Boiler Controls and Instrumentation
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The document discusses the essential instrumentation and end devices required for optimizing boiler operation, focusing on safety, reliability, and performance efficiency. It emphasizes the need for a holistic approach to boiler control, detailing various measurement technologies, flow control mechanisms, and the significance of accurate instrumentation across different boiler components. Additionally, it provides guidelines for effective installation practices and stresses the importance of understanding fuel variability and other operational challenges to achieve business results.
Boiler Controls and Instrumentation
- 1. Instrumentation and EndInstrumentation and End Devices Needed for Improved Boiler Operation Joel Lemke, Rosemount, Marketing Manager Scott Pettigrew, Emerson, Consulting Engineer Bob Sabin, Emerson, Consulting Engineer
- 2. Photography & Video Recording Policy Photography and audio/video recording is not permitted in any sessions or in the exhibition areas without press credentials or written permission from the Emerson Exchange Board of Directors. Inquiries should be directed to:Inquiries should be directed to: EmersonExchange@Emerson.com Thank you.
- 3. Presenters Joel Lemke Rosemount DP Flow Marketing Manager Scott Pettigrew Sr. Combustion Control ConsultantSr. Combustion Control Consultant Bob Sabin Consulting Engineer, Industrial Energy
- 4. Boiler Control Requirements Safety Reliability Optimized Performance – Response – Fuel cost– Fuel cost – Emissions Source: Babcock & Wilcox, Steam
- 5. Building Control from the Bottom Single-Input Automatic Regulatory Math Calculation Model Adjustment Sustainable Business Results Are at Risk if a Holistic Approach is Not UtilizedSustainable Business Results Are at Risk if a Holistic Approach is Not Utilized Process Actuation Control Platform Process Measurement Automatic Regulatory Process Understanding Issue Resolution / Mitigation Address Process, Measurement, and Actuation, then Build ControlAddress Process, Measurement, and Actuation, then Build Control Phase 0 Survey/Study, Phase 1 FEED
- 7. Oxygen Analyzer - Read under reducing condition - Zone profiling Key Boiler Devices O2 Damper Drive - Digital Positioning Fan VFD Fan/Motor Health - Predictive Air Flow - Sensor plug detection - Low P range TT FT Damper Drive - Digital Positioning Fan VFD Fan/Motor Health - Predictive monitoring PT TT Furnace Temperature - Drift detection - Hot backup when critical - Predictive monitoring Furnace Pressure - Sensor plug detection - Unstable flame detection - Low P range
- 8. Key Boiler Instrumentation PT DA Tank FT FT PT DA Tank Pressure - Sensor plug detection Drum Level Indicator Drum Pressure - Sensor plug detection Steam Flow - Sensor plug detection LT FT TT PT Feed Water Temperature - Drift detection - Hot backup Pump VFD Pump/Motor Health - Predictive monitoring Feed Water Pressure - Sensor plug detection Feed Water Flow Valve - High accuracy - Extensive diagnostics - Partial stroke testing Drum Level - Plugged line detection - Stability Feed Water Flow - High accuracy - Mass flow
- 9. Key Boiler Instrumentation PT DA Tank FT FT PT DA Tank Pressure - Sensor plug detection Drum Level Indicator Drum Pressure - Sensor plug detection Steam Flow - Sensor plug detection LT FT TT PT Feed Water Temperature - Drift detection - Hot backup Pump VFD Pump/Motor Health - Predictive monitoring Feed Water Pressure - Sensor plug detection Feed Water Flow Valve - High accuracy - Extensive diagnostics - Partial stroke testing Drum Level - Plugged line detection - Stability Feed Water Flow - High accuracy - Mass flow
- 10. Key Boiler Instrumentation Gas Pressure - Sensor plug detection Gas Pressure Regulator Fuel Flow Valve - High accuracy Gas Pressure - Sensor plug detection PT Safety Vent Valve Safety Shutoff Valves PT FT - Sensor plug detection - High accuracy - Extensive diagnostics - Partial stroke testing Gas Flow - High accuracy - Mass flow - Sensor plug detection
- 11. Key Steam System Instrumentation FTPT PT Steam Pressure Steam Pressure - Sensor plug detection Steam Flow - High accuracy - Mass flow - Short pipe run considerations Pressure Reducing Valve - High accuracy PT PT Steam Pressure - Sensor plug detection Steam Pressure - Sensor plug detection Pressure Reducing Valve - High accuracy - Extensive diagnostics - Partial stroke testing - Extensive diagnostics - Partial stroke testing
- 12. Process for Boiler Improvement Combustion Trial Performance Audit Fuel Handling Modifications Air System Upgrades Air Flow Measurement Air Damper Control SOP Modification Installation Commission and Start-Up Combustion Strategy Boiler ExampleBoiler Example –– Defined Process with Holistic ApproachDefined Process with Holistic Approach
- 13. Key Boiler Instrumentation Drum Level Fuel Flow Air Flow Steam Flow OxygenOxygen Valves Dampers Feedwater Flow Furnace Pressure
- 14. Fuel Flow Considerations Mass versus Volumetric flow Accuracy, turndown requirements Types of fuel & their variability Installed performance Installation costsInstallation costs Control combustion, monitor boiler efficiency, monitor plant energy use, environmental reporting Pressure loss allowances/meter location relative to regulator Straight pipe requirements
- 15. Mass Flow provides: Better control of combustion Better mass balance Reduced process variability 40.9 gal 42.0 gal 60°°°° F20°°°° F 342 lb342 lb 2.7% Best Practice: Measure Mass FlowBest Practice: Measure Mass Flow Regulator P = 40 psig P ≠ 40.0 psig 342 lb342 lb 0.0% • Pipe Friction • Regulator Droop • Barometric Variation extra important in fuel gas or natural gas flow
- 16. #2, #6 Fuel Oil Viscosity variations of heavier oil Natural Gas Pressure & Temperature variations; Fuel Flow Measurement Natural Gas variations; Small composition variations Fuel gases, off gases, RFG, COG, BFG Highly variable Btu content
- 17. #2, #6 Fuel Oil Viscosity variations of heavier oil Control viscosity to optimize fuel atomization & combustion efficiency Pressure & Temperature variations; Eliminate impulse piping Fuel Flow Measurement Natural Gas Temperature variations; Small composition variations impulse piping for fewer leak points; install anywhere Fuel gases, off gases, RFG, COG, BFG Highly variable Btu content Real-time Molecular Weight & Btu monitoring
- 18. Steam Flow Considerations Accuracy, turndown requirements Installed performance Indoor/outdoor, weatherization Installation cost Operating costOperating cost Control drum level, monitor boiler efficiency, balance plant steam use Technology preferences
- 19. DP Flow 0.75-4% of rate (uncomp’d) 0.5-2% of rate (comp’d) 5-12:1 turndown No heat trace with Top Mount Impulse line issues or low DP can limit turndown Vortex 1-5% of rate (uncomp’d) 1-2% of rate (comp’d) 10-30:1 turndown No heat tracing required LFC possible at extreme turndown if mis-sized Steam Flow Meters limit turndown Steam flow before header Accuracy advantage if uncomp’d where swings occur turndown if mis-sized Steam flow in header T-comp: before regulator
- 20. Uncompensated Meters: Accuracy depends on Pressure variation Saturated Steam Comparison Accuracy(%) 3 4 5 Flow Rate (lb/hr) Accuracy(%) 1 2 3 Compensated Meters: Accuracy = 0.75 – 2% of flow rate better turndown Small accuracy advantage
- 21. Drum Level Considerations Maintaining level critical for safe operation –High level can cause carryover • Damage to steam turbines • Reduced heat transfer efficiency –Low level can risk exposure of tubes to excessive heatexcessive heat • Tube damage, unplanned shut-down Measurement Challenges –Water density fluctuates with changes in pressure & temperature –Water/steam dielectric can change with pressure and temperature
- 22. Boiler Drum Level Installation Condensate Pot Slope Down to Drain Water Can compensate for dielectric in high pressure steam Uninsulated Chamber: use existing taps into drum Drum can be uneven (due to uneven heating over time); redundantly measure front & back Can detect plugging of impulse piping
- 23. Visual Indication of Drum Level Codes require visual indicator Purity of feedwater can etch sight glass Indicators can be mounted anywhere Extremely reliable* *Factory Mutual Research: Miss trip < 1 in 300,000,000 False trip < 1 in 10,000,000
- 24. Air Flow Considerations Unique geometries found in ducts: Fans and dampers Expansion joints Man-way doors Internal structural restrictionsInternal structural restrictions Conditioning vanes Service access restrictions
- 25. Air Flow Considerations Installation Considerations Thin-Wall Mounting to Flat, Round or Transition Shaped Ducts Internal Structural Supports and Conditioning Vanes Undocumented Internal Structure AdditionsUndocumented Internal Structure Additions Fiberglass Duct Material Manway and Internal Service Access Requirements External Installation Clearance and Service Access Requirements
- 26. Fan to Windbox Transition Duct Measurement Challenge: Difficult Correction Curve Burner Annubar Flow Element Inlet (Dampers) Man-Way Flow
- 27. Air Flow Tight Spaces/Square Ducts Air to boiler often (rectangular) duct with very little straight run Accuracy limited by duct flow profile Multiple Annubars can be manifolded to increase averaging Pitot traverse optimizes accuracy (~2% best) Repeatability still good
- 28. Boiler Airflow Measurement Airflow measurements can be among the most difficult applications encountered – Short duct lengths with multiple elbows – Existing air foils leak and are impossible to repair – Large ducts cause low differential pressures
- 29. Boiler Airflow Measurement Simple solutions for difficult application. Working with existing airfoils Creating dP in an existing duct Static Pressure side Standard Annubars use pressure drop created by existing airfoils Static Pressure side Devices are about 6” wide
- 30. Achieving Best O2 Measurement Typical location for O2 Probe is in middle of duct on boiler outlet after generating bank Not uncommon to see significantNot uncommon to see significant stratification in duct from combustion process Enough stratification may warrant performing duct traverse with a hand held meter to determine best location, results may show a need for two O2 units
- 31. Combustion Analyzer PlacementCombustion Analyzer Placement Temperature limit is app. 1300F. Typical placement is downstream of the Economizer, but ahead of the Air Heater “Tramp Air” leaking in through the boiler casing or air heater can bias O2 readings upwards.
- 32. Damper Types Fan variable inlet vane damper – Flow to position is a square function – Pressure to position is linear Duct parallel blade action – Pressure to position is linear Example Parallel Blade Action – Flow to position is a square function In duct oposing blade action – Flow to position is a square function – Pressure to position is linear Example Opposing Blade Action
- 33. Damper Actuators Linkages play a crucial role in good control – Linkages should be designed to provide linear control – “Z” linkage connections cause non-linear “S” shape flow characteristics – Linkage should be arranged according to damper type and control duty desiredduty desired Example of “Z” Linkage Example Good PracticePossibly a poor linkage design, but can also be used to characterize the damper relative to the process
- 34. Valve Types Ball – Used for fiberous or slurry solution flow – Minimal pressure drop across valve – Inherent equal percentage characteristic provides good throttle and control Butterfly – Economical Solution – Good control where high capacity flow control is desired – Minimal pressure drop across valve– Minimal pressure drop across valve Globe – Used in pipeline applications – Excellent throttling and control capability – Easy to maintain with multiple flow characteristic options Plug – Simple and economical – Used corrosive or difficult liquid control – Used for on/off control
- 35. Valve Characteristics Linear – Used in steady state control with constant pressure drop across valve Quick Opening – Used where large increased of flow are required quickly – Used for on/off duty Equal Percentage 0 20 40 60 80 100 0 20 40 60 80 100 %Flow % Valve Position Linear Valve Quick Opening Valve Equal Percentage – Primarily used where large drops in supply pressure are expected as flow increases – Used temperature and pressure control loops 0 20 40 60 80 100 0 20 40 60 80 100 %Flow % Valve Position Equal Percentage Valve 0 20 40 60 80 100 0 20 40 60 80 100 %Flow % Valve Position Quick Opening Valve
- 36. Instrument Installation Practices Air and flue gas installation should be above the process taps and sloped back to the process taps to insure sensing lines are Water and Steam installation should be below the process taps and sloped back to the transmitter to insure sensing lines are always full. Routing of multiple legs should be identical to eliminate potential head differential in the sensing lines. process taps to insure sensing lines are always clear of liquid.
- 37. Summary A good working base of instrumentation and end devices is needed to support safe, reliable, and optimal boiler operation Boiler measurement and actuation can sometimes be challenging, but proven technologies exist to deliver desired business resultsdesired business results
- 38. Where to Get More Information Emerson Industrial Energy Solutions Team http://www2.emersonprocess.com/en-US/industries/IndustrialEnergy
- 39. Where to Get More Information Level Engineering Guide for Power & Steam Generation 6A-2014 “The Flowmeter Formula: Selection Criteria for Flow Applications” – Tues., 1:00 – 1:45 Hilton Mezzanine 1 – Thurs., 9:00 – 9:45 Hilton Lido B R. W. Miller, Flow Measurement Eng. Handbook, 3rd Ed.R. W. Miller, Flow Measurement Eng. Handbook, 3 Ed. Fisher Control Valve Handbook, 3rd Edition. Technology Exhibit – Industrial Energy (#33 Advise & Support) – Rosemount Analytical (#16 Measure & Analyze) – Fisher Control Valves (#38 Control & Regulate) – Rosemount Measurement (#24 Measure & Analyze) – Dave Winters - air ducts – Micromotion Flow & Density (#19 Measure & Analyze)