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Demister Pad

I. Profile, working principle and characteristics of demister pad
Profile

Demister pad working principle figure

Wire mesh demister (also known as mesh mist eliminator, mist, catching mist) is used for gas entrained mist separation column, in order to guarantee the efficiency of the filter, can increase productivity by 5%. 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 that such an apparatus in the study of the gas-liquid separation process and found that is very efficient, and the gas drop through the resistance of the device is very small, which is unmatched by other gas-liquid separation device, so quickly get a lot of promotion and 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 generally set at the top of the tower, setting it, not only can ensure the mass transfer efficiency of the tray, but also to reduce the board spacing. Demister standard applicable for chemical, petroleum, pharmaceutical, light industry, metallurgy and other industrial production in the vertical cylindrical equipment vapor-liquid separation device, is currently in the imports of ethylene, ammonia and chemical fiber production equipment used demister pad, has been applied in the desulfurization, remove oil mist, toxic and hazardous industrial gases and other fields.

Demister Pad working principle

When gas with mist rises at a constant speed through the wire mesh, due to the inertia effect, the rising mist collides with the mesh filaments and attached to the filament on the surface. Mist on the filament surface diffusion, gravity settling mist make the entrainment form larger droplets flow along the filaments of the two wire intersections. The wettability of filaments, the surface tension of the liquid and the capillary action of the filaments make the droplets grow bigger, until the droplets together to produce its own gravity exceed gas rising force and liquid surface tension force, droplets isolate from the filaments on the whereabouts. Basically it does not contain the entrainment after gas goes through the demister pad.

Separate the gas in the mist, in order to improve the operating conditions, 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 gridEmbedded demister pad is made to circle shape

Features

  1. Simple structure, lightweight.
  2. High porosity, less pressure drops.
  3. Big surfaces area, high demisting efficiency.
  4. Easy installation, operation and maintenance.
  5. Long service life.

II. The selected wire mesh form of wire mesh demister 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.

The standard type wire mesh

Wire size (mm) Wire width tolerance (mm) Bulk density
(kg/m3)
Specific surface area
(m2/m3)
Porosity
Flat wire Round wire diameter +10 -0 150 475 320 0.981
0.1 × 0.4 0.23
Note: Every 100mm thick mat have 25 layers wire mesh
Standard wire mesh of demisterStand wire mesh that is used to made demister

The efficient type wire mesh

Wire size (mm) Wire width tolerance (mm) Bulk density
(kg/m3)
Specific surface area
(m2/m3)
Porosity
Flat wire Round wire diameter +10 -0 182 626 484 0.977
0.1 × 0.3 0.19
Note: Every 100mm thick mat have 32 layers wire mesh

Wire mesh demister that made of efficient wire meshCircle demisters that made of efficient type wire mesh

The high-penetration type wire mesh

Wire size (mm) Wire width tolerance (mm) Bulk density
(kg/m3)
Specific surface area
(m2/m3)
Porosity
Flat wire Round wire diameter +10 -0 98 313 217 0.9875
0.1 × 0.4 0.23
Note: Every 100mm thick mat have 20 layers wire mesh

High-penetration type wire meshCircle shape demister pad made of high-penetration type wire mesh

The shock absorber type

Type Specification Filaments specifications (mm)
Shock absorber type 33-30 type Φ0.08
38-40 type Φ0.08
20-40 type Φ0.22
30-40 type Φ0.10Φ0.12
30-50 type Φ0.16
40-60 type Φ0.12
30-80 type Φ0.22
50-120 type Φ0.22
40-120 type Φ0.22

Shock absorber type wire mesh of demister padShock absorber type wire mesh

Domestic standards
Wire mesh demister domestic standards are divided into HG5-1404 (1405, 1406) -81, HG/T21618-1998, HG/T21586-98 and other non-standard mesh demister.

● HG5-1404 (1405,1406) -81
The standards are divided into the riser-type (1404), the necking (1405) and full bore type (1406). The diameter of demister is from 300mm to 6400mm and height is 100mm and 150mm. When ordering need to offer a figure number and use of the material.

Mark example: HG5-1406-81-11, 304/304 It means that the gratings and wire mesh are made of 304 stainless steel, full bore coat type, diameter 1600mm, height 100mm demister pad.


● HG/T21618-1998
New standards merged riser type, reducing necking type and full bore type installation form; proposed SP, HP, DP and HR four kinds of network types and expanded the types of material selection; and increased the set specifications size interval density.

SP DP HR/HP
The standard wire specification: 0.1+0.03 × 0.4 The standard wire specification: 0.1+0.02 × 0.3 The standard wire specification: φ0.23 (φ0.275)\0.1+0.03 × 0.4mm

Mark example: HG/T21618 wire mesh demister S1600-100 SP 304/304 it indicates that the gratings and wire mesh are made of 304 stainless steel, coat type, diameter 1600mm, height 100mm, SP screen demister grid.
● HG/T21586-98 (drawer mesh demister device)
This standard is principally applied to the demister element often needs to be cleaned or replaced occasions, for example sulfuric acid drying tower and absorber device. Its selection of nominal diameter has 56 kinds ranging from DN300mm ~ DN5000mm. When ordering simply need to provide a figure number and choice of materials (316L, NS-80 and RS-2 wire mesh material is commonly used in sulfuric acid plant).

Mark example: HG/T21586.11-98 WME-1600-100 NS-80/Q235-A it means that the wire mesh using the NS-80, grill carbon steel diameter 1600mm, height 100mm drawer demister pad.
● Other non-standard wire mesh demister
Wavelike type, embedded type, external loading type, SWD1 type, square, rectangular and irregular, and so on.

III. Using method of demisters:

1, Mesh Block Installation
Mesh block structures of demister pad have two types: disk-shaped mesh block and bar mesh block.
It has upload type and download type two structures. When the location of the manhole opened in the above of the wire demister, or unmanned hole but equipment flange, choose the upload type wire demister; the manhole location opened in the below of it, then choose the download type wire mesh demister.

2, Demister Schematic
Horizontal separation tower Spherical separation towerScrubber Distillation columnVertical separation column packed tower

IV. Maintenance:

After using for some time because of the gas containing particles (such as sublimated sulfur, etc.), the wire mesh is partially clogged and prone to flooding, the pressure drop also increased, therefore, the demister pad needs for proper maintenance.
During the stop of a long time, air will enter the tower body, the moisture in the air and mesh acid are easily formed sweet sour, since the metal mesh generally are intolerant to dilute acid, therefore, it needs to seize the opportunity to maintain the demister.
The way of maintenance is to clean with water, but remember: to avoid the dilute acid on the demister wire mesh to affect service life, after flushing the demister pad, mesh block must be drying (in the natural state, also can in the sun). Put it inside the tower before the equipment works. Choose to use a constant efficiency or the innovative adjustable mist eliminator in the production and smelting enterprises.

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sales@demisterpads.com

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