Sulphur Tail Gas Thermal Oxidizer

This system is best suited for Claus unit tail gas and sulphur recovery operations handling H₂S, COS, CS₂, and mercaptans. It is widely used in:

Key Applications:

• Refineries - Claus sulphur recovery unit tail gas treatment
• Gas processing plants - Sour gas sweetening operations
• Petrochemical facilities - Sulphur-bearing process vents
• Hydrogen plants - PSA off-gas with sulphur species
• Chemical manufacturing - Processes using or producing sulphur compounds

System Purpose:

• Final destruction of reduced sulphur compounds to meet environmental limits
• Convert H₂S, COS, CS₂ to SO₂ (which can be scrubbed or meets direct emission limits)
• Handle variable SRU loads during start-ups, shutdowns, and upset conditions
• Reliable backup to sulphur recovery processes

Why Specialized Equipment Is Required:

• Corrosive environment - H₂S and SO₂ attack standard materials
• Variable sulphur loading - Wide range from normal to upset conditions
• High operating temperatures - Ensure complete sulphur compound oxidation
• Regulatory stringency - Very low SO₂, NOx, and unburnt hydrocarbon limits

They are designed to absorb load fluctuations during start-ups, shutdowns, and upset conditions using stable combustion design, high-integrity refractory systems, and advanced control strategies tailored for sulphur service.

Variable Load Challenges:

Normal Operation:

• Steady-state Claus tail gas - Consistent H₂S concentration (typically 0.5-2%)
• Predictable flow - Relatively stable
• Minimal fuel required

Upset Conditions:

• Claus unit upsets - H₂S concentration spikes (can reach 10-30% or higher)
• Start-up/shutdown - Variable composition and flow
• Catalyst poisoning - Increased sulphur slip through Claus beds
• Process unit upsets - Feed gas composition changes

How CRA Systems Handle Variability:

1. Combustion System Design:

• Wide turndown burners (10:1 or greater)
• Modulating fuel control responds to heat input changes
• Auto-ignition capability for high H₂S loads
• Flame stability across full operating range

2. High-Integrity Refractory:

• Thermal shock resistant materials
• Anchoring systems prevent spalling during thermal cycling
• Multi-layer design - Hot face, insulating, backup layers
• Expansion joints accommodate temperature variations

3. Temperature Control:

• Automatic modulation maintains set point during load swings
• Heat release monitoring adjusts for varying H₂S heating value
• Override controls prevent over-temperature

4. Oxygen Control:

• Trim air maintains excess oxygen set point
• Monitors combustion efficiency
• Prevents fuel-rich or oxygen-starved conditions

5. Safety Systems:

• High-temperature shutdown protects refractory
• Flame monitoring with auto-relight
• Low-oxygen alarms for combustion safety
• Bypass capability for emergency situations

Properly engineered systems typically achieve greater than 99.99% destruction efficiency for reduced sulphur compounds while maintaining stable performance across variable operating conditions.

Performance Standards:

• H₂S destruction: >99.99%
• COS and CS₂ destruction: >99.9%
• Overall sulphur recovery: Often >99.5-99.9% when integrated with Claus unit
• SO₂ emissions: Typically <250 ppm (or lower per local regulations)

Reactions in Thermal Oxidizer:

• H₂S + 3/2 O₂ → SO₂ + H₂O
• COS + 3/2 O₂ → SO₂ + CO₂
• CS₂ + 3 O₂ → 2SO₂ + CO₂
• Mercaptans + O₂ → SO₂ + H₂O + CO₂

Ensuring High DRE:

• Temperature control: 650-1,480°C depending on sulphur load
• Residence time: Minimum 1-2 seconds
• Excess oxygen: Sufficient for complete oxidation
• Burner design: Even temperature distribution
• Continuous monitoring: SO₂, O₂, CO verification

Several interconnected parameters directly influence performance:

1. Operating Temperature:

• Range: Typically about 650-1,480°C (1,200-2,700°F) depending on sulphur loading
• Normal Claus tail gas: 950-1,050°C (1,740-1,920°F)
• High H₂S upsets: May reach 1,200-1,480°C (2,190-2,700°F) auto-thermally
• Control philosophy: Balance between complete destruction and refractory protection

2. Residence Time:

• Typical: 1-2 seconds minimum at oxidation temperature
• Purpose: Complete conversion of all sulphur species to SO₂
• Design: Chamber volume sized for worst-case flow

3. Combustion Air Control:

• Excess oxygen: 2-5% in stack
• Stoichiometry: Sufficient for complete oxidation
• Trim control: Automated adjustment based on O₂ measurement

4. Refractory Selection:

• Hot face: High-alumina castable (for thermal/chemical resistance)
• Insulation: Lightweight insulating firebrick or ceramic fiber
• Thickness: Typically 200-450mm (8-18 inches) total
• Anchors: Stainless steel or Inconel for longevity

5. Corrosion-Resistant Materials:

• Shell: Carbon steel with refractory lining
• Ductwork: 316 stainless steel minimum (SO₂/SO₃ environment)
• Stack: Acid-resistant materials (FRP, exotic alloys, or brick-lined)
• Instruments: Wetted parts in Hastelloy or Teflon-coated

6. Downstream Treatment (If Required):

• SO₂ scrubbing with caustic or lime if emission limits require
• Selective catalytic reduction (SCR) for NOx control if needed
• Stack gas reheat to prevent visible plume

7. Monitoring and Controls:

• Temperature profiling - Multiple zones
• O₂ and SO₂ analyzers in stack
• Pressure differential monitoring
• Refractory temperature thermocouples
• Safety interlocks and automated controls

Critical for: Consistent oxidation of all reduced sulphur species, Equipment longevity in corrosive sulphur service, Long-term reliability during variable SRU operation, and Regulatory compliance for SO₂, NOx, and particulate emissions.

CRA's 30+ Years of Sulphur Service Experience: CRA delivers oxidizers built specifically for extreme sulphur service with proven refractory designs, corrosion-resistant materials, and advanced controls that ensure reliable performance year after year.

No. The information in these FAQs is for general guidance only. Every application is unique, and actual performance depends on your specific process conditions, site requirements, and operating parameters. Detailed engineering analysis of your process data is required to provide accurate specifications and performance guarantees. Contact CRA's engineering team for a comprehensive proposal tailored to your specific needs.

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