Integration of biomass drying with combustion/gasification technologies and minimization of emissions of organic compounds

Moisture content (MC) of green biomass or raw biomass materials (wood, bark, plants, etc.) commonly exceeds 50 mass % (wet basis). The maximum possible MC of biomass fuel for big scale combustion (e.g. fluidized bed combustion with low external heat losses) is approximately 60–65 mass %. Higher biomass MC generally causes operational problems of biomass combustors, lower stability of burning and higher CO and VOC emissions. Gasification of biomass with higher MC produces fuel gas of lower effective heating values and higher tar concentrations. In this review, various technological schemes for wood drying in combination with combustion/gasification with the assessment of factors for possible minimization of emissions of organics from the drying processes are compared. The simple direct flue gas biomass drying technologies lead to exhaust drying gases containing high VOC emissions (terpenes, alcohols, organic acids, etc.). VOC emissions depend on the drying temperature, residence time and final MC of the dried biomass. Indirect biomass drying has an advantage in the possibility of reaching very low emissions of organic compounds from the drying process. Exhaust drying gases can be simply destroyed as a part of the total combustion air (gas) in a combustion chamber or a gasifier. Liquid, condensed effluents have to be treated properly because they have relatively high content of organic compounds, some of them accompanied by odor. Drying of biomass with superheated steam offers more uniform drying of both small and bigger particles and shorter periods of higher temperatures of the dried biomass, particularly if drying to the final MC below 15 mass % is required. In practical modern drying technologies, biomass (mainly wood) is dried in recirculated gas of relatively high humidity (approaching saturation) and the period of constant rate drying is longer. Drying of moist wood material (saw dust, chips, etc.) is required in wood pellet production. Emissions of organics in drying depend on biomass properties, content of resins, storing time and on operational aspects of the drying process: drying temperature, drying medium, final MC, residence time, and particle size distribution of the dried biomass (wood). Integration of biomass drying with combustion/gasification processes includes the choice of the drying medium (flue gas, air, superheated steam). Properties of the drying media and operational parameters are strongly dependent on local conditions, fuel input of the combustion/gasification unit, cleaning of the exhaust drying media (gas, steam, wastewater), and on environmental factors and requirements.     

Heat/mass transfer characteristics and nonisothermal drying kinetics at the first stage of biomass pyrolysis

Biomass pyrolysis can be divided into three stages: moisture evaporation, main devolatilization, and continuous slight devolatilization. This present study focuses on the heat and mass transfer characteristics of biomass in the first pyrolysis stage, which takes place in the range of room temperature to 150?°C. Thermalgravimetric experiments of rice husk and cotton stalk were performed by a synchronic thermal analyzer (TG/DSC). Four nonisothermal drying models were obtained from common isothermal drying models in order to describe the drying behavior of agricultural products. The moisture content of biomass decreased rapidly as the temperature increased and an apparent water loss peak was observed in the temperature range of 65?C75?°C. DSC could be regarded as the superposition of three parts: heat flow from moisture evaporation, heat flow from the heat capacity of unevaporated moisture, and heat flow from the heat capacity of dry base biomass. The heat requirements for the dehydration of 1?kg rice husk and cotton stalk were 251 and 269?kJ, respectively. Nonisothermal drying models were evaluated based on the coefficient of determination (R ²) and reduced chi-square (??²). Page model was found to be the best for describing the nonisothermal drying kinetics. The values of activation energy were determined to be 9.2 and 15.1?kJ/mol for rice husk and cotton stalk, respectively.     

Determination of the contents of water and moisture in milk powder

According to official methods the moisture content of milk powders is determined by drying techniques and the loss of mass defined as water content. The mass loss, detecting the volatiles evaporated under the applied conditions, is strongly dependent on the drying parameters. An ideal method should be able to determine “free water” without including “bound water” in the result. Two collaborative studies showed that drying methods are not capable of distinguishing between different binding forms of water and only the total water content, measured with Karl Fischer titration, provides results which can be attributed to a defined physical property. Results from two European collaborative studies are employed to evaluate three different drying techniques and Karl Fischer titration. Adsorption isotherms of skimmed milk powder at different temperatures were used to calculate the isosteric heat of sorption. Received: 3 April 2000 / Revised: 17 May 2000 / Accepted: 24 May 2000     

Water Status and Predictive Models of Moisture Content during Drying of Soybean Dregs Based on LF-NMR

To explore the drying characteristics of soybean dregs and a nondestructive moisture content test method, in this study, soybean dregs were dried with hot air (80 °C), the moisture content was measured using the drying method, water status was analyzed using low-field nuclear magnetic resonance (LF-NMR) and the moisture content prediction models were built and validated. The results revealed that the moisture contents of the soybean dregs were 0.57 and 0.01 g/g(w.b.), respectively, after drying for 5 and 7 h. The effective moisture diffusivity increased with the decrease in moisture content; it ranged from 5.27 × 10⁻⁹ to 6.96 × 10⁻⁸ m²·s⁻¹. Soybean dregs contained bound water (T₂₁), immobilized water (T₂₂) and free water (T₂₃ and T₂₃’). With the proceeding of drying, all of the relaxation peaks shifted left until a new peak (T₂₃’) appeared; then, the structure of soybean dregs changed, and the relaxation peaks reformed, and the peak shifted left again. The peak area may predict the moisture content of soybean dregs, and the gray values of images predict the moisture contents mainly composed of free water or immobilized water. The results may provide a reference for drying of soybean dregs and a new moisture detection method.     

Fermentation Efficiency of Cells Immobilized on Delignified Brewers' Spent Grains after Low- and High-Temperature Thin Layer Thermal Drying

Low-cost dried yeasts immobilized on delignified brewers' spent grains for use in wine making and brewing were produced by simple thermal drying techniques. To optimize the thermal drying process, vacuum and air stream conditions were examined. Drying of thin layers of the biocatalysts was performed at low (30–38 °C) and high temperatures (40–70 °C). The fermentation efficiency of the thermally dried biocatalysts was acceptable, with immobilized cells showing a significantly higher thermotolerance compared with free cells. Immobilized cells dried at high temperatures presented slightly improved glucose fermentation efficiency compared with the low-temperature dried biocatalysts. Gas chromatography–mass spectrometry analysis of aroma volatiles of the fermented products revealed an increase of esters, lower higher alcohol formation, and significantly lower concentration of carbonylic compounds.     

Effective moisture diffusivity and activation energy during convective drying of bread containing clove oil/orange oil

The aim of present study was to investigate the characteristic drying behaviour of bread with the convective drying method for increasing bread shelf life. Effective moisture diffusivity and activation energy were compared in detail. According to the results, bread samples were dried between 0 and 450 min for 40 °C, 0–180 min for 50 °C and 60 °C, respectively. The experimental data with high coefficient of determination (R²) changed between 0.889 and 0.998. The values of D_eff were obtained between 1.21 × 10^?9-1.22 × 10^?8 m²/s. Also, E_a values were found to be in range of 82.47–100.49 kJ/mol for bread samples which had additive-free and additive. When the bread samples without additives and the breads with essential oils were compared, it was found that the activation energy increased with the use of additives. Moisture content values decreased with the increase in time. Drying rate and moisture content relation showed the expected behaviour, thermally and morphologically.     

The experimental study and modelling the drying kinetics of mussels using ultrasound assisted vacuum drying

In the present study, chemical compositions, drying kinetics, quality parameters and energy consumptions for mediterranean or black mussel (Mytilus galloprovincialis) subjected to ultrasound assisted vacuum drying (UAVD) were analyzed between the range of 50–70 ​°C. During drying only falling rate periods were observed. Obtained conclusions demonstrated that the moisture content and drying rate were influenced by the ultrasound assisted vacuum drying method and the drying air temperature. The ultrasound assisted vacuum drying shortened the drying period and increased the effective moisture diffusivity (D_eff). Drying led to a considerable increasing of protein and fat content. Six well-known thin layer drying models were compared with regards to coefficients of determination. The Alibas model was selected as the best one. The activation energy was calculated as 3.80 ​kW/kg. High “L1" and low "ΔE" values were obtained for dried mussels. Using of ultrasound assisted vacuum drying technique resulted in very low energy consumption.     

Sustainable Drying and Torrefaction Processes of Miscanthus for Use as a Pelletized Solid Biofuel and Biocarbon-Carrier for Fertilizers

Miscanthus is resistant to dry, frosty winters in Poland and most European Union countries. Miscanthus gives higher yields compared to native species. Farmers can produce Miscanthus pellets after drying it for their own heating purposes. From the third year, the most efficient plant development begins, resulting in a yield of 25–30 tons of dry matter from an area of 1 hectare. Laboratory scale tests were carried out on the processes of drying, compacting, and torrefaction of this biomass type. The analysis of the drying process was conducted at three temperature levels of the drying agent (60, 100, and 140 °C). Compaction on a hydraulic press was carried out in the pressure range characteristic of a pressure agglomeration (130.8–457.8 MPa) at different moisture contents of the raw material (0.5% and 10%). The main interest in this part was to assess the influence of drying temperature, moisture content, and compaction pressure on the specific densities (DE) and the mechanical durability of the pellets (DU). In the next step, laboratory analyses of the torrefaction process were carried out, initially using the Thermogravimetric Analysis TGA and Differential Scaning Calorimeter DSC techniques (to assess activation energy (EA)), followed by a flow reactor operating at five temperature levels (225, 250, 275, 300, and 525 °C). A SEM analysis of Miscanthus after torrefaction processes at three different temperatures was performed. Both the parameters of biochar (proximate and ultimate analysis) and the quality of the torgas (volatile organic content (VOC)) were analyzed. The results show that both drying temperature and moisture level will affect the quality of the pellets. Analysis of the torrefaction process shows clearly that the optimum process temperature would be around 300–340 °C from a mass loss ratio and economical perspective.     

Quantification of Flavonoids,Phenols and Antioxidant Potential from Dropped Citrus reticulata Blanco Fruits Influenced by Drying Techniques

Physiologically dropped immature Citrus reticulata Blanco fruits are regarded as waste and discarded in the citrus orchard but are a good source of bioactive compounds including flavonoids, antioxidants and total phenols. A study was undertaken to identify and quantify these bioactive compounds and to investigate the influence of different drying techniques, namely freeze drying and hot air oven drying, on flavonoids namely flavanone glycosides, antioxidant potential and total phenol content in immature dropped fruits of Citrus reticulata Blanco. Flavonoids were quantified in high-performance liquid chromatography (HPLC). The antioxidant activity were investigated with three assays azino-bis [3-ethylbenzthiazoline-6-sulfonic acid]) (ABTS), 2,2-diphenyl-1-picrylhydrazyl radical (DPPH), Ferric Reducing Ability of Plasma (FRAP) and total phenol content was determined. Freeze dried samples of 12 and 14 mm size retained maximum hesperidin flavonoid content (27.03% and 27.20%) as compared to the hot air dried samples (17.99%) and retained higher phenolic content ranged from 50.54–54.19 mg GAEL⁻¹. The antioxidant activity in freeze dried fruits was from 12.21–13.55 mM L⁻¹ Trolox and 15.27–16.72 mM L⁻¹ Trolox with ABTS, DPPH assay and FRAP values ranging from 7.31–9.07 mM L⁻¹ Trolox. Significant positive correlation was found between the flavonoid hesperidin with antioxidant assays and total phenolic content (TPC). The results showed that waste citrus fruits can act as potential source of bioflavonoids, especially hesperidin, and antioxidants for pharmaceutical as well as nutraceutical industry.     

Improvement of mechanical and oxygen barrier properties of cellulose films by controlling drying conditions of regenerated cellulose hydrogels

Mechanical, thermal and oxygen barrier properties of regenerated cellulose films prepared from aqueous cellulose/alkali/urea solutions can be markedly improved by controlling the drying conditions of the films. By pre-pressing followed by vacuum drying under compression, the tensile strength, Young’s modulus, coefficient of thermal expansion and oxygen permeability of the dried films reached 263 MPa, 7.3 GPa, 10.3 ppm K⁻¹ and 0.0007 ml μm m⁻² day⁻¹ kPa⁻¹, respectively. Thus, films produced in this way show the highest performance of regenerated cellulose films with no orientation of cellulose chains reported to date. These improved properties are accompanied by a clear increase in cellulose II crystallinity from 50 to 62% during pre-pressing/press-vacuum drying process. At the same time, the film density increased from 1.45 to 1.57 g cm⁻³, and the moisture content under equilibrium conditions decreased from 14.1 to 9.8%. Hence, the aqueous alkali/urea solvent system has potential applications in producing new and environmentally friendly cellulose films with high performances through control of the drying conditions.     

Construction of an Isoperibol Calorimeter to Measure the Specific Heat Capacity of Foods Between 20 and 90°C

A simple isoperibol calorimeter, using the modified method of mixtures, was developed to measure the average specific heat capacity of different dough types between 20 and 90°C. The method consisted of encapsulating the sample in a copper cylinder and immersing the capsule in water at a different temperature. The procedure was tested for reliability with distilled water and whole fat milk before applying it to five dough types of varying moisture and fat contents. Mean values of 4.176±0.008 kJ kg^-1 K^-1 and 3.942±0.034 kJ kg^-1 K^-1 were obtained for distilled water and milk respectively, which agree within 0.23 and 0.34% from reported values. The specific heat values for the five dough types were found to range between 2.15–2.68 kJ kg^-1 K^-1 between 2.35–3.10 kJ kg^-1 K^-1 and between 2.40–3.19 kJ kg^-1 K^-1 at the three temperature levels studied. The specific heat capacity was found to depend not only on the moisture level but also on the fat content, especially for dough types with a high percent of fat. Regression analysis was then used to correlate these values and develop a set of empirical equations. The results were used to assist in energy balance calculations in backing oven for industrial purposes. This revised version was published online in July 2006 with corrections to the Cover Date.     

生物质热反应机理与活化能确定方法Ⅰ.干燥段研究

干燥段是生物质热解的第一个过程.采用热分析仪研究了杉木木屑干燥段质量和热量的变化,推导了非等温干燥动力学模型,探讨了热质传输机理.结果表明,随着温度的升高,木屑含湿量迅速下降,80℃左右出现一个明显的失重峰;非等温干燥动力学Page模型能很好地模拟木屑干燥过程,木屑干燥活化能为12.6 kJ/mol;水分传输与热量传递...     

Fine coal dewatering using pH- and temperature-sensitive superabsorbent polymers

Water is a necessary medium in most coal preparation processes, but its presence in the final product has a negative impact on transporation costs, handling and specific energy value. A major contribution to the total moisture content may be attributed to the proportion of fine coal in the total product, which presents the greatest dewatering problem. This paper describes a novel process that seeks to reduce the moisture content of fine coal cakes to a level comparable to that achieved by thermal drying. In this process, superabsorbent polymers, which are granular highly crosslinked synthetic copolymers with excellent water-absorbing properties, are employed to draw water from moist fine coal. The drying or dewatering process is characterized by three main stages: (a) contacting of superabsorbents with high-moisture fine coal; (b) separation of dried fine coal from superabsorbents by screening; and (c) regeneration of used superabsorbent polymer, taking advantage of its response to changes in such conditions as pH, temperature or electric field. Depending on the polymer type, the dosage and the polymer/coal contact time, the moisture content of coal filter cake can readily be reduced from, say, 25% to 10% by mass or less. The results of laboratory and pilot scale tests conducted using pH- and temperature-sensitive superabsorbent polymers are discussed in this paper. © 1997 John Wiley & Sons, Ltd.     

Kinetic study of pyrolysis of waste water treatment plant sludge

Activated sewage sludge samples obtained from two different waste water treatment plants were investigated by thermogravimetric analysis. Due to a very high content of water in the sludge samples, these had to be dried at 160°C in an electrical oven in order to remove all adsorbed water. To ensure pyrolysis conditions, nitrogen atmosphere was applied. The pyrolysis decomposition process was carried out in the temperature range from ambient temperature to 900°C at three different heating rates: 2 K min⁻¹, 5 K min⁻¹, 10 K min⁻¹. TGA and DTG curves of the decomposition processes were obtained. Temperature of onset decomposition, final temperature of decomposition, maximum decomposition rate, and decomposition temperature were determined by thermogravimetric analysis for both sludge samples used. The main decomposition process takes place at temperatures in the range from 230°C to 500°C. Above this temperature, there are only small changes in the mass loss which are often attributed to the decomposition of carbonates present in the sewage sludge samples. To determine the apparent kinetic parameters such as the activation energy and the preexponential factor, the so called Friedman isoconversional method was used. Because of the requirements of this method, initial and final parts of the decomposition process, where crossings of the decomposition lines occurred, were cut off. Obtained dependencies of the apparent activation energies and preexponential factors as a function of conversion were used backwards to calculate the modeled decomposition process of sewage sludge and the experimental data were in good accordance with the data obtained by simulation.     

Porous texture of silica aerogels made with ionic liquids as gelation catalysts

The effect of four ionic liquids on the porous texture of silica aerogels synthesized from mixed tetramethoxysilane and methyltrimethoxysilane and dried by the CO₂ supercritical method, was studied. Two of these ionic liquids were composed of BF₄ ⁻ anions while the other two included Cl⁻ anions. The synthesis of gels from ionic liquids did not require another acidic catalyst for silica hydrolysis, nor a basic catalyst for silica condensation. These aerogels were compared with traditional aerogels made according to a double step catalysis, which first involved hydrolysis with HCl followed by condensation with pH 9 Tris HCl buffer. Gel mass analysis and thermogravimetric data showed that, when the initial molar of ionic liquid to Si was 1.58, only ~2% (by mass) of the initial ionic liquids consisting of BF₄ ⁻ anions and ~10% (by mass) of ionic liquids containing Cl⁻ anions, remained in the aerogels after supercritical drying. Moreover, X-ray diffraction confirmed that in ionic liquids based on BF₄ ⁻ anions, evaporation of the volatile components before supercritical CO₂ drying led to the formation of regularly ordered mesopores.     

Synthesis of silica nanoparticles by modified sol–gel process: the effect of mixing modes of the reactants and drying techniques

A modified preparation of silica nanoparticles via sol–gel process was described. The ability to control the particle size and distribution was found highly dependent on mixing modes of the reactants and drying techniques. The mixture of tetraethoxysilane and ethanol followed by addition of water (Mode-A) produced monodispersed powder with an average particle size of 10.6 ± 1.40 nm with a narrow size distribution. The freeze drying technique (FD) further improved the quality of powder. In addition, the freeze dried samples have shown unique TGA decomposition steps which might be related to the well-defined structure of silica nanoparticles as compared to the heat dried samples. DSC analysis showed that FD preserved the silica surface with low shrinkage and generated remarkably well-order, narrow and bigger pore size and pore volume and also large endothermic enthalpies (ΔH _FD = −688 J g⁻¹ vs. ΔH _HD = −617 J g⁻¹) that lead to easy escape of physically adsorbed water from the pore at lower temperature.     

Removal of ammonia emissions from waste air in a biotrickling filter: pilot-scale demonstration in real conditions

This study was aimed at testing the possibility of using a biotrickling filter for the treatment of waste air resulting from animal farming. For this purpose, a laboratory and pilot biotrickling filter with a moving bed were constructed. In the first case, the removal of ammonia emissions from waste air, by means of ammonia nitrogen utilization by present micro-organisms under laboratory conditions, was tested. The mass load of the biotrickling filter was gradually increased by slowly increasing the ammonia concentration. In the second case, the pilot biotrickling filter with a moving bed was installed inside a pig farm and it was tested under real operation conditions. In the first case, the highest value of the laboratory biotrickling filter’s elimination capacity was 6.2 g_NH3 m⁻³ of filling h⁻¹. The elimination capacity of the pilot filter was 1.6 g_NH3 m⁻³ of filling h⁻¹. The source of carbon for the present micro-organisms was a 1% sucrose solution, which simulated waste water with high content of COD_CR. [<-define what COD is, if mentioned for the first time] At the same time there was almost 89% decrease in waste water pollution. It was also shown that the contribution of the ammonia nitrogen utilization by the present micro-organisms to the removal of ammonia from the waste air was 90%.      

Determination of alkylphenols and alkylphenol ethoxylates in sewage sludge: effect of sample pre-treatment

A complete characterization of sewage sludge collected from five biological waste water treatment plants was done to determine physico-chemical parameters, heavy metals and alkylphenols, making special emphasis on sampling, homogenization, and sample pre-treatment. Ultrasonic extraction followed by gas chromatrography coupled with mass spectrometry was used to evaluate the effect of sample pre-treatment (untreated sample, freeze-drying, drying at 40 °C or drying at 100 °C) on the concentration of octylphenol (OP), nonylphenol (NP) and nonylphenol ethoxylates (NP₁EO, NP₂EO). Untreated samples and samples dried at 100 oC gave concentration levels up to 62% and 89% lower, respectively, than freeze-dried samples. In 50% of cases, freeze-dried samples led to significantly higher concentrations than those obtained by drying at 40 °C. Thus, freeze-drying is the recommended sample pre-treatment to prevent possible losses of OP, NP, and NP₁EO. Using this methodology, concentrations detected were from 3.2 to 199 mg kg⁻¹ being NP followed by NP₁EO found in highest concentration. The total concentration of NP and NP₁EO exceeded the limit of 50 mg kg⁻¹ proposed by the draft European directive on sewage sludge in three out of five samples studied. Contrarily, heavy metals were below the legislated values.     

Thermal and kinetic study of tyre waste pyrolysis via TG-FTIR-MS analysis

The world production of tyre waste amounts to 5·10⁶ ton year^–1, 2·10⁶ tons of which are produced in Europe, but the final destination of nearly 65–70% of them is the landfill, despite the high added value materials lost and the consequent environmental impact. Treatments alternative to landfilling take into account reconstruction and reuse of the tyres or the matter and/or energy recovery by means of thermal treatment processes (incineration, gasification and pyrolysis). Among these, pyrolysis seems to be a promising and realistic alternative to attain the conversion of tyre waste into valuable and reusable products. Present work relates to experimental tests and results obtained for the study of tyre waste pyrolysis, conducted by means of thermo-gravimetric analysis (TG) of the material and the simultaneous determination, through Fourier transform infrared (FTIR) and mass spectrometry (MS), of the decomposition products. The analysis of the volatile fraction allows to isolate, within the thermograms, the evolution of products referable to specific tyre components and therefore it suggests the application of a multi-component decomposition model. The kinetic model consequently developed agrees fairly well with the experimental data.     

石蜡/碱改性硅藻土/膨胀石墨复合相变储热材料的制备及性能

通过碱处理,优化了硅藻土(DIA)的孔隙结构,提高了孔隙率,增加了石蜡(paraffin)负载量。通过直接浸渍法制备了新型性状稳定的石蜡/碱改性DIA/膨胀石墨(EG-alDIAP)复合材料,并研究了其结构与性能的关系。结果表明,复合相变材料的石蜡负载量从47.4%提高到了61.1%,进而提高了复合材料的储热性能;向改性DIA中添加膨胀石墨(EG)提高了复合材料的传热能力,添加质量分数10%EG时导热系数提高了113%(从0.276 W·m^-1·K^-1提高到了0.589 W·m^-1·K^-1)。随着EG含量的升高,复合相变材料的相变潜热有所增加,但化学相容性、稳定性等无明显变化。含10%EG的石蜡/碱改性DIA复合材料具有可靠的储能性能、良好的温度调节性能和蓄放热能力。