5.1.2 Recovery by Centrifugal / Electrical pumps

One of the most common methods of recovering condensate across plants is the use of centrifugal pumps.

The prevalent system consists of open tanks installed across the plant, in which condensate is collected.
Motor-driven centrifugal pump/s operated by level controlled mechanisms are used to pump condensate from these collection tanks back to the feed water tank.
Due to high temperatures, pumps typically face issues of cavitation, thermal expansion, loss of efficiency and poor uptime.

Besides being complex to implement, this system has many other disadvantages including:

Loss of energy  :

– There is a significant loss of energy through this system as
– Flash steam which contains about 50% of the energy present in condensate is vented
– Loss of heat (due to standing losses and radiation losses) results in a drop in condensate temperature
– Overflow losses are prevalent

High downtimes :

– A combination of high temperature and flashing poses challenges for centrifugal pumps to handle condensate. Cavitation and vapour locking result in frequent pump downtimes
– Centrifugal pumps operate at high rpm, and experience high wear and tear, necessitating frequent maintenance

High operating and capital costs :

– As the system requires multiple capital costs intermediate collection tanks and centrifugal pumps (including a standby centrifugal pump), the capital costs are
high
– Additionally, as the system is both power intensive (for pumping) and inefficient in terms of heat recovery, the operating costs are also higher.

Unsafe :

– Flash steam which is vented out, condensate overflowing from the collection tank, pose a safety hazard as they can cause scalding in case of accidental contact
– The heat and humidity in the surrounding environment due to flash steam venting, leads to corrosion of pipelines, accessories and equipment in the vicinity and makes the working conditions uncomfortable