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Technical Cement Forum / POINT LOCATION OF EXPANSION JOINT IN DUCT

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guddu 16/10/2008 13:38:30

POINT LOCATION OF EXPANSION JOINT IN DUCT

here is some tech quiry i have to ask.................

While getting into upgradation project with one of our client , i stood up at one query that

1) On what basis designer decide to locate the expansion joint on down comerduct that is installed at a upper side of Preheater. What are the key factors taken into consideration

2) Propably there may be a heat disburse frame concept which is something what fuel up to decide . Forgive if iam wrong with this guess...........................

looking for your steep action..................

cheers

rahul

Michael Clark 17/10/2008 11:52:26

Fundamentally, this is an OEM issue and different equipment suppliers can and do have very different approaches
Some clearly believe that major vessels need to be separated ( by expansion joints and bellows ) but at least one OEM’s design concepts does not include joints
In that case, thermal expansion is accommodated by unrestrained structure growth and by deflections which may for example, be taken at the top of cyclone roofs
Pre-calciners can be among the largest refractory-lined structures and including the down-comer duct may exceed 70 metres in length
In fact with operators pressing for systems having long residence times ( 9 seconds) to give capability for AFR and other long burn fuel burn-out, the days of a 100 metre pre-calciner structure may have already been reached
Expansion joints in such plants may be provided, below, midway and on top of such structures with locations chosen to best suit the geometry
If OEM’s do not get the calculations right, the complete structure may lift from its support floors and consoles with all loads then being taken on one floor exposing the civil structure to risk of collapse due to forces way above the intended structural design
Unforeseen factors may also have major negative influences including:

permanent growth of the refractory lining
inner temperatures and casing temperatures above the anticipated design
changes in fuels and delayed fuel burn-out ( especially of AFR )
Weakening of the mechanical structure due to severe casing corrosion
In modern pre-calciners and pre-heater structures, expansion joint positioning, design detailing and total allowances given, are one of the most important considerations in terms of long term mechanical security

In respect of plant modifications and duct extensions, positioning of any expansion joint should be planned around preventing or minimising additional mechanical forces

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