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Blending coal combustion technology is commonly used in coal-fired power stations, and the combustion interactions (i.e., the ignition promotion and burnout inhibition) during blended coal combustion affect their combustion characteristics. The combustion interactions under conventional air-fuel condition have been well studied. Oxy-fuel firing considerably differs from air-fuel combustion and the combustion interactions of blended coals in O2/CO2 atmospheres have been investigated in our previous research. However, the H2O concentration in actual oxy-fuel condition is relatively high, which may influence the combustion interactions. This study further investigates the effect of H2O on the combustion characteristics and interactions of blended coals in O2/H2O/CO2 atmospheres. The results show that adding H2O into the oxy-fuel atmosphere remarkably affects the combustion characteristics with the more notable ignition delay, faster burnout and better comprehensive combustion characteristics (CCI). In addition, the presence of H2O strengthens the ignition promotion, the burnout inhibition and the comprehensive interactions, resulting in the more obvious non-additive behaviors of CCI. In O2/H2O/CO2 mixtures, enhancing the H2O/CO2 ratio slightly strengthens the ignition promotion, the burnout inhibition, and the comprehensive interactions, which increases the non-additive behaviors of CCI. Furthermore, both of increasing O2/H2O or O2/CO2 ratios significantly weaken the ignition promotion, strengthen the burnout inhibition and the comprehensive interactions, which increases the non-additive behaviors of CCI. The findings shed light on the interaction effects observed during blended coal combustion in O2/H2O/CO2 mixtures, which can provide useful information to improve the combustion characteristics of the blended coals in the real oxy-fuel atmospheres.

Coal blending is an effective method to reduce the slagging tendency. The mineral transformation within blended coal ashes has an important influence on the slagging behaviors, which have been well studied under conventional air-fuel condition. Oxy-fuel combustion is recognized as one of the most promising CO2 reduction technologies. However, the mineral transformation within blended coal ashes in oxy-fuel condition has yet to be fully understood. This work is aimed to comprehensively study the influence of CO2 atmosphere on Ca-containing mineral transformation behaviors during a Ca dominated coal co-firing with a Si/Al dominated coal in O2/CO2 condition by TG-DSC, XRD and HSC simulation. These results show that the atmosphere significantly affects on the transformation of Ca-containing mineral and the final existing form of Ca in the blended coal ashes. When the high content Ca coal is blended with the high content Al/Si coal in the O2/CO2 atmosphere, the CO2 promotes the transformation of Ca into CaCO3 and Ca under low temperature mainly exists in the form of CaCO3 (little CaSO4) in the blended coal ashes. CaCO3 under high temperature is decomposed to produce highly active CaO, and CaO reacts with Al/Si to form the low melting point minerals, which may aggravate the slagging tendency. The present study can provide useful information to reduce the slagging behavior of the blended coals in the O2/CO2 atmosphere.

Ionic liquids (ILs) are solvents composed of ions, containing a large asymmetric cation with an anion. With increasing and widespread applications, the toxic effects of ILs have been considerable in recent years. This study explained the effects of the new functional ionic liquids [N4444] bis(2-ethylhexyl) sulfonyl succinate (AOT) on rice seedling and the growth of rhizobacteria. The rice seeds pretreated by [N4444] AOT revealed that it exhibited a significant negative impact on rice seedlings. The inhibition of rice growth increased with increasing concentration. When the concentration of [N4444] AOT increased to 0.25 and 0.5 mL L-1, the germination potential decreased by 40.0% and 86.3%, respectively, compared with the control. The germination potential and germination rate of rice were reduced, and the stress effect of ionic liquid on the root parts was higher than the aerial parts. The biomass of rice seedlings was decreased by 34.8 to 91.2%. Iodinic propane staining showed that by increasing concentration, the root cell cytomembrane damage level was increased and also changed the cell shapes, especially under 0.25 mg L-1 concentration stress. However, rhizobacteria of rice showed strong [N4444] AOT-resistant characteristics when the concentration was reached to 120 mg L-1. The ILs even more promoted the growth of Enterobacter sp. NP1142 and Pantoea sp. BR23. It was indicated that IL [N4444] AOT can be degraded easily by rhizobacteria to eliminate the eco-risk of ILs.

Coal-fired power plants have been identified as a major source of selenium emissions that can be controlled by mineral adsorption. The adsorption capacity of CaO for SeO2 adsorption was studied in ...

A novel combustion system, consisting of moving fuel-lean nozzles from the arches to the front/rear walls, rearranging staged air, and introducing separated over-fire air (SOFA), has been proposed and successfully applied in a 600 MWe Foster Wheeler down-fired boilers to reduce high NOx emissions while limiting the carbon content in the fly ash. This study comprehensively evaluates the effect of SOFA angles on flow, combustion characteristics and NOx emissions for the novel combustion system by numerical simulation and in-situ experiment. The numerical simulation shows in acceptable consistence with the in-situ experiment. The simulated results show that significant NOx reduction is obtained for all five SOFA angles compared to the original combustion system. O2 and CO concentrations at the furnace outlet, as well as the carbon content in the fly ash decrease significantly with increasing SOFA angle from 0° to 40°. NOx emissions increase slightly and the average temperature at the re-heater entrance changes slightly with the increase of SOFA angle from 0° to 30°. However, with further increasing SOFA angle from 30° to 40°, NOx emissions increase substantially due to the smaller reducing region below the SOFA and the average temperature at the re-heater entrance falls significantly. Taking combustion, NOx and steam parameters into account, a SOFA angle of 30° is advisable. The actual industrial measurements also show that the steam can achieve the designed values when the SOFA angle is set at 30° instead of 40°. Significant NOx reduction (over 50 %) and good performance are attained after adopting the novel combustion technology of 30 °SOFA angle.

Zhundong (ZD) coal from northwest China is a high quality steam coal with reserves of more than 390 billion tons. However, the utilization of ZD coal is limited due to the high content of alkali and alkaline earth metals. This study aimed at revealing the release and transformation mechanism of Na/Ca/S compounds during combustion/gasification of ZD coal. The results demonstrate that Na was primarily influenced by temperature, mostly releases at 600–800 °C. The transformation of Ca compounds was affected by both temperature and atmosphere. The high temperature of the combustion process could accelerate the decomposition of CaCO3 and CaSO4, and the high content of CO2 during gasification prolonged the decomposition of CaCO3. The transformation of S was primarily influenced by atmosphere. SO2 could react with CaO and form CaSO4 during the combustion process. While S compounds were mainly released as S (g) and H2S (g) during gasification process. There was a significant interaction among Na/Ca/S compounds during combustion, original CaSO4 in coal could adsorb Na compounds with SO2 at 600–800 °C and then reacted with aluminosilicates, by this reaction, Na could be fixed above 1000 °C.

The SCR reaction mechanism on the Mn/γ-Al2O3 catalyst was studied using density functional theory. The intermediates, energy barriers, and rate-determining steps of N2, NO2, and N2O formation were ...

The worldwide increase in amount of sewage sludge has recently attracted considerable interest in developing an efficient and economical sludge disposal method. A sewage sludge treatment process combining the hydrothermal treatment (HT) of sludge and the catalytic hydrothermal gasification (CHTG) of its derived liquid (HT&CHTG-Process) is proposed in this paper. Liquid hourly space velocity (LHSV) value of 25–100 h−1 and liquid flow rate of 10–40 mL/min were employed with a self-designed CHTG experimental setup. During the first stage of the HT-Process, approximately 56% of the carbon in the sludge was transferred into the derived liquid at 300 °C. During the second stage of the CHTG-Process, the derived liquid was gasified into CH4, H2, and CO2 using a Ni/carbon catalyst, and the carbon conversion reached 88% at 350 °C and 20 MPa with a LHSV of 25 h−1. Using the integrated HT&CHGT-Process, approximately 0.78 Nm3 of CH4, 0.62 Nm3 of H2 and 0.31 Nm3 of CO2 were generated from 1 kg of carbon in the sewage sludge. The combined process was expected to be an efficient method for sewage sludge treatment due to its mild conditions (≤350 °C and ≤20 MPa) and high yield of fuel gases.

Coal blends are commonly used in thermal power plants and oxy-fuel combustion also attracts great concerns recently. However, little has been done on oxy-fuel combustion of coal blends. In this paper, combustion tests are performed in a drop tube furnace for various coal blends under O2/CO2 mixtures, which are also reproduced numerically. Strong combustion interactions between the parent coals in a blend are observed. The ignition of the low-volatile coal is promoted due to the rapid combustion of the volatiles from the high-volatile coal. However, the char burnout of the low-volatile coal is compromised due to the rapid O2 consumption by the large amount of volatiles. The interactions under oxy-fuel conditions are more sensitive to the excess O2, inlet oxidizer temperature and coal particle size. 1) The increase in the excess O2 tends to weaken the combustion interactions, in which both the ignition promotion and burnout inhibition effects on the low-volatile coal become less apparent. 2) The increase in the inlet oxidizer temperature further promotes the ignition of the low-volatile coal whereas weakens the burnout inhibition of the low-volatile coal. 3) The effects of reducing particle size on the combustion interactions are similar to those of increasing inlet oxidizer temperature. Since biomass often contains a high volatile content, the findings may shed light on the synergistic effects in oxy-fuel co-combustion of biomass and coal.