The near-wall air (NWA) technology is effective for resolving the high-temperature corrosion on water tube walls in large-scale utility boilers. A numerical investigation was performed to study the effect of NWA on combustion and high-temperature corrosion in an opposed firing pulverized-coal 300 MWe utility boiler. The consistency between the in situ measured and simulated CO distribution tendencies proved that the current simulation methods were reliable and appropriate. NWA not only reduced the peaks of the CO and H2S concentrations but also significantly decreased the zone with high CO and H2S near the side walls. The NWA injection weakened the reducing atmosphere on the side wall by 40%. NWA presented a slight impact on the gas temperature and the nitrogen oxide (NOx) concentration at the furnace outlet and led to an obvious increase in unburned carbon. The flow ratio of the NWA was analyzed from 3% to 12%. Considering the unburned carbon, CO, and H2S distribution, the appropriate NWA ratio was approximately 6%. High NWA ratio was beneficial to the reduction of the corrosive gases near the side walls. However, this reduction resulted in an increase in unburned carbon. A serious increase in CO and H2S concentration was observed in the ash hopper zone near the side wall when the NWA ratio exceeded 9%. This increase was caused by the growth of the recirculation zone in the ash hopper near the side walls, which resulted in high temperature and low O2 concentration.

•Studying in thermodynamics the vacuum carbothermal-chlorination reduction for Al production.•Studying the reaction efficiency and exergy efficiency with the temperature.•The optimal reaction temperature region was obtained for carbothermal-chlorination reduction.•Heat recovery was key to improve the energy consumption and exergy efficiency.•Carbothermal-chlorination reduction performs better than electricity aluminum.Carbo-thermal reduction aluminum is regarded as the future aluminum production method for its low energy consumption. A thermodynamics analysis is performed, taking the Al–C two-step model as the objective. High temperature is beneficial to the reaction efficiency, but harmful to the exergy efficiency of the first reaction (Al2O3 + 3C + AlCl3 = 3AlCl + 3CO, R1). The second reaction (3AlCl = AlCl3 + 2Al, R2) presents an opposite pattern. An optimal reaction temperature window exists for the AlCl mediated carbon reduction method. The temperature of R1 is above 1520 K and that of R2 is 398–798 K in the optimal window. Heat recovery is significantly important in enhancing both exergy efficiency and energy consumption in actual processes. Energy consumption is reduced from 11,335 kW h/t(Al) to 8063 kW h/t(Al) when an ideal heat recovery is performed. Compared with electrolytic aluminum, carbothermol-chlorination reduction presents a significantly better performance in some condition. Energy consumption is 10,151 and 13,200 kW h/t(Al) in carbothermol-chlorination reduction and electrolytic aluminum, respectively. Moreover, 67% of the exergy efficiency of the carbothermol-chlorination reduction is greater by 1.7 times than that of the electrolytic aluminum.

•Micro combustion of methane, propane and n-octane with Pt/ZSM-5 were performed.•Propane was suitable for micro combustion – low catalytic ignition temperature, high conversion and high CO2 selectivity.•Methane and n-octane showed worse combustion performance than propane.Experimental studies on the combustion of methane, propane and n-octane with Pt/ZSM-5 packed bed were performed in a tube with a diameter of 4 mm in order to acquire several performance indicators, including the self-sustaining combustion limit, conversion efficiency, and heat output among others. The increase of equivalence ratio (Φ) extended the velocity limits (v) of self-sustaining combustion in varying degrees for the three fuels under study. Methane presented a relatively narrow self-sustaining combustion region, low conversion (≤25%), high CO selectivity (5–11%) and low tube wall temperature (<250 °C) at Φ=1.0 and v=0.8–1.4 m/s. The catalytic reactivity for methane oxidization over Pt/ZSM-5 was highly activated at temperatures over 455 °C, this being responsible for the methane combustion performance. In the case of propane combustion processes, a homogenous reaction occurred downstream the catalyst section and led to high conversion. Under Φ=1.0 and v=0.8–1.4 m/s conditions, propane conversion was higher than 45% while the CO2 selectivity remained over 96%. n-Octane showed similar combustion performance than propane, with a little backward gap detected. The released heat by fuel combustion increased in the order: methane, n-octane, and propane, with the maximum heat values being 12, 19, and 32 W, respectively. Propane was suitable for micro combustion with the catalyst, as a result of the low catalytic ignition temperature (124 °C) and high catalytic reactivity.

As one of the potential candidates for fuel surrogates, n-heptane has been the focus of numerous oxidation and combustion studies. In this work, n-heptane combustion in cylinder tubes with diameters of 2, 3, and 4 mm was investigated experimentally with the use of packed catalyst beds of Pt/Ce0.8Zr0.2O2 to study the mechanism of self-sustaining combustion and the dimensional effects of the inner diameter of a tube combustor. The region of self-sustaining stable combustion, the tube wall temperature, and the combustion efficiency were examined. n-Heptane can maintain self-sustaining stable combustion in the three tubes even if the wall temperature was below 430 K. As the equivalence ratio (Φ) increased, the stability region of the Reynolds number (Re) was expanded at the expense of fuel wastage. The lower stability limit of Re decreased as the tube diameter increased, and the value could reach as low as 12 in the tube with a diameter of 4 mm. The equivalence ratio was the dominant factor of the wall tube temperature at the lower boundary, whereas Re was significant at the upper boundary. An optimal Re allowed for the achievement of the highest wall temperature, and the optimal Re was high with a small diameter. The tube with a large diameter presented both a high combustion efficiency and high heat release rate. Combustion efficiency was improved by 40% when the diameter of the tube increased from 2 to 4 mm, and over 80% combustion efficiency was achieved in the d = 4 mm tube at Φ = 2. Under a fuel-rich condition, the tube combustor outputted heat energy at a low rate and emitted heat to the atmosphere at a high rate. This resulted in the wastage of a massive ratio of the input fuel.

•Studying the reacting processes of Al–Mg–Li particles with H2O vapor below 1030 °C.•Adding Li and Mg into Al showed a good hydrolysis performance and 89% of Al reacted.•Three stages in reacting process corresponded to the reacting of Li, Mg, and Al.•The products of hydrolysis were LiAlO2, Li2Al4O7, Al2O3 and MgO.•Special promotion mechanisms of both Li and Mg on Al–H2O reaction were discovered.Hydrogen is a renewable and environmentally friendly fuel with high calorific value. Aluminum is a good option for working as hydrolyzing metal, and aluminum–water reactions at medium–high temperature serve as a good energy supply in the use of both hydrogen and released heat, which leads to high energy efficiency. This study focused on hydrogen production characteristics and the chemical kinetics of aluminum particles with the addition of magnesium and lithium below 1030 °C. The experiments were conducted with THERMO CAHN's Thermax500 pressurized thermogravimetric analyzer. The Al content was settled at 85%, and the Mg and Al contents were adjusted from 0% to 15%. The addition of Li and Mg into Al resulted in good hydrolysis performance, and the ratio of the reacted Al to the total Al was over 50% and even reached up to 89%. The reaction process showed an obvious three-stage feature, and the three stages primarily corresponded to the reactions of Li, Mg, and Al. The products of hydrolysis in our tests were LiAlO2, Li2Al4O7, Al2O3, and MgO. The different promotion mechanism of Li and Mg on the reaction of Al–H2O resulted in a hydrolysis performance that did not change monotonously with Li content.

•Comparative study of ethanol and DME combustion on Pt/ZSM-5 were performed.•DME presented larger CO2 yields and higher wall temperatures than ethanol generally.•After 48 h combustion, CO2 yields of DME and ethanol decreased by 13.8% and 38.9%, respectively.•Ethanol combustion caused more serious catalyst agglomerations and carbonaceous depositions.•The increased surface carbonaceous species were CC/CH after ethanol combustion and OCO after DME combustion.The combustion of ethanol and dimethyl ether (DME) was performed over Pt/ZSM-5 catalyst in a packed-bed reactor to investigate the combustion characteristics and catalyst deactivation. Results showed that the CO2 yield and wall temperature for the combustion of DME were higher than those for the combustion of ethanol. The maximum CO2 yield for both fuels surpassed 72%. After 48 h of continuous combustion, CO2 yields of DME and ethanol decreased by 13.8% and 38.9%, respectively, attributed to the agglomeration of Pt and the formation of carbonaceous deposits on the catalyst. Transmission electron microscopy images showed considerable Pt agglomeration after ethanol combustion. Temperature-programmed oxidation results revealed two types of carbonaceous deposits with oxidation temperatures of 225 and 345 °C after DME combustion, but only the former type was detected after ethanol combustion. X-ray photoelectron spectra revealed that the mainly increased surface carbonaceous species were CC/CH and OCO after the combustion of ethanol and DME, respectively.

•H2/air premixed micro combustion was studied by experiments and simulation.•Structure of converging–diverging expanded the stable combustion limits.•Temperature, ignition position, and flame characteristics were studied.•Effects of equivalence ratio and inlet velocity were discussed.Experimental and numerical studies of hydrogen–air premixed combustion in a converging–diverging micro tube with inner diameters of the inlet, throat, and outlet of 2, 1, and 2 mm, respectively, have been performed to study the combustion and flame characteristics. The influences of the equivalence ratio (Φ) and inlet velocity (vin) are investigated. The experiments reveal that the vin range for stable combustion—between 3.4 and 41.4 m/s—was significantly expanded, particularly when Φ = 1.4. This effect can primarily be attributed to the converging–diverging structure. As Φ increased, both the wall and the flame temperatures exhibited an increasing–decreasing trend; the largest heat loss ratio occurred at Φ = 1.0. The ignition position initially moved upstream and then moved downstream. The flame thickness increased and then decreased, reaching its peak value at Φ = 1.2. The flame length decreased monotonously. As vin increased, the wall temperature increased, the flame temperature decreased, and the flame moved downstream to grow thicker and longer.

With the focus on improving coal burnout and controlling NOx emissions in down-fired boilers, a new deep air-staging combustion technology, the hot air packing technology (HAPT), was investigated by experiments and numerical simulations. The effects of the special secondary air ports added in the furnace ash hopper (SA-H) and the furnace bottom (SA-B) were analyzed by comparing the three cases: the HAPT, no-SA-H, and no-SA-B cases. The experiments with Guizhou anthracite coal in a down-fired 3.5 MW pilot facility showed that the HAPT case presented a good performance of both NO emissions of 683 mg/Nm3 at O2 = 6% and coal burnout, 3.07% of unburned coal in fly ash. Simulation results using Fluent software satisfactorily coincided with the experiment results of the HAPT case. It was found by simulation that the HAPT case formed a rational aerodynamic field in the furnace, refrained dead recirculation zones from emerging in the ash hopper, and implemented an air-packed and deep air-staging coal combustion inside the furnace. SA-H flows took the responsibility of destroying dead recirculating zones in the ash hopper, and SB-H flows affected the penetration depth of primary air flow and the utilization rate of the ash hopper.

Urea thermolysis and isocyanic acid hydrolysis over three kinds of zeolites are investigated experimentally and the main decomposition products, NH3 and HNCO, are focused on. The results gained using thermogravimetric analysis with heating rates of 2 °C/min from 50–500 °C show NH3 releases mainly in 133–250 °C and the main thermal product above 250 °C is HNCO. NH3 release process appears double-peaked while HNCO triple-peaked. Zeolites shift urea decomposition to lower temperature and shorten the process. The experiments of urea thermolysis over zeolites were done in the fixed reactor at programmed temperature and constant temperature. Although zeolites enhance the production of both NH3 and HNCO, the yield ratio of NH3 increases to 1.1 from 0.9 when adding zeolites but the yield ratio of HNCO is always below 0.8. Under zeolites’s catalytic effect, the peak of NH3 release and the second peak of HNCO release become stronger. Moreover, zeolites can result in the HNCO peaks integrating into a stronger peak at 500 °C. The total yield of NH3 and HNCO increases about 0.1–0.2 with zeolites and the catalytic effect is more obvious at low temperature. In the experiment of thermolysis with a urea-water spray, over 96% urea could decompose to NH3 and HNCO when the temperature is over 550 °C and the residence time is more than 1.0 s. Zeolites show good catalytic performance on HNCO hydrolysis to NH3 and the conversion of HNCO to NH3 increases with increasing temperature and reaches above 80% at 250 °C and can touch 100%. The catalytic effect on urea thermolysis and HNCO hydrolysis decreases in the order H–Y > H-β > H-ZSM5, which might be due to the amount of acidic sites on the catalysts. The apparent activation energy of the hydrolysis reaction is so low that the overall hydrolysis reaction rate on catalysts is mainly determined by external and internal mass-transfer limitations.

The reaction of magnesium with water is of interest for propulsion and hydrogen generation. Reaction mechanism of Mg with water was investigated by ab initio quantum chemical methods. The geometries and frequencies of all reactants, products, intermediates and transition states were calculated at the B3LYP/6-311G++(3df, 2p) level. Energies at a higher level of accuracy were obtained at G2M (CC2) level using the B3LYP-optimized geometries. The Mg and water firstly formed an atom-molecule adduct Mg⋅OH2Mg⋅OH2, and then either formed MgOH + H by a H-dissociation process or formed HMgOH by the process of H-migration from one to the other side of the adduct molecule. The barrier heights of two processes are 48.28 kcal/mol and 32.51 kcal/mol. The rate constants were calculated by using the variational transition state theory with the zero-curvature tunneling correction in a temperature range of 1000–5000 K. The results showed that H-migration process was dominant in the studied temperature range and the branch ratio of H-dissociation process appeared bigger at higher temperature.Highlights► The reaction paths of Mg with water are obtained by ab initio quantum chemical methods. ► Higher level reaction enthalpy of Mg with water has been obtained by G2M(CC2) method. ► The rate constants of Mg with water are calculated using the variational transition state theory.

The thermolysis of urea-water solution and its product, HNCO hydrolysis is investigated in a dual-reactor system. For the thermal decomposition below about 1073 K, the main products are ammonia (NH3) and isocyanic acid (HNCO) whereas at higher temperatures the oxidation processes take effect and the products include a low concentration of nitric oxide (NO) and nitrous oxide (N2O). The gas HNCO is quite stable and a high yield of HNCO is observed. The ratio of NH3 to HNCO increases from approximately 1.2 to 1.7 with the temperature. The chemical analysis shows that H radical is in favor of HNCO hydrolysis by instigating the reaction HNCO+H·→·NH2+CO and high temperature has positive effect on H radical. The hydrolysis of HNCO over an alumina catalyst made using a sol-gel process (designated as γ-Al2O3) is investigated. The conversion of HNCO is high even at the high space velocities (6×105 h−1) and low temperatures (393–673 K) in the tests with catalysts, which enhances HNCO hydrolysis and raises the ratio of NH3 to HNCO to approximately 100. The pure γ-Al2O3 shows a better catalytic performance than CuO/γ-Al2O3. The addition of CuO not only reduces the surface area but also decreases the Lewis acid sites which are recognized to have a positive effect on the catalytic activity. The apparent activation energy of the hydrolysis reaction amounts to about 25 kJ/mol in 393–473 K while 13 kJ/mol over 473 K. The overall hydrolysis reaction rate on catalysts is mainly determined by external and internal mass-transfer limitations.

Micro-combustors have low stability, thus catalyst is applied to improve it. In this experiment, the performances of catalytic micro-combustors made of different materials (quartz glass, alumina ceramic, copper) are compared. Asbestine threads are used as the catalyst supports of Pt, and installed in the combustors. According to the experimental results, the combustors have high stability, they keep working until the extreme equivalence ratio close to 0. The stability limits of homogeneous reaction in the quartz glass and alumina ceramic combustor range from 0.0907 to 8.69 and 0.158 to 7.31 on average, respectively. But the two combustors exhibit obvious hot spots, which are 1058 and 728 K at 0.2 L/min, respectively. Whereas the copper combustor has low and uniform temperature distribution on its surface. Moreover, the heat loss in the quartz glass combustor is 4.13 W higher than in the copper one at 0.2 L/min, which is opposite to the conventional situation that heat loss increases with the wall thermal conductivity. Computational fluid dynamic simulation reveals that the reaction modes inside the combustors differ. The higher wall thermal conductivity makes the heterogeneous reaction dominate, thus induces the temperature distribution and heat loss aforementioned.

Characteristics of sodium compounds additives on NO reduction at high temperature were investigated in a tube stove and a drop tube furnace. Sodium carbonate, sodium hydroxide and sodium acetate were chosen as Na additives to research the effect on NO reduction. It was found that sodium compounds could reduce NO emission and promoted NO reduction efficiency during pulverized coal combustion, coal reburning and urea-SNCR process. Adding sodium carbonate into crude coal gained 3.2%–34.8% of NO reduction efficiency on different combustion conditions during the coal combustion process. NO reduction efficiency was affected by sodium content and coal rank. Na additive performed NO reduction effect in whole Shenhua coal combustion process and in char rear combustion of Gelingping coal. Adding sodium hydroxide into the reburning coal increased NO reduction efficiency of the reburning technology. NO reduction efficiency was increased to 82.7% from 50.0% when the weight ratio sodium to the reburning coal was 3% and the ratio of the supplied air to the theoretical air of reburning fuel was 0.6. Sodium carbonate, sodium hydroxide and sodium acetate performed the promotion of NO reduction efficiency in urea-SNCR. Sodium acetate promoted NO reduction efficiency best while sodium hydroxide promoted worst at 800 °C. Sodium additives as SNCR promoter performed much better at lower temperature than at higher temperature, and they promoted NO reduction weakly in urea-SNCR when the temperature was greater than 900 °C.

Pulverized coal-fired boilers are not nitrous oxide sources because of high temperature combustion. But selective non-catalytic reduction may produce N2O by NO reduction reactions. Chemical kinetics calculation and experimental research were used to find out the mechanism between N2O and N-agent species, N-agent/NO nitrogen stoichiometric ratio (NSR), reaction temperature, reaction time, etc. The results show that N2O emission decreases with increasing reaction temperature and NSR decreases when reaction time is enough. N2O concentration first increases then decreases as SNCR reactions keep on occuring. Ammonia SNCR tests indicated that N2O emission was 0–7 μmol/mol. About 8.7% of NO was transformed to N2O, and N2O emission was 27.8 μmol/mol at urea-SNCR test. Urea-SNCR is likely to bring N2O emission problem.

AbstractUnreacted ammonia in Selective Catalytic Reduction (SCR) and Selective Non-catalytic Reduction (SNCR) technology may be adsorbed by fly ash and lead to ash blocking in the air preheater or hindering the secondary utilization of ash. Ammonia adsorption by fly ash may have a close relationship to the concentration of ammonia in flue gas. Regarding Ximeng lignite and Yangquan anthracite as the subjects investigated, NH3 temperature-programmed desorption (NH3-TPD) was utilized to study the relationship between ammonia chemical adsorption and mineral composition of the ash, the atmosphere of ash production, cooling rate of ash as well as the amount of residual carbon in the ash. The results show that rapid cooling and reduction atmosphere could increase the amount of amorphous phase in the ash and facilitate ammonia adsorption. On the other hand, ash with residual carbon could adsorb more ammonia than mineral ash as a result of acidic functional group on the surface of residual carbon.

Dynamic compositions of lipids accumulated in two diatoms Chaetoceros gracilis and Nitzschia closterium cultured with nitrogen and silicon deprivation were studied. It was found that short-chain fatty acids (C14–C16) content was much higher than long-chain fatty acids (C18–C20) content in lipids of two diatoms. The pyrolytic characteristics of biodiesel made from two diatoms and two plant seeds were compared by thermogravimetric analysis. The highest activation energy of 46.68 kJ mol−1 and the minimum solid residue of 25.18% were obtained in the pyrolysis of biodiesel made from C. gracilis cells, which were cultured with 0.5 mmol L−1 of nitrogen (no silicon) and accumulated the minimum polyunsaturated fatty acid (C20:5). The pyrolysis residue percentage of C. gracilis biodiesel was lower than that of N. closterium biodiesel and higher than those of plant (Cormus wilsoniana and Pistacia chinensis) biodiesels.

•A novel electricity and heat co-generation system in the basis of AlH2O reaction.•Two kinds of layouts with one or two turbines were designed and analyzed.•Enhancing fuel cell conversion efficiency benefits the system, especially TTL case.With high calorific value and the environmental friendly features, hydrogen has been attached much importance. Aluminum–water reactions at medium–high temperature perform well in hydrogen generation as well as heat utilization. Active researches of the aluminum–water reactions in recent years can be attributed to the increasing interest of hydrogen generation and energy conversion.In the basis of aluminum–water reactions, the concept of a novel electricity and heat co-generation system was proposed here and it was primarily composed of a reactor, one or two turbines and generators, heat exchanger for heat user, a fuel cell and a pump. Two layouts were designed and analyzed: the one turbine layout (OTL) and the two turbine layout (TTL).The effects of key parameters, such as the steam temperature and pressure at turbine inlet, the heat user temperature and fuel cell conversion efficiency were investigated. The co-generation system could generate heat and electricity of about 22.2 MJ/kg (Al) in the OTL design. The system utilization efficiency, the ratio of the output was approximate 70% and the electricity generation efficiency could reach up to 41.52% (OTL) and 49.25% (TTL) in the two cases respectively. The OTL presented a higher heat user utilization efficiency than TTL, because of the higher turbine outlet parameters. The TTL layout with the integration of fuel cell and heat user enhanced electricity output by 45.06% in comparison with the OTL layout. The steam temperature at turbine inlet showed considerable impacts on the system utilization efficiency at the TTL case. Enhancing fuel cell conversion efficiency benefited the system and fuel cell utilization efficiencies, especially at the TTL case.