Characterization of sulphuric acid and ammonium sulphate aerosols in wet flue gas cleaning processes

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• 作者：S. Sinanis ; A. Wix ; L. Ana ; K. Schaber
• 关键词：Sulphuric acid nucleation ; Sulphuric acid aerosols ; Ammonium sulphate aerosols ; Absorption and aerosol formation
• 刊名：Chemical Engineering and Processing
• 出版年：2008
• 出版时间：January 2008
• 年：2008
• 卷：47
• 期：1
• 页码：22-30
• 全文大小：540 K

文摘

Sulphuric acid aerosols can be formed in wet flue gas cleaning processes by spontaneous condensation initiated mainly by homogeneous nucleation. Even at low gas inlet concentrations of SO₃ (2 mg/m³ (STP)) aerosol formation can be observed. For the design of absorption processes and sulphuric acid mist precipitators the aerosol characteristic data like mean diameter and number concentration are required for different process conditions and raw gas concentrations.

In the present contribution, a combination of an experimental method with the simulation tool AerCode is described, which permits the determination of the diameter and the number concentration of sulphuric acid aerosols formed in wet flue gas cleaning processes.

As a result of the extreme azeotropic phase behaviour of the H₂SO₄–H₂O system the mechanism of homogeneous nucleation is predominant for aerosol formation in absorption processes.

Furthermore, the influence of soluble and insoluble particles on homogeneous nucleation in the system H₂SO₄–H₂O is shown. The investigation of the influence of insoluble foreign nuclei shows that at high SO₃ raw gas concentrations >30 mg/m³ (STP), the mechanism of homogeneous nucleation is predominant. At lower raw gas concentrations between 2 and 10 mg/m³ (STP) SO₃ heterogeneous nucleation is the major reason for aerosol formation.

Solid (NH₄)₂SO₄ particles that are formed by the reaction between H₂SO₄ and NH₃ in the gas phase are used as soluble foreign nuclei. The studies show that aerosol formation is determined by the reaction component whose concentration is below the stoichiometric ratio. It was observed that in the case of an excess of sulphuric acid a decrease of the amount of ammonia leads to an increase of the particle size combined with a decrease in the number concentration. If ammonia is in excess, the decrease in the concentration of ammonia changes neither the particle size nor the number concentration of the aerosol significantly.