(a) Explain the term water hammer indicating possible effects on the system
(b) State how the risk of water hammer may be avoided
(c) State with reasons why the testing and treatment of boiler water is essential
(d) State with reasons now boiler problems may be miiumised if no water treatment is
inmiediately available and a steam supply must be maintained
Water hammer occurs when steam is admitted into a cold pipeline. The steam condenses producing both water, and a vacuum (when the water seals the pipeline from the steam supply). This vacuum causes the water plug to be drawn into the closed end of the pipe with increasing velocity producing high impact forces on the pipework. This impact force can be high enough to rupture the pipeline.
Water hammer is avoided by slowly admitting the steam into the cold line, and draining/venting the cold line to minimise the vacuum forming. and assist in draining the condensate.
Testing of the boiler water is important to determine that
• the level of chlorides is within acceptable limits (below 200 ppm) to prevent hard scale
and pitting
• the reserve of boiler chemicals within the boiler water is accepted (P Alk above 100 ppm and Phosphate above 2oppiu)
Treatment of the boiler water with chemicals will ensure
• Alkalinity reserve against boiler water space corrosion
• Scale build-up is minimised
• Enough coagulant levels exist to minimise sludge build-up within the boiler
• The strength of the boiler drum is maintained
Boiler problems would be minimised by:
• Reducing the steam load and demand on the aux. boiler to reduce firing temperatures
• Ensuring hotwell feed temperatures are at the recommended 95°C to minimise oxygen levels in the feed
• Minimise blowdown of boiler water, whilst ensuring chloride level is not excessive, to avoid loss of the boiler chemicals
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