In wet flue gas desulfurization system, flue gas leakage from the expansion joint of absorption tower is one of the most common and difficult equipment failures. Whether it is the cracking of the expansion joint at the entrance of the original flue or the leakage of the skin at the outlet of the clean flue, once the leakage occurs, it will cause acid fog to diffuse at the site and equipment corrosion to be aggravated, or the environmental protection data will exceed the standard and the unit will be forced to land the load. This paper will systematically explain the prevention and treatment technology of flue gas leakage of expansion joint of absorption tower from leakage cause analysis, emergency treatment to permanent repair.

1. Leak type diagnosis: identify the root cause of the problem

The type and root cause of flue gas leakage from the expansion joint of the absorption tower must be accurately judged before any repair can be carried out. According to the operation experience of desulfurization system, expansion joint leakage is mainly divided into the following three categories：

1. Leaks due to design defects

The non-metallic expansion joint is fixed with a skin and platen structure, which will naturally form an annular groove when installed. When the unit is running, the condensed acid liquid in the wet flue gas will accumulate in this groove, and the acid liquid will slowly penetrate into the fixing screw through the fabric of the expansion joint, causing the screw to loosen and corrode and break, or the fabric layer to be damaged. Finally, the acid liquid will flow out from the broken screw hole and the damaged part of the skin, and in serious cases, the phenomenon of "small waterfall" will appear。 Judging from the operation situation, corrosion and breakage will generally occur in one to two years.

2. Leakage due to improper material selection

Some manufacturers use non-corrosion-resistant materials to save costs. If the inner layer of the skin is an acid-resistant silicone rubber plate, the inner alkali-free glass filament cloth will quickly penetrate into the screws fixing the expansion joint after absorbing water, and the accumulated acid will quickly corrode the screws, causing a lot of leakage. This phenomenon usually occurs during the construction period, and leaks will occur one month after it is put into operation。

3. Leaks due to installation and operation

The skin of the non-metallic expansion joint is all soft material, and the length of the pressure plate can reach 4-6 meters. After one-time tightening, the distal bolt will loosen due to the compression deformation of the skin. During operation, the screws will also be loose due to vibration and other reasons, resulting in leakage of the expansion joint。

4. Pull cracking caused by overall displacement of flue

Within 8 months after the commissioning of the desulfurization units of two 660MW units in a power plant, a large displacement occurred from GGH to the original flue of the absorption tower, which cracked the expansion joint at the inlet of the absorption tower, resulting in the flue gas leakage from the expansion joint of the absorption tower。

2. Acid accumulation and powder accumulation: two special leakage causes

1. Water accumulation in grooves – the most common cause

The non-metallic expansion joint consists of a skeleton and a skin, a structure that develops a groove when the skin is installed and accumulates a lot of acid water during operation. Many manufacturers have taken some measures, such as adding a drainage pipe to the center hole, but it still can't stop the corrosion of the skin penetration. Instead, due to the change of temperature, the drainage pipe is misaligned and the skin is broken, forming a new leakage point。

In addition, because the expansion joint is designed with multi-layer skin, water accumulation will occur between the layers during operation, which is also the main reason why the skin of the expansion joint will seep water。

2. Powder accumulation in the cavity-causing skin to swell and burst

For the working condition with high dust content in the original flue, dust accumulates in the expansion joint cavity, resulting in skin swelling and rupture。 The medium-temperature dust-proof expansion joint needs to be equipped with a dust bag and a two-way baffle to prevent dust accumulation.

3. Emergency treatment: temporary leak plugging without stopping the machine

In an emergency situation where immediate shutdown is not possible, the following emergency schemes can be adopted to deal with flue gas leakage from the expansion joint of the absorption tower:

1. Bolt retightening

For leaks caused by loose bolts, tighten all bolts immediately with an electric wrench in diagonal order. Because the bolt of the expansion joint is easily loosened after heating, it needs to be tightened again many times。

2. Add limit tie rod

When the expansion joint at the outlet of 1C slurry circulating pump in a power plant leaks, the emergency repair personnel compress the expansion joint by adding the limit rod, and then insert the plug plate to isolate it。 This method is suitable for the parts that need to be quickly isolated, such as the outlet of the pump body.

3. Plug the package box

For large area leaks, a fitted steel box can be made outside the expansion joint for plugging.

IV. Radical repair: permanent solution

Option 1: Groove Filling Technology-From the Root Causes

To thoroughly solve the flue gas leakage of the expansion joint of the absorption tower, the key is to solve the problem of water accumulation in the groove. The only feasible way is to fill the grooves so that the acid water does not reach the expansion joint platen bolts and skin。

Construction steps：

1. After shutdown, clean up the dust around the expansion joint and remove the broken skin at the bottom
2. Cut off the deflector of the non-metallic expansion joint
3. Clean up the floating ash of the metal skeleton and repair the corroded parts by welding
4. Install the fluororubber expansion joint skin and repeatedly tighten the fixing screws
5. Apply high elastic glue on both sides of the groove of the expansion joint
6. Fill with high temperature and corrosion resistant polyurethane filler (compression ratio 7:1), and compact in layers
7. Seal the adhesive layer with each layer of filler until it is filled
8. The top layer is flattened with high elastic acid-resistant glue, and the thickness is about 3mm
9. Use high elastic corrosion-resistant adhesive to prevent corrosion around the expansion joint, with a thickness of more than 3mm

Maintenance time: It can be put into use in 6 hours.

Technical advantages: the problem of water accumulation in the groove is thoroughly solved, so that the acid water in the flue can't contact the skin of the expansion joint, and the leakage is eradicated. The life of the treated expansion joint is greatly extended, and once any damage is found after each shutdown inspection, it can be treated and repaired immediately。

Option 2: Skin Material Upgrade

In the material selection, fluororubber material should be selected as the inner lining layer. fluororubber has excellent acid resistance and can resist the erosion of condensate to the skin. Then two layers of alkali-free glass filament cloth and one layer of polytetrafluoroethylene cloth are used as heat insulation layer, and silicone rubber plate is used for the outer layer to avoid corrosion of the inner layer, and each layer is bonded into one body to prevent internal leakage。

Scheme 3: Overall Replacement and Structural Optimization

If the expansion joint body is seriously damaged and repeated repairs are ineffective, it should be replaced as a whole. Huaneng Haimen Power Plant 2025 Unit 4 Desulfurization Absorption Tower Inlet Section Leakage Comprehensive Treatment Upgrading Project, the main service scope is to remove the existing absorption tower inlet expansion joint to the absorption tower wall flue, and re-make the absorption tower inlet flue。

Preventive Measures and Routine Maintenance

After completing the repair of flue gas leakage in the expansion joint of the absorption tower, the following measures can effectively prevent the recurrence of the problem:

1. Daily inspection

• Check the appearance of the expansion joint weekly for any smoke leakage, bulging and loose bolts
• Observe whether the drainage hole is unobstructed
• Check bolts for looseness or rust

2. Regular maintenance

• Full tightening of platen bolts quarterly
• Clean up the dust in the expansion joint for each overhaul
• Check Frame Anti-Corrosion Coating Integrity

3. Regular replacement

It is a normal practice for manufacturers to regularly replace the skin of desulfurization expansion joint during overhaul. Once the replacement time is missed, it will affect production to a certain extent when it is damaged。

4. Drainage management

The expansion joint of the horizontal flue section shall be provided with a hydrophobic hole at the bottom, the diameter shall not be more than 100mm, the material shall be alloy steel or stainless steel, and the condensed acid liquid shall be discharged。

Summary of Processing Process

The treatment of flue gas leakage in the expansion joint of the absorption tower can be summarized as a four-step method of "diagnosis → emergency → radical cure → prevention":

sum up

Flue gas leakage from expansion joint of absorption tower is the most common problem in wet desulfurization system, and its root causes are:

1. Groove water accumulation: The grooves of non-metallic expansion joints accumulate acid water, which penetrates and corrodes the skin and screws-this is the source of more than 90% of leaks
2. Materials are not corrosion resistant: silicone rubber and other acid-resistant materials are rapidly aged and failed in wet flue gas environment
3. Irregular installation: Bolts are not tightened repeatedly, resulting in loosening during operation

The cure lies in "filling the groove + upgrading the material":

• Groove filling technology is adopted, and the groove is filled flat with high elastic sealant + polyurethane filler, so that acid water cannot contact the skin and screws
• Upgrading the inner layer of the skin to fluororubber (FKM), which has much better acid resistance than silicone rubber
• Tighten the bolts repeatedly during installation, and tighten them regularly after operation

An absorption tower expansion joint after standard repair can be upgraded from "one leak a year" to "zero leak in 3-5 years". It is recommended that the expansion joint inspection be included in the required inspection items during each overhaul, so as to achieve "early detection and early treatment" and avoid small leaks from turning into major failures.