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Level and Flow Solutions for Ammonia Refrigeration Skids

Refrigeration is a key component of almost every industry. Aside from the obvious applications, like air conditioning and cold storage, refrigeration is used throughout many industries to facilitate processing. It’s employed for solvent recovery, liquefaction, gas separation, condensing, and heat exchange. In power generation, it cools inlet air for improved turbine performance. In oil refineries and chemical plants, refrigeration maintains low temperature processes, as in the alkylation of butane. Pharmaceutical refrigeration chills glycol in reactor vessels and immersion chillers, and removes water vapor and CO2 from preparations. With the majority of countries now agreeing to eliminate hydro-chlorofluorocarbon coolants by 2020, absorption refrigeration (also known as ammonia refrigeration) has become a leading industrial refrigerant.

Many owner/operators, OEMs and plant engineers fabricate their refrigeration units as modular skid systems. These systems are growing in popularity due to their efficiency and minimal site disruption. This post discusses level and flow solutions for ammonia refrigeration skids and is part of an occasional Magnetrol® blog series on modular skid systems.

Ammonia Refrigeration Skids

In an ammonia refrigeration skid, the refrigeration process cycles ammonia (refrigerant) and water (absorbent) through a compressor, condenser, high and low pressure receiver tanks, a throttling device, and evaporators, from where the process recycles.

Level and Flow Applications

1. Condenser
The condenser transfers heat from the refrigerant to a coolant medium—usually ambient air. Water-cooled condensers continuously circulate water to absorb refrigerant heat. Level controls monitoring the water basin include high and low level alarms.
Continuous Level: Eclipse® Model 706 Guided Wave Radar Transmitter or E3 Modulevel® Displacer Transmitter
Point Level: Tuffy® II Float Level Switch or Echotel® Model 910 Ultrasonic Switch

2. High Pressure Liquid Receiver
A high pressure receiver tank provides a buffer for liquid refrigerant as demand varies, and uses a recirculator to pump the refrigerant to multiple evaporator units. The tank is monitored for level.
Continuous Level: ECLIPSE Model 706 Guided Wave Radar Transmitter
Point Level: Model B35 External Cage Float Switch

3. Low Pressure Liquid Receiver
A low pressure receiver tank provides a buffer for liquid refrigerant as demand varies, and uses a recirculator to pump the refrigerant to multiple evaporator units. The tank is monitored for level.
Continuous Level: ECLIPSE Model 706 Guided Wave Radar Transmitter
Point Level: External Cage Displacer Switch or ECHOTEL Model 940/941 Ultrasonic Switch

4. Evaporator
Water level in the evaporator needs to be controlled close to the setpoint. Higher levels can put the refrigerant compressor in danger due to liquid carryover, while lower levels will result in smaller heat transfer rates.
Continuous Level: ECLIPSE Model 706 Guided Wave Radar Transmitter or E3 MODULEVEL Displacer Transmitter
Point Level: Model B35 External Cage Float Switch or ECHOTEL Model 940/941 Ultrasonic Switch

Pump Protection
Pumps operating on the skid are protected by flow switches that actuate an alarm in the event of no-flow conditions.
Flow Alarm: Thermatel® Model TD1/TD2 Thermal Dispersion Switch for low-flow cutoff