Read Through Demister Pad FAQs for More Information

The drop separation in demister pad is done by the principle of inertial separation. By a deflection of the flow lines, which are caused by the individual wires in the demister pad, there is a separation process. The drops in flue gas flow cannot change direction due to its own inertia and collide with the obstacles (wires). Single droplets on the wire surface grow into larger drops which then fall to the bottom. The more deflections in the demister pad the more efficient the process.

The pressure loss is usually not more than 250 Pa. Basically, the pressure drops in the use of demister pad are very small. The pressure loss is directly dependent on the packing density.

As a rule, a separation grade of over 99% is achieved, wherein the degree of separation is dependent on the application, on the material, the speed of the packing density and the wire diameter.

Demister pad can be used for drop sizes of about 1 micron to 100/120 microns, wherein the larger drops fall directly due to gravity, as it follows the principle of inertial separation.

The following parameters are important for the design of a demister pad:

• Flow rate in m³/h
• Operating pressure in bar
• Temperature in °C
• Initial flow direction (vertical or horizontal)
• Droplet size in microns

We have metal, plastic and steel & fiber demister pads for you to choose from. In addition, these demister pads can be in round, rectangular, ring and special shapes. We have demister pads with a density of 80 kg/m³, 120 kg/m³, 160 kg/m³, 220 kg/m³, etc. For more information, see demister pad specifications.

Demister pad can be used as drop separator, oil mist separator, air filter, insulation mat or coalescence separator in gas streams for immiscible liquids.

In addition to cyclones and baffle plates are used mainly demister pad made of wire mesh. The amount of liquid droplet size and the purity to be achieved decide which system is used for droplet deposition in accordance with the requirements of the most appropriate.

Demister pad is used for dehumidification, that is, separating the liquid phase from a gas stream. The demister pad should trap gas or vapor flow drops.

The task of demister pad is to clean to erosion, sediment and product contamination from exhaust air streams.

The demister pad is placed at the flue gas outlet at the top of the absorption tower, where belongs to the “wet-dry” junction area and forms “wet-dry” fouling easily. As the absorption tower slurry contains CaSO4, CaSO3 and fly ash contains silicon, iron, aluminum and other substances that have a large viscosity, when the slurry collides with the surface of the demister pad and tower walls, some of them will adhere to the demister pad and tower walls and settle down. In addition, as the higher temperature of the flue gas accelerates the evaporation of the sediment layer, making the sediment layer gradually forms hard scale with a dense, cement-like structure.

The reasons for the fouling and blockage of the demister pad are summarized as follows:

• The demister pad has a long wash cycle. Regular demister pad washing is an effective measure to ensure the cleanliness of the demister pad. Especially when the demister pad is relatively clean, a small amount of gypsum particles and fly ash attached to the demister pad can be washed off by washing. Therefore, when the demister pad is put into operation, it must be properly washed in accordance with the design requirements. A regular wash cycle is an important guarantee for effective washing. If the wash cycle is too long, gypsum particles and flue gas keep attaching to the surface of the demister pad, making the scale become thick and hard via repeat high-temperature flue gas washing and form a thick and dense hard scale. At this time, the scale cannot be washed away by merely washing. Generally, the optimal wash cycle of the demister pad is every one or two hours. When the pressure difference between the upper and lower demister pad tends to greater, the wash cycle shall be shortened accordingly.
• The demister pad flushing water has a low pressure. When the demister pad is put into operation for a short period, the surface of the demister pad is smooth and clean, and the scale formed during operation is dispersed, and can be washed away with the flushing water under a certain pressure. However, in practice, the unreasonable design of the pipeline may cause the pressure of the flushing water of the demister pad fails to meet the design requirements, making the flushing effect is undesirable and the scale on the surface of the demister pad become larger and harder. In order to ensure enough flushing pressure, on the one hand, the pipeline and orifice plate shall be designed reasonably, on the other hand, multiple flushing doors for simultaneous flushing shall be avoided.
• The demister pad flushing doors is damaged and cannot be washed normally. The normal operation of the demister pad flushing door is a prerequisite for flushing. As the demister pad flushing door is commonly arranged in the open air, flooding water often occurs during the operation, making the flushing door cannot be put into normal operation. Therefore, the flushing door must meet the relevant protection level, provide certain protective measures like shelters, and strengthen its daily maintenance.

PTFE demister pad is one of the most corrosion-resistant demister products in the world. It can be used in any kind of chemical medium for a long period. The PTFE demister pad can withstand hydrofluoric acid, phosphoric acid, sulfuric acid, nitric acid, hydrochloric acid and various organic acids, organic solvents, strong oxidants and other strong corrosive chemical media, even the most powerful aqua regia (mixture of concentrated sulfuric acid and concentrated nitric acid) can do nothing about it. PTFE demister pad can be used normally within the temperature range from -150 °C to +250 °C, which is not possible for other plastic demister products.

The demister pad is placed on the top of the packed tower or the collection tray between two packing layers to separate droplets from the airflow, so that the discharge of droplets from the packed tower and the droplet entrainment from one stage to the next stage can be minimized.

• Gas and liquid move towards their own ways, the secondary entrainment is basically eliminated, and the defoaming effect is remarkably improved.
• Due to the tilting of the demister pad, the actual defoaming area is increased by 15%, which is convenient for adjusting the airflow, speed, resistance and defoaming effect in design.
• A single layer of wave type demister pad can achieve the defoaming effect of two-layer wire mesh demister pad, which saves installation space and reduces the cost of single tower demister.

The light weight of the demister pad will result in poor filtering effect. The wire mesh folded in the demister manufacturing process shall not be too less. The bulk density of the wire mesh shall be 168 kg/m³. The basic standard is that 100 mm of the mesh layer thickness corresponds to 26 layers of the wire mesh and 150 mm of the mesh layer thickness corresponds to 38 layers of the wire mesh, and so on. In addition, the grid used for the framework shall not be too thin. 25 × 4 mm flat steel is a prefer choice. If the grid is too thin, it can't support the demister pad and lead to it falling off the support easily, and causes unnecessary losses.

The demister pad is suitable for removing the droplets with a diameter of 3–5 μm entrained in industrial gas. It enjoys a relatively long service life under the conditions of choosing a correct demister and using it reasonably. However, if there is any inappropriate behavior in use, it will shorten the service life of the demister pad. The precautions for the use of the wire mesh demister are as follows:

• Choose an appropriate demister pad. Select an appropriate material based on the chemical characteristics of the corrosive substances in the environment. A substance has its own specific conditions of corrosion. When the surrounding environment is inert to the corrosion of the product, the product can be used smoothly and play an effective role. However, if there are substance that corrodes the product, the product will be damaged, reducing its service life and gas-liquid separation efficiency. Therefore, the correct selection of demister pad is crucial importance to your expected separation outcomes.
• Choose an appropriate spray reagent. In many cases, the demister is equipped with a sprinkler, and the sprayed liquid is the necessary material to achieve the mist elimination effect in the design. Then, on one hand, the chemical substances contained in the spray liquid shall not corrode the demister pad; on the other hand, the spray liquid shall not contain substances that are prone to sedimentation. Once the spray liquid reacts with the chemical substances to be removed and produces a poorly soluble substance, it is easy to scale on the surface of the demister pad and block the vapor-liquid filter mesh, and the demister will be scrapped in advance.

In short, the use of demister products shall conform to the characteristics of the product and avoid damage in use. Only in this way can we realize excellent gas-liquid separation performance.