When a dry air cooler is pushed beyond its original design duty, two familiar retrofits have already been examined: adding spray to the tube bundle, and humidifying the intake air. This article presents a third option — integrating a water cooler in series or in parallel — for plants where the air cooler platform simply has no spare footprint.

Where no additional space is available on the air cooler platform, the cooling demand created by a capacity upgrade can still be satisfied by arranging water coolers either in parallel or in series. Figure 1 shows a series arrangement: everything outside the red frame is the original production and operating system, while everything inside the red frame is the newly added water cooler and its associated heat exchange equipment.

Overhead vapour from the distillation column is fully or partially condensed in the dry air cooler. By regulating pressure and temperature at the air cooler, the temperature of the stream entering the reflux drum can be controlled, which prevents cavitation in downstream rotating equipment and avoids excessive column pressure.

If, in actual operation, the material leaving the air cooler is warmer than the design value, the water cooler provides a second cooling stage so that the stream meets the needs of downstream production.

As shown in Figure 2, adding a water cooler effectively raises the achievable duty. The water cooler, however, must be backed by matching cooling equipment that supplies its duty. That cooling demand can be met either from the original refrigeration system or from a newly added cooling tower.

Supplying the extra duty from the existing refrigeration system increases its load and may leave the original refrigeration capacity unable to cover the upgraded production rate. This option should therefore be considered only where a generous refrigeration margin already exists. In most cases a new cooling tower is required to serve the heat exchange demand of the water cooler.

A cooling tower rejects heat from the internal circulating water to dry ambient air; the inlet-to-outlet water temperature difference is normally held at around 10 °C.

• Plot space. The method suits sites with a large area of reserved land, since the cooling tower and its piping need room.
• Materials and temperature difference. Pipe material selection and the inlet/outlet temperature difference of the heat exchanger must be reviewed at the design stage.
• Reaction hazard with water. When a cooling tower is adopted, the risk of reaction between the process material and water must be assessed. Preventive and diagnostic measures include careful pipe material selection, water quality specification and ongoing water quality monitoring — for example installing a pH meter or other monitoring instruments in the circulating water system.
• Pressure drop. A water cooler placed in series downstream of the air cooler must be checked for excessive pressure drop. Too low a pressure after the water cooler lowers the pressure inside the reflux drum and can cause cavitation damage to the reflux pump.

• Tube Bundle Spray Cooling vs Alternative Retrofits: How to Boost Dry Air Cooler Load in Summer
• Inlet Air Humidification Cooling for Air-Cooled Condensers — Higher Load, No Extra Footprint

Series or parallel water coolers give revamp engineers a practical third lever for lifting dry air cooler duty when platform space is exhausted and climate-based measures are insufficient. The concept is simple, but its success depends on disciplined design: securing a reliable cooling source, confirming the refrigeration margin, selecting compatible materials, monitoring water quality and keeping the pressure profile at the reflux drum safely above the cavitation limit.