Boiler Combustion Optimization Advanced Instrumentation for Improved Plant Operation Presented to: McIlvaine Webinar August 8, 2013
Pulverized fuel Secondary air Primary air New Instrumentation for Boiler Optimization Steam generator MECONTROL Air/FG Burners Air preheater Electrostatic precipitator Flue gas MECONTROL Coal Coal bunker Fly ash Silo Fly ash Coal mill FD Fans Combustion Air MECONTROL UBC (Air Monitor Corporation)
Extended spatial filter method single particle laser source optical path Vp direction of movement Based on evaluation of the shadows of a laser beam created by moving particles Properties: Measuring range 30µm to 6mm Recording of particle velocity and particle size In-situ measurement on PF pipes Chord length measurement
Massflow [t/h] Particle Frequency [%] Particle Size Analysis (PSA) 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 [%]
Efficiency Optimization Principle Minimize energy losses from unburned carbon & flue gas -- function of excess air levels Losses UBC Optimum exhaust gas Flue gas Excess Air
Key Functions SAMPLING Instrument must collect a representative sample MEASUREMENT Instrument must accurately measure the amount of unburned carbon in the sample
Sampling Approaches Extractive (remove ash from handling system to make measurement) Classical approach used for early instrument design In-situ (measurement made within ash handling system) New approach providing significantly better reliability APPROACH
Sampling Location 100% Not representative Air Preheater Representative 90% 9% 0.9% Silos Electric precipitator Flue gas Flue gas Sampler (Extractive) 0.00015% Weak Correlation to Silos Fly ash Bulk ash Sampler () Strong Correlation to Silos
Sampling of the Ash Flow Ash and gas not uniform Ash discharged in dense quantities Flue Gas Duct Nozzle Extractive Sampler Ash Hopper Sampler High CO/UBC rope Cross sectional coverage: 0.000005% Fly ash concentration: 5g/m 3 Cross sectional coverage: 2-8% Fly ash concentration: 200,000 g/m 3
Typical Fly Ash Loading Distribution
Typical Fly Ash LOI Distribution
Extractive Measurement Ambient Temperature In-Situ Measurement ESP Hopper 320 o F Cyclone separation/ classification 140 o F Flue gas duct Transport through heated pipes Measurement of Air/ Ash mixture Static weighing of 5g sample Sampling and measurement in the hopper: no extraction no cyclone separation no static weighing no heating elements
Measurement Approaches Microwave Basis: Response to microwave radiation Pros: Simple; Accurate; Infrequent calibration Insensitive to fuel type or blend Can be performed in-situ Multiple sampling points w/ one instrument Cons: Higher initial cost (# sampling points?)
UBC Measurement Principle Dielectric constant of fly ash is a function of the carbon content. Measuring the shift of frequency (microwave) in a resonator ( f) enables the carbon content to be calculated. UBC = A + B A and B are the calibration coefficients f
Typical Measurement Data Accuracy 10 Laboratory Measurement (%UBC) 9 8 7 6 5 4 3 2 1 Unit Block1 1 Sensor1 1 Unit Block1 1 Sensor2 2 Unit Block2 2 Sensor1 1 Unit Block2 2 Sensor2 2-0,60% +0,60% 0 0 2 4 6 8 10 UBC Instrument (%UBC)
UBC [%] 18 16 14 12 Data from Reuter West power station, 11/12/2001 4.5 4 3.5 3 10 2.5 8 2 O 2 [%] Boiler/Mill Optimization w/ UBC Monitoring UBC Fly ash ( UBC) UBC Fly ash (Lab analysis) O 2 Boiler @ SCR outlet 6 1.5 4 1 2 0,5 0 0 7:00 7:30 8:00 8:30 9:00 9:30 10:00 10:30 11:00 11:30 12:00 12:30 13:00 13:30 14:00 14:30 15:00 15:30 16:00 16:30 17:00 Time
UBC UBC [%] [%] Kanawha River UBC Data 5 4 3 2 1 Channel 0 Channel 1 Channel 2 Channel 3 Channel 4 Channel 5 Channel 6 Standard Deviation of UBC Measurements Channel 0: 0.17% Channel 1: 0.15% Channel 2: 0.28% Channel 3: 0.15% Channel 4: 0.10% Channel 5: 0.16% Channel 6: 0.25% 0 0 1 2 3 4 5 Lab Kanawha River [%] All Channels = 0.18%
Benefits to the Power Plant Accurate measurement of a very key combustion parameter (UBC) Optimization of mill/boiler performance Improvement of NOx, CO, O2 and UBC (quantity and consistency) Operating cost savings by reduction of primary losses and increased fly ash sales
Boiler Combustion Optimization Air/Flue Gas Hot Gas Flow Measurement
Sekundärluft [Nm³] Klappenstellung [%] How accurate is your air flow measurement? 35000 30000 venturi measurement! same setpoint? 100 90 80 25000 70 20000 60 50 15000 10000 air damper position! same air flow? 40 30 5000 0 venturi cleaning air! 2:24 2:38 2:52 3:07 3:21 3:36 3:50 4:04 4:19 4:33 4:48 7.1.02 8.1.02 20 10 0 -Venturi measurements usually control dampers to a fixed set point. Therefore the venturi measurement indicates this set point during normal operation. Any deviations of inaccuracies therefore can not be observed from the measurement value itself, because it indicates the desired value. The damper curves usually do not allow the detection of deviations of the venturi measurement. But they often are not plausible(see picture) -Since the O 2 control loop usually corrects the deviations caused by a faulty air flow measurement, the problem can not therefore be detected by a flue gas O 2 monitor. This problem causes loss in efficiency as well as unnecessary damper wear!!
Sekundärluft [Nm³] Klappenstellung [%] MECONTROL Air/FG flow measurement Sekl. Vent.2 Br21 Sekl. MECONTROL Air.2 Br21 Klappe.2 Br21 35000 100 30000 25000 90 80 70 20000 60 50 15000 10000 5000 MECONTROL Air No deviation between air flow and damper position trending 40 30 20 10 0 2:24 2:38 2:52 3:07 3:21 3:36 3:50 4:04 4:19 4:33 4:48 7.1.02 8.1.02 -no measurement drift, reduced damper control error and wear -accurate air distribution to each burner -unaffected by dust and dirt in the gas stream -no pressure drop at the measurement location 0
MECONTROL Air/FG Measurement Principle Air Duct or Pipe Signal Sensor 1 Signature Signal Sensor 2 Sensor 1 X(t) S=const. Sensor 2 Y(t)=X(t-T) Optimum correlation T= 25 ms correlation Correlation Example S = 2 ft T = 25 ms V = 80.0 ft/s (average velocity) Time T
MECONTROL Air/FG Overview Main Cabinet Sensor 1 Sensor box max. 4 Sensors/2 Channels 4 x raw signals Sensor 2 Power Supply 24 VAC Sensor 3/4 Duct
Sekundärluft [Nm³] Klappenstellung [%] How do these problems affect the damper control? Sekl. Vent.1 Br23 Klappe.1 Br23 Sekl. Vent.2 Br23 Klappe.2 Br23 35000 30000 25000 Damper control before cleaning of Venturi 100 90 80 70 20000 60 50 15000 10000 5000 Damper control after cleaning 40 30 20 10 0 0 6:00 7:12 8:24 9:36 10:48 12:00 13:12 14:24 15:36 2.1.02 A venturi measurement is highly non-repeatable when exposed to dust contamination in secondary air ducts. This leads to a wrong stoicheometry as well as to increased wear of the damper actuators. The problem does not become appearant on the venturi values themselves or the O2 values at the boiler outlet, but mainly on the dynamic behaviour of the dampers themselves.
Case Study: wall-fired boiler Despite constant O2 values, combustion conditions vary from day to day! Deviation of air dampers on two consecutive days (at same load) rel. Deviation 14,0% 12,0% 10,0% 8,0% 6,0% 4,0% 2,0% 0,0% -2,0% -4,0% -6,0% -8,0% 1 Burner 2 3 4 Level 5 Level 4 Level 3 Level 2 Level 1 Venturi measurements indicated the same air flow on both days. However damper position showed large variations. This result is not plausible as the air ducts come off the same main duct which showed the same static pressure on both days. Level 1 Level 2 Level 3 Level 4 Level 5
Contact Information, Inc. 314 Collins Blvd. Orrville, OH 44667 Ph: 330-683-9074 Fax: 330-683-9082 www.promecon.us