Benefits of an air preheater replacement unit in a large CDU furnace
Content 1) Existing situation 2) Design criteria 3) Replacement 4) Results
Content 1) Existing situation 2) Design criteria 3) Replacement 4) Results
Actual process flow Duty 13,9 MW 3 heaters B-Damper 250.000 kg/h 445 C Stack 234.000 kg/h 225 C APH-A APH-B Furnace 275 C
Furnace of 170 MW, 2 DEKA APH s with both 14 MW duty
Content 1) Existing situation 2) Design criteria 3) Replacement 4) Results
Check of design data according to operation FGI: 445 C FGO: 300 C O2 out of furnace: 3%, wet DT-Air: 190 C
Check of design data according to operation 170 MW
100% - Furnace efficiency in % Benefits of an air preheater replacement New flue gas exit temperature target for the new APH 25 20 15 10 5 0 0 100 200 300 400 500 Stack temp. in C Furnace efficiency Lowering the stack temperature by 140 C would save about 7% fuel.
Check stack conditions, worst case 67 kg/s, 283 C 67 kg/s, 173 C Acid DP: 135 C 110m Draft: 6 mbar Acid DP: 135 C 110m Draft: 5 mbar 3 other heaters: 17 kg/s @ 300 C 1% H2S max. 300 C CDU4 heater 3 other heaters: 189 C 50 kg/s, 300 C 17 kg/s @ 300 C 100 ppm H2S 1% H2S max. CDU4 heater 50 kg/s, 154 C 100 ppm H2S BEFORE AFTER
Check ID-fan conditions With lower flue gas flow rate passing through ID-Fan, higher pressure increase can be used without reducing safety margin.
Design parameters of new APH Stack 250.000 kg/h 445 C 7 mbar 154 C Furnace 364 C 5 mbar 234.000 kg/h 16 C 16 C Combustion Air
Hot Air Recirculation for air preconditioning Stack 250.000 kg/h 445 C 144 C Furnace 353 C 252.000 kg/h 19 C -10 C 8 % HAR
Cold Air Bypass for performance adjustment Stack 250.000 kg/h 475 C 183 C Furnace 352 C 389 C 234.000 kg/h 16 C 10% CAB
Advantage of HAR vs. CAB For equal metal skin temperature, HAR offer 34 C hotter air, equivalent to 2,2 MW duty (difference between +25 and -10 C).
Air temperature, C Benefits of an air preheater replacement Advantage of HAR vs. CAB 35 30 25 20 15 10 5 0 05/11/2011 00:00 07/11/2011 00:00 09/11/2011 00:00 11/11/2011 00:00 13/11/2011 00:00 15/11/2011 00:00 17/11/2011 00:00 19/11/2011 00:00 21/11/2011 00:00 Date Air inlet temperature is not depending of outside conditions, less fouling and less condensation in the air preheater. HAR AMB
Air Preheater selection Counter flow plates Fully welded High efficient Compact and light
Material selection Because of acid dew point being higher than the cold end metal temperature of the heat exchanger, a plate made from SS304 has been chosen: Cr-content: 17,0-18,5 % Ni-content: 8,5-10,5 % Cold end temperature approx. 83 C
Acid Dew point C Benefits of an air preheater replacement Material selection dew point consideration 200 180 160 140 120 100 80 60 40 20 0 1 10 100 1,000 10,000 SO2 content, ppm ADP-10 Vol % H2O ADP-20 Vol % H2O Depending on H2S in the fuel (from few ppm to 100 ppm) the dew point can vary from 73 to 107 C (VDI 4760)
Content 1) Existing situation 2) Design criteria 3) Replacement 4) Results
Pre-assembly in largest possible components, with insulation
Transport by ship
Dismantling of old units within 3 days
Removal of the old DEKA-type APH: weight approx. 65 to.
Dismantling of old installation The old APH unit has been completely removed
Placing the new air plenum on the prepared structure requires a high degree of accuracy.
Installing the new APH: weight of only 42 tons with higher performance than the original.
Ready for start-upon the 1 st of November 2011
New APH Layout Benefits of an air preheater replacement
Content 1) Existing situation 2) Design criteria 3) Replacement 4) Results
Flue gas outlet temperature ( C) Benefits of an air preheater replacement Flue gas outlet temperature 350 300 250 200 150 100 50 0 24/10/2011 00:00 13/11/2011 00:00 03/12/2011 00:00 23/12/2011 00:00 12/01/2012 00:00 01/02/2012 00:00 21/02/2012 00:00 Date 2011 2008 Flue gas outlet temperature decreased from 310 C to 166 C
Air outlet temperature of APH, C Benefits of an air preheater replacement Hot air outlet temperature 450 400 350 300 250 200 Average Temp before replacement 150 100 50 2011 0 24/10/2011 00:00 13/11/2011 00:00 03/12/2011 00:00 23/12/2011 00:00 12/01/2012 00:00 01/02/2012 00:00 21/02/2012 00:00 Date Hot air outlet temperature average of 356 C after start-up.
Heat efficiency oin % Benefits of an air preheater replacement Heater efficiency 100 90 80 70 60 50 40 30 20 10 2011 2008 0 03/11/2011 00:00 08/11/2011 00:00 13/11/2011 00:00 18/11/2011 00:00 23/11/2011 00:00 28/11/2011 00:00 03/12/2011 00:00 08/12/2011 00:00 13/12/2011 00:00 Date Heater efficiency increase from 81,2% to 90,1%
Duty / Throughput, MW / m3/hr Duty / Throughput ratio 0.25 Benefits of an air preheater replacement 0.2 0.15 0.1 0.05 0 24/10/2011 00:00 13/11/2011 00:00 03/12/2011 00:00 23/12/2011 00:00 12/01/2012 00:00 01/02/2012 00:00 21/02/2012 00:00 Date 2011 2008 Duty / throughput ratio reduction from 0,126 MW/m3/hr by 22% to 0,098 MW/m3hr. (average throughput of 1110 m3/h)
NOX, corrected, mg/nm3 Benefits of an air preheater replacement NOx increase 400 350 300 Limit 250 200 Nox range in 2008 150 100 50 0 24/10/2011 00:00 13/11/2011 00:00 03/12/2011 00:00 23/12/2011 00:00 12/01/2012 00:00 01/02/2012 00:00 21/02/2012 00:00 Date NOx increase prediction to 215-290 mg/nm3 in line with API 535, fig. 9. Then back to range of 150-200 mg/n3 after burner adjustment. 2011
Summary Reduction of the flue gas outlet temperature by 144 C. Increased of Air temperature to burners by 151 C. Increase of heater efficiency by 8,9% point. Reduction of duty/throughput ratio by 22% (0,028 MW/m3/hr) Saving of approx. 10,1 MW at current average heater duty of 114 MW. CO 2 saving of 18.271 to/year Fuel saving of 855 Nm3/h. Payback less than 2 years based on fuel saving based on current average firing duty.
Questions?
Thank you for your Attention BD-Heat Recovery Inc. Dr. Olivier Brasseur Email: olivier.brasseur@bdheat.com