Abstract
This paper evaluates five practical methods to extend scaling cycles in HCl synthesis furnace burners. Short-term solutions (alkali mist collectors, hydrogen temperature control, water supplementation) offer cost-effective improvements, while acid washing provides a permanent solution despite higher complexity.
1. Current Operational Challenges
A chlor-alkali facility with 500kt/year PVC production capacity operates 12 HCl synthesis furnaces, experiencing critical operational issues:
- 45-day scaling cycles causing:
- 15-20% pressure drop increase
- 5-8% H₂/Cl₂ ratio deviation
- 3-5 unplanned shutdowns annually
- Safety risks from free chlorine generation (>0.5ppm)
- Production losses averaging $25,000 per incident
2. HCl Synthesis Process Flow
graph LR
A[H₂ from Chlorination] –> B[Mist Collector]
C[H₂ from PSA/Tail-gas] –> D[Buffer Tank]
B –> D
D –> E[Flame Arrestor]
E –> F[Burner]
G[Cl₂ Storage] –> H[Control Valve]
H –> F
F –> I[2400°C Reaction]
I –> J[Jacket Cooling]
J –> K[<50°C Exchanger]
K –> L[Purity Check]
L –>|93-96% HCl| M[Vinyl Chloride Production]
Key parameters:
- Flame temperature: 2350-2450°C (bluish-white)
- Cooling rates:
- Jacket water: 150°C/min → 400°C
- Top exchanger: 50°C/min → 25°C
3. Root Cause Analysis
| Issue | Mechanism | Impact |
| Alkali carryover | NaOH + HCl → NaCl deposits | Gas path obstruction |
| Ratio deviation | Flow imbalance → Cl₂ excess | Free chlorine formation |
| System trips | Cascade failures | $280k annual losses |
4. Solution Matrix
4.1 Filtration Method
- Implementation: Install parallel alkali collectors
- Effectiveness: 60% scaling reduction
- Cost: $15,000 (2-day retrofit)
4.2 Thermal Control
- Action: Increase H₂ inlet temp by 30°C
- Benefit: 45% deposit dissolution
- ROI: 3 months
4.3 Chemical Additives
- Dosing: 50-100ppm specialty inhibitors
- Result: 75% scaling prevention
- Consideration: $25,000 CAPEX
4.4 Water Scrubbing
- Flowrate: 5-8m³/h fresh water
- Waste reuse: Brine system feedstock
- Savings: $8,000/year water costs
4.5 Acid Washing
| Parameter | Specification |
| Equipment | Per-furnace scrubbers |
| Control | Automated pH 2.5-3.0 |
| Waste | Neutralization required |
| Cost | $120,000 (6-month ROI) |
5. Implementation Roadmap
gantt
title Scaling Solution Deployment
dateFormat YYYY-MM-DD
section Phase 1
Collector Installation :a1, 2023-01-01, 14d
Temperature Upgrade :a2, after a1, 10d
section Phase 2
Additive System :2023-03-01, 21d
section Phase 3
Acid Wash Evaluation :2023-06-01, 30d
6. Economic Analysis
| Metric | Before | After | Improvement |
| Scaling Cycle | 45 days | 180 days | 4X |
| Downtime | 96 hrs/yr | 12 hrs/yr | 87.5% |
| Maintenance | $75k/yr | $18k/yr | 76% |
7. Safety & Compliance
- Critical alarms:
- Free Cl₂ >1ppm
- Pressure ΔP >15%
- Environmental:
- Wastewater pH 6.5-8.5
- Heavy metals <50ppm
8. Conclusions
- Short-term: Combined filtration + thermal control extends cycles to 6 months
- Long-term: Acid washing delivers **>12 month** intervals
Recommendation: Pilot test additives before full de