Triboelectrostatic bogatenje odloženih pepel WOCA 2015

Triboelectrostatic Beneficiation of

Land Filled Fly Ash

L. Baker, A. Gupta, in S. Gasiorowski

ST opreme & Tehnologije LLC, 101 Hampton Avenue, Needham MA 02494 ZDA

CONFERENCE: 2015 Svet premogov pepel- (www.worldofcoalash.org)

KLJUČNE BESEDE: Triboelectrostatic, Bogatenje, Pepel, Landfilled, Dried, Ločitev, Carbon

Abstraktne

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 opreme & Tehnologija LLC (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. To, 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.

Uvod

Združenje ameriških premoga pepela (ACAA) letni pregled proizvodnje in uporabe premoga pepel poroča, da med 1966 in 2011, nad 2.3 billion short tons of fly ash have been produced by coal-fired utility boilers.1 Of this amount approximately 625 milijonov ton so bili koristno uporabljeni, predvsem za proizvodnjo cementa in betona. Vendar, preostalih 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, s trenutnimi stopnjami blizu 45%, Približno 40 milijon ton muhe pepela še naprej odlagajo letno. While utilization rates in Europe have been much higher than in the US, v nekaterih evropskih državah so bile shranjene tudi velike količine pepela muhe..

Nedavno, zanimanje za izterjavo tega odstranjenega materiala se je povečalo, delno zaradi povpraševanja po visokokakovostnem muhu za proizvodnjo betona in cementa v obdobju zmanjšane proizvodnje, saj se je proizvodnja električne energije na premog v Evropi in Severni Ameriki zmanjšala. Zaskrbljenost zaradi dolgoročnega vpliva takšnih odlagališč na okolje prav tako spodbuja javne gospodarske službe, da najdejo uporabo koristne uporabe za ta shranjeni pepel..

LAND FILLED ASH QUALITY AND REQUIRED BENEFICIATION

Medtem ko je lahko nekaj tega shranjenega pepela letenje primerna za koristno uporabo, kot je bilo prvotno izkopano, velika večina bo zahtevala nekaj predelave, da bo izpolnila standarde kakovosti za proizvodnjo cementa ali. 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. Vendar, 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+ let, most “in-spec‿ ash has been beneficially used, in ne kakovosten pepel, odstranjen. Tako, LOI reduction will be a requirement for utilizing the vast majority of fly ash recoverable from utility impoundments.

ZMANJŠANJE LOI S TRIBOELEKTRIČNO LOČITVIJO

While various workers have used combustion techniques and flotation processes for LOI reduction of recovered landfilled and ponded fly ash, ST opreme & Tehnologij (STET) has found that its standard processing system, dolgo uporablja za korekciacijo sveže ustvarjenega pepela muhe, 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. Ta predelani pepel je zelo podobno kot sveže ustvarjen pepel z eno presenetljivo razliko: 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

TECHNOLOGY OVERVIEW – FLY ASH CARBON SEPARATION

V separatorju ogljika STET (Slika 1), material se dovaja v tanko vrzel med dvema vzporednimi planar elektrode. Delci so triboelektrično, ki jih zaračuna interdelcev stik. Pozitivno nabiti ogljik in negativno nabiti mineralni (v sveže generiziranem pepelu, ki ni bil navlajen in sušen) privlačijo nasprotni elektrode. Delci se nato pometejo z neprekinjenim gibljivim trakom in se prenašajo v nasprotnih smereh.. Pas premakne delce, ki mejijo na vsako elektrodo proti nasprotni konci ločila. Visoka hitrost pasu omogoča tudi zelo visoke prepustne, do 36 ton na uro na enem ločevalniku. Majhna vrzel, high voltage field, tok števca, vigorous particle-particle agitation and self-cleaning action of the belt on the electrodes are the critical features of the STET separator. Z nadzorovanjem različnih procesnih parametrov, kot je hitrost pasu, točka dovoda, in hitrost krme, proces STET proizvaja nizek pepel muhe LOI pri vsebnosti ogljika, ki je manjši od 1.5 za 4.5% iz pepela krme muha v loi od 4% do več kot 25%.

Slika. 1 STET Separator

Ločilo design je relativno preprosta in kompaktna. Stroj, zasnovan za obdelavo 36 tone na uro je približno 9 m (30 Ft.) dolgo, 1.5 m (5 Ft.) Širok, in 2.75 m (9 Ft.) Visoko. Pas in pripadajoči valji so edini gibajoči se deli. Elektrode so stacionarne in sestavljene iz ustrezno trajnega materiala. The belt is made of non- conductive plastic. Poraba energije separatorja je približno 1 kilovatno uro na tono materiala, predelanega z večino moči, porabljene z dvema motoroma, ki vozita pas.

Postopek je popolnoma suh, requires no additional materials other than the fly ash and produces no waste water or air emissions. The recovered materials consist of fly ash reduced in carbon content to levels suitable for use as a pozzolanic admixture in

concrete, and a high carbon fraction useful as fuel. Uporaba obeh tokov izdelkov zagotavlja 100% rešitev za težave pri odstranjevanju pepela.

PREDELANA VREDNOST GORIVA VISOKOOKLJČNEGA PEPELA

In addition to the low carbon product for use in concrete, brand named ProAsh®, the STET separation process also recovers otherwise wasted unburned carbon in the form of carbon-rich fly ash, blagovno znamko EcoTherm™. EcoTherm™ has significant fuel value and can easily be returned to the electric power plant using the STET EcoTherm™ Return system to reduce the coal use at the plant. When EcoTherm™ is burned in the utility boiler, the energy from combustion is converted to high pressure / high temperature steam and then to electricity at the same efficiency as coal, Običajno 35%. The conversion of the recovered thermal energy to electricity in ST Equipment & Technology LLC EcoTherm™ Return system is two to three times higher than that of the competitive technology where the energy is recovered as low-grade heat in the form of hot water which is circulated to the boiler feed water system. EcoTherm™ is also used as a source of alumina in cement kilns, displacing the more expensive bauxite which is usually transported long distances. Utilizing the high carbon EcoTherm™ ash either at a power plant or a cement kiln, maximizes the energy recovery from the delivered coal, zmanjšanje potrebe po minah in prevozu dodatnega goriva v objekte in naprave, ki.

STET’s Raven Power Brandon Shores, msppa r.d. Morrow, NBP Belledune, RWEnpower Didcot, EDF Energija West Burton, and RWEnpower Aberthaw fly ash plants, all include EcoTherm™ Return systems. The essential components of the system are presented in Figure 2.

Slika. 2 EcoTherm™ Return system

STET ASH PROCESING FACILITIES

Controlled low LOI fly ash is produced with STET’s technology at twelve power stations throughout the U.S., Kanada, the U.K., Poljska, and Republic of Korea. ProAsh (v mestu ProAsh)® fly ash has been approved for use by over twenty state highway authorities, kot tudi številne druge specifikacijske agencije. ProAsh (v mestu ProAsh)® has also been certified under Canadian Standards Association and EN 450:2005 standardov kakovosti v Evropi. Obrati za predelavo pepela, ki uporabljajo tehnologijo STET, so navedeni v tabeli 1.

Tabela 1. STET Commercial Operations

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. Zaradi prepletanja materiala na odlagališčih, dodatne informacije o posebnih pogojih iz premoga ali pogojev izgorevanja.

Vzorci, ki jih prejme STET, ki jih vsebuje med 15% in 20% water as is typical for landfilled material. Vzorci so vsebovali tudi različne količine velikih >1/8 cola (~3 mm) Material. Za pripravo vzorcev za ločevanje ogljika, veliki odpadki so bili odstranjeni s presejanjem, vzorci pa so se pred korekcijo ogljika posušili in deaglomerirali.. 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.

Slika 3: Process flow sheet

Lastnosti pripravljenih vzorcev so bile v razponu muhe pepela, pridobljenega neposredno iz običajnih kotlov za uporabo. Najpomembnejše lastnosti za separatorje in proizvode so povzete v tabeli 2 skupaj z predelanim izdelkom.

LOČEVANJE OGLJIKA

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.

Tabela 4: Ash Chemistry of low LOI ash.

Razvoj moči 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. Glej tabelo 5 Spodaj.

Tabela 5: Compressive strength of mortar cubes.

Sklepi

Po ustreznem scalping velikega materiala, Sušenje, in deaglomeracija, fly pepel, ki se izliva iz komunalnih odlagališč lahko zmanjša vsebnost ogljika z uporabo komercializiranega triboelektrnega separatorja pasu STET. 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. Poleg tega, 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.

Sklicevanja

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

[2]ST internal report, Avgust 1995.

[3]Li,T.X,. Schaefer, J.L., Prepoved, H., Neathery, J.K., in Stencel, J.M. Dry Beneficiation Processing of Combustion Fly Ash, Proceedings of the DOE Conference on Unburned Carbon on Utility Fly Ash, Maja 19 20, Pittsburgh, Pa, 1998.

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

[5]Cangialosi (v mestu Cangialosi), F., Notarnicola (v mestu 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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