Triboelectrostatic bogatenje zemljišč napolnjena in Ponded pepel

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Triboelectrostatic Beneficiation of

Land Filled and Ponded Fly Ash

Z Lewis Baker, Abhishek Gupta, Stephen Gasiorowski, in Frank Hrach

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+ milijard ton najdemo predvsem na odlagališčih ali napolnjena ribniki zasega. 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 and deagglomeration is a necessary requirement for use in concrete since concrete producers will want to continue the practice of batching fly ash as a dry, fini prašek. 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, večina "in-spec" pepel je bil koristno uporabljen, 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

Medtem ko so drugi raziskovalci uporabljajo tehnike zgorevanja in flotacijskih procesov za zmanjšanje LOI predelanih odloženih in ribnikih muhi pepel, ST opreme & Tehnologij (STET) je ugotovila, da je njen edinstven triboelectrostatični sistem ločevanja pasu, dolgo uporablja za korekciacijo sveže ustvarjenega pepela muhe, je učinkovit tudi na predelan pepel po ustreznem sušenju in deaglomeracijo.

STET raziskovalci so testirali triboelectrostatično ločitev obnašanje posušenega na odlagališčih pepela iz več odlagališč pepela v Ameriki in Evropi. 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 The polarity of the STET triboelectrostatic separator can easily be adjusted to allow rejection of negatively charged carbon from dried landfilled fly ash sources. No special modifications to the separator design or controls are necessary to accommodate this phenomena.

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

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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 processing dried, na odlagališčih muhi pepel

Ločilo design je relativno preprosta in kompaktna. Stroj, zasnovan za obdelavo 40 ton na uro je približno 30 ft. (9 m.) dolgo, 5 ft. (1.5 m.) Širok, in 9 Ft., m (2.75 m.) 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. Predelani materiali so sestavljeni iz muhi pepela, zmanjšanega vsebnosti ogljika na ravni, primerne za uporabo kot pozzolanska priseska v betonu, and a high carbon fraction useful as fuel. Uporaba obeh tokov izdelkov zagotavlja 100% rešitev za težave pri odstranjevanju pepela.

PROASH® RECOVERED FROM LAND FILLS

Štirje viri pepela so bili pridobljeni z odlagališč: sample A from a power plant located in the United Kingdom and samples B, C, in D iz Združenih držav Amerike. Vsi ti vzorci so bili sestavljeni iz pepela iz izgorevanja bituminoznega premoga z velikimi kotli utility. 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 27% 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.. Several methods for drying/deagglomeration have been evaluated at the pilot-scale in order to optimize the overall process. STET has selected an industrially proven, feed processing system that offers simultaneous drying and deagglomeration necessary for effective electrostatic separation. A general process flow sheet is presented in Figure 2.

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Slika 2: Process Flow Diagram

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 products from all four landfill fly ash sources. The reverse charging of the carbon as discussed above did not degrade the separation in any way as compared to processing fresh ash.

The properties of the low LOI fly ash recovered using the STET process for both freshly collected ash from the boiler and ash recovered from the landfill is summarized in Table 1. The results show that the product quality for ProAsh® produced from landfilled material is equivalent to product produced from fresh fly ash sources.

Tabela 1: Properties of feed and recovered ProAsh®.

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USPEŠNOST V KONKRETNIH

The properties of the ProAsh® generated from the reclaimed landfill material were compared to that of ProAsh® produced from fresh fly ash generated by the utility boilers from the same location. The processed reclaimed ash meets all the specifications of ASTM C618 and AASHTO M250 standards. The following table summarizes the chemistry for samples from two of the sources showing the insignificant difference between the fresh and reclaimed material.

Tabela 2: Ash Chemistry of low LOI ash.

Razvoj moči 20% substitution of the low LOI fly ash in a mortar containing 600 lb cementitious/ yd3 (Glej tabelo 3 Spodaj) showed the ProAsh® product derived from landfilled ash yielded mortars with strength comparable to mortars produced using ProAsh® from fresh fly ash produced at the same location. The end product of the beneficiated reclaimed ash would support high end uses in the concrete industry consistent with the highly valuable position ProAsh® enjoys in the markets it currently serves.

Tabela 3: Compressive strength of mortar cylinders.

PROCESNA EKONOMIJA

The availability of low cost natural gas in the USA greatly enhances the economics of drying processes, vključno s sušenjem namočenega pepela muhe z odlagališč. Tabela 4 summarizes the fuel costs for operations in the USA for 15% in 20% vsebina vlage. Tipične neučinkovitosti sušenja so vključene v izračunane vrednosti. Stroški temeljijo na masi materiala po sušenju. Dodatni stroški sušenja pepela za triboelectrostatično ločevanje STET so relativno nizki.

Tabela 4: Drying costs on basis of dried mass.

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Tudi z dodatkom stroškov sušenja krme, the STET separation process offers a low cost, industrially proven, process for LOI reduction of landfilled fly ash. The STET process for reclaimed fly ash is one-third to one-half of the capital cost compared to combustion based systems. The STET process for reclaimed fly ash also has significantly lower emissions to the environment compared to combustion or flotation based systems. Since the only additional air emission source to the standard STET process installation is a natural gas-fired dryer, permitting would be relatively simple.

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 Talen Energy Brandon Shores, msppa r.d. Morrow, NBP Belledune, RWEnpower Didcot, EDF Energija West Burton, RWEnpower Aberthaw, and the Korea South-East Power fly ash plants all include EcoTherm™ Return systems.

OBRATI ZA PREDELAVO PEPELA STET

STET’s separation process has been used commercial since 1995 za muharjenje pepela in je ustvarila več kot 20 million tons of high quality fly ash for concrete production. Controlled low LOI fly ProAsh®, is currently produced with STET’s technology at eleven 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 5.

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Tabela 5. Fly Ash Processing facilities using STET separation technology

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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. Kakovost pepela letenje izdelka, ProAsh (v mestu ProAsh)® using the STET system on reclaimed landfill material is equivalent to ProAsh® produced from fresh feed fly ash. The ProAsh® product is very well suited and proven in concrete production. 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. The STET separation process with feed pre-processing equipment for drying and deagglomerating landfilled fly ash is an attractive option for ash beneficiation with significantly lower cost and lower emissions compared to other combustion and flotation based systems.

Sklicevanja

[1]American Coal Ash Coal Combustion products and Use Statistics: http://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.

AUTHORS

Lewis Baker je evropski vodja tehnične podpore za opremo ST & Tehnologija (STET) s sedežem v Združenem kraljestvu

Abhishek Gupta is a Process Engineer based at the Separation Technologies pilot plant and lab facility, STET Technical Center, 101 Hampton Ave, Needham MA 02494 +1-781-972-2300

Dr. Stephen Gasiorowski, Ph.D. is a Senior Research Scientist for ST Equipment & Tehnologija (STET) based in the New Hampshire.

Frank Hrach is Vice President of Process Engineering based at the Separation Technologies pilot plant and lab facility, STET Technical Center, 101 Hampton Ave, Needham MA 02494 +1-781-972-2300