Triboelectrostatic Beneficiation prateća letećeg pepela WOCA 2015

Triboelectrostatic Beneficiation of

Land Filled Fly Ash

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

ST oprema & Tehnologije LLC, 101 Hampton Avenue, Needham MA 02494 SJEDINJENE AMERIČKE DRŽAVE

CONFERENCE: 2015 World of Coal Ash – (www.worldofcoalash.org)

KLJUČNE RECI: Triboelectrostatic, Beneficiation, Letećeg pepela, Landfilled, Dried, Odvajanje, Indigo

SAŽETAK

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 oprema & 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. 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.

UVOĐENJE

Američki ugljena pepela Udruga (ACAA) godišnji pregled proizvodnje i korištenja ugljena pepela izvještava da je između 1966 i 2011, preko 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. Međutim, 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%, približno 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.

Nedavno, 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. Međutim, 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+ godine, 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, ST oprema & 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

TECHNOLOGY OVERVIEW – FLY ASH CARBON SEPARATION

U STET separatoru ugljika (Slika 1), materijal se hrani u tanki jaz između dvije paralelne planarne elektrode. Čestice su utrobno optužene od strane međučestica.. The positively charged carbon and the negatively charged mineral (in freshly generated ash that has not been wetted and dried) privlače ih suprotne elektrode.. Čestice su onda zahvatio neprekinutom pojasu kreće i prenio u suprotnim smjerovima. Pojas potezi uz svake elektrode prema suprotnim stranama separator čestica. Visoki pojas brzinom omogućuje vrlo visoku propusnost, do 36 tona na sat na jednom razdjelnika. Mali razmak, polja visokog napona, brojač protoka, snažan čestica-čestica uznemirenost i samočišćenja djelovanja remen na elektrode su kritične značajke STET razdjelnika. Kontroliranjem raznih parametara procesa, kao što je brzina pojasa, feed za izabrati, i brzina hranjenja, STET proces proizvodi niski LOI leteći pepeo pri sadržaju ugljika manjem od 1.5 da 4.5% od feed muha pepeo u rasponu u LOI od 4% na više 25%.

Smokvu. 1 STET Separator

Razdjelnik dizajn je relativno jednostavna i kompaktna. Mašina dizajnirana za obradu 36 tone na sat je približno 9 m (30 FT.) Dugo, 1.5 m (5 FT.) Široko, i 2.75 m (9 FT.) Visoko. Jedini pokretni dijelovi su pojas i povezan Valjci. Elektrode su stacionarni i sastoji se od odgovarajuće izdržljiv materijal. The belt is made of non- conductive plastic. The separator’s power consumption is about 1 Kilowatt-sat po tonu materijala obrađen sa većinom energije koju su konzumirali dva motora koja voze remen..

Proces je potpuno suh., ne zahtijeva dodatne materijale osim mušice pepeo i ne proizvodi otpadne vode ili emisije zraka. The recovered materials consist of fly ash reduced in carbon content to levels suitable for use as a pozzolanic admixture in

Beton, i visok ugljicni razlomak koristan kao gorivo. Utočište oba toka proizvoda pruža 100% rješenje za letenje problema s odlaganjem pepela.

RECOVERED FUEL VALUE OF HIGH-CARBON FLY ASH

In addition to the low carbon product for use in concrete, brend pod imenom ProAsh®, odvajanje STET obraditi i obnova inače izgubiti neizgorenu ugljik u obliku ugljik-bogat letećeg pepela, potpuno novo EcoTherm™. EcoTherm™ ima značajne goriva vrijednost i mogu lako vratiti do električne centrale pomoću STET EcoTherm™ Return system to reduce the coal use at the plant. Kada EcoTherm™ je izgorjela u korisnost kotla, energija izgaranja se pretvara u visokim tlakom / Visoka temperatura parne i onda na struju na istu učinkovitost kao ugljen, Obično 35%. The conversion of the recovered thermal energy to electricity in ST Equipment & Technology LLC EcoTherm™ Povratni sistem je dva do tri puta veći od konkurentne tehnologije gdje se energija oporavlja kao nisko-razredna toplota u obliku tople vode koja cirkulira u sistem vode za kotlovsku hranu. EcoTherm™ također se koristi kao izvor alumine u cementnim kilama, rasklapanje skupljeg boksita koji se obično prevozi na velike udaljenosti. Utilizing the high carbon EcoTherm™ pepeo ili u elektrani ili cementna kila, maksimizira energetski oporavak od isporučene ugljena, smanjenje potrebe za moje i prijevoz dodatno gorivo od sadržaja.

STET’s Raven Power Brandon Shores, IRENA SMEPA. Sutra, NBP Belledune, RWEnpower Didcot, EDF energije zapadni Burton, and RWEnpower Aberthaw fly ash plants, Svi sadrže EcoTherm™ Povratak sustavi. Bitne komponente sustava prikazani su na slici 2.

Smokvu. 2 EcoTherm™ Sisteme

STET ASH PROCESING FACILITIES

Controlled low LOI fly ash is produced with STET’s technology at twelve power stations throughout the U.S., Kanada, U.K., Poljska, and Republic of Korea. ProAsh® pepela je odobren za upotrebu preko dvadeset državnih autocesta vlasti, kao i mnoge druge agencije specifikacije. ProAsh® također certificirani pod kanadski standarda udruge i EN 450:2005 standardi kvalitete u Europi. Ash processing facilities using STET technology are listed in Table 1.

Tablica 1. STET komercijalne operacije

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% i 20% water as is typical for landfilled material. The samples also contained varying amounts of large >1/8 cm (~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.

Slika 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.

Tablica 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. Vidi stol 5 below.

Tablica 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. Dodatno, 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.

REFERENCE

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

[2]ST internal report, August 1995.

[3]Lija,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, Svibanj 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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