Background & Introduction
A steam generating unit (SGU), otherwise known as a boiler, generally pertains to a unit installed in the utility plant
to produce and supply low, medium or high pressure steam to the balance of plant on-sties and offsites. Some on-site units
may also be designated as a SGU but are generally unfired units. The utility plant SGU's are typically fired by oil, treated & untreated
fuel gas and CO gas streams.
In the case of a new plant, the supplier must demonstrate that the unit meets its MCR ratings (maximum continuous rating)
and stipulated over full and partial MCR ratings e.g., 110%, 75% etc. all to prove the entire system can perform to guarranteed
contract conditions. Invariably, the Supplier has the experience to achieve these conditions; but, sometimes do not
perform to design.
This was the case for a number of SG units installed in the utility plant of a multi-national refiner. The unit was plagued
by an inability to demonstrate it could reach 100% firing and flame impingement occurred during ramp up with the dual fired
burners. After several weeks of attempting to resolve the technical difficulties, the refiner threatened the Supplier with
rejection of the entire SGU equipment battery amounting to a lawsuit of eight (8) figures. Production loss,
delay of commissioning and consequential damages would add likely to that total.
Sorting out the Problems; Identifying the Root Cause
In Figure 1, SGU was jeopardized by failure to reach 100% MCR and flame impingement. Impingement against the water walls of
the unit may cause tube rupture due to excessive, highly localized heat flux.
Figure 1 Flame Impingement at Water Wall Surface
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The flame impingement occurred well prior to reaching 100% MCR and other contributing causes
were potentially identified and needed to be confirmed via engineering check and equipment inspection.
In fact there were deficiencies in sub-systems which then, required upgrading.
These upgrades were quickly proved by field measurement.
It was revealing that deficiencies occurred in basic design calculations and in sub-supplier manufacturing.
The situation met the classic pattern in incidents experienced in Loss Control Management.
The deficiencies, fortunately, resolved firing capacity targets i.e., 100% and 110% MCR but did not resolve the flame
impingement issue. As expected, the Client was not satisfied and threatened to move forward with legal action.
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This work all provided incremental insights and suggested that fluid dynamic modeling was the next step in
understanding the observed flame evolution as firing was increased. The Client begrudgingly agreed to the proposal
to do the appropriate study.
Fortunately, the fluid dynamic study revealed the cause of the observed flame behaviour. However, the solution fell
back to the expertise of the technical team since wholesale reconfiguration of the radiant box was not a practical
solution. The team identified specific design alternations to the burners themselves which overcame limitations posed
the radiant chamber.
The acceptance testing resumed and was completed to the satisfaction of the Client. The threat of litigation was
averted; the units have operated successfully since.
Please feel free to contact the author with your critique or suggestions for adding value to our tech briefs.
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