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In this study, co-gasification and catalytic co-gasification of petroleum coke with coal at high temperature are studied. The structural characteristics of high temperature petroleum coke and bituminous coal pyrolysis char are compared, and the effects of blending ratio on the gasification reactivity and synergy are explored. The effect of catalyst on the co-gasification is also investigated. The results show that, high temperature petroleum coke shows a smoother surface morphology and has a higher degree of graphitization than the coal char, as a result, the gasification reactivity of the former is much lower than the latter. The coal char gasification process shows only one reaction stage, while the high temperature petroleum coke has two significant stages. The gasification reactivity of the blends increases with the coal blending ratio, and the largest increment is obtained when high temperature petroleum coke and coal char is blended at 1:2. As the co-gasification proceeds with the temperature, it first shows an inhibition effect, then gradually a synergistic effect. The temperature at which the synergistic effect appears decreases with the coal blending ratio increasing. However, the co-gasification reaction rate and reactivity get worse at carbon conversion rate large than 0.5, leading to a longer reaction time. When catalytic co-gasification, NaAlO2 significantly increases the reactivity at carbon conversion rate larger than 0.2, and the temperature needed to finish the gasification for high temperature petroleum coke is reduced from 1460 °C to 1150 °C.

In order to understand the straw biomass gasification process in depth, the weight loss behaviors, reactivity and kinetics during non-isothermal CO2 gasification of seven straw biomass were investigated using a thermogravimetric analyzer, and the correlations between gasification characteristics and feedstock characteristics of straw biomass were also explored. It was found that, in the pyrolysis stage, the weight loss behaviors and reactivity showed a good regularity and were mainly positively correlated with the cellulose content, but negatively correlated with the lignin content. Corn straw, wheat straw and rice straw had higher pyrolysis reactivity due to the higher total contents of cellulose and hemicellulose. As for the char gasification stage, weight loss, the maximum weight loss rate and its corresponding temperature were mainly determined by the fixed carbon content, and the reactivity was largely correlated with the catalytic ash components. Corn straw, cotton straw, and soybean straw presented better char gasification performance. Kinetics results showed that, for all straw biomass, the homogeneous reaction model described the pyrolysis stage better, while for the char gasification stage, the shrinking core model was more suitable. The kinetic compensation effect existed in both pyrolysis and char gasification reaction stages for all straw biomass.

Potassium salt is a nonnegligible inorganic element in biomass, and it has a significant impact on the thermal behavior of biomass. To understand the mechanism of potassium on cellulose pyrolysis in depth, the evolution of functional groups of char combined with the characteristics of volatiles from cellulose pyrolysis with K2CO3 between 150 and 600 °C was investigated using two-dimensional perturbation correlation infrared spectroscopy (2D-PCIS). It was found that the addition of K2CO3 changed the decomposition pathway of cellulose, and reduce the initial temperature of cellulose decomposition from 250 °C to 150 °C. And K2CO3 accelerated the deconstruction of hydrogen bonding, and rupture of C5-O, C-C, glycosidic bond of cellulose crystal structure to form light molecular liner aliphatic compounds and CO, CO2 at lower temperature (150–250 °C). At higher temperature (>250 °C), it accelerated the generation of phenol C-O of pyrolysis char and inhibited the generation of aliphatic ether.

In this study, high temperature catalytic gasification of petroleum coke pyrolysis char is studied. The influence of variant catalysts with high melting point and catalysts addition amount are explored, simultaneously the catalytic mechanisms are explored in depth. The results show that the petroleum coke pyrolysis char has a high crystallinity of 65.5% and gasification process is divided into two stages at lower and higher temperature. All catalysts can significantly reduce the gasification temperature, especially the final temperature. NaAlO2 has the highest catalytic performance of improving gasification reactivity by ~1.68 times and reducing gasification final temperature by ~170 °C, while the catalytic effect of MgO, Fe2O3, CaO and Fe3O4 at lower temperature are not obvious. With NaAlO2 addition increasing, especially above 0.8%, the gasification reactivity of petroleum coke pyrolysis char is improved prominently. Different catalysts have variant catalytic mechanisms. The activation of NaAlO2 is relatively stable with temperature increasing and is proven to be an ideal catalyst for petroleum coke high temperature gasification.

The emission of fine particulate matters with an aerodynamic diameter of less than 1 µm (PM1) is usually high from straw biomass combustion, resulting in great danger to atmospheric environment and public health. In this work, the effect of three calcium phosphate additives on PM1 emission from cornstalk combustion was investigated using a lab-scale reactor. The addition of Ca(H2PO4)2, CaHPO4 and Ca3(PO4)2 reduced PM1 emission by 1.5–50.6%, 22–55.6% and 23–53.7%, respectively. For Ca(H2PO4)2, PM1 reduction rate reached its maximum values of 50.6% at P/K molar ratio equal to 1 and then decreased significantly with further increasing of P/K molar ratio. For both CaHPO4 and Ca3(PO4)2, PM1 reduction rate increased approximately linearly with increasing the amount of additives under the current operating conditions. Analyses of the collected particulate matters and residual ashes indicated that phosphorus was mainly transformed into PM1-10 and residual ash in the form of K-Ca/Mg phosphates and Ca/Mg phosphates, respectively. The PM1 reduction mechanism was proposed based on the characterization results. Finally, economic analysis showed that the addition of Ca3(PO4)2 is a potentially promising method to reduce PM1 emissions during straw biomass combustion.

Petroleum coke was gasified using non-isothermal thermogravimetric analysis (TGA). The catalytic effects of FeCl 3 , CaCl 2 , KCl, K 2 CO 3 , K 2 SO 4 , KAC and KNO 3 were studied. It was found that the gasification of petroleum coke was inefficient at temperature 2 CO 3 , gasification was completed quickly in 10 min and the final temperature was about 900 °C. To further uncover the catalytic mechanism, the structures of char samples at various conversions were investigated with Raman spectra (Raman) and X-ray diffractometry (XRD). The Raman spectra showed that with K 2 CO 3 catalyst, the formation of active intermediates C(O) and M–C–O were enhanced by the relatively small aromatic ring systems with 3–5 fused benzene rings, alkyl–aryl C–C structures and methyl carbon dangling onto an aromatic ring. K 2 CO 3 could stimulate the crackdown of big aromatic ring systems into small aromatic ring systems. Thereby, the addition of K 2 CO 3 could increase the steam gasification rate of petroleum coke. XRD analysis indicated that with char conversion increasing, char structure became more ordered with a large amount of aromatic ring formed in original samples, while the degree of graphitization was lowered with K 2 CO 3 addition, which is favorable for char gasification.

To study the influence of molten salts on structure evolution and reactivity of biochar, CO2 gasification of biochar in molten salts (Na2CO3-K2CO3) was conducted in a fixed bed reactor. The results indicated that the reactivity of biochar was significantly enhanced with the introduction of molten salts, and the apparent activation energy reduced greatly from 145 kJ/mol for C750 (char gasification without molten salts) to 46 kJ/mol for C1MS1 (mass ratio of molten salts to char was 1:1). However, the presence of molten salts would weaken the endothermic feature of Boudouard reaction with rising gasification temperature and the enhancement of reactivity decreased gradually with mass ratio of molten salts to char increasing. Respected to the structure of char, the presence of molten salts improved biochar pore structure with the increase of external pore volume. The Raman spectra showed that molten salts could promote the decomposition of large aromatic ring systems (no less than 6 rings) into small aromatic ring systems (with 3 to 5 rings). Moreover, the microcrystalline structure of biochar in molten salts contained lower aromaticity, larger microcrystalline interlayer spacing, and smaller crystallite size. The addition of molten salts improved the biochar structure and further enhanced its gasification reactivity.