In wet flue gas desulfurization (FGD) system, the expansion joint of desulfurization tower is the core flexible component connecting absorption tower with inlet and outlet flue and slurry pipeline. The internal environment of the desulfurization tower is extremely harsh-the flue gas side is in the environment of low temperature, high humidity and strong acid corrosion, while the slurry side is faced with the erosion and wear of high concentration chloride ions and solid particles. Once the expansion joints in different parts fail, leakage and corrosion will be aggravated at least, and environmental protection will exceed the standard or even the unit will be shut down at worst. This paper will systematically explain the selection points and application technology of expansion joint of desulfurization tower from different working conditions of desulfurization tower.
1. Zoning requirements for expansion joints under desulfurization tower working conditions
The expansion joints of desulfurization tower can be divided into two categories according to the installation position: flue gas side expansion joint (flue at the inlet and outlet of absorption tower) and slurry side expansion joint (inlet and outlet of circulation pump and connecting pipe of tower body). The working conditions of the two are significantly different, and the selection strategies are quite different.
1. Working condition of flue gas side expansion joint
| position | Temperature range | Media Characteristics | Core Challenges |
|---|---|---|---|
| Raw flue gas inlet | 120-180℃ | Contains SO₂, SO₃, dust | High temperature + corrosion + scour |
| Clean flue gas outlet | 45-55℃ | Saturated wet flue gas, pH 2-4 | Strong acid corrosion, condensate accumulation |
The flue gas temperature at the inlet of the absorption tower is about 120-180 DEG C, and it contains high concentration of SO₂ and dust; The net flue gas temperature at the outlet drops to 45-55℃, which is completely saturated, and the condensate is highly corrosive。
2. Working condition of slurry side expansion joint
| position | Media Characteristics | Core Challenges |
|---|---|---|
| Circulating pump inlet and outlet | Limestone-gypsum slurry, pH 4.5-6.0, Cl⁻¹ ≤20000ppm | Corrosion + Wear + Pressure Fluctuation |
| Tower connecting pipe | Slurry, solid-containing particles | Thermal displacement + vibration |
The medium transported by the expansion joint on the slurry side is a mixed slurry with density ≤1220kg/m³, particle size ≤325 mesh and pH value 4.5-6.0, mainly containing limestone and gypsum components。
2. Selection and Improvement of Expansion Joint of Flue Gas Side Desulfurization Tower
1. Pain points of traditional non-metallic expansion joints
Traditional desulfurization tower expansion joints mostly choose non-metal skin + frame structure on the flue gas side. However, in practical application, this structure has inherent drawbacks:
- Combined structure of "flange-flake-strip-skin-platen": when the platen bolts are installed, the glass flake on the end face of the flange will be compressed and corroded channels will be formed
- "Starting leakage" phenomenon: affected by thermal stress, the expansion joint is displaced and deformed, and the bolts need to be tightened repeatedly, but it will further pressure damage the flange end face scales, forming a vicious circle of "the more leakage, the tighter the leakage"
2. Applicable scenarios of non-metallic expansion joints
Non-metallic expansion joints still have advantages in situations where the flue gas temperature is high (。
3. Selection requirements of expansion joint of slurry side desulfurization tower
1. Technical requirements for rubber expansion joints
The flexible rubber expansion joint (rubber joint) is usually selected for the expansion joint of slurry side desulfurization tower, and its technical requirements are as follows：
| parameter | demand |
|---|---|
| Rubber material | Ethylene propylene monomer (EPDM), content ≥50% |
| Wear resistance | Abrasion resistance class ≥230 |
| Reinforcement layer | Sail line braid ≥12 layers |
| Resistance voltage class | ≥1.6MPa |
| Temperature range | Normal operation 80℃, maximum 120℃ |
| Chloride tolerance | ≤20000ppm |
Core function: Absorbs axial and radial displacement of all connected equipment and pipelines under all operating and accident conditions, absorbs vibration and prevents vibration from being transmitted along the pipeline。
2. Structural design requirements
The design of slurry side expansion joint needs emphasis：
- Limit pull rod: It shall have sufficient strength, and the limit block of the pull rod shall be welded into one body with the flange. It shall be compressed and filled during installation, and the limit adjustment shall be carried out after installation
- Flange design: The thickness of the flanged rubber flange is not less than 30mm. When installing, the carbon steel flange is pressed on the inside of the rubber flange to prevent slipping
- Anti-corrosion and anti-wear: EPDM rubber with anti-wear, anti-corrosion and acid and alkali resistance is selected for the rubber body
3. Installation Points
Attention should be paid to when installing expansion joint of slurry side desulfurization tower：
- Keep it in a natural state and strictly prohibit distortion
- Regularly check the rubber for aging
- The maximum temperature thermal stress and mechanical stress that the pipeline can withstand in case of failure are considered in the design
Treatment and maintenance of expansion joint leakage
1. Leak Cause Analysis
The main causes of expansion joint leakage of desulfurization tower include：
- Corrosive media attack inside flue
- Improper construction technology (such as pressure damage of glass flakes on flange end face)
- Skin material is not acid resistant (silicone rubber is not acid resistant and fluororubber should be used instead)
- The bolts were not tightened repeatedly during installation
2. Treatment measures
The following measures can be taken to solve the leakage problem of the expansion joint：
- Optimization of inlet pipeline
- Use new materials with good corrosion resistance, plasticity and strong deformation resistance (such as titanium plate) instead of traditional skin
- Upgrading stainless steel platens to more corrosion-resistant materials
3. Maintenance cycle
The expansion joint ring belt (non-metal part) needs to be repaired about once every 5 years, and the ring belt can be replaced; The service life of the metal expansion joint shall not be less than 3 years。
V. Summary of selection decision
The selection of expansion joint of desulfurization tower should be decided by regions according to specific working conditions:
| position | Type of recommendation | Core Material | Key Requirements |
|---|---|---|---|
| Raw flue gas inlet | Non-metallic expansion joint | Fluorinated rubber skin + stainless steel wire mesh | Temperature resistance and anti-corrosion |
| Clean flue gas outlet | Pure titanium expansion joint | TA2 (thickness 2mm) | Zero corrosion target |
| Circulating pump inlet and outlet | rubber expansion joint | EPDM (content ≥50%) | Wear resistance and pressure resistance |
| Slurry pipeline | flexible rubber joint | EPDM + Sail Line Enhancement | Limit tie rod design |
Core Principles:
- Smoke side: Priority is given to anti-corrosion. The traditional non-metallic expansion joint has the stubborn problem of "start leakage", while the pure titanium expansion joint can achieve "zero leakage", and the comprehensive cost is the same as that of non-metallic
- Slurry side: EPDM rubber expansion joint is selected, and the chloride ion tolerance limit (≤20000ppm) and wear resistance should be paid attention to
- Installation link: Twisting and over-tensioning are prohibited, and bolts should be tightened repeatedly
- Regular replacement: Non-metallic ring belts are replaced every 5 years, and rubber joints are regularly tested for aging
An expansion joint of desulfurization tower with reasonable design and suitable material can fundamentally solve the vicious circle of "leakage after just changing" and ensure the long-term stable operation of desulfurization system. It is recommended to make special selection according to specific working conditions (temperature, Cl⁻¹ concentration, pH value) at the design stage, and consider the application of high-performance materials such as pure titanium when necessary.