Experimental Investigation of Catalyst Deactivation Below the MOT and Full Load Regeneration

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Arnold Pope
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1 Experimental Investigation of Catalyst Deactivation Below the MOT and Full Load Regeneration S. Bogseth, B. Spang, T. Martz, L. Muzio Fossil Energy Research Corp. Laguna Hills, CA R. Himes Electric Power Research Institute Palo Alto, California EPRI SCR Workshop October 11-13, 2011 Austin, Texas 1

2 The Problem Alternative and renewable energy sources are forcing large coal-fired units to operate at low load more frequently and for longer time intervals For units without economizer bypass capability, low load requires the SCR to run at lower temperatures For scrubber-equipped units burning high-sulfur coal, these temperatures are often below the SCR catalyst minimum operating temperature (MOT) defined by the catalyst vendor (warranty issue) Operators and vendors are working together to develop procedures for safely operating below the MOT 2

3 ABS Formation SCR catalyst will deactivate at temperatures below the ABS dew point Mechanism of Pore Plugging by Liquid ABS (Bertole, 2007) 3

4 ABS Formation 1,000,000 Matsuda, Masuda et et al al Wei, et.al. Full Scale Menasha, et al 100,000 CONDENSED Low Load SCR Region (High Sulfur Coal) 10,000 NH3*H2SO4, ppm^2 1, APH Region Catalyst Vendors Put MOT on Gas Side with Margin (Site Specific) GAS Temperature, F 4

recommendations for low load operation The current 3 rd party work is intended to add

5 Previous Studies Cormetech (Bertole, 2007) Haldor Topsoe (White, 2005) Catalyst vendors have studied deactivation below MOT and regeneration at full load They can provide site-specific recommendations for low load operation The current 3 rd party work is intended to add clarity to the MOT issues, not to serve as a substitute for catalyst vendor data or recommendations 5

6 Practical Issues ABS formation will gradually deactivate the catalyst What is the maximum time allowed at low load before SCR performance is compromised? - Overnight (demand driven) - 3 to 5 days (demand driven) - 2 to 4 weeks (maintenance issue) Does ABS deactivation affect just the top layer, or all layers? How does catalyst aging impact all of the above? 6

7 Current Objectives Investigate SCR catalyst deactivation/regeneration due to ABS formation/evaporation - Catalyst type - Regeneration temperatures - ABS deactivation/regeneration cycling Investigate impact on 1 st and 2 nd catalyst layers Use experimental data and FERCo process model to develop SCR performance predictions for low load scenarios - Reactor potential change (flow and temperature) - Maximum allowable time at low load - Catalyst aging impacts 7

8 Experimental Setup Gas-fired Combustion Tunnel (No Flyash) SO 3 Generator 90mm x 90mm x 2.5m Test Section (2 x 1m catalyst layers) 8

9 Experimental Results: Proof of Concept Catalyst #1 (Single Layer, 15 ppm SO 3 ) F 550F 750F 0.80 K/K Time (hr) 9

10 Experimental Results: Two Layers Catalyst #2 (0 ppm SO3) st Layer 2nd Layer 0.80 K/K Temperature (F) 10

11 Experimental Results: Two Layers Catalyst #2 (30 ppm SO 3 ) st Layer 2nd Layer 700 F F 650 F K/K F Hours 11

12 Experimental Results: Two Layers Catalyst #3 (30 ppm SO 3 ) st Layer 2nd Layer 700 F K/K F 650 F Hours 12

13 Experimental Results: Catalyst Comparison 1 First Layers Cat #1 Cat #2 Cat #3 0.8 k/ko Catalyst #2 (30 ppm SO 3 ), 525 F 0.2 Catalyst #1 (15 ppm SO 3 ), 550 F Catalyst #3 (30 ppm SO 3 ), 525 F Hours 13

14 Experimental Results: 24-hr Cycling Catalyst #2 (30 ppm SO 3 ) st Layer F 0.80 K/K F Hours 14

15 Impacts on SCR Performance ppm NH3 Slip What is the allowable time at low load and ΔNOx = 90% before 2 ppm ammonia slip is exceeded? Process Model Assumptions: 500 MW Unit NO xi = 0.4 lb/mmbtu A v at full load = 7 m/hr K 0 = 40 m/hr Low Load: T = 525 F, Flue gas flow = 60% of full load Temperature and ABS deactivation rates from Catalyst #2 experimental data SCR Performance Goal: 90% NOx 2 ppm NH3 slip t 15

16 Impacts on SCR Performance FERCo Process Model Calculations: Catalyst #2, New K 2ppm slip RP % 2ppm NH3 slip, K RP F Full Load Operating Hours at at Low 525 Load F (525 F) 0 16

17 Impacts on SCR Performance FERCo Process Model Calculations: Catalyst #2, Aged RP/RPo=1.0 RP/RPo=0.75 2ppm NH3 slip F Full Load Operating Hours Hours at Low at 525 Load F (525 F) 17

18 ABS Deactivation Process: Ash Impact? ABS Forms on Ash ABS Forms on Catalyst Layers Flue Gas (NOx, SO2, SO3, Ash) Below ABS Dewpoint NH3 Injection Ash not included in lab experiments In full-scale systems, ABS can deposit on either flyash or catalyst Catalyst surface area >> ash surface area - Experimental deactivation comparable to field Is ABS a vehicle for transporting very fine ash particles to pores? 18

19 Topics for Further Consideration Ash impacts Does aged catalyst respond differently to ABS formation? Allowable time at low load depends on inherent K vs temperature and ABS deactivation - Does this vary with catalyst type and composition? - New catalyst vs regenerated? Monitoring activity loss at low load to prevent high NH 3 slip (air heater plugging) - Continuous ammonia monitoring - In situ catalyst activity monitoring (FERCo s KnoxCheck ) 19

20 Conclusions Different catalyst types have different ABS deactivation rates and different 2 nd layer behavior Moving from full load to low load (700 F to 525 F) can result in a net loss of RP even before ABS deactivation begins (lower catalyst activity due to decreased temperature counteracts lower flue gas flow) For new catalyst, operation at low load below the ABS dewpoint for overnight periods (8-12 hours) and then regenerating at full load does not appear to threaten SCR performance 20

21 Conclusions (continued) For new catalyst, operation at low load below the ABS dewpoint for more than 24 hours may threaten NH 3 slip target The time allowance will steadily decrease as the catalyst ages Consult your catalyst vendor for site specific recommendations 21

22 Questions? 22

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