Lean-rich combustion characteristics of methane and ammonia in the combined porous structures for carbon reduction and alternative fuel development.

Ammonia as a carbon-free alternative fuel has received much attention with the consumption of fossil fuels. In order to explore the mixed combustion of methane and ammonia, a combined porous media burner was designed with pellets embedded in annular ceramic foam. And the effects of operating parameters on combustion characteristics were investigated. The results showed that the ammonia addition increased the combustion temperature and reduced carbon dioxide emissions at the equivalence ratio of <1. And the ammonia promoted the conversion of CO2 to CO for an equivalence ratio of >1. With the increasing of the ammonia ratio, the CO selectivity increased but the CO2 selectivity decreased. In addition, the mixed combustion of ammonia and methane improved the hydrogen production. The fuel ratio of methane to ammonia (0.80: 0.20) resulted in higher syngas production and lower CO2 mole fraction. The flame propagated faster in ceramic foam with lower pore densities (20 PPI) so the preheating time was greatly reduced. Moreover, the 40 PPI ceramic foam was conducive to the stability of the flame position in the upstream zone, and the H2 mole fraction achieved 10.60 % at the inlet velocity of 14 cm/s.

Facile preparation of N-doped activated carbon produced from rice husk for CO2 capture.

Activated carbons (AC) were prepared by carbonization and KOH activation using rice husk as feedstock. The effects of impregnation ratios and activation temperatures on the properties of AC were investigated. Under optimum conditions, BET surface area, total pore volume and micropore volume of AC are as high as 1495.52 m2/g, 0.786 cm3/g and 0.447 cm3/g, respectively. Surface modification with chitosan as nitrogen source was performed simultaneously during KOH activation process. XPS and FT-IR analyses show that N-species was successfully incorporate into AC. Compared with AC-5 (general AC), CAC-5 (modified AC) exhibits better CO2 adsorption performance, reaching 5.83 mmol/g at 273 K and 1 bar, which can be attributed to the formation of the CO2-philic active sites on AC surface by N-species. The linear correlations between CO2 uptake, micropore volume within specific size section and N-content was investigated. The isosteric heat of CO2 adsorption for CAC-5 (average 30.21 kJ/mol) is much higher than that of AC-5 (average 14.48 kJ/mol). The adsorption behavior of CAC-5 can be well described by Freundlich model. The high IAST selectivity factor for N-doped ACs indicates their excellent adsorption selectivity for CO2 over N2. Both physisorption and chemisorption are present in CO2 adsorption process of N-doped ACs.

Insight to hydrophobic SiO2 encapsulated SiO2 gel: Preparation and application in fire extinguishing.

Micron-sized hydrophobic SiO2 encapsulated SiO2 gel (HSESG) was prepared successfully by using SiO2 gel as the solid core and hydrophobic nano-SiO2 particle as the shell under high-speed shear stirring. The flowability, stability, particle size distribution, bulk density and water repellency of the powder were measured separately, and it was concluded that this type of product can exhibit smaller static angle, larger flow rate and lower bulk density. After the formation of a stable spatial network of SiO2 gel in its interior, relevant fire extinguishing experiments were carried out and HSESG exhibits higher efficiency in suppressing wood stack fires than that of ordinary dry water (DW) and ABC dry powder. As a high-efficiency fire-extinguishing material, it also exhibits excellent environmental friendliness and non-toxicity, which will make it have the potential to develop a new application market.

Insight into suppression performance and mechanisms of ultrafine powders on wood dust deflagration under equivalent concentration.

Flame propagation characteristics of wood dust deflagration and suppression mechanism of ultrafine powders are investigated systematically. The deflagration reaction intensity of wood dust increases firstly and then decreases with the increase in dust cloud concentration. This is due to factors such as oxygen supply, positive feedback among flame characteristic parameters. Thus, there is an equivalent dust concentration for greatest deflagration intensity. Nano-sized ultrafine zirconium hydroxide (Zr(OH)4) and silicon dioxide (SiO2) powder are introduced to suppress wood dust deflagration at the equivalent concentration. It is found that Zr(OH)4 has a suppression effect of endothermic decomposition to generate zirconia (ZrO2), dilution of oxygen and absorption of free radicals; while SiO2 exerts suppression effect due to its high melting point and heat absorption. The suppression performance of Zr(OH)4 is better than that of SiO2. This is because that Zr(OH)4 and ZrO2 have a catalytic carbonization effect. It can not only improve thermal stability of wood particles by catalyzing production of high-temperature resistant residuals, but also promote the formation of catalytic sites to reduce crystallite size of carbon layer on wood particles surface, weakening heat and mass transfer between particles.

Suppression of wood dust explosion by ultrafine magnesium hydroxide.

The suppression effects of ultrafine Mg (OH)2 powders with different particle sizes and mass fractions on explosion flame of wood dust are experimentally studied in a half-closed vertical experimental duct. Flame structures and characteristic parameters, including flame light emission images, propagation velocity, temperature, during the flame propagation of wood dust explosion are recorded by high-speed photography and fine thermocouple. Thermal decomposition behaviors of wood dust and Mg(OH)2 powders are studied using synchronous thermal analyzer. Chemical structures of residual dust samples after the explosion are characterized by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The experimental results show that explosion flame of wood dust is obviously suppressed by physical and chemical effects of Mg(OH)2 powders, and the suppression effect of nano-Mg(OH)2 is better than that of micron-Mg(OH)2 under same mass fractions. By analyzing multiple characteristics of nano-powders, the advantages of nano-Mg(OH)2 over micron-powders are further investigated.

Facile preparation of layered melamine-phytate flame retardant via supramolecular self-assembly technology.

Melamine-phytate (MEL-PA) nanoflakes are formed by supramolecular self-assembly technology using melamine (MEL) and bio-based phytic acid (PA) as the building blocks. This work explores the possibility of this two-dimensional nanomaterial as flame retardant. The layered MEL-PA with the loading of 1, 2 and 3 wt% are incorporated into polypropylene (PP) matrix. MEL-PA is dispersed well in the PP matrix. Thermal stability and flame retardant performance of PP/MEL-PA composites are investigated. Compared with neat PP, the addition of 2 wt% MEL-PA decreases the peak heat release rate from 756 to 608 kW/m2. Char yield of PP is improved by MEL-PA, and the chemical structure and graphitization degree of residual char are studied to reveal flame retardant mechanism.

Effect of heat treatment on hydrophobic silica aerogel.

Hydrophobic silica aerogels were heat treated under various conditions. Physical and chemical analyses were conducted to study the effect of the heat treatments on the silica aerogels. The O/Si and C/Si values in the hydrophobic silica aerogels increased and decreased, respectively, with the increase in the heating temperature. C-O, -OH, and CO were detected during pyrolysis. Pyrolysis of the silica aerogels in air could be divided into 3 steps: the hydroxylation of methyl groups, the splitting of the alcoholic hydroxyl, and the oxidisation of CO. When the heat treatment temperature was lower than 350 °C, the properties of the silica aerogels showed little change. With further increase in the heat treatment temperature, the variation in the relevant parameters became more prominent. The secondary particles coalesced with one another, and the mesopores were destroyed. Consequently, the thermal conductivity and bulk density rose greatly. The carbon within the silica aerogels was released after heat treatment. As a result, the heat released in the thermal gravimetry and oxygen bomb analyses dropped remarkably with the increase in the heat treatment temperature.