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Continued From ---> Boilers Design and Components #2
A low water detector/cutout, which is fitted for each boiler. This safety
device prevents the boiler from operating with little, or no, water and
overheating, which could easily cause serious damage to the unit.
Dissolved oxygen and other chemicals in normal domestic water can cause
severe corrosion and fouling of the heating system, especially with steel
pipework. In closed hot water systems, water treatment chemicals may be
added as the system is filled. Then, periodically, the system water quality is
checked and any needed additional treatment added. In steam systems, the makeup water must be treated to remove oxygen and
dissolved solids before it enters the boiler. This is to prevent the boiler from
filling with dissolved solids, since steam (pure water) is continuously boiled
off. The steam is very corrosive, so a chemical treatment is included to offset
the corrosive characteristics. Thus, there is a need for frequent monitoring,
since any failure of treatment can cause problems in the boiler and distribution
systems.
With the two boilers in parallel, about half the water will flow through each
boiler. If just one boiler is firing, the supply temperature will be based on the
average temperature of the return water from the idle boiler and the heated
water from the firing boiler. If the supply-temperature requirement equals the
temperature that is produced by the operating boiler, then the flow through
the idle boiler must be stopped, by closing the inlet valve. For systems with
low summer loads, this is ideal since the efficiency is maintained and the idle
boiler can be serviced with no interruption of hot-water production.
Note that with steam boilers, if one is running, both will fill with steam to
the same pressure. The operating boiler keeps the second boiler hot and ready
to fire.
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