Carbon dioxide plays a diverse role in many industries, and this is on the move, particularly when seeking energy conservation alternatives and environmentally friendly applications.

I have often spoken of applications for carbon dioxide in water treatment. Logically speaking, carbon dioxide in municipal and industrial water treatment systems is one of the best applications available today.

Before reviewing the subject of Ph reduction via a merchant-grade CO2, when delivered from a bank of cylinders or the larger low pressure receivers, I will review some of today’s hot topics as related to application of CO2 for growth enhancement of seaweed, algae, and related.

These subjects are not true ‘water treatment’ applications for CO2; however, they are water borne in application.

The application of CO2 in the proposed growth of plants and organic matter such as algae in particular, are highly proposed and discussed, however in real terms most of these projects are awaiting government subsidies or seeking funding.

The technology makes a great deal of sense, however, with the economy today and the cautious investors, everyone including the energy giants are seeking government funding – even though the energy independence which the US is seeking is clearly available via biofuels such as ethanol, algae operations, and second generation biofuels.

The application of CO2 could be water borne, but not specifically water treatment when speaking of certain algae, seaweed, and crop growth procedures for the production of biofuels such as algae and seaweed – ethanol and biodiesel feedstock.

Water treatment
When speaking of water treatment, effluent streams and the like, CO2 diffused into water can yield carbonic acid – easily controllable, self-limiting, and resulting in harmless carbonates and by-carbonates as by-products.

Many geographic regions which have hard municipal potable water use CO2, or even waste water plants use the product for the reduction of PH, and the control of (calcium carbonate based) scale which accumulates and inhibits the water distribution systems.

Many lime softening potable water treatment plants use CO2 as well, which again is self limiting, and easily controlled, thus dropping the Ph in a controlled manner.

These days, and for some decades past, merchant CO2 is hauled into these municipal treatment plants and low pressure storage tanks, holding several tonnes of product, store and use this CO2 on site.

Some municipal plants have automated controls for the diffusion of CO2 into the water, often driven by the Ph requirement.

Other facilities are not so automated, but the merchant product may be used via cylinders, bulk storage, or even submerged burners, generally using natural gas as an agent for combustion.

The old-style combustion systems would be found less often in the developed world, since many of these older systems have been converted to merchant supply and storage facilities, with automation.

The older style submerged combustion system simply diffused flue gas from natural gas combustion to achieve this end, a less effective and maintenance ridden approach to achieve this requirement.

Of course, the alternatives to Ph reduction via mineral acids, such as sulfuric, yields sulfates, which are not environmentally friendly – as well as more hazardous to work with compared to CO2 when handled correctly.

This concept, in terms of looking at the water and effluent treatment schemes, amounts to a form of recycling such water, since water is recycled in the greater scheme; and CO2 can
be an agent for safe Ph reduction and also calcium carbonate scale removal in the distribution system.

CO2 has been used, and can be a bit tricky when applied in cooling water systems for Ph control, as a function of the temperatures and pressure conditions of the water when applying in a cooling system.

Many food plants could be examples for CO2 in process or waste water/effluent treatment, as could the paper/pulp industries.

The first thought in terms of applications in the paper and pulp manufacturing industries would be use for Ph reduction of an alkaline effluent, however there are more proprietary applications within the mill’s machinery in some cases.

Therefore in summary, where there is water treatment, process water usage, run-off, or effluent, the application of carbon dioxide should be investigated, particularly if mineral acids such as sulfuric are currently in place. The end result would be a safer and more environmentally friendly means of achieving a Ph adjustment.

The food sector
From an applications perspective, the food industry is among or perhaps the most interesting and versatile sector for the use of CO2.

Many decades ago, when there was an abundance of CO2, both as a vented raw gas and as a merchant product, when soft drink bottling was the major factor in the merchant trade, beverages were the main target for CO2.

In such times, older predecessor gas companies such as the former Liquid Carbonic made beverage production equipment for the soft drink plants, well beyond today’s role in the merchant gas equipment supplied to the soft drink trade.

In today’s world, most or none of the merchant firms build storage vessels for any application in the industry, while the same applies to food related application equipment, vaporizers, and control devices.

External contractors are used to build a few cryogenic machines, however much of this is sold on the independent market, which is not associated with the gas manufacturers.

Therefore, the end result is the sale of primarily CO2 as a commodity to industry, with
the claim that certain proprietary features offered in certain contracted equipment should yield significantly different results.

Some time back, gas companies installed mechanical systems inline, or so-called ‘cryo-mechanical’ freezers, with claims that the end result would yield a better quality food or industrial product to be chilled or frozen; and less CO2 and/or electric power would be consumed.

Again, most of this has been found to be simply a sales tool, and the end result is more or less the same in a final chilled or frozen product via the application of CO2.

Cryogenic freezing and other applications
The term IQF refers to ‘individually quick frozen’ and the term is used throughout the food industry, whether or not the method of freezing is via cryogenic or mechanical refrigeration.

Simply put, many merchant gas companies try to sell certain controls, valves, injectors, or cryogenic freezers and food processor-related equipment for CO2, claiming greater BTU removal via the carbon dioxide as a refrigerant when compared to other components or machines on the market.

In the end, most of the results are essentially more or less the same, and these so-called ‘specialised’ features are primarily sales tools.

As for other applications which use CO2 in the food industry, one interesting method is the extraction of essential oils from herbs, plants and organic matter, or more common applications such as coffee beans and decaffeination – where the CO2 under specific conditions acts as a supercritical fluid.

Supercritical CO2 refers to CO2 that is in a fluid state while being at or beyond both its critical temperature and pressure, yielding uncommon properties.

The application of supercritical extraction would replace the use of halogenated hydrocarbons. This could be a popular and consumer friendly method of decaffeinating coffee.

When using CO2 ‘snow’ in food grinding applications, the applications are anywhere from meat grinding to spice grinding, for example. CO2 snow is also generated and applied into bulk meat and food products which are boxed and then shipped, to keep the food cool en route.

CO2 in a gas form has often been used in conjunction with other gases or alone for gas purge applications or gas packaging environments – thus removing ambient air, oxygen, or creating an environment amiable to greater freshness and quality.

About the Author
Sam A. Rushing is president of Advanced Cryogenics, Ltd., based in South Florida, now celebrating 20 years of success as a full range supplier of CO2 consulting expertise.

The work includes source and production plant development, process evaluation, market research and development, purity, and specification development, applications expertise; thus all technical to business related work for CO2 and other cryogenic gases. Phone 305 852 2597