Inert Solids Research Articles

A novel multigrid technique for Lagrangian modeling of fuel mixing in fluidized beds

This paper presents a novel Lagrangian approach to model fuel mixing in gas–solid fluidized beds. In the mixing process, fuel particles are considerably larger than the inert bed material and therefore, the present work proposes three grids to account for the difference in size between the fuel particles and inert solids. The information between the grids is exchanged using an algorithm presented in the paper. A statistical method has been developed to analyze the distribution of the fuel particles in the bed. The results for the preferential positions, velocity vectors and horizontal dispersion coefficients are compared with experimental data in a bed applying simplified scaling relationships for different operating conditions. The effects of initial bed height and inlet gas velocity on the fuel mixing are investigated. It is found that the proposed Lagrangian modeling can capture the complex pattern of the movement of the fuel particles, in spite of the large difference in diameter between inert and fuel particles.

Motion of a large object in a bubbling fluidized bed with a rotating distributor

This work studies the effect of a low-frequency rotating distributor on the motion of a large object immersed in a bubbling fluidized bed. The object size and density differ from those of the inert solids that conform the bed. Examples of objects moving in a bubbling fluidized bed include passive particles, catalysts and reactants. The rotation modifies the bed dynamics in the surroundings of the distributor and affects the motion of the object within the bed. A set of experiments was carried out in a lab-scale cylindrical bed, equipped with a perforated plate distributor that can rotate at around 1 Hz, for different bed aspect ratios, gas velocities, and object characteristics. Sizes were far larger than that of the solids of the dense phase and densities ranged from half the bed density to values around it. The experiments were video recorded, capturing the surface of the bed from above. As have often been noted, objects might remain in stagnant regions near the distributor and be “lost” or precluded to circulate. This can be avoided in most practical cases forcing the distributor to rotate. Also, the effect of rotation on the circulation time of the objects is presented, showing a general reduction of large circulation times.

Unusual adsorption behavior of a highly flexible copper-based MOF

Due to their network flexibility, metal-organic frameworks (MOFs) may respond to external stimuli such as guest molecules, heat, pressure, humidity and so on by a dynamical transformation of their structure. In this work we present experimental studies by means of nitrogen and argon physisorption at cryogenic temperature concerning the influence of handling and storage on the recently synthesized highly flexible copper-based MOF ∞ 3 [ ( Cu 4 ( μ 4 -O ) ( μ 2 -OH ) 2 ( Me 2 trz p ba ) 4 ] . Unusual adsorption isotherms with up to three distinct steps in the adsorbed volume have been found substantiating once more: (i) the high sensitivity of flexible network structures for environmental influences, (ii) the high diversity of physisorption isotherm types for flexible materials including isotherms with several steps and large hysteresis loops, and last but not least (iii) that theoretical methods assuming inert solids cannot be applied to highly flexible materials for calculating pore sizes and other solid state parameters.

Application of a combined biological and chemical system for the treatment of phosphorus-containing wastewater from the food industry

Coagulants can be dosed at different points during the wastewater treatment process to achieve phosphorous removal. Addition of metal coagulants on the aeration basin (simultaneous precipitation) involves lowest cost; however, inert solids reduce the volatile solids percentage which can be deleterious to the biological process. The general objective of the present study was to analyze the feasibility of P removal in a wastewater model system of the dairy industry using simultaneous precipitation in a laboratory-scale activated sludge reactor by addition of ferric chloride. Results showed that the addition of a high dose Fe:P (molar ratio)= 1.9-2.3:1 on the aeration basin of the reactor caused a progressive enrichment of the sludge with inorganic solids. This phenomenon, which involved a gradual deterioration of the environmental quality of the biological system, led finally to a strong decline of the reactor performance. The organisms associated to flocs (crawling ciliates and attached ciliates) were the more sensitive to these changes. A mathematical model allowed the estimation of the concentration of total fixed suspended solids as well as the decrease in the abundance of these organism groups as a function of time of Fe(III) application, considering the influent flow rate, the influent Fe concentration, and the waste flow rate of the sludge. The Shannon-Wiener diversity index and the sludge biotic index (SBI) can early predict the decreasing of the system performance due to metal salts overload. The simultaneous application of the proposed mathematical model and the biological indices guarantee a successful control of systems operated with phosphorous simultaneous precipitation by Fe(III).

A Method for Reduction in the Start-Up Time of a Bubbling Bed Boiler Combustor

A study on the heating of inert bed solids in a bubbling fluidized bed by means of an over-bed start-up oil burner is presented in this paper. Experiments carried out in a 160 mm diameter bed shows that the bed heats up nonlinearly with time. The rate of heating and the peak temperature reached by the bed solids depend on the bed depth, the mean particle size, and the superficial velocity through the bed. It was further noted that premixing a certain amount of biomass with the inert bed solids accelerates the rate of heating, as well as increase the peak temperature attained. The internal heat generation in the biomass is found to start at temperatures as low as 200°C. Thus, premixing some biomass with inert bed materials could reduce the combustion start-up time of a fluidized bed boiler, reducing at the same time the start-up cost by saving on consumption of expensive fuel oil in the burner. Experimental data in the present laboratory-scale unit shows good agreement with those obtained earlier in an industrial fluidized bed tested with waste-coal.

Remarks on “Piezonuclear neutrons from fracturing of inert solids”

Carpinteri et al. [F. Cardone, A. Carpinteri, G. Lacidogna, Physics Letters A 373 (2009) 4158] reported that by the sudden fracture of granite blocks under pressure P ⩾ 94.4 MPa ejects a stream of neutrons catch by a 3He detector and displayed by a “BD” dosimeter. As claimed, these neutrons come from the fission reaction Fe 56 → 2 ( Al 27 + n ) being the compound Fe 2O 3 present at 3% in granite. We would like to point out the inconsistency of this endothermic nuclear reactions. No gamma rays measurements associated with any nuclear reactions and no radioactive isotopes in fractured granite blocks are reported. It is claimed strictly radiation-less reactions (except for the neutrons). Our remarks are related to the incompleteness of experimental set-up and data speculation. Mistake in the analysis of neutron detection due to intense acoustic signal or charged particle emitted in fractoemission phenomena is suggested.

Cold Flow Studies of Rice Husk, Saw Dust, and Groundnut Shell Fuels in a Fluidized Bed

Biomass is a low-grade energy source and must be upgraded for effective utilization of these residues as fuels. A fluidized bed technology permits a wide range of low-grade fuels of non-uniform size to be efficiently converted to other energy forms. Due to large density variations of fuel and inert solids in the bed, it is difficult to estimate hydrodynamic and mixing characteristics of the mixture in the bed. In the present work, three biomass fuels (i.e., rice husk, saw dust, and groundnut shells) are selected and their fluidization characteristics are estimated in the presence of sand bed. It is observed that, for good mixing and uniform distribution of biomass fuel with bed material, size of the sand particles plays a vital role and is found that the sand particles of mean diameter 0.66 mm for groundnut shells and sand particle size 0.44 mm for the other two fuels is best suited. The minimum fluidization velocity has been obtained from the experiential investigation for a fuel/sand two-component system and has been compared with the theoretical correlations available in the literature. A suitable correlation to determine the minimum fluidization velocity for the selected biomass fuels and sand mixture has been suggested.

Measuring community response of bentic macroinvertebrates in an erosional river impacted by acid mine drainage by use of a simple model

Abstract Acid mine drainage (AMD) causes different responses in riverine benthic macroinvertebrate communities than that caused by organic pollution. The response is similar to that for metal toxicity and acidity where the impact is severe, or for inert solids where the impact is moderate to mild. Biotic indices are based on saprobity and so do not accurately reflect community disturbance for either toxicity or inert solids and thus cannot be considered as reliable indicators for AMD. The expected community response to both toxicity and inert solids is best described simply in terms of suppression of both taxon richness ( S ) and abundance ( n ) regardless of saprobity. A simple model (AMD′) is proposed that provides a precise and reliable metric of the effects of AMD in rivers.

Inorganic precipitation during autotrophic denitrification under various operating conditions

The effects of hydraulic retention time (HRT, 7 h, 13.5 h and 18 h) and pH (7.5 and 8.0) on the denitrification performance and the extent of inorganic precipitation, in a H2‐driven non‐porous membrane biofilm reactor for autotrophic denitrification were investigated. The membrane was cleaned periodically to evaluate the solids contents generated in the system and identify the precipitants. The reactor that was operated under the longer HRT contained more inert solids than when operated under shorter HRT, and showed lower specific nitrate removal rates, even though the generation of volatile solids was almost identical in all tested cases. A lower pH level at shorter HRT, due to higher influent dilution rates, resulted in improved denitrification rates. However, aggressive pH control, by adding additional phosphate buffer, was not beneficial because of extensive precipitation of up to 76% of total solids. Inorganic precipitation was strongly and linearly related to the denitrification performance, indicating the inhibitory effect of inorganic precipitants on the transfer of gases or substrates in a membrane biofilm reactor. The sloughed‐off solids from the reactors were characterized by ICP analysis and revealed an abundance of various calcium‐related precipitants, which were found to be responsible for the increase in the inert solids content. Calcium phosphate precipitation was identified as the major reason for the inhibition of system performance in this study. Operation under long HRT increases the potential to generate substantial amounts of diverse, inhibitory inorganic precipitants.

Exact statistical mechanical lattice model and classical Lindemann theory of melting of inert gas solids

A modified form of Lindemann’s model shows that the melting points of the heavy inert gases and other effectively spherical molecular species are proportional to the depths of their diatomic potential wells. The success of the model when compared with experiment seems to rely on the almost constant value of the ratio of the fractional volume and entropy changes during fusion. The Lindemann proposal can be incorporated into an exactly treated statistical mechanical lattice model utilising expandable clusters which reproduces the solid–liquid melting phenomenon for argon with a realistic volume change and melting line.

Equation of state for inert gas solids

The equation of state is a fundamental relation to analyse the thermophysical properties of different class of solids and it plays a key role in basic and applied condensed matter physics research. A lot of work has been done in the field of ionic solids, minerals and metals but a very little work is done in the field of inert gas solids. Most of the equations of state failed to explain the properties of inert gas solid because of their abnormal behavior in the low temperature range. In the present paper, Singh-Gupta equation of state has been used to study the properties of these solids. The results obtained using these equations have shown a good agreement with available experimental results. Thus it is shown that these equations of states successfully explain the behavior of inert gas solids.

Heat requirements in a calciner of CaCO3 integrated in a CO2 capture system using CaO

Abstract Several systems for CO 2 capture using CaO as regenerable sorbent are under development. In addition to a carbonation step, they all need a regeneration step (calcination of CaCO 3 ) to produce a concentrated stream of CO 2 . Different options for calcination may be possible, but they all share common operating windows that appear when the mass and heat balances in the system are solved incorporating equilibrium data, sorbent performance information, and fuel composition (sulphur and ash content). These relatively narrow operating windows are calculated and discussed in this work. Due to sorbent performance limitations, low carbonation levels of the sorbent in the carbonator are expected and the heat demand in the calciner is dominated by the heating of inert solids flowing in the carbonation chemical loop. High make up flows of fresh limestone reduce this effect by increasing the average reactivity of the sorbent, but they also increase the heat demand in the calciner to calcine the fresh feed of limestone. Hence, an optimum level of sorbent activity appears under different operating conditions, processes and fuel characteristic, and these are discussed in this work.

Reactor pressure relief of fluids containing suspended solids

AbstractSome effects of addition of inert suspended solids (fine glass particles) to both reacting (water and acetic anhydride) and nonreacting systems (pure water or water/glycerol mixtures) are described. Depressurization profiles from experiments with solids present were compared with analogous profiles without solids. Experimentation was on scales of one and ten liters. Computer control meant that highly reproducible experimental sequences were followed. Mean nozzle to particle diameter ratios of between 6 and 500 were used. The particles were narrow size‐range cuts of nearly spherical glass beads with a density of 2500 kg m−3. Hollow glass beads with a density of 600 kg m−3 were also used. Glass particle concentrations were up to 16% v/v and relief set pressures were between 3 and 5 bara.Many variables affect the pressure vs. time profile during blowdown, and thus experimental (factorial) design techniques were used for efficient planning of experiments and interpretation of results. In general the glass had little statistically significant effect. There was limited evidence that the hollow glass particles could slightly increase depressurization rates. Tests with runaway reactions highlighted some inherent difficulties when comparing systems with and without glass particles present. In all cases, the vented fluids were less concentrated in glass than those in the reactor. The consistency of the amounts of liquid carryover during blowdown was poor in smaller‐scale tests; this may have important ramifications for small‐scale tests that are used to establish the flow regime during venting, as advocated in the DIERS methodology. © 2006 Health and Safety Executive. Crown Copyright. Process Saf Prog, 2006

Quality of Fluidisation for the Drying of Forestry Biomass Particles in a Fluidised Bed

The objective of this work is to analyse three methods of forest biomass particles fluidisation, applied to the drying of solids. The techniques to promote fluidisation are: vibro-fluidised bed, mechanically agitated fluidised bed and fluidised bed with inert solids. The analysis of fluidisation quality was carried out by means of an orthogonal design with nested experiments and dummy treatment. The results indicated that the drying in the agitated fluidised bed is adapted to guarantee favourable conditions of homogeneity in the bed temperature: the average temperature differences in the bed were less than 0·3 °C. The high quality of fluidisation was also corroborated with high values of the coefficient of determination R 2 (0·997) for the drying curves during the period of constant drying rate.

Effects of Complete Sludge Retention on Biomass Build-up in a Membrane Bioreactor

The work reports the main results of an experimental activity aimed at evaluating the performance of a membrane bioreactor with complete sludge retention and the characteristics of its biomass. The bench scale system was started-up without any sludge inoculum and fed on real municipal sewage in order to favour biomass selection based on the imposed operating conditions. Process performance was evaluated in terms of COD removal (above 90% on average) and nitrification under two pre-determined volumetric loading rates (0.8 and 1.7 gCOD L(react)(-1), d(-1) on average). The biomass was evaluated in terms of growth, accumulation of inert solids, and bacterial activity. The latter was measured through respirometric tests. The results showed that the suspended solids concentrations (SS) under equilibrium were proportional to the volumetric loading rates in both the experimental periods considered and a relationship between these two parameters was proposed. Also, the organic loading rates reached the same equilibrium value of 0.12 gCOD gTSS(-1) d(-1) in the two periods. Moreover, the system showed very limited sludge production under equilibrium conditions (0.12 gVSS gCOD(rem)(-1) and low biomass activity, although it readily responded to load variations.

Removal of sulfur dioxide from a continuously operated binary fluidized bed reactor using inert solids and hydrated lime

Sulfur dioxide pollutant was treated in the laboratory with hydrated lime particles having a mean diameter of 9.1 μm in a continuously operating binary fluidized bed reactor also containing inert sand particles with sizes varying from 500 to 590 μm. The influence of temperature (500, 600, 700 and 800 °C) on the reaction medium, of the superficial velocity of the gas (0.8, 1.0 and 1.2 m/s), and of the Ca/S molar ratio (1, 2 and 3) on the SO 2 removal efficiency were investigated for an inflow gas concentration of 1000 ppm and an initially static bed height of 10.0 cm. The pollutant removal efficiency proved to depend on the temperature and the velocity of the gaseous flow and was strongly influenced by the Ca/S molar ratio. The maximum efficiency of 97.7% was achieved at a temperature of 700 °C, a Ca/S ratio of 3 and a velocity of 0.8 m/s. The lime particles’ mean residence time was determined by an indirect method, which consisted of integrating the gas concentration curves normalized with respect to time. Based on a calculation of the critical transition velocities, it was concluded that the reactor operated in a bubbling regime under each condition investigated here.

Drying of Liquid Feedstocks in a Spout‐Fluid‐Bed with Draft‐Tube Submerged in Inert Solids: Hydrodynamics and Drying Performance

AbstractA spout‐fluid bed with draft tube submerged in a bed of polypropylene beads was used for drying maltodextrin solutions. The hydrodynamics of the dryer were studied by determining the annular air flow vertical profile at different spouting velocities, using an additional air flow rate through the annulus equivalent to 0.5 Umf. The drying performance of the dryer was studied through the determination of several dryer response parameters (product moisture, evaporative capacity and volumetric evaporative capacity). These parameters were compared with those obtained in a conventional spouted bed with inert solids and a spray dryer.

PROCESS ANALYSIS AND CONTROL DESIGN FOR COAL GASIFICATION IN RECIRCULATING FLUIDIZED-BED REACTOR

A most widespread method for coal gasification is the use of fluidized bed reactors. A new concept in recirculating fluidized bed gasification is the Judd two-compartment gasifier. The two compartments provide separated zones for gasification with steam and for combustion with air, within the same vessel. The circulation of inert solids transmits the heat from the combustion zone into the gasification zone. Lumped parameter model for the system is formulated by heat and mass balances and a set of simplifying assumptions. Optimal steady state - bringing the gasification rate to a maximum - is defined and the model is linearized about this state. The system is asymptotically stable, controllable and observable. An LQG controller, capable of rejecting input disturbances and measurement noise and improving the dynamical response of the system, has been developed.

Temperature excursions in reactors packed with segregated layers of catalyst and inert solids

A recent numerical studies by Yakhnin and Menzinger (Proc. 8th Int. Symp. on Catalyst Deactivation, Brugge, Belgium, 10tober, Vol. 126, 1999, pp. 291–298) suggests that activity inhomogeneity in a catalyst bed can create larger temperature excursions after changes in feed temperature than would be encountered in beds with homogeneous catalyst activity. Until now, this finding has not been confirmed experimentally. Inhomogeneous catalyst activity was simulated by constructing a packed bed reactor by successive layers of catalyst and the inert support. Oxidation of carbon monoxide (CO) with oxygen in a nitrogen carrier gas over an industrial 0.2 wt% Pt/ γ–alumina catalyst was employed. This reaction is exothermic and inhibited by CO. Step changes and periodically varying inlet temperature were used to generate disturbances. Both wrong-way behaviour and differential flow instability were observed. Temperature excursions in the layered bed significantly exceeded those in a bed of homogeneous activity at the same operating conditions.

Domestic sewage treatment in full-scale UASBB plant at Mangueira, Recife, Pernambuco

The anaerobic technology application for domestic sewage treatment in Pernambuco State (Brazil) is relatively recent. Some UASB reactors of less than 250 m3 were built in the Recife Metropolitan Region (RMR) in the 1990s. Mangueira (18,000 inhabitants) was the first neighborhood where the municipality built a plant with a bigger UASB reactor of 810 m3. It was intended to evaluate the performance and verify if such technology would be feasible. The objective would be the possible application of UASB reactors to the RMR, according to the new sewage master-plan under elaboration that would benefit about 3 million inhabitants. The monitoring of the Mangueira UASB reactor over 30 months showed that satisfactory results were obtained. Three distinct operational phases occurred, in which efficiency varied from 60% up to 90% based on COD removal. The results were very dependent on the operation and maintenance, either in the plant or in the sewage collection. Significant amount of inert solids was measured inside the reactor. Despite the operational problems, the UASB was shown to be very robust and stable. Under high fluctuation of influent concentrations (150-750 mg COD/L) during the period, resulting in applied organic loading rate of 0.5 to 2.5 kg COD/m3.d, the average values of COD removal efficiency did not change significantly. An active biomass with specific methanogenic activity varying from 0.18 to 0.25 g COD/g VSS.d was measured at the end of the period.