Shell-and-tube Heat Exchangers for Large-scale LFG Treatment

Shell-and-tube heat exchangers are employed for large-scale LFG treatment in scenarios where gas contains high dust levels or exhibits strong corrosivity.

The structural design and material selection of shell-and-tube heat exchangers directly address the stringent demands of large-scale LFG processing, offering distinct advantages in three key areas:

High corrosion resistance: The shell side (gas side) and tube side (cooling medium side) can be constructed from corrosion-resistant materials such as 316L stainless steel, duplex steel, or Hastelloy. This enables long-term resistance to corrosive components in LFG like hydrogen sulfide and ammonia, preventing pipeline leaks and extending equipment lifespan.

Easy Cleaning and Clog Resistance: Large-scale LFG processing involves high dust content. Shell-and-tube heat exchangers feature relatively spacious shell-side flow channels and can be designed with “removable tube bundles.” During shutdowns, these bundles can be directly opened for internal dust removal. Additionally, they can be paired with online high-pressure water flushing systems to periodically flush impurities from outside the tubes, preventing dust accumulation and flow channel blockages.

Scalable for Large-Scale, High-Load Applications: Shell-and-tube heat exchangers achieve extensive heat transfer area by increasing tube bundle quantity or expanding shell diameter. A single unit can process thousands of cubic meters per hour (e.g., 5,000–20,000 m³/h) of LFG, eliminating the need for multiple units in parallel. This simplifies system layout and reduces operational complexity.

For large-scale LFG treatment involving high dust content and strong corrosion, shell-and-tube heat exchangers require customized structural and component designs to ensure stable operation:

Flow Path and Tube Bundle Design:

The shell side employs large baffle plate spacing (typically ≥200mm) to minimize dust accumulation at baffles and reduce clogging risks. Simultaneously, “bow-shaped baffle plates” are selected to guide gas flow uniformly through the tube bundle, preventing localized low velocities that cause dust deposition.

The tube bundle utilizes “staggered row arrangement,” which enhances heat transfer efficiency while reducing dust retention between tubes for easier subsequent cleaning.

Sealing and Corrosion Protection Details:

Corrosion-resistant gaskets (e.g., fluororubber, graphite) are used for flange connections between tube sheets and shells to prevent corrosive LFG leakage and ensure site safety.

Shell-side inner walls can be coated with corrosion-resistant materials (e.g., epoxy resin, PTFE coating) for enhanced durability, particularly in highly corrosive environments with hydrogen sulfide concentrations exceeding 1000 ppm.

Cooling Medium Compatibility:

Circulating water or ethylene glycol solutions are preferred as cooling media for the tube side. For deep LFG cooling (e.g., below 15°C), refrigeration units can be integrated with shell-and-tube heat exchangers to achieve low-temperature cooling, ensuring effective dehydration (dew point ≤5°C).

Large-scale LFG treatment systems demand high continuous operation reliability. Maintenance of shell-and-tube heat exchangers must focus on “clogging prevention, corrosion control, and efficiency preservation”:

Regular Dust Removal: Shut down every 1-2 months to open the tube bundle housing and flush accumulated dust from the tube bundle outer surfaces with high-pressure water. For extremely high dust loads, activate the online flushing system weekly to maintain flow path integrity.

Corrosion monitoring and maintenance: Conduct “endoscopic” inspections of shell-side inner walls and tube bundles every 3 months. Inspect tube-to-tube-sheet welds every 6 months. Promptly repair corrosion points with corrosion-resistant coatings to prevent wall thinning and leakage.

Heat Transfer Efficiency Monitoring: Continuously record LFG inlet/outlet temperatures and cooling medium temperature differentials. If the differential narrows (e.g., from 20°C to below 10°C), prioritize investigating whether dust accumulation or scaling has reduced heat transfer efficiency. Promptly clean or acid-wash the tube side.