Demister Pad - Maintenance, Classification and Specification

Profiles, working principle and features of demister pad

Demister pad working principle figure.
DPZ-01: Working principle of demister pad.

Demister pad, also called mist pad, wire mesh demister, mesh mist eliminator, catching mist, mist eliminator, is used in gas entrained mist separation column to guarantee the filtering efficiency.

History of demister pad

The late fifties, the foreign used an apparatus which made of the special wrinkle woven mesh to remove inclusions of tiny liquid foam in the gas. Then it is found that is very efficient and the resistance is very small, which is unmatched by other gas-liquid separation device, so it is widely accepted and used in a wide range of applications.

Wire demister standard was formulated by the Ministry of Chemical Industry in China on December 20, 1982, the basic implementation of the Shanghai municipal government standards Q/YSZZ-88-91 wire mesh industry was in 1991, began to fully implement HG/T21618-1998 national unity standard after the year 1998. The new standard demisters are divided into HG5-1404-81 riser type, HG5-1405-81 necking type and HG5-1406-81 full bore wire mesh device.

Demister pad is commonly placed at the top of the packing tower, which can not only ensure the mass transfer efficiency, but also reduce the board spacing. Demister pad is widely used in chemical, petroleum, pharmaceutical, light industry, metallurgy and other industrial production in the vertical cylindrical equipment vapor-liquid separation device. It can also be used in the desulfurization and other productions to remove oil mist, toxic and poisonous gas.

Working principle of demister pad

When the gas with mist rises at a constant speed and passes through the wire mesh, the rising mist will collided with the mesh filament and attached to the surface filament due to the inertia effect. The mist will be diffuse on the filament surface and the droplet will follow along the filaments of the two wire intersection. The droplet will grow bigger and isolate from the filament until the droplets gravity exceeding gas rising force and liquid surface tension force while there is little gas passing through the demister pad.

Separate the gas in the droplets can improve the operating condition, optimize process indicators, reduce corrosion of the equipment, extend equipment life, increase the amount of processing and recovery of valuable materials, protect the environment, and decrease air pollution.

Circle shape SS demister pad with support grid.
DPZ-02: Round shape embedded demister pad.
Embedded demister pad is made to circle shape.
DPZ-03: Circle shape embedded demister pad.

Features of demister pad

  • Simple structure.
  • Lightweight and easy to transport.
  • High porosity, less pressure drops.
  • Large surface area and high separating efficiency.
  • Easy to install, operate and maintain.
  • Durable and long service life.
  • Corrosion and rust resistance.

Selected wire mesh form of demister pad and domestic standards

Selected wire mesh form

Selected demister pad forms have four categories: standard type, efficient type, high penetration type and shock absorber type.

Specifications of standard type demister pad
Item Wire type Wire size
(mm)
Wire width tolerance
(mm)
Bulk density
(kg/m3)
Specific surface area
(m2/m3)
porosity
STWM-01 Flat wire 0.1 × 0.4 +10/-0 150 475 0.981
STWM-02 Round wire 0.23 320
Note: every 100 mm thick mat has 25 layers wire mesh.
Standard wire mesh of demister.
DPZ-04: Flattened type standard demister pad.
Stand wire mesh that is used to made demister.
DPZ-05: Ginning type standard demister pad.
Specifications of efficient type demister pad
Item Wire type Wire size
(mm)
Wire width tolerance
(mm)
Bulk density
(kg/m3)
Specific surface area
(m2/m3)
porosity
ETWM-01 Flat wire 0.1 × 0.3 +10/-0 182 626 0.977
ETWM-02 Round wire 0.19 484
Note: every 100 mm thick mat has 32 layers wire mesh.
Wire mesh demister that made of efficient wire mesh.
DPZ-06: Rectangular shape efficient demister pad.
Circle demisters that made of efficient type wire mesh.
DPZ-07: Round shape efficient demister pad.
Specifications of high-penetration type demister pad
Item Wire type Wire size
(mm)
Wire width tolerance
(mm)
Bulk density
(kg/m3)
Specific surface area
(m2/m3)
porosity
HTWM-01 Flat wire 0.1 × 0.4 +10/-0 98 313 0.9875
HTWM-02 Round wire 0.23 4217
Note: every 100 mm thick mat has 20 layers wire mesh.
High-penetration type wire mesh.
DPZ-08: High penetration type demister pad detail.
Circle shape demister pad made of high-penetration type wire mesh.
DPZ-09: High penetration type demister pad.
Specifications of shock absorber type demister pad
Item Specification Filament specifications
(mm)
STWM-01 33-30 type 0.08
STWM-02 38-40 type 0.08
STWM-03 20-40 type 0.22
STWM-04 30-40 type 0.1/0.12
STWM-05 30-50 type 0.16
STWM-06 40-60 type 0.12
STWM-07 30-80 type 0.22
STWM-08 50-120 type 0.22
STWM-09 40-120 type 0.22
Shock absorber type wire mesh of demister pad.
DPZ-10: Shock absorber type demister pad detail.
Shock absorber type wire mesh.
DPZ-11: Shock absorber type demister pad.

Domestic standards

Wire mesh demister pad domestic standards are divided into HG5-1404 (1405, 1406) - 81, HG/T 21618-1998, HG/T 21586-98.

  • HG5-1404(1405, 1406)-81
    The standards are divided into the riser-type (1404), the necking type (1405) and full bore type (1406).
    The diameter of demister is from 300 mm to 6400 mm and height is 100 mm and 150 mm.
    Mark example: HG5-1406-81-11, 304 refers to the 304 stainless steel of grating and wire mesh, dull bore coat type, 1600 mm diameter, 100 mm height demister pad.
  • HG/T 21618-1998
    New standard merges riser type, reducing necking type and full bore type installation form and divide into SP, HP, DP and HR four kinds of network types and expanded the type of material section.
    Mark example: HG/T 21618 wire mesh demister S1600-100 SP 304 indicates that 304 stainless steel of gratings and wire mesh, coat type, 1600 mm diameter, 100 mm height, SP screen demister grid.
    A drawing of SP type demister pad.
    DPZ-12: SP type demister pad.
    A drawing of DP type demister pad
    DPZ-13: DP type demister pad.
    A drawing of HR/HP type demister pad
    DPZ-14: HR/HP type demister pad.
    Type Standard wire specification
    SP 0.1 mm + 0.03 mm × 0.4 mm
    DP 0.1 mm + 0.02 mm × 0.3 mm
    HR 0.23 mm + 0.03 mm × 0.4 mm.
    HP 0.1 mm + 0.03 mm × 0.4 mm
  • HG/T 21586-98 (drawer mesh demister device)
    This standard is appropriate for the demister element, which is often needed to be replaced or cleaned, for example sulfuric acid drying tower and absorber device. The nominal diameter has 56 kinds ranging from DN 30 mm to DN 5000 mm.
    Mark example: HG/T 21586.11-98 WME 1600-100 NS-80/Q235-A refers to the wire mesh using NS-80 carbon steel grill, 1600 mm in diameter, 100 mm in height drawer type demister pad.
  • Other non-standard wire mesh demister
    Wavelike type, embedded type, external loading type, SWD1 type, square, rectangular and irregular and so on.

Using method of demisters

Mesh pad installation

There are two kinds of wire mesh demister pad, which are disk shaped demister pad and bar type demister pad.

According to different using condition, it can be divided into upload type and download type. When the opening is located in the above of the demister pad or when there is no opening but has flange, you should choose the upload demister pad.

When the opening is in the below of the demister pad, you should choose the download type demister pad.

A drawing of upload type demister pad.
DPZ-15: Upload type demister pad.
A drawing of download type demister pad.
DPZ-16: Download type demister pad.

Schematic of demister pad

Horizontal separation tower.
DPZ-17: Horizontal separation tower.
Spherical separation tower.
DPZ-18: Spherical separation tower.
Scrubber.
DPZ-19: Scrubber.
Distillation column.
DPZ-20: Distillation column.
Vertical separation column.
DPZ-21: Vertical separation column.
Packed tower.
DPZ-22: packed tower.

Maintenance of demister pad

After using for a long time, the demister pad will clog or prone to flooding and the pressure drop will increase. All these because of the particles in the gas blocks the demister pad. So you need maintain the demister pad properly and regularly.

Maintenance method: clean the demister pad. As we all know, the dilute acid on the demister pad will shorten the service life of demister pad, so we should place the demister pad in the natural state or under the sunlight

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