Central utility plants are traditionally used in campus settings to generate and distribute steam to multiple buildings. While central steam plants are an effective way to provide heat for a campus layout, these plants are also complex and can be expensive to operate. Some owners are finding that investing in and employing advanced steam plant technologies including an “Ultra-Pure” make-up water system, comprehensive metering and monitoring, and stack/blowdown economizer help protect the boilers from corrosion, monitor and record energy use, and provide energy savings over the life of the plant.
An “Ultra-Pure” water system serving a steam plant can consists of several sub-systems such as water softeners, reverse osmosis generators, and condensate polishers. The plant’s main water service is fed from a dedicated water softening plant that removes impurities such as calcium and magnesium from the water via ion exchange. The make-up water system for the plant is fed from reverse osmosis generators. The reverse osmosis (RO) process forces the make-up water through semi-permeable membranes which further removes minerals and contaminants. Many campus’ have older buildings and piping infrastructure so dissolved/particulate iron in the steam condensate returning to the plant can create problems in the equipment. To mitigate this concern, steam condensate returned from the campus can be passed through a condensate polishing system. The condensate polishing process is similar to water softening and removes dissolved/particulate iron in the water as well as minerals. The “Ultra-Pure” water systems work together to protect the boilers and steam system from contaminants and reduces the overall chemical treatment lost to boiler blowdown.
Many central plants are monitored and controlled by a custom Supervisory Control and Data Acquisition (SCADA) control system. All aspects of the plant including flow rates of steam, steam condensate, water, gas, and oil, as well as all temperatures, pressures, and alarm status conditions can be monitored by a SCADA system and displayed at the operator interface in the plant control room. Steam plants can also utilize advanced systems for steam trap monitoring and flue gas analyzation. Steam trap monitoring systems contains a chamber installed upstream of the steam traps. A sensor is installed in the side of the chamber and is capable of distinguishing between hot steam condensate, cool steam condensate, and live steam. The sensor sensing hot steam condensate would indicate the trap is operating properly. A sensor sensing cool steam condensate or steam would indicate the trap is blocked or has failed, potentially causing damage and/or wasting energy. Many plantsalso employ continuous flue gas analyzation systems. These systems sample the flue gases and analyze them for concentrations of oxygen (O2), carbon monoxide (CO), nitrogen oxides (NOx), sulfur dioxide (SO2), and combustibles, which are reported in real time to the plant’s SCADA system helping the system and plant to optimize combustion efficiency.
Additional energy saving technologies used in steam plants include stack and blowdown economizers. Stack economizers employ a coil in the flue gas stream, which boiler feedwater is circulated through prior to entering the boiler. The coil transfers energy from hot flue gases to the boiler feedwater, increasing the feedwater temperature and reducing the amount of energy required to flash the water into steam. Blowdown economizers use a flash vessel and a heat exchanger to reclaim a portion of the energy lost through surface blowdown of the boilers. During surface blowdown, a portion of the boiler water is removed from the boiler near the surface of the water where dissolved impurities are at their highest concentrations. The surface blowdown water is piped to a flash vessel where a drop in pressure causes a portion of the water to flash into steam in the presence of a heat exchanger. This heat exchanger can be used to preheat boiler feedwater or the domestic hot water service for the building.
If you are planning a new or boiler plant upgrade project and would like to learn more about implementing any of the technologies discussed above into your boiler plant, please do not hesitate to contact Russell G. Gray, PE at rgg@ba-inc.com or (717) 845-7654.