Steam Generating Boilers Are Used For Building Heating And Process Heating And Humidification System

Steam boilers are applied in many applications for building heating and many forms of process heating and humidification systems. The use of steam boilers has dropped in recent years, but they still remain the choice method of distribution energy for heating in large facilities such as hospitals, campuses, and some downtown areas of major cities.

Steam generating boilers can be classified in several ways; however, they are either low pressure (15 psig or less) or high pressure (greater than 15 psig). They can be fire-tube Scotch marine with wet- or dry-back design, cast iron, or water tube design. Steam generating boilers require large volumes for the phase change of water to steam to reduce operational issues related to small water to steam interface area. These boilers also require proper water chemistry for proper operation. Boiler feed water/makeup must be low in hardness (typically 2 grains/lb or less) with low total dissolve solids in order to reduce water surface tension. Water surface tension is a primary cause of water spouting within the boiler’s water to steam interface area. Increased "water spouting" can result in rapid fluctuation of the water level in the boiler, which is indicative of water carryover from the steam generation volume of the boiler into the steam piping header. Water carryover from the boiler to the steam header usually leads to the boiler shutting down on its low water safety. If the steam header becomes partially or fully water-logged, complete shutdown and drainage of the system is required.

Steam boilers and steam piping systems are large thermal flywheels. The system requires a substantial start up time for boiler and piping system warm up. Large piping system usually require warmup in multiple sections to avoid or minimize vacuum (sub-atmospheric) pressure forming during the warmup process due to steam condensing back to water. Steam systems cannot react to rapidly changing system demands if the boilers are staged on from a cold state. Therefore, steam boiler staging is based upon weather, steam header pressure, and the boiler operator’s experience rather than the staging controls used in hot-water boiler systems.

While steam is an extremely effective method of transporting thermal energy (considering the latent heat of vaporization) and requires no pumping on the vapour side of the system, steam boiler systems are inherently inefficient in many applications. But as I said earlier, there are buildings like hospitals, campuses and some downtown areas of major cities where steam generating boilers are really useful.