锅炉控制一般知识 Boiler Feedwater Presentation Slides.pptx

Boiler Boiler FeedwaterFeedwater System System Industry Solution Control Valves in Boiler Feedwater System DEAERATOR FROM CONDENSATE PUMP BOILER FEEDWATER PUMP BOILER FEEDWATER RECIRCULATION VALVE BOILER FEEDWATER REGULATOR VALVE TO ECONOMIZER AND BOILER / DRUM BOILER FEEDWATER START-UP VALVE P2 : Deaerator Press = 50psig P1 : BFP Outlet Pressure = 2500 - 3500 psig P2 : Boiler/ Drum Press. = 300 - 2800 psig To fill the boiler during start-up process To control flow corresponding to load changes To protect boiler feedwater pump from cavitation Potassium Carbonate Challenges - Boiler Feedwater Control Valves Cavitation Damage due to high pressure drop during initial filling of boiler and recirculation to the deaerator (may exceed 6000psid for supercritical boilers). The damage may result in passing valve or difficulty in control Consequentially, feedwater ($) is lost and the boiler may overflow causing a plant trip Rangeability - to maintain a high flow rate after start-up, the valve need to cater to high capacity requirement. A turndown ratio of 75:1 is common. Presence of particulates Magnetites from piping are commonly found in aged plant Cavitation Phenomenon As flow goes though restriction, pressure drops Pressure drops below the fluids vapor pressure (Pvc Pv) Vapor bubbles form at restriction Vapor bubbles collapse forming destructive micro-jets Flow P2 P1 V2 V1 P1 P2 Vena Contracta Pvc Pv Fisher Anti Cavitation Technology Staged and Distributed Pressure Drop Flow P 1 P 2Pv Pressure Staging allows the design to control P2 very close to Pv without cavitation. Cavitrol III anti-cavitation trim Special shaped orifices and a unique multi-stage design for minimal recovery with maximum throughput Customized number of stages and holes at different opening percentages to meet the high turndown requirement of the boiler feedwater regulator application Fisher Solution for Boiler Feedwater Valves Cavitrol III 2-Stage Fisher Solution for Boiler Feedwater Valves CAV4 Trim can take pressure drops up to 4 stage 6000 psid 5 stage 8000 psid Protected seating surface eliminates significant pressure drop across seating surfaces - Ensures long seat life Angle body configuration eliminates possible body damage due to flashing All flow through the trim including clearance flow is staged NO SIGNIFICANT PRESSURE DROP MORE THAN 90% OF THE PRESSURE DROP VERY LOW INLET PRESSURE TO FINAL STAGE Typical Feedwater System Issues Feedwater System Issues Mechanism Theory Corrosion Erosion with use of Alloy 6 / Stellite material Amine in feedwater attacks oxide layer protecting Alloy 6 overlay Feedwater System Issues Improper transfer between startup & regulator Most common misapplication is to exhaust the capacity of the startup valve and crack the regulator off the seat Leads to low flow erosion of the plug tip and seating surface Because of high pressure drop - cavitation damage will also be seen Feedwater System Issues Throttling startup/regulator and/or recirculation valves below minimum recommended operating points May occur due to Changes in feedwater flow requirement Improper load t