Pilot Nozzle Tips for Combustor Burner Coking Prevention
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Solution Overview
Problem
Burners for annular combustors face issues with coking when using liquid fuels like light crude oil, leading to flame flashback and potential damage due to the accumulation of liquid fuel droplets on inner surfaces, particularly when the fuel evaporation time exceeds the mixing and introduction into the combustion chamber.
Innovation Solution
The burner design includes a nozzle tip with a cartridge and concentric tubes that introduce fuel and air in a way that swirls the liquid fuel and creates an air shield, reducing coking by positioning the nozzle tip at or near the burner outlet, where the flame front is fully within the combustion chamber, minimizing contact with inner surfaces and using concentric tubes with varying thickness and air channels for efficient mixing and cooling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the fuel evaporation time is extended to ensure complete mixing, then the fuel-air mixing quality improves, but the liquid fuel droplets accumulate on inner surfaces causing coking
Solution Approach 1:
The harmful function of the mixing section (where droplet accumulation occurs) is separated from the fuel injection function. The nozzle tip extends to the burner outlet to inject fuel directly into the combustion chamber, extracting the fuel injection process from the problematic mixing section where coking occurs.
Solution Approach 2:
A purge air stream is introduced as an intermediary between the fuel spray and the mixing section walls. This air stream acts as a barrier that prevents fuel droplets from contacting and accumulating on the inner surfaces, thereby preventing coking while still allowing fuel-air mixing to occur.
2Duration of action of moving object
If the nozzle tip is positioned upstream to provide evaporation time, then fuel evaporation is sufficient, but flame flashback occurs from the combustion chamber into the burner
Solution Approach 1:
Fuel injection is moved to the burner outlet where the flame front is already established. By injecting fuel at this location, the fuel immediately mixes with the hot combustion gases and ignites, preventing flashback to upstream locations while still providing sufficient evaporation time in the high-temperature combustion chamber environment.
Solution Approach 2:
High-velocity compressed air streams are used to atomize and carry the fuel spray directly into the combustion chamber. This pneumatic delivery system ensures rapid fuel-air mixing and immediate ignition upon entering the combustion chamber, preventing flashback while maintaining adequate evaporation.
3Object-generated harmful factors
If the nozzle tip is positioned at or near the burner outlet, then coking is reduced by minimizing contact with inner surfaces, but the distance for fuel-air mixing is reduced
Solution Approach 1:
High-velocity compressed air streams are introduced through concentric tubes to atomize the fuel and create intense turbulent mixing. This pneumatic mixing mechanism compensates for the reduced physical distance by increasing the mixing intensity and rate, achieving充分 mixing in a shorter length.
Solution Approach 2:
The interaction between the fuel spray and high-velocity air streams creates intense turbulent fluctuations and eddies. This turbulent mixing mechanism dramatically increases the mixing rate, allowing complete fuel-air mixing to occur over a shorter distance than would be possible with laminar mixing alone.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design significantly reduces the likelihood of coking and flame flashback, ensuring stable operation with a wide range of fuels by effectively evaporating and mixing fuels and air before introduction into the combustion chamber, thus preventing damage to the burner.
Implementation Method 1
concentric tubes with varying thickness and air channels for efficient mixing and cooling
Implementation Method 2
a first plurality of swirl vanes disposed within the center fuel passage at an outlet end of the nozzle tip; a second plurality of swirl vanes disposed in the second annular fluid passage
Implementation Method 3
effectively evaporating and mixing fuels and air before introduction into the combustion chamber
Data Source
AI summary
A burner for a combustor includes (a) a swirl generator enclosing a burner interior on an inlet side and including a tangential air inlet relative to a longitudinal center axis; (b) a mixing chamber enclosing the burner interior on an outlet side and defining a burner outlet fluidly connecting the burner interior with a combustion chamber; and (c) a lance arranged coaxially with the longitudinal center axis. The lance introduces fuel through a nozzle tip at or near the burner outlet into the combustion chamber. The nozzle tip includes a cartridge defining a center fuel passage; fuel swirl vanes within the center fuel passage at an outlet end of the nozzle tip; a first tube surrounding the center fuel passage and defining a first fluid passage; a second tube surrounding the first tube and defining a second fluid passage; and air swirl vanes in the second fluid passage.