Hydrogen production from woody biomass by steam gasification using a CO2 sorbent

In ${\mathrm{H}}_2$ production from woody biomass by steam gasification using CaO as a ${\mathrm{CO}}_2$ sorbent, the effect of reaction parameters such as the molar ratio of CaO to carbon in the woody biomass $([\mathrm{Ca}]/[\mathrm{C}])$, reaction pressure, and reaction temperature was investigated on ${\mathrm{H}}_2$ yield and conversion to gas. In the absence of CaO, the product gas contained ${\mathrm{CO}}_2$. On the other hand, in the presence of CaO ($[\mathrm{Ca}]/[\mathrm{C}]=1,2$, and 4), no ${\mathrm{CO}}_2$ was detected in the product gas. At a $[\mathrm{Ca}]/[\mathrm{C}]$ of 2, the maximum yield of ${\mathrm{H}}_2$ was obtained. The ${\mathrm{H}}_2$ yield and conversion to gas were largely dependent on the reaction pressure, and exhibited the maximum value at $0.6\mathrm{MPa}$. It is noteworthy that ${\mathrm{H}}_2$ was obtained from woody biomass at a much lower pressure compared to other carbonaceous materials such as coal $(>12\mathrm{MPa})$ and heavy oil $(>4.2\mathrm{MPa})$ in steam gasification using a ${\mathrm{CO}}_2$ sorbent. ${\mathrm{H}}_2$ yield increased with increasing reaction temperature. Woody biomass is the one of the most appropriate carbonaceous materials in ${\mathrm{H}}_2$ production by steam gasification using CaO as a ${\mathrm{CO}}_2$ sorbent, taking the reaction pressure into account.     

Experimental and kinetic study on ignition delay times of lean n-butane/hydrogen/argon mixtures at elevated pressures

Measurements on ignition delay times of n-butane/hydrogen/oxygen mixtures diluted by argon were conducted using the shock tube at pressures of 2, 10 and 20 atm, temperatures from 1000 to 1600 K and hydrogen fractions (${\mathrm{X}}_{{\mathrm{H}}_2}$) from 0 to 98%. It is found that hydrogen addition has a non-linear promoting effect on ignition delay of n-butane. Results also show that for ${\mathrm{X}}_{{\mathrm{H}}_2}$ less than 95%, ignition delay time shows an Arrhenius type dependence and the increase of pressure and temperature lead to shorter ignition delay times. However, for ${\mathrm{X}}_{{\mathrm{H}}_2}$ = 98% and 100% mixtures, non-monotonic pressure dependence of ignition delay time were observed. The performances of the Aramco2.0 model, San Diego 2016 model and USC2.0 model were evaluated against the experimental data. Only the Aramco2.0 model gives a reasonable agreement with all the measurements, which was conducted in this study to interpret the effect of pressure and hydrogen addition on the ignition chemistry of n-butane.     

Hydrogen production by coal plasma gasification for fuel cell technology

Coal gasification in steam and air atmosphere under arc plasma conditions has been investigated with Podmoskovnyi brown coal, Kuuchekinski bituminous coal and Canadian petrocoke. It was found that for those coals the gasification degree to synthesis gas were 92.3%, 95.8 and 78.6% correspondingly. The amount of produced syngas was 30–40% higher in steam than in air gasification of the coal.The reduction of the carbon monoxide content in the hydrogen-rich reformate gas for low-temperature fuel cell applications normally involves high- and low-temperature water gas shift reactors followed by selective oxidation of residual carbon monoxide. It is shown that the carbon monoxide content can be reduced in one single reactor, which is based on an iron redox cycle. During the reduction phase of the cycle, the raw gas mixture of ${\mathrm{H}}_2$ and CO reduces a ${\mathrm{Fe}}_3{\mathrm{O}}_4–{\mathrm{CeO}}_2–{\mathrm{ZrO}}_2$ sample, while during the oxidation phase steam re-oxidizes the iron and simultaneously hydrogen is being produced. The integration of the redox iron process with a coal plasma gasification technology in future allows the production of ${\mathrm{CO}}_x$-free hydrogen.     

Effects of content of hydrogen on the characteristics of co-flow laminar diffusion flame of hydrogen/nitrogen mixture in various flow conditions

Effect of content of hydrogen (H₂) in fuel stream, mole fraction of H₂$\left(X_{H_2}\right)$ in fuel composition, and velocity of fuel and co-flow air $\left(V_{avg}\right)$ on the flame characteristics of a co-flow H₂/N₂ laminar diffusion flame is investigated in this paper. Co-flow burner of Toro et al. [1] is used as a model geometry in which the governing conservation transport equations for mass, momentum, energy, and species are numerically solved in a segregated manner with finite rate chemistry. GRI3 reaction mechanisms are selected along with the weight sum of grey gas radiation (WSGG) and Warnatz thermo-diffusion models. Reliability of the newly generated CFD (computational fluid dynamics) model is initially examined and validated with the experimental results of Toro et al. [1]. Then, the method of investigation is focused on a total of 12 flames with $X_{H_2}$ varying between 0.25 and 1, and $V_{avg}$ between 0.25 and 1 ms^?1. Increase of flame size, flame temperature, chemistry heat release, and NOx emission formation resulted are affected by the escalation of either $X_{H_2}$ or $V_{avg}$. Significant effect on the flame temperature and NOx emission are obtained from a higher $X_{H_2}$ in fuel whereas the flame size and heat release are the result of increasing $V_{avg}$. Along with this finding, the role of N₂ and its higher content reducing the flame temperature and NOx emission are presented.     

Numerical investigation of a high pressure hydrogen jet of 82 MPa with adaptive mesh refinement: Concentration and velocity distributions

To investigate the safety properties of high-pressure hydrogen discharge or leakage, an under-expanded hydrogen jet flow with a storage pressure of 82 MPa from a small jet orifice with a diameter of 0.2 mm is studied by three-dimensional (3D) numerical calculations. The full 3D compressible Navier-Stokes equations are utilized in a domain with a size of about 3 × 3 × 6 m which is discretized by employing an adaptive mesh refinement (AMR) technology to reduce the number of grid cells. By AMR, the local mesh resolutions can narrowly cover the Taylor microscale $l_T$ and direct numerical simulations (DNS) are performed. Both the instantaneous and mean hydrogen concentration distributions in the present jet are discussed. The instantaneous concentrations of hydrogen $C_{{\text{H}}_2}$ on the axis presents significant turbulent pulsating oscillations. The centerline value of the intensity of concentration fluctuation ${\stackrel{?}{\sigma }}_{{\text{H}}_2}$ asymptotically comes to 0.23, which is in a good agreement with the existing experimental results. It substantiates the conclusion that the asymptotic centerline value of ${\stackrel{?}{\sigma }}_{{\text{H}}_2}$ is independent of jet density ratio. The probability distributions function (PDF) of instantaneous axial $C_{{\text{H}}_2}$ agree approximately with the Gaussian distribution while skewing a little to the higher range. The time averaged hydrogen concentration ${\overline{C}}_{{\text{H}}_2}$ along the radial directions can also be described as a Gaussian distribution. The axial ${\overline{C}}_{{\text{H}}_2}$ of 82 MPa hydrogen jet tends to obey the distribution discipline approximated with ${\overline{C}}_{{\text{H}}_2}=4200/(z/\theta )$ where z is the axial distance from the nozzle and $\theta$ is the effective ejection diameter, which is consistent with the experimental results. In addition, the hydrogen tip penetration $Z_{\text{tip}}$ is found to be in a linear relationship with the square root of jet flow time $\sqrt{t}$. Meanwhile, the jet's velocity half-width $L_{\text{Vh}}$ approximately gains an linear relation with z which can be expressed as $L_{\text{Vh}}=0.09z$.     

Drag force acting on bubbles in a subchannel of triangular array of rods

Forces acting on spherical bubbles in a subchannel of a rod bundle with triangular rod arrangement (the pitch to diameter ratio is $P/D=1.34$) have been studied at low bubble Reynolds numbers O(0.1) ? O(1). The bubble motion has been simulated resolving the interface of the bubble by using the lattice Boltzmann method. Steady drag and virtual mass forces have been determined from the simulation results. Based on the simulation data, the relation $C_D=16.375/{\mathit{Re}}_T$ could be established between the steady drag coefficient $C_D$ and the terminal Reynolds number ${\mathit{Re}}_T$ when the diameter ratio $\lambda =d/D$ of the bubble d and the channel D is less than 0.2. It is found that the virtual mass coefficient can achieve as high value as 7.2, which is a consequence of strong wall effects. Considering interactions between bubbles, cooperation in the axial direction and hindering in the lateral direction could be observed. We demonstrate that the relation between the terminal velocity of a bubble and that of the suspension follows a Richardson–Zaki like correlation, but the exponent is not only a function of the Eotvos and Morton numbers, but it also depends on the particle configuration.     

Investigation on heat and mass transfer in hygroscopic random charged fiber webs

Hygroscopic charged fiber webs include a large number of interconnected capillaries formed by randomly distributed pores. The simultaneous heat and mass transfer in hygroscopic charged fiber webs is different from traditional flows in macro-channels resulted from the electrokinetic phenomena in micro-channels. In this paper, a mathematical model is presented with consideration of a quintic polynomial pore size distribution evaluated from a series of experiments and the electrokinetic phenomena resulting in a higher flow friction. The liquid diffusion coefficient in this model can be expressed as $D_l({\epsilon }_l)=\frac{\sigma \cos \phi {\sin }^2\beta (r_{\text{max}}-r_{\text{min}})n{\epsilon }_l^{n-1}}{4\mu (1+A·\Theta ){?}^{n-1}}\frac{{\Gamma }_1{\Delta }^4-{\Omega }_1}{{\Gamma }_2{\Delta }^4-{\Omega }_2{\Delta }^2}$. With specification of initial and boundary conditions, the governing equations are solved numerically and distributions of the temperature, the moisture concentration, and liquid water content in hygroscopic fiber webs are obtained. The comparison with the experimental measurements shows the rationality of this model in simulating the coupled heat and mass transfer in hygroscopic charged fiber webs with consideration of the electrokinetic phenomena.