Seeking expert advice: What is a good material for corrosion protection in the absorption tower of a desulfurization island?

It can be directly made of fiberglass reinforced plastic; currently, there are many manufacturers in China that produce fiberglass reinforced plastic desulfurization absorption towers

The absorption tower is 22 meters tall and 8.3 meters in diameter; the liquid level during operation is 13.4 meters. Moreover, there are many accessories inside the absorption tower – will the strength of fiberglass be sufficient to meet the requirements?

Temperature? Pressure? Solvent? The general process? Other corrosive media? Analysis is impossible without either one

For FGD corrosion protection in power plants, rubber lining or glass flake coating is generally used; these technologies are quite mature. However, they require specialized construction teams to apply them, and they differ fundamentally from ordinary paints. It is recommended that rubber lining be used in absorber towers – it is a safer option based on current practices. This is especially true for the spray layer. Domestic desulfurization and environmental protection companies were not fully developed when they adopted foreign designs; for components such as flue ducts and emergency slurry tanks, vinyl resin glass flakes can be used without any problems. You can call for consultation and discussion. www.longhai-ant.com

There should be no major issues with fiberglass-reinforced plastic; the key is to ensure high quality! The fiberglass-reinforced plastic material itself should be able to meet the requirements

The issue with fiberglass-reinforced plastic is not related to strength, but rather to the process of shaping it. It was mentioned on the 3rd floor that there are many accessories inside the tower; when there are numerous such accessories, there are also many irregular corners and protrusions, which makes it very difficult to achieve proper shaping of the fiberglass-reinforced plastic. I agree with the part regarding the rubber lining in what was said on floor 5. Actually, the cost of lining with rubber isn’t that high. If you calculate the costs, the expense related to corrosion protection accounts for only a small portion of the total cost of a piece of equipment, yet it plays a very important role. With good performance, a piece of equipment can last 10 years; whereas if its performance is poor, it may need to be replaced after 1 or 2 years, or at least its components will need to be replaced. So which option is more cost-effective? This does not yet include the downtime losses caused by equipment maintenance, nor the damage to product quality resulting from equipment corrosion.

The anti-corrosion materials used in the FGD system of the desulfurization island include: 1. Non-metallic materials. In areas where the surface of metallic materials may come into contact with corrosive substances, non-metallic materials with strong resistance to corrosion and wear should be used, depending on the specific conditions in different parts of the desulfurization process. Glass flake resin – Main components: glass flakes (thin pieces of glass), vinyl ester resin, phenolic resin, furan resin, epoxy resin. Application areas: flue gas after purification, flues in the low-temperature raw flue gas section ； Lining for absorption towers, slurry tanks, etc.: Plastics such as polypropylene (PP): Used in pipes and mist eliminators. Fiberglass reinforced plastic (FRP): Main components include glass flake, glass fiber, vinyl ester resin, and phenolic resin; used in the spray layers of absorption towers and slurry pipes. Rubber: Main components include butyl rubber, neoprene, and styrene-butadiene rubber; used for lining absorption towers, slurry tanks, slurry pipes, hydrocyclones, etc., as well as on the conveyor belts of vacuum dehydrators. Ceramic: Main component is silicon carbide (SiC); used in slurry nozzles. 2. Metal materials: For those parts that come into contact with corrosive substances, when using non-metallic materials as linings on carbon steel is not sufficient for practical engineering applications, stainless steel based on nickel alloys, iron-nickel-chromium alloys should be used, depending on the corrosivity and wear resistance of the substance. Applied to clean flue gas, low-temperature raw flue gas, slurries with a pH of 3–6 and containing 60,000 mg/l of Cl‑, as well as slurries with a pH of 3–6 and containing 60,000 mg/l of Cl‑.

Scaled linings and rubber linings vulcanized (or pre-vulcanized) under atmospheric pressure have been widely recognized by relevant industries at home and abroad as the two main corrosion-resistant lining technologies used in flue gas desulfurization absorption towers in thermal power plants. Since the cost of rubber lining is higher than that of flake lining, and flake lining is required to be used in combination with it, plus the difficulty in repairing it after molding, flake lining is more commonly chosen in the application of corrosion engineering technologies in this field.

a. Bottom plate of the absorption tower, and inner surfaces on the sides at a height of 2m or less ◎ The lining in these areas must meet the following requirements； Corrosion resistance: Resistance to corrosive liquids in the absorption tower. Wear resistance: Resistance to impacts from stirred liquids. ◎ For corrosion resistance, the scale lining material HF-161 is used, which consists of a double layer of butyl rubber B-5S4mm along with a vinyl ester resin that exhibits excellent corrosion resistance as the base resin. To enhance wear resistance, glass fiber cloth is added to HF-161, and an additional layer of glass mat is applied to the surface to maintain smoothness and flatness. b. Spraying area of the absorption tower ◎ The temperature in this area is not very high, but it is exposed to the spray liquid during operation; therefore, the lining materials for these areas must meet the following requirements: Corrosion resistance: tolerance to the corrosive substances present in the absorption tower. Wear resistance: tolerance to the impact of the spray liquid. ◎ For corrosion resistance, the scale-lined material HF-161, which uses a vinyl ester resin with excellent corrosion resistance as its base resin, is employed. Regarding wear resistance, HF-161 is lined with a layer of vinyl ester resin HF-263 containing ceramic particles, followed by reinforcement with a layer of glass cloth; the glass cloth is then treated for wear resistance using another layer of HF-163 containing ceramic particles. c. Inner surface on the side surrounding the inlet of the original flue ◎ The temperature at the inlet is high, while the temperature in the tower section is not high. However, considering that there is no process fire-fighting water available at this location, and that if the flue dampers cannot be closed in the event of an accident and the spraying system does not function, the temperature inside the tower will rise; therefore, the scale lining material HF-181, which uses a heat-resistant phenolic vinyl ester resin as its base resin, is used in this area. At the same time, due to the wear caused by the spray water, a layer of HF-283 containing ceramic particles is applied to the surface of HF-181 to resist wear. d. Impact-prone area at the flue gas outlet of the absorption tower ◎ The lining in this area must meet the following requirements: Corrosion resistance: Resistance to corrosion by the gases exiting the absorption tower and any volatile liquids. Wear resistance: Resistance to wear caused by the gases exiting the absorption tower and the evaporated liquids. ◎ For corrosion resistance, the flake lining material HF-161 is used, which employs a vinyl ester resin with excellent anti-corrosion properties as its base resin. e. Installation of the inner surface on the side of the demisting area ◎ The lining in this area must meet the following requirements: Corrosion resistance: Resistance to corrosion by the gases exiting the absorption tower and any volatile liquids. Wear resistance: Resistance to wear caused by the gases exiting the absorption tower and the evaporated liquids. ◎Regarding corrosion resistance, the flake lining material HF-161 is used, which employs a vinyl ester resin with excellent anti-corrosion properties as its base resin; as for resistance to impact from outlet gases, a topcoat is applied over HF-161, and this topcoat provides wear resistance. f. Other areas: ◎ Since these areas are not subject to high temperatures or wear, the flake material HF-161, which uses a vinyl ester resin with excellent corrosion resistance as its base resin, can be used; glass fiber cloth is used for reinforcement in the corners. However, I feel that given the current quality of materials available on the market, the price difference between rubber lining and scale coating isn’t significant. Based on experience from long-term construction projects and subsequent maintenance work, as long as one finds capable manufacturers and contractors, rubber lining proves to be more durable than scale coating

The operating media in the absorption tower are gypsum slurry and clean flue gas. During normal operation, the flue gas temperature at the inlet of the absorption tower is around 94°C. The absorber tower shell is made of carbon steel, with its inner surface fitted with a rubber lining as part of the anti-corrosion design and construction. All anti-corrosion components inside the absorption tower that are made of non-alloy steel/stainless steel but come into contact with slurry or clean flue gas fall under the scope of anti-corrosion measures. These include the demister support beams, demister covers, branch pipe lugs of the spray layer, tank separators, pipe supports and hangers, screen frames, various manholes, and flange surfaces. The requirements for the lining of the tower are as follows (based on the elevation of the absorption tower’s bottom plate at +4.6m): 1. The bottom part of the absorption tower (+4.6m) and the area from the bottom plate of the tower’s cylindrical section up to +6.6m: In these areas, the medium present is a slurry containing solid particles, and there is intense stirring, which leads to high wear rates. Therefore, the seller proposes to use wear-resistant measures for the lining in these areas, by employing a double-layer rubber lining. 2. Absorption tower, from the +6.6m level up to the +26.42m level (1m below the center of the lowest spray layer), excluding the flue gas inlet area: The temperature in this area is 40~60°C, and wear and erosion are not severe. The seller took necessary measures for the lining of that area, using a 4mm rubber lining. 3. Original flue gas inlet: The flue duct at the inlet of the absorption tower and the tower walls surrounding this flue duct. Due to the relatively high temperature of the inlet flue duct, which is usually around 89°C, the temperature may temporarily reach around 130°C. The temperature in this area changes rapidly; the high-temperature flue gas sees its temperature drop quickly to 40–60°C upon entering the absorption tower, and such an environment induces significant thermal shock. 4. Absorption tower: from the +26.42 m level (1 m below the center of the lowest spray layer) to the +34.22 m level (1 m above the center of the highest spray layer): This area is the spray absorption zone of the absorption tower, where large amounts of slurry are atomized through nozzles and then sprayed into the absorption tower. The erosion wear caused by the spraying slurry in this area is quite significant; therefore, wear-resistant measures have been taken for the lining in this section, using a double-layer rubber lining. 5. From the demister area of the absorption tower to the outlet casing: from the +34.22m level up to the +41.8m level. The normal operating temperature in this area is around 40~60°C; there is little risk of slurry erosion, so a 4mm rubber lining is used. 6. Demisting support beams and covers in the absorption tower: The normal operating temperature in this area is around 40–60°C, with little to no slurry erosion. However, in actual operation, the demisters on the support beams experience some translation and vibration due to the airflow inside the tower. A 4 mm rubber lining is used for these components (with a double-layer lining on the upper surface), and a PP plate is attached to the upper surface (the PP plate is provided by the buyer). 7. Sprayer pipe support: The ends of the branch pipes in the spraying area of the absorption tower are connected to the tower wall via supports or bases. During operation, these branch pipes experience significant translation and vibration due to the airflow within the tower as well as the flow of the slurry inside; therefore, a double-layer rubber lining is used. 8. Absorption tower pool separator: At a height of +11.6m inside the absorption tower, 5 carbon steel pipes with a diameter of φ1200 are evenly arranged; these are collectively referred to as the pool separator, and their ends are welded to the walls of the absorption tower. During operation, the carbon steel pipe is immersed in the slurry of the absorption tower; the operating temperature ranges from 40 to 60°C, and it is also subject to certain mechanical erosion. Angle steel of varying quantities will be welded to each pipe to support the pulse suspension bracket at +7.3 below; this angle steel also needs to be lined with rubber for corrosion protection. 9. Others: The outlet flange surface of the absorption tower and the interface flanges on the tower are all rubber-lined flanges, equipped with a 4mm thick butyl rubber lining and a 2mm thick neoprene rubber lining.