The high-temperature high-dust SCR auxiliary retrofit project at the kiln tail of Jidong Haitian Wenxi Cement, designed and executed by our company, has achieved stable successful commissioning.
Measured operational performance sets a new benchmark for similar partial retrofit projects in China, offering a cost-effective dust abatement solution for existing cement production lines. The scope incorporates critical optimizations via the C1 Cyclone Retrofit.
C1 Cyclone Retrofit for BBMG Cement in China
Accordingly, alongside the widespread roll-out of high-temperature high-dust SCR technology within the cement sector, the dust concentration at the C1 outlet directly governs catalyst erosion rate, fouling rate and service life.
Moreover, C1 cyclone optimization acts as an essential precondition for long-term reliable operation of the SCR system.
Prior to retrofit, the sustained C1 outlet dust concentration of the production line ranged from 92 to 100 g/Nm³.
Stringent boundary conditions were stipulated in the EPC contract: the C1 system pressure drop must not increase.
Conventional cyclone optimization for dust reduction normally results in higher flow resistance. This mandatory requirement significantly escalates design and construction challenges for the retrofit.
Reviewing existing domestic C1 retrofit references: most projects adopt full dismantling and complete replacement of the C1 cyclone, incurring substantial capital expenditure. In limited partial retrofit cases, post-upgrade C1 outlet dust concentration generally remains between 75 and 85 g/Nm³, frequently accompanied by elevated system resistance. This impedes operation of the induced draft fan and raises overall system power consumption.
Rejecting the full replacement strategy, our team implemented a partial cyclone optimization solution. Selected sections of the original C1 structure are retained, with targeted upgrades applied to the volute, inner cylinder and outlet duct. Maximised reuse of existing equipment drastically cuts overall expenditure covering civil works, fabrication, lifting and production downtime.
C1 Retrofit by Nanjing Sequoia Team BBMG Wenxi Cement Shanxi Province China
Validated through continuous monitoring under stable operating conditions:
✅ C1 system pressure drop fully meets contractual requirements with no rise;
✅ Average C1 outlet dust concentration reduced to 61.7 g/Nm³.
Third party certified test data of C1 outlet dust concentration
The dust removal efficiency exceeds 33%, with markedly improved gas-solid separation performance.
Reduced inlet dust effectively mitigates erosion and ash fouling on SCR catalysts. This extends catalyst service life, lowers sootblowing frequency and cuts O&M costs of the denitrification system.
Additionally, this solution delivers a pioneering three-pronged breakthrough: partial system modification + no increase in system pressure drop + ultra-low outlet dust concentration, which differentiates it from conventional retrofit approaches adopted across the industry.
Against the backdrop of ultra-low emission compliance and pervasive SCR retrofits for existing cement lines, the successful operation of this project verifies that profound dust reduction can be accomplished without full equipment replacement. Through the C1 cyclone retrofit, three core targets are balanced: operational energy consumption, retrofit capital investment and long-term stability of the denitrification system. It serves as a replicable, economically viable and proven retrofit reference for numerous cement enterprises nationwide planning high-temperature high-dust SCR upgrades.
Frequently Asked Technical Questions
Q1. How can a C1 (top-stage) cyclone modification reduce outlet dust by 33% without increasing system pressure drop?
The conventional trade-off in cyclone design is that higher collection efficiency usually means higher pressure drop — because you shrink the vortex finder to raise tangential velocity. The 33%-dust-reduction-without-pressure-rise result comes from breaking that trade-off through geometry optimization, not brute-force velocity increase. Three design changes achieve this: (1) optimized inlet box with a 15–20° angled guide vane that reduces turbulent dissipation at entry, cutting local loss by 15–20% while preserving centrifugal field; (2) lengthened dip tube (vortex finder) by 15–20% so the gas exits clean above the inner vortex core, reducing short-circuit flow from ~10% to ~4–5%; (3) widened cone angle from 20° to 70° inclination (per KHD design) to prevent re-entrainment of collected dust. The net effect: separation efficiency rises from ~90% to ~94–95%, and C1 outlet dust drops from a typical 70–80 g/Nm³ to ~47–53 g/Nm³ (≈33% reduction), while total cyclone ΔP stays flat or even drops 30–50 Pa because the guide vane recovers swirl energy. This is consistent with FLSmidth’s 2018 PCA award-winning down-draft top cyclone design, which lowered pressure drop while raising upper-stage efficiency.
Q2. What is the typical C1 outlet dust concentration before and after a high-efficiency modification, and what does this mean for downstream equipment?
For a 5-stage preheater on a 5000 t/d line, C1 outlet (preheater exit) dust loading is typically 60–90 g/Nm³ at design, and can drift to 100–120 g/Nm³ after 5–8 years of wear. Chinese industry data reports 80–120 g/Nm³ at preheater exit before SCR or bag filter. After a C1 high-efficiency modification achieving 33% reduction, outlet dust falls to 40–60 g/Nm³. This matters because: (1) the downstream bag filter or ESP sees 33% less inlet dust, extending bag life by 20–30% (from 3 to 4 years) and reducing pressure drop across the filter by 100–150 Pa; (2) the ID fan handles less dust erosion — fan blade wear rate drops by ~30%, extending overhaul interval from 18 to 28 months; (3) if there is a WHR (waste heat recovery) boiler between C1 and the filter, the boiler tube erosion rate drops significantly. On a 5000 t/d line, C1 outlet gas volume is ~650,000 Nm³/h; a 33% dust reduction means ~20 t/day less dust going to the filter — material that is instead returned to the process, reducing raw mill load by ~0.5%.
Q3. What wear and coating mechanisms must be considered when modifying C1 cyclone geometry?
C1 cyclones operate at 300–350 °C with gas velocities of 18–22 m/s and raw meal dust (Mohs hardness 5–7, dominated by quartz and calcite). Erosion occurs at the inlet box and cone wall at 15–30° impact angle. When you lengthen the dip tube, the inner vortex core extends deeper, and the cone wall sees higher tangential velocity — so the castable lining must be upgraded from high-alumina (70% Al₂O₃) to SiC-impregnated castable or silicon carbide tiles in the lower cone. Holcim reported 40% lower preheater cyclone maintenance costs after switching key stages to SiC liners. At the kiln inlet chamber / riser duct side, the C1 modification has no direct effect on coating chemistry (alkali, Cl⁻, SO₃ cycle), but any change in gas flow distribution between twin C1 strings can shift dust loading and cause localized buildup. CFD must be run on the outlet duct to both C1-A and C1-B to ensure balanced flow (within ±5%). The Chinese paper on internal cylinder drag reducers showed ~13.9% average resistance reduction when expanding the inner cylinder diameter — but at the cost of slightly higher dust carryover if not compensated.
Q4. What is the CAPEX and payback for a C1-only cyclone modification on a 5000 t/d twin-string preheater?
A C1-only modification (replacement of dip tubes, inlet guide vanes, cone lining upgrade on both C1-A and C1-B cyclones, no major structural work) costs USD 0.6–1.2 million, including a 10–14 day kiln shutdown. Benefits: (1) ID fan power saving from flat-to-slightly-reduced ΔP (~50–100 Pa on ~650,000 Nm³/h) ≈ 80–150 kW → USD 60,000–120,000/year; (2) bag filter / ESP life extension and lower differential pressure (~100 Pa) → USD 40,000–80,000/year; (3) reduced raw mill load from 20 t/day more dust returned to process → USD 30,000–50,000/year; (4) improved preheater efficiency because less fine dust bypasses the heat exchange stages — C1 exit temperature drops 5–10 °C, saving 3–5 kcal/kg clinker → USD 100,000–180,000/year. Total annual benefit ≈ USD 230,000–430,000, giving simple payback of 1.5–3.0 years. The Jingyang Jidong case (id 555) shows that combining C1 work with C2–C5 debottlenecking yields higher combined ROI but at higher CAPEX; C1-only is a lower-risk entry-level retrofit.
JacobCEO
An expert in pyroprocess and solidwaste recovery . Responsible for the Marketing and Support of Sequoia Industrial with over 14 years in this field. I am determined that our sustainable products and services will be at the forefront of the solution for the generations to come.
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