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Thread: Air Pads or Bin Activator for Hydrated Lime Silo?

  1. #1

    Question air pads or bin activator for hydrated lime silo?

    Silo was recently converted from storing quicklime to hydrated lime. The 30 ton silo has air pads on cone to minimize clogging. Pads have detiorated or clogged and haven't worked in some time. Silo is currently experiencing clogging problems in cone. Options are to retrofit with a bin activator or replace air pads. Replacing air pads would be least costly alternative. There is no experience at facility of performance of air pads with hydrated lime. Any thoughts on expected performance of air pads vs. bin activator for hydrated lime? Thank you for any info.


  2. Re: air pads or bin activator for hydrated lime silo?

    dear peter,

    air pads or bin activators only fight the symptomps but not the cause! if you want to ensure massflow in your silo without clogging and other problems you have to care for a correct geometry of your silo in combination with a discharge aid, that feeds your material continouosly over a corect dimensioned outlet.
    i invite you to take a look at the homepage you´ll find a lot of hints regarding your difficulties choosing the menue "technology".
    geroldinger also provides a discharge system called oszillomat, especially developed for demanding bulk materials and tasks, which could surely solve your tasks.

    best regards

    Originally posted by peterj
    Silo was recently converted from storing quicklime to hydrated lime. The 30 ton silo has air pads on cone to minimize clogging. Pads have detiorated or clogged and haven't worked in some time. Silo is currently experiencing clogging problems in cone. Options are to retrofit with a bin activator or replace air pads. Replacing air pads would be least costly alternative. There is no experience at facility of performance of air pads with hydrated lime. Any thoughts on expected performance of air pads vs. bin activator for hydrated lime? Thank you for any info.

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  3. Air pads

    Pads with a porous membrane can clog with fine materials, but are particularly prone to the formation of deposits if the powder is hygroscopic, because pressurised air entering though the pads usually carries water vapour that can be released by the pressure drop. The type of air ‘button’ with a flexible rim that deflects under a supply pressure to allow air escape against the hopper wall is more likely to work better in these circumstances. Typical devices of this type, sometimes called ‘magic mushrooms’, are available from, amongst other suppliers.

    Bin activators are also fitted to overcome arching problems with hydrated lime. Both these and air pads are expedients, but common solutions, to allow the use of hoppers with more shallow wall angles and smaller outlet size demands than are necessary for mass flow. Hydrated lime settles to achieve a significant bulk strength and has high surface friction with most materials of wall construction, so these techniques may well offer the most economical choice for a storage facility. Neither method gives a ‘first-in, first-out’ flow pattern, but this does not appear to be a crucial need for most applications using this material.

    Hydrated lime is a fine powdered material that becomes highly fluid when excessively dilated so it is prudent to control the air input volume, rather than its pressure, to avoid the over-supply of air beyond that necessary to weaken the material enough to discharge.

  4. #4

    Bin Activator or air pads?

    We recommend retrofitting your existing silo to use a bin activator. The air pads will fluidize the hydrated lime and it will be difficult to handle and is prone to flooding.

  5. #5
    ALBRECHT Guest

    Flow activation for hydrated lime stone silo

    Hallo Peter,
    according to ALBRECHT experience your silo (30 tons content) should have a dia of about 2-2,5 m, a height of 6 - 7 m, and an outlet dia of 200 - 250 mm dia.
    Such silos are well known by experience. Usually these silo have a funnel angle of 60 degree, and almost always show a central flow channel, in which material - once flown out of this channel - only slides from the surface of the silo filling, if at all. There are some disadvantages: First, the material sticks to the silo walls and by time gets consolidated, and the storage capacity of the silo is reduced remarkably. Second: If material slides down the flow channel from the filling surface it gets accellerated and often penetrates through smallest slots of the outlet device, as rotary valves, or screw conveyors, at least puts a considerable high pressure on such equipment, and can flow out although the device is not switched on working.
    ALBRECHT proposed therefore to apply 2 Pulsors type 150 - installed oppositely to each other, in slight different levels at the silo cone, the lower Pulsor in a distance of 200 (250) mm of the outlet opening, the higher Pulsor in a distance of about twice the outlet dia. Preferred, the lower Pulsor should be installed on the "drive-off" side of the outlet unit.
    The main thing for defining the Pulsor install places is, that the lower Pulsor should send out the air pulses produced into the bottom area af the remaining flow channel material. This will create always the breaking of the flow channel in the funnel. The upper Pulsor serves for good additional down flow of material in the funnel.

    Normally ALBRECHT Ingenieurbuero prepares a dimesional arrangement drawing of the Pulsors at the funnel, taking care of the outlet conditiones, as there are emergency slide valves, additional reducing pipe pieces or other equipment at the outlet of the silo. This can be done as soon we recieve a silo drawing or sketch.

    The Pulsors have to be controlled electrically by a switching device, either from a local control box - which is usually done for a first (or trial) installation of Pulsors - or can be controlled by a central switching system from a central control room. The switching system should get started with the start of the outlet equipment. The Pulsor working time always is to be set to 0,7 s, the lower Pulsor started first, and after about 3 s the upper Pulor shall follow. This procedure can be repeated as is necessary.

    ALBRECHT hopes to find your interest on this type of flow activation, and will prepare a comprehensive quotation when you send a demand info for this.

    See our home page for technical details and instrument function at

    Kind regards.
    ALBRECHT Ingenieurbüro GmbH
    Dipl.-Ing. O. Albrecht

  6. Re: air pads or bin activator for hydrated lime silo?

    Fine powders such as hydrated lime respond much better to aeration than vibration. Aeration "loosens" the material, whereas with vibration there is the potential to "compact" the material. Also, since aeration is a less costly approach, it provides an economic benefit. As to the type of aeration system, air pads can be a problem as they are effectively an air filter, which can plug over time due to oil and dirt in the compressed air system. I would suggest a bin aerator such as the Dynamic Air Vibra-Jet (see This device uses a rubber seal to prevent powder from back-feeding into the air supply, and therefore will not plug over time.
    Dynamic Air Inc. (USA)

  7. #7
    WHWilson Guest
    Over the past 30 years, I have furnished over 100 storage silos and related handling equipment for hydrated lime applications. Most were used in the production of asphalt and/or concrete mix for road paving or construction (a very demanding application from the standpoint of operating environment). In 99% of these applications, aeration was successfully employed as a means of promoting product flow. Typically, the silos ranged in diameter from 9 to 14 feet (2.7-4.3M), with capacities of up to 6000 cu. ft. (170 cu. M).
    While there are a number of aerator devices commercially available that will perform well in this application, I prefer the sintered metal type that insert into a threaded fitting welded to the exterior of the silo cone. While I have seldom encountered clogging problems, they do offer the benefit of being easily maintained without having to gain access to the inside of the silo. Simply unscrew the aerator, remove it, wash it, and replace it. (Of course the silo should be empty). I have found that 8 of these aerators spaced around the base of the cone work very well for hydrated lime.
    When using any aeration device, you should filter (with automatic condensate drain) and regulate the air supply according to the manufacturer's recommendations. There should also be a means to regulate the air flow with a manual valve of some type. Maintenance intervals will be extended if you employ a desiccant dryer and coalescing filter on the air supply. Condensed moisture or oil is the worst enemy of any aeration device. If you are withdrawing material from the silo on a regular basis, you can employ a solenoid valve on the air supply to only provide air when lime is being withdrawn.
    If you would like a proposal on a complete aeration "kit", please let me know. I will need to know the diameter of the silo, the diameter of the outlet, the approximate angle of the cone, and the means of removing lime from the silo (gate, rotary valve, screw conveyor, etc., along with the approximate rate of removal).

  8. #8
    Christoph Guest

    Bin activators for hydrated lime silo

    Dear Peter

    We are a manufacturer of all kind of equipment for bulk and powder industry and also of vibration spouts (bin activator). We have in this area an experience of more than 20 years. If you would like a refernce list, please don't hesitate and contact us. We will send you a reference list and more information about our vibration spouts.
    You can visit our homepage at first to get a survey about our range of products.

    We looking forward to hear from you soon.

    Best regards


  9. #9
    I prefer aeration cones to aeration pads in your service. Select an aeration cone such as that made by Myerlin. Control the air supply pressure with a flow orifice to prevent very high air flows and resulting fluidization of the powdered material. Use dry air or N2 if the material is hygroscopic.

    This will cost much less than other big changes.


    Tim Agarwal
    Pneumatic Conveying Consultants

  10. Lightbulb

    One of the key factors that does not come across in your intitial posting is what is the envisioned service life for the silo? Your solution cost should be viewed within the context of the operational life cycle for the vessel. If you can justify the expense I would strongly recommend considering the geometry of the vessel that you are using. The use of a conical vessel in conjunction with gypsum will result in a requirement for unrealistic convergent angles - this will apply even if you install a bin activator! If you can afford to consider a fully engineered solution (which is obviously what should be required for a medium to long term operational requirement), I would suggest the retention of the storage section of the silo, but replace the cone with a plane flow transition section (i.e. round to slot). In conjunction with this type of convergence we would often recommend the use of plenums that are set back from the cone, through which dehumidified air can be introduced. The function of the air in this type of application is to facilitate the dilation of the powder as it moves towards the outlet. Any intrusion into the flow channel (in a mass flow vessel) should be avoided at all costs, or the risk will exist that material will "hang up" and lead to flow problems.

    A material such as hydrated lime requires first in, first out discharge. You must be aware that virtually all discharge aids are just that - discharge aids. They will not alter the flow pattern that develops once discharge is initiated. If your silo has regions of non moving material in it, there is a fairly good chance that you are going to get discharge or quality problems at some point in time!

    Feel free to contact me if you wish to discuss further.


    Richard Farnish, Consulting Engineer
    The Wolfson Centre for Bulk Solids Handling Technology, Univ.Greenwich, London, UK

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