Recovery Boiler Fouling 101

Transcription

1 The Significance of Char Bed-Generated Particulate on Recovery Boiler Fouling Relative to Other Sources of Combustion Aerosols Chris Verrill Steve Lien May 15, 2003 Recovery Boiler Fouling 101 Black liquor solids are about 50% inorganic salts Most salts exit with smelt 10-15% of salts as carryover and fume Source of boiler fouling from Adams et al, Kraft Recovery Boilers, p. 252

2 Na Mass Loss, % Sodium Loss During BL Pyrolysis (2-mm captive drops) 600 C 750 C 900 C Exposure Time, s Data from Verrill et al., JPPS 20:J354 (1994) Model from Verrill & Wessel Tappi J. 81(9): 139 (1998) Mechanisms of Aerosol Formation from Verrill, B&W 1996

3 Potential Sources of ISP in Recovery Boiler Spray combustion Char bed burning Black Liquor Drops Wall Deposits Na K K Air Na Na Char Bed Smelt from Wessel, B&W 1996 IPST Char Bed Studies ca % 12% Particulate (% of initial char) 10% 8% 6% 4% 2% 0% Bed Temperature (C) Total Fume ISP data from Steve Lien files and Kochesfahani et al, 1998 ICRC Proc., p

4 Results of Early Char Bed Work Kochesfahani s 1998 results suggested that char bed the major source of combustion aerosols Fume and ISP amounts based on assumed collection efficiencies in series of wet impingers Positive identification of µm particles on cooled deposition probe New reactor design needed to collect larger particulate New IPST Char Bed Studies Reactor, built in 2001 by Steve Lien, allows direct, physical capture of both fume and ISP: fume filter gas cooler hot cyclone char bed reactor impinger isolation valve

5 IPST Char Bed Reactor Twenty two char bed experiments have been performed jet and diffuser nozzles 3 different liquors no obvious influence of nozzle or liquor Char Bed Burning Rates Char Bed Temperature (C) Burning Rates From CO +CO 2 x 10 3 (mol C/sec) New Data Old Data Burning rates show good agreement with previous Kochesfahani and Lien measurements, despite different flow geometries

6 15% Particulate from Char Bed Burning - New Data Dry Collection Methods Particulates (% of initial char) 12% 9% 6% 3% Filter (rate) Cyclone 0% Bed Temperature (C) Measured ISP concentrations are low compared to Kochesfahani, but particle deposition is significant in sampling system Hot Cyclone and Gas Cooler

7 10% Particulate from Char Bed Burning - New Data Wet Collection Methods Particulates (% of initial char) 8% 6% 4% 2% Filter + Impinger Cyclone + Pipe 0% Bed Temperature (C) Adding material collected in exit piping and hot cyclone/gas cooler to cyclone catch substantially increases estimate of ISP. Impinger catch added to dry filter for estimate of fume. Total Particulates - New (Wet) vs Old Data 14% 12% Total Particulate (% of initial char) 10% 8% 6% 4% New Data Old Data 2% 0% Bed Temperature (C) Total measured particulates also shows good agreement with previous Kochesfahani and Lien measurements, despite different analysis methods

8 Summary of Char Bed Experiments Amount of Particulate (w/ wet collection) Total particulate ranged from 1.1% to 12.9% ISP ranged from 0.2% to 5.7%; avg. of 2.2%. Versus earlier studies Total 1.5% to 12.8% of the initial char mass ISP ranged from 0.4% to 9.45%; avg. of 4.6% SEM Images of Collected Particulate Filter Catch (Test 26) Cyclone Catch (Test 33)

9 SEM Images of Collected Particulate Material collected by direct filtration of hot gases leaving the char bed reactor: submicron fume dendritic structures ~ 10 µm ISP (Test 43) Uncertainties Wet collection methods give reasonable material balance closure (84-101% of initial char), but gas cooler likely contains mostly, fume overestimating amount of ISP. We plan to conduct a limited number of experiments separating the gas cooler from the cyclone after each run and accounting for the mass collected in each part separately.

10 Next Steps Modify the hot cyclone / gas cooler for separate accounting of collected material Run 10 char bed tests and analyze samples Interpret data relative to past work Estimate actual amount of ISP formed from char bed burning Questions If char bed contributes to ISP generation, what is the mechanism of formation? Physical ejection from reacting particles Entrainment of char fragments Sputtering of smelt at spouts How can ISP formation be controlled?