High-efficiency absorption of high NOx concentration in water or PEG using capillary pneumatic nebulizer packed with an expanded graphite filter

Abstract

Nitrogen oxide (NOx) absorption in water is more difficult compared with other exhausted gases such as SO2, CO2 and NH3, because NOx has low water solubility and nitrous acid is easily decomposed. We developed a NOx absorption equipment with a capillary pneumatic nebulizer equipped with an expanded graphite demister. The key parameters of the pneumatic atomizing absorption system were optimized. The selected parameters related to the high absorbent amount of NOx are as follows: diameter of the spray liquid pipe of 0.5–1.1mm, inlet gas pipe of 0.5–1.1mm diameter ratio of the gas–liquid pipe of 0.8–1.3, 0.740m of the spray height, MSP (minimum spray pressure) of 3–4, and R (gas–liquid mass flow ratio) of 300. With the optimal parameters, NOx removal efficiency and absorbent amount are highly relative to the absorbent, absorbent temperature, and absorbent time. A high feed NOx gas concentration results in high NOx removal efficiency because the surface area per water, nitric acid or polyethylene glycol (PEG) droplet volume was higher than that of the common gas–liquid surface. For the verification test, a high NOx gas concentration (200,000ppm) was treated with a series of absorption experiments and a NOx removal efficiency of 99.1% was attained. Furthermore, using PEG instead of water as an absorbent resulted in a larger absorbent amount at the same absorbent time and completely NOx removal in the gas.