A tube filter, often used in industrial settings, works by passing dirty gas through fabric tubes, effectively capturing dust particles on the tube's inner surface.
Understanding the Basics
At its core, a tube filter (often called a baghouse or fabric filter) is a device designed to remove particulate matter from a gas stream. Unlike some filters where gas flows from outside to inside, in a tube filter, the dusty gas typically enters and flows inside the tubes.
Here’s a breakdown of the process:
- Dusty Gas Entry: The contaminated gas stream enters the filter vessel, directing the flow towards the open bottom of the filter tubes.
- Filtration: As the gas flows upward through the fabric tubes, the porous material of the tubes acts as a filter. Dust and particulate matter are trapped on the inside surface of the tubes, while the cleaned gas passes through the fabric walls.
- Clean Gas Exit: The cleaned gas exits the tubes and enters a separate area of the filter vessel before being discharged from the system.
The Cleaning Process: Detaching the Dust Cake
Over time, a layer of trapped dust, known as the "dust cake," builds up on the inside surface of the tubes. This cake increases filtration efficiency but also causes a pressure drop across the filter. To maintain optimal performance, this dust cake must be removed.
As referenced, the dust cake which is built up at the inside surface of the tubes is detached by a back pulse from the outside to the inside and discharged at the bottom of the tubes.
- Back Pulse: This cleaning mechanism involves a brief burst of compressed air or gas injected from the outside of the tube towards the inside.
- Detachment: This sudden reversal of flow direction and pressure pulse flexes the tube fabric, causing the dust cake adhering to the inner surface to break away.
- Discharge: Once detached, the dust cake falls by gravity to a collection hopper at the bottom of the filter vessel, ready for disposal or recycling.
This pulsed cleaning allows the filter to operate continuously or intermittently without being shut down for manual cleaning.
Structural Components
The effectiveness and longevity of a tube filter also rely on its structural design:
- Filter Tubes (Bags): The primary filtration media, made from various fabrics chosen based on temperature, chemical compatibility, and particle size requirements.
- Cage Supports: (Not always present in inner flow designs like described, but common in outer flow designs) These internal cages prevent the bags from collapsing during filtration.
- Tube Sheets: These are plates that hold and support the filter tubes. The tubes are supported by water cooled tube sheets which divide the filter vessel into several clean gas chambers. Water cooling is often used in high-temperature applications to protect the tube sheets and potentially the bags from excessive heat damage. The division into clean gas chambers ensures that once the gas is filtered, it remains isolated from the dusty incoming gas and the collected dust.
- Hopper: Located at the bottom, this collects the dislodged dust cake.
- Pulse Jet System: The mechanism that delivers the compressed air pulses for cleaning.
Summary of How it Works
| Stage | Process | Key Action |
|---|---|---|
| Filtration | Dusty gas flows inside fabric tubes. Particles are captured on the inside surface. Clean gas passes through the fabric. | Dust separation from gas stream. |
| Cleaning | Dust cake forms on the inner tube surface. Periodically, a back pulse of air/gas is sent from the outside to the inside of the tube. | Detachment of the dust cake from the tube wall. |
| Dust Removal | The detached dust cake falls to the bottom. The dust cake... is discharged at the bottom of the tubes. | Collection of removed dust. |
| Structure | The tubes are supported by water cooled tube sheets which divide the filter vessel into several clean gas chambers. | Provides structural integrity and separates clean/dirty gas areas, manages heat. |
Tube filters are a robust solution for removing a wide range of dry particulates from industrial gas streams, essential for air pollution control and material recovery.
