Like all other substances, water can exist in several states— solid, liquid, or vapor— depending on its temperature and pressure. Steam is the name for water in its vapor state. Steam is created by heating liquid water to a point where the intermolecular forces between the molecules are broken, allowing the molecules to move apart. Steam energy is a significant proportion of the energy costs in the process industry. Just having an efficient boiler does not ensure high efficiencies of the steam cycle rather efficiently distributing and utilizing steam combined with recovery of condensate play a major role in improving steam cycle efficiencies. Every steam system consists of the following major components:
In the boiler, heat is added to liquid water to generate steam at a certain pressure. Boiler pressure is used to control the thermal capacity of the steam and to motivate the steam through the system.
Steam exits the boiler through piping referred to as the steam header. The header also serves as a reservoir that feeds steam to the individual heating circuits. The steam header must be large enough to virtually eliminate pressure drop between the boiler and the beginning of the circuit. Steam header Sizing reduces pressure drop and radiation loss. Steam pipes that are undersized cause high pressure drop and result in steam starvation at the point of usage.
Smaller diameter piping connects the steam header to a steam manifold. The manifold serves as the branch point for supplying the individual heating circuits. Steam manifolds commonly have 4-16 branches, and each branch contains an isolation valve. A steam trap is located at the bottom of the manifold for removing any condensate from the manifold.
The heating circuit is comprised of a group of heating elements (jacketed pipe, bolt-on jacketing, or tube tracing) which are connected in series. Typically, pre-insulated tubing is used to transport steam from the steam manifold to the first heating element in the circuit. Flexible metal hoses are commonly used to allow the steam to flow from one heating element to the next element in the circuit. Pre-insulated tubing is also used to transport steam and condensate from the last element in the circuit to the condensate manifold. The length and configuration of each heating circuit must be carefully designed and analyzed to ensure fresh steam is supplied to the jacketing system before the steam has lost too much pressure.
The condensate manifold resembles the steam manifold with the exception that each branch contains a steam trap in between 2 isolation valves. The steam trap serves to remove condensate from the system while “trapping” steam in the system. The steam trap has a critical role in determining the overall success of the steam system.
Condensate from each of the condensate manifolds flows into a common pipe header referred to as the condensate header. The condensate header returns liquid water to the boiler so that it can be reheated into steam. Special attention must be given to the piping design of the condensate header to avoid excessive pressure drop which could impede operation of the steam system.