Gas Turbine Combustor Venturi and Dilution for Low NOx
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Solution Overview
Problem
Gas turbines emit high levels of nitrogen oxides (NOx) and other pollutants due to high temperatures and inadequate control over air and fuel flow within the combustor, despite the use of dry low NOx combustors, which struggle to meet stringent emission requirements.
Innovation Solution
A gas turbine combustor design featuring a primary and secondary combustion chamber, a venturi, a transition piece with dilution holes, and a cap assembly with a centerbody and external turbulator, which impede fluid flow penetration, expand annular fluid flow, and guide cooling airflow to enhance air-fuel mixing and reduce NOx emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high temperatures are used in the combustor to oxidize carbon monoxide, then CO oxidation efficiency is improved, but nitrogen oxide emissions increase
Solution Approach 1:
The combustor is divided into a primary combustion chamber and a secondary combustion chamber separated by a venturi. The primary chamber performs initial combustion at lower temperatures, while the secondary chamber completes CO oxidation at higher temperatures, segmenting the thermal processes to avoid excessive NOx formation while maintaining CO oxidation efficiency
Solution Approach 2:
The patent changes temperature parameters through staged combustion and dilution air injection. Dilution air is introduced to reduce peak temperatures in the primary chamber, while the secondary chamber operates at higher temperatures for CO oxidation, dynamically adjusting thermal parameters to balance CO oxidation and NOx emission control
2Object-generated harmful factors
If dilution air is provided to reduce temperature and minimize thermal NOx formation, then nitrogen oxide emissions are reduced, but combustion stability may deteriorate
Solution Approach 1:
The combustor is segmented into primary and secondary chambers with separate air-fuel mixing zones. Dilution air is strategically introduced in the primary chamber to control NOx, while the secondary chamber maintains stable combustion with its own air supply, allowing temperature control without sacrificing overall combustion stability
Solution Approach 2:
The venturi structure acts as an intermediary between the primary and secondary combustion chambers, managing flow transitions and air-fuel mixing. It facilitates the introduction of dilution air while maintaining proper flow dynamics and combustion stability through its geometric design
3Temperature
If more cooling airflow is used to reduce emissions, then thermal management is improved, but combustion efficiency and stability decrease
Solution Approach 1:
Cooling airflow is applied locally through dilution holes in the transition piece rather than uniformly throughout the combustor. This localized cooling approach manages thermal loads in critical areas while preserving combustion efficiency and stability in the main combustion zones
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
The design achieves NOx emissions of less than 5 ppm by optimizing air-fuel mixing and reducing cooling airflow, improving combustion stability and efficiency while maintaining a balance between emissions reduction and stability.
Implementation Method 1
a mixing hole that is sized and positioned so as to impede a fluid flow penetration into a primary mixing zone
Implementation Method 2
The venturi throat is disposed within a predetermined distance upstream from the downstream end of the primary combustion chamber
Implementation Method 3
an external turbulator member in operable communication with the cap assembly
Implementation Method 4
Dilution air is provided to the combustor liner to absorb heat and reduce the temperature rise to a level where thermal NOx is not formed
Implementation Method 5
a combustor for producing a hot gas by mixing fuel and air and burning the resulting mixture
Implementation Method 6
both oxidation of molecular nitrogen and oxidation of carbon monoxide to carbon dioxide depend on the temperature
Data Source
AI summary
A gas turbine combustor including: a primary combustion chamber; a secondary combustion chamber downstream of the primary combustion chamber; a venturi having a venturi throat; a transition piece; a cap assembly attached to the primary combustion chamber, and an external turbulator member in operable communication with the cap assembly, wherein the primary combustion chamber includes a mixing hole arrangement for improving homogeneity of an air and fuel mixture in the combustor; the venturi throat is disposed within a predetermined distance upstream from the downstream end of the primary combustion chamber; the transition piece is composed of a duct body, with a plurality of dilution holes formed in the duct body; and the external turbulator member includes a step positioned at the second end of the centerbody, the step defining a radial distance about the second end of the centerbody.