Absolute Energy improves plant operations with guided wave radar 08 August 2011

Absolute Energy is reporting increased uptime and reduced energy costs since changing to Emerson's Rosemount guided wave radar to monitor water level in a condensate receiver.

The giant ethanol plant near Lyle, Minnesota, USA, installed the system on a sieve dehydration process, and reckons the equipment has helped avoid shutdowns costing up to $20,000 an hour in lost production, as well as potential equipment damage costing more than $200,000.

"Our condensate receiver levels went from being a constant headache to hardly noticeable, because the GWR is so reliable," states Travis Rosenberg, maintenance manager at Absolute Energy.

"The increased reliability has helped us to lower the risk of equipment damage, increase plant availability, decrease energy and utilities costs and reduce maintenance costs," he adds.

Rosenberg explains that the condensate receiver is critical to continuous operation of the heat exchanger and molecular sieve dehydration process.

If water levels get too high in the receiver, temperatures in the heat exchanger drop, which can cause wet ethanol to enter the molecular sieve beds. This forces the process to be shut down and the ethanol-water mix to be reprocessed.

Previously, level was measured using conventional differential pressure transmitters, mounted on wet legs. However, excursions from high vacuum to low pressure made it challenging for DP, because fill heights in the wet legs varied too much, leading to errors up to 20%, including density variance.

Unreliable level measurements were affecting operations, with high condensate levels causing the molecular sieve dehydration process shutdown.
Rosenberg says that, if temperatures dropped in the heat exchanger and the upset occurred before the wet process stream was sent into the sieve beds, the heat exchanger had to be shut down and restarted – taking 20—30 minutes for a restart and ramp up every other week.

Also, if the upset occurred and the sieve beds get wet, the process had to be shut down for 36 and 48 hours, because the beds had to be shut down, regenerated and restarted.

Hence the move to Emerson's Rosemount 5301 Guided Wave Radar transmitter and the Rosemount 9901 Chamber.
The 9901 self-contained chamber was installed for externally mounting the Rosemount GWR to the vessel, enabling the instrument to be isolated for routine maintenance while keeping the plant operational.

Rosenberg says the result is a system that manages pressure changes and provides a highly accurate and reliable direct level measurement.

Brian Tinham

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