Steam Condensate Lift Drainage - Challenge Met

Of all condensate drainage applications, one the most challenging is lift or syphon drainage. Steam users often complain of poor heat transfer, extended warmup times and sluggish steam trap operation. These issues can be solved with a little knowledge and perhaps some different equipment. First, let’s see why lift drainage is so challenging.

Equipment such as rotary drum dryers, sulfur pits, metal plating tanks and tilting cooking kettles that are heated with steam are some of the most difficult pieces of equipment from which to drain steam condensate. As the incoming steam transfers its BTU load to the product to be heated, it condenses back into its liquid form – water – but it is under almost full steam system pressure. In gravity-drainage applications, this isn’t usually a problem to consider. But lift or syphon drainage brings a different set of circumstances to the table.

As you know, steam condensate under steam system pressure will flash when the liquid passes into a lower pressure environment, such as when the liquid passes through the orifice of a steam trap. This is the vapor you see in the discharge of a steam trap that is draining to atmosphere. Of course, not all of the liquid will flash into vapor. But enough of it can to cause a reduction of the effective area of the pipe in lift or syphon applications. This, in turn, can cause poor drainage and heat transfer issues, too.

When we deal with lift or syphon drainage, a portion of that condensate will flash as it rises in the syphon tube of a rotary drum dryer or in lift-type drain piping. This is due to the pressure drop that the condensate goes through as it rises in the drain piping or syphon. Since the drain piping is not flooded with condensate, the flash vapor rises and arrives at the steam trap first.

The problem here, is that the flashing occurs upstream of the steam trap. And, since one of a steam trap’s main tasks is to close in the presence of steam, our steam trap will close until this flash vapor has condensed into liquid condensate. When the steam trap discharges, another bubble of flash vapor can arrive and the cycle repeats.

What can be done?

Some plant operators will pipe in a bypass around the steam trap in lift drainage applications. This bypass will contain a small valve that the operator “tunes” to allow the flash vapor to pass through the valve, but not too far open that steam waste would occur. In ideal conditions, this will bleed off the flash and keep liquid condensate flowing to the steam trap. But, changes in ambient conditions or a valve open too much or too little can cause operational problems. Ideally, the bypass valve should be designed for that purpose and operated only by personnel familiar with the process.

At Marspec Technical Products, we’ve been able to solve problems such as these with an option available on most #TLV Free Float? steam traps.

Most TLV J and JH series Free Float? steam traps utilize an ingenious thermostatic air vent that allows air and non-condensables to be removed on system start up. Of course, this is another one of a steam trap’s tasks: remove air.

Marspec can supply these J series Free Float? steam traps with an air vent that has a small bypass orifice added to the air vent seat. This internal bypass permits the steam trap to continuously discharge flash vapor as the trap operates normally. The continuous discharge of flash vapor allows condensate to flow to the steam trap through the syphon tube or the lift drain piping. Customers report significant improvement in the performance of their equipment when these modified steam traps are installed. Instances of sluggish operation and poor heat transfer are reduced and operator intervention isn’t required. ?

The team at Marspec Technical Products can help you solve your toughest condensate drainage issues, too. Give us a call!