Soils as Pollution Abatement Media, a Fixed Bed Study of Combustion Gases DARPA-BAA-15-12 Dr. Matthew S. Blais, Dr. Michael MacNaughton, Mr. Darrel Johnston, Ms. Alexandra Joyce, Mr. Thomas Hollingsworth Benefiting government, industry and the public through innovative science and technology May 2017 CWD 2017 1
Objectives Soil Study conducted to determine acid gas capture capacity of various soils Discover optimal conditions for Soil Performance Humidity, temperature, flow rate, bed depth Validate FTIR Performance as a process monitor 7/19/2017 2
Capture of Acid Gases Extensive industrial experience with dry and semi-dry Lime treatment of acid gases in power plants and waste incinerators Reactivity HF > HCl > >SO 2 > NO 2 > CO 2 (Calcium) 2 HCl + Ca(OH) 2 CaCl 2 2 H 2 O 2 HF + Ca(OH) 2 CaF 2 2 H 2 O 3 NO 2 + Ca(OH) 2 Ca(NO 3 ) 2 + NO + H 2 O SO 2 + Ca(OH) 2 CaSO 3 ½H 2 O + ½ H 2 O The S(IV) reaction is reversible CaSO 3 ½H 2 O + 2HCl ½ H 2 O + CaCl 2 2H 2 O + SO 2
Capture of Acid Gases Normally calcining of limestone occurs at 700-900 C CaCO 3 CaO + CO 2 Based on data from NaHCO 3 injection, at lower temperatures HCl, HF, and SO 2 will also react with calcium carbonate (CaCO 3 ) in calcareous soil Reactivity HCl > SO 2 >> HF > NO 2 > CO 2 (NaHCO 3 ) Reactivity HF > HCl > >SO2 > NO2 > CO2 (Calcium) 2 HCl + CaCO 3 CaCl 2 + H 2 O + CO 2 2HF + CaCO 3 CaF 2 + H 2 O + CO 2 SO 2 + CaCO 3 + ½ H 2 O CaSO 3 ½H 2 O + CO 2
Test Conditions Soils Gypsic Aridisol: Acidic Texas Loamy Sand Alkaline Sandy Clay Loam San Antonio Soil Ottawa Sand Parameters Temperature (20 ºC 120 ºC) Relative humidity (0 100%) 7/19/2017 5
FTIR Spectrometer 7/19/2017 Matthew Blais 6
Initial Data Summary Results Moist soils have higher capacity Alkaline soils perform significantly better that acidic soils Higher temperatures adversely impact acid gas adsorption Soils do not remove NO High calcium and carbonate content may increase soil capacity for acid gases Fluoride expected to react with calcium (CaF 2 ) and silicates (SiF 4 ) 7/19/2017 Matthew Blais 7
Detailed study Set-up Three parallel bed test system 2 1/4 x 11 inch plexiglass tubes Three bed depths (100, 300 and 450 g) 3 SLPM gas flow 500 to 10,000 ppm dependent on acid gas Automatic switching between beds at 3 minute intervals 7/19/2017 Matthew Blais 8
Test Apparatus 7/19/2017 Matthew Blais 9
Analytical FTIR 7/19/2017 Matt Blais 10
HCl Testing Dry SA Soil HCl Challenge 450 g 150 g 300 g 1% HCl in three bed depths at RT and 3 SLPM, 150, 300, 450 g, bed switches every three minute, room temperature 7/19/2017 Matthew Blais 11
PPM HCL Moist SA Soil HCl In three soil depths SA Soil, moist 6000 5000 4000 Challenge 3000 HCl ppm 2000 1000 0 Bed 1 0 5000 10000 15000 20000 25000 30000 Time in Seconds Bed 2 Moist Soil with 5515 HCl, 3 SLPM with three bed depths 150, and 300, (450g was lost) breakthrough of first bed at 15000 seconds, bed 2 appears around 25000 seconds 7/19/2017 Matthew Blais 12
PPM HF ppm HF HF SA Soil Testing SA Soil, moist,10,000 PPM HF, 3 SLPM, 150g, Room Temperature 25000 HF on Moist SA Soil, 1% loading 25000 HF Challenge SA Soil 20000 20000 15000 10000 Challenge Break through 15000 10000 HF CO2 SiF4 5000 5000 0 0 5000 10000 15000 20000 Time in Seconds 0 17670 18670 19670 time in seconds 7/19/2017 Matthew Blais 13
NO 2 Testing SA Soil NO 2 Challenge NO Break through Three beds of 50g, 100g and 150g all moist soils 7/19/2017 Matthew Blais 14
NO testing SA Soil NO Challenge at 592 PPM Water signal from 2 moist and one dry 300g beds Test was run on three 300g beds, 2 moist and 1 dry, NO shows instantaneous breakthrough at challenge concentration. Plots represent same run with different frequency selection to eliminate noise 7/19/2017 Matthew Blais 15
High Temperature SO2 Testing San Antonio Soil SA Moist Soil SA Dry Soil Challenge Conc.every 3 min. Lost humidifier SA Dry Soil SA Wet Soil SA Moist soil run at 2758 ppm, 3 SLPM 98% humidity, 120⁰C, BT 80 min SA Dry Soil run at 2758 ppm, 3 SLPM, 98% humidity, 120⁰C, BT ~0 min Soil humidity and Air humidity do impact sorption 7/19/2017 Matthew Blais 16
SO2 Retention S(IV) can be oxidized to S(VI) in the presence of oxygen or NO 2 CaSO 3 ½ H 2 O + ½ O 2 + 3 / 2 H 2 O CaSO 4 2H 2 O CaSO 4 2H 2 O is stable in presence of HCl Important for the destruction of S mustard (HD) C 4 H 8 SCl 2 + 8O 2 SO 2 + 2HCl + 6H 2 O + 4CO 2
ppm SO2 SO 2 Testing SA Soil 1% SO 2 RT, three Bed Depths Moist soil 16000 14000 12000 10000 8000 6000 4000 2000 SO2 0-2000 0 5000 10000 15000 time in Seconds SO 2 Testing with moist soil at three bed depths of 150, 300, and 450g soil, test interrupted by power fluctuation, restarted immediately, 3 clean break through curves noted until gas runs out, SO2 at 1% conc. and 3 SLPM flow per cell, room temperature 7/19/2017 Matthew Blais 18
Packed Column Design Kinetic Approach* C/C 0 = 1/[1 + e k 1(q 0 M C 0 V)/Q ] Where: C 0 = Inlet concentration (mg/m 3 ) C = outlet concentration (mg/m 3 ) M = soil weight (g) Q = gas flow rate (m 3 /sec) V = gas volume (m 3 ) K 1 = rate constant q 0 = capacity of soil (g/g) ln (C 0 /C 1) = k 1 q 0 M/Q - k 1 C 0 V/Q * Pseudo second-order reaction rate Thomas model for fixed bed adsorption 7/19/2017 Mike MacNaughton 19
Packed Bed Design SO 2, SA Soil, 150 g, Moist, Room Temp. 7/19/2017 Mike MacNaughton 20
Bench Top Breakthrough vs Model SO 2, SA Soil, 150 g, Room Temp. 7/19/2017 Mike MacNaughton 21
ppm HCl and SO 2 In Air/ Nitrogen at 55 ºC 1600 1400 1200 300 g beds three soils with 65% RH and 2535 SO 2 and 2532 HCl 1000 800 Sulfur Dioxide Hydrogen Chloride 600 400 200 0 0 5,000 10,000 15,000 20,000 Time in Seconds Reaction rate of SO 3 to SO 4 is too slow to prevent release of SO 2 7/19/2017 22
San Antonio Soil Capacity at Room Temperature Challenge Gas HF 52% HCl 4 6 % SO 2 2-3 % NO 0% NO 2 >50% Weight percent capacity at breakthrough 7/19/2017 23
Conclusions NO 2 is catalytically converted to NO in the soil Both SO 2 and HCl adsorbed on moist soil Adsorption Capacity: Alkaline Clay > Gypsisol > Acidic Loam > Ottawa Sand SA soil has greater than 5% wt. capacity for HF Ideal conditions appear to be High humidity Gas cooled to room temperature High calcium carbonate containing soil 7/19/2017 Matthew Blais 24
FTIR as a process monitor Excellent process monitor looking at destruction and scrubber process exhaust to a couple of PPM Acts as a process monitor to detect process upset very quickly Is a process record for the actual emissions 7/19/2017 25
Achnowledgements DARPA, Dr. Tyler McQuade, Deputy Director, Defense Sciences Office (DSO) ACDC Program Manager SwRI, Darrel Johnston-Program Manager Johnathan Sobey, Thomas Hollingsworth 7/19/2017 26