Study On Dry Purification Of Hydrogen Chloride At Moderate To High Temperature In A Dual-layer Granular Bed Filter

As a new technology, the dual-layer granular bed filter had been applied to remove dust from flue gas of aluminum smelting furnace in industry. Based on the new technology, in this paper the experiments on removal of hydrogen chloride from flue gas in a dual-layer granular bed filter were carried out. The experimental system consisted of flue gas simulation system, injecting sorbents system, dual-layer granular bed filter system, temperature control device and gas analysis system. The dual-layer granular bed filter was put in a tube furnace in which temperature could be controlled. The main experiments and results are as followings:1. The experiments researching on dechloridization by calcium-based sorbents in a dual-layer granular bed filter were carried out to inveatigate the effects of these factors: temperature, Ca/Cl mole ratio, CO₂ content, water vapour content and so on. The results showed that temperature had great effects on dechloridization of calcium-based sorbent in the bed and the dechloridization efficiency of Ca(OH)2 increased obviously with the increasing of temperature. At Ca/Cl mole ratio of 1, 2.5, 5, the dechloridization efficiencies were 48～52%, 73～77%, 78～88%at 500℃respectively, while 65～68%, 80～83%, 91～95%at 600℃, and 42～44%, 56～60%, 81～82%at 700℃correspondingly. At the same time, it also showed that the dechloridization efficiency increased as Ca/Cl mole ratio increased. At 500℃, at Ca/Cl mole ratio of 2.5 and 5, the dechloridization efficiencies were about 60% and 70%, respectively. At 600℃, at Ca/Cl mole ratio of 2.5, the dechloridization efficiency was about 80%, while at Ca/Cl mole ratio of 5, the dechloridization efficiency was up to 90%.At Ca/Cl mole ratio of 2.5, the addition of 10% CO₂ made the dechloridization efficiency drop 7¹0 percents, and the calcium utilization efficiency decrease from 74.4% to 36.8% compared to the case without CO₂ at 600℃.At Ca/Cl mole ratio of 2.5, the dechloridization efficiency increased by 4⁹ percents at 600℃in precence of 10% water vapour in simulating flue gas compared to the absence of water vapour, and the dechloridization efficiency of sorbent Ca(OH)2 increased 3⁵ percents when the mass ratio of the sorbent to fly ash equaled 1 compared to the case without addition of fly ash. 2. The experiments researching on dechloridization by sodium-based sorbent in a dual-layer granular bed filter were carried out to investigate the sodium utilization efficiency. The results showed that the utilization efficiencies of sodium bicarbonate were 44.3% at 100℃, 57.4% at 150℃, 51.6% at 200℃, 40.3% at 300℃, and 35.4% at 400℃. This indicated that the sodium utilization efficiency was the highest at 150℃. 3. The experiments researching on dechloridization by modified calcium-based sorbent in a dual-layer granular bed filter were carried out to investigate the effect of temperature to the calcium utilization efficiency. The result showed that the activity of modified calcium-based sorbent rapidly increased. At Ca/Cl mole ratio of 2.5, the utilization efficiencies of calcium-based were 42.4% at500℃, 53.8% at 600℃, and 45.7% at 700℃. And the calcium utilization efficiency of modified calcium-based asorbent was 1.5 times that for common calcium-based sorbent at 600℃.