We are familiar with some of the traditional uses of carbon dioxide (CO2)such as putting the \\$quot;fizz\\$quot; in soft drinks, use in breweries, food freezing/chilling applications etc. Most of the recent growth in CO2 uses has come from the need for higher quality products, cleaner and faster work processes and from the ability of science and engineering to handle and manipulate the states of CO2.

But just when you think you have heard it all, someone comes up with yet another use for CO2. The fact CO2 can be made commercially available in its 3 physical states of gas, liquid and solid helps create applications for this versatile compound. gasworld explored some of the latest uses for CO2 within our industry.

Vermin are increasingly being spotted on board aircraft but can\\$quot;t be found and removed by conventional methods, the entire aircraft can be gassed or fumigated with CO2 to ensure 100% eradication. A recent Swiss case was where a passenger \\$quot;lost\\$quot; a snake on an Airbus A320 and the whole plane was fumigated for 12 hours with 3,500kg of CO2.

Food Preparation
Mass catering and delivering them safely in the right condition has been made easier with CO2. A novel \\$quot;Cook and Chill\\$quot; process using liquid CO2 has streamlined food preparation for hospitals in Germany. Patient\\$quot;s meals are prepared in advance as normal and placed in special storage trolleys the tops of which are then filled with liquid CO2 in the kitchens. This allows the food to be held and where required transported perfectly at a maximum of +5C until a preset time is reached when the food is heated and served.

Wood Preservation
Under certain temperature and pressure conditions CO2 reaches a critical point (super critical) where it acquires a liquid like ability to dissolve compounds while retaining the ability of a gas to penetrate fine structures like wood micropores. Supercritical CO2 has been used to carry preservatives through otherwise difficult hardwoods instead of traditional dipping and pressurizing methods.

Ingot mould is cleaned with an
ASCOJET dry ice blasting machine.///

Dry Ice Blasting
Dry ice blasting is a very efficient, non-abrasive, dry and environmentally friendly cleaning method. Dry ice pellets (solid CO2 with a temperature of \\$quot;“ 79°C) are shot out (under pressure) by a blasting machine on the contaminated surfaces. A sudden thermal shock is produced and as a result, the impurity contracts separating from the base material. As dry ice pellets sublime immediately after impact, there is no blasting media to be disposed of. As dry ice blasting does not damage or alter the surfaces at all, this technology is highly recommended for gentle and effective cleaning of moulds of any type and material in all kind of industries (e.g. ingot mould, core boxes, injection moulds, tyre moulds etc.). Moulds do not have to be disassembled thus saving enormous time. Even hot moulds can be cleaned in-situ. In addition to mould cleaning there are numerous other possible applications in all kind of industries like, for example, facility management, printing industry, paper industry, food industry etc.

Cold Chain Distribution
CO2 has long been used to keep perishable goods chilled in transit but this is now an advanced industrial solution that allows sensitive cargo to maintain constant temperatures for 24 hours and over. Chilled goods, for example, can be held at between 0C and +4C and frozen products can be kept at less than -18C. Highly efficient, such systems inject precise amounts of liquid CO2 into insulated containers where the dry ice \\$quot;snow\\$quot; formed from the liquid CO2 acts as the cooling agent. The amount of liquid CO2 or \\$quot;snow\\$quot; required is automatically calculated according to the container capacity, transport time and difference between the product and outside temperatures. Delivery can be made by a standard truck.

Insect Eradication
Certain insects like mosquitoes are attracted by our exhaled CO2 as this is how they detect us. An effective commercial insect killing process has arisen from this fact that releases a controlled amount of CO2 from a high pressure cylinder (in combination with lighting) to mimic the insect\\$quot;s prey \\$quot;“ us. The attracted insects are then drawn into a capture chamber where they die naturally.

CO2 Cleaning Applications
A new cleaning method using supercritical CO2 (SCCO2) is slowly gaining a foothold in the manufacturing industry where dry cleaning is preferred \\$quot;“ such as the semi-conductor industry. As opposed to regular CO2 \\$quot;snow blast\\$quot; cleaning techniques, this application uses SCCO2, which enables improved cleaning results.

SCCO2 is at a temperature and pressure greater than the critical temperature and pressure of the liquid, which means the it is around 30ºC and at a pressure of 73 bar. SCCO2 has properties somewhere between a liquid and a gas \\$quot;“ high diffusitivity and high density. With its high diffusion it spreads easily along the items and surfaces that are to be cleaned, meaning that it can etch or remove contaminants, even in cracks and crevices. However, at the same time SCCO2 maintains its liquid ability to dissolve substances which a gas is not capable of. It can remove silicon, dielectric, and machine oils, monometers, fluorinated oils, lubricants, and organic extractable adhesive residues.

A SCCO2 cleaning system is a closed-loop system where CO2 is compressed above its critical pressure and subsequently heated. It is important that the pump used is especially designed for CO2 such as the CRYOSTAR PPC reciprocating pump. The SCCO2 then enters into a cleaning chamber where contaminants are removed and collected in a separator where the SCCO2 is returned to its gaseous form, while the contaminants remain in liquid form. The gaseous CO2 is then recompressed to liquid phase and recycled. In order to optimise the cycle and guarantee return on investment the system should be managed automatically through an electrical control panel. An electrical control panel, like the CRYOSTAR Automation panel, not only provides full automatic management and visibility of every step of the process but it is also capable of producing production reports and linking into customer IT systems such SAP.

The initial high capital costs and the perceived risks of adopting a new technology have until recently slowed the market\\$quot;s adoption of SCCO2 cleaning. However, with a continuously growing knowledge base and proven life-time cost savings, dry cleaning using SCCO2 is likely to be a preferred application of the future.

Treatment of Off-shore Drill Cuttings
Drilling activity in the Oil & Gas Industry produces large quantities of drill cuttings. Most drill cuttings used offshore, use high percentages of diesel oil in the mix. By law the drill cuttings must be disposed of after treatment to landfill. There is a new process that utilises the highly efficient solvent properties of super critical CO2 to precipitate the oil waste in a purpose built pressure vessel from the cuttings into a collection vessel. The residue is fit to be treated for disposal (offshore) and the collected oil can be recycled.

This is a cost effective alternative compared to Bio-Remedial and Thermal methods. No transhipment to onshore facilities is required and the process is rather quick compared to traditional methods.

The Future
Where next from here for CO2 applications? Industry\\$quot;s view is that the cost of CO2 will act to limit or expand its usage and science and technology plus man\\$quot;s imagination will continue to find novel applications even more startling than the above.

\\$quot;¢ gasworld would like to thank ASCO, Cryostar and Logie Mackay for their contributions.Next month a follow-up article on Nitrogen.