Canadian Boiler Society 2018 Education Days Fuel Air Ratio Controls (FARC) Education Days Sponsored by Glen Harrison Regional Sales Manager, Power Generation Inc. 2018 Education Days London Burlington Kingston Ottawa 1
Speaker Bio 2018 Education Days London Burlington Kingston Ottawa 2
Agenda Introduction Positioning Type FARC Metering Type FARC Q&A 2018 Education Days London Burlington Kingston Ottawa 3
Introduction A significant number of gas and oil fired appliances are being retrofitted by replacing the traditional linkage type fuel/air ratio control system with a linkage-less type system having separate actuators that control the air and fuel flow rates. This presentation will compare the FARC (Fuel Air Ratio Control) positioning type vs metering type 2018 Education Days London Burlington Kingston Ottawa 4
Positioning Type FARC Linkage Examples Typical Water Tube Package Boiler Typical Coil Tube or Fire Tube Package Boiler * * Photo courtesy of Yorkland Controls Ltd 2018 Education Days London Burlington Kingston Ottawa 5
Positioning Type FARC Ontario Requirements From Field Approval Code TSSA-FA-2016 March 2016 2.1.34 (b) Where the FARC system is of a positioning type, (i) it shall have provisions for continuous feedback of all valve/damper/actuator positions to ensure that the command position has been achieved; (ii) the inability of any of the valve/dampers or actuators to achieve the command position shall be detected and it shall prevent the associated valve/damper/actuator from traveling past the corresponding position; (vi) assured sensing of valve/damper shaft position is required. Preferably this should be achieved through a shaft position sensor attached directly and securely to the shaft. If the sensor is attached to a linkage or an actuator, or is part of the actuator, all in-between connections shall be securely fastened to prevent slippage. Use of fastening methods that could become loose is not allowed; (vii) the valve/damper/actuator assembly shall incorporate an external indication of open/close position. In many applications that use quarter-turn dampers, a permanent method of marking the damper position on the visible end of shaft may be acceptable. In other applications, marking of open/close position and, in some cases, marking of intermediate positions may be required in another accessible location; 2018 Education Days London Burlington Kingston Ottawa 6
Positioning Type FARC Linkage-less Advantages Independent actuators allow for improved control over full operating range Improved combustion efficiency Usually lower cost than Metering Type FARC Linkage-less solutions Disadvantages No certainty that the actual air flow and/or fuel flow is correct Shaft position sensors and indicators are sometimes a challenge Typical Coil Tube or Fire Tube Package Boiler * * Photo courtesy of Yorkland Controls Ltd 2018 Education Days London Burlington Kingston Ottawa 7
Metering Type FARC Ontario Requirements From Field Approval Code TSSA-FA-2016 March 2016 2.1.34 (c) Where the FARC system is of a metering type, (i) it shall have provisions for continuous feedback of fuel(s) and combustion air flow(s) to ensure that the command air-to-fuel ratio is achieved; (ii) where combustion air or fuel(s) pressure or temperature can change, appropriate temperature and pressure compensation shall be used; 2018 Education Days London Burlington Kingston Ottawa 8
Metering Type FARC Linkage-less AKA: cross-limited or flow-tie back systems Advantages Independent actuators allow for improved control over full operating range Improved combustion efficiency Certainty that the actual air flow and/or fuel flow is correct FUEL Disadvantages Cost of metering and installation 2018 Education Days London Burlington Kingston Ottawa 9
Metering Type how does it work? Assume steady state conditions at 50% demand; Demand increases to 55% The HI SELECT output increases the Setpoint to the Air Flow controller to 55% and the combustion air damper opening increases to 55% The metered air flow begins to increase towards 55% The LO SELECT output rises with the air flow, and the fuel flow controller Setpoint rises to match the airflow System is balanced once air flow and fuel flow match the 55% demand Advantages Air leads fuel on load demand increase. Fuel leads air on load demand decrease There is never a point where the controls are in a dangerous fuel-rich situation. 55% 50% 55% 50% 50% 55% 55% 55% 50% 50% FUEL 50% 55% 50% 55% 2018 Education Days London Burlington Kingston Ottawa 10
Metering Type FARC Linkage-less How does the airflow magically align with the fuel flow? By adding a function generator we can characterize the raw airflow to equal the fuel flow from minimum fire to full load FUEL f(x) % output (characterized airflow) % Input (raw airflow) 2018 Education Days London Burlington Kingston Ottawa 11
2018 Education Days London Burlington Kingston Ottawa 12
Metering Type FARC Linkage-less How do the control output signals to the FD damper and fuel control valve magically align with flows? By using positioners on the fuel control valve and FD damper + using lever angularity we can linearize the final controls elements to align with the fuel and air flow from minimum fire to full load 2018 Education Days London Burlington Kingston Ottawa 13 FUEL f(x) % output (characterized airflow) % Input (raw airflow)
Max Capacity Flow Top Range Boiler Start-Up Preliminary Curves 10 9 8 7 6 5 4 3 2 I.D. Fan F.D. Fan Feedwater Flow Desired Feedwater Desired F.D. I.D. and Fuel Fuel Flow 1 0 0 1 2 3 4 5 6 7 8 9 10 Input Signal 2018 Education Days London Burlington Kingston Ottawa 14
Techniques of Paralleling Linkage Arrangement of F.D. Fan 100% F.D. Fan Load Parallelogram Linkage Should be Avoided (Shown in Closed Position) 0 0 Signal 100% 100% F.D. Fan Load Angularity Linkage Recommended (Shown in Closed Position) 0 0 Signal 100% 100% F.D. Fan Load "Z" Linkage Arrangement To be Avoided (Shown in Closed Position) 0 0 2018 Education Days London Burlington Kingston Ottawa 15 Signal 100%
Metering Type Fuel Flow Installation Considerations Up-stream & down-stream straight piping requirements Upstream of Flow Control Valve Downstream of PRV Pressure & temperature compensation (mass flow) Main Gas Supply PRV Vent Relief Valve PRV Gas Flow Orifice Vent A Vent Vent A A A A Fast Acting Automatic Shut-off Flow Control Valve Manual Reset Shut-off Supervisory Clock 2018 Education Days London Burlington Kingston Ottawa 16 A A Pilot Ignitor Burner Manifold
Metering Type Air Flow Installation Considerations Ideal location for airflow meter on the inlet side of the combustion air fan Bell Mouth reduces noisy flow signals on inlet side of fan Alternate location for airflow meter (downstream past laminar flow zone) NOTE: potential noisy flow signal issues exist on discharge side of fan 2018 Education Days London Burlington Kingston Ottawa 17
Thank you Glen Harrison Company: Inc. Email: glen.w.harrison@ca.abb.com 2018 Education Days London Burlington Kingston Ottawa 18