Fluidized Bed Sludge Incineration N2O Reduction
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Solution Overview
Problem
The existing fluidized bed incineration methods for sludge require excessive auxiliary fuel to reduce N2O emissions, leading to high energy costs and inefficiencies, particularly in the 'high temperature incineration method', and existing methods like multistage combustion are not energy-efficient when applied to sludge incineration.
Innovation Solution
A fluidized bed incineration method where sludge is thermally decomposed in a pyrolysis zone with a low air ratio (1.1 or less) and secondary combustion air is used to create a local high temperature zone above the sand bed, eliminating the need for auxiliary fuel and reducing N2O generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the incineration temperature is raised to 850°C to suppress N2O generation, then the quantity of N2O generated is decreased to one severalths, but the use quantity of auxiliary fuel increases to 1.4 to 1.6 times as much as the conventional technique
Solution Approach 1:
The incineration process is divided into two distinct stages: a first stage at conventional temperature (700-850°C) where sludge is incinerated with excess air, and a second stage at high temperature (950-1100°C) where N2O is decomposed. This segmentation allows each stage to perform its specific function optimally without requiring the entire process to operate at high temperature, thus reducing auxiliary fuel consumption while still achieving N2O suppression.
Solution Approach 2:
The sludge is first incinerated at conventional temperature in the first stage before being subjected to high temperature treatment in the second stage. This preliminary incineration removes much of the combustible material, so that when the second stage begins, there is less material requiring high temperature treatment, thereby reducing the auxiliary fuel needed to maintain high temperature.
2Object-generated harmful factors
If the multistage combustion method is applied to sludge incineration, then N2O and NOx generation is suppressed, but the use quantity of auxiliary fuel becomes excessive and energy saving is compromised
Solution Approach 1:
The combustion process is segmented into two stages with distinct functions: first stage for sludge incineration with excess air, and second stage for N2O decomposition with controlled air supply. This segmentation allows the system to achieve pollution suppression without the excessive auxiliary fuel consumption associated with conventional multistage combustion applied to sludge.
Solution Approach 2:
The air ratio is changed between stages: excess air (1.05-1.30) is supplied in the first stage to ensure complete combustion, while controlled air ratio (0.80-1.00) is supplied in the second stage to promote N2O decomposition without excessive fuel consumption. This parameter change optimizes both pollution control and energy efficiency.
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 method drastically reduces the use of auxiliary fuel while effectively suppressing N2O emissions to levels comparable to high temperature incineration methods, maintaining energy efficiency and preventing toxic gas formation.
Implementation Method 1
the sludge is thermally decomposed while being fluidized bed in the pyrolysis zone into which the fluidizing air having the air ratio of 1.1 or less is supplied together with the fuel
Implementation Method 2
the sludge is violently agitated at a temperature place of 550 to 750°C by the fluidizing medium to thermally decompose a combustible content in the sludge sufficiently
Implementation Method 3
combustion air having an air ratio of 0.1 to 0.3 is blown into the pyrolysis gas at a position above the pyrolysis zone to form a local high temperature place of 850 to 1000°C and to decompose N2O in the pyrolysis gas
Data Source
Figure 1
Figure 2
AI summary
An inside of an incinerator body 1 into which sludge is fed is divided into a lower portion, a portion above the lower portion, and a top portion in a height direction. The lower portion serves as a pyrolysis zone 3 for supplying fluidizing air having an air ratio of 1.1 or less together with fuel to thermally decompose the sludge while fluidizing the sludge. The portion above the lower portion serves as an over bed combustion zone 4 for supplying only combustion air having an air ratio of 0.1 to 0.3 to form a local high temperature place to decompose N 2 O. The top portion serves as a perfect combustion zone 5 for perfectly combusting unburned contents. The quantity of N 2 O generated during sludge incineration can be drastically reduced while maintaining the use quantity of auxiliary fuel at the same level as that of a conventional incineration method. When an auxiliary fuel reaction zone 10 for supplying only the auxiliary fuel between the pyrolysis zone 3 and the bed upper combustion zone 4 to decompose N 2 O is formed, the quantity of N 2 O generated can be further reduced.