New and improved slagging and corrosion control techniques for biomass firing. Martti Aho IV Liekkipäivä

Transcription

1 New and improved slagging and corrosion control techniques for biomass firing IV Liekkipäivä

2 Organisation of the research project t Research organisations:vtt (Co ordinaator) Åbo Akademi University t Main funding: Tekes (Climbus) t Supporting companies: Metso Power Oy (boiler manufacturer) Kemira Oyj (chemical manufacturer) Pohjolan voima Oy (energy company) t Project duration: Kemira Chemicals Oyj Research project CORRAWAY IV Liekkipäivä 2008

3 Background of operational risks during biomass combustion 3

4 4 On furnace view. Recycled fuel Peat, coal Sawdust Forest residues = safe or protective = some risks or risky = very risky IV Liekkipäivä 2008

5 5 CASE 1. BARK/FOREST RESIDUE Heat transfer surface ALKALI CHLORIDES Cl releases corrosion RISKY COMPOUNDS Lack of protecting compounds KCl NaCl Risk description: Cl deposition which can lead to high temperature superheater corrosion BARK/FOREST RESIDUE Low ash content Contains wt% Cl but it can produce about 10 wt% Cl To critical deposit locations IV Liekkipäivä 2008

6 Presence of melt in fly ash makes it sticky. Presence of Cl in the fly ash lowers strongly start T of melting ( ref.:åbo Academi s calculations) 6

7 7 Recycled fuel with high Cl content, but usually <1 wt% Example: 40% REF in bark (Cl 0.24wt%) Can produce 25wt% Cl to deposits + High heating value! IV Liekkipäivä

8 8 Superheater tubes after high temperature Classisted corrosion IV liekkipäivä 2008

9 9 Destruction of alkali chlorides carrying Cl to the deposits Na Cl Additive or protective fuel HCl + X Protective fuel is fossil! K Cl IV liekkipäivät 2008

10 10 Additive spraying at critical position to the furnace. Advantage: S is immendiately in its right form (SO 3 ) at right place Strong and selective effect > SO 2 emissions will not be a problem 2MCl + SO 3 + H 2 O > M 2 SO HCl SO 3 direct SO 3 residue reacts with CaO etc. Na 2 SO 4 K 2 SO 4 HCl attach Cl carriers:nacl, KCl IV liekkipäivät 2008

11 11 Reagents invented and tested in the project: t Ammonium sulphate Chlorout patented by Vattenfall for comparison: t (NH 4 ) 2 SO 4 > SO NH 3 + H 2 O (thetmal destruction at 235 o C:) ( 2 functional: NH 3 reduces NO) *Al (III) and Fe (III) sulphates (Corr 1 ja 2) used earlier as water chemicals. The new innovation enlargens their application to energy production (1 functional) *Patent rights transferred from VTT to Metso Power & Kemira (2007) Al 2 (SO 4 ) 3 Al 2 O SO 3 (thermal destruction at 770 C Fe 2 (SO 4 ) 3 Fe 2 O SO 3 (thermal destruction at 440 C) t Dosage parameter used: S reagenssi / Cl 2 polttoaineessa IV Liekkipäivä 2008

12 12 Question 1 at the start: Is the molar flow or sulphur forming quantitatively SO 3 the only effecting parameter from the reagent? M x (SO 4 )y > SO 3 + Please, note: the real reactions are very complicated and there are differences for example in the thermal decomposition temperatures of the additives studied IV Liekkipäivä 2008

13 13 Question 2 at the start: How selective are the vital reactions (see red arrows) in relation to the wrong reactions consuming SO3? Additive SO3 SO 3 MOH MOH M 2 SO 4 (stable) MCl MCl CaO SO 3 2 CaCO 3 Sfuel +O2 M. HCl MCl + Cl. (unstable) HCl MCl + H 2 O MOH CaSO4 (stable) CaO O SO 2 M = K or Na IV liekkipäivä 2008

14 14 Fractionation results 40% REF 60% bark mg/kg D.S Insoluble Leached in HCl Leached in acetate Leached in H2O No HCl leaching with Cl! from PVC 0 Si Al Fe Ti Mn Ca Mg P Na K S Cl IV liekkipäivä 2008

15 15 BFB combustion tests with bark containing 40% recycled fuel on energy basis (Cl 0.24 wt%). Very corrosive fuel when burnt alone with high steam values! IV Liekkipäivä 2008

16 16 Typical temperature distibution in the 20 kw BFB 8 7 Freeboard top Residence time, [s] Deposit probe (Ts= 500ºC) Impactor sampling Chemical addition Tertiary air Secondary air 1 Bed zone T, [ºC] IV liekkipäivä 2008

17 17 dib. air Ejektor ELPI T C Cyclone VTT diluter MFC Ejektor Cooling system Cyclone DLPI Exh nitrogen Ftir & CO 2 Sampling to impactors from 20 kw BFB reactor

18 Results with and comparison of Al 2 (SO 4 ) 3 and Fe 2 (SO 4 ) 3 with two dosage levels 18

19 19 The effect of water soluble sulphur containing chemical to concentrations of HCl (blue) and other chlorines (red part of columns). Fuel 40% REF 60% bark with 0.24 wt% Cl in < 4um ash in HCl Cl, mg/nm Risky Cl S/Cl2 = 0.45 S/Cl2 = No additives Al2(SO4)3 Fe2(SO4)3 Al2(SO4)3 Fe2(SO4)3 IV liekkipäivä 2008

20 20 Cl in vapours and in fine fly ash, fuel 40% REF 60% bark 140 Cl mg/nm Dosage S/Cl2 = 0.45 Fly ash particle size range µm µm µm µm µm Dosage S/Cl2= No additives Al2(SO4)3 Fe2(SO4)3 Al2(SO4)3 Fe2(SO4)3 IV liekkipäivä 2008

21 21 Analysis of deposits in Åbo Akademi University by Tor Lauren t The deposit samples were collected from wind and lee sides and from 50 degrees up from the centre of the wind side position for SEM EDS analysis. Lee side =50 50 o from Wind side Wind side Flue gas flow

22 22 Deposition of Cl: 40% REF 60% bark S/Cl2= Cl wt% Wind 50o Lee 10 5 S/Cl2= No additives Al2(SO4)3 Fe2(SO4)3 Al2(SO4)3 Fe2(SO4)3 IV liekkipäivä 2008

23 Comparison of the new reagents to the only one existing in the markets ((NH 4 ) 2 SO 4 23

24 24 40%RDF+60%bark, molar dosage factor Sadditive/Cl2fuel is mg Cl/Nm µm µm µm µm µm 20 0 No additives (NH4)2SO4 Al2(SO4)3 Fe2(SO4)3 IV liekki päivät 2008

25 25 Cl depositon with S/Cl 2 W=Wind S= Side L = lee W S L Paino % 15 Paino % Alkutila Alkutila (NH 4 ) 2 SO 4 Al 2 (SO 4 ) 3 IV Liekki päivät 2008

26 26 Conclusions t There are many (stil unknown) other additive originated paramerets effecting to the sulphation power of alkalies than just the molaric sulphur flow: t The power of the reagents with constant sulphur mass flow in the reaction: 2MCl + SO 3 + H 2 O > M 2 SO HCl was: t Al 2 (SO 4 ) 3 > Fe 2 (SO 4 ) 3 >> (NH 4 ) 2 SO 4 This order is directly proportional to the temperature needed to thermal destruction. Probably ammoniun sulphate decomposes faster than the other sulphates which then produce fresh SO 3 at longer furnace zone. Complete decomposion to SO 3 at short furnace zone leading to high local SO 3 concentr. may strengthen other SO 3 consuming reactions than sulphation and reduce alkali sulphation selectivity to SO 3 t With the new reagents, sulphation of alkali chlorides dominates strongly over the other SO 3 consuming reactions which is a significant advantage: chemicals can be used with low dosages with small or insignificant increase of SO 2 emissions IV Liekki päivät 2008