How it Works

The ECOFLOW Venturi orifice steam trap, from EBE Engineering, is the most advanced Venturi orifice steam trap on the market today. The fully flanged cast housing was designed, developed and refined using 3D modelling and casting simulation software.  From these designs we have produced a Venturi orifice steam trap to meet the rigorous requirements of today’s steam plant users. Developed on a modular concept, the ECOFLOW Venturi orifice steam trap encompasses a wide range of capacities, from minimal condensate flow requirements on line drainage and trace heating systems, through to the high flow volumes and variable loads of process heating applications.

Prior to explaining the principle of operation of the Venturi orifice steam trap, it is important to understand two fundamental differences compared to conventional mechanical traps.
• Condensate from the Venturi orifice trap is discharged continuously.  
• There is no physical seal in the trap as it has no mechanical action.

1 START UP 1

When a valve is opened on a steam system, steam flows into the pipework or heat exchanging equipment. Steam velocities in pipework vary depending upon the pressure and saturation level of the steam. The higher the pressure and temperature (superheated steam for example) the higher the steam velocity. Typical steam velocities in medium pressure applications are between 25 to 40 m/s. In this first phase of start-up, air and non-condensable gases are vented through the Venturi orifice trap nozzle. As previously stated because there is no seal in the trap, these gases are easily vented. 


2 START UP 2

As all of the air and non-condensable gases are ejected from the Venturi orifice steam trap, the saturated steam approaches the nozzle. In a steam system energy losses take the form of condensate. As soon as the valve is opened the hot steam enters the pipework or heat exchanging equipment. The difference in temperature between the hot steam and the cold walls of the pipework or heat exchanger cause the steam to lose heat energy. This reduces the energy content of the steam (it’s enthalpy) and it starts to become more saturated (wet). 


3 START UP 3

As the steam approaches the nozzle it becomes progressively saturated, resulting in all the exposed cooler surfaces forming condensate. Normally a steam trap is situated at the lowest point in the steam system, enabling the condensate to drain towards this point. Once the steam reaches the nozzle it begins to eject the condensate through the orifice. At the entry and exit of the orifice there is a pressure differential. This is the point where the energy system (the steam) meets the waste system (the condensate). There is approximately a 1000 times difference between the steam density and the condensate density. This massive difference in density means the steam phase is effectively ‘blocked’ from entering the orifice. The high density condensate is also slow moving, typically 10 – 15 m/s. 


4 RUNNING LOAD 1

The “start-up” condition continues until the system reaches a steady state. At this point all parts of the pipework or heat exchanging equipment have reached a stable temperature. No more energy is required to heat them above ambient temperature. The system heat losses are now purely down to the heat required by the process. In practice, this means that the volume of condensate produced is considerably less than during start up. The orifice remains saturated with condensate but with the steam phase beginning to approach it. As the steam nears the orifice the temperature of the condensate rises.


5 RUNNING LOAD 2

A close-up of the nozzle shows how the condensate flows through the orifice into the Venturi sector. In the running condition, the condensate flowing though the orifice is very close to the steam phase. This means the temperature of the condensate is nearly the same as the steam. As the condensate is very hot it contains large quantities of energy. This energy attempts to dissipate, but as it is under pressure from the steam and throttled in the orifice, it is unable to do so. As soon as it exits the orifice the energy contained in the condensate can now discharge. This energy discharge is in the form of ‘flash steam’. The amount of ‘flash steam’ generated is proportional to the pressure differential across the orifice. At a 1 bar differential pressure approximately four percent of the condensate converts to ‘flash steam’, at 10 bar the percentage increases to sixteen percent. 


6 RUNNING LOAD 3

The orifice expanded in detail.

  1. Condensate flowing through orifice at 100% load. At start up when the condensate is cool, the orifice can accommodate two to three times the running load. 
  2. As the condensate load reduces, the hot steam mixes with the hot condensate.
  3. The steam element of the condensate increases as the load decreases. This bi-phase mixing is turbulent but contained within the orifice.
  4. A further reduction in the operating load introduces more steam and the condensate begins to laminate on the orifice walls. It is still contained within the orifice, as condensate blocks the entire diameter before the discharge in the condensate line.
  5. At this stage there is more turbulent bi-phase activity in the orifice than laminar flowing condensate. The condensate at the discharge is now at the hottest temperature and contains the most energy. This is where ‘flash steam’ pressure is at its maximum and comparable to the main steam pressure. Due to the geometry of the orifice, a localised back pressure is generated which reduces the volume of condensate that discharges. The condensate volumes increase and the orifice ‘reverses’ through steps 4, 3 and 2. Somewhere between steps 2 and 3 the temperature gradient in the orifice results in the ‘flash steam’ pressure at the discharge reduction. In practice the Venturi orifice continuously cycles between conditions 1 to 5 and back again.
  6. *If the orifice is oversized, the volume of condensate at the discharge will not block the entire diameter and system steam will begin to leak into the condensate line.
  7. *The leakage of system steam through the orifice will increase as the condensate volumes decrease.

*These conditions are typical for a simple orifice plate device but not for venturi orifice steam traps. 


7 CONTINUOUS OPERATION

As stated previously, Venturi orifice steam traps continually discharge condensate. The discharge from the orifice ‘swings’ between continuous condensate drainage (similar to water from a tap) to ‘flash steam’ which reduces the velocity of the discharging condensate and effectively ‘blocks’ the condensate from discharging. This process is auto regulating and if the process is regulated by a modulating valve the resulting ‘flash steam’ pressure will follow the modulated main steam pressure. 

The trap benefits from:

Improved production efficiency without downtime due to failed steam traps

Elimination of expensive steam leaks

Reduction in maintenance - with a full ten year performance guarantee on all Venturi orifice steam traps

Increasingly the first choice for blue chip and forward thinking businesses.