Far-infrared detection after chemical cleaning and scale removal of the tower top air cooler in the reforming depentanizer tower

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Sample name: Sediment. Sampling location: 1# Reforming unit. Sampling site: Top of the pentane removal tower. Sampling date: 2021.05.01. Date of issuance: 2021.05.02. Sample appearance: Gray sediment with light green crystalline particles mixed in it. Figure 1. Appearance of the sample. Figure 2. Crystalline particles in the sample. Figure 3. Residues after high-temperature treatment. Analysis results: 1. Water solubility test: It dissolves in water at room temperature, with the crystalline particles dissolving more quickly than the grayish powder particles. No obvious insoluble particles were observed. When just dissolved, the solution of the powder is colorless and transparent (Figure 4); after being stored for a certain period of time, it turns brownish-yellow (Figure 5). Figure 4: Solution just after dissolution. Figure 5: Solution after being stored overnight. Figure 6: Precipitate titrated with silver nitrate. 2. High-temperature calcination test: When exposed to air at high temperatures, the gray powder transforms into a reddish-brown color similar to rust (see Figure 3), and a large amount remains; the residue from the ash test amounts to 50%. It is confirmed to be not the ammonium chloride as commonly assumed. Because ammonium chloride decomposes and vaporizes at 337°C, no residues remain. 3. Silver nitrate titration test: The silver nitrate titration determined a chlorine content of 35.2% in the crystals and 38.9% in the powder. The precipitate is white, ruling out the possibility of sulfides (silver sulfide is a black precipitate). Ion chromatography analysis confirmed it to be chloride ions. 4. Atomic absorption analysis for iron content: The iron content in different parts ranges from 20% to 40%. Conclusion: 1. This precipitate is a hydrate of ferrous chloride (with some ferric chloride). 2. The white powder is a derivative of the light green crystals. Due to water loss during the weathering process, the chlorine content of the powdery material is slightly higher than that of the crystalline material. 3. The ferrous chloride solution is oxidized by dissolved oxygen in water, with part of it converting to ferric ions; as a result, the color of the solution changes from colorless (or light green) to brownish-yellow. ----------- Solution: In May 2023, Dalian Tianfan adopted AOLO’s proprietary technology for online cleaning and descaling using ammonium chloride salts and similar substances, achieving excellent results.