I. Reasons inherent in the filter cloth itself

1. The quality of filter cloth is determined by a variety of factors, including its material, weaving technique, and joining process.

2. Polyester material: This material is an ideal choice under acidic conditions, with high temperature resistance (operating temperature below 150°C when the pH ranges from 1 to 9). It exhibits strong tensile strength and stable performance in both longitudinal and transverse directions, and its abrasion resistance is second only to that of nylon.

3. Polypropylene: This material exhibits relatively good acid and alkali resistance (pH range: 1–13) and can be used at temperatures below 90°C; however, its tensile strength is not very high. Most overseas filter cloth manufacturers do not choose this material. Since the slurry exiting the absorption tower typically has a pH between 4 and 7, and the gypsum temperature ranges from 70 to 80°C, filter cloths used for flue gas desulfurization are woven from 100% polyester filaments that offer excellent high-temperature and alkali-resistant properties.
4. Weaving Process: Internationally, the common practice is to use a blended weaving technique that combines monofilament and multifilament yarns with satin weave. The advantage of this weaving method lies in its surface being smooth while the reverse side remains rough, and the sizes of the front and back openings differ. The front-side openings are larger, whereas the back-side openings are smaller. This design facilitates the efficient capture of solids and promotes easy drainage. Moreover, the smooth surface enhances the effective removal of solids from the filter cloth. Many polyester filament manufacturers incorporate polypropylene into their polyester filaments—not using 100% polyester material. As a result, the filter cloth can easily become deformed or torn under the influence of the gypsum slurry’s temperature and pH level inside the absorption tower.

II. Due to reasons inherent in the filter itself:

1. Main Machine Rinse System: Since the filter cloth rinse water uses process water, it generally does not cause blockages. However, the filter cake rinse water typically consists of a mixture of process water, filtered cloth rinse water return, and vacuum pump circulating water return (using a liquid-ring vacuum pump). Primarily, it’s the combination of vacuum pump circulating water and filtered cloth rinse water return; process water is only occasionally added as a supplement. Because the filtered cloth rinse water return contains a relatively high gypsum content, it can easily lead to clogging of the filter cake rinse water nozzles. The pressure at the nozzles in the main machine rinse system is generally above 3 kg. When the pressure falls below this value, the rinsing effect on the filter cloth will be inadequate. If the rinsing remains insufficient for an extended period, gypsum will accumulate on the surface of the filter cloth, eventually causing blockages on the filter cloth surface as well.

2. The gap between the scraper and the filter cloth surface is too large, resulting in substantial gypsum buildup on the filter cloth surface, making it extremely difficult to clean. Over time, this buildup can easily lead to scaling on the filter cloth surface, causing surface blockage.

3. Sealing performance of the main unit: If the moisture content of the secondary-dehydrated gypsum exceeds 10%, the sealing performance of the main unit should also be considered. Poor sealing can lead to low vacuum levels throughout the system, resulting in significantly higher moisture content in the gypsum filter cake after dehydration and adversely affecting the filtration efficiency. The main reasons for this issue are:

A. Delamination at the joint of the vacuum chamber—vacuum chambers are typically made from polymeric materials that exhibit significant thermal expansion and contraction. If these chambers are not promptly or properly secured, delamination may occur. In such a case, the only solution is to stop the operation, lower the vacuum chamber, reapply adhesive, and securely fasten each segment of the chamber.

B. Leakage at the flange connection below the vacuum chamber—this typically produces a whistling sound. To resolve this issue, you’ll need to stop the equipment, lower the vacuum chamber, and inspect the gasket condition. If the gasket is defective, replace it. If the problem isn’t with the gasket, simply tighten the flange bolts at the leaking area.

C. If there’s a leak in the main filtrate pipe, simply tighten the bolts at the leaking area. However, if the issue lies with the gasket, you’ll need to stop the system and replace the gasket. To prevent vacuum leaks, it’s essential to conduct a vacuum test after the system is installed but before the filter cloth is put in place. This way, any potential problems can be identified and addressed before starting up the system, thus avoiding unnecessary trouble once the system is operational.

How to clean a clogged filter cloth:

1. For filter cloths used with alkaline filter media, when cleaning, they should be soaked in a weak acid solution.

2. For filter cloths used with acidic filter media, when cleaning, they should be soaked in a weak alkaline solution.

The soaking time is from 1 to 2 days. Then rinse it clean.

Or:

1. High-pressure water gun cleaning;

2. Clean with a washing machine and add detergent;

3. Clean using hydrochloric acid or citric acid;

4. Clean with caustic soda or hydrogen peroxide;

5. The laundry cycle should be determined based on actual conditions and generally should not exceed 2 months.