Often in the headlines for other reasons, carbon dioxide is in fact utilised throughout a range of applications. Sam A. Rushing explores these and the challenges ahead.

BACKGROUND
The average person on the street would often see CO2 today as an agent for beverage carbonation, a gaseous agent in the atmosphere which is a normal part of many biological processes and also now viewed strongly as a major greenhouse gas.

In reality, this is just starting to scratch the surface of what this product represents, whether this be something viewed some years ago; today and tomorrow. CO2 is a versatile gas and chemical agent used in many phases of manufacturing, well beyond beverage carbonation. This includes carbonic acid formation for PH reduction, cryogenic freezing, cooling; and packaged food atmosphere modification. Also, there would be uses for pest control, environmentally friendly cleaning alternatives, solvent applications in many forms of industry, agricultural applications, and the enhanced production of oil and gas; all of which to name a few of the growing list of uses for this versatile product.

The successful and long term application in industry is driven by strategic availability, as driven by raw feedstock availability; as well as time-tested and well liked applications rather than alternate forms of achieving a similar end. Such alternate means can often be environmentally unfriendly, hazardous, or more expensive than CO2 applications in industry.

Region sensitive to product availability and cost effective applications in the merchant sector
In terms of the strategic supply of CO2 and the nature of today’s CO2 markets, in most developed world regions such as North America, Japan, and Western Europe, the variety of applications for merchant CO2 is roughly summarised in the table provided. Also as shown in the developing world markets, at least for the moment, quite a different story is shown.
With respect to the distribution-sensitive nature of CO2, as with most other gases, when selling as a truck delivered bulk product this would usually be sold within an approximate 150 – 250 (maximum) mile radius of the production plant, or the point of origin.

As to rail shipments, this distance can sometimes be an extraordinarily long journey, however, generally substantially longer than via trucking. With diesel fuel and gasoline on the rise today, selling prices for CO2 are of course higher, often via fuel surcharges being added to the invoices. As for the rail system in the US, many major railroads are either overwhelmed with current freight commitments, some of which are either a feedstock for, or a finished product from the growing ethanol industry. The railroads are also sometimes highly inefficient, thus producing unreliable availability of CO2.

If the expansion of ethanol continues to grow, either as an oxygenate alternative, or simply as a ‘biomass’ related form of energy compared to fossil fuel based energy products, it will become ever more important to construct ethanol and of course more strategically viable CO2 plants within, or closer to, markets which are currently being served from long distance sources.

With regards to long distance sources, this has historically been achieved via railroad deliveries to depot locations, or in a few cases, direct to the customer’s consuming location. On the other hand, with the cost of fuel rising, and the railroads turning away business, more strategically located CO2 sourcing will become more and more essential, if at all possible. Some of this is being planned with new ethanol plants, however, progress is slow and the majority of ethanol plants which are discussed initially, never achieve financing and are therefore never constructed.

Developing world markets – facts and challenges ahead for CO2 supply and sourcing
As is shown in Table 1, the lion’s share of CO2 is being consumed in the beverage industry through soft drinks, beer, and fountain beverage gas service. The balance can sometimes be small food related applications and/or a small presence of industrial usage. Industrial, as noted above, is often in the form of packaged cylinder gas.

With respect to the value or selling price for CO2 in many developing countries, this selling price, when delivered in bulk, can often start at and range well beyond $200 per tonne. The tonnage is often relatively small when comparing with CO2 consumption by much larger plants found in the developed world.

Historically, many developing world markets without available substantial raw traditional forms of feedstock, such as from sizable reformer, ammonia, or fermentation plants, would use CO2 combustion plans on site or via certain gas companies. This, simply put, is combustion of coal, coke, fuel oil, natural gas, recovering (concentrating) CO2 via usually an MEA solvent process and then liquefying and purifying to meet beverage standards. The cost of doing so is often from $150 to $300 per tonne; which would fit the economic standards for pricing CO2, as mentioned above – often $200 per tonne or more. These plants are sometimes disappearing in favour of new larger modern plants with enriched by-product CO2, which commonly serve developed markets. Such an example would be in the Middle East, where small combustion plants have commonly served individual beverage facilities for their CO2 needs; or certain resellers have operated these combustion plants as well for high priced CO2 markets. Today, with interest in enhanced oil recovery and gas well stimulation, these developing regions are evaluating and sometimes building CO2 plants sourced from a concentrated and traditional form of feedstock. The end result, assuming the plant is sufficiently sized and well loaded, can mean much lower costs for the production of an industrial or beverage grade product.

If such concentrated viable feedstock is available in the developing world markets, the challenge is to place this product into an industry which has often never used CO2 to achieve various tasks, such as refrigeration, insect control, or PH reduction. Often the markets are there, but require development from ground zero, over and above the beverage and cylinder gas interests already in place. This takes time and is sufficiently challenging.

CO2 applications found in the developed world – delivered via truck and rail
Refrigeration and food processing
I have offered an approximate percentage of CO2 found in average developed world markets being consumed by various sectors of the food industry. More specifically, a significant percentage of this application would be found in cryogenic freezing applications. Cryogenic freezing machines are often offered by specific gas companies to complement or sell their CO2. Such machines are also available from a variety of surplus suppliers, or from new suppliers, who are not owned or affiliated with the gas concerns. With respect to this application of CO2, in some regions, this would account for most of this approximate 40% volume for the merchant markets. In terms of cryogenic freezing, CO2 liquid is stored and then piped to the freezers, often multiple pass, single pass, or a spiral-configuration. Attempts to boost the refrigeration capabilities for CO2 in cryogenic freezing have included mechanical refrigeration of the liquid CO2 prior to entering the cryogenic freezer, hoping for greater BTU removal capabilities than without such treatment; and so-called ‘cryo mechanical’ freezers have also been attempted. The end results however, in terms of the benefits and costs, are difficult to interpret.

Other applications in the food industry would include producing a CO2 snow for grinding and blending of meat and other food products, while often a mixture of gases including CO2 or pure CO2 is used in modified atmosphere packaging applications. The packaged cheese business is an example of this.

Beverage applications
The application for CO2 in the carbonation of soft drinks and use of fountain beverage CO2 are commonplace and constitute perhaps 30% of the total market in the developed world, while in the developing world this is up to 80-90%. Carbonation of beverages is common in all world markets and in the case of the developing world, there is simply no substitute for CO2 use as a carbonation agent, so the expensive combustion plants are often the only form of sourcing.

The beverage industry has continuously created greater stringency for purity, handling, and production of CO2; somewhat due to claims of CO2 contamination by the major soft drink beverage firms in Europe and the US. These claims include various source types for CO2; which has resulted in a careful watch of the make-up for the raw gas, as well as continuous and often testing every load of delivered product to the soft drink beverage plant site.

When meeting this level (ISBT standard) of CO2 purity, this will usually meet or exceed all other specifications for CO2 purity, short of USP standards sought for a very small medical market. The beverage industry growth is often consistent with population fluctuations, but is often offset by bottled water sales. In the end, this market may be experiencing a flat to modest (1-3% per year) growth rate, but will always be essential as long as certain beverages are being produced. In certain beer producing plants, CO2 can be used for supplemental carbonation, as would be champagne, or in some large US breweries the merchant CO2 is simply used as a back-pressure agent in the brewing process, sometimes never touching the actual beer being produced. The specific point of application can vary somewhat in this overall beverage market; however the general use of CO2 for beverages will always be required.

Industrial applications
• Acid replacement/pH reduction
Within a range of pressure and temperature, CO2 in water can yield carbonic acid. Carbonic acid is a relatively weak acid, which is self-limiting at a moderate pH. By-products are generally benign carbonates and bicarbonates compared with sulfates found when using sulfuric acid. Common applications for many years in the US have been in water treatment plants, often affiliated with hard water and lime treatment. CO2 applications in municipal water treatment plants once originated via submerged or underground burners, generally combustion of natural gas, and the flue gas containing CO2 was the old fashioned form of making CO2 available to these plants. Today, many of these combustion systems have been replaced by a CO2 liquid storage, vaporizer, and diffuser system; as would be the modern water treatment plants. This application has been tested, and sometimes applied in power plant environments, and in environments where lower pH levels are sought, with the advantages of CO2 well understood and priced competitively.

• Insect/pest control
In select markets, particularly in year round warmer, humid environments CO2 has successfully replaced some of the long used halogenated hydrocarbon products, and other agents, which can have long term toxic or even carcinogenic effects upon humans and animals. This application has been used in grain storage facilities at large. Reference has been made to devices which trap mice and rats, subsequently asphyxiating these pests and this may become a growing market as well.

• Gas well stimulation agent
Many of the natural gas fields have successfully chosen the use of CO2 rather than other agents such as nitrogen, and non-gaseous products for well stimulation, often referred to in generic terms as ‘frac’ service. In short, under sufficient pressure, fracturing occurs thus releasing greater natural gas in the production process; plus the effects of carbonic acid can have a desired effect upon select geological compositions, and can also reduce swelling of clay in the formations.

• Solvent applications
This is a growing sector of the CO2 market, ranging from dry cleaning solvent applications in specific dry cleaning machines which operate under pressure, as well as closed system applications for the extraction of essential oils. CO2 is being tested in a range of other applications for use as a solvent replacement, which would be safer than what would be found, for example with dry cleaning, currently perchlorethylene, or ‘perc’. As with CO2 use for replacing sulfuric acid, many of the solvent applications replace agents which are deemed carcinogenic, or are being banned from release into the atmosphere, such as VOC materials in dry cleaning operations.

• Carbon dioxide usage in livestock operations
For many years, CO2 has been used to stun cattle and birds prior to slaughter. This is the humane method of preparing such animals for processing; and will probably grow as the food industry grows.

• Fire/welding/metallurgy
Fire abatement is a common application for CO2, as would be the application in welding gas mixtures. Some foundries have commonly used CO2, as have large steel mills for specific applications.

• Greenhouse enrichment applications
In lieu of burning natural gas for flue borne CO2, merchant CO2 has been used in a variety of greenhouse environments for plant growth enrichment programs. CO2 has been tested for enhanced crop growth usage, in irrigation projects and with some successful results. Commercial algae plants often require CO2 as well. The sum total of these agricultural applications can be significant in some markets.

• Enhanced coal bed recovery
As the thirst for natural gas grows and as enhanced recovery methods are used, CO2 has been studied and tested for use in coal bed methane (recovery) applications. In short, CO2 molecules would replace methane in this application.

• Dry ice
Dry ice is a form of CO2 pressed into blocks, extruded into various forms and sizes, often called ‘pellets’ or ‘rice’ dry ice and often simply flashed from liquid under pressure to atmospheric pressure, thus producing CO2 snow and vapour in the process. The applications for dry ice are wide ranging, often of a refrigeration nature, in food processing, preservation, and shipping applications. One application which has gained favour is so-called ‘blast cleaning’, using dry ice product for blast cleaning and paint removal, which replace the use of various hazardous solvents, steam or sand. This is a growing application in the industry, and should continue this way.

• Chemical feedstock use
Whether this is a captive application for production of methanol, urea, or sodium bicarbonate, or for use in a wide variety of chemical feedstock, the base is wide for CO2 use, as well as the volume ranging from mega sized to very small.

Enhanced oil recovery
CO2 is a common agent for enhanced oil recovery (EOR), which is a tried and tested agent in this ever growing application. Again as with natural gas, sought highly as the thirst for petroleum grows. CO2 in some US markets, such as Mississippi, often use natural underground wells as a feedstock for this type of service, already under high pressure. If the source is from a low pressure by-product source, such as reformer, fermentation, and ammonia, for example, this low pressure by-product from the source plant is usually between atmospheric and 15 psi. The application for EOR requires high pressure and pipeline operations, thus a sufficient capital investment, particularly if not sourced from an already high pressure natural source. For example, the pipeline capacity for one particular plant, that of Dakota Gasification, is about 10,000 tpd. EOR demands in Saskatchewan have been growing in volume to fulfill this total pipeline capacity, traveling from North Dakota into Saskatchewan for EOR projects owned by EnCana and Apache.

The natural high pressure sources serving the Texas Permian Basin; plus further regional operations are much greater in volume than this Dakota operation.

Summary
The above mentioned applications for CO2 include a food/beverage nature and industrial applications which represent the ever-growing use for CO2 in industry at large, or the so-called merchant market demands for the product. As we can see, some environmentally friendly forms of CO2 from blast cleaning to acid replacement, to solvent replacement exist, and will continue to grow. The industry will continue to develop and expand volume in new and existing sectors of industry. The product is one of the most versatile gases and chemical agents found in industry today.