MIST ELIMINATORS LIFE STORIES

Transcription

1 MIST ELIMINATORS LIFE STORIES

2 8 th Mesa Redonda, Rd d Chile

3 THELIFEOFMESHPAD DEMISTERS 1. CORROSION OF METAL WIRES This Lewmet demister was removed for washing and there corrosion of one D section s mesh was found. There was an inlet pipe directly below the position of this section in the tower, with SO 3 vent vapour from an Oleum tank. The pipe was shut & the tank was fitted with our Becoflex BFCF vent system

4 THELIFEOFMESHPAD DEMISTERS 1. CORROSION OF METAL WIRES There is often a detrimental effect of ferrous sulphate falling down onto a demister from the central carbon steel exit duct above. If left like that corrosion of the small diameter wires can increase. As the corrosion will attack the whole circumference of the wire, the wire can disappear quickly.

5 THELIFEOFMESHPAD DEMISTERS 1. CORROSION OF METAL WIRES Sulphates and sulphuric acid left ignored in a meshpad during a shutdown, or during an outage where moist air can enter the tower, have a high risk of increasing corrosion as weak acid attacks the wires. In most European plants where metal mesh is used, 316L Stainless Steel lasts well. Alloy 20 and SX are examples of more corrosion resistant wire materials for non EU duty. We supplied SX wire demisters for the 3 Outotec Ma aden plants in 2009.

6 THELIFEOFMESHPAD DEMISTERS 2. HEAT SHRINKAGE OF PLASTIC WIRES Shrinkage of sides of sections of D.T. meshpad made in Halar E.C.T.F.E. material SO 3 effect on Halar E.C.T.F.E. Softeningand relaxing of HalarE E.C.T.F.E. CTFE mesh material layers all the formed crimp wave is gone

7 THELIFEOFMESHPAD DEMISTERS 2. HEAT SHRINKAGE OF PLASTIC WIRES Heat shrinkage of sides of sections of D.T. upper meshpad made in Hostaflon E.T.F.E. material + gaps filled with Halar E.C.T.F.E. material, which is discoloured dand damaged dby SO 3 attack SO3 damaged Halar E.C.T.F.E. wire melted onto packing Heat shrinkage of lower Hostaflon + PTFE fibre coalescer + blackened Halar material in gaps

8 THELIFEOFMESHPAD DEMISTERS 3. SOLIDS BLOCKAGE AND WASHING DAMAGE Sulphur sublimation in Smelter plant D.T. meshpad Sulphates Nitrosyl crystals in Spent Acid Regen plant D.T. meshpad

9 THELIFEOFMESHPAD DEMISTERS 3. SOLIDS BLOCKAGE AND WASHING DAMAGE Every time that a meshpad is washed it is at risk from damage during handling and poor refitting into the vessel. In this photo you can see a damaged section of demister with the grid obviously not fitted properly p at the end. This then affects mesh to mesh (or mesh to wall) seals Puerto Varas October

10 THELIFEOFMESHPAD DEMISTERS 3. SOLIDS BLOCKAGE AND WASHING DAMAGE

11 THELIFEOFMESHPAD DEMISTERS 3. SOLIDS BLOCKAGE AND WASHING DAMAGE Although metal mesh pads are generally resistant to rough handling, damage can be done if the fitters are not careful. As can be seen when aligning 2 sections on the right, a mesh tomesh seal will only be possible if the sections are over compressed when re fitted, leading to other gaps.

12 THELIFEOFMESHPAD DEMISTERS 4. MAINTENANCE SUGGESTIONS All meshpads are made with +/ 25mm space between adjacent section grids. Use simple U clips on the top grids when fitting, to act as a mesh compression guide. Angle the final meshpad sections in the remaining space using a thin metal sheet against the mesh sides ; push down on the ridge and slide the sections in place

13 THELIFEOFMESHPAD DEMISTERS 4. MAINTENANCE FRIENDLY DESIGN SUGGESTION Early versions of an externally removable meshpad used a traditional horizontal arrangement, with awkward, risky results when removing heavy, wet sections, high up a tower. The externally removable, Vertical meshpad design was developed between Begg Cousland and Outotec, and the new Noracid idchile plant features it.

14 THELIFEAND DEATH OF FIBRE BED MIST ELIMINATORS 1. CORROSION OF METAL FILTER STRUCTURES The wires of the inner and outer mesh cages of a fibre bed mist eliminator are the main victims of corrosive attack. The wire is corroded over the whole circumference, so a 2.5mm.5mmdia. wire survives < 1.25mm corrosion. The wires at the bottom of cages are the most at risk, from un drained acid / sulphates on the tubesheet for standing type, and residual acid in the fibre for all types

15 THELIFEAND DEATH OF FIBRE BED MIST ELIMINATORS 1. CORROSION OF METAL FILTER STRUCTURES The use of raised stool flanges (part of tubesheet or part of candle filter as shown), avoid these extra corrosion risks.

16 THELIFEAND DEATH OF FIBRE BED MIST ELIMINATORS 1. CORROSION OF METAL FILTER STRUCTURES Inspection from below did not show anything obvious.

17 THELIFEAND DEATH OF FIBRE BED MIST ELIMINATORS 1. CORROSION OF METAL FILTER STRUCTURES From above the sulphate deposits on the wall showed serious abnormality.

18 THELIFEAND DEATH OF FIBRE BED MIST ELIMINATORS 1. CORROSION OF METAL FILTER STRUCTURES The missing top part of one filter was then obviously the issue.

19 THELIFEAND DEATH OF FIBRE BED MIST ELIMINATORS 1. CORROSION OF METAL FILTER STRUCTURES The cage was corroded by localised weak acid formation, due to vent pipe inlet below this filter.

20 THELIFEAND DEATH OF FIBRE BED MIST ELIMINATORS 1. CORROSION OF METAL FILTER STRUCTURES Corroded hanging type candles (or the bits that remained of them) viewed at the distributor level. This Russian customer had decided to wash the tubesheet and filters with water.

21 THELIFEAND DEATH OF FIBRE BED MIST ELIMINATORS 1. CORROSION OF METAL FILTER STRUCTURES Corroded top flange (8mm) Corroded cage mesh Corroded bottom plate (8mm) Puerto Varas October

22 THELIFEAND DEATH OF FIBRE BED MIST ELIMINATORS 1. CORROSION OF METAL FILTER STRUCTURES High Velocity type candle filters from a D.T. in a plant that had been shutdown for some months due to the Financial Crisis. No preventive maintenance, washing / neutralising of the filters Retained H2SO4 in the filters and sulphates led to (random) weak acid corrosion of the cages The wire of the cage mesh was 3mm dia. Cage corroded here below the top plate

23 THELIFEAND DEATH OF FIBRE BED MIST ELIMINATORS 2. CORROSION OF FIBRES Corroded dglass fibre in Asian Ai Cu Smelter plant Carbon Fibre : Resistant to HF Brownian Diffusion efficiency Corroded glass fibre in European Cu Smelter plant

24 THELIFEAND DEATH OF FIBRE BED MIST ELIMINATORS 3. BLOCKAGE WITH SOLIDS AND WASHING DAMAGE Hanging candle filters blocked by sulphates Sublimed sulphur blocking the fibre 5 year old hanging candle filters blocked by insoluble solid dusts, with a new filter added.

25 THELIFEAND DEATH OF FIBRE BED MIST ELIMINATORS 3. BLOCKAGE WITH SOLIDS AND WASHING DAMAGE Washing mist eliminators is an obvious way of extending filter life and saving money on a new set. It is not always easy or quick, and can be expensive to do. Only wash when you really need to. Washing can involve risk of damage. Washing Guide available from Begg Cousland

26 THELIFEAND DEATH OF FIBRE BED MIST ELIMINATORS 3. BLOCKAGE WITH SOLIDS AND WASHING DAMAGE Only wash when you really need to. Washing can involve risk of damage. Although h these hanging filters look kdiscoloured d in the tower, when removed you can see that there is no serious surface solids. Washing without reason can lead to fibre damage and mishandling of the structures, which can finish a filter s life.

27 THELIFEAND DEATH OF FIBRE BED MIST ELIMINATORS 3. BLOCKAGE WITH SOLIDS AND WASHING DAMAGE The mist eliminator below was automatic removed for washing under a shutdown schedule. Unnecessary washing causes abnormal liquid load stress to the fibre, a risk to High Velocity fibres ThePD hd had only risen by 10% over 18 The lighter density fibre bd beds can also months so neither the PD nor the be damaged easily by too high water visible solids justify washing pressure & handling

28 THELIFEAND DEATH AND REBIRTH OF FIBRE BED MIST ELIMINATORS 4. MAINTENANCE COST SAVING SUGGESTION REPACKING STRUCTURES WITH NEW FIBRE BEDS / RECYCLING FLANGES Why leave re useable parts lying in a scrap heap because they are not able to be cleaned or have been damaged when being removed / washed. hd? Re cycle the structure by sending it to us for repacking in the USA, Italy or India. Alternatively re cycle only the top and bottom flange sets.

29 THELIFEAND DEATH AND REBIRTH OF FIBRE BED MIST ELIMINATORS 4. MAINTENANCE COST SAVING SUGGESTION REPACKING STRUCTURES WITH NEW FIBRE BEDS / RECYCLING FLANGES If a structure has this amount of damage and distortion, then it will not be possible to repack it. Cut off the top and bottom flanges and only return them to us. So save freight cost. So save fibre stripping time and cost. Those savings can off set the cost of a new set of cages welded to the returned flanges, and boxes.

30 EXTENDING THE MIST ELIMINATORS LIFE 1. COLLECTING INFORMATION Mist eliminators performance can be monitored by : Pressure Loss Stack Exit Appearance

31 EXTENDING THE MIST ELIMINATORS LIFE 1. COLLECTING INFORMATION Mist eliminators performance can be monitored by : Pressure Loss Acid Drainage

32 EXTENDING THE MIST ELIMINATORS LIFE 1. COLLECTING INFORMATION Mist eliminators performance can be monitored by : Pressure Loss Sludge Presence

33 EXTENDING THE MIST ELIMINATORS LIFE 1. COLLECTING INFORMATION Mist eliminators performance can be monitored by : Pressure Loss High Corrosion Rate

34 EXTENDING THE MIST ELIMINATORS LIFE 1. COLLECTING INFORMATION Mist eliminators performance can be monitored by : Pressure Loss Mist Sampling and / or Stick Test

35 EXTENDING THE MIST ELIMINATORS LIFE 2. UNDERSTANDING / INTERPRETING THE INFORMATION Stick Test result changes with gas volume? Stick Test result changed noticeably but the gas volume is the same?

36 EXTENDING THE MIST ELIMINATORS LIFE 2. UNDERSTANDING / INTERPRETING THE INFORMATION Stick Test result does not relate to stack plume? Droplets not very visible Spitting marks on & not seen at stack exit. ground may be Droplets only usually seen or car owners indicate reentrainment. t may find paintwork Check PD and trend. damaged & claim.

37 EXTENDING THE MIST ELIMINATORS LIFE 2. UNDERSTANDING / INTERPRETING THE INFORMATION An updated Troubleshooting Guide is available, as well as Guides to Shutdown Inspection, Stick Tests and to Mist Eliminator Design & Selection

38 MIST ELIMINATORS LIFE STORY FOOTNOTE OLEUM /SO3 TANK VENT SCRUBBER PACKAGE The 1 st use of our Becoflex Rotary Brush Scrubber in a H 2 SO 4 plant was in the UK, at the plant where a tank vent pipe led to corrosion of the candle filter shown. The customer stomerinstalled the Becoflex BFCF unit on top of the Oleum tank, spraying water onto the rotating brush to hydrolyse the SO 3 very effectively within the fan volute. All the H 2 SO 4 mist formation took place before the 2 nd stage candle filter, so there is an invisible exit.

39 MIST ELIMINATORS LIFE STORY FOOTNOTE OLEUM /SO 3 TANK VENT SCRUBBER PACKAGE The unit has its own recirculation tank to minimise the water effluent. The combination of dynamic contact between gas and liquid within the fan volute minimises unit size. A key feature is the suction generated by the rotating brush, which means that there is no need for a separate fan unit. The Becoflex is also self cleaning if any solid matter is entrained from the tank.

40 MIST ELIMINATORS LIFE STORY FOOTNOTE OLEUM /SO 3 TANK VENT SCRUBBER PACKAGE The 2 nd user of our Becoflex Rotary Brush Scrubber was in S. America, at the plant where the Oleum tank vent pipe led to the corrosion of the demister seen earlier. They also use the Becoflex to treat the fugitive vapours fromthe wagon loadingstation station. For further information ask for a copy of the Becoflex Brochure or a copy of the Data Questionnaire.

41 THEBEGG COUSLANDLIFESTORYLIFE STORY