METHOD – 1: RETURNING CONDENSATE USING TRAP PRESSURE
Inlet pressure of the steam trap can be used as the driving force for transportation of condensate to the collection tank at positive differential pressure. This recovery method is most reliable and cost effective. It is relatively easy to implement as there is no special equipment required for the same. There are two different types of installations where recovery can be done by using trap inlet pressure:
1. BY GRAVITY
As the differential pressure is always positive from downward drainage by gravity to an atmospheric system or vessel, the basic equipment required is steam trap and transport piping.
2. ELEVATED RETURN
If the differential pressure remains positive and appropriate safety standards are followed, the steam trap can discharge overhead to an elevated return. A typical example is the draining of condensate from steam traps installed on main utility steam lines. The system back pressure increases with the increase in vertical and horizontal distance. The simple trap option will fail if the differential pressure becomes negative.
DISADVANTAGES OF THE ABOVE SYSTEM
- Higher backpressure reduces capacity.
- Open Bypass valve to avoid condensate flooding inside the equipment.
- Live steam leakage through the bypass.
- Higher steam consumption in the process.
- Especially detrimental where steam traps are operating at different inlet pressures.
- The entire system gets pressurized and stops functioning, even if one steam trap fails.
METHOD – 2: USING ELECTRIC PUMP
A common centrifugal or turbine condensate pump can be used to increase delivery pressure and obtain positive differential pressure when the pressure differential from source to destination is negative. Pumping can make the transport and recovery of condensate over much longer and higher distances possible. Condensate is first collected in a tank, and then electrically pumped to the location(s) where it is to be reused.
DISADVANTAGE OF THE ABOVE SYSTEM
- Back pressure on steam traps
- Flash steam is vented
- Drop in condensate temperature due to radiation loss - across the collection tank
- Too many components to maintain
- Dry running / cavitations of electric pumps o High water treatment cost
- Low feedwater temperature
- Use of electricity – the costliest utility
METHOD – 3: USING STEAM / AIR OPERATED PUMPS
There is no danger of cavitation as the mechanical condensate pumps rely on positive displacement for pumping and do not use impeller rotation. They are relatively unaffected by broad differences in back pressure and are not as critical in their sizing. Additionally, they are well-suited for explosion proof areas and remote locations because they do not require any electricity.
The types and capacities of mechanical pumps have increased in recent years, making them one of the most commonly preferred methods for recovering condensate
ADVANTAGES OF ABOVE SYSTEM:
- Condensate pumping temperature is in range of 950C – 1000C.
- 100% Flash steam recovery
- Higher feedwater temperature. o Lesser requirement of makeup water
- Low chemical treatment costs o Increased S : F
- Consumes only 3kgs of steam per ton of condensate.
- Deaerator – ensures proper mixing of condensate, flash steam & makeup water.
- Reduced boiler blowdown.