Fluidized-bed Reformer Research Articles

Hydrogen production from biomass via moving bed sorption-enhanced reforming: Kinetic modeling and process simulation

This study explored a process intensification approach for hydrogen production through biomass gasification. Sorption-enhanced reforming (SER) in an autothermal countercurrent moving bed reformer is proposed as an alternative to multiple units traditionally required for syngas conditioning. This process utilizes the selective sorption and catalytic properties of calcium oxide to integrate multiple reforming reactions into a moving bed reactor. A multistage kinetic model was used to analyze and optimize the key operating parameters of the reformer. Results showed that the moving bed reformer completely converts all tars and increases the hydrogen concentration of syngas from 23 mol% to 80 mol% (dry basis). A comparison between equally sized models showed that the moving bed reformer outperforms a fluidized bed reformer under similar conditions. Simulation of the entire process showed that the hydrogen yield of the proposed SER process is 5% higher than the conventional process. In addition, the proposed process produces surplus electricity, while the conventional process has a 26% power deficit. The overall efficiency of the proposed process is 3.5% higher than the conventional process. The improved process efficiency, coupled with the potentially lower costs of a streamlined process, indicates that the proposed process is a promising route for green hydrogen production.

Small-scale production of synthetic natural gas by allothermal biomass gasification

The gasification of biomass can be coupled to a downstream methanation process that produces synthetic natural gas (SNG). This enables the distribution of bioenergy in the existing natural gas grid. A process model is developed for the small-scale production of SNG with the use of the software package Aspen Plus (Aspen Technology, Inc., Burlington, MA, USA). The gasification is based on an indirect gasifier with a thermal input of 500 kW. The gasification system consists of a fluidized bed reformer and a fluidized bed combustor that are interconnected via heat pipes. The subsequent methanation is modeled by a fluidized bed reactor. Different stages of process integration between the endothermic gasification and exothermic combustion and methanation are considered. With increasing process integration, the conversion efficiency from biomass to SNG increases. A conversion efficiency from biomass to SNG of 73.9% on a lower heating value basis is feasible with the best integrated system. The SNG produced in the simulation meets the quality requirements for injection into the natural gas grid. Copyright © 2012 John Wiley & Sons, Ltd.

Producer gas cleaning in a dual fluidized bed reformer—a comparative study of performance with ilmenite and a manganese oxide as catalysts

Secondary catalytic gas conditioning is one strategy to eliminate tars formed in a producer gas during biomass gasification. However, most catalysts tend to lose their tar reforming activity after a short period of operation due to carbon formation. A novel technique for catalytic gas cleaning based on two interconnected fluidized beds has been investigated; this technique can be applied to all types of gasifiers. The idea is to reform the tar components into useful molecules—even at high tar contents—by means of a circulating catalyst. More precisely, the producer gas is cleaned with catalyst in one of the reactors, referred to as the fuel reactor, while the catalyst is continuously regenerated in another reactor, the air reactor (AR). The system described here is coupled with the Chalmers 2–4 MWth biomass gasifier while the AR is fed with nitrogen-diluted air. The effect of different catalysts on both the tar content and the gas composition was investigated. Some of the tested materials do not only reform tars, they also influence the H2/CO ratio in a beneficial manner; in particular, ratios closer to 3 in the reformed gas are favorable if subsequent methanation is implemented. In this paper, comparative results based on testing with manganese- and iron-based catalysts are presented. The former is a manufactured catalyst while the latter is a natural ore. Results suggest that both show satisfying ability for regeneration from carbon deposits. Higher temperature enhances tar decomposition during the experiment with both catalysts. Moreover, the iron-based catalyst enhances the water–gas shift activity, which in turn impacts the total amount of produced gas. On the other hand, the manganese-based catalyst seems to display a higher propensity for tar conversion.

CO2 capture with calcined dolomite: the effect of sorbent particle size

This investigation is set in the more comprehensive study of an innovative fluidized bed reformer configuration for producing hydrogen from either biomass/coal syngas or natural gas, in which capture of carbon dioxide by-product occurs in parallel with steam reforming and water–gas shift reactions. Reported here are experimental data of carbon dioxide absorption by particles of calcined dolomite included in a bed of otherwise inert material; the bed, initially fluidized by nitrogen, was subjected to a step concentration input of carbon dioxide and the sorption kinetics was obtained from the outlet response of the entire system. The influence of dolomite particle size was investigated—from 98 to 1,550 μm—and a previously developed grain model was used to relate the observed effect of particle diameter to the complex mechanism of carbon dioxide capture in a solid sorbent. The results show that pore shrinking effects during the carbon dioxide capture process become increasingly more significant as the particle size is increased.

CO2 Capture and Hydrogen Production in an Integrated Fluidized Bed Reformer-Regenerator System

Thermodynamic analysis of CO2 capture and hydrogen production for steam methane reforming was carried out using ASPEN simulation software. The integrated reaction system is composed of a sorbent-enhanced fluidized bed reformer coupled with a fluidized bed sorbent regenerator (calciner) where fine CaO-based sorbents (∼100 μm mean particle diameter) were used. The system performance is evaluated as a function of a number of operating parameters for both the reformer and regenerator. The results indicate that the optimum operating parameters for reformer are temperatures from 550 to 600 °C, low pressure, steam-to-carbon molar feed ratio of 3.5, and sorbent circulation flow rate exceeding the minimum stoichiometric feed rate of active sorbent. For the sorbent regenerator, the optimum conditions are temperatures above 850 °C, low pressure, and enough sweep gas flow to completely calcine CaCO3. On the basis of thermodynamics, it should be possible to achieve a hydrogen purity of ∼98% and a CO2 purity in excess ...

Two‐Phase Sequential Simulation of a Fluidized Bed Reformer

AbstractA two‐phase flow model is adapted in order to predict the performance of a fluidized bed reformer using the sequential modular simulator. Since there are physical and chemical phenomena interacting in the reformer, two sub‐models appear to be necessary to describe the overall model. These are the hydrodynamic and reaction sub‐models. The hydrodynamic sub‐model is based on the dynamic two‐phase model and the reaction sub‐model is derived from the literature. In the overall model, the bed is divided into several sections. At each section, the flow of the gas is considered as plug flow through the bubble phase and to be perfectly mixed through the emulsion phase. Two sets of experimental data from the literature at different hydrodynamic regimes were used in order to validate the proposed model. A close agreement was observed between the model predictions and the experimental data. The model proposed in this work may be used as a framework for the development of sophisticated models for non‐ideal reactors inside process simulators.

Simulation of effect of catalytic particle clustering on methane steam reforming in a circulating fluidized bed reformer

Abstract Effect of catalytic particle clustering on methane steam reforming in a circulating fluidized bed (CFB) reformer is analyzed numerically using a two-dimensional hydrodynamic model coupling with methane steam reforming reaction kinetics. Gas flow fields and distributions of temperature and gas species in a Haldor Topsoe Ni/Mg Al2O4 spinel catalytic particle cluster are predicted. The computed results indicate that the rates of methane steam reaction of a catalyst particle in the cluster are less than that of an isolated catalyst particle out side the cluster. The yields of H2, CO and H2O in the cluster increase with the increase of operating temperature and inlet gas velocity but decrease with the increase of reactor pressure and feed steam.

Coupled Steam and Oxidative Reforming for Hydrogen Production in a Novel Membrane Circulating Fluidized-Bed Reformer

A novel circulating fluidized-bed membrane reactor employing a reactor-regenerator type of configuration is proposed for hydrogen production by the steam reforming of natural gas. The removal of hydrogen through hydrogen-permeable membranes pushes the equilibrium toward higher production of hydrogen. In the present paper, modeling studies are carried out on the reactor section of this configuration. Cases with and without hydrogen-selective membranes (cocurrent and countercurrent) are considered and compared. The model results show the great advantages associated with the breaking of the thermodynamic limitations coupled to the hydrodynamic limitations associated with the previous generations of bubbling fluidized-bed reformers. It is shown that autothermal operation can be achieved through simultaneous oxidative reforming, giving high hydrogen yields and productivities with low net consumption of energy.

Steam reforming of a clean model biogas over Ni/Al 2O 3 in fluidized- and fixed-bed reactors

Simultaneous steam, carbon dioxide reforming of methane was conducted over 11.5 wt.% Ni/Al 2O 3, at 1 atm in micro-fluidized- and fixed-bed reactors using a constant molar ratio of CH 4/CO 2≈1.5 as a model biogas. The performance of a fluidized reactor was compared to that of a fixed-bed reactor under similar conditions (feed gas to steam ratios of 1.5 and 0.75 at a reactor temperature of 750 °C, GHSV of 300 min −1). Conversions of CH 4 and CO 2 were 75 and 67%, respectively, in a fixed-bed reactor under the ratio of 1.5. Overall higher conversions (7–15%) were observed in the fluidized-reforming reactor. The initial activity of the fixed-bed reformer decreased rapidly and massive carbon deposition caused reactor blockage at the low steam concentration. Decreased the feed gas to steam ratio to 0.75 reduced carbon deposition and the nature of the carbon was suggested not to be the cause of the catalytic enhancement of the fluidized reforming. A study of the fluidized-bed reformer under decreasing feed gas to steam ratios from 3.0 to 0.3 showed an almost complete CH 4 conversion (98% for feed gas to steam ratios below 1.0). With decreasing feed gas to steam ratio the H 2/CO ratios increased as expected from 1.5 to 2.7. At the highest feed gas to steam ratio, a poor catalyst fluidization was observed due to massive carbon deposition, which was reduced dramatically when steam was provided in excess. Increasing temperatures from 650 to 850 °C enhanced both conversions and lowered H 2/CO ratios.

Novel Circulating Fluidized-Bed Membrane Reformer for the Efficient Production of Ultraclean Fuels from Hydrocarbons

An integrated novel fluidized-bed membrane steam reformer for the efficient production of hydrogen is proposed and investigated. It consists of two connected subsystems, viz., a circulating fluidized-bed membrane reformer and a reactor−regenerator for dry reforming. The steam-reforming part is an extension of the previous successful work regarding a bubbling fluidized-bed membrane reformer. The fast fluidization regime is more efficient and productive than the bubbling regime. Hydrogen-permeable membranes to remove hydrogen are used together with a CO2 acceptor to remove carbon dioxide and enhance the performance. An in situ supply of heat through oxidative steam reforming is also suggested. The deactivated catalyst is regenerated and recirculated back to the reformer. The CO2-rich stream from the efficient fast fluidized membrane steam reformer is used in a reactor−regenerator dry reforming subsystem, and additional syngas is produced. A reliable reaction engineering model is utilized to investigate this novel configuration. A comparison between the predicted performance of the fast fluidized-bed reformer and the industrial data for a fixed bed as well as the pilot-plant data of the bubbling fluidized-bed configurations investigated earlier shows that the fast fluidized bed is more efficient and productive.