Two-Stage Sulfur Combustion for Low NOx Production
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Solution Overview
Problem
Conventional sulfur combustion systems face challenges in producing high sulfur dioxide concentrations while minimizing nitrogen oxides (NOx) formation, which limits the preheating of combustion gases and increases costs due to complex and expensive multistage installations.
Innovation Solution
A two-stage combustion process is implemented, where sulfur is first combusted substoichiometrically in a furnace, followed by immediate post-combustion in the waste heat boiler, with tangential introduction of combustion air to enhance mixing and rapid cooling to minimize NOx formation, and adjusting sulfur dioxide concentrations through controlled air and sulfur supply.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If sulfur is combusted at high temperatures to produce high sulfur dioxide concentration, then combustion efficiency is improved, but nitrogen oxides formation increases
Solution Approach 1:
The combustion process is divided into two distinct stages: first stage with limited air supply at high temperature to maximize SO2 concentration, and second stage with additional air supply to complete combustion and reduce NOx. This segmentation allows each stage to optimize for its specific function, resolving the contradiction between high SO2 production and NOx control.
Solution Approach 2:
The first stage of combustion is performed preliminarily with substoichiometric air supply to create high SO2 concentration conditions before the second stage. By preparing the combustion environment in advance with controlled oxygen availability, the system achieves high SO2 yields while preventing excessive NOx formation that would occur in a single-stage high-temperature combustion.
2Reliability
If excess air is supplied to ensure complete combustion, then unburnt sulfur deposition is prevented, but sulfur dioxide concentration decreases
Solution Approach 1:
Air supply is segmented into two phases: first phase with limited air (0.9-0.95 stoichiometric ratio) to maximize SO2 concentration, and second phase with additional air to ensure complete combustion. This temporal segmentation of air supply allows the system to achieve both high SO2 concentration and complete combustion, resolving the contradiction between these two requirements.
Solution Approach 2:
The first stage of combustion is performed preliminarily with controlled air supply to achieve high SO2 concentration, and then the second stage with excess air is introduced to complete the combustion. This preliminary action followed by completion strategy allows the system to optimize for SO2 concentration first, then ensure complete combustion without compromising the previously achieved concentration.
3Productivity
If multistage plant is used to produce high sulfur dioxide concentration with low nitrogen oxides, then combustion efficiency is improved, but device complexity increases
Solution Approach 1:
The two-stage combustion process is merged into a single furnace structure, combining the functions of high SO2 concentration generation and NOx control within one integrated device. The first and second air supply systems operate in sequence within the same combustion chamber, eliminating the need for separate furnaces or complex multistage installations while achieving the desired combustion performance.
Solution Approach 2:
The single furnace is designed to perform multiple functions: it conducts both the first stage combustion with limited air for high SO2 concentration and the second stage combustion with excess air for complete combustion and NOx reduction. This multi-functionality within a single device simplifies the overall plant configuration while maintaining the benefits of staged combustion.
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 approach effectively produces high sulfur dioxide concentrations with reduced NOx formation, optimizing combustion temperatures and reducing capital costs by minimizing retention time at high temperatures and eliminating unburnt sulfur deposition, thus enhancing the economy of the sulfur combustion process.
Implementation Method 1
the sulfur is evaporated and subsequently oxidized in a first portion of the furnace
Implementation Method 2
the sulfur is evaporated and subsequently oxidized in a first portion of the furnace
Implementation Method 3
tangential introduction of combustion air to enhance mixing
Implementation Method 4
rapid cooling to minimize NOx formation
Implementation Method 5
the liquid sulfur is atomized in the furnace and is thoroughly mixed with the combustion air
Implementation Method 6
burns at temperatures of 600 to 1,600 °C
Data Source
Figure 1
Figure 2a~2b
Figure 3a~3b
AI summary
During the combustion of sulfur with air for producing sulfur dioxide, sulfur is burnt in a first portion of the combustion furnace under substoichiometric conditions. The sulfur dioxide formed in the first portion and unburnt sulfur are supplied to a second portion of the furnace adjoining the first portion, in that they are subjected to post-combustion with air. This provides for the production of sulfur-dioxide- containing gas free from nitrogen oxide.