Indirect Dryer Research Articles

Excel-Based Tool to Analyze the Energy Performance of Convective Dryers*

An algorithm to examine the energy performance of convective dryers was developed and transformed into an Excel-based calculation tool. Provided with the input data for a given industrial dryer, this tool allows the energy use to be quantified in terms of the specific energy consumption and energy efficiency. The energy use can then be compared with the corresponding values for an ideal adiabatic dryer to identify the potential for energy savings. The algorithm accounts for direct and indirect dryers as the single- and multistage units operated in closed or open cycles. In addition, the maximum energy efficiency can be determined for nonhygroscopic materials through the sorption isotherms. The tool permits the identification of the major sources of dryer inefficiency and allows energy savings to be calculated for several low- and medium-cost measures such as dryer insulation, partial recycling of exhaust air, feed preheating, and others. The tool is built as a modular system comprising the following main components: dryer identification, calculation of actual energy consumption, comparison with the theoretical energy consumption, identification of sources of energy inefficiency, and analysis of options to reduce energy consumption.

Modeling and Energetic Analysis of Soybean Meal Drying in the Indirect Rotary Dryer

The process of soybean meal industrial drying requires a high consumption of energy, and it is usually performed in an indirect rotary dryer. A study aiming for the reduction of this energy consumption is vital for the competitiveness of this product. Thus, the purpose of this work was to develop a mathematical model of soybean meal drying, in permanent regime, in order to assess the optimal operational conditions of the dryer and its energetic performance. The developed model is based on balances of mass and energy, and using constitutive and empirical equations. The model validation was carried out through operational data. From this, the influences of the initial temperature, initial moisture, and relative humidity of air, as well as the dryer energetic performance, were investigated.

A study on the dewatering of industrial waste sludge by fry-drying technology

In sludge treatment, drying sludge using typical technology with high water content to a water content of approximately 10% is always difficult because of adhesive characteristics of sludge. Many methods have been applied, including direct and indirect heat drying, but these approaches of reducing water content to below 40% after drying is very inefficient in energy utilization of drying sludge. In this study, fry-drying technology with a high heat transfer coefficient of approximately 500 W/m 2 °C was used to dry industrial wastewater sludge. Also waste oil was used in the fry-drying process, and because the oil's boiling point is between 240 and 340 °C and the specific heat is approximately 60% of that of water. In the fry-drying system, the sludge is input by molding it into a designated form after heating the waste oil at temperatures between 120 and 170 °C. At these temperatures, the heated oil rapidly evaporates the water contained in the sludge, leaving the oil itself. After approximately 10 min, the water content of the sludge was less than 10%, and its heating value surpassed 5300 kcal/kg. Indeed, this makes the organic sludge appropriate for use as a solid fuel. The wastewater sludge used in this study was the designated waste discharged from chemical, leather and plating plants. These samples varied in characteristics, especially with regard to heavy metal concentration. After drying the three kinds of wastewater sludge at oil temperatures 160 °C for 10 min, it was found that the water content in the sludge from the chemical, leather, and plating plants reduced from 80.0 to 5.5%, 81.6 to 1.0%, and 65.4 to 0.8%, respectively. Furthermore, the heat values of the sludge from the chemical, leather, and plating plants prior to fry-drying were 217, 264, and 428 kcal/kg, respectively. After drying, these values of sludge increased to 5317, 5983 and 6031 kcal/kg, respectively. The heavy metals detected in the sludge after drying were aluminum, lead, zinc, mercury, and cadmium. Most importantly, if the dried sludge is used as a solid fuel, these heavy metals can be collected from the dust collector after combustion.

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

AbstractMoisture 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.

Effect of Drying Methods on Crystal Transformation of Trehalose

Dihydrate trehalose was transformed into anhydrous crystals by dehydration using fluidized bed drying, indirect heat drying, and vacuum drying, and characteristics of the reaction of crystal transformation were compared. In any drying method, the dihydrate trehalose was transformed into the stable β-form anhydrous trehalose crystal. However, the surface structure and drying characteristics were different. The moisture change was correlated by the Avrami equation, which can be generally applied to the crystal transformation.

Análise energética da secagem de farelo de soja em secador rotativo indireto

The soybean meal is an important product of the Brazilian agribusiness. Soybean meal drying, one of the stages of the production, is a great consumer of energy and, normally, it is conducted in a rotary dryer of indirect heating. The study of the soybean meal drying aims to reduce its consumption of energy and it is important to increase market competition of this product. Thus, the objective of this work was to develop a mathematical model, in stationary regimen, in order to evaluate the energy consumption and the efficiency of the process. The model was based on the mass and energy balances, constitutive and empirical equations. The validation of the model was made from operational data of an indirect rotary dryer of Coamo (Cooperativa Agricola Mouraoense)

Drying of municipal sewage sludge: from a laboratory scale batch indirect dryer to the paddle dryer

Among available technologies, disk and paddle dryers are often encountered in France to process municipal sewage sludge but their thermal design is still a question of know how rather than scientific knowledge. From experiments performed on an industrial Naratherm® paddle dryer and the literature, a simple model has been developed. The dryer is divided into two parts depending on the sludge consistency. A constant evaporating flow rate is assumed in the pasty zone whereas its linear decrease with the moisture content is taken into account in the granular zone. To compute this model, some of the sludge properties have to be characterized with a set of laboratory scale experimental techniques. The agreement with the experimental data is good.

A Comparative Study of Performance of Natural Convection Solar Dryers

This publication is based on experimental study that was made on the performance of three types of natural convection solar dryers, classified as direct dryer, indirect dryer and mixed mode dryer.

3611 中圧水蒸気を用いた湿潤バイオマスの革新的前処理技術(S55 再生可能エネルギー)

High efficiency drying is one of the challenges to utilize wet biomass as solid fuel. In addition, usually wet biomass has stinky smell and includes hazardous bacteria, so to collect and convey wet biomass is difficult. We propose a novel pretreatment technology for wet biomass. It is the hydrothermal reforming employing saturated steam at 473K with mixing rice husk. This pretreatment technology has two features; one is increasing effect of apparent drying rate of solid products, another is reforming effect of stinky and distinct odor of sewage sludge. As results of experiments used sewage sludge as model wet biomass, the apparent drying rate of the solid product became four times as large as that of the reactant. And, concerning the stinky smell, the concentrations of H_2S and NH_3 originated from the solid product decreased compared with the sewage sludge by this reforming. This hydrothermal reforming needs little energy compared with conventional indirect heating drying. So, this hydrothermal treatment is appropriate as pretreatment for wet biomass fuelization.

Análise energética preliminar da secagem industrial do farelo de soja

The soybean meal is an important product of the Brazilian agribusiness. One of the steps of the meal production process is drying, which is a large energy consumer. The meal drying study to reduce the energy consumption is vital to the competitivity of this product. Thus, the aim of this work is to develop a mathematic modeling, into a stationary regimen of a drying soybean meal process, to evaluate the preliminar energetic consumption and the process efficiency. The model is based on mass and energy balance and heat transfer equations. The validity of the model is confirmed with operational data from an indirect rotary dryer used by the Cooperativa Agrícola Mourãoense (Mourãoense Agricultural Cooperative). The final results show that the best steam temperature is around 120ºC

SLUDGE DEWATERING AND DRYING

ABSTRACT The production of wastewater treatment sludge, the basic characteristics of the sludge and the state of the water in the sludge are described in this paper. The methods for the determination of bound water content are discussed. The literature (including patents) on sludge dewatering and drying is reviewed, including vacuum filters, belt presses, centrifuges, direct dryers, indirect dryers and combined mode drying systems. The issues related to drying are briefly discussed. Photographs or schematics of typical dewatering and drying systems are also included.

HEAT, MOMENTUM, AND MASS TRANSFER MEASUREMENTS IN INDIRECT AGITATED SLUDGE DRYER

ABSTRACT Whereas indirect agitated drying has been extensively studied for granular materials, little is known in the case of pasty products. We describe an experimental set up specially designed for the investigation of drying kinetics, of heat transfer coefficient evolution, and of the mechanical torque necessary for stirring. This device was applied to municipal sewage sludge. Preliminary experiments were performed to investigate the influence of ageing of sludge on the drying kinetics. It appears that ageing does have no effect except for the first two days. The influences of the wall temperature, the stirrer speed, the dryer load and the location of the stirrer against the heated wall were studied. Three different rheological behaviors were observed during sludge drying. In particular, the sludge goes through a “glue” phase, and high levels of mechanical strain are recorded when the compact mass begins to break up. A critical stirrer speed is found within the range 40–60 rpm. To shorten the drying time, it seems better to adjust the wall temperature in accordance with the moisture content of the sludge.

Wastewater biosolids: an overview of processing, treatment, and management

Treated as a valuable resource, municipal sludge, often today referred to as biosolids, is processed through a variety of novel unit operations leading to a safe, aesthetically pleasing, and sought-after product. The design engineer is concerned first with the ultimate disposal and utilization of the biosolids, providing at least two options for the final disposal. Volume reduction, stabilization or vector attraction reduction, and pathogen inactivation are the key goals; process trains combining them into one unit process are the target technologies. Drying and pelletization are now being applied at much smaller plants because of the introduction of indirect dryers, which have fewer air pollution problems than the direct dryers still used at some larger plants. Stabilization of biosolids in newer plants is more often combined with disinfection at thermophillic temperatures, in anaerobic and particularly in aerobic regimes. For the smallest plants, dewatering is now available in drying bags or vacuum drying beds, and larger plants benefit from an array of new devices offering sludge cakes as dry as 22 to [Formula: see text]40% total solids. The ultimate dryness will depend on the quality of sludge, polymer conditioning program, and machine parameters. Emphasis on cost reduction, with simultaneous demand for an excellent quality end product, calls for innovative and case-specific solutions that go beyond the treatment plant and also address the quality of industrial–commercial discharges to the municipal sewers. Key words: sludge, biosolids, process design, dewatering, digestion.

QUANTITATIVE QUALITY TESTS FOR FISH MEAL. II. AN INVESTIGATION OF THE QUALITY OF SOUTH AFRICAN FISH MEALS AND THE VALIDITY OF A NUMBER OF CHEMICAL QUALITY INDICES

ABSTRACT This report indicates that the quality of fish meal can conveniently be expressed by two independent indices: a pre-processing spoilage index and a heat abuse index. It is shown that indices of spoilage such as total volatile basic nitrogen (TVBN) or free fatty acid (FFA) can be misleading. As an additional quality index the phospholipid (PL) content is suggested. This index measures the PL content of the residual lipids in the meal and allows the quality of the dried presscake to be assessed separately from the added stickwater. The polyunsaturated fatty acid (PUFA) content of the meal lipids is also an excellent guide for detecting heat abuse during drying of the meal. Using this measurement no evidence was found to conclude that steam (indirect) dryers cause more heat damage to meals than flame (direct) dryers.

Power generation using dedicated woody crops: thermodynamics and economics of integrated plants

Biomass will continue to play a significant and probably increasing role in the world's future energy mix, due to the strategic role it has for large availability, environmental concerns and technological advances. The raw biomass has a relatively high moisture content, requiring thermal drying processes in order to minimise stack losses. In this paper, integrated plant configurations burning dedicated woody crops for electric power generation and different options for pre-drying the biomass are discussed. Conventional indirect drying, using steam extracted from the turbine, and direct drying processes with hot gas turbine exhaust gases, are compared, assessing their influence on plant layout and performance. Moreover, a detailed economic analysis has been carried out for evaluating the levelized cost of the electricity produced, as well as the profitability of each plant configuration. The study shows that using the heat recovered from gas turbines for biomass drying enhances the feasibility of biomass-fired power plants, improving performance and reducing woody biomass crop requirements with respect to conventional configurations. The analysis also demonstrates that the proposed solutions allow reducing the cost of electricity produced and shorten payback periods.

SIMULATION OF THE MIXED-MODE NATURAL-CONVECTION SOLAR DRYING OF MAIZE

A mathematical model for mixed mode natural convection solar drying of maize grain is presented. The drying is described by a deep bed procedure that includes conduction within the grain bed. The conduction is due to radiative energy falling on the upper surface of the bed. The results show that temperatures at the top and bottom of the bed are higher than that in the middle resulting in two drying fronts one at the top and the other at the bottom of the bed and moving in opposite directions. This results in more uniform moisture content distribution than in an indirect dryer. The results are verified against experimental data from a prototype mixed mode natural convection maize solar dryer. The laboratory solar dryer was constructed at Newcastle University, U.K. and the experiments carried out under a solar simulator. The agreement between theory and experiment is very good.

Wastewater biosolids: an overview of processing, treatment, and management

Treated as a valuable resource, municipal sludge, often today referred to as biosolids, is processed through a variety of novel unit operations leading to a safe, aesthetically pleasing, and sought-after product. The design engineer is concerned first with the ultimate disposal and utilization of the biosolids, providing at least two options for the final disposal. Volume reduction, stabilization or vector attraction reduction, and pathogen inactivation are the key goals; process trains combining them into one unit process are the target technologies. Drying and pelletization are now being applied at much smaller plants because of the introduction of indirect dryers, which have fewer air pollution problems than the direct dryers still used at some larger plants. Stabilization of biosolids in newer plants is more often combined with disinfection at thermophillic temperatures, in anaerobic and particularly in aerobic regimes. For the smallest plants, dewatering is now available in drying bags or vacuum drying beds, and larger plants benefit from an array of new devices offering sludge cakes as dry as 22 to [Formula: see text]40% total solids. The ultimate dryness will depend on the quality of sludge, polymer conditioning program, and machine parameters. Emphasis on cost reduction, with simultaneous demand for an excellent quality end product, calls for innovative and case-specific solutions that go beyond the treatment plant and also address the quality of industrial-commercial discharges to the municipal sewers.Key words: sludge, biosolids, process design, dewatering, digestion.

Steady state modelling and simulation of an indirect rotary dryer

A steady state model for a fish meal indirect pilot plant rotary dryer with steam tubes is developed. The model is based on mass and energy balances and heat transfer constitutive equations. Simulated and experimental results are presented. The moisture condition of fish meal predicted by the model agrees satisfactorily with experimental values obtained in the pilot plant dryer within the range of operating conditions explored.

HYBRID NEURAL APPROACHES FOR MODELLING DRYING PROCESSES FOR PARTICULATE SOLIDS

ABSTRACT This work presents methods for synthesizing drying process models for particulate solids that combine prior knowledge with artificial neural networks. The inclusion of prior knowledge is investigated by developing two applications with the data from two indirect rotary steam dryers. The first application consisted in the modelling of the drying process of soya meal in a batch indirect rotary dryer, The external and internal mass transfer resistances were associated in the hidden layer of the network to linear and sigmoidal nodes, respectively. The second application consisted in the modelling of the drying process of soya meal in a continuos indirect rotary dryer. The model was constructed using the Semi-parametric Design Approach. The model predicts the evolution of solid moisture content and temperature as a function of the solid position in the dryer. The results show that the hybrid model performs better than the pure “ black box” neural network and default models. They also shows that prior knowledge enhances the extrapolation capabilities of a neural network model,

Some quality characteristics of solar-dried cocoa beans in St Lucia

A -eld comparison of solar drying and open-air sun-drying of cocoa (T heobroma cocoa L) beans was carried out in St Lucia. Four methods of drying (indirect solar drier, direct solar drier, open air/perforated steel surface and open air/non-perforated wooden surface) were examined at three loading rates: 13E7, 26E9 and 40E 4k g m~2. Beans from the open air had a higher incidence of exter- nal mould and poorer external appearance, though di†erences were minor. Beans dried at the lower rate of 13 kg m~2 showed the best colour, but the highest titratable acidity. Conversely, beans dried at the higher loading rate of 40E 4k g m~2 showed signi-cantly lower titratable acidity, but poorer colour. Dif- ferences in cut-test score, colour, pH and titratable acidity between the open air and closed driers were small or not signi-cant. While not signi-cant, the indirect drier did show the highest cut-test score and the direct drier the poorest. Beans from the indirect drier were darker and more purple, while those from the direct drier were lighter coloured and less purple. The beans from the direct drier, dried to 6% moisture (WB) were, though not signi-cantly so, more brittle and higher in titratable acidity than those from either the open air or indirect drier. Overall the beans from the indirect drier showed the highest quality and those from the direct drier the poorest. Whether the modest improvement of the indirect drier over the open air driers is sufficient to warrant investment in such a drier is unclear. 1998 SCI. (