guddu
32 posts
TimePosted 16/10/2008 13:38:30
guddu says

POINT LOCATION OF EXPANSION JOINT IN DUCT

HI

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

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Michael Clark
312 posts
TimePosted 17/10/2008 11:52:26

Re: POINT LOCATION OF EXPANSION JOINT IN DUCT

  • 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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