Youjun Lu

Supercritical Water Gasification of Biomass and Organic Wastes

With the exhaustion of fossil fuels and the severe pollution of the environment, it’s urgent to find substitute renewable energy resources. Biomass is a kind of widespread and abundant renewable resource with lower sulfur content than fossil fuels, so the pollution to environment from biomass usage is much slighter than that from fossil fuels usage. Besides, zero emission of CO

Hydrogen Production by Supercritical Water Gasification of Biomass with Homogeneous and Heterogeneous Catalyst

Biomass gasification in supercritical water is a clean and efficient way to convert biomass to hydrogen-rich gaseous products. Appropriate catalyst can lower the reaction temperature to guarantee the technological and economic feasibility. This paper selects Ca(OH)2, Na2CO3, K2CO3, NaOH, KOH, LiOH, and ZnCl2 as typical homogeneous catalysts and three kinds of Raney-Ni, dolomite, and olivine as typical heterogeneous catalysts. The catalyst effects are investigated in the process of biomass gasification in supercritical water with the temperature of 400°C, pressure of MPa, and residence time of 20 min. The experimental results show that Raney-Ni has the best hydrogen selectivity and hydrogen yield. The mixture of NaOH with Raney-Ni was investigated in order to research the synergistic effect of different catalysts. The experimental results show that Raney-Ni and NaOH have a synergistic effect in the biomass gasification in supercritical water.

Numerical Study on the Mixed Convection Heat Transfer between a Sphere Particle and High Pressure Water in Pseudocritical Zone

Mixed convection heat transfer between supercritical water and particles is a major basic problem in supercritical water fluidized bed reactor, but little work focused on this new area in the past. In this paper, a numerical model fully accounting for thermophysical property variation has been established to investigate heat transfer between supercritical water and a single spherical particle under gravity. Flow field, temperature field and Nusselt number are analyzed based on the simulation results. Results show that buoyancy force has a remarkable effect on flow and heat transfer process. When the direction of gravity and flow are opposite, the gravity enhances the heat transfer before the separation point and inhibits the heat transfer after the separation point. When gravity is incorporated in calculation, a higher temperature gradient and a thinner boundary layer in the vicinity of the particle surface are observed before separation point, and the situations are just the reverse after separation point. Variation of specific heat and conductivity plays a main role in determination of heat transfer coefficient.

Catalysis in Supercritical Water Gasification of Biomass: Status and Prospects

High pressure and temperature demand containment structure of costly alloys for the supercritical water gasification (SCWG) apparatus. The catalyst is of great significance for realizing high gasification efficiency of biomass under milder circumstances in supercritical water (SCW). This chapter gives a comprehensive review on the original work in the area of catalysis in SCWG of biomass. The development status and role of different catalysts including homogeneous and heterogeneous catalysts used in SCWG were discussed. The alkali catalyst is a homogeneous catalyst, which has a key role in the SCWG of model compounds, biomass, organic wastes and coal. As a heterogeneous catalyst, Ni has been widely used in sub or supercritical water gasification due to its low cost and high activity. The crystallite sintering, supports’ breakdown and carbon deposition under SCW conditions will cause deactivation of catalysts. Therefore, the work of the Ni catalysts modification mentioned in this chapter is necessary and of great value.

Effect of cohesive powders on pressure fluctuation characteristics of a binary gas-solid fluidized bed

The effect of cohesive particles on the pressure fluctuations was experimentally investigated in a binary gas-solid fluidized bed. The pressure fluctuation signals were measured by differential pressure sensors under conditions of various weight percentages of cohesive particles. The cohesive particles increased the fixed bed pressure drop per unit height and decreased the minimum fluidization velocity. The Wen & Yu equation well predicts the minimum fluidization velocity of the binary system. The addition of cohesive particles slightly decreased the bubble size in bubbling flow regime when the cohesive particles and the coarse particles mixed well, while the bubble size greatly decreased when the cohesive particles agglomerated on the bed surface. The time series of pressure fluctuations was analyzed by using the methods of time domain, frequency domain and wavelet transformation. The normalized standard deviation of pressure fluctuations decreased with increasing weight percentages of cohesive particles. A wide bandwidth frequency of 0 to 1Hz got narrower with a single peak around 0.6Hz with an increase in proportion of the cohesive particles. The meso-energy and micro-energy of pressure fluctuations were decreasing with increasing cohesive particles proportions, which indicated that adding cohesive particles could reduce the energy dissipation of bubble and particle fluctuations.