Supercritical Water Gasification Technology Research Articles

CFD modeling of sawdust gasification in a lab-scale entrained flow reactor based on char intrinsic kinetics. Part 2: Parameter study and multi-objective optimization

Supercritical water gasification technology is widely applied to convert organic waste into valuable substances as a clean and efficient method. Biomass gasification in SCW is a complex process and complicated chemical reactions like decomposition and poly-condensation take place, thus, reaction mechanism of real biomass needs to be further investigated. In this paper, experimental study on cornstalk gasification in SCW was conducted at the temperature of 500–800 °C, reaction time of 1–15min and feedstock concentration of 1–9%. The effects of various operating parameters on evolution of gas, liquid and solid products were conducted. It was discovered that pore structure and carbon microspheres appeared successively on the surface of solid residue. Mechanism study showed that the biomass was first depolymerized into monomer and its derivatives, then cracked and poly-condensed into a nuclear to generate carbon microspheres as its concentration reached the critical concentration. As the reaction proceeds, reduction reaction, coke combustion and secondary reaction occurred, thus carbon microspheres decreased. The results indicated that higher reaction temperature, longer reaction time and lower feed concentration were conducive to improving reaction performance of biomass. Finally, it was discovered that carbon gasification efficiency reached 99% at the temperature of 700 °C, reaction time of 15 min and biomass concentration of 3%.

Experimental study on hydrogen production by lignite gasification in supercritical water fluidized bed reactor using external recycle of liquid residual

The technology of supercritical water gasification provides a novel way to convert high-moisture lignite to hydrogen-rich products directly. According to the energy analysis of the whole system for supercritical water gasification, the energy recovery of liquid residual played a key role in the energy efficiency improvement. Moreover, previous research findings showed that some chemical compounds such as phenols and formic acid contained in liquid residual can be recycled to increase the yield of hydrogen. Therefore, an external recycle of liquid residual was used in the supercritical water fluidized bed system to recover not only the heat energy but also the chemical energy by re-gasification of the liquid residual. Besides, the separation of gaseous products from the system enhanced the gasification process. Hydrogen production experiments were operated in this system and the influence of operating temperature 470–550°C, pressure 23–27MPa, concentration 3–35wt% and cycling flow rate 0–70g/min were studied. The experimental results showed that hydrogen yield and carbon gasification efficiency reached 32mol/kg and 82%, respectively, at 530°C.

Experimental Investigation on the Gasification Kinetic Model of a Char Particle in Supercritical Water

Supercritical water gasification technology has bright prospects because it can convert biomass into hydrogen-rich gaseous products in an effective and clean way. The devolatilization process is relatively fast, and char conversion is the rate-determining step in the whole gasification process. To discuss the kinetic model of char gasification in supercritical water, the quartz tube reactor was adopted as the reactor to omit the undesired catalytic effect of the reactor wall and bamboo charcoal was selected as typical char as a result of the low volatile content. The experiments were investigated within the operating range of temperatures of 700–900 °C and residence times of 5–20 min. The experimental results were analyzed within the framework of homogeneous, non-reacted core, and random pore models. Dependences of the carbon gasification rate, residence time, and temperature were described in an assumption of the first-order reaction and the Arrhenius dependence. The calculation results showed that the r...

Supercritical Water Gasification of Biomass: A Literature and Technology Overview

The supercritical water gasification process is an alternative to both conventional gasification as well as anaerobic digestion as it does not require drying and the process takes place at much shorter residence times; a few minutes at most. The drastic changes in the thermo-physical properties of water from the liquid state to the supercritical state make it a promising technology for the efficient conversion of wet biomass into a product gas that after upgrading can be used as substitute natural gas. The earliest research goes back as far as the 1970s and since then, supercritical water has been the subject of many research works in the field of thermochemical conversion of wet biomass. This article reviews the state of the art of the supercritical water gasification technology starting from the thermophysical properties of water and the chemistry of reactions to the process challenges of such a biomass based supercritical water gasification process plant.

Economic analysis of a combined production of hydrogen-energy from empty fruit bunches

This work relates to an economic analysis and a comparison between different process solutions for the production of hydrogen and the co-production of hydrogen and energy by means of a zero emission biomass integrated supercritical water gasification (SCWG) and combined cycle power plant. The case study will be located in Malaysia. Energy will be produced in agreement with the Small Renewable Energy Power Plant (SREP) Program, promoted by the Government of Malaysia. Hydrogen is obtained by supercritical water gasification (SCWG) of empty fruit bunches (EFB), a technology of interest for the processing of biomass with high moisture content. The economic analysis has been carried out to demonstrate the feasibility of the process solutions and to compare their convenience. The feedstock is 35 Mg h−1 of empty fruit bunches (EFB), a biomass obtained in the Palm Oil Industry. The location of the site is Teluk Intak District in the State of Perak (Malaysia). The study is performed with Aspen Plus® V7.2. The aim of this work is to investigate the economic convenience of supercritical water gasification technology applied to a potential industrial case study in order to state the possibilities and the trade-off for the production of hydrogen and the co-production of hydrogen and energy from biomass, using an innovative technology (SCWG) instead of a typical unit for syngas and energy production. The processes have been developed to reach zero emissions and zero wastes. CO2 and solid residuals are recycled inside palm oil lifecycle.

Hydrogen production by coal gasification in supercritical water with a fluidized bed reactor

The technology of supercritical water gasification of coal can converse coal to hydrogen-rich gaseous products effectively and cleanly. However, the slugging problem in the tubular reactor is the bottleneck of the development of continuous large-scale hydrogen production from coal. The reaction of coal gasification in supercritical water was analyzed from the point of view of thermodynamics. A chemical equilibrium model based on Gibbs free energy minimization was adopted to predict the yield of gaseous products and their fractions. The gasification reaction was calculated to be complete. A supercritical water gasification system with a fluidized bed reactor was applied to investigate the gasification of coal in supercritical water. 24 wt% coal-water-slurry was continuously transported and stably gasified without plugging problems; a hydrogen yield of 32.26 mol/kg was obtained and the hydrogen fraction was 69.78%. The effects of operational parameters upon the gasification characteristics were investigated. The recycle of the liquid residual from the gasification system was also studied.

Hydrogen production from coal gasification in supercritical water with a continuous flowing system

The technology of supercritical water gasification can convert coal to hydrogen-rich gaseous product efficiently and cleanly. A novel continuous-flow system for coal gasification in supercritical water was developed successfully in State Key Laboratory of Multiphase Flow in Power Engineering (SKLMF). The experimental device was designed for the temperature up to 800 °C and the pressure up to 30 MPa. The gasification characteristics of coal were investigated within the experimental condition range of temperature at 650–800 °C, pressure at 23–27 MPa and flow rate from 3 kg h −1 to 7 kg h −1. K 2CO 3 and Raney-Ni were used as catalyst and H 2O 2 as oxidant. The effects of main operation parameters (temperature, pressure, flow rate, catalyst, oxidant, concentration of coal slurry) upon gasification were carried out. The slurry of 16 wt% coal + 1.5 wt% CMC was successfully transported into the reactor and continuously gasified in supercritical water in the system. The hydrogen fraction reached up to 72.85%. The experimental results demonstrate the bright future of efficient and clean conversion of coal.

Detailed Analysis of Heat and Mass Balance for Supercritical Water Gasification

The process energy efficiency of supercritical water gasification was determined by a detailed calculation of the energy balance. Ten tons (wet) per day of chicken manure, the moisture content of which was adjusted, was employed as the model feedstock. An efficiency ratio of 70% was obtained for chicken manure having a water content of 80%. The key operating parameters for ensuring high process energy efficiency were the heating value of feedstock and heat recovery efficiency. This result, along with the heat exchanger efficiency measured in the pilot plant, clearly indicates the high potential of supercritical water gasification technology as a wet biomass gasification process.

Hydrogen production by biomass gasification in supercritical water: A systematic experimental and analytical study

Hydrogen production from biomass gasification in supercritical water is a new technology, which was developed in last two decades. Biomass energy of low quality can be converted to hydrogen energy of high quality by supercritical water gasification. Particularly, supercritical water gasification is an elegant way of wet biomass utilization. Up to now, many important progresses have been made in supercritical water gasification technology by the studies of researchers around the world. Since 1997, supercritical water gasification, which include reaction system, rule of biomass gasification and theory, have been studied in State Key Laboratory of Multiphase Flow in Power Engineering of Xi’an Jiaotong University. In this paper, we summarize the results from systematic experimental and analytical study on biomass gasification in supercritical water in our laboratory. Also, the development status and future prospect on supercritical water gasification is evaluated.

The flow characteristics of an interactive particle at low Reynolds numbers

For any flow process of mixtures containing dispersed reactive particles, especially highly concentrated particles, the particle-particle, and fluid-particle interactions are very complex and affect the overall flow. Supercritical water gasification technology is a complex multiphase-flow process that occurs in high-temperature reactors. Under these conditions, the components of the particle surface are heated and gasify to form a Stefan flow (i.e., a mass flow), which modifies fluid-particle interactions. The interaction between particles and the influence of Stefan flow cannot be ignored. In this work, we consider the simplest case of two identical spherical particles with different relative orientations and particle distances and discuss the flow and fluid-particle heat-transfer characteristics by numerical simulation of supercritical water flowing around the fixed two-particle system. We are particularly interested in the fluid-particle interactions with different particle configurations under the influence of Stefan flow. Three particle configurations are possible: tandem, cross, and parallel. The flow field, Nusselt number, drag coefficient, and temperature distribution around the particles are all analyzed. In comparison with a single particle, the two-particle configurations significantly affect the drag coefficient, Nusselt number, and vortex structure and Stefan flow strongly affects the wake vortex structure of two particles with small particle distance, reducing the drag coefficient and Nusselt number.