Triboelectrostatic Beneficiation din depozitul cenuși zburătoare WOCA 2015

Triboelectrostatic Beneficiation of

Land Filled Fly Ash

L. Baker, ADRIAN. Gupta, şi S. Gasiorowski

Echipament de ST & Tehnologii SRL, 101 Hampton Avenue, Needham MA 02494 STATELE UNITE ALE AMERICII

Conferinţă: 2015 Lume de cenuşă de cărbune- (www.worldofcoalash.org)

CUVINTE CHEIE: Triboelectrostatic, Beneficiation, Cenuși zburătoare, Landfilled, Dried, Separarea, Carbon

REZUMAT

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. Cu 18 separatoare în 12 centrale electrice pe bază de cărbune din întreaga lume, Echipament de ST & Tehnologie SRL (STET) separator electrostatic patentat a fost utilizat pentru a produce peste 15 Milioane de tone de produs cu emisii scăzute de dioxid de carbon.

Până în prezent, 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. Acest lucru, 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.

Introducere

American cărbune cenuşă Asociaţiei (ACAA) anchetă anuală de producție și utilizarea cărbunelui cenuși zburătoare rapoarte că între 1966 şi 2011, peste 2.3 billion short tons of fly ash have been produced by coal-fired utility boilers.1 Of this amount approximately 625 milioane de tone au fost utilizate efectiv, cea mai mare parte pentru producţia de ciment si beton. Cu toate acestea, rămase 1.7+ billion tons are primarily found in landfills or filled ponded

impoundments. În timp ce ratele de utilizare pentru cenușa zburătoare proaspăt generată au crescut considerabil în ultimii ani, cu rate curente aproape 45%, aproximativ 40 million tons of fly ash continue to be disposed of annually. În timp ce ratele de utilizare în Europa au fost mult mai mari decât în SUA, de asemenea, au fost depozitate volume considerabile de cenușă zburătoare în depozitele de deșeuri și în sechestrele din unele țări europene.

Recent, 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. Cu toate acestea, assuring the chemical composition of the ash meets specifications, most notably the carbon content measured as loss-on-ignition (LOI), is a greater challenge. As fly ash utilization has increased in the last 20+ ani, most “in-spec‿ ash has been beneficially used, and the off-quality ash disposed. Thus, 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, Echipament de ST & 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: the particle charging was reversed from that of fresh ash with the carbon charging negative in relation to the mineral.2 Other researchers of electrostatic separation of fly ash carbon have also observed this phenomena.3,4,5

PREZENTARE GENERALĂ A TEHNOLOGIEI – SEPARAREA CARBONULUI DE CENUȘĂ DE ZBOR

În separatorul de carbon STET (Figura 1), materialul este alimentat în decalajul subţire între doi electrozi plane paralele. Particulele sunt practicate triboelectrically de interparticle contact. Carbonul încărcat pozitiv și mineralul încărcat negativ (în cenușă proaspăt generată care nu a fost udată și uscată) sunt atrase de electrozi opusi. Particulele sunt apoi măturat printr-o centură în mişcare continuă şi transmisă în directii opuse. Centura se mută particule adiacent la fiecare electrod spre capetele opuse ale separatorul. Viteza mare, de asemenea, permite cererea foarte mare, până la 36 tone pe oră pe un singur separator. Spațiu liber mic, câmp de înaltă tensiune, contra fluxul de curent, viguros de particule-particule agitaţie şi auto-curatare de acţiune a centurii pe electrozii sunt caracteristici critice separatorului STET. Prin controlul diverse parametrii de proces, cum ar fi viteza curelei, feed punct, şi hrana pentru animale rata, procesul de STET produce mici LOI cenuși zburătoare la conţinutul de carbon mai mică 1.5 pentru a 4.5% la feed zbura cenuşă variind în LOI din 4% la peste 25%.

Fig. 1 STET Separator

Separatorul de proiectare este relativ simplu şi compact. O maşină concepute pentru a prelucra 36 tone pe oră este de aproximativ 9 m (30 ft.) lung, 1.5 m (5 ft.) largă, şi 2.75 m (9 ft.) mare. Curea si role asociate sunt doar piesele mobile. Electrozii sunt staționari și compus dintr-un material durabil în mod corespunzător. The belt is made of non- conductive plastic. Consumul de energie al separatorului este de aproximativ 1 kilowaţi-oră pe tonă de material procesat cu cea mai mare parte a puterii consumate de doua motoare centura de conducere.

Procesul este complet uscat, necesită nici materiale suplimentare, altele decât cenuși zburătoare şi produce fără emisii reziduale de apa sau aer. The recovered materials consist of fly ash reduced in carbon content to levels suitable for use as a pozzolanic admixture in

beton, şi o fracţiune de carbon de înaltă utile drept combustibil. Utilizarea a două fluxuri de produs oferă o 100% soluţie pentru problemele de eliminare cenuși zburătoare.

VALOAREA COMBUSTIBILULUI RECUPERAT AL CENUȘII ZBURĂTOARE CU EMISII RIDICATE DE CARBON

În plus față de produsul cu emisii scăzute de carbon pentru utilizarea în beton, brand numit ProAsh®, separarea STET procesa, de asemenea, Recupereaza pierdut altfel nearse de carbon sub formă de bogate în carbon cenuși zburătoare, marcă EcoTherm™. EcoTherm™ are valoare semnificativa de combustibil şi cu uşurinţă pot fi returnate centralei electrice folosind STET EcoTherm™ Sistem de returnare pentru a reduce utilizarea cărbunelui la uzină. Atunci când EcoTherm™ este ars în cazan de utilitate, energia de ardere este convertit la presiune inalta / abur de temperatură ridicată şi apoi la electricitate la aceeaşi eficienţă ca cărbune, de obicei 35%. Conversia energiei termice recuperate în energie electrică în echipamente ST & Tehnologie LLC EcoTherm™ Sistem de retur este două-trei ori mai mare decât cea a tehnologiei competitiv, în cazul în care energiei este recuperată, grad scăzut de căldură sub formă de apă fierbinte, care este circulat la cazan apa sistem de alimentare. EcoTherm™ este de asemenea folosit ca o sursă de alumină în cuptoarele de ciment, deplasarea bauxită mai scump, care este, de obicei, transportat distanţe lungi. Utilizand EcoTherm ridicat de carbon™ cenuşă, fie la o centrala sau un cuptor de ciment, Maximizează recuperare de energie de cărbune livrate, reduce necesitatea de a mea si combustibil suplimentare la facilităţile de transport.

STET’s Raven Power Brandon Shores, RALUK SMEPA. Morrow, CORNEL Belledune, RWEnpower Didcot, FED energie Burton vest, și RWEnpower Aberthaw zbura plante de cenușă, Toate includ EcoTherm™ Sisteme de returnare. Componentele esenţiale ale sistemului sunt prezentate în figura 2.

Fig. 2 EcoTherm™ Sistem de retur

STET ASH PROCESING FACILITIES

Controlat scăzut LOI zbura cenușă este produs cu tehnologia STET la douăsprezece centrale electrice din ÎNTREAGA SUA., Canada, Marea Britanie, Polonia, and Republic of Korea. ProAsh® cenușă zburătoare a fost aprobată pentru utilizare de peste douăzeci de autorități rutiere de stat, precum și multe alte agenții de specificații. ProAsh® a fost, de asemenea, certificată în conformitate cu Canadian Standards Association și EN 450:2005 standardele de calitate în Europa. Instalațiile de prelucrare a cenușii care utilizează tehnologia STET sunt enumerate în tabelul 1.

Tabel 1. Operațiuni comerciale 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% şi 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. A general process flow sheet is presented in Figure 3.

Figura 3: Process flow sheet

The properties of the prepared samples were well within the range of fly ash obtained directly from normal utility boilers. The most relevant properties for both the separator feeds and products are summarized in Table 2 along with recovered product.

CARBON SEPARATION

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.

Tabel 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. A se vedea tabelul 5 Sub.

Tabel 5: Compressive strength of mortar cubes.

Concluziile

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. Suplimentar, 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.

Referinţe

[1]American cărbune ash cărbune produse de ardere și statistici de utilizare: https://www.acaa-usa.org/Publications/Production-Use-Reports/

[2]ST internal report, August 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, Poate 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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