the external energy. The pyrolysis gas could be used to provide energy for the system. |
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