Flame impingement of boiler tubes and how to prevent it

Flame impingement of steam raising boiler components can cause a number of severe issues that are detrimental to the integrity of the asset. When burner flames make direct contact with the furnace side water walls (or shell plate of the furnace in water tube boilers), the result is potential corrosion on the tubes/shell plate at the flame interface. Corrosion at this point is accentuated when firing on heavy oils with high contaminants since the products of combustion features compounds that flux the external oxide on the tube continuously, subsequently eating the metal surface below. The most obvious other effect on the incident components is increased metal temperatures. This can induce failures by either short-term or long-term overheating, depending upon the localised stress distribution and the extent of the temperature increase.

Flame impingement is identified by regular visual survey of a boiler’s furnace space and burners. If left unaddressed, any one of the above issues can lead to tube failures. Boilers are designed around a correct modulating flame and combustion process. When flame impingement occurs, complete combustion cannot be achieved resulting in chemical contaminants contacting the boiler tube metal. Oil residue on the external surface of the boiler tube will result in corrosion as described above.  It is essential to ensure that burners are effectively inspected and maintained to avoid scenarios such as those shown below. Water treatment problems can accentuate the problems associated with flame impingement.

Clinker build up in the burner swirl plate

Furnace plate within a fire tube ready to rupture

 Effect on Operations

Flame impingement ultimately leads to reduced operational efficiency due to incomplete combustion. This can drive the boiler control system to increase the firing of the furnace to meet the outlet temperature requirement, leading to problems in areas not directly affected. Within the immediate vicinity tube failures can occur rapidly, leading to a significant loss of boiler water and an unplanned outage.

Preventative Actions

Flame impingement can be corrected by adjusting the burner, causing the impingement to be removed from the affected area. The burner air register should be checked to confirm that it is open and the gas tips should be inspected for blockages to evaluate if this has caused the redirection of the flame. Additionally, excess oxygen and draft requirements should be check against the design requirements.

Green’s offers inspections and surveys provided by its dedicated, highly qualified team. They enable the identification of current and potential problems with their boilers and ancillary equipment so that they can be addressed before they become overly costly or result in avoidable outages.

Available for worldwide mobilisation 365 days of the year, Green’s team are experts at inspecting and assessing boilers to check that they are performing as they should and operating at optimum efficiency. Potential problems found and associated recommendations are made as part of a detailed report so that plans can be put into place, cost and downtime is kept to a minimum and boiler life is extended.

In addition to inspections and surveys Green’s provides asset integrity assessment, failure analysis, chemical cleaning, repair and other services, all of which can be tailored to meet companies’ specific needs.