Lower Adiabatic Flame Temperature Research Articles

Operation of Blast Furnaces at Low Raceway Adiabatic Flame Temperature

Operation of Blast Furnaces at Low Raceway Adiabatic Flame Temperature

Unraveling combustion chemistry of tetramethoxysilane in flow reactor pyrolysis and laminar flame propagation

Tetramethoxysilane (TMOS, Si(OCH3)4) is a widely used precursor in the vapor-fed aerosol flame synthesis (VAFS) of silica nanoparticles. This work reports the first attempt to investigate the flow reactor pyrolysis and laminar flame propagation of TMOS. Pyrolysis species were detected using gas chromatography (GC) at 1.09 atm and 930–1250 K, such as methane, methanol, ethylene, ethane and carbon monoxide, and their mole fraction profiles versus the heating temperature were also measured. The laminar flame propagation of TMOS/air mixtures was investigated in a constant-volume cylindrical combustion vessel at the initial pressure (Pu) of 1 atm, initial temperature (Tu) of 373 K and equivalence ratios from 0.7 to 1.4. TMOS has generally lower laminar burning velocities (LBVs) than many hydrocarbon fuels due to the high oxygen content and consequently low adiabatic flame temperature of TMOS. A kinetic model of TMOS combustion was developed and validated against both the new data in this work and the shock tube pyrolysis data in literature. Rate of production (ROP) analysis and sensitivity analysis were performed to provide insight into the key pathways in TMOS decomposition. In the flow reactor pyrolysis, the methanol elimination reaction and the H-abstraction reactions dominate the decomposition of TMOS. Among the primary decomposition products, CH2OSi(OCH3)2 mainly isomerizes to CH3OSi(=O)OC2H5, while CH2OSi(OCH3)3 and OSi(OCH3)3 mainly decompose via β-Si-O scission reactions producing OSi(OCH3)3 and OSi(OCH3)2, respectively. The primary decomposition pathways of TMOS can all eventually lead to the formation of SiO2. In the laminar flame propagation, the modeling analyses indicate formaldehyde and methyl radical are abundantly produced, making many reactions involving the two intermediates influential on the laminar flame propagation of TMOS.

A detailed experimental analysis of air–steam gasification in a dual fired downdraft biomass gasifier enabling hydrogen enrichment in the producer gas

The use of ambient air as an oxidizing agent in the biomass gasification process is well understood. Ambient air contains 79% nitrogen (N2) and 21% Oxygen (O2) by volume. Consequently, producer gas generated through air gasification comprises of non-combustible gases around 62% (on a volume basis). As a result, the heating value of the producer gas is low, which results in low adiabatic flame temperature (AFT), low AFT results in reduced efficiency and higher specific fuel consumption (SFC) when the producer gas (PG) is used in internal combustion (IC) engines. This study is focused on the reduction of the non-combustible fraction in producer gas, thereby to increase the heating value of the producer gas through the air- steam gasification. The results of the experimental study are presented in details. A detailed mass and energy balance analysis conducted. A maximum of 27.24% (by volume) hydrogen achieved at equivalence number (EN) 1.54 suitable for bio-hydrogen production. Whereas EN 1.5–2.2 is more suitable for power generation applications since maximum higher heating value (HHV) occurs in this range, i.e., 6.33 MJ Nm−3. The enrichment of producer gas resulted in an increase of HHV by 44%. The cold gas efficiency is 86–87%.

Comparative study on the laminar flame speeds of methylcyclohexane-methanol and toluene-methanol blends at elevated temperatures

Laminar flame speeds of methylcyclohexane (MCH)-methanol and toluene-methanol blends were experimentally determined with spherically expanding flame method in a constant volume bomb at atmospheric pressure, initial temperatures of 393 and 433 K, covering wide equivalence ratio range. The blending ratio of methanol in liquid volume varies as 0%, 20%, 40%, 60%, 80%, 100%. Nonlinear methodology was employed to remove the stretch effect in the data processing. Experimental results show that MCH-air flame propagates faster than toluene at the same condition. The addition of methanol into MCH and toluene results in acceleration of laminar flame speed especially at the rich mixtures. Since the published model suffers difficulty in reproducing experimental data, model refinements were carried out and the refined model yields better performance. Comprehensive analyses were developed regarding thermal and chemical kinetic properties. For MCH has lower adiabatic flame temperature than toluene and methanol addition into the two cyclic fuels decreases the adiabatic flame temperature, the thermal effect on laminar flame speed difference is negligible. Therefore, the effect of chemical kinetics was specifically discussed. MCH and toluene have different ring structures. The disintegration of aromatic ring plays as the limiting step in the high-temperature oxidation of toluene, resulting in low concentration of active radical pool and overall reactivity. However, the ring opening reaction of MCH occurs easily after the initial H-abstraction reaction, which favors the production of active intermediates and the enhancement of flame propagation. For the blending fuels, the analyses show that the laminar flame speed variation of the blends are primarily caused by the methanol substitution and the disturbance of reaction pathway through affecting the generation of important intermediates.

Firing blast furnace gas without support fuel in steel mill boilers

In this study, the combustion characteristics of firing blast furnace gas (BFG) individually or in combination with coke oven gas (COG) were investigated theoretically and experimentally. The theoretical results showed that at the same heat release rate under the operating conditions of stoichiometry, firing BFG individually had a greater amount of fuel gas volume flow rate, a smaller amount of air volume flow rate, and a lower adiabatic flame temperature than firing BFG with support fuel without preheating. Meanwhile, the volume flow rate of flue gas for the former was greater than the latter. The experimental results obtained from a co-firing of BFG and COG fueled-boiler in a steel company showed that whether at a higher or lower boiler load, with gradually decreasing the amount of COG supply, flame instability (lift-off and blow-out) did not occur and the rate of CO emission was very low. In addition, a decrease in the amount of COG supply brought about a great benefit to the reductions of both CO 2 and NO x emissions.

Hydrogen addition effects in a confined swirl-stabilized methane-air flame

The effect of hydrogen addition in methane-air premixed flames has been examined from a swirl-stabilized combustor under confined conditions. The effect of hydrogen addition in methane-air flame has been examined over a range of conditions using a laboratory-scale premixed combustor operated at 5.81 kW. Different swirlers have been investigated to identify the role of swirl strength to the incoming mixture. The flame stability was examined for the effect of amount of hydrogen addition, combustion air flow rates and swirl strengths. This was carried out by comparing adiabatic flame temperatures at the lean flame limit. The combustion characteristics of hydrogen-enriched methane flames at constant heat load but different swirl strengths have been examined using particle image velocimetry (PIV), micro-thermocouples and OH chemiluminescence diagnostics that provided information on velocity, thermal field, and combustion generated OH species concentration in the flame, respectively. Gas analyzer was used to obtain NO x and CO concentration at the combustor exit. The results show that the lean stability limit is extended by hydrogen addition. The stability limit can reduce at higher swirl intensity to the fuel-air mixture operating at lower adiabatic flame temperatures. The addition of hydrogen increases the NO x emission; however, this effect can be reduced by increasing either the excess air or swirl intensity. The emissions of NO x and CO from the premixed flame were also compared with a diffusion flame type combustor. The NO x emissions of hydrogen-enriched methane premixed flame were found to be lower than the corresponding diffusion flame under same operating conditions for the fuel-lean case.

Synthesis of Carbon‐Rich Hybrid Foam from GAP‐Modified Polyurethane

Abstract4,4′‐Diisocyanato diphenylmethane (MDI)‐based polyurethanes melt and start to burn at 150–200 °C. Mainly H2O, CO2, CO, HCN, and N2 are formed. The new modified polyurethane shows a different pyrolysis behavior. GAP‐diol (glycidyl azide polymer), which was used as a modifying agent, is a well‐known energetic binder with a high burning velocity and a very low adiabatic flame temperature. The modified polyurethane starts to burn at approximately 190 °C because of the emitted burnable gases, but it does not melt. The PU foam shrinks slightly and a black, solid, carbon‐rich hybrid foam remains. TGA and EGA‐FTIR revealed a three‐step decomposition mechanism of pure GAP‐diol, the isocyanate‐GAP‐diol, and PU‐GAP‐diol formulations. The first decomposition step is caused by an exothermic reaction of the azido group of the GAP‐diol. This decomposition reaction is independent of the oxygen content in the atmosphere. In the range of 190–240 °C the azido group spontaneously decomposes to nitrogen and ammonia. This decomposition is assumed to take place partly via the intermediate hydrogen azide that decomposes spontaneously to nitrogen and ammonia in the range of 190–240 °C. The second decomposition step was attributed to the depolymerization of the urethane and bisubstituted urea groups. The third decomposition step in the range of 500–750 °C was attributed to the carbonization process of the polymer backbone, which yielded solid, carbon‐rich hybrid foams at 900 °C. In air, the second and the third decomposition step shifted to lower temperatures while no solid carbon hybrid foam was left. Samples of PU‐GAP‐diol, which were not heated by a temperature program but ignited by a bunsen burner, formed a similar carbon‐rich hybrid foam. It was therefore concluded that the decomposition products of the hydrogen azide, ammonia and mainly nitrogen act as an inert atmosphere. FTIR, solid‐state 13C‐NMR, XRD, and heat conductivity measurements revealed a high content of sp2‐hybridized, aromatic structures in the hybrid foam. The carbon‐rich foam shows a considerable hardness coupled with high temperature resistance and large specific surface area of 2.1 m2⋅g−1.