Condensation Problems (Stall) and Solution Methods in Steam Consumables

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Under normal conditions, condensate evacuation can be done and guaranteed as long as P1> P₂ with conventional steam traps; high differential pressures, venting to atmosphere at full height, installation without high counter pressure in continuous operation, condensate removal to a higher point, use of controlled heat exchanger on the condensate side.

Figure-1: Conventional condensate evacuation without process control in normal condition

Causes of condensation-discharge problems in processes with a steam- side control are:pressure drop due to the control valve closing, vacuum formation in the heat exchanger in an unusual condition, cut-off operation, variable condensate-load, stalling in the system with P 1 dropping below P 2, condensate unloading and condensing into the heat exchanger.

Note: Stall words; it means to lose speed and fall, to become static, to stop.

Figure-II: Conventional condensate evacuation with process control in normal condition

If the steam-side controlled boiler is returned, the condensate can not be discharged or removed;stall ‘can occur when P₁ ≤ P₂ with insufficient pressure and high counter pressure in front of the steam trap due to static height. The condensate can not be discharged and the heat exchanger (water block) into the heat exchanger, the system goes out of control. The heat exchanger may be damaged due to the risk of ram impingement.

Figure-III: Prosthetic condensate evacuation problem with a control

In the heat exchanger system in Figure-IV below, the passage at the required level of vapor is provided by full opening of the control valve so that the secondary fluid can be brought to the desired temperature. As a result, the differential pressure required for the steam trap to drain the condensate can be established.

Figure-IV: Prostate normal condensate evacuation condition with a control (control valve open)

The heat exchanger system in Figure-V below changes the secondary fluid to the desired temperature. The system does not require too much steam input and brings the control valve to an almost fully closed position. As a result, the steam trap does not have differential pressure to discharge the condensate, so the condensate returns and the condensate can not be removed.This can lead to thermal inefficiency and damage to the heat exchanger resulting from the ram impulse.

Figure-V: Prosthetic condensate evacuation problem with a control (control valve almost completely closed)

‘Stall’ problem solution; the condensate is removed by means of a pushing CONLIFT mechanical condensate pump and the result is discharged. It is recommended that the difference between the counter pressure and the pushing pressure is maximum 2 bar and the filling mouth height is minimum 600 mm.

The CONLIFT float-controlled condensate pump (without electricity) is used to lift fluids to areas and installations that have lower pressures from a lower level point to higher pressures at higher points. Gas-phase fluids are carried out using propellant (transport principle). fluid for propellant pressure; steam, compressed air, inert gas (e.g., nitrogen)

Atmospheric open systems; the pump sends the air to the atmosphere, the condensate is pressurized and an accumulator with air is collected. The condensate in the front of the pump must not be applied when the counter-pressure at the pump outlet is exceeded.

Atmospheric closed systems; the exhaust line is balanced by turning it into the installation (collector or heat exchanger outlet). When the pressure gauge is evacuated and vice versa, the vapor field (heat exchanger) is evacuated. The condensate in the front of the pump can exceed the counter-pressure at the pump outlet. In the case of vacuum, the condensate can be removed from the vapors of steam and other fluids.

Atmosfere open pump systems – collector

During the evacuation cycle, the condensate may not flow into the pump. During the evacuation cycle, a collector may be required as a buffer for the condensate-charge. Condensate and flash steam can be collected from different discharge points. A large number of users can be evacuated. Flash steam and gas are evacuated by air. The condensate flows into the pump by gravity. The minimum fill opening height must be considered and this is important for pump performance.

The table below offers the recommended measures:

Pump diameter DN 25/25 DN 40/40 DN 50/50 DN 80/50
Collector volume 65 liters 65 liters 80 liters 80 liters
Overflow DN 40 DN 50 DN 65 DN 80
Ventilator for collector DN 50 DN 65 DN 80 DN 100
Condensate line from the pump DN 25 DN 40 DN 50 DN 80
Lift line after pump DN 25 DN 40 DN 50 DN 50
Pump exhaust line DN 25 DN 25 DN 25 DN 25
Pusher pressure line DN 15 DN 15 DN 15 DN 15

Table-I: Aggregator and links recommended measures

Practical suggestions

The condensate line to the pump must be short and the nominal diameter not smaller than the pump inlet diameter. Filling head height: the height of the CONLIFT from the base level to the outlet of the collector and the heat exchanger is a defined height. Hydrostatic pressure with gravity is required to allow condensate flow into the pump and to open the inlet check valve. The larger fill mouth increases the pump head. After the pump, the lifting line should be short and the nominal diameter not smaller than the pump outlet diameter. Otherwise friction losses should be taken into consideration on long return lines.

Choosing the right condensate pump

The data required to select the correct pump diameter; total counter pressure (condenser + lift height + pipeline friction loss), propellant pressure, fluid, flow quantity required (condensate load), filling height.

In order to be able to determine the diameter, 3 of the 4 must be known. The pushing pressure is max. 2 bars should be big.

Figure-VI: Atmosfere open system condensate pump station diagram

Sample selection, open system – short condensate line

Lifting height (H2): 10 m
Condensate return line pressure (4): 0,5 bar (g)
Pipeline friction loss: negligible (short condensate)
Pushing pressure (pT): 6.0 bar (g)
Pushing fluid: saturated steam
Condensate load: 1,800 kg / h
Filling height (H1): 1.000 mm
Total back pressure: pG = 10 mx 0.0981 bar / m + 0.5 bar (g) = 1.48 bar (g)
Result: DN40 / 40
Alternative: DN 50/50

Condensation-relief demanded by the pushing force of 2.5 bar is achieved. Emissions capacities can be checked from Table-II.
Table-II: CONLIFT condensate-discharge capacities

In Table III below, the consumption of steam required by CONLIFT per 1,000 liters of condensate per pressure can be seen.

Table-III: Amount of propellant that the pumped fluid consumes 1,000 liters per liter

Ersun Gürkan 
ARI-Armaturen Turkey Product Manager
Ayvaz

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