To carry out an effective dry ice cleaning task the following is required:
- A dry ice cleaning unit with the right nozzle for the job and enough hoses to reach the working area.
- A source of compressed air with sufficient power to ensure the cleaning is economically efficient.
- Sufficient 3 mm dry ice pellets in an insulated container.
- Appropriate PPE for all personnel involved and clearance to commence work.
Dry ice Network can provide all the equipment required either for purchase or rental. Generally, a site inspection will quickly clarify the type of equipment and the amount of hoses required. Please call 0116 224 0072 to arrange a site visit.
2. Compressed Air
Compressed air for dry ice blasting can be taken from a shop air supply system fed by a stationary rotary screw compressor powered with an electric motor, or from a portable Diesel driven compressor. Whichever source is chosen the air specification and capacity requirements are the same.
The power of a dry ice blaster is governed by its nozzle size and the air pressure available to drive it. Most standard nozzles fall within the following three categories:
|Low pressure||2.5 m3/min ( 90 ft3/min)||at||5.5 bar (80 psi)|
|Medium Pressure||5.0 m3/min (180 ft3/min)||at||7.5 bar (110 psi)|
|High Pressure||7.5 m3/min (270 ft3/min)||at||9.5 bar (140 psi)|
The capacity of each size will change as the air pressure supplied to the nozzle is varied above or below the design pressures given above.
Varying the air supply above or below the design rating will increase or decrease the aggressiveness and efficiency of cleaning. Thus, tougher jobs will take less time at high airflows, whilst less arduous tasks, especially those where coated surfaces should not be damaged, will be better executed at lower airflows.
The amount of dry ice required for efficient cleaning is dependent on the type of blaster being used. With dual hose blasters dry ice usage remains roughly the same for each nozzle size and the full range of airflow, but as the efficiency of cleaning increases with nozzle size and the speed of the air, then it makes economical sense to clean with the largest nozzle at the highest sensible pressure. A small nozzle run off low pressure plant air may complete a task in several hours whilst the same task run from a 10 bar compressor using a large nozzle could be completed in less than an hour. It is therefore important to consider the overall economics when selecting the compressed air source and nozzle for a task.
3. Dry Ice Pellets
It is important that only 3mm dry ice pellets are purchased for blasting. Other sizes are available for other applications so all orders should be carefully specified. It is very embarrassing to open up the ice container at the start of a job and find unusable large pellets or blocks. To avoid this, always specify 3 mm pellets, or simply buy from Dry ice Network either direct on 0116 224 0072 or go to our dry ice website at www.dryicenetwork.com and buy on-line.
4. Personal Protection Equipment (PPE)
It is essential that the correct PPE is used by all personnel involved in dry ice cleaning as well as any bystanders. This includes ear plugs and ear muffs, insulated gloves, eye protection and a respirator. Our standard PPE pack includes all these plus an ice bucket with scoop. When used with safety shoes and a good overall this provides adequate protection for straightforward dry ice cleaning. It is important that the PPE is regularly replaced with equipment of the same technical standard and that its suitability is reviewed for each blasting job undertaken by conducting a thorough risk assessment.
Using Plant Air:
In some cases plant air can only be used successfully when the plant itself is not running or the standby compressor is brought on line.
To confirm the suitability of your plant air, please carry out the following checks:
The maximum output volume and pressure rating of your compressor(s)
What pressure the compressor(s) maintain when supplying the normal plant load.
The size of the receiver and the main supply pipe or network ring main.
The distance from the compressor to the point of connection for the blaster.
The size of the connection pipe for the blaster.
The dew point achievable by the drying system.
To run one blast unit over its full capacity range we use in our test facility an Atlas Copco GA 55 (300 cfm at 10 bar) with water separator and dryer package.
The current trend is to use Variable Speed Drives (VSD) on compressors to save energy. These are inverter-controlled units and not very suitable for driving a dry ice blaster unless a properly sized air receiver is used, as they require considerable time to attain their full output pressure.
The compressor should be sited as near as possible to the blasting location or enclosure and connecting pipe sizes should be chosen to give minimal pressure drop. A safe choice is to follow the compressor outlet pipe size right through to the blaster connection point, which will be 2 ½” for a GA55
Our choice of Atlas Copco is by no means mandatory and any comparable compressor can be chosen provided that it delivers the minimum required compressed air output of at least 300 cfm (8.0 m3/min) at 10 bar gauge.
Mobile Diesel Driven Compressors
To run one blast unit over its full capacity range a compressor fitted with an integrated water separator and aftercooler package capable of providing a minimum of 7.5 m3/min (280 cfm) at 9.5 bar (145 psig) is required. Depending on the manufacturer and location, most industrially available mobile compressors capable of providing dry air (Dew Point of 4 deg C or less) are larger than this. The most common standard is 400 cfm at 175 psig or near metric equivalents in the range 8-10 m3/min at 10-12 bar. Some typical examples are:
Atlas-Copco XAHS 146
For less arduous tasks a compressor with an output of 260 cfm at 125 psig can be used with good effect.
The compressor should be sited as near as possible to the blasting location and connecting hoses should be chosen to give minimal pressure drop. A safe choice is 1″ up to 30 metres and 1½” over 30 m.
For a truly mobile blasting set up the compressor can be towed with a vehicle that has sufficient capacity to carry the blasting equipment and the dry ice requirements.