The manufacturing process of waste heat recovery heat exchangers is a systematic engineering project integrating precision machining, materials science, and thermodynamic design. Its core objective is to achieve efficient, stable, and long-life heat energy recovery under complex operating conditions such as high temperature, corrosion, and high pressure. The entire manufacturing process can be divided into five key stages: core component processing, shell and frame fabrication, tube bundle assembly and welding, quality inspection, and surface anti-corrosion and coating.
Core Heat Exchange Component Manufacturing: The Foundation for Heat Transfer Efficiency
Heat exchange components are the "heart" of the equipment; their performance directly determines the overall efficiency and durability.
Finned Tube Processing (Suitable for Flue Gas Waste Heat)
High-quality seamless steel or stainless steel tubes are used as the base tube. Steel strips are fixed to the surface of the base tube using high-frequency welding or mechanical winding processes to form fins, significantly increasing the heat exchange area. High-frequency welding achieves a metallurgical bond between the fins and the base tube, resulting in a thermal resistance as low as ≤0.001㎡・℃/W, ensuring highly efficient heat conduction.
Common materials include:
ND steel: Suitable for medium- and low-temperature sulfur-containing flue gas (≤400℃)
316L stainless steel: Resistant to chloride ion corrosion, suitable for highly corrosive environments such as chemical plants and seawater sources
Duplex stainless steel/nickel-based alloy: Used in ultra-high temperature (>800℃) or high-pressure scenarios, such as waste incineration and metallurgical industries.
Plate heat exchanger plate forming (suitable for liquid waste heat):
Uses stainless steel (304/316L) or titanium alloy plates, formed into corrugated plates through stamping process to enhance turbulence and improve heat transfer coefficient. Plates are sealed by welding or gaskets, with a pressure resistance of 1.0–2.5MPa.
Heat pipe element manufacturing (suitable for medium- and low-temperature waste heat):
Utilizes a carbon steel-water gravity heat pipe structure, internally evacuated and filled with working fluid, utilizing evaporation-condensation phase change to achieve ultra-high thermal conductivity (heat transfer coefficient nearly an order of magnitude higher than traditional metals), suitable for operating conditions of 50–400℃.
Shell and Frame Fabrication: Ensuring Structural Strength and Sealing
The sheet metal is made of Q345R carbon steel or stainless steel, with the thickness determined based on the design pressure (typically 0.1–0.6 MPa). Forming is achieved through laser cutting and plate rolling.
The longitudinal and circumferential seams of the shell are welded using automatic submerged arc welding or gas shielded welding, employing a multi-layer, multi-pass welding process, and undergoing 100% ultrasonic testing to ensure the absence of defects such as incomplete fusion and porosity.
The tube sheet is machined from forgings, with precise holes drilled using a CNC milling machine (hole diameter 0.1–0.2 mm larger than the heat exchange tubes) to ensure the accuracy of expansion joints or welding.
Tube Bundle Assembly and Welding: Ensuring Structural Stability and Leakage Prevention
The machined finned tubes or heat exchange tubes are inserted into the tube sheet, and a hydraulic tube expander is used to complete the expansion joint, ensuring a tight connection between the tubes and the tube sheet to prevent media leakage.
For high-temperature flue gas equipment, baffles or guide plates are also required to optimize airflow paths and avoid localized blockages or wear.
Plate heat exchangers are sealed with a uniform pressure of 20–30 MPa using clamping bolts to ensure a leak-free seal between the plates.
Strict Quality Inspection: Key Control Before Shipment
Each piece of equipment must pass multiple tests:
Hydraulic Pressure Test: Pressure is maintained at 1.5 times the design pressure for 30 minutes to check for leaks in welds and expansion joints.
Air Tightness Test: Compressed air is introduced, and the weld points are tested with soapy water to ensure no air bubbles are generated.
Heat Transfer Performance Test: Simulating actual operating conditions, the heat transfer efficiency is verified to meet standards. For example, waste heat recovery equipment requires a waste heat recovery rate of ≥80%.
Corrosion Resistance Test: Equipment used with corrosive media undergoes a neutral salt spray test (48 hours without rust).