Influence of liquid and gas flow rates on sulfuric acid mist removal from air by packed bed tower

Abstract

The possible emission of sulfuric acid mists from a laboratory scale, counter-current packed bed tower operated with a caustic scrubbing solution was studied. Acid mists were applied through a local exhaust hood. The emissions from the packed bed tower were monitored in three different categories of gas flow rate as well as three liquid flow rates, while other influencing parameters were kept almost constant. Air sampling and sulfuric acid measurement were carried out iso-kinetically using USEPA method 8. The acid mists were measured by the barium-thorin titration method. According to the results when the gas flow rate increased from 10 L/s to 30 L/s, the average removal efficiency increased significantly (p < 0.001) from 76.8 ± 1.8% to 85.7 ± 1.2%. Analysis of covariance method followed by Tukey post-hoc test of 92 tests did not show a significant change in removal efficiency between liquid flow rates of 1.5, 2.5 and 3.5 L/min (p = 0.811). On the other hand, with fixed pressure loss across the tower, by increasing the liquid/gas (L/G) mass ratio, the average removal efficiency decreased significantly (p = 0.001) from 89.9% at L/G of <2 to 83.1% at L/G of 2–3 and further to 80.2% at L/G of >3, respectively. L/G of 2–3 was recommended for designing purposes of a packed tower for sulfuric acid mists and vapors removal from contaminated air stream.

Honeycomb Wet Scrubber For Acidic Gas Control: Modeling And Long-term Test Results&nbsp;

“…determining the optimal operating conditions [16,26,28], attempting to improve the performance of the existing WSs operating in high-tech industries [9,10,22], and designing lab-scale WSs for shortterm study only [13,19,29]. A WS packed with a multi-parallel-plate (MPP) module (PPWS) developed by our group can achieve very high removal efficiencies for HCl (> 99%), HNO3 (> 98%), and CH3COOH (> 99%) and very low pressure drop (23.5 Pa) at a regulated residence time of 0.5 s, a low inlet concentration (< 3 ppmv), and a high L/G ratio (18.5 L m -3 ) [11].…”

“…However, the measured removal efficiency (RE) of most of the traditional WSs can't meet the required value of greater than 95% [1]. For instance, the removal efficiency of a vertical packed WS with 1,500 CMM flow rate were 70.6-93.4% for HF, HCl, HNO2, HNO3, and CH3COOH at a high-tech factory while the removal efficiency of a lab-scale packed WS with 0.6-1.8 CMM flow rate was found to be as low as 76.8%-85.7% for H2SO4 mist [13]. When the removal efficiency of the WSs can't meet the standard value, they must follow the design criteria and operating conditions in which the specific surface area of packing materials must be ≥ 90 m 2 m -3 , the residence time through the scrubbing section must be ≥ 0.5 s, a wetting factor must be ≥ 0.1 m 3 h -1 , and the pH of scrubbing liquid must be ≥ 7 as shown in Table 1 [1].…”

“…For example, the removal efficiency of a multistage dual-flow sieve plate WS was 93.8% as Cin was as high as 100-300 ppmv for HCl [15] while a packed tower was found to have a removal efficiency of less than 90% when Cin was lower than 1.0 ppmv for HF and HCl [9,14]. The WSs normally have high pressure drop resulting in high power consumption and operation cost [13,16]. For example, a WS installed mesh MV filters operated at 90 CMM flow rate achieved > 95% removal efficiency for NH3 (L/G of 2.0 L m -3 ) at a high pressure drop of > 1,411 Pa [17].…”

“…The packing materials also need to resist fouling and corrosion, avoid particle clogging, and enhance water retention to minimize the pressure drop and maintenance cost for long-term use. In addition, they need to provide good air distribution for uniform absorption [13] and low pressure drop in the WSs. The pressure drop of a WS with conventional plastic packing materials is about 413-830 Pa (4.2-8.5 cmH2O) per meter of the packing column [23][24][25].…”

Honeycomb wet scrubber for acidic gas control: modeling and long-term test results

“…However, the measured removal efficiency (RE) of most traditional WSs cannot meet the required value of greater than 95% [1]. For instance, the RE of a vertical packed WS with a 1500 CMM (m 3 min − 1 ) airflow rate were 71-93% for HF, HCl, HNO 2 , HNO 3 , and CH 3 COOH at a high-tech factory while the RE of a lab-scale packed WS with a 0.6-1.8 CMM airflow rate was found to be as low as 77-86% for H 2 SO 4 mist [13]. When the RE of the WSs cannot meet the standard value, they must follow the design criteria and operating conditions in which the specific surface area of packing materials must be ≥90 m 2 m − 3 , the residence time through the scrubbing section must be ≥0.5 s, a wetting factor must be ≥0.1 m 3 h − 1 , and the pH of scrubbing liquid must be ≥7 as shown in Table 1 [1].…”