Ceramic Flat Plate Diffuser

a. Application
b. Product Description
c. Installation and operation
d. Health & Safety
e. Specification
f. Maintenance
g. Warranty & Conditions

 

The contents of this information leaflet must be read and fully understood prior to using the product.


 

Applications

The Dryden flat plate ceramic diffuser is a high performance micro-bubble diffuser designed for use with the following gases

Oxygen Ozone Carbon dioxide Nitrogen Air


If other gases are to be used with the ceramic diffusers, please advise Dryden Aqua for clearance. If the diffuser is to be used with air, the air supply must be 100% oil free and filtered down to 0.1 microns using a cartridge filter and a carbon filter in order to remove any solids that may block the diffuser internally.  If your gas supply is not clean, then it is important to fit filters, this can sometimes be a problem with compressed cylinder industrial gas supplies



Industrial sectors

Aquaculture 

The ceramic diffusers are designed for use in aquaculture for both freshwater and marine systems. Typical applications for the diffuser include the following aspects within the aquaculture industrial sector;

Oxygenation of tanks, cages, ponds, fish transportation.

The diffusers may also be fitted inside header tanks or pipes supplying the water to the farm. If the diffusers are fitted inside a pipe it is important that there is sufficient residence time in the pipe to allow all of the oxygen to dissolve in the water, in order to avoid the potential for air or oxygen locks in the pipe work. If the diffuser is being used to diffuse oxygen into pressurised vessels, the oxygen should be 100% pure. Any nitrogen or other gases present in the gas stream will also dissolve into the water, which could lead to gas bubble trauma in the fish or aquatic animals.

Anaesthetics of fish in marine and freshwater systems using carbon dioxide.

In marine systems or hard water conditions when carbon dioxide is used there may be excessive carbonate precipitation in and on the ceramic plate air. In order to avoid back-pressure and possible cracking of the diffuser it is important that the emery paper is used to thoroughly clean the surface of the plate after use, or at regular intervals. This will prevent or reduce the accumulation of carbonates.

Activated sludge tanks.

The diffusers can be used in activated sludge plants, or effluent treatment systems as a means of providing oxygen to aerobic bacteria.

Discharge channels.

The diffuser can be used in the discharge channel from humus tanks or discharge tanks as a means of increasing the dissolved oxygen content of the discharge water. This process can be used as a means of complying with the discharge consent of the facility.

 

Product Description

 

The Dryden Aqua ceramic diffuser is a high performance flat plate ceramic diffuser. The diffuser frame is manufactured from cast aluminium and then enamelled. The ceramic plate is secured in place using a high performance industrial epoxy. Ceramic is a very strong material, however if miss-treated there is a risk that the plate can crack. The design of the Dryden diffuser is such that the plate is fully supported internally to improve the structural strength and impact resistance. If a diffuser breaks from gas hammer shock loads, then usually the plate will just crack and all parts of the ceramic should be held in place.  This is a unique safety feature of the Dryden Aqua Product.  All diffusers are pressure tested to 20 bar.

The key performance feature of the Dryden ceramic diffuser is the mist of fine bubbles produced from the plate. When used according to the instructions, the plate will produce bubbles of a size between 10 microns and 200 microns to give a diffusion cloud like milk.



Installation & Operation

The diffuser when used in a tank should be installed in accordance to the following instructions;

Mechanical installation

  1. Use a two stage regulator with a maximum pressure of 3 bar
  2. Fit a needle valve and rotometer after the regulator
  3. Fit a pressure relief valve set at 5 bar on the gas line

Start-up

  1. Close the needle valve after the regulator
  2. Open up the regulator and then slowly open the needle valve to give the required gas flow.  This procedure must be followed because even although the regulator may be 3 bar,  it takes a fraction of a second before it functions and during this period a transient high pressure pulse of 100 bar or more may be sent down the hose.
  3. It is also a good idea to use a long hose before the diffuser to act as a spring and in order to reduce the affect of gas hammer.

Positioning

  • The diffuser should be sitting horizontally to avoid bubble coalescence
  • Install diffuser in the deepest point in the tank, this will give the longest residence time of the bubble cloud in the water
  • There should be no obstructions in the path of the bubble cloud; obstructions will cause the bubbles to coalesce.
  • A horizontal flow of water across the diffuser will improve performance
  • Do not place two diffusers side by side
  • Minimum operating depth is 500mm, never turn the gas supply on with the diffuser out of the water
  • If the water has a high lipid contend from oils then performance will be reduced to to coalescence of the bubbles

Any number of diffusers may be connected to the one oxygen or gas supply, the connection onto the diffuser is by use of the taper threaded 1/4" hose tail. No PTFE or similar type of tape sealant is to be used on the fittings. Four 6mm mounting holes are provided on the diffuser. These mounts may be used to secure the diffuser to a specific location. Do not over tighten these mounts, any distortion of the frame will cause stress to the ceramic plate and may result in damage. 

Gas feed pressure & flow
The maximum operating pressure of the diffuser is 35psi, the gas lines supplying the diffuser must be fitted with pressure relief valves or automatic shut down facilities that prevent any differential pressure in excess of 50psi across the diffuser. Typical operating pressures are between 30 and 35psi for the Dryden ceramic diffusers, the table below gives the flow rates for oxygen that can be expected.

Type Ceramic Plate area oxygen flow (maximum)
DAD 6 400mm x 90mm 6 litres per minute

Health & Safety

Oxygen can be a very dangerous gas with a risk of fire or explosion. All health and safety issues relating to the use of oxygen (and other gases) should strictly adhered to at all times.

Explosion and fire hazard

Specific attention should be paid to insure that all fittings in contact with oxygen are de-greased and are always free from oil, fats or other potentially combustible hydrocarbons. All fittings used with the Dryden ceramic diffusers should be compatible with the gas employed. In some cases not all of the oxygen will be dissolved into the water, under these conditions there may be an increase in the oxygen levels on the surface of the water, in the gas space above the tank, or in the room where the equipment is located. This point should be noted and the appropriate health and safety features implemented appropriate to the gas employed.

Pressure and ceramic hazard

The maximum operating pressure of the diffuser is 35psi, the gas lines supplying the diffuser must be fitted with pressure relief valves or automatic shut down facilities that prevent any differential pressure in excess of 50psi across the diffuser. Do not operate the diffuser, or pressurise the diffuser when out of water. The diffuser must always be at least 500mm below the surface of the water when the gas is applied. Do not touch or remove the diffuser when in use, do not put your had or any part of your body closer than 500mm to the diffuser when in operation. The use of the Dryden diffuser, and all aspects relating to health and safety are the responsibility of the users. Dryden Aqua accepts no liability or consequential loss as a result of the use of the diffuser.

Safety feature

Dryden Aqua ceramic diffusers are the strongest and safest diffuser available, the diffusers are batch pressure tested to 20 bar. The static pressure test is therefore up to 10 times the working pressure. For health and safety you normally only need to pressure test to 1.5 times the working pressure.  The diffuser plate is fully support in a very strong cast aluminium frame and epoxy bonded to the frame. If the diffuser is over pressurised or subjected to a transient high pressure spike, then normally the diffuser will just crack to release the pressure without the ceramic shattering.  This is a unique feature of the Dryden Aqua diffuser.

Specification

Parameter TYPE DAD6
Bubble size 10 to 200 microns
Efficiency (depends strongly on conditions) approx. 40 to 80%
Connection 1/4" BSP tapered thread, fitted with 1/4" hose tail, 3/8" tail optional extra
Materials of construction enamelled cast aluminium ceramic porous plate brass connections
Plate surface area 400mm x 90mm
Overall dimensions 446mm x 107mm x 26mm
Plate weight 3.1kg
Maximum operating pressure 35psi ( 300 kPa)
Setting for relief valve or shut down 50 psi ( 345 kPa)
Maximum gas flow rate 6.0 l/min
Recommend gas flow rate range 1.0 to 4.0 l/min


Maintenance

 

 The Dryden Aqua micro pore ceramic diffusers have been designed to give a long and trouble free life. When the diffuser is used in water it will be prone to both chemical and biological fouling. The diffuser should therefore be cleaned at periodic intervals. If the diffuser appears to be fouled, or if the gas flow rate starts to fall off, then it is and indication that cleaning may be required.

Cleaning procedure

  1. Turn off gas supply
  2. Remove diffuser from water
  3. Clean with a bristle brush to remove gross debris
  4. Wash in clean fresh water, or water containing a mild detergent
  5. Allow to dry
  6. Rub with emery paper 240 grade
  7. Rinse in fresh clean water
  8. Dry diffuser and place in store, or put back into use

Diffuser Blockage

The pressure differential across the diffusers should be approx 2 bar during normal use, however occasionally the diffusers can become blocked for the following reasons;

  1. Ferric and carbonate salts form on the surface of the plate, they are usually removed by the 240 grade abrasive paper, however if it is not affect then a dilute acid such as acetic acid or citric acid may be used to dissolve the carbonates and metal salts.
  1. If the diffusers are not cleaned after use, a biofilm can gradually develop inside the diffuser, in order to remove the biofilm soak the diffusers in a 1 % solution of sodium hypochlorite  at a pH between 6.5 and 7.5 for a period of 12 hours. If chlorine dioxide is available, this is much better as removing biofilm.  Never mix hypochlorite with an acid, this will release toxic chlorine fumes...extremely dangerous....
  1. The hypochlorite is usually effective at removing biofilm contamination, but if the diffusers have been allowed to become grossly contaminated then a 2% solution of sodium hydroxide at 50 deg C for 1 hour works well. However caution should be exercised when dealing with sodium hydroxide because it is very caustic. Comply with all health and safety regulations.
  1. If none of the above work, the diffusers may have been exposed to a dirty gas, compressed gas cylinders do not always provide a clean gas unless you use hospital grade. Liquid oxygen should be clean, and oxygen provide by PSA systems is usually very good. The problem is mainly with gas cylinders.  The above procedure should be able to clean the inside of the diffuser, but if there is gross contamination of the plate it may require an extended soak period in a dilute acid such as acetic or citric acid. Only ever use organic acids with the diffuser. The brass fitting may experience erosion from the acid, so only use a weak acid and do not soak for any longer than is absolutely necessary.
  1. If the diffusers are not cleaned the plate becomes blocked,  the effect of gas hammer becomes more pronounced and the plates  can crack, especially if the installation and start up procedure is not in accordance to the instructions.

Disinfecting

The diffuser may be disinfected using a maximum of 50mg/l of hypochlorite solution. Fill the diffuser with the hypochlorite solution and allow to sit submerged for 10 minutes. Remove the diffuser, drain out the hypochlorite solution and then wash in clean freshwater to remove all traces of the disinfectant.

Storage

Storage temperatures should be between +5 degrees centigrade and 60 degrees centigrade. Do not expose the diffusers to temperatures above 60 degrees centigrade.

Warranty & Conditions

Dryden Aqua provides a guarantee against any defect in the goods that is attributable to the manufacture of the product for a period of one year from the date of purchase or 16 months from the date of manufacture, (which ever is the shorter time period). Defective goods should be returned to Dryden Aqua suitably packaged for inspection. If it is determined that the fault was due to defective parts or manufacture, the goods will be repaired or replaced free of charge within the UK. For goods returned from out-with the UK there will be a returned goods charge at cost price.

Dryden Aqua guarantee is conditional upon the following;

The equipment must have been used and maintained according to Dryden Aqua instructions

The guarantee will not cover any defects resulting from misuse of the product, neglect, accidental damage, over pressurising or operation of the diffuser out-with the design specifications

Any attempt of the purchaser to repair the ceramic diffuser will render the guarantee null and void

Any defect should be reported within three days by fax or email to Dryden Aqua. The goods should be returned to Dryden Aqua or an official representative of Dryden Aqua, along with a written report on the circumstances leading up to the defect. Cost of returning the goods to be born by the purchaser.

The purchaser certifies acceptance of the guarantee as set out.

Limits of Liability Dryden Aqua obligations specifically exclude any liability whatsoever for claims by the purchaser or user or any other persons or parties; In respect of merchantability, or fitness for a specific purpose. Or consequential damages resulting from the use, or as a result of a malfunction of the equipment. For personal injury or any medical or disability claims or for compensation arising there from. The warranty and conditions, limitation and exclusions are accepted by the purchaser as the only authorised and applicable warranty and that there are no other warranties or conditions, oral or written, expressed or implied.

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