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Buffer Tank Sizing Upstream Screw Compressor

buffer tank sizing

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#1 Process_1601


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Posted 09 May 2024 - 11:41 AM

Hello Everyone


I'd like to discuss a challenge we've encountered during testing of our installed compressor and seek your input on potential solutions.


Our setup involves a screw compressor tasked with compressing CO2 from approximately 0.2 barg to 23 barg continuously. A Pressure Transmitter (PT) is installed at the compressor inlet to regulate both the compressor speed and the opening of a recycling valve in response to inlet pressure, thus controlling the gas flow output. Notably, the compressor is designed to trip at high-pressure (PHH) 450 mbarg and low-pressure (PLL) -100 mbarg.


Upstream from the compressor, we receive a variable CO2 feed continiously from an epuration station, resulting in monthly/daily supply curves resembling a sawtooth pattern. During startup, the screw compressor struggles to keep pace with the rapid fluctuations in the CO2 feed, leading to shutdowns.


To address this issue, we are considering the addition of a buffer tank upstream of the compressor to mitigate the variability in the CO2 feed. The aim is to maintain a consistent CO2 flow, such as 40 Nm3/h, within a pressure range of 150 mbarg to 350 mbarg.


This buffer tank would need to be replenished by the CO2 feed from the epuration station.


We welcome your suggestions on resolving this situation. Additionally, we seek guidance on sizing the buffer tank. Should we also consider installing a booster compressor upstream of the buffer tank for filling operations? If so, would any compressor be capable of handling the rapid fluctuations in the CO2 feed?


Many thanks

#2 breizh


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Posted 09 May 2024 - 08:31 PM


Consider this resource

Air-cooled compressors for medium pressure K 22 – K 28: Intake buffer vessel (bauer-kompressoren.de)

You may want to call or email them


#3 Pilesar


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Posted 10 May 2024 - 07:59 AM

A buffer tank seems reasonable. I wonder whether a pressure regulating control valve on the source line upstream of the compressor would be helpful if the valve could act fast enough. Setpoint for the compressor suction pressure at 350 mbarg might resolve the overpressure trip. Another pressure control loop with a lower pressure setpoint but above the underpressure trip point might control a compressor kickback flow. A buffer tank would make these pressure control loops more reliable.

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