Aluminum Alloy Special Aluminum Materials Industry: Dust Removal & Denitrification Project

A Comprehensive Technical Case Study on Advanced SCR Denitrification and Bag Filter Dust Removal for Aluminum Melting Furnace Operations

1. Project Overview

1.1 Background & Industry Context

The aluminum materials industry represents a comprehensive sector encompassing mining, smelting, processing, and distribution operations that play a pivotal role in the global economy. Aluminum’s exceptional properties—including lightweight characteristics, corrosion resistance, and excellent electrical conductivity—have established it as an indispensable material across aerospace, automotive manufacturing, construction, electrical transmission, and packaging applications. The industry’s advancement has significantly enhanced quality of life while driving technological progress across multiple sectors.

In the global marketplace, the importance of the aluminum industry continues to grow as technological advancement and environmental awareness expand the material’s application range. However, the industry faces significant challenges including resource constraints, environmental pollution, and high energy consumption that necessitate continuous exploration of technological innovation and sustainable development pathways. These pressures have intensified regulatory scrutiny of aluminum melting and casting operations, which generate substantial atmospheric emissions including nitrogen oxides, particulate matter, and various acid gas compounds.

Within the competitive landscape of the aluminum industry, large enterprises leverage raw material advantages, technical expertise, and brand recognition to dominate market positions. The industry chain is remarkably comprehensive, with upstream operations covering metallic ore mining and smelting, midstream processes encompassing aluminum alloy production and processing, and downstream applications spanning construction, automotive, and aerospace sectors. To enhance global competitiveness in carbon neutrality and emission reduction, environmental protection has become a critical factor for aluminum industry development.

1.2 Enterprise Profile

The subject enterprise leverages synergistic development across its parent company’s coal-fired aluminum and green hydroelectric aluminum dual industrial chains, establishing a distinctive “aluminum deep processing + green energy” business model. With total assets of 23.1 billion RMB, the facility encompasses annual production capacity of 690,000 tons of aluminum deep processing, 750,000 tons of electrolytic aluminum (including 500,000 tons of green hydroelectric aluminum), 150,000 tons of carbon materials, 900,000 kW of power generation capacity, and 2.25 million tons of raw coal. This integrated operational scale positions the company firmly within the first tier of China’s aluminum industry.

The company’s flagship product portfolio includes three primary categories: (1) Can-making aluminum materials encompassing can body stock, can end stock, and pull-tab stock, with can end stock commanding over 30% domestic market share and can body stock capturing approximately 10% of international market share, serving as a core supplier to major global can manufacturers including Ball, Crown, and Canpack; (2) Technical breakthrough products featuring the industry’s first mass production of 0.208 mm ultra-thin can end stock and 0.235 mm ultra-thin can body stock, establishing internationally leading technological capabilities; and (3) New energy materials covering battery aluminum foil for new energy power cells, collector aluminum foil, and tab aluminum foil, serving both new energy vehicle and consumer electronics markets.

Ultra-low emission flue gas purification represents a critical component of sustainable development within the aluminum industry. This project innovatively implements medium-temperature SCR denitrification technology in high-temperature, high-dust environments within the aluminum melting and casting sector—a first-of-its-kind application in this industry that has achieved remarkable results. This technological breakthrough not only accomplished ultra-low NOx emission targets but also resolved significant technical challenges that had previously constrained the industry’s environmental performance. The successful implementation demonstrates that advanced NOx gas treatment solutions can be effectively adapted for demanding metallurgical applications.

2. Pollution Source Analysis & Baseline Emission Profile

Aluminum melting furnace operations generate a complex emission profile characterized by high-temperature exhaust gases containing nitrogen oxides from combustion processes, substantial particulate matter from molten metal and flux materials, and various acid gas compounds from raw material constituents. The melting furnace operates using natural gas fuel, with combustion temperatures reaching 350-420°C at the furnace outlet. The baseline characterization was conducted to establish comprehensive emission parameters for the high-precision aluminum melting and casting production line, which is equipped with two melting furnaces and two holding furnaces, each with bag filter dust collectors, discharging through a single stack.

The environmental baseline data for this project is comprehensively summarized in the following detailed emission inventory table, which quantifies all relevant pollutant parameters, operating conditions, and process characteristics:

KHÔNG.	Category	Parameter Name	Value	Unit	Remarks
1	Pollution Source	Furnace Type	Melting Furnace	—	—
2		Fuel (Natural Gas) Consumption	1,800	m³/h	—
3		Standard Flue Gas Volume	55,000	Nm³/h	—
4		Flue Gas Temperature	350-420	°C	—
5		Operating Flue Gas Volume	125,000	Nm³/h	—
6		Actual Oxygen Content	18	%	—
7		Reference Oxygen Content	11	%	—
8		Fan Power	160	kW	—
9		Wind Pressure	5,000	Pa	—
10		Duct Diameter	φ1,820	mm	—
11	Initial Concentration Parameters	Nitrogen Oxides	100	mg/Nm³	—
12		Sulfur Dioxide	5	mg/Nm³	—
13		Particulate Matter	2,000	mg/Nm³	—
14		Carbon Monoxide	100	mg/Nm³	—
15		Hydrogen Fluoride	5	mg/Nm³	—
16		Hydrogen Chloride	15	mg/Nm³	—
17		Temperature (Pre-Dedusting)	200	°C	—
18		Temperature (Pre-Denitrification)	350	°C	—
19		Humidity (At Denitrification Inlet)	4	%	—
20		Other Corrosive Substances & Concentration	30	mg/Nm³	Sodium Salt
21	Treatment Process	Desulfurization	—	—	—
22		Denitrification	SCR Denitrification	—	—
23		Dust Removal	Bag Filter Dust Collector	—	—
24	Emission Standard	Standard Reference	Integrated Emission Standard of Air Pollutants (GB 16297-1996)	—	—
25	Tiêu chuẩn khí thải	Nitrogen Oxides	50	mg/Nm³	—
26		Sulfur Dioxide	35	mg/Nm³	—
27		Particulate Matter	10	mg/Nm³	—
28		Carbon Monoxide	100	mg/Nm³	—
29		Hydrogen Fluoride	5	mg/Nm³	—
30		Hydrogen Chloride	15	mg/Nm³	—
31	Treatment Efficiency	Desulfurization Efficiency	—	%	—
32		Denitrification Efficiency	99.6	%	—
33		Dust Removal Efficiency	85.5	%	—

The baseline characterization reveals several distinctive emission control challenges specific to aluminum melting operations. The extremely high particulate matter concentration of 2,000 mg/Nm³ represents the dominant treatment challenge, reflecting the substantial dust generation from molten aluminum surface oxidation, flux additives, and charge materials. The relatively moderate NOx concentration of 100 mg/Nm³ requires efficient removal to achieve the stringent 50 mg/Nm³ regulatory limit. The low SO₂ concentration of 5 mg/Nm³ indicates that sulfur content in natural gas fuel and raw materials is minimal, allowing the treatment focus to concentrate on NOx and particulate control. The presence of hydrogen fluoride and hydrogen chloride at concentrations of 5 mg/Nm³ and 15 mg/Nm³ respectively introduces material compatibility considerations for downstream SCR catalyst systems, as halogen compounds can cause catalyst deactivation through chemical poisoning.

The elevated flue gas temperature of 350-420°C at the furnace outlet provides favorable conditions for medium-temperature SCR denitrification, as this temperature range falls within the optimal catalyst activity window. The low humidity content of 4% is advantageous for SCR operation, as excessive moisture can suppress catalytic activity and promote ammonium salt formation. The presence of sodium salt compounds at 30 mg/Nm³ represents a critical concern for catalyst longevity, as alkali metals are known to cause severe catalyst poisoning in SCR systems. These characteristics informed the selection of specialized catalyst formulations and protective measures designed to withstand the aggressive chemical environment of aluminum melting furnace exhaust.

3. Integrated Treatment Process Design

3.1 Process Flow & System Architecture

The treatment system was engineered to address the increasingly stringent environmental requirements for aluminum melting and casting operations. The high-precision aluminum melting furnace production line is equipped with 120-ton capacity furnace groups, comprising two melting furnaces and two holding furnaces, each with dedicated bag filter dust collectors. The flue gas from all units is collected and discharged through a single stack. The melting furnace combustion system utilizes natural gas fuel, with the exhaust gas containing significant NOx concentrations that require treatment to meet regulatory standards.

In accordance with environmental protection requirements, an SCR denitrification system was installed upstream of the air-cooling heat exchanger to achieve NOx emissions ≤ 50 mg/Nm³ (calculated at 12% oxygen content), ensuring hourly average emission compliance. The SCR system includes denitrification reactor systems, urea pyrolysis systems, urea preparation systems, urea storage systems, power supply systems, AICR intelligent control systems, and auxiliary subsystems. The process flow is illustrated in the following schematic:

The SCR system installation position was selected at the melting furnace outlet, upstream of the air cooler. This location maintains a temperature of 350-400°C, and the flue gas at this position contains no SO₂, enabling the use of medium-temperature denitrification catalysts. The SCR denitrification reactor catalyst is designed with a 3+1 layer configuration, with urea serving as the reducing agent. The overall pressure distribution of the SCR system is illustrated in the following figure, which demonstrates the uniform pressure profile achieved through optimized flow distribution design:

The process sequence initiates with flue gas extraction from the melting furnace at 350-420°C, which passes directly through the SCR denitrification reactor where NOx is reduced to nitrogen and water vapor through reaction with ammonia generated from urea pyrolysis. The deNOxed gas then enters the air-cooling heat exchanger, where the temperature is reduced to approximately 200°C to protect downstream bag filter media. The cooled gas passes through the bag filter dust collector, where particulate matter is captured with high efficiency. The cleaned gas is then discharged through the stack at conditions that ensure complete compliance with all regulatory parameters. This integrated approach exemplifies the synergistic control capabilities of advanced regenerative thermal oxidizer (RTO) and SCR technologies adapted for metallurgical applications.

3.2 Design Model & 3D Layout

The physical arrangement of treatment equipment was optimized through three-dimensional modeling to ensure efficient spatial utilization, adequate maintenance access, and logical process sequencing. The structural design accommodates the substantial equipment sizes required for handling 125,000 Nm³/h flue gas volumes while maintaining the vertical integration necessary for gravity-assisted material flow and equipment accessibility. The design model is illustrated in the following 3D rendering:

The structural configuration features the SCR denitrification reactor positioned immediately downstream of the melting furnace outlet to maximize the available temperature window for catalytic reaction. The urea pyrolysis and storage facilities are situated adjacent to the reactor for efficient reagent supply. The air-cooling heat exchanger is positioned between the SCR reactor and the bag filter to provide the necessary temperature reduction for filter media protection. The bag filter dust collector is elevated on a structural steel platform to facilitate dust discharge and maintenance access. All structural components were specified with high-temperature resistant materials and protective coatings suitable for the aggressive thermal and chemical environment, with foundation designs accounting for dynamic loads and seismic requirements for the facility location.

3.3 Process Requirements & Design Considerations

The design of the aluminum alloy flue gas purification system addressed several critical technical requirements specific to this application. The aluminum industry flue gas purification system is used to treat nitrogen oxides, dust, and other pollutants generated by melting furnaces. The following design considerations were systematically incorporated:

High Dust and Alkali Metal Content: The flue gas from melting furnaces and holding furnaces contains high dust concentrations, with dust particles carrying significant potassium and sodium salt content. This presents a critical challenge for denitrification catalyst selection, as alkali metals are known to cause severe catalyst poisoning that reduces catalyst life and activity. The design specifically addresses this challenge through careful catalyst formulation selection and the implementation of protective measures to mitigate alkali metal poisoning effects.

System Control Integration: The system incorporates soot blowing and temperature control, ammonia consumption control feedback to the control system, with automatic adjustment of equipment operation and process parameters based on monitored flue gas temperature. This integrated control approach ensures optimal catalyst performance while preventing thermal damage and maintaining emission compliance under variable operating conditions.

Urea System Automation: The urea preparation and urea pyrolysis systems provide real-time feedback to the control system, with interlocked valve and pump operation enabling one-button automatic startup functionality. This automation reduces operator workload while ensuring consistent reagent supply and preventing operational errors that could compromise denitrification performance.

These design considerations reflect the comprehensive engineering approach that characterizes modern RTO systems for DeSOx and related multi-pollutant control installations, where process optimization and automated control are essential for achieving consistent environmental performance in demanding industrial environments.

3.4 Equipment Selection & Sizing Calculations

Comprehensive equipment sizing calculations were performed to ensure that all system components are appropriately dimensioned for the design operating conditions while providing adequate capacity margins for variable load operation. The following detailed specification tables summarize the key parameters for the SCR catalyst system:

I. Geometric Parameters & Quantities

Category	Item	Unit	Value	Remarks
Điều kiện hoạt động	Operating Flue Gas Volume	m³/h	125,000	—
	Standard Flue Gas Volume	m³/h	55,000	—
	Flue Gas Temperature	°C	350	—
Element	Number of Holes	—	18	—
	Element Dimensions	mm×mm	150×150	Cross-section
	Element Height	mm	800	H
	Pitch	mm	8.2	—
	Inner Wall Thickness	mm	1	—
	Outer Wall Thickness	mm	1.7	—
	Element Volume	m³	0.018	—
	Element Effective Surface Area	m²	7.362	—
	Element Mass	kg	7.2	—
	Porosity	%	72.59	—
Catalyst Specific Surface Area	m²/m³	409	—
Catalyst Bulk Density	kg/m³	400	—
Module	Module Dimensions	mm×mm	1,910×970	L×W
	Module Height	mm	1,040	H
	Number of Catalyst Elements per Module	pcs	72	—
	Catalyst Volume per Module	m³	1.296	—
	Catalyst Specific Surface Area per Module	m²	530.064	—
	Catalyst Net Weight per Module	kg	518.4	—
	Module Total Weight	kg	799.2	Including module casing
Single Reactor	Initial Layer Count	Layers	3	Đã cài đặt
	Reserve Layer	Layers	1	—
	Catalyst Modules per Layer	pcs	5	—
	Module Arrangement per Layer	—	1×5	5
	Total Catalyst Volume	m³	19.44	—
	Total Catalyst Surface Area	m²	7,950.96	Effective
Total Catalyst Net Weight	kg	7,776	—

II. Catalyst Composition & Physical Properties

Category	Item	Unit	Value	Remarks
Geometric Parameters & Quantities	Catalyst Total Weight per Reactor	kg	11,988	Including module casing
	Reactor Cross-sectional Area	m²	1.9594	—
	Catalyst Flow Area	m²	1.85658	—
	Number of Reactors	pcs	1	—
	Total Catalyst Volume	m³	19.44	—
Total Catalyst Surface Area	m²	7,950.96	Effective
Total Catalyst Net Weight	kg	7,776	—
Total Catalyst Weight	kg	11,988	Including module casing
Unit Set	Number of Unit Sets	pcs	1	—
	Total Catalyst Volume	m³	19.44	—
	Total Catalyst Surface Area	m²	7,950.96	Effective
	Total Catalyst Net Weight	kg	7,776	—
Total Catalyst Weight	kg	11,988	Including module casing
Test Block	Test Block Type	—	Honeycomb	—
	Test Block Dimensions	mm×mm	150×150	L×W
	Test Block Height	mm	1,040	H
	Test Block Quantity per Layer	pcs	1	—
Catalyst Composition	Active Component Type	—	Vanadium, Tungsten	—
	Active Component Content	%	1-5	—
	Catalyst Carrier	—	TiO₂	—
	Carrier Content	%	80-85	—
	Design Temperature	°C	230	—
Nhiệt độ hoạt động	Maximum Operating Temperature	°C	350	—
	Minimum Operating Temperature	°C	200	—
	Allowable Heating Rate	°C/min	≤ 5 (≤ 70°C); ≤ 10 (70-120°C); ≤ 50 (120-420°C)	—
	Heat Capacity	kJ/(kg·°C)	0.8-0.9	—
Mechanical Properties	Axial Compressive Strength	MPa	≥ 2.5	—
	Radial Compressive Strength	MPa	≥ 0.8	—
	Wear Rate	%/kg	≤ 0.15	—
	Hardened End Length	mm	20	—
Thông số vận hành	Catalyst Channel Velocity	m/s	5.742420725	Operating, wet basis, actual oxygen
	Space Velocity	h⁻¹	2,817.658482	Standard, wet basis, actual oxygen
	Face Velocity	m/h	6,889.140544	Standard, wet basis, actual oxygen

III. Operating Parameters & Performance Guarantees

Category	Item	Unit	Value	Remarks
Thông số vận hành	Urea Consumption	kg/h	9.5	Urea (98%), 5% deviation
	Activity Coefficient	m/h	35-45 (Initial activity); 25-35 (24,000 h activity)	—
Performance Guarantees	Denitrification Efficiency	%	88	24,000 h
	SO₂/SO₃ Conversion Rate	%	≤ 1	24,000 h
	Trượt amoniac	ppm	≤ 6	24,000 h
	Giảm áp suất	Pa	≤ 600	24,000 h
	Catalyst Chemical Life	h	24,000	—
	Catalyst Mechanical Life	Một	10	—

The comprehensive catalyst specifications demonstrate the advanced engineering incorporated into this SCR system. The honeycomb-type catalyst with 18 holes per element and a specific surface area of 409 m²/m³ provides exceptional catalytic activity for NOx reduction. The vanadium-tungsten active components on a TiO₂ carrier represent the industry-standard formulation for medium-temperature SCR applications, offering optimal balance between activity and resistance to poisoning. The 3+1 layer configuration with one reserve layer provides operational flexibility for catalyst replacement or augmentation without system shutdown. The guaranteed denitrification efficiency of 88% at 24,000 hours, combined with the maximum pressure drop of 600 Pa, ensures sustained performance over the catalyst design life. These specifications reflect the rigorous design standards that characterize modern dust collector and emission control systems operating in demanding metallurgical environments.

3.5 As-Built Project Documentation

Following completion of construction and commissioning activities, comprehensive as-built documentation was prepared to record the actual installed configuration and verify conformance with design specifications. The as-built drawings provide an accurate record of the completed installation for future maintenance, modification, and regulatory compliance purposes. The following image presents the as-built documentation of the completed project:

The as-built documentation confirms that all major equipment was installed in accordance with design specifications, with the SCR denitrification reactor, urea pyrolysis system, air-cooling heat exchanger, and bag filter dust collector positioned as shown in the 3D design model. The urea storage and preparation facilities are fully operational, with the automated control system providing integrated management of all treatment stages. The completed installation demonstrates that medium-temperature SCR denitrification technology can be successfully implemented in high-temperature, high-dust aluminum melting environments while maintaining production continuity during the construction phase.

4. Operational Performance Analysis

4.1 Energy Consumption Analysis

The energy performance of the integrated treatment system was comprehensively monitored to verify compliance with design efficiency targets and quantify operating cost implications. The SCR system incorporates multiple energy-intensive components including urea dissolution agitators, urea storage tank heaters, urea pyrolysis heaters, and rake-type soot blowers. The following detailed energy consumption table presents the installed and actual operating power requirements for each equipment category:

KHÔNG.	Tên thiết bị	Single Unit Rated Power (kW)	Total Installed Units	Total Installed Power (kW)	Actual Operating Units	Actual Operating Power (kW)	Remarks
1	Urea Dissolution Agitator	3	1	3	1	3	—
2	Urea Storage Tank Heater	20	1	20	1	20	Full operation considered
3	Urea Pyrolysis Heater	160	1	160	1	120	—
4	Rake-Type Soot Blower	4.5	3	13.5	3	4.5	—
—	TOTAL	—	—	196.5	—	147.5	—

The total installed power capacity of 196.5 kW represents the maximum potential electrical demand, while the actual operating power of 147.5 kW reflects the optimized operating configuration. The urea pyrolysis heater constitutes the dominant energy consumer at 120 kW actual operating power, representing approximately 81% of total operating power. This substantial thermal energy requirement is necessary to decompose urea into ammonia at temperatures exceeding 350°C for effective NOx reduction. The rake-type soot blowers, while representing a modest power draw at 4.5 kW, provide the critical function of maintaining catalyst surface cleanliness to prevent dust accumulation and preserve catalytic activity. The energy analysis confirms that the system operates within design efficiency targets, with the actual operating power representing approximately 75% of installed capacity, indicating appropriate equipment sizing with adequate operational margins.

The project operates at a maximum actual load of 196.5 kW with 24-hour daily operation. At an average electricity rate of 0.36 RMB/(kW·h), the daily electricity cost is 1,697.76 RMB, resulting in an annual electricity expense of 565,920 RMB based on 8,000 operating hours per year. Water consumption is primarily for urea dissolution, with a water usage rate of approximately 40 kg/h. At a water rate of 2 RMB/t, the daily water cost is 1.92 RMB, yielding an annual water expense of 640 RMB at 8,000 operating hours. Urea consumption is 7.2 kg/h at a unit price of 1,100 RMB/t, generating a daily cost of 190.08 RMB and an annual expense of 63,360 RMB at 8,000 operating hours. These operating costs are consistent with the economic projections for medium-temperature SCR installations and are substantially offset by the avoided regulatory penalties and operational license security benefits.

4.2 Compliance Emission Data

Following system commissioning and stabilization, comprehensive emission monitoring was conducted to verify compliance with all design guarantees and regulatory requirements. The monitoring protocol employed continuous emissions monitoring systems (CEMS) for primary parameters supplemented with periodic stack testing for verification. The following detailed compliance data table presents the achieved emission performance across all regulated parameters:

KHÔNG.	Category	Parameter Name	Value	Unit
1	Treatment Process	Desulfurization	—	—
2		Denitrification	SCR Denitrification	—
3		Dust Removal	Bag Filter Dust Collector	—
4	Emission Standard	Standard Reference	Integrated Emission Standard of Air Pollutants (GB 16297-1996)	—
5	Tiêu chuẩn khí thải	Nitrogen Oxides	50	mg/m³
6		Sulfur Dioxide	35	mg/m³
7		Particulate Matter	10	mg/m³
8		Carbon Monoxide	100	mg/m³
9		Hydrogen Fluoride	5	mg/m³
10		Hydrogen Chloride	15	mg/m³
11	Treatment Efficiency	Desulfurization Efficiency	—	%
12		Denitrification Efficiency	90	%
13		Dust Removal Efficiency	99.8	%
14	Post-Treatment Actual Emission Data	Nitrogen Oxides	25	mg/m³
15		Sulfur Dioxide	2	mg/m³
16		Particulate Matter	4	mg/m³
17		Carbon Monoxide	100	mg/m³
18		Hydrogen Fluoride	5	mg/m³
19		Hydrogen Chloride	15	mg/m³
20		Post-Treatment Efficiency	—	%
21	Post-Treatment Efficiency Analysis	Desulfurization Efficiency	—	%
22		Denitrification Efficiency	95	%
23		Dust Removal Efficiency	99.8	%

The operational data demonstrates exceptional achievement of ultra-low emission targets across all measured parameters. The denitrification efficiency of 95% achieved an actual NOx outlet concentration of 25 mg/m³, substantially below the regulatory limit of 50 mg/m³ and representing a remarkable 75% reduction from the inlet concentration of 100 mg/m³. The particulate matter was reduced to 4 mg/m³, achieving 99.8% removal efficiency and comfortably meeting the 10 mg/m³ standard. The SO₂ concentration was reduced to 2 mg/m³, well below the 35 mg/m³ regulatory threshold. The halogen compounds remained within regulatory limits, with HF at 5 mg/m³ and HCl at 15 mg/m³, both at their respective standard boundaries. These results confirm that the medium-temperature SCR denitrification system, combined with bag filter dust removal, can achieve exceptional multi-pollutant control performance even in the challenging high-dust environment of aluminum melting operations.

4.3 Operating Diagram & Control System

The intelligent control system provides comprehensive monitoring and automated management of all treatment processes through a centralized human-machine interface (HMI). The operating diagram illustrates the real-time status of all major equipment, process parameters, and alarm conditions, enabling operators to maintain optimal system performance with minimal manual intervention. The following image presents the operating diagram of the flue gas treatment system:

The control interface displays real-time data for all critical process parameters including flue gas flow rates, temperatures at key locations, NOx concentrations at inlet and outlet, urea injection rates, and equipment operating status. The system incorporates automatic control loops for urea pyrolysis temperature regulation, ammonia injection rate optimization, and catalyst soot blowing scheduling, with alarm provisions for out-of-range conditions and equipment malfunctions. The AICR intelligent control system enables remote monitoring and diagnostics, facilitating proactive maintenance and minimizing unplanned downtime. This level of automation is characteristic of modern chất oxy hóa nhiệt tái sinh and SCR systems operating at industrial scale, where consistent performance and regulatory compliance depend on precise process control.

4.4 Operational Risk Analysis

A comprehensive operational risk assessment was conducted to identify potential failure modes and develop mitigation strategies for sustained compliance and system reliability. The primary risks identified include:

Primary Risk 1: Flue Gas Temperature and NOx Concentration Fluctuation — Variations in melting furnace operating conditions can cause significant fluctuations in flue gas temperature and NOx concentration, potentially compromising system emission stability. The mitigation strategy involves maintaining close communication between the furnace control room and the flue gas treatment system, with advance notification of operating condition changes to enable proactive adjustment of treatment parameters.

Primary Risk 2: High Dust Content Causing Catalyst Plugging — The high particulate matter content in the flue gas can lead to catalyst surface dust accumulation and channel blockage, reducing catalyst efficiency and increasing pressure drop. The mitigation strategy involves enhanced personnel patrols and inspection routines, maintaining equipment in normal operating condition, and implementing regular catalyst cleaning procedures to prevent excessive dust buildup.

Additional Mitigation Measures: Continuous improvement of operator safety awareness and operational skills, regular revision of safety measures and emergency response plans, and ensuring effective emergency response capabilities. These comprehensive risk management practices ensure that the system maintains reliable performance under all anticipated operating scenarios.

5. Experience Summary & Operational Insights

This project was built upon existing process foundations, fully leveraging available process conditions, conducting in-depth research into the flue gas composition and operating conditions of this industry. For the first time, a medium-temperature, high-dust SCR denitrification technology solution was proposed and successfully implemented, achieving ultra-low pollutant emissions in the flue gas and meeting requirements below the emission standard limits. The core of this technology lies in continuously debugging and optimizing based on variations in nitrogen oxide concentration in the flue gas, ultimately achieving the ultra-low emission target. Furthermore, this technology successfully resolved the catalyst alkali metal poisoning problem that had previously constrained SCR application in aluminum melting environments.

5.1 As-Built Project Images

The following images present the completed project installation, documenting the actual field implementation of the SCR denitrification system, bag filter dust collector, and associated infrastructure. These images provide visual verification of the system’s physical configuration and integration with the existing aluminum melting facility.

5.2 Operating Images

The operating images demonstrate the real-time control interface and system performance during normal operation, confirming that all treatment processes are functioning within design parameters and achieving the targeted emission reduction performance.

5.3 Key Technical Breakthroughs

The successful implementation of this project represents several significant technical achievements that advance the state of the art in aluminum industry emission control:

First Application of Medium-Temperature SCR in Aluminum Melting: This project marks the first successful application of medium-temperature SCR denitrification technology in the aluminum melting and casting industry. The high-temperature, high-dust environment of aluminum melting furnaces had previously been considered unsuitable for SCR technology due to concerns about catalyst poisoning and dust plugging. This project demonstrated that with appropriate catalyst selection, protective measures, and operational protocols, SCR can achieve exceptional performance in this challenging application.

Resolution of Alkali Metal Poisoning: The presence of potassium and sodium salts in aluminum melting flue gas had historically caused rapid catalyst deactivation in SCR systems. This project successfully addressed this challenge through specialized catalyst formulation and operational strategies that minimize alkali metal contact with active catalytic sites. The achieved catalyst life of 24,000 hours confirms that the poisoning mitigation measures are effective and sustainable.

Integrated Multi-Pollutant Control: The system achieves simultaneous control of NOx, particulate matter, and acid gas compounds through the integrated combination of SCR denitrification and bag filter dust removal. This synergistic approach ensures that all regulated pollutants are controlled to levels well below regulatory limits, providing comprehensive environmental protection rather than single-pollutant focus.

6. Conclusions & Industry Implications

This case study demonstrates that medium-temperature SCR denitrification technology, when properly adapted and optimized, can reliably achieve ultra-low NOx emission standards for aluminum melting and casting operations while simultaneously providing exceptional particulate matter control. The key technical insights from this implementation include the critical importance of catalyst selection for resistance to alkali metal poisoning, the effectiveness of medium-temperature operation for avoiding thermal degradation while maintaining catalytic activity, and the synergistic benefits of integrating SCR with bag filter dust removal for comprehensive multi-pollutant control.

For facilities contemplating similar emission control upgrades, several recommendations emerge from this experience. First, comprehensive characterization of flue gas composition, including alkali metal content and dust characteristics, is essential for appropriate catalyst selection and protective measure design. Second, the medium-temperature operating window (350-400°C) provides optimal balance between catalytic activity and thermal stability, avoiding the high-temperature degradation risks of high-temperature SCR while maintaining sufficient activity for efficient NOx reduction. Third, the 3+1 layer catalyst configuration with reserve capacity provides operational flexibility for catalyst replacement or augmentation without production interruption. Finally, integrated control of urea pyrolysis, ammonia injection, and catalyst soot blowing is essential for maintaining consistent performance under variable operating conditions.

As environmental regulations continue to tighten globally and the aluminum industry faces increasing pressure to reduce its environmental footprint, the technologies and design approaches validated in this project will become increasingly relevant across the non-ferrous metallurgical sector. The successful integration of medium-temperature SCR denitrification and bag filter dust removal within a single, optimized treatment train provides a replicable model for facilities facing similar high-temperature, high-dust emission challenges. The demonstrated performance confirms that advanced NOx gas treatment solutions and related SCR technologies represent mature, reliable solutions capable of meeting the most stringent contemporary emission requirements, even in applications previously considered unsuitable for catalytic treatment.