Pilot-scale Work Research Articles

Leaching of Ca-Rich Slags Produced from Reductive Smelting of Bauxite Residue with Na2CO3 Solutions for Alumina Extraction: Lab and Pilot Scale Experiments

Sustainable utilization of Bauxite Residue (BR) is currently one of the greatest challenges being tackled by the alumina industry, due to its high production rates and limited reuse options. The present work is concerned with the use of BR as a candidate metallurgical raw material for iron (Fe) production and aluminum (Al) extraction. In more detail, at first, BR undergoes reductive smelting to extract its Fe content and produce a slag of mainly calcium aluminate composition. In a second step, Al contained in the calcium aluminate phases is extracted hydrometallurgically by leaching with a Na2CO3 aqueous solution. The focus of the current study is the optimization of this leaching process, and it was performed in two stages. The first was a laboratory scale investigation on the main parameters affecting the extraction rate of Al. The second stage was performed in pilot scale and incorporated observations and suggestions based on the laboratory scale investigation. Laboratory work showed that more than 50% of aluminum could be easily extracted in less than 1 h, in 5% S/L, at 70 °C and with an 20% excess of Na2CO3. Pilot scale work, by successfully applying the suggestions derived from laboratory scale work, achieved an average Al extraction of 68% from a 10% S/L pulp, with a slag of optimized composition in relation to the one used in the laboratory scale.

Biological control of soil-borne phytopathogenic fungi through onion waste composting: implications for circular economy perspective

The production of onion waste derived mainly from bulbs affected by fungal diseases, during onion classification and storage presents an important agro-environmental issue in onion production regions. Composting is an environmentally friendly strategy to recycle agricultural waste and produce organic fertilizers. Modifications of the microbial community in soil can affect the ability of pathogen propagules to survive, germinate and infect plant roots. Hence, the main objective of this work was to exploring the mechanisms involved on the presence of three soil-borne phytopathogenic fungi during the composting process of onion waste under the hypothesis if that the resulting compost effectively prevents or minimizes the dispersion of phytopathogenic fungi. To this end, three composting piles of 60 tonnes each were built by layering onion waste affected by phytopathogenic fungi and cow dung at 1:1 ratio. Temperature, moisture, pH, electrical conductivity (EC) and Aspergillus niger, Penicillium sp. and Fusarium sp. growth were monitored for 100 days. During the first 28 days of composting, the presence of phytopathogenic fungi increased significantly showing thereafter a downward trend. Final estimations of fungal populations densities indicated a predominance of A. niger and an effective reduction in the abundance of Fusarium sp. This pilot-scale work demonstrates the feasibility of composting onion waste contaminated with phytopathogenic fungi and highlights the positive environmental impact associated with this practice. Therefore, the composting of onion waste and cow dung is a feasible and sustainable procedure to recycle onion waste and to promote circular economy in onion production regions.

CO2 Absorption from Gas Turbine Flue Gas by Aqueous Piperazine with Intercooling

Amine scrubbing is the most mature technology for postcombustion carbon capture. Much bench- and pilot-scale work has been focused on CO2 capture from coal-fired flue gas. Because natural gas is inexpensive and readily available in the United States and other countries, the natural gas combined-cycle (NGCC) has been replacing coal for electricity generation. Carbon capture for NGCC is therefore an important technology for the modern power plants. The Piperazine (PZ) Advanced Stripper (PZAS) technology has been established as a benchmark system for second-generation amine scrubbing for CO2 capture from coal-fired flue gas. It has a fast absorption rate, good energy performance, and strong resistance to thermal degradation and oxidation. PZAS was operated with simulated NGCC flue gas (4.3 mol % (dry) CO2) at the National Carbon Capture Center (NCCC) in Wilsonville, Alabama in 2019. This paper presents the absorber performance and model validation for the campaign. The absorber was tested with in-and-out and with pump-around intercooling. The variable operating conditions included lean loading (0.19–0.25 m CO2/mol alkalinity), gas temperature (40, 78 °C), and intercooling temperature (35, 40 °C). Using 5 m PZ CO2 removal from 82% to 96% was achieved with intercooling and only 12 m of packing. A rigorous, rate-based absorber model accurately predicted the CO2 removal and temperature profile. The model shows that the delta loading of the solvent at NGCC conditions for 90% removal is greater than at coal conditions, but high CO2 removal (99%) is more difficult to achieve with NGCC gas than with coal-fired flue gas. The pump-around intercooling was effective, and the intercooling temperature had a large impact on the absorber performance. With pump-around, the delta loading penalty for hot gas feed into absorber without a direct contact cooler was less than 5%.

The effect of disintegrated iron-ore pellet dust on deposit formation in a pilot-scale pulverized coal combustion furnace. Part II: Thermochemical equilibrium calculations and viscosity estimations

Fly ash particles from the combustion of solid-fuels together with disintegrated particles arising from iron-ore pellets result in accumulation of deposits on the refractory linings of the grate-kiln induration machine during the iron-ore pelletizing process. The deposits amass in the high-temperature regions of the induration furnace thus disturbing the flow of gas and pellets. Therefore, to tackle the above-mentioned issues, an understanding of deposit formation mechanism is of crucial importance. This study was conducted with the objective of addressing the effect of disintegrated iron-ore pellet dust on deposit formation and the mechanisms behind deposition (slagging) in the grate-kiln process. A comprehensive set of experiments was conducted in a 0.4 MW pilot-scale pulverized-coal- fired furnace where three different scenarios were considered as follows; Case 1 (reference case): Coal was combusted without the presence of pellet dust. Case 2: Natural gas was combusted together with simultaneous addition of pellet dust to the gas stream. Case 3: Coal was combusted together with the addition of pellet dust simulating the situation in the large-scale setup. Fly ash particles and short-term deposits were characterized and deposition was addressed in Part I of this study. In light of the experimental observations (Part I) and the thermochemical equilibrium calculations (Part II), a scheme of ash transformation during the iron-ore pelletizing process was proposed. The dissolution of hematite particles into the Ca-rich-aluminosilicate melt (from the coal-ash constituents) decreased the viscosity and resulted in the formation of stronger (heavily sintered) deposits. Overall, this pilot-scale work forms part of a wider study which aims at deepening the understanding of ash transformation phenomena during the large-scale pelletizing process.

Free solute content and solute-matrix interactions affect apparent solubility and apparent solute content in supercritical CO2 extractions. A hypothesis paper

This manuscript stresses the need of experimental measurements and mathematical models of sorption isotherms/isobars to properly account for mass transfer in the SuperCritical (SC) Fluid Extraction (SCFE) processes. A reliable sorption isotherm/isobar model is a requirement, on one hand, for the determination of relevant inner mass transfer coefficients in SC CO2 extractions of vegetable substrates and other biological materials at the laboratory scale, and on the other hand, for a simulation tool successfully applicable to describe industrial SCFE process, which should be based both on a reliable mathematical descriptions of SC CO2 extraction processes. Having a reliable simulation model and model parameters would allow limiting expensive experimental pilot-scale work to validation purposes. Based on simulations of oil extraction from pre-pressed oilseeds using SC CO2 at 353K and 90MPa, this manuscript shows that the initial oil content in the pre-treated seed affects the apparent solubility of the oil, that the partition of the oil between the seed and CO2 affects oil yield, that it is difficult to discriminate oil partition from inner mass transfer effects, that the best-fit parameters from a mathematical model are adequate only when the model accounts for the true physical picture of the extraction process, and that failure of the mathematical model to account the true physical picture of the extraction process impedes reliable simulations, scale-up, and economical evaluation of industrial SCFE process. Being sorption phenomena of such paramount importance to build a reliable mathematical model for simulation of SCFE processes, this manuscript proposes a mathematical model that fits experimental sorption isotherm/isobars for oil from seeds.

Mercury removal from coal combustion by Fenton reactions – Part A: Bench-scale tests

This series of papers describes the development of technology to convert Hg(0) to Hg(II) in coal-derived flue gas based on the well-known Fenton reactions so that a Hg control strategy can be implemented in a wet scrubber. This effort consists of both bench-scale and pilot-scale work. This first paper reports on the bench-scale tests. The bench-scale results showed that Hg(0) oxidation can be achieved by the Fenton reactions and the oxidation rate is quantitatively dependent on the residence time of the Hg stream in the solution. An average of 75% oxidation of Hg(0) was achieved. Iron-based Fenton-type additives gave much more promising results compared to Cu-based Fenton-like additives for Hg(0) oxidation. The pH value of the sorbent solution also had a significant effect on the oxidation of Hg(0) and a suitable pH window was found to lie between 1.0 and 3.0 for this application. This may be attributed to the chain reaction mechanisms of Fe 3+/H 2O 2 for Fenton reactions, i.e., the decomposition of H 2O 2 for the production of OOH radicals in the Fe 3+/H 2O 2 system which is kinetically favoured under a wide range of conditions at pH values of 3 or less. At higher pH values, H 2O 2 is converted to H 2O instead of OOH radicals in the presence of Fe 3+.

Recent advances in mercury removal technology at the National Energy Technology Laboratory

The in-house research effort on mercury studies at the National Energy Technology Laboratory is an integrated, multi-task approach, including experimentation at both the laboratory-scale and the pilot-scale, as well as a numerical modeling effort to aid in interpretation of pilot-scale results. In the laboratory-scale work, novel sorbents and techniques for the removal of mercury from flue gas are being investigated using a small packed-bed reactor. The reactor system is used to screen novel sorbents for their capability to remove mercury from gas streams. The capacities of these novel sorbents are determined as a function of gas composition and temperature and are compared to results with commercially available activated carbons. In the pilot-scale work, an existing pilot unit has been characterized with respect to the distribution and fate of hazardous air pollutants in flue gas, with an emphasis on mercury. The pilot unit is a 500-lb/h (227-kg/h) pulverized coal-fired (PCFC) combustion system that includes a furnace, air preheater, spray dryer, ductwork and a pulse-jet fabric filter. The investigations with this unit have entailed evaluation of various activated carbons and novel sorbents, as well as comparisons of various sampling techniques for the determination of total and speciated forms of mercury. The impact of various parameters (temperature, sorbent-to-mercury ratio, baghouse pressure drop) on the removal of mercury has been investigated. Additionally, a slipstream allows for the investigation of sorbent injection in a fly ash-free flue gas over a wide range of operating conditions, including residence time. A summary of the results for mercury measurement and control from the 500-lb/h (227-kg/h) PCFC combustion system will be presented, as well as the evaluation of methods for measurement of in-duct removals using the slipstream. Finally, a discussion of the numerical modeling effort will be given.

Residual moisture reduction in coarse coal centrifuges using air purging. Part 3. Commercial scale trials

CSIRO/Novatech Consulting have been developing air purging as a new way of reducing the moisture content of coarse coal products from vibrating basket centrifuges. The process involves injecting a turbulent stream of high velocity air, via an air knife manifold, through the coal bed as it traverses the centrifuge basket. This paper describes the results obtained when the process was trialled in a commercial scale centrifuge, following successful previous bench and pilot scale work reported previously. Five manifolds of different shapes and sizes were tested. The best results were achieved with units of square cross-section, located close to the outlet edge of the basket. Depending on air speed, product moisture was reduced by between 0.7 and 0.9 wt% at a confidence level exceeding 95%. The best results approached closely the 1.0 wt% moisture reduction target which had been adopted as the project objective. Air purging had no significant effect on the content or size distribution of the solids in the centrate. Increasing air speed led to larger moisture reductions. Higher air speeds were needed compared with previous pilot scale work probably due to the thicker beds encountered in the full scale centrifuge. Despite the higher air speed, the actual air usage (cfm/t of coal) was much more efficient at full scale, being less than half that at pilot scale.

Investigation of Ammonia Formation during Gasification in an Air-Blown Spouted Bed: Reactor Design and Initial Tests

A laboratory scale, pressurized gasifier has been developed to simulate the operating conditions of air-blown spouted bed gasifiers. The new 28 mm i.d. reactor operates with a continuous coal feed of typically 3 g min-1, at temperatures up to 980 °C and pressures up to 20 bara. Fluidizing gases can be combinations of air, steam, and nitrogen. The gases and coal enter the gasifier through the inverted conical base of the reactor, as a high velocity jet, which induces the rapid mixing of the fresh coal with the bed char. At the pilot scale this mode of operation had been found to avoid the operating difficulties associated with the agglomeration of sticky coal particles. Gases within the reactor may be sampled from the spout jet (using a specially designed water-cooled probe) and from the exit of the reactor. In the present study, the reactor has been used to study NH3 formation under conditions relevant to those of the pilot-scale gasifier that was used during the process development stage of the Air-Blown Gasification Cycle. The pilot-scale work had found high, variable, and at times difficult-to-predict concentrations of NH3 in the fuel gas. The present stage of the work was aimed to help understand the pilot-scale data by focusing on the effect of operating conditions on NH3 formation reactions. The gasifier has been shown to run with continuous feed for periods of up to 30 min, before sinter builds up on the base and prevents normal operation. Within this time data are collected on the spout and exit gas compositions. In this paper we report preliminary findings, which suggest that the NH3 is produced during pyrolysis and by the effect of steam on the char-N. The latter is the most important reaction and the mechanism is at present unclear. High concentrations of NH3 appear to form through the latter mechanism and to vary with operating conditions, temperature, steam content, presence of sorbent, and coal:air ratio.

Application of simplified rapid equilibrium models in simulating experimental breakthrough curves from fixed bed biosorption reactors

A modelling approach for a fixed bed biosorption column is presented. The Advection–Dispersion–Reaction (ADR) equation has been applied as the basic modelling equation for the special case of Local Equilibrium (LE). The model implements the minimum parameters for describing a fixed bed biosorption column, employing the geometrical dimensions of the bed, the packing arrangement, the operating conditions of the system, and the sorptive characteristics of the biosorbent material. An apparent axial dispersion coefficient has been used as a key parameter of the model. The authors compare model predictions to selected examples of experimental biosorption breakthrough curves reported from pilot scale work. Although the main assumption of the model is that biosorption equilibrium is rapid, the use of an apparent overall dispersion coefficient makes the model applicable for the cases where mass transfer resistances are present in the liquid and solid phases.

Supercritical water oxidation of sludges contaminated with toxic organic chemicals

Supercritical water oxidation (SCWO) is a proven technology for the treatment of contaminated organic wastes. Bench and pilot-scale work completed at The University of Texas at Austin's SCWO Laboratory have proven the technology effective for treating a variety of sludge types, including sludge contaminated with hazardous compounds. The studies included pulp and paper mill sludges and sludges derived from the treatment of municipal and industrial wastewaters. The results presented in this paper confirmed that the removal of the organic component of sludge, including the trace toxic organic compounds, using SCWO exceeded 99.9%. For example, the results show that the destruction removal efficiencies (DRE's) of the PCBs reached 99.99% in the contaminated sludge. No dioxins or furans were detected in the gaseous effluent resulting from the treatment of the PCB-contaminated sludge. These results demonstrate the technical effectiveness of SCWO as a sludge remediation technology.

99/00604 Reburning using biomass for NO x control

This study examines the use of wood reburning for NOx reduction in a cyclone-fired boiler. Reburning is an in-furnace NOx control technology that uses fuel injected above the main firing system to reduce NO formed in the main heat release zone. Bench- and pilot-scale work done over the past several years suggests that NOx reductions up to sixty percent are possible using reburning under the right conditions. The practical implementation of reburning technology depends upon the ability to contact the reburning fuel with NO formed in the cyclone barrel at the optimum stoichiometry for he maximum time. Thus, reburning effectiveness in practical systems is determined by the performance of he mixing system. This paper describe the results of a computer modeling study of the TVA Allen Station Unit No. 2 to evaluate various reburning fuel injection and overfire air injection designs and estimate he NOx reduction potential using wood as a reburning fuel. Results of this study showed the best mixing was obtained using opposed fired reburning injectors located as close to the cyclone barrels as possible with opposed-wall overfire air injectors at as high a velocity as pressure drop constraints allow. Under these conditions, NOx reductions of ∼ 45% are expected. When the wood carrier air is replaced by fuel gas, the expected NOx reduction increases to ∼ 55%. Further NOx reduction was possible if the stoichiometric constraints in the reburning zone could be relaxed to allow deeper staging.

Reburning using biomass for NO x control

This study examines the use of wood reburning for NOx reduction in a cyclone-fired boiler. Reburning is an in-furnace NOx control technology that uses fuel injected above the main firing system to reduce NO formed in the main heat release zone. Bench- and pilot-scale work done over the past several years suggests that NOx reductions up to sixty percent are possible using reburning under the right conditions. The practical implementation of reburning technology depends upon the ability to contact the reburning fuel with NO formed in the cyclone barrel at the optimum stoichiometry for he maximum time. Thus, reburning effectiveness in practical systems is determined by the performance of he mixing system. This paper describe the results of a computer modeling study of the TVA Allen Station Unit No. 2 to evaluate various reburning fuel injection and overfire air injection designs and estimate he NOx reduction potential using wood as a reburning fuel. Results of this study showed the best mixing was obtained using opposed fired reburning injectors located as close to the cyclone barrels as possible with opposed-wall overfire air injectors at as high a velocity as pressure drop constraints allow. Under these conditions, NOx reductions of ∼45% are expected. When the wood carrier air is replaced by fuel gas, the expected NOx reduction increases to ∼55%. Further NOx reduction was possible if the stoichiometric constraints in the reburning zone could be relaxed to allow deeper staging.

The strengthening of embrittled books using gamma radiation

The embrittlement of papers, manufactured through processes introduced in the mid-19th century, has caused many millions of books to become fragile, even to the point of being unusable. During the 1980s the British Library funded a research programme, carried out at the University of Surrey, to develop a technology which could be used to treat brittle books on a large scale, with the goal of greatly extending their useful life. The process developed, known as graft co-polymerization, involves three stages:i)application of a cocktail of monomers to the book's pages;ii)equilibration of these monomers throughout the text block;iii)a low, slow dose of γ-radiation to effect polymerization.The work at the University of Surrey studied various combinations of monomers, as well as equilibration times and dose régimes; it also examined the environment necessary to achieve polymerization within the pages of the book, whilst leaving it in an otherwise original condition.In collaboration with the British Library, Nordion International has designed a full-scale bookstrengthening plant capable of processing between 200,000 and 500,000 books per year, with estimated prices to customers in the region of £8–£10 per volume (US S12–16). In order to test the equipment and procedures that would be involved in such a plant, pilot-scale equipment has been designed and assembled on the premises of Isotron plc, where use is made of a conventional irradiator. This paper gives details of the graft co-polymerization process, and some results of the pilot-scale work, in terms of both efficacy and controllability. It also discusses the technical and economic feasibility of building and running a full-scale plant.

Development of an improved steel for pipe fittings

The requirements for steels for pipe fittings include a move to lower levels of carbon equivalent (CEV), improved strength, increased thickness, and improved weldability. The work on the development of a new pipe-fittings steel, untertaken within BSC, is described from the early laboratory casts through pilot-scale work to the production and assessment of a commercial cast. The new steel has a low value of proof stress in the normalized condition which, on tempering, is changed to a high level of yield stress coupled with good levels of toughness. X60 properties can be achieved with a target CEV of 0·47. The strength of the steel is not greatly affected by normalizing temperature and tempering temperature, thus providing the fabricator with a flexible process route.

Rotary-vacuum filtration of coal flotation concentrates

Vacuum-filter capacity can only be reliably determined if accurate data is available from laboratory and pilot-scale tests with samples of the material ultimately to be filtered by the commercial unit. Pilot units are invariably relatively flexible models of the commercial unit but the scope of the testwork must be minimised wherever possible because of the large sample volume involved. Laboratory bench-scale apparatus must therefore be used to provide the basis for determining the extent of specific information required from pilot-plant work. All too often however, this apparatus bears no resemblance to the operational behaviour of a particular filter type. Laboratory tests conducted with a closely simulated apparatus can provide valuable information and because the apparatus is very flexible, the type of testwork which can be accomplished can take into account varying operating conditions and allow optimized operation to be predicted. Such testwork need not involve a very large bulk sample of the slurry. It is not however satisfactory to base filter design totally on laboratory data and it is essential that pilot-scale work be carried out with a suitable model of the eventual commercial machine. Pilot units are now readily available from filter manufacturers and it is possible for testwork service to be obtained or for the machine to be hired. The paper contains an approach to obtaining rotary-vacuum-filter capacities for coal concentrate treatment and demonstrates comparative results obtained with bench, pilot and full-scale tests.