Analysis of the reasons for high hydrogen sulfide levels in ammonia-vaporization wastewater

When analyzing the reasons for the high content of hydrogen sulfide ions (which generally refer to sulfides, such as the anions HS- and S2- of hydrogen sulfide H2S) in ammonia-vaporized wastewater, we need to consider all the stages of the coking process where hydrogen sulfide ions may be generated. The following are some factors that may lead to an increase in hydrogen sulfide levels: 1. Sulfur content in the raw material (coal): Even if tests on the coal show that the hydrogen sulfide level is below 100, the sulfur present in the raw material can still be converted into sulfides during the coking process. Sulfur in coal exists mainly in the form of organic sulfur and inorganic sulfur (such as pyrite FeS2); during the coking process, organic sulfur is converted into sulfides such as H2S. 2. Coke oven operating conditions: Although the standard temperature for heating coke ovens remains stable, local temperature fluctuations can occur during operation. The temperature distribution and degree of coking may vary among different coke ovens, resulting in differences in sulfur release. 3. Waste gas treatment facilities for coke ovens: The efficiency of equipment used to treat sulfides, such as ammonia vaporization towers and sulfur recovery systems, may decline, resulting in some sulfides entering the ammonia vaporization wastewater without being effectively treated. 4. Gas condensation and cleaning process: High levels of thiocyanate after gas condensation indicate that sulfides may not have been completely removed during the gas cleaning process, or there could be equipment leaks or operational issues that result in the conversion of sulfides into hydrogen sulfide during cleaning. Regarding the mechanism of hydrogen sulfide formation, the following are the possible chemical reactions during the coking process: – During coking, the organic sulfur in coal decomposes and releases H2S. $\\text{Organic sulfur} → \text{Coke} + H_2S$ – During the coking process, inorganic sulfur present in coal, such as pyrite FeS2, decomposes at high temperatures to produce hydrogen sulfide. $\$\text{FeS}_2 + \text{oxygen} → \text{FeO} + 2H_2S$ – The reducing atmosphere inside the coke oven may cause some sulfates to be reduced to sulfur or hydrogen sulfide. $\$\text{Sulfates} + \text{reducing agent (such as carbon)} → \text{sulfur} (or H_2S) + \text{other products}$ – During the washing of coal gas, if ammonia solution is used for this purpose, hydrogen sulfide can be converted into ammonium sulfide (NH4HS) or ammonium bisulfide ((NH4)2S); however, excess sulfides may not be completely converted and are discharged along with the wastewater. To accurately determine the reasons for the high hydrogen sulfide content, recommended approaches include: conducting a comprehensive inspection of the entire coking and gas treatment system, with a focus on the efficiency of the waste gas and wastewater treatment systems. - Monitor the coal quality and operating conditions of different coke ovens at various times to determine whether there are local conditions causing abnormal sulfur release. - Consider the potential for cross-contamination, such as checking whether there is any leakage of waste fluid from desulfurization equipment or other sulfur-containing waste fluids into the ammonia vaporization wastewater. - Regularly inspect and maintain exhaust gas treatment equipment to ensure its efficient operation. Through these analyses and inspections, you should be able to more accurately identify the reasons for the high hydrogen sulfide content and take appropriate measures to resolve the issue. .