Dual Fluidized Bed System Research Articles

Numerical simulation of hydrogen production by chemical looping reforming in a dual fluidized bed reactor

Although exploitation of Dual Fluidized Bed systems (DFB) is currently being explored in various fields, DFBs present some criticalities, mainly related to effective control of solids recirculation and to avoidance of gas leakage between the beds, extremely critical in Chemical Looping Reforming (CLR) for hydrogen production. For the latter, the choice of the degree of oxygen carrier oxidation/reduction, operation temperature and loop design makes the design even more challenging. This paper aims at the quantitative assessment of the influence of design variables by means of the numerical simulation of a DFB-CLR process operated at steady state conditions. The model couples a simple hydrodynamic simulation of a DFB system equipped with non-mechanical valves for bed solids circulation with a 1D, dynamic and non-isothermal CLR model developed to determine temperature and oxidation degree of solids and gaseous species concentration at the exit of both Air and Fuel Reactors. The DFB, consisting of a riser and of a bubbling fluidized bed (BFB) as Air and Fuel Reactors respectively, was modeled as a combination of interconnected blocks (riser, cyclone, L-valve, BFB, loop-seal) after selection of constitutive equations. Methane and Nickel (II) oxide were selected as fuel and oxygen carrier.Results corresponding to steady state operation are presented and the effects of operating conditions on the expected process performance are assessed. It is concluded that an appropriate choice of both operating temperature and amount of oxygen transported by oxygen carrier from AR to FR is an essential prerequisite in order to ensure process feasibility and good performances in terms of CH4 conversion and H2 selectivity.

Operating parameter effects on the solids circulation rate in the CFD simulation of a dual fluidized-bed gasification system

The solids circulation is crucial for sustaining biomass gasification within dual fluidized-bed gasification systems, because the heat utilization between the gasifier and combustor is mainly implemented through the circulation of bed material. In this work, a three-dimensional model was established to simulate the hydrodynamics of a dual fluidized-bed gasification system. The purpose of this work was to find effective ways to improve the solids circulation. In this CFD (computational fluid dynamics) model, the MP-PIC (multiphase particle-in-cell) method was applied to simulate the gas-solid flows in the dual fluidized-bed system. This model simulated the hydrodynamics of the bubbling fluidized-bed gasifier, chute, pneumatic-riser combustor, cyclone separator, and loop-seal in the dual fluidized-bed system. Studies of grid resolution and numerical parcel were conducted to examine the model accuracy. A series of case studies were implemented to investigate the impact of operating parameters on the solids circulation rate, such as particle diameter, solid inventory, steam supply to gasifier, and air supplies to combustor.

CFD studies on biomass gasification in a pilot-scale dual fluidized-bed system

A comprehensive CFD (Computational Fluid Dynamics) model using the MP-PIC (Multiphase Particle-In-Cell) method was developed to simulate a pilot-scale (6 tons/day, 1 MW th) dual fluidized-bed biomass gasification system. In this model the particulate phase was described with the blended acceleration model. The momentum, mass, and energy transport equations were integrated with the kinetics of heterogeneous biomass and char reactions and homogeneous gas-phase reactions to predict the particle circulation, producer gas composition, and reactor temperature. The simulation results were compared with experimental data from the pilot-scale gasification system to validate the model at different operating conditions. Parametric studies were conducted to investigate the impact of gasifier temperature, steam to biomass ratio (S/B), and air supply to the combustor on the producer gas composition. The studies showed that increasing gasifier temperature and steam to biomass ratio (S/B) promoted syngas (CO + H2) production and increased hydrogen content in producer gas. The effect of air supply was minor, because for the dual fluidized-bed system air was not directly involved in biomass gasification.

Influence of coated olivine on the conversion of intermediate products from decomposition of biomass tars during gasification

Steam gasification of solid biomass in dual fluidized bed systems is a suitable technology for the production of chemicals, fuels for transportation, electricity, and district heating. Interaction between biomass ash and bed material leads to the development of Ca-rich bed particle layers. Furthermore, incomplete decomposition of biomass leads to the formation of tar components; among these are stable intermediate products such as 1H-indene and stable gaseous hydrocarbons such as methane. In this work, the influence of bed particle layers on the conversion of intermediate products such as 1H-indene and methane via steam reforming was investigated by conducting experiments in a lab-scale test rig. Satisfying conversion of 1H-indene into gaseous molecules (e.g., CO, CO2, H2) was achieved with used, layered olivine, whereas fresh olivine showed significantly poorer performance. Since steam reforming was connected to the water-gas-shift reaction for the tested hydrocarbons, investigations regarding carbon monoxide conversion in the presence of steam were conducted as well. Furthermore, a comparison of the influence of fresh and used bed material concerning the conversion of methane is presented, showing that methane is not affected by the bed material, independent of the presence of particle layers.

CFD Simulations of Complete Circulating Dual Fluidized Bed Systems for Chemical Looping Combustion

CFD Simulations of Complete Circulating Dual Fluidized Bed Systems for Chemical Looping Combustion

Comparison of Direct Combustion in a Circulating Fluidized Bed System and Decoupling Combustion in a Dual Fluidized Bed System for Distilled Spirit Lees

At present in China, a fluidized bed combustor is not suitable to treat a high-water-containing (30–60 wt %) industrial biomass residue, such as distilled spirit lees (DSL), which can cause a low bed temperature and inflammation retardation. Our previous fundamental studies showed that the so-called dual fluidized bed gasification decoupling combustion technology (or decoupling combustion for short) can ensure the highly efficient and stable combustion for high-water-containing biomass fuel and lower NOx emission as well. In this study, the combustion characteristics of DSL in a circulating fluidized bed (CFB) system and a dual fluidized bed (DFB) system will be examined and compared systematically. For direct combustion of DSL in a CFB system, the high moisture of 30 wt % decreased the bottom temperature of the combustor significantly and brought in unstable combustion, thus leading to s large amount of auxiliary fuel (such as coal) needed to raise the temperature to reach an adiabatic flame temperature ...

An Eulerian Approach to Computational Fluid Dynamics Simulation of a Chemical-Looping Combustion Reactor With Chemical Reactions

Chemical-looping combustion (CLC) is a next-generation combustion technology that shows great promise in addressing the need for high-efficiency low-cost carbon capture from fossil fueled power plants. Although there have been a number of experimental studies on CLC in recent years, computational fluid dynamics (CFD) simulations have been limited in the literature. In this paper, simulation of a CLC reactor is conducted using the Eulerian approach in the commercial CFD solver ansys fluent based on a laboratory-scale experiment with a dual fluidized bed CLC reactor. The solid phase consists of a Fe-based oxygen carrier while the gaseous fuel used is syngas. The salient features of the fluidization behavior in the air reactor and fuel reactor beds representing a riser and a bubbling bed, respectively, as well as the down-comer, are accurately captured in the simulation. This work is among the few CFD simulations of a complete circulating dual fluidized bed system for CLC in 3D in the literature. It highlights the importance of 3D simulation of CLC systems and the need for more accurate empirical reaction rate data for future CLC simulations.

Influence of bulk solids cross-flow on lateral mixing of fuel in dual fluidized beds

In typical dual fluidized bed systems — used e.g. in chemical looping combustion or indirect gasification of biomass for production of second-generation biofuels — the bulk solids are continuously circulating between a tall high-velocity riser and a bubbling bed. This circulation results in a solids cross-flow in the bubbling bed, which creates a net convective solids flow. The aims of this paper are to describe this convective flow by means of mathematical modeling and to investigate the effect of the cross-flow of bulk solids on the lateral mixing of fuel particles.Experiments relevant for industrial conditions are carried out in a fluid dynamically downscaled cold flow model of an existing indirect gasifier. It is found that the velocity field of the bulk solids induced by the solids cross-flow can be described by a potential function obtained from a diffusion equation. As for the fuel particles, their slip respect to the bulk solids cross-flow is quantified using a cross-flow impact factor, θ, which is found to be a linear function of fluidization velocity and in the range 0.18–0.68 for the conditions investigated. Finally, we conclude that the fuel mixing in fluidized beds with a significant cross-flow of bed material can be described by a convection–diffusion equation.

Integration of a Gas Switching Combustion (GSC) system in integrated gasification combined cycles

Chemical Looping Combustion (CLC) is a promising technology for achieving economically viable CO2 capture from fossil fuel energy conversion processes. However, complexities and costs surrounding the standard interconnected fluidized bed concept for CLC have prompted the investigation of alternative process configurations. This paper investigates one such configuration, Gas Switching Combustion (GSC), via combined reactor and process modelling. The GSC concept utilizes a standard bubbling/turbulent fluidized bed reactor where an oxygen carrier material is alternatively exposed to feeds of air and fuel (syngas from coal gasification in this case). This configuration maintains the good mixing characteristics of fluidized bed reactors while eliminating the solids handling challenges related to the standard dual fluidized bed system. It was shown that a cluster of GSC reactors operating in a well-controlled manner could supply sufficiently steady streams to a downstream gas turbine and CO2 purification and compression unit. The simplest configuration where fuel and air are fed alternatively to the reactors, with steam purging but no advanced heat management procedures returned a significantly higher electric efficiency (40.7%) than a baseline IGCC plant with currently available gas turbine and CO2 capture technology (35.3%), while also achieving slightly higher overall CO2 avoidance. It was also shown that there exists significant scope for trading further increases in electric efficiency for reductions in overall CO2 avoidance through adjustment of the reactor operating strategy. More complex purging and heat management strategies could further improve the electric efficiency to as high as 41.9%, with overall CO2 avoidance higher than 90%.

Experimental Study of a Carbon Stripper in Solid Fuel Chemical Looping Combustion

In chemical looping combustion of solid fuels, carbon slip from the fuel reactor to the air reactor is a critical issue. This paper presents the design and experimental evaluation of a carbon stripper (CS) in a cold flow model of a 70 kW chemical looping combustor of solid fuels. In the dual fluidized bed system, stable long-term operation was achieved. Plexiglas beads simulating the behavior of fuel particles were mixed with ilmenite particles to study the separation characteristics of the carbon stripper. The factors affecting the carbon stripper performance, such as the gas velocity in the carbon stripper, the solids circulation rates, and the inner structure of the carbon stripper, were experimentally investigated. The results showed that the separation efficiency of the Plexiglas beads was in the range of 0 to 60%. The carbon stripper added 160% additional residence time in the reducing atmosphere for the fuel particles.

Experimental and numerical investigation of the dynamics of loop seals in a large‐scale DFB system under hot conditions

The dynamics of the loop seals in a large‐scale dual fluidized bed (DFB) system is investigated as a function of variations in the flux of the bed material through the seal and changes in the bed material density. These investigations are performed numerically with a computational fluid dynamics (CFD) model and experimentally for the loop seals of the Chalmers 2–4 MWth DFB gasifier. Both experiments and simulations show that more of the aeration gas leaves the loop seal in the direction of the solids when a low‐density bed material (silica) is used rather than a high‐density one (bauxite). The simulations also reveal homogeneous fluidization in a vertical connection to the loop seal, whereas an inclined connection yields heterogeneous fluidization. The minor discrepancies between the experiments and simulations with silica are attributed to particle agglomeration, and it is proposed that CFD models applied to loop seals should account for this phenomenon. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3580–3593, 2015

Calcium looping process simulation based on an advanced thermodynamic model combined with CFD analysis

Abstract The current study presents a new methodology for the simulation of the Calcium Looping (CaL) process based on the coupling of CFD and advanced thermodynamic models. As a first step, CFD models for the two reactors, i.e. the carbonator and the calciner, of a pilot scale Dual Fluidized Bed system are developed and validated by comparing the numerical predictions with corresponding experimental data for pressure distribution, carbonator capture efficiency and sorbents regeneration in the calciner. For the carbonator modeling, the Two-Fluid-Model (TFM) approach is combined with the advanced EMMS scheme in order to provide results with high accuracy, even for the difficult to model dense bottom zone of the riser. A similar approach is adopted for the calciner; numerical results indicate that CO2 follows an almost linear trend along the bubbling bed height, while the bubbling formations might result in a reduced efficiency for the calcination reaction due to the entrapment of CO2 bubbles inside the emulsion phase. Numerical results related mostly to the hydrodynamics of the reactors, such as the solids distribution and residence time are then used as input parameters in a kinetics-based process algorithm. Process modeling simulations reveal the importance of splitting the carbonator riser into two distinct sections, i.e. the bottom zone with dense solid phase and the upper one (freeboard) with a more dilute solid concentration. The heat balance calculation for these two regions demonstrates a big gap between the heat flux density for the bottom zone (19.26 kW/m2) and the freeboard (0.46 kW/m2), which should be taken into account for the design of an effective heat removal system for scaled-up reactors. As a final step, a sensitivity analysis is performed for the optimization of the parameters governing the operation of the whole carbonation–calcination cycle. Efficient sorbent regeneration and high looping ratio enhances the CO2 capture efficiency in the carbonator, whilst low CO2 concentration in the calciner is suggested for more effective lime regeneration.

Integration of calcium looping technology in existing cement plant for CO2 capture: Process modeling and technical considerations

Cement sector is currently responsible for approximately 5% of the global CO2 emissions. CO2 originates principally from the raw meal calcination stage and conventional fuel (e.g. coal) combustion for the thermal needs of the process. Carbon capture and storage (CCS) is among the examined technologies for mitigating CO2 emissions generated in a cement plant. A very competitive technology for CO2 capture from flue gases appears to be Calcium Looping (CaL). The process is realized in a dual fluidized bed system where CO2 is absorbed by CaO in the first reactor (carbonator), and the produced CaCO3 is regenerated in the second oxy – fired reactor (calciner). During calcination, CO2 is released from the sorbents, purified, compressed and finally led to storage. Among the advantages of CaL when compared against other CO2 capturing technologies that could be applied in the cement industry, are the familiarity of the sector with the management (extraction, storage, feeding, etc.) of CaO-bearing materials and the prospect of reusing purge CaO in cement making as it is chemically compatible with cement raw meal.This study describes the process modeling of the CaL implementation on a typical (no by-pass) five-stage preheater with pre-calciner cement plant as a retrofit option, in order to capture the CO2 produced through the clinker production. The process simulations were performed with the commercial software ASPEN Plus™ in conjunction with house-built models for the CaL process itself. A detailed description of the process configuration of the CO2 capture unit including its integration with the CO2 purification scheme and the basic parameters for the clinker production line are presented. Simulation results revealed that high S content in the supplementary fuel affects negatively the CaL performance and the quality of purge CaO in terms of replacing limestone in the kiln feed. Using low-sulfur coal for a 90% capture rate, a total purge CaO utilization can be achieved along with a raw limestone substitution of 8% and a net electricity yield of 426.66kWh/t clinker. The economic evaluation of the proposed concept was also performed, estimating that the cost for CO2 avoidance equals approx. 68.75€/tCO2. In terms of economic efficiency, CaL was found to be comparable to amine scrubbing. Give that CaL has not been examined so extensively as MEA, it has the potential for technical improvements in order to become more competitive by the adoption of novel concepts with smaller equipment cost.

Gas leakage between reactors in a dual fluidized bed system

The leakage of gas between two interconnected gas–solid fluidized beds is investigated for 48 operating conditions in a lab-scale dual fluidized bed (DFB) consisting of a riser and a bubbling fluidized bed (BFB). Helium is used as the tracer gas with a spent FCC catalyst bed in ambient conditions. Gas leakage occurs from the riser to the BFB via the downcomer; and from the BFB to the riser via the loop-seal. Gas leakage from the riser to the BFB varied between 0.1 and 0.6%, translating to 1 and 7% of the BFB being contaminated with riser gas. This leakage is dependent on pressure difference across the downcomer and the solids circulation flux. Leakage in the downcomer is proposed to be caused by the riser gas being dragged down by the falling particles in the upper section of the downcomer.

Chemical-looping combustion of raw syngas from biomass steam gasification – Coupled operation of two dual fluidized bed pilot plants

Product gas from a 100kW fuel power dual fluidized bed (DFB) steam gasifier for solid biomass was used as fuel for chemical looping combustion in a continuously operated dual circulating fluidized bed (DCFB) 120kW chemical looping combustion (CLC) pilot plant. The two pilot units were coupled through a hot product gas fan. Olivine was used as bed material in the gasifier and a synthetic oxygen carrier containing 9wt% CuO was used as oxygen carrier in the CLC unit. Standard wood pellets with a water content of 6wt% were used as primary fuel. In the gasifier, conditions were kept constant at 850°C and a steam/fuel ratio of 1.6kg/kg dry biomass. Two operating conditions were employed at 850°C and 900°C in the fuel reactor of the CLC unit. The composition was monitored with respect to CO, CO2, H2, and CH4 for product gas, fuel reactor exhaust gas and air reactor exhaust gas. Also, H2S and SO2 were measured in the product gas and CLC off gas streams. A product gas with 41.9vol% (db) H2, 31.2vol% (db) CO, 17vol% (db) CO2, and 7.8vol% (db) CH4 was obtained from the gasifier. While CH4 conversion in CLC was between 53% and 64%, almost full conversion of the CO and H2 contained in the product gas were achieved. The effect of temperature was significant only with respect to CH4 conversion. Analysis of particulate matter in product gas and CLC off gas streams indicate that fines contained in the product gas tend to pass through the CLC unit. No performance drop was evident during the experiment, which lasted for 10h. It can be concluded that it is possible to couple two DFB systems in a robust way when using a high temperature fan and that biomass gasifier product gas can be effectively converted to CO2 and H2O in CLC using copper-based oxygen carriers.

Role of char in NOx formation during coal combustion at a regenerator temperature of calcium looping process

Coal of three kinds was burned in an oxygen-enriched atmosphere using two types of reactor both of which had the same fast fluidized bed for coal combustion. One was a dual-fluidized bed system (dual-FB), simulating Calcium Looping process comprised a fast fluidized bed regenerator and a bubbling bed carbonator. The other was a conventional single circulating fluidized bed combustor (single-CFBC). In both systems, coal combustion in oxygen-enriched atmosphere was carried out under regenerator temperature condition of Calcium Looping process. Inert quartz sand was used as the bed material to evaluate carbon consumption in the carbonator of dual-FB. Formation of NOx in the fast fluidized beds was measured for both reactors. For dual-FB, formation of CO and CO2 in the carbonator was also measured. High-volatile matter coal was found to be favorable to reduce CO and CO2 formation in the carbonator, but conversion of the fuel-N to NOx of high-volatile matter coal was higher than that from low-volatile coal. The emissions of NOx from single-CFBC were less than those from the regenerator of dual-FB under the same combustion condition. From the emissions of CO and CO2 from the carbonator, the decrease in char combustion in the regenerator of dual-FB was calculated. An empirical relationship between the conversion of fuel-N to NOx in the fast fluidized bed and the ratio of fixed carbon to volatile matter of the fuel was obtained.

Cold model study of a dual fluidized bed system for the gasification of solid fuels

Sorption-enhanced reforming (SER) is a process that couples steam gasification with carbonation/calcination reaction of limestone to enhance the hydrogen concentration in a product gas. Inspired from lab scale results a 200kWth pilot plant is constructed at IFK, University of Stuttgart. This pilot plant is a dual fluidized bed (DFB) system comprised of a bubbling fluidized bed (BFB) gasifier and a circulating fluidized bed (CFB) regenerator. These two fluidized beds are coupled with an L valve and a lower loop seal located at the bottom of the gasifier. This paper delineates the cold model studies of this pilot plant carried out during the design phase. The cold model is based on the Glicksman’s simplified scaling ratios, which determine the particle properties and operating conditions of the cold model. Results of the cold model can be extrapolated to the pilot plant using the scaling ratios. The results validate long term stable operation is possible with the planned DFB system. The solid circulation patterns in the BFB are studied and results show that the proposed BFB design is suitable for the gasifier. The parameters such as gasifier inventory, riser velocity and riser entrainment rates are tested under scaled conditions to prove the feasibility of the pilot plant. The results show that the required design criteria of the 200kWth DFB pilot plant are fulfilled and the proposed DFB pilot plant is feasible.

CaMnO3-δ Made from Low Cost Material Examined as Oxygen Carrier in Chemical-looping Combustion

Carbon Capture and Storage is a promising method to limit the increasing amount of greenhouse gases in the atmosphere. In this method high purity carbon dioxide is captured at large emission sources, e. g. fossil fuelled power plants. The carbon dioxide can then be transported to a long term storage site, rather than being emitted to the atmosphere. Among the different alternatives for obtaining high purity carbon dioxide during combustion of fossil fuels, Chemical-looping Combustion (CLC) is one of the most promising. Here, the oxygen needed to oxidize a fuel is provided by a solid oxygen carrier. The oxygen carrier is subsequently circulated to another reactor where it is reoxidized with air. By separating these two operations mixing of the combustion products and the nitrogen in the air is avoided. An energy demanding gas separation is thus not necessary.The most crucial part of Chemical-looping Combustion is the solid oxygen carrier. The oxygen carrier should have high reactivity with fuel and oxygen, sufficient oxygen carrying capacity and preferably also low cost. Furthermore it is important that it is able to withstand the tough conditions it is exposed to in a hot fluidizing environment, both with respect to physical attrition and chemical degradation. The most commonly suggested setup of Chemical- looping Combustion is a dual fluidized bed system where gas velocities and mechanical abrasion can be high. When the technology was first demonstrated, nickel oxide based oxygen carriers were typically used. But as nickel is quite costly as well as potentially harmful, alternatives have been sought after.In 2009 Leion et al. [1] investigated an oxygen carrier based on calcium manganite of perovskite structure CaMnO3-δ for chemical looping combustion. The results were very promising and similar materials have since then been successfully tested in pilot rigs up to 120 kWth, including extended operation in continuously operating 10 kWth reactor with very positive results, see Källén et al. [2]. A key feature of these materials is that they are able to release gas phase oxygen at relevant conditions, so called Chemical-looping with Oxygen Uncoupling, see Rydén et al. [3]. Having gas phase oxygen available for fuel oxidation makes gas-solid mixing less critical and thus makes it easier to reach complete fuel conversion.2Most studies in which CaMnO3-δ based oxygen carriers have been examined have been using particles manufactured from high quality chemicals. While that is reasonable in the early stages of development, cheaper raw materials would be favourable for industrial applications. Promising oxygen carriers based on manganese ores have been manufactured and characterized by Fossdal et al. [4] and Mohammad Pour et al. [5].This study aims to further examine CaMnO3-δ based oxygen carriers made from low cost, commercial raw materials available in large quantities such as manganese ore. The materials are examined during continuous Chemical- looping Combustion and Oxygen Uncoupling in an experimental reactor with the nominal fuel power 300 Wth. The reactor has previously been used in numerous studies which make comparisons with materials made from high purity chemicals straightforward. During operation several gas concentrations as well as temperatures and pressure drops are measured which allows monitoring of the chemical reactions and fluidization behaviour in the reactor.Fines (particles <45μm) are collected from exiting gas streams which gives an indication of the degree of attrition of the particles. Attrition was also studied in separate jet cup attrition test.The study show that it is possible to manufacture CaMnO3-δ based oxygen carrier with appropriate properties for continuous operation from low-cost materials. The ability to release gas phase oxygen to an inert atmosphere and high conversion of natural gas is demonstrated. The results indicate that this approach should be feasible also for large-scale applications.

Cold model hydrodynamic studies of a 200 kWth dual fluidized bed pilot plant of calcium looping process for CO2 Capture

The calcium looping (CaL) process is a post combustion CO2 capture technology which is currently under development, offering power plants a low cost and energy efficient solution for carbon capture. At IFK, University of Stuttgart, a 200kWth CaL dual fluidized bed (DFB) pilot plant has been built consisting of two circulating fluidized bed (CFB) reactors. This study presents detailed results of tests conducted on a hydrodynamically scaled cold model of the 200kWth CaL DFB facility. The preliminary aim of the cold model studies was to check the workability of the major novelty of this facility which is the implementation of two cone valves to control the solid looping rate between the two CFBs. Furthermore, initial cold model tests, based on the relative CaL process boundary conditions, determined the suitability of the 200kWth CaL DFB system and further tests suggested design improvements for the pilot plant. The novel geometric configurations in a CFB such as a wide bottom CFB reactor and a loop seal with increased weir depth were tested and found to be a useful application for the pilot plant operation. All important process parameters of the cold model DFB system, namely total solid inventory (TSI), riser superficial velocity, air staging ratio, and cone valve opening, were varied in order to fully characterize the DFB operation. The study shows that the proposed solid looping mechanism works satisfactorily and the required operational boundary conditions can be met in the pilot plant with suggested design improvements.

Gasification of Low‐Grade Coal in a Dual Fluidized‐Bed Steam Gasifier

AbstractThe gasification of a bituminous coal was performed in a dual fluidized‐bed (DFB) steam gasifier at a fuel power of 90 kWth. The main aim of these tests was to prove the suitability of the DFB system for cheap low‐grade coals that are often delivered with a wide range of particle sizes and ash loads. The fine fraction in particular can become entrained in the gas stream and thus be responsible for changes in the system performance and gas quality. The selected gasifier bed material was olivine, with an applied particle size of 375 μm, the steam‐to‐carbon ratio was 1.3 kg kgC−1, and the gasification temperature was 850 °C. In addition to standard online analysis of the main components of the product gas, impurities that included NH3, H2S, and tar were also examined.