Throughout the process industry, modular fabrication has increasingly become a viable option to field construction for owner/operators, OEMs, and plant engineers. From zero site disruption during fabrication to plug-and-play commissioning, single- and multiple-skid systems have become popular options in recent years.
Nearly any unit operation can be fabricated as a self-contained, modular skid system. While most skids are housed within an open structural framework, a skid maker can fabricate the skid system inside a standard shipping container.
This week’s blog post discusses instrumentation for ammonia skid systems and is part of an occasional series devoted to level and flow control for skid system applications.
Ammonia Skid: Aqueous Ammonia Vaporization
Anhydrous and aqueous ammonia are skid-configured for unloading, storage, transfer, vaporization, stripping, metering, injection, and urea-to-ammonia (U2A) conversion. Skids range from compact, single-process systems to multi-unit utility systems.
Ammonia vaporization changes the state of ammonia from a liquid to a gas. Vaporized ammonia is important for use in industrial refrigeration and in pollution abatement technology, such as selective catalytic reduction (SCR) systems used to neutralize nitrogen oxides from large electric utility and industrial boilers.
Aqueous ammonia vaporization uses heat to evaporate an ammonia and water mixture. The liquid is mixed with atomizing air and dispersed into the vaporization chamber as a fine mist where it is heated until it vaporizes. The air, ammonia, and water vapor mixture are then transferred to the injection grid.
Level and Flow Applications
1. Ammonia Storage Tank Pure ammonia is stored in a pressure vessel rated at 250 to 300 psig. Aqueous ammonia (70 to 80% water) is stored in a tank rated at 25 to 30 psig.
Continuous Level: Eclipse® Model 706 Guided Wave Radar Transmitter or Atlas™ or Aurora® Magnetic Level Indicators
Point Level: Model A10/A15 Single Stage Displacer Switch
2. Mixing Tank The mixing tank uses an agitator for blending. Level controls trigger alarms in underfill and overfill incidents.
Continuous Level: Pulsar® Model RX5 Radar Transmitter or ATLAS or AURORA Magnetic Level Indicators
Point Level: Echotel® Model 961 Ultrasonic Switch or Model T20 Single Stage Float Switch
3. Pump Protection A flow switch along a pump’s discharge piping will actuate an alarm and shut down the pump when liquid flow drops below a minimum flow rate.
Flow Alarm: Thermatel® Model TD1/TD2 Thermal Dispersion Switch for low-flow cutoff
4. Air Flow Monitoring Flow meters help ensure efficient operation at rated SCFM output and detect air leaks. A flow meter with a totalizer provides an accurate measurement of compressed air consumption.
Flow Alarm: THERMATEL Model TD1/TD2 Thermal Dispersion Switch for low-flow cutoff
Flow Transmitter: THERMATEL Model TA2 Thermal Dispersion Mass Flow Meter
5. Vaporizer Liquid Level Functioning as an essential safety measure, a level switch in a vaporizer can provide high liquid level alarm, overfill tank alarm, leak detection alarm, or low level alarm.
Continuous Level: PULSAR Model RX5 Radar Transmitter; ECLIPSE Model 706 Guided Wave Radar Transmitter or ECHOTEL Model 355 Non-Contact Ultrasonic Transmitter
Point Level: THERMATEL Model TD1/TD2 Thermal Dispersion Switch for high/low alarm