Entrained Flow Biomass Gasification Research Articles

An Entrained Flow Biomass Gasification Technology with the Fluidized Bed Concept for Low-carbon Fuel Production

For accomplishing the vision of building of a net-emission zero society, low-carbon fuels such as e-fuel, Sustainable Aviation Fuel (SAF), and chemical products generation, plays a significant role. Especially, among the low carbon fuels, SAF is the most crucial. Ammonia and electric aircraft are under way as alternatives to fossil-derived jet fuel (kerosene). However, none of these have yet found their way to commercialization. Among the SAF production technology, biomass gasification and Fischer-Tropsch (FT) synthesis technology are one of the lowest CO2 emission processes, according to Life Cycle Assessment (LCA) analysis. However, at present there are some issues about biomass grinding, tar, ash treatment, gas purification and wastewater. We, at Mitsubishi Heavy Industries (MHI) R&D laboratory have developed entrained bed gasification, adopting the fluidized bed concept in which biomass particles are recirculated in the gasifier without fluidizer. Principally desired outcomes of this development was to reduce the grinding power, simplify the structure by using atmospheric pressure process, and lower tar concentration while maintain suitable temperature to prevent ash from melting inside gasifier. Empirical and actual results showed that the developed gasifier can obtain high carbon conversion ratio and low tar as compared to the traditional gasification processes for low-carbon fuel production and produce reliably stable syngas for low-carbon fuel synthesis with single gasifier. Based on the pilot plant operation results, effectiveness of moderate (1223 – 1323 K) temperature gasification with this concept has been demonstrated too. As a conclusion, development needs and expectation of gasification technology for contributing to carbon neutral society are mentioned.

Following fuel conversion during biomass gasification using tunable diode laser absorption spectroscopy diagnostics

The efficiency of the gasification process and product quality largely depend on the degree of fuel conversion. We present the real-time in-situ tunable diode laser measurements of main carbon and oxygen-containing species in the hot reactor core of a pilot-scale entrained flow biomass gasifier (EFG). The concentrations of CO, CO2, CH4, C2H2, H2O, soot, and gas temperature were measured during the air and oxygen-enriched gasification of stem wood at varying equivalence ratios. The experiments were made at the upper and lower optical ports inside a 4 m long, ceramic-lined, atmospheric EFG, allowing to access the degree of the fuel conversion inside the reactor. The exhaust composition was measured by micro-GC, FTIR, and low-pressure impactor. There was a good agreement between the data measured inside the reactor and at the exhaust for oxygen-enriched gasification implying that the chemical reactions are practically frozen downstream the optical ports. For air, the data indicated that the gasification reactions are still active at the measurement locations. Significant concentrations of C2H2, up to 5000 ppm, were found inside the reactor.

Experimental and simulation studies of oxygen-blown, steam-injected, entrained flow gasification of lignin

This article presents results from experimental and simulation studies on a laboratory-scale pressurized O2-blown Entrained Flow biomass gasification Reactor (EFR) using pulverized commercial lignin pellets as feedstock. The primary focus lies in the assessment of the EFR’s performance indicators such as the H2/CO ratio, the Cold Gas Efficiency (CGE), and the Carbon Conversion Efficiency (CCE). The gasifier was operated at an absolute pressure of 8.2 bars, with varying amounts of O2 and steam. In the first series of experiments, the O2 equivalence ratio varied between 0.2 and 0.8, with no steam injection. This yielded a maximum CGE of 47%, a CCE of 94%, and an H2/CO ratio within the range of 0.4–0.7. In the last series of experiments, a perforated horizontal steam tube was installed allowing for a variation of the steam-to-biomass ratio (S/B), between 0.5 and 1.5. At a S/B of 1.5, the CGE and the CCE were at their highest levels of 91% and 99%, respectively. Based on the experimental setup, a 3D multiscale Eulerian-Lagrangian computational particle fluid dynamics (CPFD) model for the reactor was developed and validated against the experimental data. This model was then employed to explore the impacts of reactor temperature, S/B, equivalence ratio (λ), and the lignin particle size distribution (PSD) on the gasification process. The findings show that increased reactor temperature enhances H2 and CO production. Higher S/B ratios lead to greater H2 production but reduced CO production. Increased S/B ratios improve both CGE and CCE. Larger particles and higher λ values decrease CO and H2 production. Without steam injection, the peak CGE occurs at λ ≈ 0.45, corresponding to complete CH4 conversion. Beyond this point, as λ increases, reactor temperatures rise while CGEs decrease. Simulations reveal the optimal λ range for steam injection is 0.15–0.35. A sensitivity analysis highlights the significant impact of reactor temperature on H2 and CO production. While λ shows high sensitivity for H2 production, the S/B ratio exerts a greater impact on CO production.

Numerical Simulations of Gasification of Low-Grade Coal and Lignocellulosic Biomasses in Two-Stage Multi-Opposite Burner Gasifier

Thermochemical processes utilizing biomass demonstrate promising prospects for the generation of syngas. In this work, a gasification process employing combination of an indigenous low-grade coal with two distinct biomass sources, namely rice husk (RH) and wood sawdust (WS), was explored. The gasification of the selected feedstock was performed using a double-staged multi-opposite burner (MOB) gasifier. A 3D computational fluid dynamics (CFD) model was employed to analyze the effect of kinetic and diffusion rates on the overall gasification performance of an entrained flow biomass gasifier. DPM was employed to track the particles’ trajectory, while the gas phase was treated as the continuous phase, and its behavior was predicted using a standard k-epsilon turbulent model. To calculate both the homogeneous and heterogeneous reaction rates, the finite rate/eddy dissipation model was implemented. The findings indicate that the char conversion efficiency exceeded 95% across all instances. Among the different reaction schemes, scheme E (which involved complete volatile and char combustion reactions) produced better results in comparison with published results, with less than 1% error. Hence, scheme E was validated and utilized for the rest of the simulated cases. The feeding rate has an inverse effect on the overall performance of the gasifier. An increase in feed rate decreases the CO and H2 composition in syngas. The maximum CO value was observed to be 57.59% at a 1.0 O/C ratio with a 0.005 kg/s feed rate, and the maximum H2 value was observed to be 16.58% in the same conditions for Lakhra coal samples. In summary, Lakhra coal exhibited better performance than other biomass samples due to its better fixed carbon and volatiles in its composition.

Biomass Entrained Flow Gasification Technology and CFD Numerical Simulation

Aiming at the dry pulverized biochar fuel refined by thermochemical conversion technology, its properties were obtained through experiment. By blending 5% additives to improve the ash fusion characteristics of biomass particles and considering the viscosity-temperature characteristics and the matching principle of CO2 reaction activity, the entrained flow gasification technology scheme of biomass particles was formulated. Based on the gasification reaction kinetics of dry pulverized biochar, a numerical simulation model was established to predict the flow characteristics, syngas composition, and particle conversion process in the gasifier. The results show that under the swirling entrainment and centrifugal force, the oxidizing reaction of particles is completed in the upper part of the gasifier quickly after mixing with oxygen. And the gasification reduction reaction occurs in the recirculating area and the pipe flow area. These effectively complete the conversion of char. The simulation results are in good agreement with the equilibrium calculation values, which proves the feasibility and rationality of the biomass particle entrained flow gasification technology scheme based on the HT-L.

Experimental study on a small-scale oxygen-enriched entrained flow biomass gasifier assisted by non-thermal arc plasma

A small-scale oxygen-enriched entrained flow biomass gasifier consisting of a non-thermal arc plasma torch and a stainless steel bellows was developed. The characteristics of the non-thermal arc plasma were diagnosed. The effects of oxygen concentration and bellows length on the gasification process using rice husk powder as feedstock at a feed rate of 27.1 g/min were studied. The results show that increasing the oxygen concentration of gasifying agent and using longer bellows both lead to the improvement of cold gas efficiency, carbon conversion efficiency, and yields of H2 and CO. The cold gas efficiency of the gasifier at a bellows length of 500 mm and oxygen concentration of 34.7% is 65.8%. And benefiting from low auxiliary energy consumption, the gasifier’s energy efficiency reaches 60.5%. The non-thermal arc plasma assists the entrained flow gasification by converting part of the feedstock into activated reactants.

Quantitative real-time in situ measurement of gaseous K, KOH and KCl in a 140 kW entrained-flow biomass gasifier

Photofragmentation tunable diode laser absorption spectroscopy (PF-TDLAS) was used to simultaneously measure the concentrations of gas phase atomic potassium (K), potassium hydroxide (KOH) and potassium chloride (KCl) in the reactor core of a 140 kWth atmospheric entrained-flow gasifier (EFG). In two gasification experiments at air-to-fuel equivalence ratio of 0.5, the EFG was first run on forest residues (FR) and then on an 80/20 mixture of FR and wheat straw (FR/WS). Combustion at air-to-fuel equivalence ratio of 1.3 was investigated for comparison. A high K(g) absorbance was observed in gasification, requiring the photofragmentation signals from KOH(g) and KCl(g) to be recorded at a fixed detuning of 7.3 cm−1 from the center of the K(g) absorption profile. In combustion, the fragments recombined instantly after the UV pulse within around 10 µs, whereas in gasification, the K(g) fragment concentration first increased further for 30 µs after the UV pulse, before slowly decaying for up to hundreds of µs. According to 0D reaction kinetics simulations, this could be explained by a difference in recombination kinetics, which is dominated by oxygen reactions in combustion and by hydrogen reactions in gasification. The K species concentrations in the EFG were stable on average, but periodic short-term variations due to fuel feeding were observed, as well as a gradual increase in KOH(g) over the day as the reactor approached global equilibrium. A comparison of the average K species concentrations towards the end of each experiment showed a higher total K in the gas phase for FR/WS, with higher K(g) and KCl(g), but lower KOH(g), compared to the FR fuel. The measured values were in reasonable agreement with predictions by thermodynamic equilibrium calculations.

Laser-based detection of methane and soot during entrained-flow biomass gasification

Methane is one of the main gas species produced during biomass gasification and may be a desired or undesired product. Syngas CH4 concentrations are typically >5 vol-% (when desired) and 1–3 vol-% even when efforts are made to minimize it, while thermochemical equilibrium calculations (TEC) predict complete CH4 decomposition. How CH4 is generated and sustained in the reactor core is not well understood. To investigate this, accurate quantification of the CH4 concentration during the process is a necessary first step. We present results from rapid in situ measurements of CH4, soot volume fraction, H2O and gas temperature in the reactor core of an atmospheric entrained-flow biomass gasifier, obtained using tunable diode laser absorption spectroscopy (TDLAS) in the near-infrared (1.4 µm) and mid-infrared (3.1 µm) region. An 80/20 wt% mixture of forest residues and wheat straw was converted using oxygen-enriched air (O2>21 vol%) as oxidizer, while the global air-fuel equivalence ratio (AFR) was set to values between 0.3 and 0.7. Combustion at AFR 1.3 was performed as a reference. The results show that the CH4 concentration increased from 1 to 3 vol-% with decreasing AFR, and strongly correlated with soot production. In general, the TDLAS measurements are in good agreement with extractive diagnostics at the reactor outlet and TEC under fuel-lean conditions, but deviate significantly for lower AFR. Detailed 0D chemical reaction kinetics simulations suggest that the CH4 produced in the upper part of the reactor at temperatures >1700 K was fully decomposed, while the CH4 in the final syngas originated from the pyrolysis of fuel particles at temperatures below 1400 K in the lower section of the reactor core. It is shown that the process efficiency was significantly reduced due to the C and H atoms bound in methane and soot.

Modeling and Simulation of the Motion and Gasification Behaviors of Superellipsoidal Biomass Particles in an Entrained-Flow Reactor

Biomass entrained-flow gasification has aroused lots of interest because of its great potential in syngas production. For simplification purposes, traditional computational fluid dynamics simulatio...

Interpreting biomass gasification histories with CBK/G. Part 2. Extrapolations to entrained-flow gasification conditions

This study characterizes how biochars’ distinctive kinetics affect the predicted performance of a pilot-scale oxygen-blown, entrained-flow biomass gasifier, where temperatures and pressures are much greater than those in the laboratory database used to assign kinetic parameters in Part 1. The gasifier operates at pressures of 0.2 and 0.7 MPa, temperatures from 1050 to 1550 °C, stoichiometric ratios from 0.25 to 0.50, and firing rates from 200 to 600 kW. Predicted product gas compositions are generally accurate to within 2% for CO and 4% for H2 across the testing domain with various raw and torrefied wood products. Fifty to 70% of the CO and 65 to 90% of the H2 in the syngas form during the reforming of volatiles along with the combustion of small amounts of char and soot during the early stages while O2 is still present. Among diverse biomass forms, the crucial kinetic parameter assignment is the activation energy for oxide desorption. High energies extrapolate to nearly complete carbon conversion and nearly uniform CO levels across a broad range of SR. Low energies extrapolate to much lower carbon conversions and a corresponding fall-off in CO levels for progressively greater SR. Only biochars with the highest energies for oxide desorption have the potential to give more soot than char in their unconverted carbon emissions. This paper also presents a quantitative evaluation of extrapolated CBK/G kinetics with measured temperatures of individual particles for two gasification conditions in a lab-scale burner at 1600 °C.

Phase equilibria and liquid phase behavior of the K2O-CaO-SiO2 system for entrained flow biomass gasification

Experimental data of solid-liquid phase equilibria in the K2O-CaO-SiO2 systems vital for many technologies and industrial applications are very limited and even not available at some primary phase fields. In the present study, by using Equilibration-Quenching-Phase compositional analysis (EPMA/EDS) method, liquidus compositions in equilibrium with pure solid SiO2, CaO·SiO2, 3CaO·2SiO2, 2CaO·SiO2, K2O·6CaO·4SiO2 and K2O·2CaO·2SiO2 compounds and 2CaO·SiO2 solid solution were measured. By knowing the evaporation behavior of K2O during the equilibration process, specific initial mixtures could be selected to obtain liquidus data for targeted final equilibrium assemblages. EPMA and EDS analysis results were compared. The experimental data obtained in the present study were discussed and compared with the results from previous experimental investigations and the assessed ternary phase diagrams. Some novel experimental data of the liquid at single and double solid phase saturations were obtained in the present study and they can be used to correct and support the predictions and thermodynamic assessments of the K2O-CaO-SiO2 system. Present investigation reports liquidus projections and detailed phase relations among the phases in isothermal sections at 1000, 1100, 1200, 1300 and 1400 °C. Viscosity calculations of the liquid at different compositions between 1000 and 1400 °C also have been made. A combination of phase equilibria study and the viscosity predictions in the present investigation provides suitable temperature and ash composition regions for optimal flow properties of the slag in entrained flow biomass combustion or gasification processes.

Advanced design optimization of combustion equipment for biomass combustion

Designof engineered combustion equipment normally involves laborious “build and try” designs to identify the best possible configuration. The number of design iterations can be reduced with engineering experience of what might work. The expensive cut-and-try approach can be improved using computational aided engineering tools coupled with optimization techniques to find the optimal design. For example, the “best” air duct configuration with the lowest pressure loss and smallest fan size for an air-fed biomass gasifier may take several weeks using the standard computational fluid dynamics (CFD) “cut and try” approach. Alternatively, coupling an efficient design optimization algorithm with an existing CFD model can reduce the time to find the best design by more than 50% and can allow the engineer to examine more design options than possible using the “cut-and-try” approach. Combining an efficient optimization algorithm with an existing CFD model of a biomass gasifier to find the “optimal” design is the focus of this work. Shape optimization has been performed by combining the optimization tool Sculptor® with the commercial CFD code STARCCM+. This work illustrates how the “linked” approach is used to examine design factors to optimize an entrained flow biomass gasifier to improve overall system performance in a methodical comprehensive fashion.

Numerical simulation of lignocellulosic biomass gasification in concentric tube entrained flow gasifier through computational fluid dynamics

Thermochemical conversion of biomass is an encouraging way for the production of syngas. In the present research, four different biomass materials were used for gasification which includes rice husk, cotton stalks, sugarcane bagasse, and sawdust. These biomass sources were selected because they are common Pakistani feedstocks. Gasification of selected biomasses was performed using concentric tube entrained flow gasifier. Three-dimensional computational fluid dynamics model was used to investigate the impacts of kinetic rate and diffusion rate on the gasification performance. The Euler–Lagrange method was used for the development of entrained flow biomass gasifier using commercial computational fluid dynamics code ANSYS FLUENT®14. Discrete phase model was used to predict the movement of particles, whereas the gas phase was treated as the continuous phase with a standard k–ε turbulent model to predict the behavior of gas phase flow. Finite rate/Eddy dissipation model was applied for the calculation of homogenous and heterogeneous reaction rates. Oxygen was used as a gasifying agent. Cotton stalks and sugarcane bagasse produced higher mole fractions of hydrogen (H2) and carbon monoxide (CO) than sawdust and rice husk. Regarding carbon conversion efficiency, cold gas efficiency, and higher heating value cotton stalks and sugarcane bagasse produced better syngas quality as compared to sawdust and rice husk. The oxygen/fuel (O/F) ratio is a key operating parameter in the field of gasification and combustion. The O/F ratio above 0.42 favored combustion reactions and increased mole fraction of water vapor (H2O) and carbon dioxide (CO2) in syngas composition, whereas gasification reactions dominated below 0.42 O/F ratio, resulting increased mole fraction of H2 and CO in syngas composition.

Effects of operating conditions and reactor structure on biomass entrained-flow gasification

A Eulerian-Lagrangian CFD model is utilized to investigate the effects of three different factors on biomass entrained-flow gasification, including the gasifying medium, reactor structure, and feedstock properties. For gasifying medium, O2, CO2, steam, and a blend of steam and CO2 are used. Results show that the introduction of O2 improves the CO production and carbon conversion but an excessive use leads to a decline in combustible gas yield, steam decomposition and cold gas efficiency. Introducing CO2 raises the CO yield, carbon conversion and cold gas efficiency but reduces the steam decomposition. Moreover, the H2 production, carbon conversion and lower heating value rise while the steam decomposition declines with steam addition. Besides, steam-CO2 composite gasification is better than both pure CO2 gasification and steam gasification in syngas yield, carbon conversion and lower heating value but worse in steam decomposition. Regarding reactor structure, enlarging the biomass inlet has little effect on the product gas yield but accelerates the pyrolysis process. Keeping the biomass inlet away from the gasifier axis improves the combustible gas yield and conversion efficiencies. Finally, for feedstock properties, the biomasses with a higher volatile or fixed carbon content and a lower moisture content generate a high combustible gas yield.

Alkali enhanced biomass gasification with in situ S capture and a novel syngas cleaning. Part 2: Techno-economic assessment

Previous research has shown that alkali addition has operational advantages in entrained flow biomass gasification and allows for capture of up to 90% of the biomass sulfur in the slag phase. The resultant low-sulfur content syngas can create new possibilities for syngas cleaning processes. The aim was to assess the techno-economic performance of biofuel production via gasification of alkali impregnated biomass using a novel gas cleaning system comprised of (i) entrained flow catalytic gasification with in situ sulfur removal, (ii) further sulfur removal using a zinc bed, (iii) tar removal using a carbon filter, and (iv) CO2 reduction with zeolite membranes, in comparison to the expensive acid gas removal system (Rectisol technology). The results show that alkali impregnation increases methanol production allowing for selling prices similar to biofuel production from non-impregnated biomass. It was concluded that the methanol production using the novel cleaning system is comparable to the Rectisol technology in terms of energy efficiency, while showing an economic advantage derived from a methanol selling price reduction of 2–6 €/MWh. The results showed a high level of robustness to changes related to prices and operation. Methanol selling prices could be further reduced by choosing low sulfur content feedstocks.

Development of a vision-based soft sensor for estimating equivalence ratio and major species concentration in entrained flow biomass gasification reactors

A combination of image processing techniques and regression models was evaluated for predicting equivalence ratio and major species concentration (H2, CO, CO2 and CH4) based on real-time image data from the luminous reaction zone in conditions and reactors relevant to biomass gasification. Two simple image pre-processing routines were tested: reduction to statistical moments and pixel binning (subsampling). Image features obtained by using these two pre-processing methods were then used as inputs for two regression algorithms: Gaussian Process Regression and Artificial Neural Networks. The methods were evaluated by using a laboratory-scale flat-flame burner and a pilot-scale entrained flow biomass gasifier. For the flat-flame burner, the root mean square error (RMSE) were on the order of the uncertainty of the experimental measurements. For the gasifier, the RMSE was approximately three times higher than the experimental uncertainty – however, the main source of the error was the quantization of the training dataset. The accuracy of the predictions was found to be sufficient for process monitoring purposes. As a feature extraction step, reduction to statistical moments proved to be superior compared to pixel binning.

Alkali enhanced biomass gasification with in situ S capture and novel syngas cleaning. Part 1: Gasifier performance

Previous research shows that alkali addition in entrained flow biomass gasification can increase char conversion and decrease tar and soot formation through catalysis. This paper investigates two other potential benefits of alkali addition: increased slag flowability and in situ sulfur capture.Thermodynamic equilibrium calculations show that addition of 2–8% alkali catalyst to biomass completely changes the chemical domain of the gasifier slag phase to an alkali carbonate melt with low viscosity. This can increase feedstock flexibility and improve the operability of an entrained flow biomass gasification process. The alkali carbonate melt also leads to up to 90% sulfur capture through the formation of alkali sulfides. The resulting reduced syngas sulfur content can potentially simplify gas cleaning required for catalytic biofuel production.Alkali catalyst recovery and recycling is a precondition for the economic feasibility of the proposed process and is effected through a wet quench. It is shown that the addition of Zn for sulfur precipitation in the alkali recovery loop enables the separation of S, Ca and Mg from the recycle. For high Si and Cl biomass feedstocks, an alternative separation technology for these elements may be required to avoid build-up.

Effect of moisture in gasification of biomass using entrained flow gasifier at constant equivalence ratio

Biomass entrained flow gasification is a promising technology due to its commercial availability, high efficiency and high potential for the production of biofuels and chemicals from biomass. The entrained flow gasification has been investigated in order to evaluate the effect of the moisture content at a fixed equivalence ratio on the gasifier performance and the producer gas quality. The composition of the producer gas and the adiabatic flame temperature has been analysed with moisture varying from 10% to 30% at an equivalence ratio of 0.2609. The results show that steam gasification gives more yield of fuel while the temperature reduces with moisture content. The optimum moisture content to maximise the fuel content maintaining the reaction temperature at 1,000 K is found to be 18% to 19%. Simultaneously, the optimum calorific value of the fuel is found to be 7–8 MJ/Nm3.

Multiscale Reactor Network Simulation of an Entrained Flow Biomass Gasifier: Model Description and Validation

AbstractThis paper describes the development of a multiscale equivalent reactor network model for pressurized entrained flow biomass gasification to quantify the effect of operational parameters on the gasification process, including carbon conversion, cold gas efficiency, and syngas methane content. The model, implemented in the commercial software Aspen Plus, includes chemical kinetics as well as heat and mass transfer. Characteristic aspects of the model are the multiscale effect caused by the combination of transport phenomena at particle scale during heating, pyrolysis, and char burnout, as well as the effect of macroscopic gas flow, including gas recirculation. A validation using experimental data from a pilot‐scale process shows that the model can provide accurate estimations of carbon conversion, concentrations of main syngas components, and cold gas efficiency over a wide range of oxygen‐to‐biomass ratios and reactor loads. The syngas methane content was most difficult to estimate accurately owing to the unavailability of accurate kinetic parameters for steam methane reforming.

Pure oxygen fixed-bed gasification of wood under high temperature (>1000 °C) freeboard conditions

In this paper, the performance (syngas composition, syngas production and gasification efficiency) of an 18kW atmospheric fixed bed oxygen blown gasifier (FOXBG) with a high temperature (>1000°C) freeboard section was compared to that of a pressurized (2–7bar) oxygen blown entrained flow biomass gasifier (PEBG). Stem wood in the form of pellets (FOXBG) or powder (PEBG) was used as fuel. The experimentally obtained syngas compositions, syngas production rates and gasification efficiencies for both gasification technologies were similar. Efficient generation of high quality syngas (in terms of high concentration and yield of CO and H2 and low concentration and yield of CH4, heavier hydrocarbons and soot) is therefore not specific to the PEBG. Instead, efficient gasification seems to be linked to high reactor process temperatures that can also be obtained in a FOXBG. The high quality of the syngas produced in the FOXBG from fuel pellets is promising, as it suggests that in the future, much of the cost associated with milling the fuel to a fine powder will be avoidable. Furthermore, it is also implied that feedstocks that are nearly impossible to pulverize can be used as un-pretreated fuels in the FOXBG.