Wheat Straw Pellets Research Articles

Experimental Study and Mathematical Modelling of Straw Co-firing with Propane

The goal of this study is to provide a more effective use of wheat straw for energy production by co-firing it with a gaseous fossil fuel – propane. The study includes experimental work and mathematical modelling of the processes developing at co-firing – the influence of the additional heat supply on the thermal decomposition of straw, on the formation, ignition and combustion of volatiles, on the heat output from the device and on the flue gas composition. Experimental results give evidence that the straw co-firing with propane enhances the thermal decomposition of wheat straw pellets providing so faster formation, ignition and more complete burnout of the volatiles. By increasing the propane supply into the device up to 0.6 l/min (˜ 0.9 kW), the volume fractions of H2 and CO at the gasifier outlet increase by about 36 % and 45 %, respectively. The improved combustion of the volatiles downstream the combustor results in correlating increase of the temperature in the flame reaction zone (from 1,060 K up to 1,200 K), hence, increasing the heat power of the device by about 44 %. In addition, the wheat straw co-firing with propane improves the flue gas composition, decreasing the mass fraction of unburned CO in the products from 1.800 ppm to 800 ppm, H2 from 250 ppm to 40 ppm and the mass fraction of the hazardous NOx emission from 400 ppm to 250 ppm. A mathematical model of the combustion dynamics at co-firing straw with propane has been developed using MATLAB, considering the variations of the additional heat energy supply from the propane flame flow.

Operating Conditions Affecting the Behavior of Wheat Straw Pellets During Slow Pyrolysis Process: a Full Insight

A deep study on the effects of absolute pressure, peak temperature, gas residence time and gas atmosphere on the pyrolysis behaviour of wheat straw pellets in a bench-scale fixed-bed reactor has been carried out.

Electric Field Effect on the Thermal Decomposition and Co-combustion of Straw with Solid Fuel Pellets

The aim of this study was to provide more effective use of straw for energy production by co-firing wheat straw pellets with solid fuels (wood, peat pellets) under additional electric control of the combustion characteristics at thermo-chemical conversion of fuel mixtures. Effects of the DC electric field on the main combustion characteristics were studied experimentally using a fixed-bed experimental setup with a heat output up to 4 kW. An axisymmetric electric field was applied to the flame base between the positively charged electrode and the grounded wall of the combustion chamber. The experimental study includes local measurements of the composition of the gasification gas, flame temperature, heat output, combustion efficiency and of the composition of the flue gas considering the variation of the bias voltage of the electrode. A mathematical model of the field-induced thermo-chemical conversion of combustible volatiles has been built using MATLAB. The results confirm that the electric field-induced processes of heat and mass transfer allow to control and improve the main combustion characteristics thus enhancing the fuel burnout and increasing the heat output from the device up to 14% and the produced heat per mass of burned solid fuel up to 7%.

Comparing severity of continuous torrefaction for five biomass with a wide range of bulk density and particle size

This study presents five continuous torrefaction experiments using five lignocellulosic biomass feedstocks: coppiced willow, wheat straw, cattail (typha), moringa leaf, and spruce pellets. Experiments were conducted in a horizontal moving bed pilot plant operating at 250 °C and 6.8–10 min residence time to evaluate the flexibility of this torrefaction reactor. Differences in particle mass, bulk density, and physical form were examined as to how they affect the severity of torrefaction.Torrefaction mass yield for these experiments ranged from 73.7 wt% (moringa) to 91.2 wt% (spruce pellets), increasing with particle mass and bulk density. Individual particle mass had the most direct linear correlation to mass yield, while the bulk density correlated indirectly to mass yield through mass feed rate for 4/5 biomass; Ym = 0.35Q+0.7 (R2 = 0.98).Wheat straw was the outlier in both correlations, having significantly higher mass yield than expected. The long, slender shape and resulting low sphericity are thought to limit heating and mass loss for this feedstock.These and other experiments along with the correlations presented illustrate the flexibility of the horizontal moving bed pilot plant; a wide range of biomass particle size, and form can be accommodated; however some shapes/forms of biomass may limit mass loss.

A kinetic model considering the heterogeneous nature of the enzyme hydrolysis of lignocellulosic materials

AbstractIn this work, a mathematical model is proposed to predict the kinetic behaviour of the enzymatic conversion of various types of lignocellulosic biomass into fermentable sugars. Digestion of the cellulosic polymers is carried out using enzymatic hydrolysis under different conditions. Unlike other kinetic models, published previously for this process, this one considers the heterogeneous nature of the process by which a solid, in the form of small particles, is decomposed to monosaccharides by the action of a diverse set of enzymes in solution. The effect of the particle size on the hydrolysis rate has also been taken into consideration.To assess the model's goodness of fit to any general situation, the experimental data obtained in the hydrolysis of three different lignocellulosic residues have been analysed. Thus, the hydrolysis data of wheat straw, rice husks and exhausted sugar beet pellets have been compared with the theoretical values calculated by the model. The results obtained show that this model predicts the enzyme's hydrolysis of lignocellulosic substrates under different conditions very accurately and it could therefore be used efficiently in the optimization of the hydrolysis processes implemented in the bio‐refinery industry. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd

Time-Resolved Study of Silicate Slag Formation During Combustion of Wheat Straw Pellets

Ash formation during single-fuel pellet combustion of wheat straw at 700 and 1000 °C was studied throughout fuel conversion by quench cooling and analysis at different char conversion degrees. The combination of X-ray microtomography analysis and scanning electronic microscopy with energy-dispersive X-ray spectroscopy showed that ash accumulated in rigid net structures at 700 °C with streaks or small beads surrounding the char, and the pellet mostly maintained its size during the entire fuel conversion. At 1000 °C, the ash formed high-density melts that developed into bubbles on the surface. As the conversion proceeded, these bubbles grew in size and covered parts of the active char surface area, but without entirely blocking the gas transport. The successive char conversion dissolved increasing amounts of calcium in the potassium silicate melts, probably causing differences in the release of potassium to the gas phase. Similarities were found with slag from a combustion experiment in a domestic boiler, w...

Anaerobic co-digestion of Baltic seaweeds with wheat straw and straw pellets: synergetic effects on biomethane yield and kinetic biodegradability constant

Abstract Cladophora sp. and Ulva intestinalis are green macroalgae abundantly available in the Baltic Sea. Their low degradability could hamper the fully exploitation as resource for energy recovery through anaerobic digestion. For this reason, a co-digestion with lignocellulosic biomass represents a viable solution. This study aims to assess the potential effectiveness of the use of seaweed from Latvian nearshore co-digested with lignocellulosic biomass both in terms of increased BMP and kinetic constant of biodegradability. Specifically, biomethane potentials (BMP) in batch tests of 100 ml were assessed co-digesting Cladophora sp. and Ulva intestinalis from the Gulf of Riga with wheat straw and straw pellet from Brescia Region (Italy). The BMP tests were performed to evaluate the synergetic effect of co-digestion through a synergy index. A mechanical pre-treatment was also executed and its final effect assessed on the mono- and co-digestion experimental trials. The co-digestion ratio (seaweed/lignocellulosic biomass) used based on the volatile solids content was 1:1. The used ratio substrate-to-inoculum was 1:3 on total solid base. The inoculum use was sewage sludge was collected waste water treatment plant in the Riga district. Two different rounds of experiments with duration of 30 days were performed in order to have a more consistent analysis of results. Results for mono-digestion show the lowest BMP for Ulva intestinalis (277.7 ± 8.6 mL CH4/gVS) and the highest for the Cladophora sp. 523.3 ± 23.24 mL CH4/gVS. The straw pellet and wheat straw present values in a range of 395.6 ± 25.07 mL CH4/gVS and 470.4 ± 7.40 respectively. The effect of the co-digestion results in a slight increase of the synergy index (i.e. from 1.9% to 4.7%) but not for all the co-digestion trials. The higher effect was detected for co-digesting of finely treated straw pellet and Ulva intestinalis. The kinetic degradation constant improvements are evident for all the tested trials with the most evident effect for finely treated Ulva intestinalis in the mono-digestion conditions (i.e. 53.8%). The experiments show that the co-digestion with seaweeds and lignocellulosic can be beneficial.

Sustainable bio-based earth mortar with self-healing capacity

This paper describes the hygrothermal and mechanical properties and self-healing capacity of a sustainable bio-based mortar repair system for earth construction. There is currently limited characterisation of materials that directly compare earth, bio-fibres and self-healing behaviour. Additionally, the thermal performance of self-healing materials has been under-researched. Both prismatic and 0.1 m × 0.1 m samples were cast with plain mixes, saw mill residue (SMR), straw, wool and wood pellets. Executing both structural and hygrothermal experimentation provided an indication of the performance and durability of the samples. The bio-based agent added to the bio-based composite consisted of bacteria. Adding the bio-based agent to an earth matrix with (wheat) straw, (sheep) wool, SMR and wood pellets showed promising results for the hygric properties, as the initial water adsorption and absorption were lessened. The thermal conductivity was reduced from 0.32 to 0.23 W/m.K when bio-based agents were combined into the earth-based mix design with SMR. Overall, it is evident that out of all ten mix designs, bio-SMR provided the best environmental conditions for the bio-agent.

Physical and calorific properties of wheat straw briquettes and pellets

Wheat straw briquettes are high performance combustible products obtained by densification from the wheat straw biomass without the use of additional adhesives or additives. The purpose of the paper is to analyze and to detail the physical properties (SR EN ISO / CEI 322 for moisture content by method of drying and weighing, and effective density method according to SR EN ISO / CEI 323: 2005) and calorific properties of these briquettes (high and low calorific value according to ÖNORM M7135 using the XRY-1C / China Calorimeter and ash content according to ASTM D1102-84: 2013 and ISO 18122: 2015) and to make a comparison between these briquettes and other briquettes obtained from wooden biomass. The tested briquettes had a moisture content of 8%, an effective density of 1214 kg/m3, a high calorific value of 17.670 MJ/kg, the low of 17.525 MJ/kg and an ash content of 5.6%. All these values correspond to the permissible limits of the standards in the field. The final conclusion of the paper shows that wheat straw briquettes had physical and calorific properties similar to those of wooden biomass.

Evolution of the mass-loss rate during atmospheric and pressurized slow pyrolysis of wheat straw in a bench-scale reactor

In the present study, the effects of the absolute pressure (0.1 or 0.5 MPa) and the reactor atmosphere (pure N2 or a mixture of CO2/N2) on the pyrolysis behavior of wheat straw pellets (at 500 °C) were investigated. The most interesting aspect of this work was the use of a weighing platform (with a maximum capacity of 100 kg and a resolution of 0.5 g) to monitor the real-time mass-loss data for the biomass sample (with an initial mass of 400 g). It was observed that an increased pressure considerably affects the mass-loss profiles during the pyrolysis process, leading to higher devolatilization rates in a shorter period of time. Regardless of the pyrolysis atmosphere, an increase in the absolute pressure led to higher yields of gas at the expense of produced water and condensable organic compounds. This finding could be due to the fact that an increased pressure favors the exothermic secondary reactions of the intermediate volatile organic compounds in both liquid and vapor phases. The switch from pure N2 to a mixture of CO2 and N2 at 0.1 MPa also led to a remarkable increase in the yield of produced gas at the expense of the total liquid. This could be mainly due to the promotion of the thermal cracking of the volatile organic compounds at a high partial pressure of CO2, which is also consistent with the measured higher yields of CH4 and CO. The increased yield of CO can also be seen as a direct result of the enhanced reverse Boudouard reaction, which can also explain the much higher specific surface area (and ultra-micropore volume) measured for the biochar produced under the same operating conditions (0.1 MPa and a mixture CO2/N2 as pyrolysis medium).

Brown pellet production using wheat straw from southern cities in Chile

In this study, the torrefaction process was optimized to improve the energy yield (Yenergy) in wheat straw pellet production. Wheat is the main agricultural product of Chile and cultivated in approximately 262 000 ha of land. Additionally, solid biofuel alternatives are necessary in the southern cities of Chile to reduce the pollution produced by low-quality firewood used as fuel. That being the case, it appears that wheat straw is a feasible raw material for solid biofuel production. In the current study, the torrefaction of wheat straw was optimized in a thermogravimetric analyzer using the response surface methodology (RSM). The polynomial model generated from the RSM study showed that heating rate and temperature were significant variables on the response variable, Yenergy; time was insignificant. It was shown that a decrease in temperature of up to 130 °C resulted in an enhancement of the Yenergy value, and at the aforementioned temperature, a low heating rate improved Yenergy. Following the conditions predicted by the model, torrefaction assays were conducted in a bench scale reactor under light torrefaction conditions: a torrefaction temperature of 145 °C, heating rate of 3 °C/min, and final torrefaction time of 50 min. The torrefied biomass was employed in a pellet production process that was performed in a pilot plant facility. The pellet produced from the torrefied biomass under light torrefaction conditions was named “brown pellet” because of its color. Most of the pellet properties satisfy the Standards for Industrial pellets (ISO 17225-6). This showed that light torrefaction temperature can be a potential pretreatment to achieve a commercial production process. Finally, an interesting result was obtained—the bulk density of brown pellets (568 ± 8 kg/m3) was considerably higher compared to that of wheat straw pellets (469 ± 8 kg/m3). This was probably caused by an increment in grinding characteristics. Further studies that focus on identifying the effects of light torrefaction conditions on the mechanical properties of wheat straw pellets should be conducted.

Mechanical strength and combustion properties of biomass pellets prepared with coal tar residue as a binder

To reutilise the hazardous waste material coal tar residue (CTR) to bring environmental and economic benefits, CTR was first used as a binder to prepare biomass pellets with enhanced mechanical strength and heating values. CTR, which mainly contained asphaltenes (40.06%), aliphatics, aromatics and non-hydrocarbon components, had a high viscosity (72,276 mPa·s) and heating value (27.46 MJ/kg). When the CTR percentage increased from 0 to 40 wt%, the abrasive resistance of wheat straw, sawdust and moso bamboo pellets significantly increased from 10.62–69.20% to 95.66–98.24%, while their water resistance time increased from 6 s to >30 min and their heating value increased by 20.62–25.96%. The ignition temperature of wheat straw pellets increased from 275.7 to 280.7 °C as the CTR content increased from 0 to 30 wt%, whereas the maximum burning rate decreased from 1.28 to 0.82 mg/min and the burnout temperature increased from 465.33 to 563.33 °C.

Oxidative pyrolysis of pine wood, wheat straw and miscanthus pellets in a fixed bed

Oxidative pyrolysis is a key step in the autothermal operation of many fixed-bed reactors for staged gasification and advanced carbonisation. In these reactors, biomass is converted into charcoal, condensates and permanent gases inside a moving Oxidation Zone (OZ) which also produces energy to self-sustain the process. Oxidative pyrolysis of three different biomass types: pine wood, miscanthus and wheat straw pellets, was performed in a batch 20 cm diameter fixed bed reactor. Results showed that the OZ consumed 11% to 14% of the stoichiometric air to self-sustain the process and reached a peak temperature around 720 °C whatever the biomass. The propagation velocity and thickness of the OZ were inversely proportional to the ash content and to the bulk density of the biomass. Ash was also shown to influence the yield and composition of the resulting products due to a catalytic effect on primary and secondary pyrolysis reactions.

Oxidative Pyrolysis of Agricultural Residues in Gasification and Carbonization Processes

Oxidative pyrolysis, in which heat is provided by the partial oxidation, occurs in many fixed bed reactors of air staged gasification and advanced carbonization processes. In these reactors, an Oxidation Zone (OZ) propagates and separates the virgin biomass from the produced char, and self-sustains the process. To investigate the energy transfer efficiency and to characterize the OZ features, oxidative pyrolysis was performed in a 20 cm diameter fixed bed reactor with Wheat straw pellets. Temperatures and biomass bed height were measured continuously during the experiment. The OZ propagated at 0.41 cm/min and consumed about 11 % of the biomass. The role of bed compaction on the effective propagation velocity was highlighted. Char yield was measured to 28.6 % and char accounted for 39.56 % of the total energy content of the Wheat straw. Maximum temperature in the bed reached 780°C. This paper proposes a new insight into the OZ features when it propagates in a biomass fixed bed.

Experimental Study and Mathematical Modelling of Straw Co- Firing with Peat

The goal of this study is to provide a more effective use of wheat straw for energy production by co-firing it with a gaseous fossil fuel – propane. The study includes experimental work and mathematical modelling of the processes developing at co-firing – the influence of the additional heat supply on the thermal decomposition of straw, on the formation, ignition and combustion of volatiles, on the heat output from the device and on the flue gas composition. Experimental results give evidence that the straw co-firing with propane enhances the thermal decomposition of wheat straw pellets providing so faster formation, ignition and more complete burnout of the volatiles. By increasing the propane supply into the device up to 0.6 l/min (˜ 0.9 kW), the volume fractions of H2 and CO at the gasifier outlet increase by about 36 % and 45 %, respectively. The improved combustion of the volatiles downstream the combustor results in correlating increase of the temperature in the flame reaction zone (from 1,060 K up to 1,200 K), hence, increasing the heat power of the device by about 44 %. In addition, the wheat straw co-firing with propane improves the flue gas composition, decreasing the mass fraction of unburned CO in the products from 1.800 ppm to 800 ppm, H2 from 250 ppm to 40 ppm and the mass fraction of the hazardous NOx emission from 400 ppm to 250 ppm. A mathematical model of the combustion dynamics at co-firing straw with propane has been developed using MATLAB, considering the variations of the additional heat energy supply from the propane flame flow.

Mechanical properties and characteristics of wheat straw and pellets

Wheat straw pellets can be easily handled, transported and stored with reduced costs as compared with the raw material. The effect of pelletization process and densification parameters on the properties of the mixture of wheat straw powder and 40% epoxy 1092 as a binder was investigated. The samples were compressed into pellets using the lab-scale hydraulic press under various compacting pressures of 10, 12 and 15 bars and different die shapes and sizes (two cylindrical dies with diameters 10 and 18 mm (S1, S2), respectively, and a new hexagonal die of side length (s) = 6 mm (S3)). It was found that the pelleting process increased the fixed carbon content from 7.14% to 17.36%, the heating value from 15,600 kJ kg−1 to 27,800 kJ kg−1 and the bulk density 10 times when compared to a raw wheat straw powder. It was also found that type S2 at pressure 15 bar is the densest pellet and it had the maximum compression stress that reached 2798.54 kg m−3 and 70.02 MPa, respectively. The cylindrical pellet (type S1) of D = 18 mm at a pressure of 15 bar had the lowest water permeability of 2.35%. Pelletizing process had improved combustion characteristic parameters compared to raw biomass where combustion temperature ranges became higher, maximum weight loss rates and residues became lower that led to a higher combustion efficiency. Thermogravimetric analysis of wheat straw before and after pelleting process was analyzed to evaluate the combustion properties. Scanning electron microscopy images showed that the particle bonding was formed mainly from solid bridges, areas of cohesive failure due to lignin flow, and inter-diffusion between neighboring biomass particles. Images were investigated to explore the importance of compaction process. The images also showed that as the pressure decreases, the gap between the particles increases and produces the less durable pellet. It was found that the slagging index equals 0.38, which indicates that the pellet has a medium slagging inclination and for the fouling inclination (1.79), the wheat straw pellet has a relatively high fouling inclination.

Investigation of K*, Na* and Ca* flame emission during single biomass particle combustion

ABSTRACTNowadays biomass is widely used to produce electricity and heat. The growing demand for these stocks and their price results in the usage of low-quality biomass. In some cases, such biomass is mixed with herbaceous fuels and supplied to the heating plants. As such mix contains higher levels of volatile K, Na and Ca, there occurs ash-related problems such as slagging, fouling and agglomeration during combustion process.The aim of this work was to investigate the possibility to detect alkali-metals emission by chemiluminescence analysis during combustion in purpose to reduce the risk of ash-related problems. For experimental investigation, wood particle, wood pellet and wheat straw pellet were used. The chemiluminescence intensities of alkali species Na*, K* and Ca* and its variation during combustion of different biomass particle were evaluated. Results revealed that when fuel is changing during combustion, it is possible to predict the emissions of aforementioned radicals of different fuels and adjust appropriate regime of combustion.

Investigation of regularities of pelletized biomass thermal deformations during pyrolysis

Gasification process is a fairly complicated matter and using pelletized biomass for the gasification mostly results in fuel agglomeration. The pelletized biomass moving from the pyrolysis zone to the oxidation zone sticks together in lumps and disrupts entire process. In order to determine the regularities of thermal deformations, experimental research of pelletized biomass thermal deformations during pyrolysis were performed in a horizontal pyrolysis reactor from 300-900?C temperature capturing wood particle, wheat straw and wood pellet radial changes by a digital camera. Also the center temperature and the mass loss of samples were measured to determine cause of biomass thermal deformations. Observed results reveal that when increasing the pyrolysis temperature from 400-900?C, the wheat straw and wood pellets expand at the beginning of pyrolysis process and after it start to shrink, while wood particle is only affected by shrinkage. The swelling effect of pelletized samples starts decreasing over 600-650?C heating temperature and disappears when the temperature is higher than 850?C. Biomass shrinkage intensifies exponentially as the heating temperature increases till 700-750?C. However, the final shrinkage starts to decrease as the heating temperature increases from 700-750 to 900?C due to swelling of formed char. Determined phenomenon of pelletized biomass swelling explains cause of fuel adhesion in pyrolysis zone of gasifier. Besides estimated regularities of biomass thermal deformations upon pyrolysis could be used to improve the existing numerical models of biomass pyrolysis.

Mechanisms of biochar assisted immobilization of Pb2+ by bioapatite in aqueous solution

Bioapatite (BAp) is regarded as an effective material to immobilize lead (Pb2+) via the formation of stable pyromorphite. However, when applied in contaminated soil, due to its low surface area and low adsorption capacity, BAp might not sufficiently contact and react with Pb2+. Biochar, a carbon storage material, typically has high surface area and high adsorption capacity. This study investigated the feasibility of using biochar as a reaction platform to enhance BAp immobilization of Pb2+. An alkaline biochar produced from wheat straw pellets (WSP) and a slightly acidic biochar produced from hardwood (SB) were selected. The results of aqueous adsorption showed the combination of biochar (WSP or SB) and BAp effectively removed Pb2+ from the aqueous solution containing 1000 ppm Pb2+. XRD, ATR-IR, and SEM/EDX results revealed the formation of hydroxypyromorphite on both biochars’ surfaces. This study demonstrates that biochars could act as an efficient reaction platform for BAp and Pb2+ in aqueous solution due to their high surface area, porous structure, and high adsorption capacity. Therefore, it is mechanistically feasible to apply biochar to enhance BAp immobilization of Pb2+ in contaminated soil.

An Experimental Study of Combustion and Emissions of Wheat Straw Pellets in High-Temperature Air Flows

ABSTRACTThe present work is performed to investigate the combustion and emission behavior of wheat straw pellets of different sizes and shapes in a high temperature air flow. Prior to the combustion experiments, thermogravimetric analysis of the pellet was carried out to understand the thermo-chemical characteristics of the wheat straw pellet. A sequential method was used to determine the kinetic parameters. A combustor using preheated air is used to investigate the effect of different parameters, such as pellet size, starting temperature, and primary air flow velocity on combustion and emission characteristics of biomass pellets. The surface temperatures as well as the time-dependent mass loss rates are recorded to study the ignition behavior of pellets. The results showed that the increase in starting temperature, and air flow velocity and decrease in pellet size leads to a reduction in combustion time and increase in the total combustion rate. The results also showed that the concentration of CO formed increases as the heating time increases and the formation of CO2 increased with increasing the starting air temperature and air flow velocity inside the combustion chamber. It was found that the combustion efficiency ranged from 99% to 100% and the combustion efficiency reached 100% in some experiments due to complete combustion.