Correction to: Study of the influence of catalyst on wet biomass torrefaction process in fluidized bed with superheated steam

The drying characteristics and properties (color and shrinkage) of carrots (as a representative agricultural product) were experimentally examined in a fluidized bed under reduced pressure. Dry hot air and superheated steam were used as the drying gases. Rice and carrot powders (0.125–0.355 mm in diameter) were used as the fluidizing particles, in addition to glass beads (0.12 mm in diameter). It was confirmed that the drying rate using a fluidized bed was much higher than without a fluidized bed (hot-air drying), regardless of the type of fluidizing particles used. Under reduced pressure, both with and without a fluidized bed, the drying rate was higher than that at atmospheric pressure using hot air. The drying rate was sufficiently high for fluidized-bed drying with superheated steam, though the drying rate was higher with hot air than with superheated steam. As the drying temperature increased, the volume ratio (befor/after drying) of the sample increased. At high drying temperatures (373 and 423 K in the present study), the color of the sample changed; in other words, a heat-induced change in the properties of the carrot was observed. At a low drying temperature (333 K in the present study), the drying method did not affect the color of the carrot; i.e., the color of the dried material was maintained even in a fluidized bed under reduced pressure when the drying rate was higher.

Study of the influence of catalyst on wet biomass torrefaction process in fluidized bed with superheated steam

The drying characteristics of porous materials immersed in the fluidized bed of fluidizing particles with superheated steam were examined. A B-1 brick ball, in which the gas diffusion was governed by Knudsen diffusion, was used as the drying sample and the glass beads (0.12 mm in diameter) were used as the fluidizing particles. N2 gas was also used as the drying gas for the comparison. N2 gas was the substitute of air. The temperature of the fluidized bed and the mass velocity of drying gas were changed, respectively. The theoretical analysis including the convective gas transfer in the sample and condensation of the steam in the sample was also preformed.There is a period when the temperature of the sample center is almost constant in the fluidized bed drying with superheated steam and with hot air. The temperature of the sample center in superheated steam is higher than that in hot air. In the case of superheated steam, the temperature during the period when the temperature of the sample center is almost constant is equal to the boiling point of water. When the mass transfer resistance in a sample is large, the temperature in the sample increases because of the increment of the pressure in the sample. This phenomenon was confirmed by the calculated pressure in the sample. The effect of the bed temperature on the drying characteristics is significant, while that of the mass velocity of drying gas is very slight.

Fluidized bed-steam drying combines the energetic and operationally safe advantages of steam drying with the excellent heat and mass transfer conditions of fluidized bed technology. The existing moisture loading of the particles, as dependent variables in drying processes, is relatively difficult to determine through balancing the quantity of the escaping gas, since, in the case of the superheated steam drying observed in this paper, both the particle moisture and the drying medium are water. Temperature progressions however can be determined easily and without great demand on the apparatus. The experiments presented in this paper serve to establish a connection between the temperature and moisture progression, as well as between all other relevant drying parameters such as gas mass flow, gas temperature or particle mass. To do this, the components involved (fluidization gas, fluidized bed particles and apparatus wall) are balanced for mass and energy. With the help of modeling based on physical laws, the mechanism of fluidized bed drying with superheated steam as fluidizing and drying medium are resolved. The result is that any drying time progression can be simulated. Discontinuous fluidized bed drying in batches serves as the basis for the experiments. In order to use also the mathematical modeling of a discontinuous fluidized bed apparatus for continuously operated processes, a longitudinal mixture of the material being dried in a continuous drying apparatus, e.g. in a fluidized bed channel, must be suppressed or presumably disregarded. The local coordinate of the continuous fluidized bed apparatus and the time coordinate of the discontinuous fluidized bed apparatus are then connected to one another by the product velocity being set to a constant.

Superheated steam is a vital drying media due to inherently passive, nonpoisonous, no fire risk, antioxidant, and compatible with food products with superb thermophysical properties than hot air. Moreover, it will improve energy efficiency by energy-saving due to reusing the energy from exhausted steam, mainly by recirculation, and the use of partial exhaust of excess steam for other operations reduces the additional energy requirement. Additionally, the specific heat at constant pressure for superheated steam is nearly double that of the hot air, reducing the quantity required for drying. In general, superheated steam as a drying medium instead of hot air has significant potential. In this study, past, present, and prospects of the superheated steam drying (SSD) are critically analyzed and are presented systematically, such as classification, working, and recent developments. This study also focused on various areas such as analytical modeling, experimental work, and pilot-test of SSD with covering energy recovery and energy efficiency. Out of different drying systems, Fluidized bed dryers, Vacuum dryers, Rotary dryers, Flash dryers, Impingement dryers, and Spray dryers applicable for SSD are discussed in details as the current stage of development and probable potential. The SSD is having bright future for diverse applications including vegetable drying and fruit processing, chemical process industries, wood drying, chemicals, dyestuff and pigments recovery, effluent drying, etc.

In this paper authors present research results which are the optimum parameters of the torrefaction process using straw from oats and maize. The most important parameters for the torrefaction process are temperature and residence time. Both parameters are essential to designing and construction of industrial biomass torrefaction installations. Energy crops and waste coming from agricultural production have the most promising perspective from all kind of renewable energy sources in Poland. Currently, intensive studies on the process of biomass torrefaction are being carried out. In this experimental investigation, authors examined the torrefaction process of two types of agriculture biomass, such as: oats, maize. The main overarching objective of the experimental studies described below is the development of various biochar as an additive to agricultural fertilizers resulting from the conversion of biomass from agriculture residues – straw from oats and maize. The last of enumerated biomasses is treated through different conversion processes such as: drying, torrefaction to homogenize their physical and chemical properties. Among many of its areas, it is extremely important to optimize the production of biomass energy plants and its refinement (in the torrefaction process), which will improve the balance and profitability of energy production from RES, and reduce the logistics and storage costs of this fuel and improve the efficiency of biomass combustion process. When implementing new technologies indicated in this work and optimizing the harvesting of plant biomass, the negative impact on the environment caused by stored municipal waste can be reduced. This biomass torrefaction process temperature and residence time were necessary for the design and construction of semi-pilot scale biomass torrefaction installations with dryer and torrefaction reactor to perform a continuous biomass torrefaction process using superheated steam

Effects of heating media and operating conditions on drying kinetics and quality of germinated brown rice

Drying rates of lignite particle groups in superheated steam are evaluated using a single-particle model developed for Australian lignite. Size distributions of the particles are assumed to obey the Rosin–Rammler equation with the maximum particle diameters defined as 100, 50, and 6 mm. The results show the drying rate of a lignite group depends strongly on the maximum particle size, and removal of large particles prior to drying is shown to be effective to reduce the drying time. The calculation model is available for simulations of drying behaviors of lignite in various dryers when an appropriate heat transfer coefficient is given. This study simulates the drying of particles smaller than 6 mm using a heat transfer coefficient in a fluidized bed dryer reported elsewhere. The required drying time estimated from the calculation is comparable to the processing time reported in an actual fluidized bed dryer, supporting the validity of the calculation model.

A bench-scale indirect pulsation-assisted fluidized bed dryer with a 0.24 m2 cross-section area has been built to confirm the drying performance of lignite. The fluidized bed dryer with tube bundles was utilized to investigate the scale-up effect on the drying rate of the pulsed flow using superheated steam as the drying medium. Particles agglomeration was found a serious problem when to increase the scale of the fluidized bed dryer. Agglomeration reduction could be achieved through increasing horizontal diffusion rate using the pulsation-assisted flow and then drying rate was enhanced. Drying rate enhancement effect increased with the increase of the pulsation-assisted flow velocity. The pulsation-assisted flow could enhance the drying rate by nearly 40% compared to that of the steady flow at the gas velocity of 0.29 m/s, and 20% at the gas velocity of 0.19 m/s. Frequency of pulsed flow also affected the drying rate, which 3 and 5 Hz-pulsed flow has a higher drying rate than that of 1 Hz.HighlightsDrying characteristics of lignite in pulsation-assisted fluidized bed was studied.Pulsation-assisted flow enhanced the lignite drying rate.Particle horizontal dispersion rate increased by pulsation-assisted flow.3 and 5 Hz pulsed flow increased the drying rate than 1 Hz.

Experimental and theoretical investigation on drying of a single coal particle in fluidized bed combustor is presented. Coal particle drying was considered via the moist shrinking core mechanism. The results of the drying test runs of low-rank Serbian coals were used for experimental verification of the model. The temperature of the coal particle center was measured, assuming that drying was completed when the temperature equalled 100°C. The influence of different parameters (thermal conductivity and specific heat capacity of coal, fluidized bed temperature, moisture content and superheating of steam) on drying time and temperature profile within the coal particle was analyzed by a parametric analysis. The experimentally obtained results confirmed that the moist shrinking core mechanism can be applied for the mathematical description of a coal particle drying, while dependence between drying time and coal particle radius, a square law relationship, implicates heat transfer control of the process and confirms the validity of assumptions used in modeling.

ABSTRACTMost commercial parboiled rice is produced from high-amylose content rice. Glutinous rice, which is lacking in amylose content, is generally consumed in Southeast Asian countries. Rare study of parboiling glutinous rice has been observed. In this study, glutinous rice was improved in head rice yield by a novel parboiling process. Two rough glutinous rice, rice department 6 (RD6) and black glutinous rice (BGR) cultivars, were soaked in hot water at 70 ± 5°C for 3 h. The ricer 3moisture content after soaking was 50–52% (d.b.), it was dried with hot air and superheated steam (SHS) at 110, 130, and 150°C in a fluidized bed dryer. The results show that SHS at all drying temperatures can improve the high head rice yield in both parboiled glutinous rice cultivars better than hot air drying. Higher temperature drying caused L* value to decrease but the b* value increases in RD6, whereas in BGR, all color values decreased and ΔE* was increased when the drying temperature increased. Increasing drying temperature presented a softer texture of both glutinous rice cultivars. Upper 130°C, completed gelatinization of both varieties can be obtained and seen by scanning electron microscope and differential scanning calorimeter (DSC). This technique of using high-temperature fluidized bed drying can produce completely parboiled glutinous rice in a single process instead of two conventional processes, steaming and drying, in series.

Modelling of the batch treatment of wet granular solids with superheated steam in fluidized beds

In the paper, we theoretical analysis the gas-particle flow behaviors in the drying chamber. Then establish a small experimental device and conduct a comparative fluidization experiment with superheated steam and hot air, which the dried rapeseed particles are the experimental material. The critical fluidizing velocity of the rapeseed particles in superheated steam is 1.26 m/s in the experimental condition. The experimental results show that the inlet operating flow velocity of superheated steam fluidized bed drying is greater than which of the traditional hot air fluidized bed dying under the same conditions.

Biomass is increasingly becoming an internationally traded commodity fuel. In this context, biomass upgrading technologies such as torrefaction and hydrothermal carbonization (HTC), which increase the energy density and improve the storability and handling of the biomass, have recently gained attention. This work provides a techno-economic assessment of commercial-scale HTC plants and their competing technologies. In the first part of this work, energetic efficiency, GHG emissions and costs of HTC are compared to those of wood pelletizing, torrefaction and anaerobic digestion. Moreover, the substitution of fossil fuels by the aforementioned biofuels in existing power stations is analyzed. The second part focusses on the potential role of biomass upgrading technologies for bioenergy with carbon capture and storage (BECCS). Torrefaction and HTC cause the biomass to lose its fibrous structure, thus facilitating entrained flow gasification. In order to investigate the merits of this conversion pathway, torrefaction or HTC followed by entrained flow gasification is compared to the direct fluidized bed gasification of raw wood. The analysis is based on flowsheet simulations created with Aspen Plus. Exergy analysis is employed to locate thermodynamic losses within the respective processes. Exergoeconomic analysis is applied to the HTC plant design to reveal potentials for reducing the biocoal production costs. A simple model of the entire supply chain is developed in order to assess the costs and GHG emissions related to biomass and biofuel transport and storage and their dependency on the plant capacity. The results indicate that HTC can only be economically competitive with conventional wood pelletizing if waste biomass is used as a feedstock. Depending on the remuneration for waste disposal, relatively large processing capacities of up to 100 kt/a of feedstock are required year-round to make HTC an economically viable proposition. Potential feedstocks include park and gardening waste and empty fruit bunches from palm oil production. Exergy analysis reveals that drying of the feedstock or biofuel is the most significant source of exergy destruction in all the analyzed processes generating solid biofuels. HTC and anaerobic digestion also suffer large exergy losses through their waste streams. Measures to improve the efficiency and cost of HTC include efficient heat recovery, drying in superheated steam, and using the waste water to produce biogas. Integration of HTC with a rankine-cycle CHP plant may reduce the biocoal production cost and increase operability by omitting the complex heat recovery scheme required for a standalone HTC plant. IGCC power plants with carbon capture are more efficient when employing entrained flow gasification fired on torrefied wood or HTC biocoal than when using fluidized bed gasification of raw wood. However, the higher efficiency of the IGCC cannot compensate for the conversion losses of the biomass upgrading. Moreover, the carbon capture rate for scenarios with biomass upgrading is only 66–69%, compared to 82–86% for the direct fluidized bed gasification of the raw biomass. The unit cost of electricity generated by the BECCS plants is strongly dependent on the CO2 price. The results indicate that if the carbon price is sufficiently high to incentivize CCS from fossil fuels, then favourable BECCS configurations are also close to economic viability.

According to the principle of sustainability, modern industry should preserve nonrenewable energy sources and develop more efficient processes, especially in terms of energy consumption. The depletion of fossil energy reserves, the environmental impact of greenhouse gases, and the possible threats of environmental taxes are the main reasons to develop new processes in general, and new drying processes in particular, for the existing industries. Using superheated steam as a drying medium instead of hot air can improve the energy efficiency by reusing the energy from exhausted steam and prevent gas emission into the atmosphere by condensation. The present review is focused on both lab-scale pilots—including impingement jet, fluid bed, kiln, fixed bed, and flash drying—described in the literature and existing industrial facilities, with a specific analysis focused on energy efficiency. The usefulness of superheated steam drying pilots for experimental research and for the design of industrial dryers is analyzed. The impact on quality specifications of the dried product for different operating conditions is also presented. Documentation on industrial superheated steam dryers is very rare. Nevertheless, this work presents and analyses the key data available for superheated steam drying of beet, alfalfa, industrial pulp, and paint sludge. Energy recovery and process integration, with a focus on specific technological challenges for industrial dryer implementation, are also presented. This document will result in a discussion of some new ideas for possible R&D in superheated steam drying.