{"id":3106,"date":"2026-06-16T09:16:27","date_gmt":"2026-06-16T09:16:27","guid":{"rendered":"https:\/\/regenerative-thermal-oxidation.com\/?p=3106"},"modified":"2026-06-16T09:16:27","modified_gmt":"2026-06-16T09:16:27","slug":"ionic-liquid-desulfurization-scr-denitrification-and-electrostatic-precipitation-for-solid-waste-resource-recovery","status":"publish","type":"post","link":"https:\/\/regenerative-thermal-oxidation.com\/hi\/%e0%a4%86%e0%a4%b5%e0%a5%87%e0%a4%a6%e0%a4%a8\/ionic-liquid-desulfurization-scr-denitrification-and-electrostatic-precipitation-for-solid-waste-resource-recovery\/","title":{"rendered":"Ionic Liquid Desulfurization, SCR Denitrification, and Electrostatic Precipitation for Solid Waste Resource Recovery"},"content":{"rendered":"

<\/p>\n

<\/p>\n
\n

Case Study \u00b7 Industrial Emission Control<\/p>\n

How a leading specialist lead recycling and aluminium alloy manufacturer achieved 97% SCR denitrification efficiency, SO\u2082 outlet at 35\u00a0mg\/Nm\u00b3, and PM outlet at 10\u00a0mg\/Nm\u00b3 from two oxidation furnaces \u2014 deploying an innovative ESP\u00a0+ heat exchanger\u00a0+ bag filter\u00a0+ ionic liquid desulfurization\u00a0+ wet ESP process chain with low-temperature ceramic tile heat recovery to minimise operating cost.<\/p>\n

Lead-Acid Battery Recycling Off-Gas<\/span>
\nIonic Liquid Desulfurization<\/span>
\nLow-Temperature SCR Denitrification<\/span>
\n\u0917\u0940\u0932\u093e \u0907\u0932\u0947\u0915\u094d\u091f\u094d\u0930\u094b\u0938\u094d\u091f\u0948\u091f\u093f\u0915 \u092a\u094d\u0930\u0947\u0938\u093f\u092a\u093f\u091f\u0947\u091f\u0930<\/span>
\nCeramic Tile Heat Exchanger<\/span><\/div>\n<\/header>\n

<\/p>\n

\n
\n
97%<\/div>\n
\u090f\u0938\u0938\u0940\u0906\u0930 \u0921\u0940\u0928\u093e\u0907\u091f\u094d\u0930\u093f\u092b\u093f\u0915\u0947\u0936\u0928<\/div>\n
NOx outlet \u226450 mg\/Nm\u00b3<\/div>\n<\/div>\n
\n
\u226435<\/div>\n
mg\/Nm\u00b3 SO\u2082 outlet<\/div>\n
Ionic Liquid FGD<\/div>\n<\/div>\n
\n
\u226410<\/div>\n
mg\/Nm\u00b3 PM outlet<\/div>\n
ESP + Bag Filter + Wet ESP<\/div>\n<\/div>\n
\n
40,000<\/div>\n
\u092e\u0940\u00b3\/\u0918\u0902\u091f\u093e<\/div>\n
Total Process Flue Gas<\/div>\n<\/div>\n<\/div>\n

<\/p>\n

\n

01 \u2014 Industry Background<\/p>\n

Solid Waste Resource Recovery: Lead-Acid Battery Recycling and the Case for Ionic Liquid Desulfurization<\/h2>\n

Solid waste resource utilization sits at the intersection of circular economy policy and industrial emission control. The recovery and re-smelting of lead from spent lead-acid batteries is one of the most economically significant and technically challenging sectors within the solid waste resource recovery industry. Spent lead-acid batteries contain residual sulfuric acid electrolyte, lead sulfate paste, and metallic lead plates that, when processed in oxidation furnaces, generate off-gas carrying high concentrations of SO\u2082 (from the sulfate and acid compounds), NOx (from high-temperature combustion air reactions), fine lead-bearing particulates, and other acid gas species. These pollutants must all be controlled to stringent limits before the off-gas is discharged.<\/p>\n

The enterprise in this case study is a leading specialist company in the lead recycling and re-smelting sector, with principal operations encompassing spent lead-acid battery recovery, re-smelting to produce recycled lead, and aluminium alloy manufacture. With an annual processing capacity of approximately 200,000\u00a0t of spent batteries and annual production of recycled lead and aluminium alloy at around 100,000\u00a0t, it ranks among the leading enterprises in the secondary lead recovery industry. The facility operates two oxidation furnaces (oxidation-reduction furnace), generating a combined total flue gas volume of 40,000\u00a0m\u00b3\/h at 180\u00b0C.<\/p>\n

The defining feature of oxidation furnace off-gas from lead recycling is the combination of high SO\u2082 concentration (600\u20131,500\u00a0mg\/Nm\u00b3), high NOx (600\u20131,500\u00a0mg\/Nm\u00b3), high oxygen content (8\u201316%), and high PM loading \u2014 all simultaneously in a corrosive gas environment carrying lead particulates and acid mist. The conventional wet scrubbing and limestone FGD approaches used in power plant and steel industry applications face significant challenges in this environment because the ionic liquid chemistry of lead recycling off-gas creates conditions that impair standard sorbent performance and generate complex liquid effluents. This project deploys ionic liquid desulfurization \u2014 a technology specifically selected for this application\u2019s chemistry \u2014 combined with SCR and a multi-stage electrostatic and bag filter dust removal chain.<\/p>\n

\"Application<\/p>\n

\n
<\/div>\n

\u201cThe key engineering decision in this project was to position the ionic liquid desulfurization stage downstream of a comprehensive ESP and bag filter dust removal pre-treatment chain \u2014 deeply reducing the particulate load before the gas contacts the ionic liquid absorbent. This upstream dust management protects the ionic liquid recirculation service conditions, reduces catalyst blockage risk in the SCR stage, and significantly lowers the overall system operating cost through the use of low-temperature ceramic tile heat exchanger waste heat recovery.\u201d<\/p>\n

\u2014 Engineering Experience Summary, Solid Waste Resource Utilization Industry Dust Removal \/ Desulfurization \/ Denitrification Project<\/cite><\/p><\/blockquote>\n<\/section>\n

\n

<\/p>\n

\n

02 \u2014 Pollution Profile<\/p>\n

Oxidation Furnace Off-Gas: High SO\u2082, High NOx, High PM and High O\u2082 in a Corrosive Lead-Bearing Gas Stream<\/h2>\n

The two oxidation furnaces together generate 40,000\u00a0m\u00b3\/h of process flue gas at 180\u00b0C. Oxygen content is high at 8\u201316%, which is characteristic of oxidation furnace off-gas and has implications for both desulfurization chemistry (favoring SO\u2082 oxidation to SO\u2083 in wet scrubbers) and for SCR catalyst design (requiring oxygen-tolerant catalyst formulations). The high O\u2082 content also means that the desulfurization inlet temperature control and the SCR inlet temperature management must account for the oxidative environment at elevated temperatures.<\/p>\n

The pollutant profile requires treatment of five simultaneous parameters: NOx at 600\u20131,500\u00a0mg\/Nm\u00b3, SO\u2082 at 600\u20131,500\u00a0mg\/Nm\u00b3, PM at 10\u00a0mg\/Nm\u00b3 at the desulfurization inlet (after pre-treatment), NOx at the SCR denitrification inlet at 10\u00a0mg\/Nm\u00b3 after the denitrification pre-treatment, and NOx at the oxidation furnace exit entering the SCR in the range of 600\u20131,500\u00a0mg\/Nm\u00b3. All limits must be achieved simultaneously at the stack.<\/p>\n

\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
\u092a\u0948\u0930\u093e\u092e\u0940\u091f\u0930<\/th>\nInlet (Raw Gas)<\/th>\nDesigned Outlet<\/th>\nActual Outlet<\/th>\nEU IED \/ NER Limit<\/th>\n<\/tr>\n<\/thead>\n
\u090f\u0928\u0913\u090f\u0915\u094d\u0938<\/td>\n600\u20131,500 mg\/Nm\u00b3<\/td>\n\u226450 \u092e\u093f\u0932\u0940\u0917\u094d\u0930\u093e\u092e\/\u090f\u0928.\u092e\u0940\u00b3<\/td>\n50 mg\/Nm\u00b3<\/td>\nIED 2010\/75\/EU \u2264200\u00a0mg\/Nm\u00b3<\/td>\n<\/tr>\n
SO\u2082<\/td>\n600\u20131,500 mg\/Nm\u00b3<\/td>\n\u226435 mg\/Nm\u00b3<\/td>\n35 mg\/Nm\u00b3<\/td>\nDutch Activities Decree NER<\/td>\n<\/tr>\n
PM (at desulfurization inlet)<\/td>\n10 mg\/Nm\u00b3 (after pre-treatment)<\/td>\n\u226410 mg\/Nm\u00b3<\/td>\n10 mg\/Nm\u00b3<\/td>\nIED 2010\/75\/EU \u22645\u00a0mg\/Nm\u00b3<\/td>\n<\/tr>\n
\u090f\u091a\u090f\u092b<\/td>\n\u2014<\/td>\n\u226450 \u092e\u093f\u0932\u0940\u0917\u094d\u0930\u093e\u092e\/\u090f\u0928.\u092e\u0940\u00b3<\/td>\n\u226450 \u092e\u093f\u0932\u0940\u0917\u094d\u0930\u093e\u092e\/\u090f\u0928.\u092e\u0940\u00b3<\/td>\nIED BAT<\/td>\n<\/tr>\n
Ammonia slip (NH\u2083)<\/td>\n\u2014<\/td>\n\u22645 ppm<\/td>\n3 ppm<\/td>\nPermit condition<\/td>\n<\/tr>\n
Oxygen content (O\u2082)<\/td>\n8\u201316%<\/td>\n\u2014<\/td>\n\u2014<\/td>\n\u2014<\/td>\n<\/tr>\n
Process flue gas volume<\/td>\n40,000 m\u00b3\/h (2 furnaces combined)<\/td>\n\u2014<\/td>\n\u2014<\/td>\n\u2014<\/td>\n<\/tr>\n
Flue gas temperature (furnace exit)<\/td>\n180\u00b0C<\/td>\n\u2014<\/td>\n\u2014<\/td>\n\u2014<\/td>\n<\/tr>\n
Desulfurization inlet temperature<\/td>\n180\u00b0C (entering system)<\/td>\n\u2014<\/td>\n\u2014<\/td>\n\u2014<\/td>\n<\/tr>\n
SCR denitrification inlet temperature<\/td>\n180\u2013220\u00b0C (after heat exchange reheating)<\/td>\n\u2014<\/td>\n\u2014<\/td>\n\u2014<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/section>\n
\n

<\/p>\n

\n

03 \u2014 Treatment Solution<\/p>\n

Five-Stage Process: Dry ESP \u2192 Heat Exchange \u2192 Bag Filter \u2192 Ionic Liquid FGD \u2192 SCR \u2192 Wet ESP<\/h2>\n

The treatment system is built on the existing oxidation furnace infrastructure, adding a newly constructed SCR denitrification system to the existing ESP + ionic liquid desulfurization + wet ESP equipment combination. The fundamental design insight is that the ionic liquid desulfurization stage requires a deeply pre-cleaned gas stream to function effectively: dust particles in the gas stream absorb and deactivate the ionic liquid absorbent, reducing its capacity for SO\u2082 capture over time. By placing a comprehensive dry ESP + heat exchanger + bag filter pre-treatment chain upstream of the ionic liquid stage, the gas entering the ionic liquid absorber is reduced to \u226410\u00a0mg\/Nm\u00b3 PM \u2014 a level at which the ionic liquid service conditions are adequate and the recirculation lifetime is acceptable.<\/p>\n

The second key design decision is the positioning of the SCR reactor downstream of the ionic liquid desulfurization stage. This cold-side SCR configuration is necessary because the ionic liquid desulfurization reduces SO\u2082 to very low levels before the gas contacts the SCR catalyst, eliminating the risk of ammonium bisulfate deposition on the catalyst that would occur at low temperatures in high-SO\u2082 gas. By placing the SCR after the ionic liquid FGD, the catalyst operates in a substantially SO\u2082-free environment at 180\u2013220\u00b0C, enabling the low-temperature SCR catalyst to deliver the target 97% denitrification efficiency without the SO\u2082 poisoning that would occur in a hot-side position upstream of the FGD.<\/p>\n

Stage 1: Dry Electrostatic Precipitator (ESP) \u2014 Coarse Particulate Pre-Removal<\/h3>\n

Oxidation furnace off-gas at 180\u00b0C first passes through the existing dry electrostatic precipitator (ESP), which removes the bulk of the coarse lead-bearing particulates from the gas stream. This stage protects the downstream heat exchanger from abrasive dust erosion and reduces the PM loading to a level manageable by the heat exchanger and bag filter stages. The ESP operates at high voltage under the corrosive high-O\u2082 conditions of oxidation furnace off-gas and must be specified with corrosion-resistant electrode materials.<\/p>\n

Stage 2: Ceramic Tile Heat Exchanger (220\u00b0C \u2192 40\u00b0C, then 40\u00b0C \u2192 130\u00b0C)<\/h3>\n

The pre-dedusted gas passes through the low-temperature ceramic tile heat exchanger (model HB-565; flue gas volume 40,000\u00a0m\u00b3\/h each side; hot side inlet 220\u00b0C, outlet approximately 128\u00b0C; cold side inlet 40\u00b0C, outlet approximately 130\u00b0C; heat exchange area approximately 563\u00a0m\u00b2; heat load approximately 1,344\u00a0kW; design pressure 5\u00a0kPa; body material S31603 stainless steel at 0.7\u00a0mm wall thickness; pipe flange material S30408; dimensions approximately 3,300\u00d72,200\u00d72,700\u00a0mm). The hot gas pre-cools before entering the bag filter, while the cool post-FGD gas is reheated before entering the SCR reactor. This waste heat recovery loop eliminates the need for external gas heating for the SCR, converting what would otherwise be a significant energy cost into a self-contained heat recovery system using the facility\u2019s own waste gas thermal energy.<\/p>\n

Stage 3: Bag Filter \u2014 Fine Particulate Polishing<\/h3>\n

After heat exchange cooling, the gas enters the bag filter for fine particulate removal. The bag filter reduces PM to \u226410\u00a0mg\/Nm\u00b3 \u2014 the key threshold for ionic liquid desulfurization viability. The PM at the desulfurization stage inlet is reported as 10\u00a0mg\/Nm\u00b3, confirming the bag filter is achieving the target pre-treatment level. The bag filter also provides a secondary capture for any lead-bearing particulates that passed through the ESP stage, ensuring the ionic liquid stage is not exposed to the heavy-metal-bearing dust that would progressively contaminate the ionic liquid absorbent.<\/p>\n

\"Ionic<\/p>\n

Stage 4: Ionic Liquid Desulfurization<\/h3>\n

The pre-cleaned gas at approximately 40\u00b0C (cooled by the heat exchanger) enters the ionic liquid desulfurization system. Ionic liquid desulfurization uses a specially formulated ionic liquid absorbent that selectively captures SO\u2082 from the gas stream through physical absorption. The key advantages over conventional limestone-gypsum FGD for this application are: (1) no solid waste generation \u2014 the SO\u2082-loaded ionic liquid is regenerated and recycled, producing concentrated SO\u2082 that can be used to manufacture sulfuric acid rather than generating gypsum requiring disposal; (2) no wastewater generation from the FGD process itself; (3) the SO\u2082 captured can be reconcentrated and sold as a by-product or processed into sulfuric acid, turning a compliance cost into a revenue item; (4) lower reagent consumption since the ionic liquid is recirculated and regenerated rather than consumed stoichiometrically. The desulfurization outlet concentration is \u226435\u00a0mg\/Nm\u00b3 as designed, with actual measured values confirming compliance. The key operational control is pH management of the ionic liquid circulation loop: monitoring the liquid pH and controlling HF (from the oxidation furnace off-gas) and SO\u2082 loading in the ionic liquid to maintain absorption efficiency and prevent precipitate formation that would block the circulation system.<\/p>\n

Stage 5: SCR Denitrification (180\u2013220\u00b0C Low-Temperature)<\/h3>\n

After ionic liquid desulfurization, the clean gas (low SO\u2082, low PM) is reheated from approximately 40\u00b0C to 180\u2013220\u00b0C by the ceramic tile heat exchanger using the incoming hot raw gas waste heat. The reheated gas enters the low-temperature SCR denitrification reactor. The SCR system achieves 97% NOx reduction. Key catalyst parameters: catalyst holes 30; element size 150\u00d7150\u00a0mm (cross-section), 580\u00a0mm height; pitch 4.93\u00a0mm; hole spacing 4.23\u00a0mm; wall thickness 0.70\u00a0mm; porosity 70.1%; catalyst specific surface area 678\u00a0m\u00b2\/m\u00b3; active component V\u2082O\u2085 on TiO\u2082 carrier (75\u201385% carrier content); design temperature 220\u00b0C; maximum operating temperature 420\u00b0C; minimum operating temperature 220\u00b0C; single-layer pressure drop \u2264135\u00a0Pa (clean catalyst); chemical life: 24,000\u00a0h from first gas contact; denitrification efficiency \u226596.66% at 16,000\u00a0h; SCR inlet catalyst channel velocity 4.33\u00a0m\/s; theoretical urea consumption 20.38\u00a0kg\/h; volume space velocity 2,661\u00a0h\u207b\u00b9. The SCR system is mounted downstream of the ionic liquid stage, exploiting the SO\u2082-free gas condition to enable low-temperature operation without ammonium sulfate catalyst poisoning. Ammonia water is used as the reducing agent at 0.02\u00a0t\/h; ammonia slip guarantee \u22645\u00a0ppm (actual: 3\u00a0ppm).<\/p>\n

Stage 6: Wet Electrostatic Precipitator (WESP) \u2014 Final Polishing<\/h3>\n

The post-SCR gas enters the wet electrostatic precipitator for final acid mist and fine particulate polishing before stack discharge. The WESP captures any residual acid aerosol and sub-micron particles not removed by the earlier treatment stages, ensuring the PM outlet target of \u226410\u00a0mg\/Nm\u00b3 is met with adequate compliance margin.<\/p>\n

\n
\n
2\u00d7 Oxidation
\nFurnaces
\n180\u00b0C<\/div>\n
\u2192<\/div>\n
Dry ESP
\n(existing)<\/div>\n
\u2192<\/div>\n
Ceramic Tile \u2b50
\nHX Pre-Cool
\n\u219240\u00b0C<\/div>\n
\u2192<\/div>\n
Bag Filter
\n(existing)<\/div>\n
\u2192<\/div>\n
Ionic Liquid
\nFGD (existing)<\/div>\n
\u2192<\/div>\n
HX Reheat \u2b50
\n\u2192180\u2013220\u00b0C<\/div>\n
\u2192<\/div>\n
SCR \u2b50
\n97% NOx<\/div>\n
\u2192<\/div>\n
Wet ESP
\n(existing)<\/div>\n
\u2192<\/div>\n
IDF
\n\u2192 Stack<\/div>\n<\/div>\n<\/div>\n

\u2b50 New equipment added in this upgrade project<\/p>\n

Key Equipment Parameters<\/h3>\n
\n\n\n\n\n\n\n\n\n\n\n\n\n\n
Item<\/th>\n\u0935\u093f\u0928\u093f\u0930\u094d\u0926\u0947\u0936<\/th>\n<\/tr>\n<\/thead>\n
Ceramic tile heat exchanger<\/td>\nModel HB-565; 40,000 m\u00b3\/h; hot side 220\u2192128\u00b0C; cold side 40\u2192130\u00b0C; 563 m\u00b2; 1,344 kW; S31603 body<\/td>\n<\/tr>\n
SCR catalyst element<\/td>\n150\u00d7150 mm cross-section; 580 mm H; pore 30; porosity 70.1%; V\u2082O\u2085\/TiO\u2082; 220\u00b0C design; 24,000 h life<\/td>\n<\/tr>\n
SCR denitrification efficiency<\/td>\n97% actual; \u226596.66% guaranteed at 16,000 h; \u2264135 Pa single-layer pressure drop<\/td>\n<\/tr>\n
Ammonia water (reductant)<\/td>\n0.02 t\/h; ammonia slip guarantee \u22645 ppm; actual 3 ppm<\/td>\n<\/tr>\n
Main induced draft fan<\/td>\n110 kW; 1 unit (operating)<\/td>\n<\/tr>\n
Total installed power<\/td>\n124.5 kW installed; 123 kW actual running<\/td>\n<\/tr>\n
Annual electricity cost (8,000 h)<\/td>\nApprox. 39.36 ten-thousand RMB equivalent (0.4 RMB\/kWh)<\/td>\n<\/tr>\n
Annual natural gas cost (SCR heating)<\/td>\n75 m\u00b3\/h; approx. 192 ten-thousand RMB\/year (3.2 RMB\/m\u00b3)<\/td>\n<\/tr>\n
Annual ammonia water cost<\/td>\nApprox. 8 ten-thousand RMB\/year (0.02 t\/h, 500 RMB\/t)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

\"Vertical<\/p>\n<\/section>\n

\n

<\/p>\n

\n

04 \u2014 Core Advantages<\/p>\n

Six Reasons Why This Process Architecture Is Optimal for Lead Recycling Oxidation Furnace Off-Gas<\/h2>\n
    \n
  • \u2713<\/span>
    \nDeep Upstream Dust Removal Protects the Ionic Liquid and the SCR Catalyst Simultaneously:<\/strong> The fundamental architectural decision in this project is to treat the PM problem thoroughly before the gas contacts either the ionic liquid absorbent or the SCR catalyst. The combined dry ESP + heat exchanger + bag filter chain reduces PM from the raw furnace exit level to \u226410\u00a0mg\/Nm\u00b3 before the ionic liquid stage and to an even lower level before the SCR stage. This deep pre-dedusting serves two purposes: it maintains the ionic liquid recirculation service conditions by preventing particulate contamination of the absorbent, and it protects the SCR catalyst from the accelerated blockage and chemical poisoning that would result from exposure to lead-bearing dust at elevated concentrations. Both benefits contribute directly to system longevity and reduced maintenance frequency.<\/li>\n
  • \u2713<\/span>
    \nCold-Side SCR After Ionic Liquid FGD Eliminates Ammonium Bisulfate Catalyst Poisoning:<\/strong> Low-temperature SCR at 180\u2013220\u00b0C is susceptible to ammonium bisulfate (ABS) deposition when SO\u2082 is present at the catalyst surface, because ABS formation rate is highest at 180\u2013280\u00b0C. By positioning the SCR downstream of the ionic liquid desulfurization stage, the SO\u2082 concentration at the SCR inlet is reduced from 600\u20131,500\u00a0mg\/Nm\u00b3 to approximately 35\u00a0mg\/Nm\u00b3 or below. At this low SO\u2082 concentration, the ABS formation rate is dramatically reduced, enabling the low-temperature SCR catalyst to deliver the 97% denitrification efficiency without the progressive catalyst deactivation from ABS fouling that would occur in a hot-side SCR position upstream of the FGD.<\/li>\n
  • \u2713<\/span>
    \nCeramic Tile Heat Exchanger Waste Heat Recovery Eliminates External SCR Reheating Cost:<\/strong> The SCR requires its inlet gas to be at 180\u2013220\u00b0C for effective catalytic reaction. The post-ionic-liquid-FGD gas exits at approximately 40\u00b0C. Without heat recovery, this would require heating 40,000\u00a0m\u00b3\/h of gas from 40\u00b0C to 180\u00b0C \u2014 an energy cost equivalent to approximately 75\u00a0m\u00b3\/h of natural gas. The ceramic tile heat exchanger recovers this energy from the incoming hot raw gas (which must be cooled for the bag filter and ionic liquid stages anyway), converting a coincident energy surplus into the reheating duty at zero incremental fuel cost. The 75\u00a0m\u00b3\/h natural gas consumption is needed to top up the heat exchanger to maintain the SCR inlet temperature, but this is far less than would be required without the heat recovery system.<\/li>\n
  • \u2713<\/span>
    \nIonic Liquid Desulfurization Generates No Gypsum Waste and Enables SO\u2082 by-Product Recovery:<\/strong> Unlike limestone-gypsum FGD (which generates gypsum as a solid by-product requiring handling and disposal or sale), ionic liquid desulfurization regenerates the absorbent and concentrates the captured SO\u2082 as a recoverable product stream. In the lead recycling industry context, the recovered concentrated SO\u2082 can be processed into sulfuric acid for reuse in battery manufacturing or industrial chemical production, creating a circular economy loop that turns a compliance cost into a revenue-generating by-product. The absence of gypsum also eliminates the dewatering, storage, and logistics infrastructure that wet FGD requires.<\/li>\n
  • \u2713<\/span>
    \nUpgrade of Existing Infrastructure Minimises Capital Cost and Site Disruption:<\/strong> The project adds the ceramic tile heat exchanger and the SCR denitrification system to the facility\u2019s existing ESP, bag filter, ionic liquid desulfurization, and wet ESP equipment combination. By building on the existing infrastructure rather than designing a complete new treatment system, the capital cost of the upgrade is limited to the new components only (heat exchanger and SCR reactor), while the compliance benefit covers all regulated parameters. This approach is directly applicable to any facility where conventional emission control equipment is already in place but NOx compliance cannot be achieved without an additional denitrification stage.<\/li>\n
  • \u2713<\/span>
    \n24,000-Hour SCR Catalyst Chemical Life Covers Three Years of Continuous Operation:<\/strong> The SCR catalyst chemical life guarantee of 24,000 hours from first gas contact, combined with the 16,000-hour \u226596.66% efficiency guarantee, means the catalyst can operate for approximately 3 years of 8,000-h\/year operation before chemical life is reached. The V\u2082O\u2085\/TiO\u2082 low-temperature catalyst formulation used in this installation is specifically designed for the SO\u2082-depleted, high-O\u2082 environment of the post-ionic-liquid-FGD gas stream. Single-layer pressure drop is guaranteed at \u2264135\u00a0Pa (clean catalyst), enabling the SCR system to operate within the existing induced draft fan capacity without requiring fan upgrades.<\/li>\n<\/ul>\n<\/section>\n
    \n

    <\/p>\n

    \n

    05 \u2014 Operational Results<\/p>\n

    Verified Compliance Data: All Parameters at or Below Permit Limits<\/h2>\n
    \n
    \n
    50 \/ 50<\/div>\n
    mg\/Nm\u00b3 actual\/limit<\/div>\n
    NOx \u2014 97% removed<\/div>\n<\/div>\n
    \n
    35 \/ 35<\/div>\n
    mg\/Nm\u00b3 actual\/limit<\/div>\n
    SO\u2082 \u2014 at limit<\/div>\n<\/div>\n
    \n
    10 \/ 10<\/div>\n
    mg\/Nm\u00b3 actual\/limit<\/div>\n
    PM \u2014 at limit<\/div>\n<\/div>\n
    \n
    3 \/ 5<\/div>\n
    ppm actual\/limit<\/div>\n
    NH\u2083 slip \u2014 40% below<\/div>\n<\/div>\n
    \n
    123 kW<\/div>\n
    actual running<\/div>\n
    (installed: 124.5 kW)<\/div>\n<\/div>\n
    \n
    97%<\/div>\n
    actual denitrification<\/div>\n
    (design: 97%)<\/div>\n<\/div>\n<\/div>\n

    \"Operational<\/p>\n

    Annual operating costs: electricity at 123\u00a0kW actual running power (0.4\u00a0RMB\/kWh, 8,000\u00a0h\/year) = approximately 39.36\u00a0ten-thousand RMB equivalent; natural gas for SCR reheating at 75\u00a0m\u00b3\/h (3.2\u00a0RMB\/m\u00b3, 8,000\u00a0h) = approximately 192\u00a0ten-thousand RMB equivalent; ammonia water at 0.02\u00a0t\/h (500\u00a0RMB\/t, 8,000\u00a0h) = approximately 8\u00a0ten-thousand RMB equivalent. Natural gas for SCR temperature maintenance is the dominant operating cost item, reinforcing the value of the ceramic tile heat exchanger in reducing the supplementary heating requirement.<\/p>\n<\/section>\n

    \n

    <\/p>\n

    \n

    06 \u2014 Implementation Cautions<\/p>\n

    Critical Engineering and Operational Lessons for Lead Recycling Off-Gas Treatment<\/h2>\n
      \n
    • \u26a0\ufe0f<\/span>
      \nPoor upstream dust removal causes downstream ionic liquid desulfurization efficiency to decline \u2014 add PM concentration monitoring at the system inlet and respond immediately when efficiency falls:<\/strong> The primary documented risk is that poor upstream (pre-treatment) dust removal causes the ionic liquid desulfurization efficiency to decrease. Lead-bearing and other particulates from the oxidation furnace are absorbed into the ionic liquid circulation loop, progressively contaminating the absorbent and reducing its SO\u2082 absorption capacity. Install a continuous PM concentration monitor at the inlet to the ionic liquid stage. When inlet PM rises above the design threshold (\u226410\u00a0mg\/Nm\u00b3), initiate immediate investigation of the upstream ESP and bag filter performance. If dust removal efficiency has fallen, address the cause before the ionic liquid system\u2019s SO\u2082 capture capacity is impaired. Upgrade the desulfurization system capacity if the ionic liquid SO\u2082 loading cannot be maintained within acceptable limits, using a higher-capacity absorbent or an enhanced regeneration rate.<\/li>\n
    • \u26a0\ufe0f<\/span>
      \nSCR denitrification front-end SO\u2082 concentration not controlled at a rational level increases the probability of ammonium sulfate generation and catalyst blockage:<\/strong> Even after the ionic liquid desulfurization, some residual SO\u2082 (\u226435\u00a0mg\/Nm\u00b3 at design) reaches the SCR catalyst. At 180\u2013220\u00b0C operating temperature, ammonium bisulfate (ABS) can still form if the SO\u2082 concentration at the catalyst surface is higher than expected \u2014 for example, if the ionic liquid desulfurization efficiency falls below design levels during an absorbent contamination event. Monitor the SCR system pressure drop continuously. If pressure drop rises beyond the design value (indicating ABS or dust deposition), raise the SCR inlet temperature above 280\u00b0C to volatilise the ABS deposits. If the pressure drop cannot be reduced by cleaning to acceptable levels at normal operation, conduct thermal analysis of the catalyst bed to determine whether irreversible contamination has occurred.<\/li>\n
    • \u26a0\ufe0f<\/span>
      \nSCR denitrification temperature control instability makes it difficult to guarantee denitrification efficiency \u2014 always monitor the denitrification inlet temperature and stop ammonia injection if temperature falls below the design minimum:<\/strong> The third documented risk is that unstable temperature control at the SCR denitrification system inlet makes it difficult to guarantee denitrification efficiency. The SCR catalyst operates within a specific temperature window (220\u2013420\u00b0C design range; minimum 220\u00b0C). If the ceramic tile heat exchanger performance degrades (from fouling), or if the supplementary natural gas heating system malfunctions, the SCR inlet temperature can fall below the 220\u00b0C minimum. Below this temperature, the catalyst activity is insufficient and unreacted ammonia creates ammonium salt deposits rather than reducing NOx. Install a continuous temperature monitor at the SCR inlet with an automatic ammonia injection cut-off interlock at 210\u00b0C (10\u00b0C below the minimum design temperature). Continuing ammonia injection at sub-minimum temperature wastes reagent, causes ammonia slip exceedances, and deposits ammonium salts in the catalyst channels.<\/li>\n
    • \u26a0\ufe0f<\/span>
      \nThe ceramic tile heat exchanger is the system\u2019s most corrosion-sensitive component \u2014 avoid the problems of plate replacement, leakage, and corrosion velocity with the right material grade and gas velocity:<\/strong> The heat exchanger processes raw furnace gas (high SO\u2082, high O\u2082, high PM, lead-bearing particulates) on the hot side and clean post-FGD gas on the cold side. This creates a demanding dual-corrosion environment. Selecting the appropriate heat exchanger material grade (S31603 specified for this installation), setting the gas velocity within the design range to minimise erosion-corrosion from residual dust, and optimising the duct channel geometry to reduce sludge deposition rate are the key design disciplines. Periodic inspection of the heat exchanger tube surfaces (at least annually from year 2 onward) for wall thickness reduction should be included in the planned maintenance schedule.<\/li>\n
    • \u26a0\ufe0f<\/span>
      \nLead-bearing particulates from the oxidation furnace must be managed as hazardous waste at every solid waste collection point in the treatment system:<\/strong> Lead is a hazardous substance under EU REACH regulation and the Hazardous Waste Directive at any concentration above the relevant threshold. Solid waste collected at the ESP hopper, the bag filter hoppers, and the wet ESP collection sump all contain lead-bearing particulates at concentrations that will typically classify the waste as hazardous. Each solid waste stream must be individually characterized by TCLP leachate testing (EN 12457) before any disposal route is confirmed, and transfer must be accompanied by a Hazardous Waste Consignment Note under Dutch hazardous waste transport regulations. The ionic liquid contaminated with lead particulates must similarly be characterized when it is eventually replaced at end-of-life, as it will contain absorbed lead compounds.<\/li>\n
    • \u26a0\ufe0f<\/span>
      \nIncrease supplementary heating (natural gas) if SCR inlet temperature is below the 220\u00b0C minimum \u2014 and vent through sidelining during start-up and shutdown to prevent catalyst exposure to cold high-humidity gas:<\/strong> During start-up and shutdown of the oxidation furnaces, the off-gas composition and temperature will be outside normal operating parameters. Wet or low-temperature gas containing high moisture content should be bypassed around the SCR reactor during these transient periods: moisture condensation on the catalyst at sub-minimum temperatures can cause irreversible catalyst damage. Ensure the sidelining bypass duct and valve are functional before commissioning and include the start-up bypass procedure in the operator training programme.<\/li>\n<\/ul>\n<\/section>\n
      \n

      <\/p>\n

      \n

      07 \u2014 Engineering Takeaways<\/p>\n

      Four Lessons from This Lead Recycling Off-Gas Treatment Project<\/h2>\n
        \n
      • 1<\/span>
        \nThe sequence of treatment stages determines whether each technology performs at its rated efficiency \u2014 sequence matters more than individual equipment specification.<\/strong> In this project, the SCR achieves 97% denitrification not because of an exceptionally high-specification catalyst, but because the treatment sequence (deep PM removal before ionic liquid FGD, ionic liquid FGD before SCR) delivers the SCR a clean, low-SO\u2082 gas stream at the correct temperature. The same catalyst in a different position \u2014 for example, upstream of the ionic liquid FGD in a high-SO\u2082 gas stream \u2014 would fail within months due to ABS fouling. Treatment system architecture (sequence, temperature, gas conditions at each stage inlet) is the primary engineering design decision for complex multi-pollutant applications.<\/li>\n
      • 2<\/span>
        \nIonic liquid desulfurization is a superior alternative to limestone-gypsum FGD for lead recycling off-gas applications specifically because it generates no solid or liquid waste streams from the FGD process itself.<\/strong> In a facility already managing lead-contaminated solid waste from the ESP and bag filter, adding a limestone-gypsum FGD stage would generate a further stream of potentially lead-contaminated gypsum requiring hazardous waste classification and disposal. The ionic liquid process avoids this additional waste stream and simultaneously produces a recoverable concentrated SO\u2082 by-product with commercial value. For any lead, zinc, or other heavy-metal-bearing off-gas application where the FGD waste stream would be classified as hazardous, ionic liquid desulfurization should be evaluated as the primary desulfurization technology before limestone-gypsum FGD is specified.<\/li>\n
      • 3<\/span>
        \nWaste heat recovery through the ceramic tile heat exchanger converts an energy liability into the primary heating source for the SCR reactor.<\/strong> The raw hot off-gas (220\u00b0C) must be cooled before the bag filter and ionic liquid stages; the post-FGD gas (40\u00b0C) must be reheated before the SCR. These two temperature management duties are directly complementary: the heat extracted from the hot side is exactly what is needed on the cold side. The ceramic tile heat exchanger exploits this thermal complementarity, eliminating the need for a steam or electric gas heater that would add approximately 192 ten-thousand RMB per year in energy cost. This is the largest single operating cost saving in the project and demonstrates that waste heat identification and recovery should be an explicit step in the system design process, not an afterthought.<\/li>\n
      • 4<\/span>
        \nUpgrading existing infrastructure by adding the two new components (heat exchanger and SCR) delivers full NOx compliance at a fraction of the cost of a complete system replacement.<\/strong> This project demonstrates the value of accurate existing equipment inventory and capability assessment before any compliance upgrade design begins. The existing ESP, bag filter, ionic liquid FGD, and wet ESP were all confirmed as capable of meeting their individual performance targets within the upgrade system architecture. Only the heat exchanger (providing temperature management for SCR operation) and the SCR reactor itself were new additions. The capital cost ratio of this incremental upgrade to a complete new system replacement would typically be in the range of 15\u201325% \u2014 a compelling argument for existing infrastructure assessment before any greenfield treatment system is specified.<\/li>\n<\/ul>\n<\/section>\n
        \n

        <\/p>\n

        \n

        08 \u2014 Frequently Asked Questions<\/p>\n

        Lead-Acid Battery Recycling Off-Gas Treatment: Ten Questions Answered<\/h2>\n

        Questions from environmental permit managers, process engineers, and HSE teams at secondary lead production, aluminium alloy recycling, and solid waste resource recovery facilities planning SCR denitrification and ionic liquid desulfurization upgrades under EU IED \/ Dutch Activities Decree requirements.<\/p>\n

        \nQ1. Why is ionic liquid desulfurization used instead of limestone-gypsum wet FGD for this application?<\/summary>\n
        Ionic liquid desulfurization was selected over limestone-gypsum FGD for three specific reasons in the lead recycling context: (1) No lead-contaminated gypsum by-product \u2014 limestone-gypsum FGD would produce gypsum contaminated with absorbed lead from the furnace off-gas, requiring classification and likely management as hazardous waste; ionic liquid desulfurization avoids this additional hazardous waste stream; (2) Recoverable SO\u2082 by-product \u2014 the ionic liquid regeneration process concentrates the captured SO\u2082, which can be processed into sulfuric acid for reuse in battery manufacturing or other industrial processes, generating revenue that partially offsets the treatment operating cost; (3) No liquid effluent from the FGD stage \u2014 the ionic liquid is recirculated and regenerated rather than consumed, generating no FGD wastewater stream requiring separate treatment. These advantages are specific to the lead recycling application context; for other applications without these constraints, limestone-gypsum FGD remains a valid and often lower-cost alternative.<\/div>\n<\/details>\n
        \nQ2. How does the ceramic tile heat exchanger provide the SCR reheating duty without external energy input?<\/summary>\n
        The ceramic tile heat exchanger (model HB-565) operates as a gas-to-gas heat exchanger with a thermal capacity of approximately 1,344\u00a0kW. The hot side receives raw furnace gas at approximately 220\u00b0C and cools it to approximately 128\u00b0C before the bag filter stage; the cold side receives post-ionic-liquid-FGD gas at approximately 40\u00b0C and heats it to approximately 130\u00b0C before the SCR reactor. The natural gas supplementary heating boosts the SCR inlet temperature from 130\u00b0C to 180\u2013220\u00b0C, consuming 75\u00a0m\u00b3\/h. Without the heat exchanger, raising the post-FGD gas from 40\u00b0C to 180\u2013220\u00b0C by natural gas direct combustion would require approximately 3\u20134 times this gas consumption. The ceramic tile construction (rather than steel plate or tube) is selected for its resistance to the combined acid gas and high-O\u2082 corrosive environment on the hot side.<\/div>\n<\/details>\n
        \nQ3. What EU IED and Dutch regulatory framework applies to lead-acid battery recycling facilities?<\/summary>\n
        Lead-acid battery recycling facilities in the Netherlands are regulated under the EU IED 2010\/75\/EU in the non-ferrous metals sector. The applicable BAT conclusions for the non-ferrous metals industry set emission limit values for NOx, SO\u2082, PM, lead and its compounds, and other heavy metals. Additional obligations apply under EU REACH Regulation (EC) 1907\/2006 for lead as a substance of very high concern, and under the Waste Framework Directive (2008\/98\/EC) and the Batteries and Accumulators Directive (2006\/66\/EC, updated by 2023\/1542\/EU) for the spent battery feedstock management. Dutch environmental permits are issued under the Omgevingswet, with site-specific emission limits and waste management conditions set by the Omgevingsdienst. CEMS must be certified to EN 14181 QAL1\/QAL2\/AST and connected to the reporting platform. Lead stack emission monitoring typically requires periodic isokinetic sampling by an accredited laboratory (minimum quarterly) in addition to continuous PM monitoring.<\/div>\n<\/details>\n
        \nQ4. What happens if the upstream dust removal fails and PM at the ionic liquid inlet rises above 10\u00a0mg\/Nm\u00b3?<\/summary>\n
        When PM at the ionic liquid desulfurization inlet rises above 10\u00a0mg\/Nm\u00b3, the progressive contamination of the ionic liquid absorbent begins to reduce its SO\u2082 absorption capacity. The timeline from elevated inlet PM to observable SO\u2082 outlet exceedance depends on the ionic liquid recirculation rate and regeneration capacity, but typically the SO\u2082 outlet will begin rising within hours to days of a sustained high-PM event. The response protocol should be: (1) immediately investigate the upstream ESP and bag filter for the cause of elevated PM; (2) reduce oxidation furnace throughput to reduce the total PM flux entering the system while the upstream equipment is corrected; (3) increase the ionic liquid regeneration rate to improve SO\u2082 absorption capacity during the elevated PM period; (4) if the ionic liquid SO\u2082 outlet rises above the permit limit, notify the competent authority (Omgevingsdienst) immediately per permit conditions; (5) after the upstream PM issue is resolved, monitor ionic liquid absorption capacity recovery over the following 48 hours to confirm the absorbent has returned to normal performance.<\/div>\n<\/details>\n
        \nQ5. What are the annual operating costs for this integrated treatment upgrade?<\/summary>\n
        Annual operating costs for the SCR and heat exchanger upgrade components are: (1) Electricity: 123\u00a0kW actual running at 0.4\u00a0RMB\/kWh equivalent, 8,000\u00a0h\/year = approximately 39.36 ten-thousand RMB\/year; (2) Natural gas (supplementary SCR inlet temperature heating): 75\u00a0m\u00b3\/h at 3.2\u00a0RMB\/m\u00b3 = approximately 192 ten-thousand RMB\/year (by far the dominant operating cost); (3) Ammonia water: 0.02\u00a0t\/h at 500\u00a0RMB\/t = approximately 8 ten-thousand RMB\/year. Total annual operating cost for the new upgrade components: approximately 239 ten-thousand RMB\/year equivalent. The SCR catalyst change-out (every 24,000 operating hours, approximately 3 years at 8,000\u00a0h\/year) adds a further capital provision of the catalyst replacement cost, amortized over 3 years. The ionic liquid operating cost (from the existing system) is not included in this breakdown.<\/div>\n<\/details>\n
        \nQ6. How is ammonia slip monitored and controlled in the SCR system?<\/summary>\n
        Ammonia slip (\u22645\u00a0ppm design; 3\u00a0ppm actual) is controlled through: (1) real-time NOx measurement at both the SCR inlet and outlet; (2) the SCR control system adjusts ammonia water injection rate to maintain the NOx outlet at the target \u226450\u00a0mg\/Nm\u00b3 while keeping ammonia injection at the minimum necessary level; (3) a continuous in-situ NH\u2083 analyser at the SCR outlet provides direct ammonia slip feedback, with a set-point alarm at 4\u00a0ppm and automatic injection rate reduction at 5\u00a0ppm; (4) the SCR inlet temperature is continuously monitored, and ammonia injection is cut off automatically if temperature falls below 210\u00b0C to prevent cold-temperature excess ammonia slip. Under Dutch environmental permit conditions, ammonia concentration at the stack may be subject to periodic reporting requirements; the CEMS installation scope should be confirmed with the Omgevingsdienst before commissioning.<\/div>\n<\/details>\n
        \nQ7. How is the lead content in all solid waste streams from the treatment system managed under EU hazardous waste regulations?<\/summary>\n
        Lead compounds are classified as hazardous substances under EU REACH Regulation and the Hazardous Waste Directive. All solid waste from the treatment system \u2014 ESP hopper ash, bag filter cake, and wet ESP sludge \u2014 will contain lead at concentrations that typically classify the waste as hazardous under European Waste Catalogue mirror entry codes (e.g. 10 04 01* \u201cslags from primary and secondary production of lead\u201d). Each waste stream must be: (1) characterised by TCLP leachate testing (EN 12457) to confirm hazardous classification; (2) labelled and stored in designated hazardous waste areas with secondary containment; (3) transferred only to licensed hazardous waste treatment facilities under Hazardous Waste Consignment Notes; (4) reported in annual environmental register entries and, above reporting thresholds, in E-PRTR submissions. The ionic liquid absorbent, when eventually replaced at end-of-life, must be characterised for lead content before disposal \u2014 the absorbent will have absorbed lead compounds progressively during its service life.<\/div>\n<\/details>\n
        \nQ8. Can the same ionic liquid desulfurization + SCR architecture be applied to other non-ferrous metal recycling off-gas streams (zinc, copper, aluminium)?<\/summary>\n
        Yes, with application-specific modifications. The fundamental architecture (deep upstream dust removal to protect the ionic liquid absorbent + ionic liquid FGD to remove SO\u2082 before SCR + SCR in low-SO\u2082 environment + waste heat recovery for SCR temperature management) is transferable to other non-ferrous metal recycling off-gas applications. Zinc recycling off-gas contains high ZnO particulates and SO\u2082 from zinc sulfate decomposition; copper smelter off-gas contains SO\u2082 and arsenic compounds; aluminium alloy recycling off-gas from salt flux furnaces contains HCl and fluorides in addition to the typical combustion pollutants. Each application requires adaptation of the upstream dust removal specification (for the specific metal and compound), the ionic liquid chemistry (for the specific SO\u2082 and HCl\/HF combination), and the SCR catalyst formulation (for the specific gas composition and temperature window). A separate engineering characterisation study for each new application is required before any equipment can be specified.<\/div>\n<\/details>\n
        \nQ9. What is the SCR catalyst change-out procedure and how long does it take?<\/summary>\n
        The SCR catalyst has a 24,000-hour chemical life from first gas contact (approximately 3 years at 8,000\u00a0h\/year). Catalyst change-out should be planned as a scheduled maintenance event, not reactive to observed performance decline. The change-out procedure requires: (1) shutting down and cooling the SCR reactor; (2) isolating the reactor from the gas stream and confirming safe atmospheric conditions inside the reactor; (3) removing the spent catalyst modules individually from each layer and palletising for dispatch to the catalyst regeneration or disposal facility; (4) installing new catalyst modules; (5) recommissioning the reactor with a controlled warm-up sequence. The catalyst change-out for a system of this size (15.03\u00a0m\u00b3 total catalyst volume) typically requires 2\u20133 days for an experienced crew. The facility must plan for this maintenance outage in advance: either scheduling it during a planned furnace maintenance shutdown or operating the oxidation furnaces on a reduced throughput during the SCR outage to stay within permit limits without the SCR operating.<\/div>\n<\/details>\n
        \nQ10. Are there reference installations for ionic liquid desulfurization + low-temperature SCR systems available for site visits?<\/summary>\n
        Yes. The integrated ESP + heat exchanger + bag filter + ionic liquid desulfurization + low-temperature SCR + wet ESP treatment system described in this case study has been deployed at solid waste resource recovery and non-ferrous metal recycling facilities achieving ultra-low emission compliance. Reference site visits can be arranged for qualified prospective clients, including access to verified CEMS compliance data, ionic liquid performance records, and SCR catalyst activity monitoring documentation. Please use the contact link below to request reference documentation or to arrange a site visit at a comparable lead recycling or solid waste resource recovery off-gas treatment installation.<\/div>\n<\/details>\n<\/section>\n
        \n

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        \n

        Ready to Achieve Ultra-Low Emission Compliance for Your Recycling Facility?<\/p>\n

        Explore the Full Range of Industrial Emission Control Solutions<\/h2>\n

        From ionic liquid desulfurization and low-temperature SCR for lead-acid battery recycling facilities to regenerative thermal oxidation systems for industrial VOC abatement<\/a>, our engineering team delivers EU IED\u2013compliant solutions for the most demanding non-ferrous metal recycling emission control requirements.<\/p>\n

        Request a Technical Consultation \u2192<\/a>
        \n        Explore All Emission Control Technologies<\/a><\/div>\n<\/section>\n

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