In steam generator why the CBD line take out from high point than IBD?
Answers
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04/01/2017
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Eric Hennings, Technip Stone & Webster, EHennings@technip.com
Mud and other suspended solids are more concentrated at the bottom of the drum and are removed by IBD. TDS is controlled continuously based on appropriate cycles of concentration of key minerals.
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04/01/2017
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Bruce Carr, Suncor Inc, matukaze1@hotmail.com
The highest concentration of contaminates and suspended salts are at the surface that is a phenomenon of boiling anything (think of the scum that forms in a pot when boiling potatoes). This must be removed to prevent carrying over into the superheater (if it is equipped with one) or the header.
We had an issue with our superheater tubes plugging and rupturing every 6 months... we tried everything... couldn't figure out why. Turned out the Boilermakers had added a double elbow on the CBD line so they could swing it out of their way when they entered the boiler rather that having to remove it. They forgot to swing it back when the exited... the CBD line was drawing from the bottom of the drum, It should be located about ~2" below the surface. Remember the CBD line is also normally where the boiler water is sampled for TDS you want to sample near the surface where the TDS is at its highest.
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04/01/2017
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Peter Marsh, XBP Refining Consultants Ltd, peter.marsh@xbprefining.co.uk
All dissolved and suspended solids in the feed water to the boiler tend to concentrate in the boiler water as steam is generated. The boiler water has concentration limits (eg. total solids, silica content, alkalinity, etc) to avoid foaming and solids carryover. Continuous blowdown is taken from the zone of highest solids concentration in the steam drum and is usually capable of keeping solids within the required concentration limits. Intermittent blowdown is taken from the bottom of the steam drum and is used to keep it sludge-free during operation.
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01/01/2017
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Sridhar Balakrishnan, Bharat Oman Refineries Limited , laksrid@yahoo.com
Continuous Blow Down (CBD) removes suspended salts , where as Intermittent Blow Down (IBD) removes dissolved salts. This is the reason CBD line take out kept from high point than IBD.
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