Properties,combustion behavior,and kinetic triplets of coke produced by low-temperature oxidation and pyrolysis:Implications for heavy oil in-situ combustion

This work aimed at investigating the crucial factor in building and maintaining the combustion front during in-situ combustion(ISC),oxidized coke and pyrolyzed coke.The surface morphologies,elemental contents,and non-isothermal mass losses of the oxidized and pyrolyzed cokes were thoroughly examined.The results indicated that the oxidized coke could be combusted at a lower temperature compared to the pyrolyzed coke due primarily to their differences in the molecular polarity and microstructure.Kinetic triplets of coke combustion were determined using iso-conversional models and one advanced integral master plots method.The activation energy values of the oxidized and pyrolyzed cokes varied in the range of 130-153 k J/mol and 95-120 kJ/mol,respectively.The most appropriate reaction model of combustion of the oxidized and pyrolyzed cokes followed three-dimensional diffusion model(D_(3)) and random nucleation and subsequent growth model(F_(1)),respectively.These observations assisted in building the numerical model of these two types of cokes to simulate the ISC process.

Simulation of gas-solids heat transfer in cyclone pyrolyzer using CFD-DEM model

Fast heat transfer in the pyrolyzer can increase the yield of pyrolysis gas and tar,and improve the quality of tar.Compared with the downer pyrolyzer,the cyclone pyrolyzer can simultaneously achieve high solids holdup and violent turbulence,and correspondingly faster heat transfer.In this work,the heat transfer behavior in the cyclone pyrolyzer is specifically studied using the computational fluid dynamics-discrete element method.The simulation results reveal that the gas-solids heat convection contributes mainly to the heat transfer process,and the heat radiation and conduction are relatively small and almost negligible,respectively.Compared with the downer pyrolyzer under the same operating conditions,the heating rate is significantly increased in the cyclone pyrolyzer.By analyzing the flow characteristics in the cyclone pyrolyzer,it is found that the region of high convective heat transfer rate coincides with that of natural cyclone length.Additionally,the final coal temperature increases with the increase of gas velocity and exists a maximum value.These results can offer some qualitative understanding of the heat transfer behavior in the cyclone pyrolyzer.

Analytical study on pyrolyzed products of Desmodesmus sp.cultivated in BG11

Pyrolysis-Gas Chromatography-Mass Spectrometry(Py-GC/MS)was adopted to determine the changes in component of BG11-cultivated Desmodesmus sp.(BG11/8-10)pyrolyzed products at different temperatures(300℃-800℃).The results of analysis on a series of total ions chromatogram(TIC)showed that pyrolyzed products of BG11/8-10 at different temperature mainly included aliphatic hydrocarbons,nitrogen compounds,aromatic hydrocarbons,fatty acids,ketones,alcohols,aldehydes and furan compounds.Compared to the bio-oil(42.36%)generated by pyrolysis at 700℃,the relative content of bio-oil generated at 800℃was the highest up to 56.96%.However,higher temperature could easily cause the generation of large quantities of such pollutants as nitrogen compounds and polycyclic aromatic hydrocarbons(PAHs).Therefore,based on lower pollutant discharge and higher bio-oil yield,the optimal pyrolysis temperature of BG11/8-10 was around 700℃.

Downer reactor simulation and its application on coal pyrolysis:A review

Pyrolysis technology has received increasing attention in recent years due to its great potential in the field of lowrank coal clean and efficient conversion.Since pyrolysis reaction is very fast and prone to overreaction,the downer-type reactor is considered as a pyrolyzer due to its unique plug flow reactor characteristics.However,the low solids holdup,which is not beneficial for the fast heat transfer,limits its industrial application.Thus,how to realize high-density operation is crucial to the successful application of the downer reactor.Herein,the definition and strategies of high-density operation in the downer were introduced at first.And then,considering the increasing influence of computational fluid dynamics(CFD)in the fluidization industry,the state-of-the-art progress in downer simulation was reviewed,in which the newly developed drag models for downers were carefully discussed and compared.Also,to help prediction of the pyrolysis behaviors,the widely used pyrolysis kinetic models were systematically summarized.Combined with the potential of the downer in the field of coal pyrolysis,the relevant research progress of hot-state simulation of the downer pyrolyzer were introduced and analyzed.Finally,the suggestions on how to carry out follow-up work were given.It is expected that this review could give a better understanding for designing and optimizing downer pyrolyzer.

Effects of pyrolyzed semi-char blend ratio on coal combustion and pollution emission in a 0.35 MW pulverized coal-fired furnace

The effects of blend ratio on combustion and pollution emission characteristics for co-combustion of Shenmu pyrolyzed semi-char (SC), i.e., residuals of the coal pyrolysis chemical processing, and Shenhua bituminous coal (SB) were investigated in a 0.35 MW pilot-scale pulverized coal-fired furnace. The gas temperature and concentrations of gaseous species (O2, CO, CO_(2), NO_(x) and HCN) were measured in the primary combustion zone at different blend ratios. It is found that the standoff distance of ignition changes monotonically from 132 to 384 mm with the increase in pyrolyzed semi-char blend ratio. The effects on the combustion characteristics may be neglected when the blend ratio is less than 30%. Above the 30% blend ratio, the increase in blend ratio postpones ignition in the primary stage and lowers the burnout rate. With the blend ratio increasing, NO_(x) emission at the furnace exit is smallest for the 30% blend ratio and highest for the 100% SC. The NO_(x) concentration was 425 mg/m^(3) at 6% O_(2) and char burnout was 76.23% for the 45% blend ratio. The above results indicate that the change of standoff distance and NO_(x) emission were not obvious when the blend ratio of semi-char is less than 45%, and carbon burnout changed a little at all blend ratios. The goal of this study is to achieve blending combustion with a large proportion of semi-char without great changes in combustion characteristics. So, an SC blend ratio of no more than 45% can be suitable for the burning of semi-char.

Influence of nozzle height to width ratio on ignition and NOx emission characteristics of semicoke/bituminous coal blends in a 300 kW pulverized coal-fired furnace

To improve the ignition behavior and to reduce the high NOx emissions of blended pulverized fuels(PF)of semicoke(SC),large-scale experiments were conducted in a 300 kW fired furnace at various nozzle settings,i.e.,ratios(denoted by hf/b)of the height of the rectangular burner nozzle to its width of 1.65,2.32,and 3.22.The combustion tests indicate that the flame stability,ignition performance,and fuel burnout ratio were significantly improved at a nozzle setting of hf/b=2.32.The smaller hf/b delayed ignition and caused the flame to concentrate excessively on the axis of the furnace,while the larger hf/b easily caused the deflection of the pulverized coal flame,and a high-temperature flame zone emerged close to the furnace wall.NOx emissions at the outlet of the primary zone decreased from 447 to 354 mg/m3(O2=6%),and the ignition distance decreased from 420 to 246 mm when the hf/b varied from 1.65 to 3.22.Furthermore,the ratio(denoted by SR/SC)of the strong reduction zone area to the combustion reaction zone area was defined experimentally by the CO concentration to evaluate the reduction zone.The SR/SC rose monotonously,but its restraining effects on NOx formation decreased as hf/b increased.The results suggested that in a test furnace,regulating the nozzle hf/b conditions sharply reduces NOx emissions and improves the combustion efficiency of SC blends possessing an appropriate jet rigidity.