Fluidized Bed Roaster Research Articles

CFD modelling and simulation of an industrial scale continuous fluidized bed roaster

In the present work, computational fluid dynamics (CFD) based modelling of an industrial scale continuous fluidised bed roaster (FBR) has been carried out to study its performance at different operating conditions, so that the sulphide-sulphur content in the product is within 0.4% at the designed feed rate of 39.75 DMT/h. Eulerian-Eulerian multiphase model, considering four granular phases and one gas phase has been implemented to investigate the velocity and mass fraction profile of the particles in the FBR. The heat and species mass balance calculations have been performed external to CFD, by dividing the roaster into several sections. The conversion of ZnS to ZnO at various sections of the roaster has been estimated using reaction kinetics under isothermal condition (1203 K). The heat liberated and possible temperature rise at each section was predicted based on the heat of reaction and sensible heat of the solid and gaseous products. The CFD model was validated with the plant data for a feed rate of 36.5 DMT/h, air flow rate of 65,000 Nm3/h and O2 content of 21%. The proposed model predicted the sulphide-sulphur content in the product to be 0.4% for the designed feed rate of 39.75 DMT/h, when the O2 content in the inlet air was increased to 25%.

Experimental study on fluidization characteristics of different-sized particles in a U-type reduction chamber

A novel fluidized bed reactor, which is an improvement of the loop seal, was applied successfully to iron ore reduction roasting. For this U-type reduction chamber, the fluid dynamic behaviors of different-sized particles were investigated via a cold experimental apparatus using the pressure measurement method in this study. The results showed that the measured Umf of 71, 101 and 147 μm-sized particles were 0.033, 0.040 and 0.059 m/s, while the Uc were 0.167, 0.190 and 0.223 m/s, respectively, demonstrating that the decrease of particle size caused a rapid transition from both the fixed to bubbling regime, and the bubbling to turbulent flow regime. Under stable operation, the pressure drop, average solids holdup and axial nonuniformity index across the FC increased when particle size increased, along with the solids height and pressure drop gradient in the SC, though the differential pressure fluctuation decreased. These consequences indicated that larger particle size promotes the opportunity for particle mixing and contacting, accordingly increasing the preferential formation of the particle aggregation and deteriorating the reduction performance. These can provide guidelines for the regulation and control of industrial iron ore fluidized bed roasting.

Removal of Zinc and Lead from Blast Furnace Dust in a Fluidized-Bed Roaster

Industrial trials were carried out, using a fluidized-bed roaster, to investigate the effect of the roasting time, roasting temperature, basicity, and CaCl2 dose on the removal rates of Zn and Pb from blast furnace dust. Increasing the roasting time improved the Zn and Pb removal rates, and the maximum amounts of the Zn and Pb removal were achieved within the first 30 min. Increasing the roasting temperature favored the facile removal of both Zn and Pb, but the effect of the roasting temperature on Pb removal was more obvious than that on Zn removal. When CaCl2 is added, CaCl2 reacts with ZnO and PbO in the ore to form ZnCl2 and PbCl2, respectively. They are discharged along with sintering gas. Therefore, both the Zn and Pb removal rates improved evidently when CaCl2 was added, especially when the added amount of CaCl2 was in the range of 10–12%. Removal rates of up to 96% were achieved for Zn, while Pb removal rates of higher than 80% were achieved. During the sintering process, silicon and iron which are in the form of oxide negative ions will form complex compounds with zinc. This can make zinc removal difficult. If CaO is added as flux, the basicity increases and Ca replaces Zn, alleviating this problem of difficulty in Zn removal. Thus, upon increasing the basicity, the removal rate of Zn is improved, especially, increasing the basicity from 0.8 to 1.4 improved the Zn removal rate significantly.

Optimization of roasting conditions of Pistacia terebinthus in a fluidized bed roaster

Pistacia terebinthus fruit after roasting has a similar aroma and flavor to conventional roasted coffee beans, and it can be a promising caffeine-free alternative to coffee. P. terebinthus beans were roasted at 180 °C, 200 °C and 220 °C for 5, 20 and 35 min at each roasting temperature. The effects of the roasting conditions on color, moisture content, density, breaking force and sensory properties (appearance, odor, texture, flavor and overall impression) of the P. terebinthus beans were investigated using a three-level two factor (32) full factorial design. The effect of roasting temperature and roasting time on quality attributes of P. terebinthus beans roasted in a fluidized bed roaster was analyzed using response surface methodology. Quality attributes of the roasted P. terebinthus beans were significantly (p ≤ 0.05) affected by the roasting temperature and roasting time. Based on the superimposed contour plot, optimum region of roasting temperature and time was determined. The quadratic models developed adequately described the relationship between the factors and the responses. Dark roasted P. terebinthus beans took the highest scores in sensory tests by the panelists.

원두의 배전 강도와 추출 시간이 커피 추출물의 항산화 활성에 미치는 영향

The effect of roasting intensity and extraction time of coffee bean on the antioxidant activity of roasted ground coffee extract was investigated. Coffee was roasted at 185oC using a rotating fluidized bed roaster for 5.17 (medium roasting) and 6.00 (dark roasting) min, respectively. Both roasted coffees were extracted in 90°C hot water according to the increased extraction time. Until 20 min, an increase in extraction time significantly increased soluble solute, caffeine, brown color, and phenolic compound. The soluble solid and caffeine contents showed no significant difference among medium- and dark-roasted coffee extracts. The brown color intensity and free radical scavenging activity of dark-roasted coffee extract were higher than those of medium-roasted coffee. On the contrary, the total phenolic content of dark-roasted coffee extract was lower than that of medium-roasted coffee. The free radical scavenging activity of coffee extracts showed a positive correlation with brown color intensity, as well as total phenolic content.

Development of the Semi-Rotating Fluidized Bed Roaster and Processing System

Development of the Semi-Rotating Fluidized Bed Roaster and Processing System

Extraction of vanadium from stone coal by roasting in a fluidized bed reactor

In order to improve leaching efficiency of vanadium pentoxide (V2O5) from stone coal and to reduce its connected environmental pollution, this article investigated the oxidizing roasting of stone coal in a laboratory fluidized bed reactor to optimize the roasting method and conditions. The examined parameters included reaction temperature, reaction time and amount and mixing method of additive. The removal of Cl from the generated effluent gas was implemented using CaO as the adsorbent, and comparison was made between the fluidized bed roasting and static roasting in a muffle oven. The results show that the fluidized roasting is more favorable to leach V2O5 from stone coal, which can shorten roasting time for reaching the maximal leaching rate, while the realized leaching rate is also higher. Comparing the mixing method applied to stone coal and additive, the impregnation method of additive on stone coal not only increased the leaching rate and shortened the roasting time for reaching the maximal leaching rate, but also reduced the amount of additive required. Adding CaO in stone coal roasting sharply decreased the content of Cl-containing gases in flue gas, which can greatly alleviate the possible environmental pollution. The optimal conditions for fluidized bed roasting were found to be impregnating 6wt.% additive on coal, adding 3wt.% CaO and performing roasting at 800°C for 0.75h.

Effect of roasting conditions on carbon dioxide degassing behavior in coffee

CO2 is one of the major gases formed during coffee roasting, which has important implications on coffee's quality and packaging requirements. In this study, the residual CO2 content and CO2 degassing behavior of an Arabica coffee processed using a fluidized bed roaster, as affected by the roasting temperature–time conditions, were investigated. The results showed that positive correlations existed between the degree of roast (expressed as lightness value) and residual CO2, implying that lightness could be used as an indicator of initial CO2 content in roasted coffee. At the same degree of roast, coffee roasted with high-temperature–short-time process had significantly higher CO2 degassing rate than those with low-temperature–long-time process. Moreover, the CO2 releasing rate increased with the degree of roast. The degassing rate of CO2 in ground coffee was highly dependent on the grind size and roasting temperature, but less dependent on the degree of roast. The different degassing behaviors observed between roasted coffee samples were explained on the basis of chemical composition and microstructural differences.

Functional and antioxidant properties of ready-to-eat flakes from various cereals including sorghum and millets

Introduction Nowadays, ready to eat snacks are gaining much importance, as they are convenient to use, easy to handle compared with ready-to-cook snacks. ObjectivesTo study the effects of cereal flaking and blistering process on the properties of the starch and nutraceutical content. Methods Ready-to-eat flakes from cereals such as maize grits, pearled barley, hulled oats, wheat, pearl millet and sorghum were prepared by hydration, hydrothermal treatment, flaking and blistering in a fluidized bed roaster. Commercial rice flakes were also considered. Results Grains hydrated slowly but flakes hydrated rapidly, indicating the effect of hydrothermal treatment where parboiling was imparted. Equilibrium moisture content on soaking was very high in barley (46%, wet basis) and lowest in maize grits and sorghum (approximately 30%). Swelling power in grains was 11‐17% and solubility was 8‐29%. On flaking, the swelling power of different flakes remained almost the same. However, the solubility increased significantly. Maize showed the highest amylose content (~29%) and wheat had the lowest. Soluble amylose was lowest in wheat and highest in oats. Gelatinization temperature was highest in pearl millet (77.4 °C) and lowest in barley (59.5 °C). Peak viscosity was high in all the grains, except pearl millet. On flaking and blistering, the gelatinization temperature values and peak viscosity reduced to different extents. Conclusion These blistered cereal flakes are excellent ready-to-eat snacks, as they are rich in total polyphenols (16-58 mg gallic acid equivalents/100 g) and exhibit high anti-oxidant activity and possess good functional properties.

Demonstration of the conditions conducive to agglomeration of zinc calcine in fluidized bed roasters

Agglomeration in the fluidized bed roasting of zinc sulphide concentrate was investigated in a continuous pilot-scale fluidized bed roaster. Alone or together, low stoichiometric excess oxygen (<10%) and high temperature (>940 °C) contributed most significantly to agglomeration of zinc calcine particles. Only one test – with 0% excess oxygen at 940 °C – led to severe agglomeration and subsequent defluidisation. Neither large initial particle size nor low gas superficial velocity promoted agglomeration as much as the combination of low stoichiometric excess oxygen and high temperature. Lead sulphide, a common impurity in zinc sulphide concentrate, also appeared to have played a key role in agglomeration. Both low excess oxygen and high temperature favoured a high partial pressure of sublimated lead sulphide. Upon contact with oxygen, lead sulphide oxidised to lead oxide, which then precipitated as a liquid onto the rather inert bed particles. As a liquid, lead oxide formed coatings that caused small particles to adhere to larger ones, as well as liquid bridges that bound particles together.

Effect of two different roasting techniques on the Ochratoxin A (OTA) reduction in coffee beans (Coffea arabica)

The roasting of green coffee beans (Coffea arabica) artificially contaminated by Ochratoxin A (OTA) after inoculation with Aspergillus westerdijkiae was carried out with two different roasting techniques (Rotating Cylinder [RC] and Fluidized Bed [FB]). The green coffee beans were contaminated at two different toxin levels (L1=5.3μgkg−1 and L2=57.2μgkg−1). Different roasting points (light, medium, dark and very dark) were set according to the L∗ color coordinate. The cylinder roasting conditions were 0, 3, 6, 9, 12, and 15min at 230°C and the fluidized bed roasting conditions were 0, 0.9, 1.7, 2.6, 3.5 and 4.3min, at 230°C. The roasted beans were compared for their physical properties (bean swell and weight loss) as well as for their residual OTA content. The results indicated that the OTA reduction was similar for the two contamination levels: 95.1% and 97.2% with the rotating cylinder and 81.3% and 79.2% with the fluidized bed at the maximal roasting time. The OTA degradation kinetics differed between the two processes. The complete degradation of OTA within the limit of this study (230°C) was not observed but the rotating cylinder roasting was the most efficient technical process for the OTA reduction in a commercial dark roasted coffee (88%).

Studies on roasting of wheat using fluidized bed roaster

Roasting is normally done to enhance the flavour and to improve organoleptic properties of the food grains. Roasting is a high temperature short time (HTST) heat treatment process and the temperatures used are normally in the range of 280–350 °C. In the present study a continuous fluidized bed roaster (FBR) using flue has been designed and used to roast wheat grain. The product obtained thus has been compared to that obtained by using a traditional method, i.e., roasting in a bed of hot sand. Parameters such as moisture content, bulk density, product colour, crispness, microstructure, and total and acid insoluble ash, are considered in the study. Sand contamination in traditionally roasted wheat has been shown by the presence of acid insoluble ash (0.12%). The bulk density decreased from 833 kg/m 3 for raw wheat to 526 and 555 kg/m 3 for sand and fluidized bed roasted wheat , respectively. The moisture content decreased from 10% to 3% for sand as well as fluidized bed roasted wheat. Colour (expressed as Chroma) of the sand roasted wheat was in the range of 18–32 and that of the fluidized bed roasted wheat 23–32. Textural measurements in terms of compressive strength was between 222–331 N and 129–299 N for sand and fluidized bed roasted wheat , respectively. It is noted that the optimally roasted wheat using FBR has peak force of 30 N with colour (Chroma) value of about 31, total ash of 1.2% and acid insoluble ash of 0.04%. SEM images of the microstructure have indicated FB roasted wheat to have greater porosity which will result in this wheat requiring lower energy for size reduction.

Soviet design for roasting zinc concentrates in a fluidized bed

Although many zinc plants attempt to increase a fluidized bed roaster’s capacity by employing an oxygen-enriched air blast, work in the former Soviet Union shows the advantages of redesigning the roasting complex to optimize concentrate flow and process hydrodynamics. A redesigned furnace in operation for five years demonstrates, as compared to conventional Soviet furnaces, greater versatility, improved charge capacity, better heat recovery, ease of control, and operational stability.

Fluidized Bed Roasting Process for Desulphurization of Scheelite

Studies on roasting of sheelite concentrate have been carried out in fluidized bed to reduce its sulphur content to <5%. Initial investigations have been done using a 10 cm I.D. fluidized bed roaster and the data so generated was used for the design of a fluidized bed roaster of 50 kg/hr capacity. The experiences on roasting of sheelite concentrate with the fluid bed reactor and the methods for scale up to large size reactor are presented.

The mechanism of ferrite formation from iron sulfides during zinc roasting

The formation of zinc ferrite (ZnFe2O4) during the fluidized-bed roasting of zinc concentrates presents subsequent processing difficulties both for zinc recovery and for iron separation and disposal. A major source of iron in these concentrates is from the iron sulfides — pyrite and pyrrhotite. This study examined the changes undergone by these iron minerals when roasted together with sphalerite at 1223 K in a fluidizing gas mixture of 3 pct oxygen and 97 pct nitrogen. Optical microscopy and electron microprobe analysis were employed to identify the three stages that lead to ferrite formation and to examine the processes that occur within each stage. The first stage is oxidation of the sulfides to highly vesicular, amorphous magnetite particles containing small amounts of zinc. The second stage involves both densification of these particles by sintering and counterdiffusion of iron and zinc cations to form a continuous phase of homogeneous zinc-rich spinel and a precipitate of hematite. In the third stage, continuation of cation diffusion and increasingPo 2 results in the formation of stoichiometric zinc ferrite. These observations have been interpreted by reference to the established phase relationships that occur in the Zn-Fe-O system, and a detailed, solid state reaction mechanism for the formation of zinc ferrite has been proposed.

Residual oil cracking with generation of hydrogen (Part 4). Proposal for a new cracking process with desulfurization of iron sulfide by roasting.

A sulfur-containing residual oil has been cracked in a fluidized bed of an iron-containing catalyst with hydrogen generation of 180Nl-H2/kg-feed oil by reaction of ferrous oxide with steam and of 30Nl-H2/kg-feed oil by dehydrogenation of the feed oil. The iron sulfide formed in the catalyst during partial oxidation of coke has been desulfurized by roasting with air in a fluidized bed roaster. The desulfurization reaction has been found to be fast enough to attain equilibrium during roasting. Based on these results, a new cracking process has been proposed. It consists of cracking sulfur-containing residual oil, generation of hydrogen, partial oxidation of coke on the catalyst, fixation of gaseous sulfur compounds in the catalyst, and roasting of the iron sulfide.

岡山製錬所の最近の操業について

Okayama Plant, Dowa Mining Co., Ltd., was established in 1953 for the effective utilization of domestic pyrites. In 1969, it added to its facilities a large-scale double-contact sulfuric acid plant which utilizes the scrap and build system. The expansion of facilities in 1974 turned Okayama Plant into one of the largest such manufactories of the nation, and it is contributing tothe stable supply of sulfuric acid through intensive treatment of pyrites. The total full capacity of the facilities is 800, 000 mtpyof sulfuric acid and oleum.The pyrite cinders produced in this process is treated at the Tobata Plant and the Amagasaki Plant of Dowa's affiliate companies to make iron pellets for steel production, and the recovery of valuable metals is also carried out by means of the chloridizing volatilization.On the other hand, in 1970, a train of facilities to produce the high-grade ferric oxide for raw materials of ferrite magnets was constructed to permit the high-level utilization of pyrites from Yanahara Mine. In this process, the raw materials are ground and polished up to high grade pyrite concentrates remaining less than 0.15% of SiO2 by flotation and roasted in a fluidized-bed roaster. The calcine is then re-roasted in a rotary kiln to reduce its sulfur content less than 0.03%, and finely ground by vibromills down to 1μm in average diameter. The production of the ferric oxide is 28, 000 mtpy in total.Okayama Plant provides an unique and perfect desulfurizing process for the waste gas treatment using basic aluminum sulfate solution as absorbent. Pregnant solution is neutralized by limestone after air oxidation and, eventually, the sulfur oxidein waste gas is eliminated as the gypsum. This process is developed in Okayama and several plants are now being operated successfully inside and outside of Japan.

Fluidized bed roasting of molybdenite-effect of operating variables

The results of an investigation on the fluidized bed roasting of molybdenite are reported. Molybdenite mixed with quartz was subjected to an oxidizing roast in a 22 mm diam stainless steel batch fluidized bed reactor. Enriched air (with O2) or diluted air (with N2) was used as the fluidizing and oxidizing gas. In addition to the MoS2 content of the solids and the O2 content of the gas, the effect of temperature and flow rate was also examined. For the range of variables investigated, it was found that the temperature influences the rate of the roasting reaction greatly. The gas flow rate affects the conversion favorably up to a certain fluidizing flow rate. An increase in the O2 content of the gas and the MoS2 of the solids results in higher conversion levels. The unreacted core kinetic model was applied to the results; and the energy of activation for the reaction was obtained from the Arrhenius plot as 31,100 cal/gmol of MoS2. The data obtained should be useful in the design and operation of larger scale roasting reactors.

Fluidized bed roasting of lime copper concentrate pellets

Fluidized bed roasting of lime copper concentrate pellets

流動焙焼の湿式冶金への応用

流動焙焼の湿式冶金への応用