The steam loop is the process by which useable steam is created for its various industry applications. Level instrumentation impacts virtually every aspect of the steam loop in order to ensure greater efficiency, safety and accuracy. In last week’s blog post, we discussed level solutions for the first three steps of the steam loop: make-up water treatment, feed water deaeration, and boiler feed water treatment. This blog post covers instrumentation for the final two steps: boiler steam generation and the condensate return system.
STEAM LOOP: 4. Boiler Steam Generation
Feed water routed to the boiler is heated in an economizer before being chemically treated upon entering the boiler. After heat converts the water into steam, the steam is routed to its applications.
Boiler drum level control must maintain water level within critical set points. Ancillary boiler systems requiring level control include fuel storage, flash tanks and the boiler’s blowdown tank.
1. Fuel Storage
A boiler can be fueled by natural gas, propane, fuel oil, coal, biomass or biogas. Storage of liquid fuel oils with low flash points requires safety-certified controls due to the hazardous location.
Continuous Level: Eclipse® Model 706 High Performance Guided Wave Radar Transmitter; Pulsar® R95 Thru-Air Radar Transmitter; Model R82 Thru-Air Radar Transmitter; Echotel® Model 355 Non-Contact Ultrasonic Transmitter.
Point Level: Model B10/B15 Dual Stage Displacer Level Switch.
2. Boiler Drum
Low water level can cause severe, even catastrophic, damage. If necessary, level controls add feed water or shut down the burner operation. Excessive high level can cause damaging carryover and priming in which a large, rapidly applied load results in a sudden reduction in steam pressure that pulls boiler water into piping. In this event, the level control actuates a valve to throttle down feed water supply.
Continuous Level: ECLIPSE Model 706 High Performance Guided Wave Radar Transmitter; Digital E3 Modulevel® Displacer Transmitter; APM MODULEVEL Pneumatic Controller; Atlas™ or Aurora® Magnetic Level Indicators.
Point Level: Series 3 ASME 31.1 External Caged Level Switch; Model B40 HT/HP External Caged Level Switch.
3. Blowdown Tank
Undesirable solids in boiler water can be reduced through a continuous purge or blowdown system. Blowdown tanks allow the blowdown to cool before it is discharged into the sewer system.
Continuous Level: ECLIPSE Model 706 High Performance Guided Wave Radar Transmitter; Digital E3 MODULEVEL Displacer Transmitter.
4. Flash Tank
Boiler water blowdown can be used to heat process streams. Boiler water blowdown heat recovery systems use flash steam from the flash tank for deaeration. The blowdown from the flash tank is passed through an exchanger and used to preheat the boiler make-up water.
Continuous Level: ECLIPSE Model 706 High Performance Guided Wave Radar Transmitter; ATLAS or AURORA Magnetic Level Indicators.
STEAM LOOP: 5. Condensate Return System
After steam does its work it condenses to water and is collected in the condensate return system for reuse in the boiler plant. Since condensate has already been treated with chemicals and has been through the steam system, it will take far fewer resources to turn it back into steam than it would to make steam from an equal quantity of cold water. A condensate return unit thus provides a significant savings in make-up and the associated water treatment chemicals.
1. Condensate Receiver Tank
Level controls in receiver tanks ensure that water is returned to the boiler house for reuse. When the control senses the upper level in the receiver tank it will actuate a pump to route the condensate to the deaerator. Typically, these tanks range from 65 to 1,800 gal. (250 to 7,000 L).
Continuous Level: ECLIPSE Model 706 High Performance Guided Wave Radar Transmitter; Digital E3 MODULEVEL Displacer Transmitter; ATLAS Magnetic Level Indicator.
Point Level: Thermatel® TD1/TD2 Flow/Level/Interface Switch; ECHOTEL Model 961 Single Point Ultrasonic Level Switch; Sealed External Caged Level Switch; Model B40 External Caged Liquid Level Switch.