Abstract
The synthesis gas leaving from the coal gasification process is having particulate matter and other gaseous pollutants majorly hydrogen sulphide and hydrogen chloride (HCl). Wet scrubbers can simultaneously remove the gaseous pollutants and dust particles from effluent gas streams. Dual-flow sieve plate column wet scrubbers can be used for the removal of acid gases from the exhaust gases. A three stage lab scale dual-flow sieve plate scrubber has been designed, fabricated and installed. Experiments were conducted to remove the HCl from the synthesis gas at different gas-liquid ratios within the gas flow rates (QG) 8.297 × 10-4 Nm3/s, 13.829 × 10-4 Nm3/s and 19.36 × 10-4 Nm3/s, liquid flow rates (QL) 20.649 × 10-6 m3/s, 34.415 × 10-6 m3/s and 48.183 × 10-6 m3/s and at different inlet HCl concentrations (CHCl,i) 100 ppm, 200 ppm and 300 ppm range using sodium hydroxide solution as scrubbing liquid. The maximum percentage removal of HCl (%ηHCl) 93.98% are observed at QG=8.297 × 10-4 Nm3/s, QL= 48.183 × 10-6 m3/s and CHCl,i=300 ppm with 0.005 kmol/m3 NaOH solution. A semi empirical model has been developed to predict the efficiency of the HCl scrubbing using the experimental results and the variables which show the impact on the scrubber performance. Almost 80% of the experimental results are matched well with the predicted values with less than ± 15% deviation.
Highlights
Coal is a combustible substance composed of carbon along with several impurities like sulphur, chlorine, and nitrogen and metal compounds
The percentage removal of hydrogen chloride (HCl) is increased with the increase in scrubbing liquid flow rate and decreased with the increase in gas flow rate at constant inlet concentrations of HCl
It can be concluded from the results that the percentage removal of HCl increased with inlet concentration of HCl which increases the solute concentration gradient between gas and liquid phase
Summary
Coal is a combustible substance composed of carbon along with several impurities like sulphur, chlorine, and nitrogen and metal compounds. These impurities get converted to gaseous species such as H2S, HCl and NH3 when this coal is processed. The chlorine present in the coal is volatilized to HCl or metal chlorides. The chloride content is high in US coals with 0.01% to 0.5% and during coal gasification process these chlorides will produce HCl [1]. The chlorine content of coal volatilizes to metal chlorides or HCl. But major portion of chlorine is converted into HCl. Reports show that there is a wide variation in the HCl concentrations in synthesis gas streams. Perkins et al [6] reported that the chloride deposited on syngas coolers accelerate the corrosion of the heat exchanger material and HCl reacts with the deposited scum of slag, forming low-melting iron chlorides, thereby expediting the corrosion rate
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