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Petroleum cokes prepared from naphthenic crude oil differ significantly in terms of the oxygen content and hydrogen/carbon (H/C) ratio, which mainly depend on the different coking temperatures. Thermogravimetric-differential scanning calorimetry was applied to study the heat release and combustion weight loss of petroleum cokes prepared at 350 and 500 °C, respectively. The effect of different coke formation temperatures on the combustion properties of the coke formed during air injection in situ combustion (ISC) was also investigated. The results showed that the petroleum coke formed under oxygen exhibited an H/C ratio of 0.895 and an O/C ratio of 0.109 at 350 °C and an H/C ratio of 0.395 and an O/C ratio of 0.054 at 500 °C. As the temperature rises, the hydrogen atoms on the petroleum coke molecules intensify to separate and form water molecules and thus giving off heat. It can be further inferred that under the combustion temperature of air injection ISC, the coke at 350 °C can release more heat in the lower combustion temperature range, and the combustion weight loss is faster; however, the formation temperature continues to rise due to combustion at 500 °C, coke begins to release massive heat, and the combustion weight loss is as high as 97.95%. The combustion residuals of both temperature cokes and the residual solid content of the formation after combustion in porous media are both little, which can be used as fire flooding fuels at different formation temperatures to provide heat energy for oil displacement.

Low temperature oxidation (LTO) of heavy oils involves many complex reaction mechanisms that are important for the success of ignition and front propagation during in situ combustion (ISC). In this...

In situ combustion is an enhanced method to recover heavy oil. The formation and oxidation of coke are crucial to promote the combustion front. Heavy oil from China and montmorillonite, a major type of clay, were used as samples in this study. The thermogravimetric analyzer (TGA) was applied to temperature-programmed oxidation/pyrolysis experiments to study the effect of montmorillonite on the thermal conversion characteristics of heavy oil. A fixed-bed reactor was then used to obtain coke and study the effect of montmorillonite on coke properties. The characteristic temperatures of thermal conversion decreased with montmorillonite in the oxidizing atmosphere but remained unaffected in the pyrolysis atmosphere. The fuel deposition increased in both atmospheres because of montmorillonite’s strong adsorption. In the oxidizing atmosphere, the presence of montmorillonite obviously promoted the progress of coke formation and increased coke yield. The content of O was increased, and the contents of C and H were...

Coke formation during the process of in-situ combustion is affected by clay minerals, among which montmorillonite shows the most significant effect. A fixed-bed reactor was used to conduct the thermal conversion experiments of heavy oil and model compounds to reveal the mechanism of montmorillonite affecting the coke formation. Under the inert atmosphere, in the presence of montmorillonite, the temperature at which aromatic C–C groups of coke appeared decreased from 500 °C to 450 °C and polymers were formed when toluene was heated, indicating that montmorillonite catalyzed aromatization and polymerization, respectively. The increase in the supporter surface area promoted the formation of coke from pyrolysis by shortening the induction of coking. Under the oxidizing atmosphere, in the presence of montmorillonite, the initial temperature of O2 consumed by heavy oil decreased from 270 °C to 250 °C, indicating that montmorillonite catalyzed oxygen-adding reaction. The temperature of COx released by acetaldehyde and acetic acid decreased, and the release amounts increased, indicating that montmorillonite catalyzed decarbonylation and decarboxylation. Polymers were formed when acetaldehyde, acetic acid, ethanol, and acetone were heated, indicating that montmorillonite catalyzed polycondensation. When the oil mass fraction in the sample was within 18%, further increase in the supporter surface area did not affect the formation of coke from oxidation. The catalysis of montmorillonite was the main mechanism affecting coke formation during the thermal conversion of heavy oil under the inert and oxidizing atmospheres.

When in situ combustion is applied to reservoirs that have been exploited by steam recovery, the influence of high water saturation on the thermal conversion of heavy oil into coke needs to be evaluated. A Xinjiang heavy oil was used as the sample. A thermogravimetric analyzer and a pressurized reactor were used to study the influence of steam on the pyrolysis and oxidation characteristics of heavy oil under atmospheric pressure (0.1 MPa) and reservoir pressure (4 MPa), respectively. Under atmospheric pressure, the presence of steam showed little effect on the pyrolysis and low temperature oxidation characteristics of heavy oil but accelerated the rate of coke oxidation. Under reservoir pressure in an inert atmosphere, steam showed little influence on the coke yield but increased the proportion of alkanes and hydrogen in gas products due to the hydrogen donation of steam. Additionally, the oxidation activity of coke produced with steam decreased. The main reason was a decrease in the number of active sites of coke oxidation according to kinetic analysis. Under reservoir pressure in an oxidizing atmosphere, the coke yield decreased significantly because of the existence of steam, but the coke oxidation activity remained unchanged. The main reason for this coke yield decrease was that steam accelerated coke oxidation and increased the oxidation consumption of the produced coke in the coking temperature range of 250–400 °C. In addition, steam promoted the cleavage of oxygen-containing functional groups in heavy oil conversion intermediates, thus inhibiting the formation of coke precursors.

The selective non-catalytic reduction (SNCR) deNOx process was influenced by high-concentration CaO particles in the pre-calciners when applied to cement industry. The influence of CaO on the SNCR deNOx process was investigated using a fixed bed reactor at temperature that ranges from 873 K to 1373 K and the mechanism of the process was analyzed. The experimental results demonstrated that CaO has catalytic effects on NH3 decomposition, NO reduction by NH3, and NH3 oxidation. It inhibits the SNCR deNOx process mainly via catalyzing NH3 oxidation to NO. The catalytic effect of CaO can be ignored at temperatures higher than 1273 K. NH3 was found that first adsorbed onto the CaO surface and then dissociated to NH2 by Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The mechanism analysis of CaO catalysis during the SNCR deNOx process showed that NH3 dissociation on the CaO surface is the rate-controlling step, and the intermediate substance, NH2, reacts with O2 or NO to produce NO or N2. The competition of the two reactions determines the product selectivity. A kinetic model including CaO-catalyzed NH3 conversion and gas phase SNCR deNOx reaction was developed, which well predicted the CaO-involved SNCR deNOx process.