Gasification Of Chips Research Articles

CFD-DEM study of thermal behaviours of chip-like particles flow in a fluidized bed

Chip-like particles are increasingly practised in various thermal applications, yet the unique heat transfer characteristics are not well understood. In this work, a recently developed super-quadric computational fluid dynamics-discrete element method (CFD-DEM) is extended to couple with heat transfer sub-models to study the cooling behaviours of chip-like particles in a three-dimensional (3D) cylindrical fluidized bed. The effect of aspect ratio (AR) on the flow and thermal behaviours of chip-like particles are studied at the particle scale. The results show that the chip-like particles with an AR of 6 show the steepest temperature decrease and thus the fastest cooling process under the given conditions. The unimodal distributions of particle temperature for the small ARs (i.e., 2 and 4) but bimodal distributions for the large AR (i.e., 6) are captured. Further, a large convective heat flux appears in the dilute phase due to vigorous slip velocity and temperature difference while a small convective heat flux occurs in the dense phase where the chip-like particles tend to be in a close-packing status. Finally, the underlying mechanism is explored: the chip-like particles with larger ARs show better heat transfer performance because the AR enhances gas-solid relative movement intensity and the convective heat transfer flux, and the convective heat transfer dominates the whole particle cooling process. The fundamental study sheds light on the design and optimization of fluidized beds of chip-like particles including solar panel recycling and wood chip gasification.

Hydrogen production from biomass steam gasification: Experiment and simulation

In pine chips gasification experiment, at 700 °C and 15 % H2O, with the mass ratio of Ca90Fe10/B to 1.5, the H2 yield is 210.50 mL/g. The H2 yield improves by 2.39 times and the tar yield decreases by 16 % compared to without CaO. In the pine chips gasification simulation with the system's own thermal equilibrium, at 700 °C, the heat release of Ca90Fe10 adsorption of CO2 is 56.91 MJ/h for Ca90Fe10/B mass ratio of 1.5, and the required O2 inflow is 1.9 kg/h, the molar flow of H2 is 0.58 kmol/h. To achieve material circulation, 0.5 kg/h of CH4 is added to the calciner for combustion to satisfy heat absorption of CaCO3 to regenerate CaO, which consumes 2.0 kg/h of O2. The whole cycle O2 consumption is 3.90 kg/h, which is 1.02 kg/h less than without CaO, and the H2 yield has increased by 1.35 times.

Two-stage fluidized bed gasification enhanced with oxidative pyrolysis for low-tar producer gas from biomass

Oxidative pyrolysis of fuel was adopted to configure an advanced two-stage fluidized bed gasification system, aiming to produce low-tar producer gas efficiently. A series of tests were carried out to investigate the effect of oxygen allocation in supply on gasification of pine chips in terms of both efficiency and producer gas quality. Compared with the case without pre-oxidation, coupling oxidative pyrolysis increased gas volume fraction of CO, CH4, and CnHm while decreasing that of CO2 and H2 in the produced gas. Further analysis showed that adopting oxidative pyrolysis reduced fuel gas yield, but the tar in the produced gas was lighter. The generated tar is easily transformed into small-molecule combustible gas by the catalytic action of hot char, thus increasing the calorific value of product gas. The long-term operation of the pilot plant presents a great steady continuous running with a minimum tar content in the producer gas of 1.3 g/Nm3. The above-mentioned results thus well verified the technical advantage and feasibility of the two-stage fluidized bed gasification with oxidative pyrolysis.

Numerical investigation of drag property for fluid flow through packed beds of super-quadric chip-like particles

Drag property of fluid flow through chip-like particles is essential for describing the microscale flow pattern of this unique system, yet it is not well developed. In this work, a correlation of drag force (Fd) specific for the super-quadric chip-like particles is formulated under the conditions of porosity ε = 0.48–1.0 and Reynolds number Re = 10–200, using the Lattice Boltzmann method (LBM) and discrete element method (DEM). The LBM-DEM model is validated against previous data with an average deviation of 5% (max ∼15%). The results indicate that the ε and Re are two dominant parameters that determine the Fd on chip-like particles. A new Fd correlation consists of ε and Re is developed. Comparisons are conducted between this Fd correlation with previous approximate correlations including Di Felice-Holzer/Sommerfeld hybrid drag model for arbitrary-shaped particles and Chen/Müller drag model specific for cubes, indicating that an accurate description of the particles' shapes is vital in providing suitable Fd information. The new Fd correlation can be applied to Euler-Euler simulations of industrial-scale processes of chip-like particles involved in fluid flow systems such as end-of-life (EoL) solar panels recycling and biomass chips gasification.

On the Possibility of Cleaning Producer Gas Laden with Large Quantities of Tars through Using a Simple Fixed-Bed Activated Carbon Adsorption Process

The study presents the results of research on using fixed-bed, activated carbon (AC) adsorbers in the cleaning of heavily tar-laden producer gas from the gasification of biomass. The efficiency of removal of organic compounds as well as the remaining adsorption capacity of the bed were determined using a spectrum of commonly applied diagnostic methods, including qualitative and quantitative analyses of the adsorbed compounds and changes in the pore volume of the bed material (IN, MN). The authors compare these lab quantifications with a simple technique which is based on the analysis of the changes in the position of temperature front in the bed. The main benefit of the latter is the possibility of performing the diagnostics of the bed “online” and using low-cost temperature measurements. The test was performed using a commercially available AC Desotec AIRPEL 10-3 and real producer gas obtained through the gasification of alder chips. For tar, VOC and C2–C5 compounds, the removal efficiencies reached respectively 74.5%-wt., 52.8%-wt., and 85.5%-wt. Obtained results indicate that depending on the final application of the gas, the use of dry adsorption systems is an interesting alternative to the well-established but complicated, cumbersome, and costly wet scrubbers. Moreover, a concept for in situ regeneration of the adsorbent, coupled with direct reforming of the tars, is presented and discussed.

Analysis of biochars produced from the gasification of Pinus patula pellets and chips as soil amendments

In this work, biochar (BC), a co-product of the fixed bed gasification process of Pinus patula wood pellets (PL) and chips (CH), was characterized as soil amendment. The physicochemical properties and the mineral content of the pellet’s biochar (PL-BC) and the chips biochar (CH-BC) were analyzed following the NTC5167 Colombian technical standard. The BET surface area values of the BCs were 367,33 m2/g and 233,56 m2/g for the PL-BC and the CH-BC, respectively, and the pore volume was 0,20 cm3/g for the PL-BC and 0,13 cm3/g for the CH-BC. These characteristics favor the increase of the BCs water-holding capacity (WHC). Properties such as the pH (8,8-9,0), the WHC (219 %-186,4 %), the total organic carbon (33,8 %-23,9 %), the metalloid presence (Ca, Mg, K, Mn, Al, Si, and Fe), and the ash (1,92wt % - 2,74 wt %) and moisture contents (11,13wt %-11,63 wt %) for both BCs were found to be within the limits set by the standard. Furthermore, the presence of micro and macronutrients, such as Fe and phosphorus (P), and the alkaline pH, make possible the use of these BCs as amendments for acid soils.

Experimental Analysis of Lenga Chips (Nothofagus Pumilio) Gasification in a Fixed Bed System for its Implementation in Rural Areas

Experimental Analysis of Lenga Chips (Nothofagus Pumilio) Gasification in a Fixed Bed System for its Implementation in Rural Areas

Pilot verification of a two-stage fluidized bed gasifier with a downer pyrolyzer using oxygen-rich air

A novel two-stage fluidized bed gasification system coupling a downer pyrolyzer and a riser gasifier was proposed, and a pilot facility of 15 kg/h of feedstock was further built and tested, by which the resulting technology gains its advantages of realizing the two-stage gasification principle in fluidized beds and having the large tolerance to biomass quality and size. Gasification of pine chips was in turn investigated at various equivalent ratios of air by changing the O2 concentration of gasifying agent composed of nitrogen and oxygen. The pilot facility was successfully operated at an ER value of 0.15, which generated 1.33 Nm3 product gas per kilogram of feedstock and containing 26.5% CO, 13.6% CO2, 8.89% H2, 12.6% CH4 and 0.63% CnHm. The LHV of the obtained fuel gas was as high as 9.35 MJ/Nm3 with a reasonably low tar content at 8.08 g/Nm3. By increasing the ER from 0.15 to 0.3, the temperatures of the pyrolyzer and gasifier were increased from 790 to 823 °C and from 881 to 925 °C, respectively. The gas yield was decreased to 1.1 Nm3/kg to have a reduced cold gas efficiency of 65.5% and a lower tar content of 4.35 g/Nm3 in the gas. These thus verified the technical feasibility of the proposed two-stage gasifier consisting of a downer and a riser.

Fluidized bed gasification of eucalyptus chips: Axial profiles of syngas composition in a pilot scale reactor

Air gasification tests have been carried out in a pilot scale bubbling fluidized bed gasifier, able to treat up to 100 kg/h of Eucalyptus wood chips, and operated, under chemical and thermal steady-state conditions, at different values of equivalence ratio. The results are reported in terms of the main process performance parameters and transfer coefficients, which indicate the fate of carbon in the different output streams (syngas, fines, tars). The results can be transferred to commercial scale reactors and confirm the technical feasibility of the air gasification of the biomass in the range 0.25–0.34 of equivalence ratio, yielding a good quality syngas, with a low heating value between 5000 and 6000 kJ/m3N,syngas. The measured axial syngas composition profiles along the reactor indicate a monotonic reduction of methane and carbon dioxide concentrations and an increase of that of hydrogen. This suggests that water gas shift and steam and dry reforming reactions play a significant role, together with a limited contribution of tar cracking reactions, probably enhanced by alkali and alkaline earth metallic species contained in the inorganic fraction of elutriated fines. Results can support the implementation of reliable numerical models of bubbling fluidized bed gasifiers and the optimisation of design/operating criteria.

Airlift photo-bioreactors for Chlorella vulgaris cultivation in closed-loop zero waste biorefineries

This study aims to set up the operating conditions of a battery of airlift photo-bioreactors (AL-PBRs) for Chlorella vulgaris cultivation integrated into a pilot-scale Biowaste-to-Biofuels (BtB) production plant, producing both biodiesel by transesterification of waste frying oils and syngas by wood chips gasification. Microalgae are fed with both wastewater rich in glycerol and flue gas. Mixing, mass transport, kinetics, and light conditions inside the AL-PBRs are chosen by keeping some dimensionless numbers (Re, Sh, DaII and A) fixed around the values found at lab-scale (11000, 1550, 23, 35, respectively). pH, T, nutrient-related ratios, and light intensity are adjusted inside the optimal ranges found at indoor conditions. The number of AL-PBRs, feeding/extraction time intervals, and flowrates are designed by mass balancing the entire pilot-plant in order to operate in continuous quasi-zero waste.Outdoor tests confirmed that 12–15 AL-PBRs with a total volume of 125–155 L reuse 28.8 L d−1 of wastewater by-produced from the biodiesel units providing 228 L d−1 of biodiesel and reuse the total of about 90 m3 h−1 of flue gas in exit from the syngas combustion unit with power generation of 9–9.5 kW. The battery works at an initial concentration for each cycle of around 0.5 g L−1 and concentration at extraction of around 1.05 g L−1.

Wood chips gasification in a fixed-bed multi-stage gasifier for decentralized high-efficiency CHP and biochar production: Long-term commercial operation

Gasification of woody biomass coupled with combined heat and power (CHP) production is an effective way to produce renewable energy from woody biomass. The tar content of the producer gas is considered to be the most problematic aspect of a biomass gasification for CHP production. Staged gasification allows the minimization of the tar production by the optimization of individual thermochemical subprocesses. This paper presents the operational results from a newly developed type of fixed-bed multi-stage gasifier GP750, which combines the principles of both twin-fire and two-stage gasification. This unique construction enables the production of a low-tar producer gas even by units with a power output as high as 0.7 MW. Here, we present the data measured during stable operation of the gasifier in a CHP plant operated by BOR Biotechnology company, including the composition of permanent gases measured on-line and the comprehensive gas and tar composition from the long-term operation, measured off-line. The measurements proved that the gasifier can produce a gas with low tar content (5–50 mg/m3), which is well beyond the limits for internal combustion engines. The energetic balance showed that the gross efficiency of the production of electricity of the whole power plant was as high as 32.9%. The gasifier also produced 36 kg of char per tonne of dry fuel on average. This char had a surface area in the range of 350–700 m2/g and very low content of both volatile matter and PAHs. Therefore, the char produced could potentially be sold as biochar.

УТИЛІЗАЦІЯ СТІЧНИХ ФЕНОЛВМІСНИХ ВОД ГАЗОГЕНЕРАТОРНИХ УСТАНОВОК ШЛЯХОМ МЕТАНОВОЇ АНАЕРОБНОЇ ПЕРЕРОБКИ

Наведено результати експериментів з метанової анаеробної переробки конденсату сумісно з коров’ячим гноєм. Конденсат було отримано під час часткової газифікації березової тріски. Наведено вихід деревного вугілля та конденсату, сорбційні показники деревного вугілля, а саме питому внутрішню поверхню та йодне число. Визначено концентрацію фенольних сполук в конденсаті. Процес бродіння відбувався за мезофільної температури 35 °С. Незважаючи на інгібування процесу бродіння фенольними сполуками конденсату, що призвело до більш тривалої лаг-фази, має місце переробка органічних речовин конденсату в біогаз та інтенсифікація бродіння. Лаг-фаза під час бродіння конденсат-вмісних субстратів триває довше в 2,9–4,8 рази, ніж для контрольного субстрату, який не містив конденсату. Встановлено гранично допустиму концентрацію фенольних сполук в субстраті 103 мг/дм3, за якої має місце процес бродіння. Визначено вихід та склад біогазу, ступінь переробки органічної речовини та фенольних сполук. Кумулятивний вихід біогазу з одиниці об’єму субстрату на 40,3–58,6 % більший з конденсат-вмісних субстратів. Середня концентрація метану у виробленому біогазі на 9,6–13,6 % більша з конденсат-вмісних субстратів. Показано, що об’єм виробленого біогазу та вміст метану в біогазі підвищився за рахунок переробки фенольних сполук. При цьому деструкція фенольних сполук в конденсат-вмісних субстратах становила від 45,5 % до 80,3 %. На основі отриманих експериментальних результатів розроблена принципова схема для промислової реалізації наведеного способу перероблення конденсату. Це дасть змогу використати фізичну теплоту генераторного газу або для підтримування сталої температури всередині біогазового реактора, або для попереднього підігрівання субстрату. Органічні кислоти, розчинна смола та фенольні сполуки, що присутні в конденсаті переробляються в біогазовому реакторі для отримання біогазу. Бібл. 13, табл.1, рис. 2.

Experimental assessment of pine wood chips gasification at steady and part-load performance

The trend towards decentralised electricity generation and combined heat and power (CHP) is continuously increasing. The transition towards a decentralised power system relies on small-scale and often intermittent generation, bringing new challenges such as matching the demand with supply. A possible solution is the use of renewable energy technologies able to accommodate the demand profile, such as biomass gasification. However, operation at part-load is required and thus limiting the gasification performance efficiency. In this paper, a novel experimental assessment and performance results of a biomass gasification system are presented, consisting on the evaluation of the system performance for steady-state conditions at different loads. Gasifier performance at steady-state conditions showed relatively stable reduction and throat temperatures, with average values of about 729 °C and 915 °C, respectively. These high temperatures assure a producer gas LHV of about 5.5 MJ/kg. Decreasing the gas flow rate resulted in a decrease of both reduction and throat temperatures. Nonetheless, the gas LHV increased until 62.5% where a maximum of about 6 MJ/kg was measured. Concerning the equivalence ratio, it decreased with load, attaining a minimum value at 80%, where the best cold gas efficiency results were found (74%).

Modelling of wood chips gasification process in ASPEN Plus with multiple validation approach

A thermochemical equilibrium model is formulated for wood chips downdraft gasification. Steady state ASPEN Plus simulator was utilized to evaluate producer gas composition and low heating value. Three cases are considered, due to mathematical model developed issues, and described in details. Experimental work was carried out within commercial small-scale CHP system where twelve beech wood samples were taken. Equivalence ratio is between 0.32 and 0.38 and air-fuel ratio ranges from 1.49 to 1.81, when gasifier capacity is optimal, at 250 kW. Mole fractions of CO2, H2, CO, CH4 and N2, in dry producer gas, are respectively, 16.06-17.64, 17.98-20.33, 13.71-17.26, 1.65-2.89 and 43.21-48.36. Multiple validation approach was applied for model verification. The results are in reasonable agreement with different literature sources (experimental work and modeling) and in a great agreement with the modified equilibrium model developed in Engineering Equation Solver found in the literature. Result deviations are explained by two major facts: wood downdraft gasification experiments are to a certain extent different and the model parameters could not be adjusted enough to fully minimize differences between model results. Predicted low heating value of dry producer gas is between 4.67-5.61 MJ/Nm3.

Gasification of waste from coffee and eucalyptus production as an alternative source of bioenergy in Brazil

This paper presents results of a study about the gasification process of waste from eucalyptus production, as wood chips, and wastes from coffee production, as coffee husks and coffee wood. These wastes were subjected to gasification in an open-source commercial small-scale downdraft gasifier, using air as the gasifying agent. The fuel gas composition was monitored in a fuel gas analyzer to determine the volume concentration of CO, CO2, H2 and CH4, and higher heating value (HHV). The coffee husk fuel gas presented the average HHV of 7.76 ± 1.27 MJ Nm−3 containing predominantly methane, carbon monoxide and carbon dioxide. The fuel gas from coffee wood gasification reached the lowest HHV (5.45 ± 0.42 MJ Nm−3), containing predominantly carbon monoxide (14.03 ± 0.72%). The gasification of eucalyptus chips presented average HHV of 6.81 ± 0.34 MJ Nm−3, with predominance of carbon monoxide (20.24 ± 0.93%), showing a regular composition during the experimental trials, and superior operational performance among the three biomasses investigated. This study demonstrates that gasification is an attractive alternative for waste-to-energy conversion and the energy upgrade can be used for on farm sustainable activities.

Modeling downdraft biomass gasification process by restricting chemical reaction equilibrium with Aspen Plus

Thermo-chemical conversion of biomass has been regarded as one of attractive routes of producing the clean and environmental friendly bio-fuels. Downdraft biomass gasification process has been served as a key technology to provide the bio-syngas with high quality, which can be used to produce the renewable liquid transportation fuels through Fischer Tropsch Synthesis in Mississippi State University. In order to provide the performance data of the integrated Biomass to Liquid system and future process optimization, a comprehensive model of the downdraft biomass gasification process based on Aspen Plus by minimizing Gibbs free energy with restricting chemical reaction equilibrium in the gasification reduction zone has been developed. The model was successfully validated with the experimental data from the hardwood chips gasification. Sensitivity analysis was also performed to investigate the effects of gasification temperature, equivalence ratio, and biomass moisture content on the quality of bio-syngas. All the investigated factors have been found with a significant effect.

Optimization of a flexible multi-generation system based on wood chip gasification and methanol production

Flexible multi-generation systems (FMGs) consist of integrated and flexibly operated facilities that provide multiple links between the different sectors of the energy system. The present study treated the design optimization of a conceptual FMG which integrated a methanol-producing biorefinery with an existing combined heat and power (CHP) unit and industrial energy utility supply in the Danish city of Horsens. The objective was to optimize economic performance and minimize total CO2 emission of the FMG while it was required to meet the local district heating demand plus the thermal utility demand of the butchery. The design optimization considered: Selection, dimensioning, location and integration of processes; operation optimization with respect to both hourly variations in operating conditions over the year as well as expected long term energy system development; and uncertainty analysis considering both investment costs and operating conditions.Applying a previously developed FMG design methodology, scalable models of the considered processes were developed and the system design was optimized with respect to hourly operation over the period 2015–2035. The optimal design with respect to both economic and environmental performance involved a maximum-sized biorefinery located next to local industry rather than in connection with the existing CHP unit. As the local industry energy demands were limited when compared to the biorefinery dimensions considered, process integration synergies were found to be marginal when compared to the economic and environmental impact of the biorefinery for the present case.Assessing the impact of uncertainties on the estimated FMG performances, the net present value (NPV) of the optimal design was estimated to vary within the range 252.5–1471.6M€ in response to changes of ±25% in investment costs and methanol price, and considering two different electricity price scenarios. In addition, a change in the interest rate from 5% to 20% was found to reduce the lower bound of the NPV to 181.3M€ for reference operating conditions. The results suggest that the applied interest rate and operating conditions, in particular the methanol price, would have a much higher impact on the economic performance of the designs than corresponding uncertainties in investment costs. In addition, the study outcomes emphasize the importance of including systematic uncertainty analysis in the design optimization of FMG concepts.

Comparing the life cycle impacts of using harvest residue as feedstock for small- and large-scale bioenergy systems (part I)

In part I of our two-part study, we compare the timing-adjusted GHG (greenhouse gas) balance and life cycle impacts of potentially using harvest residue (unmerchantable small-diameter roundwood) in an existing large (211 MWe) wood pellet-fired (formerly coal-fired) power plant in Ontario, Canada, versus a hypothetical small (250 kWe) wood chip gasification plant that recovers heat in addition to producing electricity. Although the large, retrofitted power plant has a higher electrical efficiency, the small plant has lower environmental impacts (TRACI 2.1), mainly due to the benefits of drying the biomass inputs with recovered heat, having a shorter fuel shipping distance, and reduced biomass processing. The small plant emits 38 g of fossil fuel-derived CO2 eq./kWh, versus 134 g/kWh from its large-scale counterpart. Although these GHG emissions are insignificant relative to the forest carbon emissions from gasification and combustion (1.3–1.4 kg CO2/kWh), the harvest residue would have decomposed over time had it been left on the forest floor. After 100 years, forest carbon storage decreases by 3.8–4.1 kg from the sustained production of 1 kWh of electricity per year. The decline in carbon storage delays net GHG mitigation by 4 (small-scale system) to 7 years (large-scale system) when displacing electricity from coal.

Comparing the life cycle costs of using harvest residue as feedstock for small- and large-scale bioenergy systems (part II)

In part II of our two-part study, we estimate the nominal electricity generation and GHG (greenhouse gas) mitigation costs of using harvest residue from a hardwood forest in Ontario, Canada to fuel (1) a small-scale (250 kWe) combined heat and power wood chip gasification unit and (2) a large-scale (211 MWe) coal-fired generating station retrofitted to combust wood pellets. Under favorable operational and regulatory conditions, generation costs are similar: 14.1 and 14.9 cents per kWh (c/kWh) for the small- and large-scale facilities, respectively. However, GHG mitigation costs are considerably higher for the large-scale system: $159/tonne of CO2 eq., compared to $111 for the small-scale counterpart. Generation costs increase substantially under existing conditions, reaching: (1) 25.5 c/kWh for the small-scale system, due to a regulation mandating the continual presence of an operating engineer; and (2) 22.5 c/kWh for the large-scale system due to insufficient biomass supply, which reduces plant capacity factor from 34% to 8%. Limited inflation adjustment (50%) of feed-in tariff rates boosts these costs by 7% to 11%. Results indicate that policy generalizations based on scale require careful consideration of the range of operational/regulatory conditions in the jurisdiction of interest. Further, if GHG mitigation is prioritized, small-scale systems may be more cost-effective.

Euler–Lagrange modeling of wood chip gasification in a small-scale gasifier

The mathematical model for physical and chemical processes during wood chips gasification in a gasifier is presented in this paper to offer some reference data for the gasifier structure design and operation optimization. The RNG k–ε model is employed in the numerical simulation of turbulent combustion gas flow. Non-premixed combustion model is used to describe the species reaction and transportation. The movement and gasification of wood chip particle is described by Lagrange model. The Eulerian conservation equations of gas phase are solved using the control volume approach. The distributions of temperature and chemical species, residence time of wood particles are numerically obtained. The results indicate that this design will cause vortex structure at lower chamber for the interaction between the forwarding flow of air and the reverse flow of syngas. This vortex will make produced syngas to combust further; the productions are CO2 and H2O substituting CO and H2, which will decrease the temperature inside the chamber and quality of syngas. In order to optimize operational case, five different equivalence ratios of airflow are computed and compared with experimental test. The predicted temperatures of outgoing gas agree well with the experimental results. Modeling results can provide some references for gasifier structure design and optimum operation case.