Search

A novel Swiss-roll micro-combustor with double combustion chambers is proposed to improve flame stability and extend blow-off limits. This study is aimed to numerically investigate the effect of solid material (i.e., SiC, stainless steel and copper) on premixed CH4/air flame blow-off limit and reveal the flame stability mechanism. The simulated results show that this developed novel Swiss-roll micro-combustor not only can significantly anchor the flame owing to the flow recirculation behind the flame holders and the backward-facing steps, but also can further extend CH4 blow-off limits owing to heat recirculation in the long Swiss-roll preheating channels. The three solid material micro-combustors present the relatively slight difference in the recirculation-zone size but the remarkably difference in heat recirculation and heat loss. Good heat recirculation and low heat loss rate are the dominant reason that is responsible for the differences of the blow-off limits in this micro-combustor. The stainless steel micro-combustor achieves the highest blow-off limits while the copper micro-combustor achieves the lowest blow-off limit. These deep insights can give some useful information to design a similar Swiss-roll micro-combustor.

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.

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.

The combustion interactions during blended coal combustion affect their combustion characteristics, and the combustion interactions under air–fuel conditions have been well studied. However...

The deep and ultra-deep oil and gas has been a prominent exploration direction in the field of petroleum industry in recent years. The deep oil and gas resources are mainly distributed in the carbonate rocks, clastic rocks and igneous rocks, of which the carbonate rock reservoirs account for about 40% of global oil and gas reserves for their superior reservoir properties. Currently, a number of large oil and gas fields have been discovered in the deep marine carbonate rocks in China, especially in the Sichuan and Tarim Basin, thus showing a broad oil and gas exploration potential in the deep marine carbonate rocks. In this paper, the genesis and source of deep natural gas in the Tarim and Sichuan Basin has been systematically studied. The results show that the natural gas in the deep marine carbonate rock reservoirs is not only sourced from the deep-source rocks, but the substantial crack of crude oil in the reservoir under the condition of high burial depth and high geotemperature can provide abundant natural gas sources for the deep reservoir. Accordingly, the contribution of gas from oil cracking should be concerned in evaluation on deep natural gas resources.

In learning English, learners are faced with various challenges, such as listening, speaking, reading and writing. Among them, writing is the most important and difficult one, and grammatical errors are the most common type of errors in English writing. The research and implementation of grammatical error detection and correction in English writing is of great significance to both English learners and English teachers. In this paper, we propose a sequence annotation model based on recurrent neural network to solve the problem of the influence of grammar errors and other noises in English writing corpus on sequence information extraction. Aiming at the grammatical errors in English writing, this paper proposes two methods of English grammatical error detection and correction. The experimental results show that the accuracy of RNN is higher than that of CAMB after 10 to 20 iterations, ranging from 0.848 to 0.916.

As a new form of education, the language education software based on AI (Artificial Intelligence) technology effectively improves the timeliness and interest of language teaching, and enrich and improve the English education system to a certain degree. Second language acquisition (SLA) theory integrates linguistics, language education, sociology, psychology and other disciplines, focusing on the study of people’s acquisition of foreign languages and the mechanism of language ability. This article is based on teaching practice materials and students’ English learning data, and uses the Noticing Hypothesis theory to try to solve the problems emerged from artificial intelligence teaching courses.