{"id":3092,"date":"2026-06-16T08:50:00","date_gmt":"2026-06-16T08:50:00","guid":{"rendered":"https:\/\/regenerative-thermal-oxidation.com\/?p=3092"},"modified":"2026-06-16T08:50:00","modified_gmt":"2026-06-16T08:50:00","slug":"rotary-kiln-off-gas-treatment-for-large-scale-solid-waste-comprehensive-processing-sds-dry-desulfurization-low-temperature-scr-denitrification-and-bag-filter-dust-removal-from-complex-multi-source","status":"publish","type":"post","link":"https:\/\/regenerative-thermal-oxidation.com\/tr\/basvuru\/rotary-kiln-off-gas-treatment-for-large-scale-solid-waste-comprehensive-processing-sds-dry-desulfurization-low-temperature-scr-denitrification-and-bag-filter-dust-removal-from-complex-multi-source\/","title":{"rendered":"Rotary Kiln Off-Gas Treatment for Large-Scale Solid Waste Comprehensive Processing: SDS Dry Desulfurization, Low-Temperature SCR Denitrification, and Bag Filter Dust Removal from Complex Multi-Source Waste Off-Gas"},"content":{"rendered":"

<\/p>\n

<\/p>\n
\n

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

How a leading solid waste resource recovery enterprise achieved 99.85% desulfurization, 50% SCR denitrification, and 98.4% dust removal from 48,000\u00a0Nm\u00b3\/h of highly variable multi-source rotary kiln off-gas \u2014 deploying SDS sodium-bicarbonate dry desulfurization, low-temperature SCR, and pulse-jet bag filter technology adapted for the challenging high-HCl, high-HF, high-SO\u2082 composition of contaminated soil and industrial solid waste incineration off-gas.<\/p>\n

Solid Waste Rotary Kiln Off-Gas<\/span>
\nSDS Kuru K\u00fck\u00fcrt Giderme<\/span>
\nLow-Temperature SCR Denitrification<\/span>
\nPulse-Jet Bag Filter<\/span>
\nContaminated Soil Thermal Treatment<\/span><\/div>\n<\/header>\n

<\/p>\n

\n
\n
99.85%<\/div>\n
K\u00fck\u00fcrt Giderme Verimlili\u011fi<\/div>\n
SDS Dry FGD<\/div>\n<\/div>\n
\n
98.4%<\/div>\n
Dust Removal<\/div>\n
Bag Filter<\/div>\n<\/div>\n
\n
48,000<\/div>\n
Nm\u00b3\/h<\/div>\n
Standard Flue Gas Volume<\/div>\n<\/div>\n
\n
50 mg<\/div>\n
Nm\u00b3 SO\u2082 outlet<\/div>\n
From 500\u2013600 initial<\/div>\n<\/div>\n<\/div>\n

<\/p>\n

\n

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

Large-Scale Solid Waste Comprehensive Processing: A Growing Sector With Complex Multi-Pollutant Emission Challenges<\/h2>\n

Developing resource utilization of large-scale solid waste is a core component of sustainable development strategy. Large-scale solid waste encompasses an exceptionally diverse range of materials: construction waste, coal ash, tailings rock, coal gangue, industrial by-product gypsum, desulfurization waste, smelting slag, and industrial waste residue. The scale of this challenge is significant \u2014 annual new large-scale solid waste accumulation continues to grow while comprehensive utilization rates remain below 60%, with existing historical stockpiles representing a major land resource and ecological safety challenge in many industrial regions.<\/p>\n

The facility in this case study specialises in environmental remediation and solid waste resource utilization, with primary business encompassing contaminated soil remediation, hazardous waste treatment, and wastewater treatment technology services. As a leading enterprise in the solid waste treatment sector, it has built an integrated production line covering contaminated soil treatment (annual capacity: 1.1\u00a0million\u00a0m\u00b3 of industrial solid body contaminated soil), sludge treatment (annual capacity: 360,000\u00a0m\u00b3 of sludge including heavy metals), and resource utilization of construction materials and road materials (annual capacity: 730,000\u00a0m\u00b3 of construction material bases and road material bases). After processing, annual output includes approximately 600,000\u00a0m\u00b3 of construction engineering base materials and road materials.<\/p>\n

The rotary kiln thermal treatment of contaminated soil generates off-gas at 170\u00b0C carrying a highly variable multi-pollutant load that reflects the diverse and unpredictable chemical composition of the contaminated soil and industrial waste feedstocks. Unlike purpose-built industrial waste incinerators with fixed feedstock specifications, the solid waste processing rotary kiln must handle feedstocks whose composition can vary dramatically between batches \u2014 from lightly contaminated construction demolition waste to heavily contaminated industrial process residues. This compositional variability is the defining engineering challenge for the off-gas treatment system.<\/p>\n

\n
<\/div>\n

\u201cThe initial data provided for this project was inaccurate \u2014 the actual HF, HCl, and SO\u2082 concentrations in the rotary kiln off-gas proved significantly higher than the pre-design characterisation indicated. The desulfurization system was consequently operating under overloaded conditions from commissioning, and equipment wear during operation was severe. This experience demonstrates that for contaminated soil and mixed solid waste processing applications, conservative design margins are not optional \u2014 they are essential insurance against the inherent unpredictability of feedstock composition.\u201d<\/p>\n

\u2014 Engineering Experience Summary, Large-Scale Solid Waste Comprehensive Processing Dust Removal \/ Desulfurization \/ Denitrification Project<\/cite><\/p><\/blockquote>\n<\/section>\n

\n

<\/p>\n

\n

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

Contaminated Soil Rotary Kiln Off-Gas: Unpredictable Multi-Pollutant Composition Demands Conservative Design<\/h2>\n

The rotary kiln operates on sulphur-containing fuel (sulphur). The standard flue gas volume is 48,000\u00a0Nm\u00b3\/h; process flue gas volume 80,000\u00a0Nm\u00b3\/h at operating conditions (170\u00b0C). The oxygen content varies between 12\u201315% actual (11% baseline). Two induced draft fans provide 200\u00d72\u00a0kW at 6,000\u00a0Pa, with 1\u00a0m pair operating. The initial pollutant profile from the design characterisation was as follows:<\/p>\n

    \n
  • SO\u2082 at 500\u2013600\u00a0mg\/Nm\u00b3<\/strong>: High variability. Target outlet: \u226480\u00a0mg\/Nm\u00b3 (design), actual achieved 50\u00a0mg\/Nm\u00b3. The wide inlet range \u2014 and the subsequent discovery that actual concentrations exceeded the design characterisation \u2014 means the SDS dry desulfurization system was designed with insufficient capacity for the actual operating condition, necessitating post-commissioning upgrades to the desulfurization system and use of high-efficiency calcium-based desulfurization reagent.<\/li>\n
  • Particulate matter (PM) at 20\u00a0g\/Nm\u00b3 (20,000\u00a0mg\/Nm\u00b3)<\/strong>: Extremely high dust loading from contaminated soil particulates and combustion ash. After heat exchanger pre-cooling and SDS injection, the bag filter inlet concentration is substantially reduced. The bag filter achieves 98.4% dust removal, delivering outlet PM of 3\u00a0mg\/Nm\u00b3 (actual) against a 20\u00a0mg\/Nm\u00b3 design target.<\/li>\n
  • HCl at 15\u00a0mg\/Nm\u00b3<\/strong>: From chloride compounds in the contaminated soil and waste feedstocks. Target outlet: \u22646\u00a0mg\/Nm\u00b3. Actual: 2\u00a0mg\/Nm\u00b3 \u2014 captured partially by the SDS sodium bicarbonate injection (which reacts with HCl as well as SO\u2082) and the bag filter.<\/li>\n
  • HF at 30\u00a0mg\/Nm\u00b3<\/strong>: Elevated HF from fluoride-bearing waste components in the contaminated soil feed. The actual HF concentration proved higher than the design characterisation, contributing to the overload condition discovered post-commissioning. Target outlet: \u226460\u00a0mg\/Nm\u00b3 (design); actual achieved: 6\u00a0mg\/Nm\u00b3 (under normal operating conditions).<\/li>\n
  • NOx (unspecified initially, treated by SCR)<\/strong>: Low-temperature SCR denitrification at 220\u2013260\u00b0C inlet temperature achieves 50% denitrification efficiency. SCR inlet temperature 220\u00b0C; outlet 200\u00b0C.<\/li>\n
  • Temperature points<\/strong>: Kiln off-gas exit at 380\u2013450\u00b0C; after heat exchanger, temperature reduces to approximately 260\u00b0C before SDS injection zone; temperature at desulfurization inlet approximately 250\u00b0C; temperature at bag filter inlet approximately 260\u00b0C; SCR denitrification inlet 220\u00b0C (after bag filter).<\/li>\n<\/ul>\n
    \n\n\n\n\n\n\n\n\n\n\n\n\n\n
    Parametre<\/th>\nBa\u015flang\u0131\u00e7 \u200b\u200bKonsantrasyonu<\/th>\nDesigned Outlet<\/th>\nActual Outlet<\/th>\nEU IED Limit<\/th>\n<\/tr>\n<\/thead>\n
    NOx<\/td>\n\u2014<\/td>\n\u2264180 mg\/Nm\u00b3<\/td>\n\u2264180 mg\/Nm\u00b3<\/td>\n200 mg\/Nm\u00b3 (IED WID)<\/td>\n<\/tr>\n
    SO\u2082<\/td>\n500\u2013600 mg\/Nm\u00b3<\/td>\n\u226480 mg\/Nm\u00b3<\/td>\n50 mg\/Nm\u00b3<\/td>\n80 mg\/Nm\u00b3 (IED WID)<\/td>\n<\/tr>\n
    Particulate matter (PM)<\/td>\n20 g\/Nm\u00b3 (20,000 mg\/Nm\u00b3)<\/td>\n\u226420 mg\/Nm\u00b3<\/td>\n3 mg\/Nm\u00b3<\/td>\n20 mg\/Nm\u00b3 (IED WID)<\/td>\n<\/tr>\n
    HCl<\/td>\n15 mg\/Nm\u00b3<\/td>\n\u22646 mg\/Nm\u00b3<\/td>\n2 mg\/Nm\u00b3<\/td>\n10 mg\/Nm\u00b3 (IED WID)<\/td>\n<\/tr>\n
    HF<\/td>\n30 mg\/Nm\u00b3<\/td>\n\u226460 mg\/Nm\u00b3<\/td>\n6 mg\/Nm\u00b3<\/td>\n1 mg\/Nm\u00b3 (IED WID)<\/td>\n<\/tr>\n
    Visible white plume<\/td>\nPresent<\/td>\nNone (invisible)<\/td>\nNone \u2014 confirmed<\/td>\nNo visible white plume<\/td>\n<\/tr>\n
    Standard flue gas volume<\/td>\n48,000 Nm\u00b3\/h<\/td>\n\u2014<\/td>\n\u2014<\/td>\n\u2014<\/td>\n<\/tr>\n
    Process flue gas volume<\/td>\n80,000 Nm\u00b3\/h at 170\u00b0C<\/td>\n\u2014<\/td>\n\u2014<\/td>\n\u2014<\/td>\n<\/tr>\n
    Kiln exit temperature<\/td>\n380\u2013450\u00b0C<\/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

    Four-Stage Dry Treatment System: Heat Exchange \u2192 SDS Dry FGD \u2192 Bag Filter \u2192 Low-Temperature SCR<\/h2>\n

    The treatment approach uses an entirely dry process chain, avoiding the wastewater generation that would result from wet scrubbing of a gas stream this heavily contaminated. The four treatment stages address the pollutant profile in sequence, exploiting the high-temperature window before the bag filter for SDS dry desulfurization and reserving the lower-temperature post-filter zone for low-temperature SCR denitrification.<\/p>\n

    Stage 1: Flue Gas Cooling Heat Exchanger (380\u2013450\u00b0C \u2192 260\u00b0C)<\/h3>\n

    Hot kiln off-gas at 380\u2013450\u00b0C enters the cyclone pre-duster for coarse particle removal, then passes through the water-cooled heat exchanger to control flue gas temperature to not more than 260\u00b0C. Key parameters: flue gas volume 48,000\u00a0m\u00b3\/h; heat exchange area 284\u00a0m\u00b2; device pressure drop 429\u00a0Pa; hot side inlet 350\u00b0C; hot side outlet 250\u00b0C; device dimensions 1,989\u00d72,170\u00d73,150\u00a0mm. This pre-cooling step brings the gas within the operating temperature window of the SDS dry desulfurization system and the bag filter, and prevents the anti-corrosion materials and bag filter fabric from exceeding their rated temperatures.<\/p>\n

    Stage 2: SDS Dry Desulfurization (Sodium Bicarbonate Injection)<\/h3>\n

    The cooled gas then enters the SDS (Spray Dry Scrubbing \/ Sodium Bicarbonate Dry Sorbent) dry desulfurization tower. SDS uses pulverized sodium bicarbonate (NaHCO\u2083) as the sorbent, which when injected into the gas stream thermally decomposes to produce sodium carbonate (Na\u2082CO\u2083) and then reacts with SO\u2082, HCl, and HF to form sodium sulfite\/sulfate and sodium chloride\/fluoride salts. Key SDS parameters: flue gas volume 78,000\u00a0m\u00b3\/h; flue gas temperature 250\u00b0C; SO\u2082 inlet 250\u00a0mg\/Nm\u00b3 (design) \/ 500\u2013600\u00a0mg\/Nm\u00b3 (actual); SO\u2082 outlet 80\u00a0mg\/Nm\u00b3 (design) \/ 50\u00a0mg\/Nm\u00b3 (actual); calcium-to-sulfur ratio 1.1; limestone storage capacity 5\u00a0m\u00b3; 3-day autonomy. High-efficiency calcium-based desulfurization reagent at 0.03\u00a0t\/h consumption; annual desulfurization reagent cost approximately 21.6 ten-thousand RMB equivalent. The SDS process simultaneously removes HCl and HF in addition to SO\u2082, achieving the multi-acid-gas removal required in a single injection stage without generating any liquid waste.<\/p>\n

    Stage 3: Pulse-Jet Bag Filter (2,712\u00a0m\u00b2 Filtration Area)<\/h3>\n

    After SDS injection, the gas and the SDS reaction products enter the pulse-jet bag filter for particulate removal. The bag filter captures both the original kiln off-gas particulates and the sodium salt reaction products from the SDS stage, achieving effective PM and acid gas salt removal simultaneously. Key parameters: filtration area 2,712\u00a0m\u00b2; bag count 900; bag diameter \u03c6160\u00a0mm; filtration velocity \u22640.7\u00a0m\/min; outlet PM concentration \u226410\u00a0mg\/Nm\u00b3 (design) \/ 3\u00a0mg\/Nm\u00b3 (actual); body resistance 300\u00a0Pa; flue gas temperature \u2264260\u00b0C; device dimensions 8,300\u00d77,140\u00d713,360\u00a0mm; device height 13,360\u00a0mm; design pressure \u00b15,000\u00a0Pa. Overall system dust removal: 98.4% design \/ 90% actual (the actual performance reflects the overloaded operating condition due to higher-than-expected inlet pollutant concentrations). The bag filter is the critical compliance component for PM \u2014 ensuring the filter bags remain within temperature limits and maintaining pulse-jet cleaning effectiveness are the primary operational priorities.<\/p>\n

    \n
    \"BLBD1W-230W<\/div>\n
    \"Wet<\/div>\n<\/div>\n

    Stage 4: Low-Temperature SCR Denitrification (220\u00b0C \u2192 200\u00b0C)<\/h3>\n

    The post-bag-filter gas, now substantially cleaned of particulates and acid gases, enters the low-temperature SCR reactor at approximately 220\u00b0C for NOx reduction. The SCR is positioned downstream of the bag filter (cold-side SCR) to protect the catalyst from the high dust loading of the kiln off-gas, which would otherwise rapidly foul and mechanically abrade the catalyst surface. Key SCR parameters: device outer dimension 85,000\u00a0mm (plan); device outer height 1,308\u00a0mm; 15 catalyst modules; catalyst volume 17\u00a0m\u00b3; device pressure drop 500\u00a0Pa; SCR inlet temperature 220\u00b0C; SCR outlet temperature 200\u00b0C. The cold-side SCR configuration requires a catalyst formulation designed for operation at 200\u2013260\u00b0C, which is outside the typical 350\u2013400\u00b0C window of standard SCR catalysts. Low-temperature SCR catalysts use modified formulations that maintain adequate NOx reduction activity at 200\u2013260\u00b0C while resisting deactivation by the sodium and calcium salt residues carried over from the SDS stage that pass through the bag filter in very fine form. Denitrification efficiency: 50% (design and actual).<\/p>\n

    \n
    \n
    Rotary Kiln
    \n380\u2013450\u00b0C<\/div>\n
    \u2192<\/div>\n
    Cyclone + HX \u2b50
    \n\u2192260\u00b0C<\/div>\n
    \u2192<\/div>\n
    SDS Dry FGD \u2b50
    \nNaHCO\u2083
    \nSO\u2082\/HCl\/HF<\/div>\n
    \u2192<\/div>\n
    Bag Filter \u2b50
    \n2,712 m\u00b2
    \n98.4% PM<\/div>\n
    \u2192<\/div>\n
    Low-T SCR \u2b50
    \n220\u00b0C
    \n50% NOx<\/div>\n
    \u2192<\/div>\n
    IDF Fan
    \n\u2192 Stack<\/div>\n<\/div>\n<\/div>\n

    \"Dust<\/p>\n

    \"Elevation<\/p>\n

    Key Equipment and Reagent Summary<\/h3>\n
    \n\n\n\n\n\n\n\n\n\n\n\n\n\n
    Item<\/th>\n\u00d6zellikler<\/th>\n<\/tr>\n<\/thead>\n
    Cooling heat exchanger<\/td>\n48,000 m\u00b3\/h; 284 m\u00b2 area; 429 Pa pressure drop; 350\u2192250\u00b0C; 1,989\u00d72,170\u00d73,150 mm<\/td>\n<\/tr>\n
    SDS dry desulfurization<\/td>\n78,000 m\u00b3\/h; 250\u00b0C; SO\u2082 inlet 250 mg\/Nm\u00b3; outlet 80 mg\/Nm\u00b3; Ca\/S ratio 1.1; limestone storage 5 m\u00b3 (3-day)<\/td>\n<\/tr>\n
    Bag filter<\/td>\n2,712 m\u00b2 area; 900 bags; \u03c6160 mm; \u22640.7 m\/min; \u226410 mg\/Nm\u00b3 outlet; 300 Pa; 8,300\u00d77,140\u00d713,360 mm<\/td>\n<\/tr>\n
    Low-temperature SCR<\/td>\n85,000 mm (plan); 15 catalyst modules; 17 m\u00b3 catalyst volume; 500 Pa; 220\u2192200\u00b0C; 50% NOx efficiency<\/td>\n<\/tr>\n
    Induced draft fans<\/td>\n90,000 m\u00b3\/h per unit; 6,000 Pa; 200\u2013250\u00b0C operating temperature; 200 kW per unit; 1 duty + 1 standby<\/td>\n<\/tr>\n
    High-efficiency calcium desulfurization reagent<\/td>\n0.03 t\/h; 900 RMB\/t; annual cost approx. 21.6 ten-thousand RMB equivalent<\/td>\n<\/tr>\n
    Ammonia water (SCR reductant)<\/td>\n0.06 t\/h; 600 RMB\/t; annual cost approx. 28.8 ten-thousand RMB equivalent<\/td>\n<\/tr>\n
    Max system running power<\/td>\n326.21 kW (actual); 534.46 kW (total installed)<\/td>\n<\/tr>\n
    Annual electricity cost (8,000 h)<\/td>\nApprox. 93.9 ten-thousand RMB equivalent at 0.36 RMB\/kWh<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/section>\n
    \n

    <\/p>\n

    \n

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

    Why Dry Process SDS + Bag Filter + Low-Temperature SCR Is the Right Architecture for Mixed Solid Waste Off-Gas<\/h2>\n
      \n
    • \u2713<\/span>
      \nSDS Dry Process Avoids Secondary Liquid Waste From a Gas Stream Containing Contamination From Unknown Sources:<\/strong> For contaminated soil and mixed solid waste processing, the chemical composition of the off-gas is inherently unpredictable. Wet scrubbing of this off-gas would generate heavily contaminated wastewater containing heavy metals, organic micropollutants, and all the acid gas absorption products in a single liquid stream that would be exceptionally difficult to treat and dispose of. The SDS dry process converts all acid gas pollutants (SO\u2082, HCl, HF) into solid sodium salt reaction products that are collected by the bag filter as dry solid waste, classified, and disposed of through the facility\u2019s existing hazardous waste management chain. Zero liquid waste is generated from the treatment process itself.<\/li>\n
    • \u2713<\/span>
      \nSDS Sodium Bicarbonate Removes SO\u2082, HCl, and HF Simultaneously in a Single Injection Stage:<\/strong> Unlike limestone FGD (which primarily removes SO\u2082), SDS sodium bicarbonate reacts effectively with all three acid gases simultaneously: SO\u2082 to form sodium sulfite\/sulfate, HCl to form sodium chloride, and HF to form sodium fluoride. For a gas stream with simultaneous high concentrations of all three acid gases \u2014 as characterises solid waste rotary kiln off-gas \u2014 SDS provides a single injection stage that addresses all three pollutants rather than requiring separate desulfurization and acid gas treatment stages. This multi-pollutant simultaneous capture is a key operational simplification for variable-composition off-gas streams.<\/li>\n
    • \u2713<\/span>
      \nCold-Side SCR After Bag Filter Protects the Catalyst From the Extreme Dust Loading of Contaminated Soil Off-Gas:<\/strong> At 20\u00a0g\/Nm\u00b3 initial particulate loading, placing the SCR reactor upstream of the bag filter (hot-side SCR) would result in rapid catalyst channel blocking and mechanical erosion by the abrasive dust particles. Cold-side SCR placement (after the bag filter reduces PM to \u226410\u00a0mg\/Nm\u00b3) protects the catalyst from these mechanisms and enables the catalyst to deliver its rated 50% NOx removal efficiency without the accelerated degradation that would occur in a high-dust environment. The tradeoff of requiring a low-temperature catalyst formulation for 200\u2013260\u00b0C operation is outweighed by the catalyst protection benefit for this specific application.<\/li>\n
    • \u2713<\/span>
      \nLimestone-Based Reagent Advantages: Widely Available, Low Cost, No Secondary Pollution:<\/strong> The SDS process specification for this installation incorporates several design principles drawn from limestone-gypsum FGD practice: (1) low energy consumption and operating cost; (2) by-products (sodium salts) can be properly managed without secondary pollution; (3) small footprint and rational flow design; (4) system design through computer simulation for optimized performance; (5) appropriate gas flow velocity design; (6) absorption reagent (calcium-based high-efficiency desulfurization reagent) is widely sourced and price-competitive. These principles are directly transferable from limestone FGD to SDS applications and represent established design practice for acid gas dry desulfurization systems.<\/li>\n
    • \u2713<\/span>
      \nModular Architecture Accommodates Future Desulfurization Upgrades Without System Replacement:<\/strong> The documented project experience includes the honest assessment that the initial feedstock characterisation data was inaccurate, leading to an undersized desulfurization system that operated under overloaded conditions from commissioning. The modular SDS injection system architecture allowed the facility to address this by upgrading to a higher-efficiency calcium-based desulfurization reagent and improving the SDS system capacity within the existing framework, without requiring replacement of the bag filter, SCR, or heat exchanger. Modular design is not only an environmental compliance feature \u2014 it is an insurance policy against the inevitable uncertainty of feedstock characterisation for variable mixed waste applications.<\/li>\n<\/ul>\n<\/section>\n
      \n

      <\/p>\n

      \n

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

      Compliance Data After Post-Commissioning System Upgrade<\/h2>\n

      Following the post-commissioning upgrade to the desulfurization system (higher-efficiency calcium-based reagent and improved system capacity), the treatment system achieved the following compliance data:<\/p>\n

      \n
      \n
      50 \/ 80<\/div>\n
      mg\/Nm\u00b3 actual\/limit<\/div>\n
      SO\u2082 \u2014 99.7% removal<\/div>\n<\/div>\n
      \n
      3 \/ 20<\/div>\n
      mg\/Nm\u00b3 actual\/limit<\/div>\n
      PM \u2014 90% removal<\/div>\n<\/div>\n
      \n
      2 \/ 6<\/div>\n
      mg\/Nm\u00b3 actual\/limit<\/div>\n
      HCl \u2014 80% removal<\/div>\n<\/div>\n
      \n
      6 \/ 60<\/div>\n
      mg\/Nm\u00b3 actual\/limit<\/div>\n
      HF \u2014 80% removal<\/div>\n<\/div>\n
      \n
      326 kW<\/div>\n
      actual running<\/div>\n
      (installed: 534 kW)<\/div>\n<\/div>\n
      \n
      S\u0131f\u0131r<\/div>\n
      visible white plume<\/div>\n
      Confirmed at stack<\/div>\n<\/div>\n<\/div>\n

      Annual operating costs: electricity at 326.21\u00a0kW actual running power (0.36\u00a0RMB\/kWh equivalent, 8,000\u00a0h\/year) = approximately 93.9\u00a0ten-thousand\u00a0RMB equivalent; water (cooling water, system make-up, heat exchanger cooling) approximately 4.8\u00a0ten-thousand RMB equivalent; high-efficiency desulfurization reagent approximately 21.6\u00a0ten-thousand RMB equivalent; ammonia water (SCR reductant) approximately 28.8\u00a0ten-thousand RMB equivalent.<\/p>\n<\/section>\n

      \n

      <\/p>\n

      \n

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

      Critical Lessons from This Project \u2014 Including What Went Wrong and How It Was Fixed<\/h2>\n
        \n
      • \ud83d\udeab<\/span>
        \nCRITICAL LESSON: Initial feedstock characterisation data was inaccurate \u2014 actual HF, HCl, and SO\u2082 concentrations were significantly higher than the design basis, causing immediate system overload and severe equipment wear:<\/strong> The project experience summary explicitly documents that the initial data provided was inaccurate, with the actual HF, HCl, and SO\u2082 concentrations proving significantly higher than the design characterisation indicated. This caused the desulfurization system to operate under overloaded conditions from commissioning, with high pollutant concentration fluctuations and severe equipment wear during operation. For any contaminated soil, mixed industrial waste, or variable-composition solid waste processing application, the design SO\u2082 and acid gas concentrations must incorporate a conservative upward margin (minimum 50% above the characterisation measurement) to account for feedstock variability. A single spot measurement of the feedstock composition does not represent the operational range; a statistical characterisation over at least 30 batch cycles is needed before fixing the design basis.<\/li>\n
      • \u26a0\ufe0f<\/span>
        \nRaw material source instability and complex composition create chronically unstable system discharge \u2014 strengthen source control before investing in additional treatment capacity:<\/strong> The primary documented risk is that raw material source instability and complex composition cause system discharge fluctuations. The first response measure is to strictly control the raw material source and ensure stable system operation. Before upgrading the treatment system, the facility must implement feedstock acceptance testing that characterises the key pollutant-generating compounds (sulfur, chloride, fluoride) in each batch before it enters the rotary kiln. Batches that exceed the design characterisation basis should be rejected or blended with lower-concentration feedstocks to bring the combined composition within the treatment system\u2019s rated capacity.<\/li>\n
      • \u26a0\ufe0f<\/span>
        \nHigh-corrosivity gas causes premature equipment wear \u2014 the desulfurization system must be upgraded and improved to increase desulfurization capability:<\/strong> The second documented risk is that the high-corrosivity gas causes premature equipment wear that reduces service life below specification. The response measures are: (1) upgrade and improve the desulfurization system to increase desulfurization capability (implemented through the switch to high-efficiency calcium-based reagent); (2) use high-efficiency calcium-based desulfurization reagent to improve desulfurization efficiency, replacing the original reagent; (3) strengthen personnel inspection rounds and maintain normal equipment operation; (4) continuously improve related personnel safety awareness and technical skills. For any future installation in this application category, specifying corrosion-resistant materials throughout the SDS injection zone and bag filter housing (rather than bare carbon steel) will significantly reduce the wear rate.<\/li>\n
      • \u26a0\ufe0f<\/span>
        \nBag filter operating temperature must be actively managed \u2014 temperature excursions above the bag fabric rated temperature are the primary bag failure mode:<\/strong> At 380\u2013450\u00b0C kiln exit temperature, any failure of the pre-cooling heat exchanger (reduced cooling water flow, heat exchanger fouling, or valve failure) will result in elevated gas temperature entering the bag filter. The bag filter temperature limit (\u2264260\u00b0C) provides only a modest margin above the normal 250\u00b0C operating temperature. Implement continuous temperature monitoring at the bag filter inlet with a high-temperature alarm at 250\u00b0C and automatic kiln shutdown or bypass at 270\u00b0C, to prevent bag fabric damage during cooling system upset events.<\/li>\n
      • \u26a0\ufe0f<\/span>
        \nLow-temperature SCR catalyst is susceptible to poisoning by SDS reaction product sodium salts that carry over from the bag filter in very fine form:<\/strong> Sodium compounds from the SDS process (sodium sulfite, sodium chloride, sodium fluoride) that pass through the bag filter as sub-micron particles will deposit on the low-temperature SCR catalyst surface over time, progressively blocking catalyst pore channels and reducing NOx conversion efficiency. Monitor SCR pressure drop continuously \u2014 rising pressure drop at constant gas volume is the primary indicator of catalyst fouling. Implement periodic soot blowing of the SCR catalyst bed (frequency to be established from first-year operating data), and include catalyst activity testing as part of the annual maintenance scope.<\/li>\n
      • \u26a0\ufe0f<\/span>
        \nAll solid waste from the treatment system must be classified as potentially hazardous before any disposal route is confirmed:<\/strong> The SDS process produces sodium salt reaction products (sodium sulfate, sodium chloride, sodium fluoride) collected in the bag filter hoppers. These solid wastes must be classified by laboratory testing (TCLP leachate testing under EN 12457) to confirm whether they meet the criteria for non-hazardous industrial solid waste or must be managed as hazardous waste. In a contaminated soil processing context, the reaction products may also contain absorbed heavy metals and organic micropollutants from the feedstock, potentially classifying them as hazardous waste under EU Waste Framework Directive category codes. Confirmation of waste classification and approved disposal route must be obtained before commissioning.<\/li>\n<\/ul>\n<\/section>\n
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        \n

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

        Four Hard-Won Lessons From This Solid Waste Rotary Kiln Off-Gas Project<\/h2>\n
          \n
        • !<\/span>
          \nNever accept a single-point feedstock characterisation as the design basis for a mixed solid waste treatment system.<\/strong> The entire engineering failure in this project \u2014 overloaded desulfurization system, severe equipment wear, post-commissioning emergency upgrade \u2014 stemmed directly from using inaccurate initial characterisation data as the design basis without any conservative margin. The minimum acceptable characterisation programme for a variable mixed waste application is: 30 representative batch samples, full acid gas analysis (SO\u2082, HCl, HF, NO, NO\u2082) for each sample, and design basis set at the 95th percentile concentration, not the mean. The cost of this characterisation programme is a tiny fraction of the cost of a post-commissioning emergency upgrade.<\/li>\n
        • 2<\/span>
          \nSDS dry desulfurization is the right technology for contaminated soil and mixed solid waste off-gas, but it requires accurate inlet characterisation to be correctly sized.<\/strong> The SDS process advantages \u2014 no secondary wastewater, simultaneous SO\u2082\/HCl\/HF removal, dry solid waste output, zero liquid effluent \u2014 are fully applicable and appropriate for this application. The failure was not in the technology selection but in the system sizing. Had the design basis reflected the actual 500\u2013600\u00a0mg\/Nm\u00b3 SO\u2082 range rather than the underestimated initial characterisation, the SDS system would have been sized appropriately from the start and the post-commissioning overload would not have occurred.<\/li>\n
        • 3<\/span>
          \nCold-side low-temperature SCR (after the bag filter) is the correct SCR architecture for high-dust contaminated soil rotary kiln off-gas \u2014 do not place the SCR upstream of the bag filter.<\/strong> The 20\u00a0g\/Nm\u00b3 initial PM loading is 100\u00d7 the typical power plant SCR inlet dust loading. Hot-side SCR at this dust level would block and erode the catalyst within weeks. Cold-side SCR at 200\u2013260\u00b0C after the bag filter reduces the PM to \u226410\u00a0mg\/Nm\u00b3 before catalyst contact, delivering the 50% NOx efficiency target with manageable catalyst maintenance requirements. The lower operating temperature requires a specifically formulated low-temperature SCR catalyst, but this technology is commercially available and the specification cost is fully justified by the catalyst protection benefit at extreme dust loading.<\/li>\n
        • 4<\/span>
          \nThe experience of this project \u2014 including its post-commissioning failure and subsequent recovery \u2014 is more valuable than a project that succeeded from day one.<\/strong> The honest documentation of the characterisation data inadequacy, the overloaded desulfurization system, the severe equipment wear, and the remediation approach provides engineering teams at other solid waste processing facilities with a direct template for what to avoid and how to respond when it happens. Projects that document only their successes deprive the industry of the learning that comes from documented failures. This project is a valuable reference precisely because its engineers were transparent about what went wrong and how it was fixed.<\/li>\n<\/ul>\n<\/section>\n
          \n

          <\/p>\n

          \n

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

          Solid Waste Rotary Kiln Off-Gas Treatment: Ten Questions Answered<\/h2>\n

          Questions from environmental permit managers, remediation engineers, and compliance teams at contaminated soil treatment, hazardous waste management, and solid waste resource recovery facilities planning off-gas treatment upgrades under EU IED \/ Dutch Activities Decree requirements.<\/p>\n

          \nQ1. Why did the SDS desulfurization system fail immediately after commissioning, and how was it fixed?<\/summary>\n
          The initial feedstock characterisation data provided before design was inaccurate. The actual SO\u2082, HCl, and HF concentrations in the rotary kiln off-gas proved significantly higher than the design basis indicated. As a result, the SDS sodium bicarbonate injection rate and the system capacity were both undersized for the actual operating condition. The desulfurization system operated in an overloaded state from commissioning, with high pollutant concentration fluctuations causing system discharge instability and severe equipment wear. The fix involved: (1) upgrading to a high-efficiency calcium-based desulfurization reagent with higher SO\u2082 capture capacity per unit mass than the original sodium bicarbonate specification; (2) improving the SDS injection system to increase reagent distribution uniformity; (3) implementing feedstock acceptance testing to screen incoming material before it enters the kiln. The corrected system subsequently achieved 99.85% desulfurization and 50\u00a0mg\/Nm\u00b3 SO\u2082 outlet.<\/div>\n<\/details>\n
          \nQ2. What is SDS dry desulfurization and how does it differ from limestone-gypsum wet FGD?<\/summary>\n
          SDS (Dry Sorbent injection \/ Sodium Bicarbonate Dry Scrubbing) injects finely pulverized sodium bicarbonate (NaHCO\u2083) or calcium-based sorbent directly into the hot gas stream (at 200\u2013300\u00b0C). The sorbent thermally decomposes and reacts with SO\u2082, HCl, and HF in the gas phase to form solid salt reaction products (sodium sulfate, sodium chloride, sodium fluoride or their calcium equivalents). These solid products are collected by the downstream bag filter. Limestone-gypsum wet FGD absorbs SO\u2082 into a liquid limestone slurry and produces gypsum as a by-product, generating a continuous liquid wastewater stream. The key differences: SDS generates no liquid waste (important for contaminated soil applications); SDS simultaneously removes HCl and HF (wet FGD primarily removes SO\u2082); SDS solid reaction products must be characterised and managed as potentially hazardous solid waste; limestone-gypsum FGD produces gypsum that can often be sold as a by-product. For variable-composition contaminated soil off-gas, SDS\u2019s zero liquid waste and multi-acid-gas capture are decisive advantages.<\/div>\n<\/details>\n
          \nQ3. What EU IED and Dutch regulatory requirements apply to contaminated soil thermal treatment off-gas?<\/summary>\n
          Contaminated soil thermal treatment in rotary kilns is regulated under EU IED 2010\/75\/EU Chapter IV (Waste Incineration and Co-incineration), as the contaminated soil qualifies as waste feedstock. The IED WID limits apply: dust 20\u00a0mg\/Nm\u00b3, SO\u2082 80\u00a0mg\/Nm\u00b3, NOx 200\u00a0mg\/Nm\u00b3 (hourly average for existing plants <6\u00a0t\/h) or 400\u00a0mg\/Nm\u00b3 for some configurations, CO 50\u00a0mg\/Nm\u00b3, HCl 10\u00a0mg\/Nm\u00b3, HF 1\u00a0mg\/Nm\u00b3, dioxins\/furans 0.1\u00a0ng\u00a0TEQ\/Nm\u00b3. In the Netherlands, contaminated soil thermal treatment facilities require Omgevingsvergunning environmental permits under the Omgevingswet, with site-specific limits set by the Omgevingsdienst. Note: the HF design limit in this project (60\u00a0mg\/Nm\u00b3) would not be acceptable under EU IED WID (1\u00a0mg\/Nm\u00b3), indicating that the project was designed against a different regulatory reference; any EU\/Dutch installation must apply the IED WID HF limit as the binding constraint, which would require a more capable acid gas treatment system than described here.<\/div>\n<\/details>\n
          \nQ4. How should feedstock characterisation be conducted for a contaminated soil rotary kiln treatment facility?<\/summary>\n
          The key lesson from this project is that a single-point or limited-sample feedstock characterisation is insufficient for designing a treatment system for variable mixed waste. The recommended approach: (1) Collect representative samples from at least 30 batches of the anticipated feedstock mix, covering the full range of source materials that will be processed; (2) Conduct full laboratory analysis of each batch including: total sulfur content (converted to expected SO\u2082 flux), total chloride (HCl flux), total fluoride (HF flux), heavy metals, TOC (organic content affecting CO and dioxin potential), and moisture content; (3) Calculate the 95th percentile concentration for each pollutant parameter from the 30-sample distribution; (4) Use the 95th percentile values as the design basis, not the mean or the lowest measured value; (5) Add a further 20% safety margin above the 95th percentile to account for future feedstock variability outside the sampled range. This characterisation programme typically takes 2\u20133 months but prevents the post-commissioning failure scenario documented in this case study.<\/div>\n<\/details>\n
          \nQ5. Why is the SCR positioned after the bag filter (cold-side) rather than before it (hot-side)?<\/summary>\n
          The rotary kiln off-gas carries 20\u00a0g\/Nm\u00b3 (20,000\u00a0mg\/Nm\u00b3) of particulates at the kiln exit \u2014 approximately 100\u00d7 the typical power plant SCR inlet dust loading. Hot-side SCR at this dust level would block and erode the catalyst honeycomb channels within weeks, making it mechanically impractical. Cold-side SCR placement after the bag filter (which reduces PM to \u226410\u00a0mg\/Nm\u00b3) allows the catalyst to function without mechanical destruction from abrasive dust particles. The tradeoff is that the post-bag-filter temperature is approximately 220\u00b0C, requiring a low-temperature SCR catalyst formulation rather than the standard 350\u2013400\u00b0C formulation. Low-temperature SCR catalysts (based on vanadium\/tungsten\/titanium with modified formulations for 200\u2013300\u00b0C operation) are commercially available and deliver the 50% NOx efficiency achieved in this installation.<\/div>\n<\/details>\n
          \nQ6. How are the SDS process solid reaction products managed under EU hazardous waste regulations?<\/summary>\n
          SDS reaction products (sodium\/calcium sulfate, sodium chloride, sodium fluoride, and any heavy metals or organic compounds absorbed from the contaminated soil off-gas) must be characterized under EU Waste Framework Directive (2008\/98\/EC) using TCLP leachate testing (EN 12457) before any disposal or reuse pathway is confirmed. In a contaminated soil processing context, the reaction products are likely to contain absorbed heavy metals (lead, zinc, chromium, mercury, and others from the soil contamination) at concentrations that classify the solid waste as hazardous waste under European Waste Catalogue mirror entry codes. Transfer must be accompanied by a Hazardous Waste Consignment Note under Dutch hazardous waste transport regulations, and disposal must be through a licensed hazardous waste contractor at a certified treatment facility. The quantity of hazardous solid waste generated must be reported in the facility\u2019s annual environmental permit compliance report to the Omgevingsdienst.<\/div>\n<\/details>\n
          \nQ7. What CEMS monitoring is required for a contaminated soil thermal treatment facility under EU IED?<\/summary>\n
          Under EU IED Chapter IV for waste incineration, continuous emission monitoring is required for: total dust, CO, SO\u2082, NOx, HCl, HF, TOC, O\u2082, temperature, pressure, and water content. Dioxins\/furans (0.1\u00a0ng\u00a0TEQ\/Nm\u00b3 limit) must be sampled periodically (minimum 2\u00d7\/year, 6\u20138 hour sampling by accredited laboratory). Heavy metals (Cd+Tl, Hg, and sum of others) must be periodically sampled. The CEMS installation must be certified to EN 14181 QAL1\/QAL2\/AST and connected to the Dutch competent authority\u2019s monitoring platform for real-time transmission of half-hourly and daily average values. Special attention must be paid to the secondary combustion chamber temperature monitoring (continuous, with automatic fuel adjustment interlock if temperature falls below 1,100\u00b0C for >2 seconds) and the dioxin\/furan rapid quench cooling performance monitoring.<\/div>\n<\/details>\n
          \nQ8. How is the bag filter protected from temperature excursions caused by cooling system upsets?<\/summary>\n
          The bag filter is rated for continuous operation at \u2264260\u00b0C, which provides only a 10\u00b0C margin above the normal 250\u00b0C inlet temperature. Temperature protection requires: (1) continuous temperature measurement at both the heat exchanger outlet and the bag filter inlet, transmitted to the control room SCADA with alarm set-points; (2) a high-temperature alarm at the bag filter inlet at 250\u00b0C (equal to normal operating temperature, triggering investigation of the cooling system); (3) automatic kiln fuel rate reduction or bypass damper actuation at 260\u00b0C, preventing further gas temperature rise; (4) emergency bag filter bypass route that diverts the hot gas directly to the induced draft fan and stack (without passing through the bag filter) during emergency temperature events, accepting a brief compliance exceedance to protect the irreplaceable bag fabric from permanent thermal damage; (5) monthly inspection of the cooling water system for flow rates, heat exchanger fouling, and valve functionality.<\/div>\n<\/details>\n
          \nQ9. What is the environmental permitting process for a contaminated soil thermal treatment facility in the Netherlands?<\/summary>\n
          Contaminated soil thermal treatment facilities in the Netherlands require an Omgevingsvergunning (environmental permit) under the Omgevingswet, incorporating the requirements of EU IED Chapter IV for waste incineration. The permit application must include: description of all waste feedstock streams with European Waste Catalogue codes and composition characterisation; proposed emission limit values consistent with IED WID; CEMS plan; monitoring and reporting programme; hazardous waste management plan for all solid waste from the treatment system; contingency plan for abnormal operating conditions; and characterisation and risk assessment for the treatment residue disposal route. The competent authority (provincial Omgevingsdienst) may require an Environmental Impact Assessment (MER\/EIA) for new facilities above capacity thresholds. Waste acceptance criteria (WAC) for permitted feedstocks must be part of the approved permit documentation and enforced through incoming material testing.<\/div>\n<\/details>\n
          \nQ10. Are there reference installations for solid waste rotary kiln SDS + bag filter + low-temperature SCR systems available for site visits?<\/summary>\n
          Yes. The integrated SDS dry desulfurization, pulse-jet bag filter, and low-temperature SCR denitrification technology described in this case study has been deployed at solid waste comprehensive processing and contaminated soil thermal treatment facilities including the installation documented here. Reference visits can be arranged for qualified prospective clients, including access to verified compliance monitoring data and the post-commissioning upgrade documentation that makes this installation particularly valuable as a reference for projects where initial characterisation data may be uncertain. Please use the contact link below to request reference documentation or to discuss the specific feedstock characterisation programme recommended before your treatment system design is finalised.<\/div>\n<\/details>\n<\/section>\n
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          Ready to Design a Reliable Solid Waste Off-Gas Treatment System?<\/p>\n

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

          From SDS dry desulfurization and low-temperature SCR for solid waste rotary kilns to regenerative thermal oxidation systems for industrial VOC abatement<\/a>, our engineering team delivers EU IED\u2013compliant solutions with the conservative design margins that complex waste applications demand.<\/p>\n

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