Hydrogen Gasification Efficiency Research Articles

Influence of NaOH and Ni catalysts on hydrogen production from the supercritical water gasification of dewatered sewage sludge

Dewatered sewage sludge was treated with NaOH additive and Ni catalyst in supercritical water in a high-pressure autoclave to examine the effects of separate and combined NaOH additive and Ni catalyst on hydrogen generation. The effects of Ni/NaOH ratio on hydrogen production were also investigated to identify possible catalytic mechanism and interactions. NaOH and Ni, separately or in combination, improved the hydrogen production and hydrogen gasification efficiency. The addition of NaOH additive not only promoted the water–gas shift reaction, but also favored H2 generation of Ni catalyst by capturing CO2. The hydrogen yield of combined catalysts with different Ni/NaOH ratios was higher than the theoretical sum of hydrogen yield from the mixture by 10–33%. The largest hydrogen yield, of 4.8 mol per kilogram of organic matter, which was almost five times as much as without catalyst, was achieved with the addition of 3.33 wt% Ni and 1.67 wt% NaOH. The combined NaOH additive and Ni catalyst also improved the gasification of several other dewatered sewage sludges, increasing the hydrogen yield by four to twelve times that seen without catalyst. Combined NaOH additive and Ni catalyst are effective in dewatered sewage sludge gasification at low temperature.

Thermo-Chemical Analysis of Biomass Gasification by Gibbs Free Energy Minimization Model-Part: II (Optimization of Biomass Feed and Steam to Biomass Ratio)

Thermo-chemical gasification of biomass with steam is an effective way for yielding higher hydrogen concentration and better lower heating value (LHV) of the producer gas. But the major limiting factor for steam gasification is the energy requirement for steam production. Biomass feed necessitates adequate amount of steam for achieving better hydrogen yield in gasification. Thus, the estimation of optimum values of steam to biomass mass ratio (SBR) and biomass feed is necessary such that these variables maximize the hydrogen concentration, LHV, and energy efficiency. This article presents a thermodynamic equilibrium model based on minimization of Gibbs free energy with gases obeying Redlich--Kwong (R--K) real gas equation of state. The objective is to arrive at a global optimum point for steam gasification of biomass in terms of SBR and biomass feed. Simulations are carried out in MATLAB® with simulated annealing (SA) algorithm for achieving the global minima. The parametric variations are studied by varying SBR, biomass feed, and both in order to get the concentration of gases, LHV, and efficiencies of the resulting mixture, for arriving at the optimum utilization of biomass and gasifying agent. In addition, variations in cold gas efficiency, hydrogen gasification efficiency and total gas yield are also investigated. The simulated results are validated with existing experimental and model results. For maximum specific LHV, energy performance, and hydrogen concentration, the global optimum value arrived for SBR is 0.8 per unit mass of biomass gasified. Sensitivity analysis is conducted for the model to investigate the effect of variables on the optimized process.

Effect of Reaction Temperature and Type of Catalyst on Hydrogen Production in Supercritical Water Gasification of Biomass

The aim of this study was to investigate the feasibility of hydrogen production from sugarcane bagasse by supercritical water gasification (SCWG) at low temperature and in presence of alkali catalyst. Experiments were carried out in a batch autoclave reactor at 400 °C and 9% solid content. Effect of reaction time and alkali catalyst on gas yield, gas composition, carbon gasification efficiency (CGE) and hydrogen gasification efficiency (HGE) were investigated. Influence of reaction time on gas yield and composition as well as on CGE was found to be insignificant. Extending the reaction time even up to 4 h could not cause an attractive conversion of bagasse. In the presence of catalysts (K CO , KHCO , NaHCO and NaOH), sugarcane

Experimental research on catalysts and their catalytic mechanism for hydrogen production by gasification of peanut shell in supercritical water

Peanut shell, mixed with sodium carboxymethyl-cellulose, was gasified at a temperature of 450°C and a pressure range from 24 to 27 MPa with the presence of different catalysts, including K2CO3, ZnCl2 and Raney-Ni. The experimental results show that different catalysts have greatly different effects on the reaction. Gasification efficiency (GE), hydrogen gasification efficiency (GHE), carbon gasification efficiency (GCE), yield of hydrogen production \((Y_{H_2 } )\) and potential yield of hydrogen production \((Y_{PH_2 } )\) are applied to describe the catalytic efficiency. From the result of gaseous components, ZnCl2 has the highest hydrogen selectivity, K2CO3 is lower, and Raney-Ni is the lowest, but Raney-Ni is the most favorable to gasify biomass among the three catalysts, and its GE, GHE, GCE reach 126.84%, 185.71%, 94.24%, respectively. As expected, hydrogen selectivity increased and CH4 reduced rapidly when the mixture of ZnCl2 and Raney-Ni is used under the same condition. The optimization mixture appeared when 0.2 g of ZnCl2 was added to 1 g of Raney-Ni, 43.56 g·kg−1 of hydrogen production was obtained. In addition, the catalytic mechanisms of different catalysts were analyzed, and the possible reaction pathway was brought forward, which helped to explain the experiment phenomena and results correctly.