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Amerikansk kul aske Association (AOG) årlig undersøgelse af produktion og anvendelse af kul flyveaske rapporter der mellem 1966 og 2011, over 2.3 billion short tons of fly ash were produced by coal-fired utility boilers. Of this amount, ca 625 millioner tons har været gavnlig anvendt, mest til produktion af cement og beton. Men, de resterende 1.7+ milliarder tons findes primært på lossepladser eller fyldt ponded impoundments.
Triboelectrostatic forberednings af deponeret og Ponded flyveaske
Af Lewis Baker,Abhishek Gupta, Stephen Gasiorowski, og Frank Hrach
Amerikansk kul aske Association (AOG) årlig undersøgelse af produktion og anvendelse af kul flyveaske rapporter der mellem 1966 og 2011, over 2.3 billion short tons of fly ash were produced by coal-fired utility boilers.1 Of this amount, ca 625 millioner tons har været gavnlig anvendt, mest til produktion af cement og beton. Men, de resterende 1.7+ milliarder tons findes primært på lossepladser eller fyldt ponded impoundments. While use rates for freshly generated fly ash have increased considerably over recent years, med nuværende priser tæt 45%, ca 40 millioner tons flyveaske fortsat afsættes hvert år. While use rates in Europe have been much higher than in the United States, store mængder flyveaske har også været gemt i lossepladser og impoundments i nogle europæiske lande
Seneste, interessen for at inddrive dette bortskaffede materiale er steget, delvis på grund af efterspørgslen efter flyveaske af høj kvalitet til beton- og cementproduktion i en periode med reduceret produktion, da kulfyret elproduktion er faldet i Europa og Nordamerika. Bekymringer om de langsigtede miljøpåvirkninger af sådanne lossepladser er også anledning forsyningsselskaber til at finde gavnlige anvendelse applikationer til denne lagrede aske.
Mens noget af denne lagrede flyveaske kan være egnet til gavnlig brug som oprindeligt udgravet, langt de fleste vil kræve en vis forarbejdning for at opfylde kvalitetsstandarder for cement- eller betonproduktion. Because 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 because concrete producers will want to continue the practice of batching fly ash as a dry, fint pulver. Men, 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 use has increased in the last 20+ år, mest "in-spec" aske er blevet anvendt med fordel, og den off-kvalitet aske bortskaffes. Således, LOI reduction will be a requirement for using the vast majority of fly ash recoverable from utility impoundments.
Mens andre forskere har brugt forbrændingsteknikker og flotation processer for LOI reduktion af genvundet deponeret og ponded flyve aske, ST udstyr & Teknologier (STET) has found that its unique triboelectrostatic belt separation system, længe brugt til beneficiation af friskgenereret flueaske, er også effektiv på genvundet aske efter passende tørring og deagglomeration.
STET forskere har testet den triboelektrostatiske adskillelse adfærd tørret deponeret aske fra flere flyve aske lossepladser i Amerika og Europa. Denne genvundne aske adskilt meget på samme måde som friskgenereret aske med en overraskende forskel: 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 phenomenon.3-5 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 his phenomena
I STET carbon separator (Figen. 1), materialet føres ind i tynde hullet mellem to parallelle plane elektroder. Partiklerne debiteres triboelectrically ved interparticle kontakt. De positivt ladede kulstof og negativt ladede mineralet (i frisk genererede aske, der ikke er blevet chloroformvædet og tørret) er tiltrukket af overfor elektroder. Partiklerne er så fejet op af en kontinuerlig bevægelige bælte og formidles i modsatte retninger. Bæltet flytter de støder op til hver elektrode mod modsatte ender af separatoren partikler. The high belt speed also enables very high throughputs up to 36 tons i timen på en enkelt separator. Det lille hul, high-voltage field, counter—current flow, vigorous particle-particle agitation, and self-cleaning action of the belt on the electrodes are the critical features of the STET separator. Ved at kontrollere forskellige parametre, såsom bælte hastighed, feed punkt, og foder sats, STET proces producerer lav LOI flyveaske på CO2 indholdet af mindre end 1.5 til 4.5% fra foder flyve asken spænder i LOI fra 4% til over 25%.
Separator design er relativt enkel og kompakt. En maskine designet til at behandle 40 tons i timen er ca. 30 Ft (9 m) lang, 5 Ft (1.5 m) bred, og 9 Ft (2.75 m) Høj. Bælte og tilknyttede rullerne er de eneste bevægelige dele. Elektroderne er stationære og består af en passende holdbart materiale. Bæltet er fremstillet af ledende plast. Den separator strømforbrug er om 1 kilowatt-time pr. ton materiale, der forarbejdes med det meste af den effekt, der forbruges af to motorer, der driver bæltet.
Processen er helt tør, requires no additional materials other than the fly ash, and produces no waste water or air emissions. De nyttiggjorte materialer består af flyveaske reduceret i kulstofindhold til niveauer egnet til brug som en pozzolanic blanding i beton, and a high-carbon fraction useful as fuel. Use of both product streams provides a 100% løsning på problemer, flyveaske bortskaffelse.
Der blev indhentet fire askekilder fra lossepladser: Sample A from a power plant located in the United Kingdom and Samples B, C, og D fra USA. Alle disse prøver bestod af aske fra forbrænding af bituminøs kul af store forsyningskedler. På grund af sammenblandingen af materiale på lossepladserne, der foreligger ingen yderligere oplysninger om specifikke kulkilde- eller forbrændingsforhold.
Prøverne, som blev modtaget af STET, indeholdt mellem 15 og 27% Vand, as is typical for landfilled material. Prøverne indeholdt også varierende mængder af store >1/8 i. (3 mm) Materiale. For at forberede prøverne til kulstofadskillelse, det store affald blev fjernet ved screening, og prøverne tørrede og deagglomererede før. Several methods for drying/deagglomeration have been evaluated at the pilot scale 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 flowchart is presented in Fig. 2.
The properties of the prepared samples were well within the range of flyveaske obtained directly from normal utility boilers. De mest relevante egenskaber for både separatorfeeds og produkter er opsummeret i tabel 2, sammen med genvundet produkt.
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 previously 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.
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 M 250 standards. Tabel 2 summarizes the chemistry for samples from two of the sources showing the insignificant difference between the fresh and reclaimed material.
Styrkeudvikling af en 20% substitution of the low-LOI fly ash in a mortar containing 600 lb/yd3 cementitious material (see Table 3) 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.
The availability of low-cost natural gas in the United States greatly enhances the economics of drying processes, herunder tørring af vådflueaske fra lossepladser. Tabel 4 summarizes the fuel costs for operations in the United States for 15% og 20% fugtindhold. Typiske ineffektiviteter ved tørring indgår i de beregnede værdier. Omkostningerne er baseret på massen af materiale efter tørring. De ekstraomkostninger til tørring af flueaske til STET-triboelektrostatisk separationsbehandling er relativt lave.
Selv med tilsætning af fodertørringsomkostninger, 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. Because the only additional air emission source to the standard STET process installation is a natural gas-fired dryer, permitting it would be relatively simple.
| Feed sample to separator | LOI, % | ProAsh LOI, % | ProAsh fineness, % +325 mesh |
ProAsh mass yield, % |
|---|---|---|---|---|
| Frisk A | 10.2 | 3.6 | 23 | 84 |
| Landfilled A | 11.1 | 3.6 | 20 | 80 |
| Frisk B | 5.3 | 2.0 | 13 | 86 |
| Deponeret B | 7.1 | 2.0 | 15 | 65 |
| Frisk C | 4.7 | 2.6 | 16 | 82 |
| Deponeret C | 5.7 | 2.5 | 23 | 72 |
| Landfilled D | 10.8 | 3.0 | 25 | 80 |
| Material source | SiO2 | Al2O3 | Fe2O3 delte et link. | Cao | MgO | K2O | Na2O | kr. |
|---|---|---|---|---|---|---|---|---|
| Frisk B | 51.60 | 24.70 | 9.9 | 2.22 | 0.85 | 2.19 | 0.28 | 0.09 |
| Deponeret B | 50.40 | 25.00 | 9.3 | 3.04 | 0.85 | 2.41 | 0.21 | 0.11 |
| Frisk C | 47.7 | 23.4 | 10.8 | 5.6 | 1.0 | 1.9 | 1.1 | 0.03 |
| Deponeret C | 48.5 | 26.5 | 11.5 | 1.8 | 0.86 | 2.39 | 1.18 | 0.02 |
| 7-day compressive strength, % af frisk aske kontrol | 28-day compressive strength, % af frisk aske kontrol | |
|---|---|---|
| Frisk B | 100 | 100 |
| Deponeret B | 107 | 113 |
| Frisk C | 100 | 100 |
| Deponeret C | 97 | 99 |
| Vandindhold, % | Heat requirement KWhr/T wet basis | Drying cost/T dry basis (natural gas cost $3.45/mmBtu) |
| 15 | 165 | $ 2.28 |
| 20 | 217 | $ 3.19 |
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, mærkevare 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, typisk 35%. The conversion of the recovered thermal energy to electricity in the STET 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. Using the high-carbon EcoTherm ash either at a power plant or a cement kiln maximizes the energy recovery from the delivered coal, at reducere behovet for at udvinde og transporterer ekstra brændstof til faciliteter.
STET's Talen energi Brandon kyster, SMEPA RD. Morrow, GITTE Belledune, RWEnpower Didcot, EUF energi West Burton, RWEnpower Aberthaw, and the Korea South-East Power fly ash plants all include EcoTherm Return systems.
STET’s separation process has been used commercially since 1995 til flyveaske beneficiation og har genereret over 20 millioner tons af høj kvalitet flyveaske til beton produktion. Controlled low-LOI ProAsh is currently produced with STET’s technology at 12 kraftværker i hele USA, Canada, Det Forenede Kongerige, Polen, og Republikken Korea. ProAshfly ash has been approved for use by more than 20 State highway myndigheder, samt mange andre specifikation agenturer. ProAsh has also been certified under the Canadian Standards Association and EN 450:2005 kvalitetsstandarder i Europa. Aske behandlingsanlæg ved hjælp af STET teknologi er angivet i tabel 5.
Efter passende skalpering af stort materiale, Tørring, og deagglomeration, flyve aske inddrives fra utility anlæg lossepladser kan reduceres i kulstofindhold ved hjælp af kommercialiseret STET triboelektrisk bælte separator. Kvaliteten af flueaskeproduktet, 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. Desuden, power plants that need to remove ash from landfills to meet changing environmental regulations will be able to use the process to alter a waste product liability into a valuable raw material for concrete producers. The STET separation process with feed preprocessing 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. ❖
1. American Coal Ash Coal Combustion Products and Use Statistics, http://www.acaausa.org/Publications/Production-Use-Reports.
2. ST Internal Report, August. 1995.
3. Li, T. X.; Schaefer, JØRGENSEN. L.; Forbud, H.; Neathery, JØRGENSEN. K.; og Stencel, JØRGENSEN. M., “Dry Beneficiation Processing of Combustion Fly Ash,” Proceedings of the DOE Conference on Unburned Carbon on Utility Fly Ash, Pittsburgh, Pa, Maj 19-20, 1998.
4. Baltrus, JØRGENSEN. P.; Diehl, JØRGENSEN. R.; Soong, Y.; and Sands, W., “Triboelectrostatic Separation of Fly Ash and Charge Reversal,” Fuel, V. 81, 2002, PP. 757-762.
5. Cangialosi, F.; Notarnicola, M.; Liberti, L.; og Stencel, J., “The Role of Weathering on Fly Ash Charge Distribution during Triboelectrostatic Beneficiation,” Journal of Hazardous Materials, V. 164, 2009, PP. 683-688.
Lewis Baker er European Technical Support Manager for ST Equipment & Teknologi (STET) med hjemsted i Det Forenede Kongerige
Abhishek Gupta is a Process Engineer based at the STET pilot plant and lab facility in Needham, MA.
Stephen Gasiorowski is a Senior Research Scientist for ST Equipment & Teknologi (STET) based in New Hampshire.
Frank Hrach is Vice President of Process Engineering based at the STET pilot plant and lab facility in Needham, MA.
| Utility and power station | Beliggenhed | Påbegyndelse af kommercielle aktiviteter | Oplysninger om facilitet |
|---|---|---|---|
| Duke Energy—Roxboro Station | North Carolina | Sept. 1997 | 2 separators |
| Talen Energy—Brandon Shores Station | Maryland | Apr. 1999 | 2 separators 35,000 ton storage dome Ecotherm Return 2008 |
| ScotAsh (Lafarge / Scottish Power Joint Venture)—Longannet Station | Skotland, UK | Okt. 2002 | 1 separator |
| Jacksonville Electric Authority— St. John's River Power Park, FL | Florida | Maj 2003 | 2 separators Coal/petcoke blends Ammonia removal |
| South Mississippi Electric Power Authority R.D. Morrow Station | Mississippi | Jan. 2005 | 1 separator Ecotherm return |
| New Brunswick Power Company Belledune Station | Ny Brunswick, Canada | Apr. 2005 | 1 separator Coal/petcoke blends Ecotherm return |
| RWE npower Didcot Station | England, U | August. 2005 | 1 separator Ecotherm return |
| Talen Energy Brunner Island Station | Pennsylvania | Dec. 2006 | 2 separators 40,000 ton opbevaring dome |
| Tampa Electric Co. Big Bend Station | Florida | Apr. 2008 | 3 separators, dobbelt pass 25,000 ton storage dome Ammonia removal |
| RWE npower Aberthaw Station (Lafarge Cement UK) | Wales, UK | Sept. 2008 | 1 separator Ammonia removal Ecotherm return |
| EDF Energy West Burton Station (Lafarge Cement UK, Cemex) | England, UK | Okt. 2008 | 1 separator Ecotherm return |
| ZGP (Lafarge Cement Polen / Ciech Janikosoda JV) | Polen | Mar. 2010 | 1 separato |
| Korea South-East Power Yeongheung Enheder 5&6 | Sydkorea | Sept. 2014 | 1 separator Ecotherm return |
| PGNiG Termika-Siekierki | Polen | Planlagt 2016 | 1 separator Ecotherm return |
| To Be Announced | Polen | Planlagt 2016 | 1 separator Ecotherm return |
