how does air to air heat exchanger work in nmp heat recovery

An air-to-air heat exchanger in NMP heat recovery transfers thermal energy between a hot, NMP-laden exhaust air stream from an industrial process and a cooler incoming fresh air stream, improving energy efficiency in industries like battery manufacturing.

The hot exhaust air (e.g., 80–160°C) and cooler fresh air pass through separate channels or over a heat-conductive surface (e.g., plates, tubes, or a rotary wheel) without mixing. Heat transfers from the hot exhaust to the cooler fresh air via sensible heat transfer. Common types include plate heat exchangers, rotary heat exchangers, and heat pipe heat exchangers.

NMP-specific designs use corrosion-resistant materials like stainless steel or glass fiber-reinforced plastic to withstand NMP’s aggressive nature. Larger fin spacing or clean-in-place systems prevent fouling from dust or residues. Condensation is managed to avoid blockages or corrosion.

The hot exhaust air transfers heat to the fresh air, preheating it (e.g., from 20°C to 60–80°C) and reducing energy needs for subsequent processes. The cooled exhaust air (e.g., 30–50°C) is sent to an NMP recovery system (e.g., condensation or adsorption) to capture and recycle the solvent. Heat recovery efficiency is 60–95%, depending on the design.

This reduces energy consumption by 15–30%, lowers greenhouse gas emissions, and improves NMP recovery by cooling the exhaust air for easier solvent capture. Challenges like fouling are addressed with wider gaps, extractable elements, or cleaning systems, while robust sealing prevents cross-contamination.

In a battery manufacturing plant, a plate heat exchanger preheats fresh air from 20°C to 90°C using 120°C exhaust air, reducing oven energy demand by ~70%. The cooled exhaust air is processed to recover 95% of NMP.