Triboelectrostatic benefiċjazzjoni ta ' terraferma Fly Ash WOCA 2015

Triboelectrostatic benefiċjazzjoni ta ' l-

Land Filled Fly Ash

L. Furnar, A. Gupta, u S. Gasiorowski

ST Tagħmir & Teknoloġiji LLC, 101 Hampton Vjal, Needham MA 02494 USA

CONFERENCE: 2015 Dinja ta ' l-irmied tal-Faħam – (www.worldofcoalash.org)

KEYWORDS: Triboelectrostatic, Beneficiation, fly Irmied, Landfilled, Dried, Separazzjoni, Carbon

ASTRATTI

Triboelectrostatic separation has been used for the commercial beneficiation of coal combustion fly ash to produce a low carbon product for use as a cement replacement in concrete for nearly twenty years. With 18 separators in 12 coal-fired power plants across the world, ST Tagħmir & Technology LLC’s (STET) patented electrostatic separator has been used to produce over 15 Million tonnes of low carbon product.

To date, commercial beneficiation of fly ash has been performed exclusively on dry “run of station‿ ash. Recent environmental legislation has created, in certain markets, a need to supply beneficiated ash in times of low ash generation. This, coupled with a requirement in some locations to empty historical ash landfill sites, has created the need to develop a process to beneficiate historically landfilled ash.

Previous studies have shown that the exposure of fly ash to moisture, and subsequent drying influences the triboelectrostatic charging mechanism, with carbon and mineral particles charging in the opposite polarity to that experienced with run of station ash. Studies have been performed by the authors to determine the effect of moisture exposure on separation efficiency of several ashes that have been reclaimed from landfills and dried. Charge reversal was experienced following drying, but overall separation efficiency was achieved equivalent to that experienced with fresh run of station ash.

The effect of dried ash feed relative humidity on triboelectrostatic separation efficiency was examined, and sensitivity was greatly reduced compared to that experienced with run of station ash, lowering overall process costs.

INTRODUZZJONI

The American Coal Ash Association (ACAA) annual survey of production and use of coal fly ash reports that between 1966 u l- 2011, Fuq 2.3 billion short tons of fly ash have been produced by coal-fired utility boilers.1 Of this amount approximately 625 million tons have been beneficially used, mostly for cement and concrete production. Madankollu, the remaining 1.7+ billion tons are primarily found in landfills or filled ponded

impoundments. While utilization rates for freshly generated fly ash have increased considerably over recent years, with current rates near 45%, Madwar 40 million tons of fly ash continue to be disposed of annually. While utilization rates in Europe have been much higher than in the US, considerable volumes of fly ash have also been stored in landfills and impoundments in some European countries.

Riċentement, interest in recovering this disposed material has increased, partially due to the demand for high-quality fly ash for concrete and cement production during a period of reduced production as coal-fired power generation has decreased in Europe and North America. Concerns about the long-term environmental impact of such landfills are also prompting utilities to find beneficial use applications for this stored ash.

LAND FILLED ASH QUALITY AND REQUIRED BENEFICIATION

While some of this stored fly ash may be suitable for beneficial use as initially excavated, the vast majority will require some processing to meet quality standards for cement or concrete production. Since the material has been typically wetted to enable handling and compaction while avoiding airborne dust generation, drying will probably be a minimal requirement for use in concrete since concrete producers will want to continue the practice of batching fly ash as a dry powder. Madankollu, assuring the chemical composition of the ash meets specifications, most notably the carbon content measured as loss-on-ignition (LIĠI), is a greater challenge. As fly ash utilization has increased in the last 20+ Snin, most “in-spec‿ ash has been beneficially used, and the off-quality ash disposed. Għalhekk, LOI reduction will be a requirement for utilizing the vast majority of fly ash recoverable from utility impoundments.

LOI REDUCTION BY TRIBOELECTRIC SEPARATION

While various workers have used combustion techniques and flotation processes for LOI reduction of recovered landfilled and ponded fly ash, ST Tagħmir & Technologies (STET) has found that its standard processing system, long used for beneficiation of freshly generated fly ash, is equally effective on recovered ash after suitable drying and deagglomeration at lower overall operating costs.

During the ramp-up to commercial application of the STET processing system for fly ash, STET researchers tested the separation of dried landfilled ash. This recovered ash separated very similarly to freshly generated ash with one surprising difference: l-imponiment ta ' partiċella kien imdawwar minn dak ta ' l-irmied frisk mal-karbonju iċċarġjar negattivi fir-rigward tal-minerali.2 Riċerkaturi oħra ta ' separazzjoni elettrostatiċi ta ' l-irmied li jtir karbonju kienu wkoll osservati dan il-fenomenu.3,4,5

TEKNOLOĠIJA ĦARSA ĠENERALI – IS-SEPARAZZJONI TAL-KARBONJU TAL-IRMIED LI JTIR

Fis-separatur tal-karbonju STET (Il-figura 1), il-materjal jiddaħħal fid-distakk irqiq bejn żewġ elettrodi planari paralleli. Il-partiċelli huma triboelectrically mitluba mill-kuntatt interparticle. The positively charged carbon and the negatively charged mineral (in freshly generated ash that has not been wetted and dried) huma attirati lejn elettrodi opposti. Il-partiċelli mbagħad jiġu mimsuħa minn ċinturin kontinwu li jiċċaqlaq u jitwasslu f'direzzjonijiet opposti. Iċ-ċintorin imexxi l-partiċelli maġenb kull elettrodu lejn truf opposti tas-separatur. Il-veloċità taċ-ċintorin għolja wkoll jippermetti produzzjoni għolja ħafna, sa 36 tunnellati fis-siegħa fuq separatur wieħed. Id-distakk żgħir, qasam ta 'vultaġġ għoli, fluss tal-kurrent tal-kontro, aġitazzjoni vigoruża tal-partiċelli ta' partikuli u azzjoni ta' awto-tindif taċ-ċinturin fuq l-elettrodi huma l-karatteristiċi kritiċi tas-separatur STET. Billi jikkontrollaw parametri varji ta ' proċess, bħalma huma l-veloċità taċ-ċintorin, punt ta ' l-għalf, u r-rata tal-għalf, il-proċess STET jipproduċi rmied li jtir LOI baxx f'kontenut ta' karbonju ta' inqas minn 1.5 biex 4.5% minn irmied li jtir fl-għalf li jvarja f'LOI minn 4% għal aktar 25%.

Fig. 1 STET Separator

Id-disinn tas-separatur huwa relattivament sempliċi u kompatt. Magna disinjata biex tipproċessa 36 tunnellati fis-siegħa hija bejn wieħed u ieħor 9 m (30 FT.) twil, 1.5 m (5 FT.) Wiesgħa, u l- 2.75 m (9 FT.) għoli. Il-belt u rombli assoċjati huma l-partijiet li jiċċaqalqu biss. L-elettrodi huma wieqfa u magħmula minn xi materjal dejjiemi kif jixraq. The belt is made of non- conductive plastic. The separator’s power consumption is about 1 kilowatt-sieg ħa għal kull tunnellata ta ' materjal ipproċessat bil-bi ċċa l-kbira tal-ener ġija kkunsmata minn żewġ muturi li jsuqu ċ-ċintorin.

Il-pro Ċess huwa kompletament niexef, ma jeħtieġ l-ebda materjal addizzjonali għajr l-irmied li jtir u ma jipproduċi l-ebda ilma mormi jew emissjonijiet tal-arja. The recovered materials consist of fly ash reduced in carbon content to levels suitable for use as a pozzolanic admixture in

concrete, u frazzjoni għolja ta' karbonju utli bħala fjuwil. Użu ta ' żewġ nixxigħat prodott jipprovdi a 100% soluzzjoni għall-problemi ta ' rimi ta ' rmied.

RECOVERED FUEL VALUE OF HIGH-CARBON FLY ASH

In addition to the low carbon product for use in concrete, marka bl-isem ProAsh®, il-proċess ta' separazzjoni tal-STET jirkupra wkoll karbonju mhux maħruq mod ieħor fil-forma ta' rmied li jtir b'kontenut ta' karbonju, EkoTherm tad-ditta™. Eotherm™ għandu valur sinifikanti tal-fjuwil u jista 'jiġi rritornat faċilment fl-impjant tal-enerġija elettrika billi juża l-STET EcoTherm™ Return system to reduce the coal use at the plant. Meta EkoTherm™ jinħaraq fil-bojler tal-utilità, l-enerġija mill-kombustjoni tiġi kkonvertita għal pressjoni għolja / fwar b'temperatura għolja u mbagħad għall-elettriku bl-istess effiċjenza bħall-faħam, Tipikament 35%. The conversion of the recovered thermal energy to electricity in ST Equipment & Technology LLC EcoTherm™ Is-sistema tar-ritorn hija darbtejn sa tliet darbiet ogħla minn dik tat-teknoloġija kompetittiva fejn l-enerġija tiġi rkuprata bħala sħana ta' grad baxx fil-forma ta' ilma sħun li jiġi ċċirkolat lis-sistema tal-ilma tal-għalf tal-bojler. Eotherm™ jintuża wkoll bħala sors ta' alumina fil-fran tas-siment, tneħħi l-boksajt l-aktar għali li ġeneralment jiġi ttrasportat fuq distanzi twal. Użu tal-EkoTherm b'karbonju għoli™ irmied jew f'impjant tal-enerġija jew f'forn tas-siment, timmassimizza l-irkupru tal-enerġija mill-faħam ikkunsinnat, it-tnaqqis tal-ħtieġa li l-minjieri u t-trasport ta' fjuwil addizzjonali għall-faċilitajiet.

STET’s Raven Power Brandon Shores, SMEPA R.D. Morrow, NBP Belledune, RWEnpower Didcot, EDF Energy West Burton, and RWEnpower Aberthaw fly ash plants, kollha jinkludu EcoTherm™ Sistemi ta' ritorn. Il-komponenti essenzjali tas-sistema huma ppreżentati fil-Figura 2.

Fig. 2 Eotherm™ Sistema ta' ritorn

STET ASH PROCESING FACILITIES

Controlled low LOI fly ash is produced with STET’s technology at twelve power stations throughout the U.S., Kanada, ir-Renju Unit, Il-Polonja, and Republic of Korea. ProAsh® irmied li jtir ġie approvat għall-użu minn aktar minn għoxrin Stat highway awtoritajiet, l-aġenziji speċifikazzjoni oħra kif ukoll kemm. ProAsh® ukoll ġiet ċertifikata taħt assoċjazzjoni Standards Kanadiżi u EN 450:2005 standards ta ' kwalità fl-Ewropa. Faċilitajiet ta ' ipproċessar irmied bl-użu ta ' teknoloġija ta ' l-STET huma elenkati fit-tabella 1.

Tabella 1. Operazzjonijiet Kummerċjali STET

COAL ASH RECOVERED FROM LAND FILLS

Two sources of ash were obtained from landfills: sample A from a power plant located in

the United Kingdom and sample B: from the United States. Both these samples consisted of ash from the combustion of bituminous coal by large utility boilers. Due to the intermingling of material in the landfills, no further information is available concerning specific coal source or combustion conditions.

The samples as received by STET contained between 15% u l- 20% water as is typical for landfilled material. The samples also contained varying amounts of large >1/8 inch (~3 mm) material. To prepare the samples for carbon separation, the large debris was removed by screening and the samples then dried and deagglomerated prior to carbon beneficiation. Various methods for drying/deagglomeration are being evaluated in order to optimize the overall process. F'karta ta ' fluss tal-proċess ġenerali jkun ppreżentati fil-Figura 3.

Il-figura 3: Process flow sheet

Il-propjetajiet tal-kampjuni preparati kienu ukoll fi ħdan il-medda ta ' l-irmied li jtir miksub direttament mill-utilità normali kaldaruni. Il-proprjetajiet aktar relevanti għall-separatur feeds u l-prodotti huma riassunti fit-tabella 2 flimkien ma ' prodott irkuprat.

IS-SEPARAZZJONI TAL-KARBONJU

Carbon reduction trials using the STET triboelectric belt separator resulted in very good recovery of low LOI product. The interesting phenomena observed was the reversal of charging of the carbon discussed above. While this behavior has been observed previously by STET and other researchers, the mechanism that changes the relative work functions and thus contact charging behavior of the material is not understood. One suggested mechanism is the redistribution of soluble ions on the mineral and

following table summarizes the chemistry for samples from source B. Testing on source A material has not been completed.

Tabella 4: Ash Chemistry of low LOI ash.

Strength development of a 20% substitution of the low LOI fly ash in a mortar containing 600 lb / yd3 showed the material derived from landfilled ash performed somewhat better than material from fresh production. Ara t-Tabella 5 below.

Tabella 5: Compressive strength of mortar cubes.

CONCLUSIONS

After suitable scalping of large material, drying, and deagglomeration, fly ash recovered from utility plant landfills can be reduced in carbon content using the commercialized STET triboelectric belt separator. The efficiency of the STET system is essentially equivalent for ashes obtained freshly from boiler operations and dried landfilled material. The separator product is suitable for use in concrete production without further beneficiation with nearly identical performance properties. The recovery and beneficiation of landfilled ash will provide a continuing supply of high quality ash for concrete producers in spite of the reduced production of “fresh‿ ash as coal-fired utilities reduce generation. Addizzjonalment, power plants that need to remove ash from landfills to meet changing environmental regulations will be able to utilize the process to alter a waste product liability into a valuable raw material for concrete producers.

REFERENZI

[1]American Coal Ash Coal Combustion products and Use Statistics: https://www.acaa-usa.org/Publications/Production-Use-Reports/

[2]ST internal report, awissu 1995.

[3]Li,T.X,. Schaefer, J.L., Ban, H., Neathery, J.K., and Stencel, J.M. Dry Beneficiation Processing of Combustion Fly Ash, Proceedings of the DOE Conference on Unburned Carbon on Utility Fly Ash, jista ' 19 20, Pittsburgh, PA, 1998.

[4]Baltrus, J.P., Diehl, J.R., Soong, Y., Sands, W. Triboelectrostatic separation of fly ash and charge reversal, Fuel 81, (2002) pp.757-762.

[5]Cangialosi, F., Notarnicola, M., Liberti, L, Stencel, J. The role of weathering on fly ash charge distribution during triboelectrostatic beneficiation, Journal of Hazardous Materials, 164 (2009) pp.683-688.

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