Flue Gas Purification and Waste Heat Recovery for EAF Steelmaking
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Solution Overview
Problem
Current flue gas treatment processes for electric arc furnace (EAF) steelmaking fail to effectively reduce dioxin emissions and recycle waste heat simultaneously, leading to unsatisfactory pollutant removal and energy conservation in the steel industry.
Innovation Solution
A flue gas purification and waste heat utilization system that includes a sequential arrangement of units for NOx and dioxin removal, utilizing ammonia injection for selective non-catalytic reduction and catalytic decomposition, combined with scrap steel preheating and waste heat boiler utilization to inhibit dioxin resynthesis and achieve deep purification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If flue gas quenching technology is used to control dioxin emission, then doxin emission is effectively controlled, but waste heat cannot be recycled
Solution Approach 1:
The flue gas treatment process is divided into multiple temperature zones: high-temperature section (1000-1200°C) for dioxin destruction, medium-temperature section (200-800°C) for heat recovery with dioxin suppression, and low-temperature section for final cooling. This segmentation allows different treatment objectives to be achieved in different zones without mutual interference.
Solution Approach 2:
Ammonia is injected into the flue gas before it enters the medium-temperature heat recovery zone, creating a reducing atmosphere that prevents dioxin resynthesis during heat exchange. This preliminary chemical preparation ensures that dioxin formation is suppressed before the flue gas reaches the temperature range where resynthesis could occur.
2Loss of energy
If waste heat boiler technology is used to recycle heat, then heat recovery is effective, but dioxin resynthesis occurs in the operating range (200°C to 800°C)
Solution Approach 1:
The heat recovery system is designed with different functional zones: the first heat exchanger operates in a high-temperature range where dioxin destruction occurs, while the second heat exchanger operates in the medium-temperature range with ammonia injection to maintain a reducing atmosphere that suppresses dioxin resynthesis. Each zone has optimized local conditions for its specific function.
Solution Approach 2:
Ammonia serves as a chemical intermediary that modifies the flue gas atmosphere in the medium-temperature heat recovery zone. By decomposing to form a reducing environment, ammonia prevents doxin resynthesis during heat exchange without interfering with the heat transfer process.
3Use of energy by moving object
If scrap steel preheating is used to reduce energy consumption, then energy conservation is achieved, but doxin formation increases
Solution Approach 1:
Ammonia is injected into the flue gas before it enters the scrap steel preheating zone, establishing a reducing atmosphere that prevents dioxin formation during the preheating process. This preliminary chemical preparation ensures that even though the temperature is in the doxin formation range, the chemical environment suppresses dioxin synthesis.
4Object-affected harmful factors
If multiple purification units and waste heat utilization units are arranged in sequence, then deep purification and multi-effect utilization are achieved, but system complexity increases
Solution Approach 1:
The flue gas treatment system integrates multiple functions into a unified process: dioxin destruction, NOx removal, heat recovery, and dust collection all occur in a coordinated sequence within a single treatment line. The ammonia injection system serves dual purposes of NOx reduction and dioxin suppression. This multi-functionality reduces the need for separate dedicated systems for each function.
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 system achieves ultra-low emission standards for dioxin and NOx, while recycling waste heat, thereby reducing energy consumption and costs in EAF steelmaking, realizing a synergistic effect of pollutant emission reduction and energy conservation.
Implementation Method 1
injecting ammonia gas into the flue gas exhausted from the flue gas exhaust unit to perform selective non-catalytic reduction for removing NOx
Implementation Method 2
the secondary flue gas purification unit is used for removing NOx and dioxin in the flue gas through catalytic decomposition
Implementation Method 3
a waste heat boiler utilized to perform heat exchange with a medium in the flue gas
Implementation Method 4
the heat of the flue gas is subjected to multi-effect utilization by a scrap steel preheating device
Data Source
AI summary
Disclosed are a flue gas purification and waste heat utilization system and method. The system comprises a flue gas exhaust unit, a primary waste heat utilization unit, a primary flue gas purification unit, a secondary waste heat utilization unit and a secondary flue gas purification unit that are sequentially connected in a flue gas flow direction, wherein the primary flue gas purification unit is configured for removing NOx, large particles and CO in the flue gas, the secondary flue gas purification unit is configured for removing NOx and dioxin in the flue gas, an ammonia-spraying device is externally connected between the flue gas exhaust unit and the primary waste heat utilization unit, and the ammonia-spraying device is configured for injecting ammonia gas into the flue gas exhausted from the flue gas exhaust unit.