Systems Page 1
Presentation Our Target: Boiler Combustion Optimization with Get a better view into the combustion of your boiler! Page 2
Presentation Boiler Combustion Optimization UBC On-line measurement of the unburned carbon in the fly ash Coal On-line measurement of the coal mass flow between the mill and the burner Air On-line flow measurement of preheated excess air or flue gas Page 3
Pulverized fuel Secondary air Primary air System Application for Boiler Optimization Steam generator Air Burner Air preheater Electric precipitator Flue gas Coal bunker Coal Coal mill FD-Fans Intermed. Flyash bunker Excess Air Fly ash UBC Page 4
UBC Page 5
UBC Measurement Principle: Unburned carbon content Dielectric constant of fly ash is a function of the carbon content. Measuring the shift of frequency in a resonator ( f) the carbon content can be calculated. UBC = A + B f A and B are the calibration coefficients Page 6
UBC Accuracy of the values 10 9 8 7 6 5 4 3 2 1 0 0 2 4 6 8 10 Unit Block1 1 Sensor Sensor1 1 Unit Block1 1 Sensor2 2 Unit Block2 2 Sensor1 1 Unit Block2 2 Sensor2 2-0,60% +0,60% Single calibration at different coal types for several month Page 7
Coal Page 8
Coal Measurement Principle: Density Microwave measurement: 2 sensors in one pipe are used to measure the coal concentration over the FULL cross sectional area of the pipe Transmitter Receiver Easy installation: The sensors are mounted through easy drill and tap holes (14x1 mm) In case of roping: cover full cross section Page 9
Coal Measurement Principle: Velocity Coal Dust Pipe Velocity W=S/T Signal Sensor 1 Signature Signal Sensor 2 Sensor 1 X(t) S=const. Sensor 2 Y(t)=X(t-T) correlation Correlation T=-26 ms Optimum of correlation Example S=54 cm T=26 ms Time T w=20,8 m/s (average velocity of the particles!) Page 10
Coal Absolute mass flows and velocities Page 11
Coal psa Particle Size Analysis Page 12
Coal psa Particle size distribution Example: Biomass PSA Page 13
AIR System Air Page 14
Air Measurement Principle: Velocity Air Duct or Pipe Signal Sensor 1 Signature Signal Sensor 2 Sensor 1 X(t) S=const. Sensor 2 Y(t)=X(t-T) correlation Correlation T=-26 ms Optimum of correlation Example S=54 cm T=26 ms w=20,8 m/s (average velocity of the air!) Time T Page 15
Air Velocity trends and 4-20mA outputs Page 16
13 golden rules for efficient combustion I. Fuel preparation: No 1. Fuel shall be consistent in size and quality No 2. Fuel shall be fed to pulverizer by an accurate feeder (gravimetric feeder) No 3. Pulverized fuel shall be 75% below 70 µm Coal psa and less than 0.1% larger than 200 µm. Page 17
13 golden rules for efficient combustion II. Fuel conveying to the burners: No 4. Primary air flow needs to be measured and Air controlled to a tolerance of 3% of full scale value No 5. Primary air to fuel ratio shall be accurately Coal controlled when above the minimum No 6. Fuel velocities shall always be higher than 23 m/sec Coal No 7. Mill outlet temperature shall be consistent and controlled temp to a tolerance of 5 K No 8. The balance of coal velocities on all pipes shall be Coal within a tolerance of 2 m/sec No 9. The coal mass flow distribution shall be within Coal a tolerance of 5 % Page 18
13 golden rules for efficient combustion III. Combustion: No 10. Secondary air distribution controlled Air to a tolerance of 5% No 11. Overfire air distribution controlled Air to a tolerance of 5% No 12. Swirl air settings controlled Air to a tolerance of 5% No 13. Excess air level reduced to the point UBC where UBC is below max taget value (usually 5%) Page 19
Checking the 13 Rules on a boiler Boiler Secondary Air PA FD Fan Primary Air Coal Bunker Feed Coal bunker Air 16 Brenner Burner pipes Coal Coal psa Burner Air Four pulverizers Page 20
Massflow [t/h] Particle Frequency [%] Rule No 3: Particle size consistency This mill has no coarse particles in the Pf Test Data: PS Reuter West, Berlin 10.06.2007 25,0 MECONTROL Coal Measurement with Feedersignal and Particlesize Distribution 90 80 20,0 70 60 15,0 50 10,0 40 30 5,0 20 10 0,0 06:00 08:24 10:48 13:12 15:36 18:00 20:24 22:48 0 Sum Burner 1-4 [t/h] Feeder [t/h] > 200 µm [%] 90-200 µm [%] < 90 µm [%] Page 21
[m/s] [Nm³/h] [ C] Rule No 4: Accurate PA flow control can check the PA flow into the mill as well as out of the mill 27.07.2006 PROMECON MECONTROL Air Primärluft Mühle 40 45000 500 40000 450 35000 400 30000 350 300 25000 250 20000 200 15000 150 10000 100 5000 50 0 0 0:00 2:24 4:48 7:12 9:36 12:00 14:24 16:48 19:12 21:36 0:00 Graph shows PA flows into the mill as well as Mill inlet temperature PL M40-1 PL M40-2 M 40 dp Mühle 40 M 40 Temp. Mühle 40 BlnPA_D_IPC2 27.07.2006 MECONTROL Air Kohlenstaubgeschwindigkeit Mühle 40 PROMECON 40,0 35,0 30,0 25,0 20,0 15,0 10,0 5,0 0,0 00:00 02:24 04:48 07:12 09:36 12:00 14:24 16:48 19:12 21:36 00:00 Brenner 41 Brenner 42 Brenner 43 Brenner 44 Graph shows the resulting velocities out of the mill. It can be checked if the velocities into the mill are appropriate for each load point and coal type. Page 22
Velocity (cm/s), Temperatur Dichte Rule No 5: Accurate control of coal concentration Underperforming pulverizer High standard deviation of concentrations and velocities Pipe 42 3000 20000 Variation of velocity 1s: 2500 2000 15000 1.53 m/s (4.6 ft/sec) 10000 1500 1000 5000 Velocity Density Variation of coal loading 1s: 500 0 123 g/m 0-5000 14:24:00 16:48:00 19:12:00 21:36:00 00:00:00 02:24:00 04:48:00 07:12:00 09:36:00 Page 23
09:59 10:19 10:40 11:00 11:20 11:40 12:00 12:20 12:41 13:01 13:21 13:41 14:01 14:21 14:41 cm/se c Rule No 6: Control of minimum coal velocities Low velocities cause pulsations in the coal flow Results Coal Velocities Velocities Velocities 2200 2000 1800 1600 1400 1200 Pipe 1 Pipe 2 Pipe 3 Pipe 4 1000 Vertical piping Horizontal piping Page 24
Rule No 7: Accurate control of mill outlet temperature Drifting Mill outlet temperature at constant load Page 25
Rule No 8: Adjustment of coal velocities Adjustment of coal flow velocity Burner Coal Valve Coal Splitter Box Pulverizer Example Pipe Arrangement Page 26
Rule No 8: Adjustment of coal velocities Here a large velocity spread has been corrected by a variable orifice Page 27
Rule No 9: Adjustment of coal mass flows Same coal mass flow to every burner Coal distribution before the adjustment Coal distribution after the adjustment Page 28
Rule No 10, 11 and 12: Adjustment of SA and OFA Typical Problems with delta P measurement 15% deviation Page 29
Rule No 13: Adjustment of O2 set point with UBC value O 2 set point reduction Page 30
UBC [wt.-%]; O 2 [vol.-%] Secondary air x 1000 [m³/hr] STP UBC Optimisation Results Rule No 13: Adjustment of O2 set point with UBC value Trial run at Wedel power plant 8 7 6 Excess air: n abs = 7.6 %-pts = 0.5 %-pts Secondary air Basis: n = 1.259 Resulting efficiency increase: 0.42 %-pts! 400 380 360 340 320 5 4 UBC: C abs = -2 %-pts = -0.08 %-pts O 2 right duct O 2 left duct 300 280 260 3 UBC Basis: gash = 3.6 % Excess Air Reduction 240 220 2 Time 200 Page 31
Example: Power station Stigsnaes, DONG Energy Capacity 265 MW el Erected in 1969 as oil fired unit Later converted to coal 4 pulverizers with dynamic classifier 24 burners Individually ducted secondary air Page 32
Stigsnaes firing system Burner Coal Splitter Box Pulverizer Page 33
NOx optimization Page 34
Boiler / Mill optimization by UBC monitoring General example calc.: Black coal utility plant Increase in efficiency* 0.45% 0.40% 0.35% 0.30% 0.25% 0.20% 0.15% 0.10% 0.05% UBC at 7.2 % g A UBC at 3.6 % g A O 2 0.00% 0% 1% 2% 3% 4% 5% 6% O 2 -content of flue gas; UBC in fly ash *) Without power savings of fans Excess Air Reduction Page 35
Boiler efficiency increase Page 36