20 år av Triboelectrostatic malmkarakterisering av Fly Ash – Vietbuild 2015 –

STET 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 20 years….

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F. Hrach, S. Gasiorowski, H.Guicherd

ST utstyr & Teknologiene LLC (STET), 101 Hampton Avenue, Needham MA 02494 USA

CONFERENCE: Vietbuild Ho Chi Minh City-juni 2015

SØKEORD: Triboelectrostatic, Malmkarakterisering, Dry Fly Ash, Carbon Separation ABSTRACT

STET 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 utstyr & Teknologien 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. STET’s electrostatic beneficiation technology reduces the carbon content of coal fly ash, producing consistent, low carbon ash for use as a substitute for cement. Fly ash with carbon levels up to 25% have been used to produce ash with a controlled carbon level of 2 ± 0.5%. A carbon-rich product is simultaneously produced to recover the fuel value of the carbon.

Introduksjon

Den amerikanske kull aske Association (ACAA) årlige undersøkelse av produksjon og bruk av kull fly ash rapporterer at mellom 1966 og 2011, over 2.3 billion short tons of fly ash have been produced by coal-fired utility boilers.1 Of this amount, omtrent 625 million tons have been beneficially used, mest for sement- og betongproduksjon. Men, 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%, omtrent 40 million tons of fly ash continues 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. An excessive amount of unburned carbon in fly ash is the most common problem. The American Association of State Highway and Transportation Officials (AASHTO) and European Standards (NO 450 Category A) require that the amount of unburned carbon in fly ash, measured by loss on ignition (LOI) not exceed 5% by weight. Men, starting in the mid-1990s, installation of mandated NOx control equipment at coal-fired power plants increased the carbon (LOI) content of much of the previously marketable fly ash. Further requirements to reduce NOx and other power plant emissions have resulted in the contamination of fly ash with ammonia. As a consequence, while understanding the benefits of using fly ash in concrete continues to increase, the availability of suitable quality fly ash is decreasing. Processes to economically beneficiate off-quality fly ash are thus also of increasing interest to the power and concrete industries. STET has pioneered such processes for both carbon and ammonia removal from fly ash.

TECHNOLOGY OVERVIEW – FLY ASH CARBON SEPARATION

In the STET carbon separator (Figur 1), the material is fed into the thin gap between two parallel planar electrodes. The particles are triboelectrically charged by interparticle
contact. The positively charged carbon and the negatively charged mineral (in freshly generated ash that has not been wetted and dried) er tiltrukket av motsatte elektroder. The particles are then swept up by a continuous moving belt and conveyed in opposite directions. Beltet beveger partiklene ved siden av hver elektrode mot motsatte ender av separatoren. Høy beltehastighet muliggjør også svært høye gjennomstrømninger, opptil 36 tonn per time på en enkelt separator. Det lille gapet, high voltage field, countercurrent flow, vigorous particle-particle agitation and self-cleaning action of the belt on the electrodes are the critical features of the STET separator. Ved å kontrollere ulike prosessparametere, for eksempel beltehastighet, the feed point, og matehastighet, STET-prosessen produserer lav LOI-flyaske ved karboninnhold på mindre enn 1.5 til 4.5% from feed fly ashes ranging in LOI from 4% til over 25%.

Fig. 1 STET Separator
Fig. 1 STET Separator

The separator design is relatively simple and compact. En maskin designet for å behandle 36 tonn per time er ca. 9 m (30 Ft.) lang, 1.5 m (5 Ft.) Bredt, og 2.75 m (9 Ft.) Høy. Beltet og tilhørende valser er de eneste bevegelige delene. Elektrodene står stille og består av et passende holdbart materiale. The belt is made of nonconductive plastic. The separator’s power consumption is about 1 kilowattime per tonn materiale behandlet med det meste av kraften som forbrukes av to motorer som kjører beltet.

Prosessen er helt tørr, requires no additional materials other than the fly ash and produces no wastewater 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. Bruk av begge produktstrømmene gir en 100% løsning for å fly askeavhendingsproblemer.

RECOVERED FUEL VALUE OF HIGH-CARBON FLY ASH

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, branded EcoTherm™. EcoTherm (ecotherm)™ has significant fuel value and can easily be returned to the electric power plant using the STET EcoThermReturn system to reduce the coal use at the plant. When EcoThermis 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, typically 35%. The conversion of the recovered thermal energy to electricity in ST Equipment & Technology LLC EcoThermReturn 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 (ecotherm)™ is also used as a source of silica and alumina in cement kilns, displacing the more expensive raw materials, such as shale or bauxite, which are used in cement production. Utilizing the high carbon EcoThermash either at a power plant or a cement kiln, maximizes the energy recovery from the delivered coal, reducing the need to mine and transport additional fuel to the facilities.

STET’s Talen Energy Brandon Shores, SMEPA R.D. Morrow, NBP Belledune, RWEnpower Didcot, EDF Energy West Burton, and RWEnpower Aberthaw fly ash plants, all include EcoThermReturn systems. The essential components of the system are presented in Figure 2.

Fig. 2 EcoTherm (ecotherm)™ Return system
Fig. 2 EcoTherm™ Return system

STET ASH PROCESSING FACILITIES

Controlled low LOI fly ash is produced with STET’s technology at twelve power stations throughout the U.S., Canada, the U.K., Polen, og Republikken Korea. ProAsh® fly ash
has been approved for use by over twenty state highway authorities, samt mange andre spesifikasjonsbyråer. ProAsh® er også sertifisert i henhold til Canadian Standards Association og EN 450:2005 kvalitetsstandarder i Europa. Ash processing facilities using STET technology are listed in Table 1.

Tabell 1. STET Commercial Operations

Verktøyet / Power StationPlasseringenBegynnelsen av
Kommersielle
Operasjoner
Facility Details
Duke Energy – Roxboro
Station
North Carolina
USA
Sept. 19972 Skilletegn
Talen energi - Brandon
Shores Station
Maryland
USA
April 19992 Skilletegn
35,000 ton storage dome.
Ecotherm™ Return 2008
ScotAsh (Lafarge / Scottish
Power Joint Venture) -
Longannet stasjon
Scotland
STORBRITANNIA
Oktober. 20021 Skilletegn
Jacksonville Electric Authority -
St. John’s River Power Park,
FL
Florida
USA
Mai 20032 Skilletegn
Coal/Petcoke blends
Ammonia Removal
South Mississippi Electric
Power Authority R.D. Morrow
Station
Mississippi
USA
Januar. 20051 Skilletegn
Ecotherm™ Return
New Brunswick Power
Company
Belledune Station
Nye
Brunswick,
Canada
April 20051 Skilletegn
Coal/Petcoke Blends
Ecotherm™ Return
RWE npower
Didcot Station
England
STORBRITANNIA
August 20051 Skilletegn
Ecotherm™ Return
Talen Energy Brunner Island
Station
Pennsylvania
USA
Desember 20062 Skilletegn
40,000 Ton storage dome
Tampa Electric Co.
Big Bend Station
Florida
USA
April 20083 Skilletegn, dobbel pass
25,000 Ton storage dome
Ammonia Removal
RWE npower
Aberthaw Station (Lafarge
Cement UK)
Wales
STORBRITANNIA
September 20081 Skilletegn
Ammonia Removal
Ecotherm™ Return
EDF Energy West Burton
Station
(Lafarge Cement UK, Cemex)
England
STORBRITANNIA
Oktober 20081 Skilletegn
Ecotherm™ Return
ZGP (andre er i seg selv (Lafarge sement Polen /
Ciech Janikosoda JV)
PolenMars 20101 Skilletegn
Korea South-East Power
Yeongheung Units 5&6
Sør-KoreaSeptember 20141 Skilletegn
Ecotherm™ Return
Lafarge sement Polen
Warsaw
Polen20161 Skilletegn

CONCLUSIONS

Maximizing the utilization of fly ash as a cement substitute in concrete production substantially reduces the carbon dioxide emissions associated with construction activity. Men, pollution control systems implemented by the coal-fired power stations have resulted in a reduction of available fly ash meeting concrete-grade specifications. Further degradation of fly ash quality is expected due to further reductions in allowable gas emissions. In order to avoid loss of this valuable resource of material for concrete production as well as reduction of greenhouse gas emissions associated with concrete construction, processes for restoring the quality of the fly ash in an economic and environmentally viable way are needed.

The beneficiation of fly ash with STET processes further increases the supply of this important material. The STET beneficiation processes continue to be the most extensively applied methods to upgrade otherwise unusable fly ash to high-value materials for cement replacement in concrete. Eighteen SETT carbon separators are currently in place with over 100 machine-years of operation.

ProAsh® has found wide acceptance in the concrete industry as a premium fly ash requiring far less monitoring of air entrainment requirements due to less LOI variability than other ashes. Returning the high-carbon concentrate from the STET process to the boiler at a power plant allows recovery of the recovered carbon fuel value at an efficiency similar to coal. STET offers economical means to recover ash for high-value use that would otherwise be landfilled. Electrostatic carbon separation and Ecothermreturn to the boiler provide a modular solution to a utility’s fly ash needs. These processes can be implemented in phases, or as a single project.

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