Installation Guide for Simplifying Your Demister Pad Installation

Step 1 New demister pad inspection

1. Check the shipment Upon the receipt of a demister pad, check if you have received the right demister pad. Inspect and measure its dimensions to ensure the size of the demister pad consists with the size on the drawing. Check if there is any potential demister pad damage. Check if there are documents come along with the product.
2. Demister pad storage Store the new demister pad in a dry and clean environment. Dust, sand and other contaminants may foul the demister pad. A warehouse is recommended for long term storage.
3. Ready to install Lay out all demister pad sections in a clean area close to the vessel. Place all demister pad pieces towards the correct orientation of flow direction. And then make out an installation plan.

Keep in mind the mesh pad will be manufactured slightly larger than the diameter of the vessel to be installed into.

Step 2 Removing the existing demister pad

Before removing the existing demister pad, it is highly recommended to study how the existing one was installed. Check the existing demister pad if there are signs of excessive corrosion or fouling and if there are dislodged sections.

If the existing pad was built in sections, pull the center section first. As a properly installed demister pad fits tightly to the wall of the vessel, a larger pulling force is required to remove the center section. Once the center section is removed, the other sections will be removed much more easily. Remove one section at a time. And then remove other sections one by one to prevent loose sections fall off.

After removing all sections, check all support structures carefully if there are cracks, excessive corrosion signs, and damaged support hardware. Repair all defects that might impair the proper installation and operation of the new demister pad. Make sure the existing supports are suitable for your new one, pay attention to what hold down hardware you will be employing. You may orient or turn the new pad into the exact position of the demister pad to be removed for reference purposes later.

Hold Down Options

• Tie Wires

  Tie wires are the most common and simplest way of attaching the demister pad to its supports. The tie wires are typically 0.051" in diameter and are made of the same material as the mesh. This can be achieved by looping the tie wire between the bottom support grid and the annular ring hole and twisting the ends to tie it in place. (Do not run the wire through the mesh, just the support and grid.) Tie down the four corners of the grids in each section. Annular ring hole spacing is typically 4" to 5" apart with 1/4" diameter holes.

  

  Demister pad – tie wire installation

  

  Demister pad – tie wire installation details

  For plastic mesh materials, use several loops of tie wires.

• J-Bolts

  J-bolts can be used instead of tie wires and are stronger. The hook portion of the "J" connects around the demister pad’s bottom grid, extends through a clamp or holes in the annular ring and is secured by a nut and lock nut. Once again, 4 bolts should be used per section. Another variant is a "welded stud."

  

  Demister pad – J-bolt installation

  

  Demister pad – J-bolt installation details

  Please Note: make sure your J-bolt connections are secure and can withstand heat and vibration. Double nuts or locknuts are highly recommended.

• Latch Keys

  Latch keys can be used to secure a demister pad when having to work from the stop, and access to the bottom is not possible. Simply turn the flag toward the vessel wall and tighten the double lock nuts.

  

  Demister pad – latch key installation

• Dual Support Rings

  Dual support rings have removable ring sections on the manway side. When the last demister pad section is installed, bolt the ring sections into place. Dual support rings are more common for topside installations but are also used in bottom installations. Dual support rings also help prevent wall bypass.

  

  Demister pad – dual support ring installation

  

  Demister pad – dual support ring installation details

  

  Demister pad – dual support ring removable section installation

• Offset Rings

  Offset rings are held away from the vessel wall by a standoff. Secure the demister pad using tie wire or J-bolts and clamps.

  

  Demister pad – tie wire with offset ring installation

  

  Demister pad – tie wire with offset ring installation details

• Hold Down Bars

  Hold down bar bolts into position above the demister pad after it is installed and is an effective mean to keep the demister pad pieces intact.

  

  Demister pad – hold down bar installation

• Basket Cages

  Basket cages for one-piece demister pad are held in place by the vessel top flange. You simply slide the cage on top of the demister pad and fasten the head or top flange, when installing one-piece demister pads.

  

  Demister pad – basket cage installation

• Expansion Rings

  Expansion rings can be used for either a support ring or a hold down ring when welding to the shell is a problem.

  

  Demister pad – expansion ring installation

  For demister pad installed in small diameter vessels with a flanged top, the pad must be made into two sections to clear hold down bar clips welded to the shell.

  

  Demister pad in small vessels is separated into two sections to clear hold down bar clips welded to the shell.

  Hold down method with exit above demister pad

  If installers must exit from manway above the demister pad, install demister pad tie wiring from below working from the outer sections toward the center. Install the last section from the top and secure to adjacent sections by placing 3 hold down bars (1/4" x 1" flat bar) across the last section installed and tie wiring or J-bolting to adjacent sections.

  

  Manway section and hold down bars for demister pad installation

Step 3 Installation

• One Piece Demister Pads

  Any fastening method except J-bolts can be used for one piece demister pads. For new vessels make sure the vessel walls are smooth and free of weld splatter and other debris before pushing the demister pad into the vessel. Keep in mind the mesh diameter should slightly exceed the vessel diameter to ensure a snug fit as shown to the right.

  

  One piece demister pad installation method

• Installing Multi-Section Demister Pads in Vertical Vessels
  • Vessels with Single Support Rings
    1. Before installing any sections, mark lines on the support ring that indicate where each section edge should sit. Align the sections in accordance to your marks as you install each section.
    2. Work from the outside in on each side by placing the end sections on top of the support ring.
    3. Compress the installed sections to your measurements and keep opposing sections parallel.
    4. Use a hold down to secure each section after it is properly in place.
    5. Move toward the center as you add sections until only one section remains. Use sheet metal or cardboard to facilitate installation.
    6. If you are installing from below, lift the entire last section through the void space between the opposing pad sections, position it carefully and then pull it down into place.
    7. If you are installing from above, simply push the section into place after a careful alignment.
    

    Multi-section demister pad with single support ring installation step 1

    

    Multi-section demister pad with single support ring installation step 2

    

    Multi-section demister pad with single support ring installation step 3

  • Vessels with Dual Support Rings
    1. Mark lines on the support grids that indicate where the mesh sections should sit. Align the sections in accordance to your marks as you work from the vessel wall inward, one side of the vessel at a time.
    2. Compress the installed sections to fit your measurements and keep the opposing sections parallel. Use C-Clamps or an equivalent on the ring to hold the sections in place as you proceed.
    3. To install the section, make a simple installation aid using two thin pieces of sheet metal or some smooth yet strong material that extends the length of the section and is taller than the section.
       You may even wish to cut handles in the aid. Place the installation aids on either side of the mesh to reduce the friction of the mesh surfaces. A compression is necessary, so expect resistance as you push the section into place. Push the section in and pull the aids out.
    4. Replace the removable section on the support ring and beam(s).
  

  Multi-section demister pad with dual support rings installation step 1

  

  Multi-section demister pad with dual support rings installation step 2

  

  Multi-section demister pad with dual support rings installation step 3

  

  Multi-section demister pad with dual support rings installation step 4

  

  Multi-section demister pad with dual support rings installation step 5

  

  Multi-section demister pad with dual support rings installation step 6

  

  Multi-section demister pad with dual support rings installation step 7

  

  Multi-section demister pad with dual support rings installation step 8

• Installing Multi-Section Demister Pads in Horizontal Vessels
  • Horizontal Vessels with a Vertical Demister Pad
    1. Mark the support ring and beams indicating where each compressed section of mesh should sit.
    2. Work from the vessel wall toward the center aligning each compressed section to your support ring and beam marks.
    3. To install the final section, make a simple installation aid using two thin pieces of sheet metal or some smooth yet strong material that extends the length of the section. You may even wish to cut handles in the aid. Place the installation aids on either side of the mesh to reduce the friction of the mesh surfaces. A compression fit is necessary, so expect resistance as you push the final section into place. Push the section in and pull the aids out.
    4. Replace the removable sections on the support ring and beam(s).
    

    Installation procedures of vertical demister pad in horizontal vessels

    

    Top view of the demister final section installation diagram

  • Horizontal vessels with horizontal demister pads
    1. Mark the supports to indicate the position of each section.
    2. Start at the ends, making sure each section is properly aligned, compressed and tied down securely. Move toward the removable section, adding sections to both sides until the final section remains.
    3. To install the final section, make a simple installation aid using two thin pieces of sheet metal or some smooth yet strong material that extends the length of the section. Place the installation aids on either side of the mesh to reduce the friction of the mesh surfaces. A compression fit is necessary, so expect resistance as you push the final section into place. Push the section in and pull the aids out.
    

    Horizontal demister pad in horizontal vessels installation step 1

    

    Horizontal demister pad in horizontal vessels installation step 2

    

    Horizontal demister pad in horizontal vessels installation step 3

    

    Horizontal demister pad in horizontal vessels installation step 4

Final Notes:

Make certain and check your work when all installation procedures are finished.

1. Check for any gaps between sections. A uniform compression fit throughout the demister pad is important.
2. Check to make sure your tie-downs are secure and even with one another. Make sure the rings and beams adequately support your demister pad.
3. If your demister pad is of a dual density design, make certain all sections are installed with the correct flow orientation.
4. Be sure to remove all tools and installation materials before start-up.