Steam generation can be spread around the plant in many heat recovery devices, but the main controllable production occurs in a boiler room or power plant. Here, for didactic reasons, steam and power generation are described separately.
Usually the main steam generation unit comprises the main capacity boilers, the boiler fuel system, the steam system, the condensate treatment, the feed water system and the internal water treatment system. Considering steam pressure generation, a considerable preheating water exchangers train is included. Proper operation and design of this preheating, that uses steam and hot flue gas from the boiler, is essential if the boiler is to achieve design capacities and higher energy efficiencies.
The feed water system consists of water tanks and pumps, to provide water to the boiler and automatically regulating it to match steam demand. The steam system collects and controls the steam produced, which is directed by piping to users at appropriate controlled pressure. The fuel system includes all equipment, like tanks and pumps for liquid fuel or compressors and valves for gaseous, to provide fuel for steam generation.
All the variations in steam demand are sensed in this unit by pressure drop and this demand may be cyclic or fluctuating, complicating boiler operation and control. For reliability reasons, multiple boilers are available to comply with these many and varying loads.
Managing this unit as efficiently as possible is a fundamental energy efficiency opportunity; any inefficiencies in steam generation are spread to the whole plant.
Scheduling load properly for each boiler, concerning its expected performance, helps to achieve optimum system performance while guaranteeing reliability. To accomplish this, the maximum efficiency firing range of individual boilers has to be taken into account. Efficiencies should be determined for each boiler over the full capacity range. Steady, high capacity and energy efficient boilers should hold the continuous steam load and less efficient and more flexible generators should be used at peak loads. The overall energy performance is ensured by the more efficient equipment.
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