Western Canada BLRBAC Conference Selecting the Right Power Supply and Electrode for a Recovery Boiler ESP

Transcription

1 Western Canada BLRBAC Conference Selecting the Right Power Supply and Electrode for a Recovery Boiler ESP April 15, 2015 John A. Knapik Application Engineer B&W Preciptech Overland Park, KS jaknapik@babcock.com

2 How Precipitators Work.2

3 First, the Basic Parts of an ESP for 90 years ESP Switching Power Supply SCR s Waveshaping CLR Full Wave Rectification TR Set.3

4 The T/R set energizes the HV electrodes with 15 70KVDC, negative polarity The HV creates a corona glow which ionizes the surrounding gas molecules The negative gas ions migrate towards the collecting plates How an ESP Works (Simplified Version).4

5 The negative ions, in turn, charge the dust negatively The HV also creates an electric field which drives the dust toward the grounded plates The charging process occurs within a fraction of a second How an ESP Works (Simplified Version).5

6 How much Dust is caught and the Power Levels in each Field.6

7 If the Recovery ESP had hoppers, the catch in each Field AVC Readings KV ma SPM Voltage Control Readings 100 lbs of Salt Cake in flue gas Field 1 Field 2 Field 3 80% Efficiency 70% Efficiency 20 lbs 6 lbs 60% Efficiency 2.4 lbs 2.4 lbs of Salt Cake to stack THIS EXAMPLE IS FOR PRESENTATION OF THE CONCEPT, ONLY, AND SHOULD NOT BE ASSUMED TO REPRESENT ANY SPECIFIC APPLICATION. 80 lbs 14 lbs 3.6 lbs Total = 97.6 lbs removed out of 100 lbs in = 97.6% Efficient

8 Recovery ESP Current Density by Field RECOVERY BOILER ESP CURRENT BY FIELD 70 LOW RANGE HIGH RANGE ESP SECONDARY CURRENT ua/ft ESP FIELD NUMBER 3 4.8

9 Recovery Boiler ESP s Efficiency 1. Older direct contact kraft boilers had salt cake with very good conductivity, and high moisture content of the gas stream, further aided the dust collection 2. Newer indirect-contact (low odor) had slightly higher resistivity and lower moisture content, but still powered up very well. The ESP s on these units needed to be bigger because of the finer particle size distribution and higher inlet grain loading. 3. Both applications had a high concentration of fine particulate in the ESP inlet field which creates a space charge, affecting ESP HV Electrode selection.9

10 Salt Cake has a Low Resistivity, which is Good for ESP Performance. It Can Power Up Resistivity ohm - cm Good Electrical Conductor Difficult Potentially Difficult Normal Temperature F

11 Precipitators and Collection Efficiency 1. Precipitator Efficiency is directly proportional to: a) How quickly the dust in the ESP migrates toward the collecting plates (Best monitored thru ESP Total KW) b) The relative size of the ESP (SCA) 2. Therefore, whatever we can do to maximize the above two parameters, will increase the ESP collection efficiency 3. In most cases (except high resistivity), the more power one can get into the ESP, the higher the overall collection efficiency..11

12 In General, the more ESP Power, the Higher the ESP Collection Efficiency THIS GRAPH IS FOR PRESENTATION OF THE CONCEPT, ONLY, AND SHOULD NOT BE ASSUMED TO REPRESENT ANY SPECIFIC APPLICATION.

13 For Decades, Single-Phase Pulsating DC Power supplies were used.13

14 Single Phase = Conventional TR Set Secondary Current Secondary Voltage Peak Min Peak 1. It produced an ESP DC waveform for current and voltage that looked like this. 2. Because the wave does not cross zero (change polarity), it is DC and not AC. 3. It is said to have a lot of ripple (35-45%) True DC:

15 Switch Mode Power Supply Secondary Current Peak Secondary Voltage True DC: 1. Over the last decade, a lot of conventional ESP TR sets have been replaced with power supplies that provide a more true DC (very little ripple (<1%) in the waveform). 2. Their advantage is more output power with a potential for lower input power 3. More ESP power equates to higher collection efficiencies.

16 3-Phase Power Supply Secondary Current Secondary Voltage True DC: Peak 1. Since the 1960 s, the Europeans have been using 3 Phase power supplies on ESP s to reduce waveform ripple ( %) and increase total power 2. Their advantage is higher output power, almost as high as the SMPS, but with a higher reliability than a SMPS

17 Conventional TR Sets and Switch Mode Power Supplies (SMPS) NWL SMPS Units on Left Side Conventional T-R Units on Right Side

18 Single Phase = Conventional TR Set Secondary Current Peak Secondary Voltage Peak Min Higher Power How? 1. Sparking in the ESP is relative to the peak value of the secondary voltage waveform 2. The 3 phase and the switch mode allow you to run at that peak voltage value 3. That is why they produce more ESP current for the same peak voltage than a single phase transformer can True DC:

19 Why SMPS and 3 Phase Power Supplies get more power into the ESP Corona Current 1. Single Phase 2. 3-Phase 3. Switch Mode Sparking Limit Peak to Average Voltage Ratio 1.0 2, 3 With sparking, a power supply that has a peak to average voltage ratio near 1.0 (True DC) provides for operation higher on the V-I curve. A spark in an ESP Peak to Average Voltage Ratio This explains the advantage of 3-Phase and Switch Mode power supplies! Average KV

20 Harmonics Harmonics are produced in all devices because of the switching (SCR s or IGBT s) The 3 phase transformer has the lowest total harmonic distortion at 13%, followed by the single phase (21%), and the switch mode at (35%). High harmonics on the input to any transformer can cause heating of the incoming line breaker and trips High harmonics on the output to any transformer can cause every connection to have a voltage drop and attention to grounding becomes critical. It is important with SMPS to have a low impedance ground return path from the ESP collecting plates to the SMPS.20

21 * For Switch Mode Power Supply, the controls are at the transformer. With a lot of heat being generated by the Insulated Gate Bipolar Transistors (IGBT). Not an ideal environment for sensitive electronic equipment. SMPS S CONTROLS * For the 3-phase transformer, the controls are usually located where the original single phase transformers AVC cabinets were. A less hostile environment for longer electronic component life and a more conducive place to work on them.21

22 But choosing the correct power supply has a lot of things to consider PSIM (POWER SIMULATION SOFTWARE) - OPERATING VALUES FOR 80KV, 1000mA DC AVG OUTPUT SWITCH UNIT(S) SINGLE PHASE 3 PHASE MODE INPUT LINE CURRENT AMPS POWER FACTOR APPARENT POWER KVA REACTIVE POWER KVAR TOTAL HARMONIC DISTORTION % OUTPUT RIPPLE FREQUENCY Hz >20kHz RIPPLE VOLTAGE ON AN ESP LOAD % <1 PEAK/AVG VOLTAGE RATIO PEAK/AVG CURRENT RATIO EFFICIENCY EFFICIENCY % DESIGN CAPABILITY SEPARATE CONTROL FROM TRANSFORMER Y/N YES YES NO HEAT LOSS WATTS RELIABILITY RANKING 1=HIGH/7=LOW

23 In Summary, on Power Supplies 1. All 3 varieties of power supplies will work on a Recovery Boiler ESP 2. Each has its advantages and disadvantages 3. Conventional power supplies are the most reliable, but the lowest in terms of power output 4. Switch mode power supplies (SMPS) have the highest relative power output, but a below average rating on reliability and harmonics problems 5. 3 Phase power supplies are very close to the power output of the SMPS and much more reliable. Their one drawback could be that they are physically bigger 6. Conventional and 3 phase power supplies are less expensive than the SMPS.23

24 The distinct advantage of both the 3 Phase and Switch Mode Power Supplies is that they produce at least 25% higher ESP current than a conventional single-phase TR set.24

25 Types of HV electrodes in ESPs.25

26 Typical Non-Rigid HV electrodes.26

27 Typical Non-Rigid HV electrodes.27

28 Types of Rigid HV electrodes in ESPs.28

29 Space Charge impact on HV electrodes TR Set Rating Area Energized Current Density Amps Volts KV ma SPM Ft 2 ua/ft , TR Set Operating Values - Round Wire Area Energized Current Density Amps Volts KV ma SPM Ft 2 ua/ft ,

30 Space Charge Diminished - Barbed Electrode TR Set Rating Area Energized Current Density Amps Volts KV ma SPM Ft 2 ua/ft , TR Set Operating Values - Round Wire Area Energized Current Density Amps Volts KV ma SPM Ft 2 ua/ft , TR Set Operating Values - Barbed Wire Area Energized Current Density Amps Volts KV ma SPM Ft 2 ua/ft ,

31 Recovery ESP Current Density by Field RECOVERY BOILER ESP CURRENT BY FIELD 70 LOW RANGE HIGH RANGE ESP SECONDARY CURRENT ua/ft ESP FIELD NUMBER

32 Typical Non-Rigid HV electrodes Non aggressive = Hog fired Boiler Aggressive = Recovery Boiler.32

33 Types of Rigid HV electrodes in ESPs Non aggressive = better on high resistivity fly ash Aggressive = Best on inlet fields of Recovery Boiler ESP.33

34 B&W V-Pin HV electrode.34

35 Types of Rigid HV electrodes in ESPs Staggered Pipe and Spike electrode shown. Not aggressive enough for recovery boiler ESP Downstream fields on a recovery boiler ESP would use an opposed pin pipe and spike.35

36 B&W s Corona Study / Electrode Study Results 1.This is a photo of a Discharge Electrode and Collecting Plate in a precipitator on a coal fired boiler 2.The darkened image is not from the camera s flash, but from the relative deposition of dust on the collecting plate.

37 Corona Study / Electrode Study Results 1. The light areas represent areas of greater dust collection. 2. The dark areas represent little or no dust collection. 3. A somewhat similar pattern would appear for all types of rigid electrodes, not just this one. 4. The question is: Why and how are these dust patterns created?

38 B&W R&D Facility Newport News, VA To unravel the corona generation and distribution mystery, funding was obtained and a testing facility was set up at B&W s ESP test facility in Newport News, VA

39 Corona Distribution We built an ESP test stand and a special corona current measurement board. The board allowed us to measure the current from each square (0.25 in 2 ) and therefore equating it to current density (ua/ft 2 ) on the ESP collecting plate

40 Corona Distribution of a Rigid Electrode Now we had a means to gather the current density at the collecting surface. However, we had no method to objectively show and compare data sets until we created a software program to clearly show it. Corona Display

41 Corona Distribution For example this plot shows: 1. Average current density in mapped area = 83.62uA/ft 2 at 45KV 2. Highest cell of current density was ua/ft % of mapped area had negligible current density due to the shadowing effect of the body of the HV electrode

42 A larger measurement Board was Created Test ESP with 2 Popular Discharge Electrodes Plate current density measurement grid with 3,840 cells Discharge electrode Discharge electrode

43 Our Prototype research, to develop an even better RDE, has reduced the Dead Zone. Before After

44 Questions? Thank you.