The piping geometry is often the primary driver in designing the routing of the steam heating circuits. Steam must be able to freely flow through the jacketing system and contact all heat transfer surfaces. Air and condensate must be efficiently removed from the jacketing, or the system’s heat transfer capability will be compromised. The following circuit design guidelines are helpful for dealing with elevation changes in the piping system:
Run circuits downhill. In other words, the steam supply point to the circuit should be at a relatively higher elevation than the condensate return point. This allows the condensate to gravity drain out of the circuit. As a rule, there should not be a vertical rise in the jacketing that would force the condensate to flow uphill. This situation can lead to condensate collecting in the jacketing, which can prevent the free flow of steam to and through the jacketing.
Provide a clear path for air removal. Upon startup, the jacketing will be full of air. The air must be removed from the jacketing since air is a good insulator and will prevent the steam from contacting the internal heat transfer surfaces of the jacketing. At pressures above 20 psig, air removal is complicated by the fact that the density of steam is greater than the density of air. Unless there is a clear flow path for the steam to push the air out of the jacketing, buoyancy will drive the air towards high spots in the jacketing. Vertical dead legs in the jacketing system should be avoided since the steam will only compress the air into the dead leg but not be able to remove it.
Allow condensate collection in jumpers instead of the jacketing. If the steam jacketing circuit contains more than one heating element, some condensate collection within the circuit is inevitable. It is not desirable for this condensate to collect in the jacketing since it would impede the system’s heat transfer. Rather, it is preferred to allow the condensate to temporarily collect in the jumpers which interconnect the heating elements of the circuit. This will not affect the system’s heat transfer. To allow condensate collection in the jumper, the steam inlet connection on the jacketing must be at a high elevation, and the condensate outlet connection must be at a relatively lower elevation. The jumper must dip below the condensate outlet before entering the steam inlet of the next element. If the connections and/or jumpers are installed in the opposite manner, the entire jacketing will fill with condensate.