Enlarged operation ranges for thermosiphon reboilers using pillow plates

•The suitability of pillow plates for thermosipon reboilers was shown.•Stable natural circulation at low temperature differences.•Stable natural circulation even at 200mbar.•Increased heat transfer compared to tube thermosiphon reboilers.•The enlarged operation for thermosiphon reboilers using pillow plate is shown. Thermosiphon reboilers are widely used as reboilers in distillation columns and as evaporators in the chemical and petrochemical industry. The main reasons are the low investment and operating costs. Heat transfer and fluid dynamics are strongly linked in thermosiphon reboilers. Therefore the operation range of these evaporators is limited. Pillow plates offer a very good heat transfer with a low pressure drop. Therefore great potential is expected for their use in thermosiphon reboilers. Evaporation experiments with a pillow plate thermosiphon reboiler were carried out with water and a water–glycerol mixture. The total pressure, the submergence and the temperature difference between heating and evaporation side were varied. Circulation rate and heat transfer were measured. Stable natural circulation was seen over a wide range of influence parameters. Even at low total pressures and at low submergences the natural circulation was stable. Compared to literature data for tubular thermosiphon reboilers the operating limits for pillow plate thermosiphon reboilers can be increased, especially at low total pressures, low submergences and low temperature differences. The measured heat transfer is increased compared to tubular stainless steel thermosiphon reboilers.