Biomass Moisture Content Research Articles

The influence of partial oxidation mechanisms on tar destruction in TwoStage biomass gasification

TwoStage gasification of biomass results in almost tar free producer gas suitable for multiple end-use purposes. In the present study, it is investigated to what extent the partial oxidation process of the pyrolysis gas from the first stage is involved in direct and in-direct tar destruction and conversion. The study identifies the following major impact factors regarding tar content in the producer gas: oxidation temperature, excess air ratio and biomass moisture content. In a experimental setup, wood pellets were pyrolyzed and the resulting pyrolysis gas was transferred in a heated partial oxidation reactor and oxidized between 800 and 1050°C with excess air rations between 0 and 0.7 and fuel moisture content between 8% and 30%. The gas composition was analyzed before and after oxidation by means of gas chromatography and mass spectrometry. The tar compounds were sampled by solid phase adsorption and determined by stable isotope dilution analysis. The results have shown that partial oxidation reduces and converts primary tars into low molecular weight, polycyclic aromatic hydrocarbons (PAHs), primarily naphthalene. At temperatures above 950°C practically all phenol is converted. The resulting PAH tar compounds are readily converted in the subsequent char-bed of the TwoStage gasification process and the partial oxidation process thus contributes directly as well as in-directly to the overall tar destruction. A high temperature and excess air ratios contribute positively to the direct tar destruction and a high moisture content of the biomass enhances the decomposition of phenol and inhibits the formation of naphthalene. This enhances tar conversion and gasification in the char-bed, and thus contributes in-directly to the tar destruction.

Woodchip drying in a screw conveyor dryer

Moisture content of raw biomass materials is a crucial parameter for system efficiency and the main purpose of the drying process is to reduce moisture content of the wet biomass. In this study, the drying characteristics of woodchip dried in a screw conveyor dryer had investigated experimentally. The experimental results demonstrated that drying rate had increased with the increasing drying air temperature and flow rate; however, the amount of volatile organic matters in the sample has kept constant. Furthermore, the results have showed that the best drying conditions in this study is 30 m3/h drying airflow rate, 200 °C drying air temperature, and co-current dryer type. With these conditions, moisture content of woodchip decreased from 60% to 27% (wet basis, mass %).

Modeling Air Drying of Sitka Spruce (Picea sitchensis) Biomass in Off-Forest Storage Yards in Ireland

Abstract Moisture management, through storage and drying in the supply chain between harvesting and use, is key to improving both transportation costs and market values of woody biomass. Storage can take place at sites within the forest or in off-forest storage yards. A model for predicting the moisture content of Sitka spruce roundwood and energy wood under an open, off-forest, environment was developed for Ireland. Experimental data for the model were gathered over a 16-month period beginning in April 2007. The major factors affecting biomass moisture content change are cumulative precipitation and evapotranspiration (ET0), biomass type, and type of cover. ET0 was computed using the FAO Penman-Monteith method, which requires temperature, solar radiation, wind, and relative humidity data. The model was easily used in a spreadsheet to estimate drying times for different locations in Ireland, different starting seasons for drying, different biomass types, and different types of cover. The model should not be used for estimating drying times for in-forest biomass storage because it will overestimate drying rates considerably.

Biomass fueling of a SOFC by integrated gasifier: Study of the effect of operating conditions on system performance

Biomass gasification can be efficiently integrated with Solid Oxide Fuel Cells (SOFCs) to properly deploy the energy content of this renewable source and increasing the ratio of electric to thermal converted energy. The key objective of this work is to analyze in a systematic and wide process the integration of a biomass gasifier process with the SOFC operation. In particular the work aims at identifying the role of SOFC H2 utilization as a basic parameter to maximize the system output and avoid gasifier bad operation issues such as tar production and carbon deposition. An efficient simulation framework is used to that purpose allowing for a detailed analysis of the influence of key driving parameters. The performance of the integrated system is thoroughly analyzed in the range of 1–2 kW electric power by also varying the input biomass characteristics in terms of Moisture Content (MC). Results show how a variation of the SOFC H2 utilization, a parameter whose effects are also correlated with the gasifier air requirement, affects electrical power output also depending on the biomass Moisture Content.

Mathematical Modeling of Coal Gasification Processes in a Well-Stirred Reactor: Effects of Devolatilization and Moisture Content

The devolatilization process and the moisture content in coal and biomass play an important role on the gasification performance of these fuels. To theoretically understand the complex chemical processes in a gasifier, we developed a multiphysics model to simulate the gasification processes in a well-stirred reactor. This model is a first-of-its-kind: it considers detailed gas-phase chemistry, drying and devolatilization kinetics, particle-phase reactions, boundary layer diffusion, pore evolution, as well as full coupling between the two phases at various scales for mass, species, and energy exchange. Numerical simulations were conducted using an in-house code to understand the comprehensive gasification process, and the focus was on the effects of devolatilization and moisture content. Sensitivity analysis was performed to identify the most influential parameters among various chemical and physical processes on the overall gasification performance (conversion time and syngas production). The results show that the syngas yield is most sensitive to the reaction rates of carbon-steam and carbon-CO2 reactions; the rates of drying and devolatilization have little impact on the syngas composition. The coal conversion time is most sensitive to the heat transfer rates including both radiation and convection, and its secondary sensitivity is to the reaction rate of the carbon-steam reaction. Lastly, the coal conversion time increases with increasing moisture content. This is because high moisture content causes a decrease of temperature, which reduces the reaction rates.

Performance evaluation of a diesel engine by using producer gas from some under-utilized biomass on dual-fuel mode of diesel cum producer gas

Producer gas through gasification of biomass can be used as an alternate fuel in rural areas due to high potential of biomass resources in India. Experiments were conducted to study the performance of a diesel engine (four stroke, single cylinder, 5.25 kW) with respect to its thermal efficiency, specific fuel consumption and diesel substitution by use of diesel alone and producer gas-cum-diesel (dual fuel mode). Three types of biomass, i.e. wood chips, pigeon pea stalks and corn cobs were used for generation of producer gas. A producer gas system consisting of a downdraft gasifier, a cooling cum cleaning unit, a filtering unit and a gas air mixing device was designed, fabricated and used to power a 5.25 kW diesel engine on dual fuel mode. Performance of the engine was reported by keeping biomass moisture contents as 8%, 12%, 16%, and 21%, engine speed as 1 600 r/min and with variable engine loads. The average value of thermal efficiency on dual fuel mode was found slightly lower than that of diesel mode. The specific diesel consumption was found to be 60%-64% less in dual fuel mode than that in diesel mode for the same amount of energy output. The average diesel substitution of 74% was observed with wood chips followed by corn cobs (78%) and pigeon pea stalks (82%). Based on the performance studied, the producer gas may be used as a substitute or as supplementary fuel for diesel conservation, particularly for stationary engines in agricultural operations in the farm.

The characteristics of torrefied microalgae

In order to utilize microalgae and their residues as biomass solid fuels for co-firing in the existing pulverized coal-fired power plants, this study is to investigate the properties of fuels from those feedstock prepared by the torrefaction process. The microalgae were cultivated by using flue gas emitted from coal-fired power plants of Taipower Co., and the residue was from extraction of microalgae by hot water. The operating conditions for the torrefaction temperature and residence time were set as 200, 250, 300 and 350°C, and 30, 60, 120min, respectively. Also, 30°C/min and 50°C/min as the heating rates were chosen to examine the mass yield of solid torrefied biomass from microalgae. After torrefaction, the ultimate analysis, proximate analysis, and higher heating value analysis of the torrefied biomass were carried out. In addition, the Hardgrove Grindability Index (HGI) of microalgal residue and its torrefied solid were measured. The results show that carbon content, ash content, fixed carbon content, higher heating value, and HGI of torrefied biomass increased with increasing the operating temperature and residence time. At the condition of 300°C and 30min, the higher heating value of torrefied microalgae and microalgal residue were 25.92MJ/kg and 26.76MJ/kg, respectively. Compared to raw materials, the increases were 26.70% and 17.16%, respectively. At the same circumstances, hydrogen content, oxygen content, moisture content and mass yield of solid torrefied biomass decreased with increasing temperature and residence time. After torrefaction at 300°C, the moisture content were all down to 1%, and the mass yield of solid torrefied biomass under 350°C by torrefaction were also kept up to 50%. The HGI of torrefied microalgal residue was 48.53, which exceed the sub-bituminous coal when the operation condition temperature was up to 250°C.

Ultrasonic vibration-assisted pelleting of wheat straw: a predictive model for pellet density using response surface methodology

Background: Cellulosic biomass can be used as the feedstock for liquid biofuel manufacturing. However, high costs associated with transportation and storage of low-density cellulosic biomass has hindered cost-effective manufacturing of cellulosic liquid biofuels. Pelleting can increase biomass density and reduce transportation and storage costs. Results & discussion: This article reports the development of a predictive model, using response surface methodology, for pellet density in ultrasonic vibration-assisted pelleting of wheat straw. The results show that pellet density increases as ultrasonic power and cylinder pressure increase, and as biomass moisture content and particle size decrease. Conclusion: This model can predict the effects of process parameters on pellet density in ultrasonic vibration-assisted pelleting. The methodology can also be applied to investigations of pellet durability and power consumption.

Fuel quality changes in full tree logging residue during storage in roadside slash piles in Northwestern Ontario

The procurement of logging residue for energy production can be uneconomical due to high moisture content and low gross calorific value. High moisture content in biomass lowers the energy density and transportation becomes less efficient. Logging residue, from full tree logging operations stored in roadside beehive and windrow piles, were examined to determine the effect of storage method and duration on fuel quality in northwestern Ontario, Canada. The fuel attributes assessed were moisture content, gross calorific value and ash content. Windrows displayed lower moisture content than beehives. Softwoods generally displayed lower moisture content and higher gross calorific values than hardwoods. Smaller diameter stems displayed higher gross calorific value and ash content than larger diameter stems. The moisture content (green basis) reduced from a green state to 15.1% after two years of storage in roadside slash piles, whereas gross calorific value and ash content did not change significantly with storage time. The gross calorific values ranged from 19.5 to 23.1 MJ kg −1 and the ash content ranged from 0.4% to 8.4% for all species, components and storage years. The study demonstrates that the storage regime plays a significant role on the fuel quality of logging residue. Proper storage and drying techniques improve the fuel quality and net energy yield from logging residue biomass, thereby leading to an overall cost reduction of the biomass feedstock. ► Feasibility of using full tree logging residues for bioenergy investigated. ► Effect of storage duration, pile type, species and diameter effect on fuel quality. ► Fuel qualities measured were gross calorific value, ash and moisture content. ► Moisture reduced during storage, no effect on gross calorific value or ash content. ► Field storage for certain period can improve energy yield and transportation cost.

Steam and air fed biomass gasification: Comparisons based on energy and exergy

Abstract Results are reported of thermodynamic analyses of a biomass gasification unit in which sawdust is the biomass feed and the gasifying medium is either air or steam. Energy and exergy analyses are performed for the system and each of its components. A parametric study reveals the effect of design and operating parameters on the system's performance and energy and exergy efficiencies. The results show that the adiabatic temperature of biomass gasification significantly changes with the type of the gasifying medium. In addition, the exergy and energy efficiencies are observed to be higher when air is the gasifying medium rather than steam, while the system performance and exergy efficiencies are dependent on the moisture content of the feed biomass. The results are significant because they quantify the strong dependence of biomass gasification, which can be used for syngas or hydrogen production, on moisture content, and gasifying medium.

Effect of Torrefaction on Water Vapor Adsorption Properties and Resistance to Microbial Degradation of Corn Stover

The equilibrium moisture content (EMC) of biomass affects transportation, storage, downstream feedstock processing, and the overall economy of biorenewables production. Torrefaction is a thermochemical process conducted in the temperature regime between 200 and 300 °C under an inert atmosphere that, among other benefits, aims to reduce the innate hydrophilicity and susceptibility to microbial degradation of biomass. The objective of this study was to examine water sorption properties of torrefied corn stover. The EMC of raw corn stover, along with corn stover thermally pretreated at three temperatures, was measured using the static gravimetric method at equilibrium relative humidity (ERH) and temperatures ranging from 10 to 98% and from 10 to 40 °C, respectively. Five isotherms were fitted to the experimental data to obtain the prediction equation that best describes the relationship between the ERH and the EMC of lignocellulosic biomass. Microbial degradation of the samples was tested at 97% ERH and 30 °...

Effect of operating and design parameters on the gasification/combustion process of waste biomass in fixed bed downdraft reactors: An experimental study

The main objective of this paper is to study the effect of operating and design parameters, mainly reactor geometry, air superficial velocity, biomass moisture content, particle size and biomass type (pine bark and sewage sludge), on the performance of the gasification/combustion process of waste biomass in fixed bed downdraft reactors. This experimental approach allows optimizing the dynamic behavior of the thermochemical process. Emphasis was put on interactions between the mentioned parameters with output or response variables, such as biomass consumption rate, fuel/air equivalence ratio, producer gas heating value and composition, tars concentration, and flame front velocity. The effect of the operating and design parameters on response variables was studied by means of multifactorial experimental designs. The statistical R2 obtained through the data fitting of the multifactorial experimental designs indicated that the factors taken into account explained between 80.8% and 98.8% of the variability of the response variables. For the particular experiments carried out, the optimal gasification conditions were obtained with the following set of inlet conditions: air superficial velocity of 0.06m/s, biomass particle size between 2 and 6mm, and biomass moisture content of 10.62%. The corresponding response variables were: flame front velocity=11mm/min, fuel air equivalence ratio=3.2, biomass consumption rate=125kg/h/m2, lower heating value of the producer gas=2965.6kJ/Nm3, tar concentration=7.73g/Nm3, and an average composition of the producer gas of 8.0% H2, 13.0% CO, 1.4% CH4, 14.9% CO2, and 62.7% N2.

Simulation of biomass gasification in a dual fluidized bed gasifier

Biomass gasification with steam in a dual-fluidized bed gasifier (DFBG) was simulated with ASPEN Plus. From the model, the yield and composition of the syngas and the contents of tar and char can be calculated. The model has been evaluated against the experimental results measured on a 150 KWth Mid Sweden University (MIUN) DFBG. The model predicts that the content of char transferred from the gasifier to the combustor decreases from 22.5 wt.% of the dry and ash-free biomass at gasification temperature 750°C to 11.5 wt.% at 950°C, but is insensitive to the mass ratio of steam to biomass (S/B). The H2 concentration is higher than that of CO under the normal DFBG operation conditions, but they will change positions when the gasification temperature is too high above about 950°C, or the S/B ratio is too low under about 0.15. The biomass moisture content is a key parameter for a DFBG to be operated and maintained at a high gasification temperature. The model suggests that the gasification temperature is difficult to be kept above 850°C when the biomass moisture content is higher than 15.0 wt.%. Thus, a certain amount of biomass needs to be added in the combustor to provide sufficient heat for biomass devolatilization and steam reforming. Tar content in the syngas can also be predicted from the model, which shows a decreasing trend of the tar with the gasification temperature and the S/B ratio. The tar content in the syngas decreases significantly with gasification residence time which is a key parameter.

Effect of various leachate recirculation strategies on batch anaerobic digestion of solid substrates

Various leachate recirculation strategies were applied to a batch-wise operated solid-phase digestion system in laboratory-scale tests. Comparative experiments with both continuous and intermittent leachate recirculation revealed no advantages of a continuous flow. Results suggest that leachate recirculation should not be carried out continuously during process initialisation when methanogenesis is the rate-limiting step. Continuous watering resulted in the accumulation of Volatile Fatty Acids (VFA) during process start-up. In addition, no need for continuous water circulation was found for the following digestion process when hydrolysis was rate-limiting. Even in the absence of liquid recirculation, degradation was only slightly retarded when the biomass moisture content was adjusted.

Biomass sorghum production and components under different irrigation/tillage systems for the southeastern U.S.

Renewable energy sources are necessary to reduce the U.S. dependence on foreign oil. Sorghum (Sorghum bicolor L.) may be a reasonable alternative as an energy crop in the southern U.S. because it could easily fit into existing production systems, it is drought resistant, and it has large biomass production potential. An experiment was conducted to evaluate several types of sorghum as bioenergy crops in Alabama: grain sorghum – NK300 (GS), forage sorghum – SS 506 (FS), and photoperiod sensitive forage sorghum – 1990 (PS). These sorghum crops were compared to forage corn (Zea mays L.) – Pioneer 31G65 in 2008 and 2009 with and without irrigation, and under conventional (total disked area, 0.15m deep) and conservation tillage (in-row subsoiling, 0.30m deep) in a strip-split-plot design. The parameters evaluated were: plant population (PP), plant height (PH), sorghum/corn aboveground dry matter (ADM), biomass moisture content (ABMC), and biomass quality (holocellulose, lignin, and ash). Sorghum had greater ADM than corn; however, corn had lower ABMC than sorghum. Lodging was observed in PS and FS, probably due to high plant populations (>370,000plantsha−1). Irrigation affected ADM positively in both years, but conservation systems improved ADM production only in 2009. Holocellulose, lignin, and ash variation differed significantly among crops but were lower than 8.3%, 2.0% and 1.9%, respectively, for both years and considered minor. Under conditions of this study, PS was considered the best variety for ADM production as it yielded 26.0 and 30.1Mgha−1 at 18 and 24 weeks after planting (WAP).

Hydrothermal conversion of water lettuce biomass at 473 or 523 K

The high moisture content of an aquatic biomass was used advantageously in a hydrothermal process. Reducing sugars, amino acids, proteins, and crude oil were extracted from water lettuce (Pistia stratiotes L.) using subcritically heated water. The highest yields of reducing sugars and amino acids were obtained after treatment at 473 K for 30 min (23.70 ± 0.52 g kg−1 and 4.35 ± 0.09 g kg−1 dry mass respectively), while protein was obtained at 3.60 ± 0.04 g kg−1 feedstock after treatment at 523 K for 60 min. The greatest solubilization occurred at 523 K after 60 min. The solid residues could be applied as fertilizers as hemicellulose and cellulose were hydrothermally converted to humus. The crude oil components that were extracted from the liquid residues differed markedly between the two treatment temperatures. The conversion of furan compounds to cyclopentenone and its derivatives only occurred at the higher reaction temperature and was increased by a longer reaction time.

Design and Implementation of an Efficient Biomass Drier System for a Wood Gasification Based Power Plant

The use of woody biomass gasification based power plants to generate electricity is on the rise with the fast depletion of fossil fuels and ever increasing energy demands. An important sub-system of such a plant is the drier which is used to reduce the moisture content of biomass to an optimum level for trouble free and optimum performance of the gasification system. This work concerns with the design, development and implementation of a drier system which utilizes waste heat available from the power plant to dry biomass. The drier designed is simple yet effective in capturing the waste heat from the engine exhaust as well as the radiator hot air. The drier is also easy to implement in rural areas.

Study of the influence of the composition of several biomass pellets on the drying process

Abstract In this work, theorical and experimental research in the field of the drying has been made. For this purpose, the exhaust gases and hot air generated from the exchange body of a 6.7 kW boiler for domestic heating were used for a biomass drying process. The fuels used were different densified biomass materials: pine, peartree and coniferous ( Pinus pinaster, Pynus communis and mixing of Pyrus sylvestris , respectively). The pellets were characterised by means of the lower heating value, proximate and ultimate analyses. The combustion parameters (CO 2 , CO, NO, NO 2 and NO x contents, fumes temperature and the moisture content in biomass) were analysed in order to detemine what fuel was more suitable for the drying process of common reed ( Arundo donax. L). The influence of the residue type and fuel mass flow on the combustion parameters have been studied. Finally, a global energy balance of the drying process and obtained losses have been evaluated, as well as the coefficients and the global yield of the process drying for common reed. From the results obtained, it was infered that the coniferous residue was the material presenting the most interesting yield of combustion and drying yield (80.2 and 47.5% respectively).

Development of fuzzy based methodology to commission co-combustion of unprepared biomass on chain grate stoker fired boilers

AbstractThis paper describes the development of an intelligent commissioning system to enable operators to maximise the utilisation of unprepared biomass by combusting the biomass with the minimum amount of support fuel to achieve a desired boiler output and thermal efficiency on chain grate stoker fired boilers. Tests were conducted on a 0·8 MWth chain grate stoker fired hot water boiler to investigate the combustion of different types of biomass blended with a support fuel over a wide range of boiler operating conditions and biomass moisture contents. The commissioning system was developed using fuzzy logic and expert system type rules developed while gathering the experimental data. The system was validated on untested blends of unprepared biomass with two support fuels where it was shown that it is possible to efficiently burn unprepared, high moisture content biomass with a support fuel on a chain grate stoker. This system could enable operators of chain grate stoker fired boilers to maximise the use...

Effects of torrefaction process parameters on biomass feedstock upgrading

Biomass is a primary source of renewable carbon that can be utilized as a feedstock for biofuels or biochemicals production in order to achieve energy independence. The low bulk density, high moisture content, degradation during storage and low energy density of raw lignocellulosic biomass are all significant challenges in supplying agricultural residues as a cellulosic feedstock. Torrefaction is a thermochemical process conducted in the temperature range between 200 and 300°C under an inert atmosphere which is currently being considered as a biomass pretreatment. Competitiveness and quality of biofuels and biochemicals may be significantly increased by incorporating torrefaction early in the production chain while further optimization of the process might enable its autothermal operation. In this study, torrefaction process parameters were investigated in order to improve biomass energy density and reduce its moisture content. The biomass of choice (corn stover) was torrefied at three moisture content levels (30%, 45% and 50%), three different temperatures (200, 250 and 300°C), and three unique reaction times (10, 20 and 30min). Solid, gaseous, and liquid products were analyzed, and the mass and energy balance of the reaction was quantified. An overall increase in energy density (2–19%) and decrease in mass and energy yield (3–45% and 1–35% respectively) was observed with the increase in process temperature. Mass and energy losses also increased with an increase in the initial biomass moisture content.