Characteristics of Solid waste Residues Gardanne Coal Power Plant Geochemistry, Petrography, Mineralogy

Transcription

1 Characteristics of Solid waste Residues Gardanne Coal Power Plant Geochemistry, Petrography, Mineralogy Naze - Nancy Masalehdani & Jean-Luc Potdevin Naze-Nancy.Masalehdani@univ-lille1.fr

2 Introduction Provence-Gardanne Thermal Power Plant Situated in: Gardanne - Meyreuil Owned and operated: by SNET Exploit two Chimney-Units: T4 &T5 o T4: CFBC, 268 MWe, known to combust high Sulphur, low rank coal o T5: 600 MWe, combust pulverized coal Total capacity: 868 MWe Types of Fuel: o T4: Petroleum coke (Pet-coke) & Imported coal (e.g.s- Africa ) o T5: Imported coal Sorbent (SB): Limeston to trap the acidic SO 2 before the atmospheric emission Temperature of combustion: T4 850 C, T C Residues: o Fly Ash (FA) resulting from dust filtration of the flue gas o Bottom Ash (BA) extracting from the bottom of the boiler

3 Dumping waste location: «Terril Bramefan» Area: 76ha Waste heap Stockage of Ash Source:

4 Objectives Principal: Investigate characteristics of Solid waste - Residues Petrology, Mineralogy & Chemical compositions Divers: Chemical composition of Pet-Coke Methodes X-Ray Diffraction (XRD) Optical microscope (OM) Scanning Electron Microscope -energy-dispersive spectroscopy (SEM-EDS) Electron Probe Micro Analysis-wavelength dispersion spectrometry(empa-wds) Raman spectroscopy (RS) Chemical analysis (ICP-FIMS-INAA)

5 Results Combustion by-products from T4CFBC and T5 Unit T4 Unit T5 Bottom ash a coarse, granular, incombustible by-product collected from the bottom of boiler. Fly ash, fine material transported from the combustion chamber by exhaust gases (i.e. dust filtration of the flue gas). A B C D A: S-African Coal B: Colombian Coal C: Pet-Coke D: Limestone

6 Imported Coal: S-African Coal (example) Mineral Matter: South African coals have relatively high amount of clay minerals (illite and kaolinite), quartz, sulphides, carbonates in the form of dolomite and siderite as the minor minerals. Proximate analysis

7 Components of Pet-Coke: Gardanne Thermal Power Plant SEM-SE SEM-EDS S: 19,33 % C: 80,67 % P E T C O K E Is a solid by-product of heavy oil refining process Has high heat (carbon-fuel) & low ash content Contains relatively high sulphur ± trace metals Is cheaper than coal Should be co-fired with coal in coal-fired plants

8 Chemical Composition: Pet-Coke, Gardanne Thermal Power Plant Major elements (wt%) SiO 2 Al 2 O 3 CaO Na 2 O K 2 O Fe 2 O 3 MgO MnO P 2 O 5 TiO 2 N C S H LOI Trace elements (ppm) As Ba Be Bi Cd Ce Co Cr Cs Cu Dy Er Eu Ga Gd ID ID ID ID Ge Hf Hg Ho In La Lu Mo Nb Nd Ni Pb Pr Rb Sb ID Se Sm Sn Sr Ta Tb Th Tm U V W Y Yb Zn Zr ID 7.54

9 Identified mineral phases in Fly and Bottom Ashes Minerals Anhydrite CaSO 4 Lime CaO Calcite CaCO 3 Dolomite MgCa(CO 3 ) 2 Hematite Fe 2 O 3 Maghemite Fe 2 O 3 Magnetite Fe 3 O 4 Quartz SiO 2 Tridymite SiO 2 Mullite Al 6 Si 2 O 13 Anorthite CaAl 2 Si 2 O 8 Barite BaSO 4 Brookite TiO 2 Anatase TiO 2 Al-Si-Oxide Ca-Al-Si-Oxide Compounds Al-P-Si-Ba-Ca Si-Na-Ca-Mg XRD RM OM SEM-EDS EPMA-WDS FA4 BA4 FA5 BA5 Methods Samples & Units Glass

10 Characteristics of Solid Residues:Sorbent «LM T4» OM-CPL XRD Patterns Calcite (CaCO 3 ) Quartz (SiO 2 ) Major elements (wt%) SiO 2 Al 2 O 3 CaO Na 2 O K 2 O Fe 2 O 3 MgO MnO P 2 O 5 TiO 2 N C S H LOI ND ND Trace elements (ppm) As Ba Ce Co Cr Cs Dy Er Eu Ga Gd Hf Hg Ho La Lu Mo Nb Nd pb Pr Rb Se Sm Sr Ta Tb Th Tm U V Y Yb Zr

11 Characteristics of Solid Residues: Fly Ash «T4» Ba H L Q Q AlSi-oxide AlSi-oxide Lime > Anhydrite L An L H Al- P-Si-Ba-Ca-compound XRD Patterns: Anhydrite, Lime, Quartz, Hematite

12 Characteristics of Solid Residues: Bottom Ash«T4» Bottom Ash from unit T4 has relatively homogenous mineralisation. Concentration of Anhydrite is being higher than Lime. Mineral zoning occurs between Anhydrite & Lime as observed in Fly ash. Amorphous AlSi-Oxide (? metakaolinite) occurs as small isolated phase or within Anhydrite -Lime grains. Anhydrite > Lime L Q Al-Ca-Si-Oxide L A Si-Na-Ca-Mg compound Al-Si-oxide L

13 ICPS-MS Analysis: Residues from «T4» Wt % SiO 2 Al 2 O 3 CaO Na 2 O K 2 O Fe 2 O 3 MgO MnO P 2 O 5 TiO 2 N C S H LOI FA BA ND ppm As Ba Be Bi Cd Ce Co Cr Cs Cu Dy Er Eu Ga FA BA ppm Gd Ge Hf Hg Ho In La Lu Mo Nb Nd Ni Pb FA BA ppm Pr Rb Sb Se Sm Sn Sr Ta Tb Th Tm U V W FA BA FA: Fly Ash BA: Bottom Ash ppm Y Yb Zn Zr FA BA

14 Characteristics of Solid Residues: Fly Ash «T5» Spherical texture, Fly Ash from Unit T5 contains high temperature T 1000 C mineral phases, more Si-bearing minerals and Iron oxides compared to T4 Fly Ash. Quartz and Tridymite (both SiO 2 ) occur together. Mineral Mullite Al 6 Si 2 O 13 was also identified. Lesser amounts of Lime and Anhydrite were observed. Q Mh L Mh AlSi-oxide

15 Characteristics of Solid Residues: Bottom Ash «T5» OM-CPL SEM-BSE SEM-EDS Microphotographs showing hoste Magnetite (Fe 3 O 4 ) crystallised in glass matrix. Quenched texture indicates rapid crystallisation from melt. Glass composition is: Al-Si-Na-silicate.

16 ICPS-MS Analysis: Residues from T5 Wt % SiO 2 Al 2 O 3 CaO Na 2 O K 2 O Fe 2 O 3 MgO MnO P 2 O 5 TiO 2 N C S H LOI FA ND BA , ppm As Ba Be Bi Cd Ce Co Cr Cs Cu Dy Er Eu Ga FA BA ppm Gd Ge Hf Hg Ho In La Lu Mo Nb Nd Ni Pb FA BA ID ppm Pr Rb Sb Se Sm Sn Sr Ta Tb Th Tm U V W FA BA ppm Y Yb Zn Zr FA: Fly Ash BA: Bottom Ash FA BA

17 Process of mineral formation during Ashing (Kaolinite) Al 2 Si 2 O 5 (OH) % Al 2 O % SiO % H 2 O C Loss of H 2 O Al 2 Si 2 O 5 + H 2 O C Dehydroxylated Endothermic process Metakaolinite % Al 2 O % SiO 2 * AlSi-Oxide found in Flay Ash and Bottom Ash from Unit T4 is an amorphous phase i.e. metakaolinite which was not decomposed into Al-Si-spinel because the combustion temperature remained T 850 C. EPMA - Result: Al 2 O %, SiO %, with 1.34% K 2 O, 0.54% CaO, 3.19%TiO 2 as impurities. ** Al-Ca-Si-Oxide found in Flay Ash and Bottom Ash from Unit T4 is an amorphous phase. A reaction of decomposed clays with lime (CaO) and partly quartz (SiO 2 ) to form Al-Si-Oxide (? pre-formation of Gehlenite) at C. EPMA - Result: Al 2 O %, SiO %,CaO 28.86%, with 1.98% FeO and 0.93% TiO 2 as impurities. *** Al-P-Si-Ba-Ca-Compound in Fly Ashes (T4 & T5) and Bottom Ash (T4) could be a mixed amorphous phase (Apatite + Lime + Al-Silicate ± Barite)

18 Ternary diagram chemical composition (wt%): Fly and Bottom Ashes T4 Fly Ash: Ca >Al >Si T4 Bottom Ash: Ca >Si >Al T5 Fly Ash: Si > Al > Ca T5 Bottom Ash: Si > Al > Ca Fly & Bottom Ashes from T4: produced from burning bituminous coals & Pet-Coke have Sulfo-Calcic compositions, contain lime (CaO) and Anhydrite (CaSO 4 ) Fly & Bottom Ashes from T5: produced from burning bituminous coals have Silico-Aluminous compositions, contain higher concentration of Al-sioxides

19 Concentration of Sulphur,Carbon & Iron in Residues Wt % S C Fe 2 Unit T4: Unit T5: 0 T4 FA T5 FA T4 BA T5 BA Residues Higher sulphur concentration in residues confirmes the presence of Anhydrite (CaSO 4 ) * Higher iron concentration in residues confirmes Magnetite (Fe 3 O 4 ), Hematite and/or Maghemite (Fe 2 O 3 ) as principal Fe-Oxides * Higher concentration of Carbon in bottom ash is related to presence of Calcite (CaCO 3 ), and probably to ± char (i.e.unburnt carbon)

20 ppb ppm Concentration of Trace elements in Residues ppm ICP-FIMS-INAA Analysis As Cu Cr Ni Sr V Zn Pb Elements T4 FA T5 FA T4 BA T5 BA CP Hg Se T4 FA T5 FA T4 BA T5 BA CP LM 0 T4FA T5FA T4BA T5BA CP LM

21 The Pet-Coke-Coal residues (Ashes) produced by Provence-Gardanne Thermal Power Plant are: enriched in Vanadium and Nickel V & Ni compounds are not toxic as Hg, Cd, As, Pb or other «heavy metals». Most health problems related to Nickel deal with skin & respiratory exposure (Nielsen,1977, p.134). The most common health problems associated with Vanadium (if present as V 2 O 5 ) exposure result from inhalation e.g. coughing, bronchitis, eyes, nose & throat irritation (Waters, 1977, p.148, pp ).

22 Conclusions Thank you for your attention The ash chemical composition for both Fly ash and Bottom ash from the particulate control device at Provence-Gardanne Thermal Power Plant directly arises from the fuel characteristics & sorbent composition They result: 1. from the chemical composition of the inorganic fraction of the fuel, 2. from the fuel sulphur content and the SO 2 removal rate.