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SAM A. RUSHING
ADVANCED CRYOGENICS, LTD.
P.O. Box 419, Tavernier, FL 33070 USA
Tel 305 852 2597 Fax 2598
rushing@terranova.net
www.carbondioxideconsultants.com
Background
In the world of biofuels, algae is under the spotlight as a major destination of interest for CO2 usage from power and chemical projects, from the perspective as a greenhouse gas / carbon sink. Today, more than ever, methods for viable sequestration alternatives are essential to meet the changing political and environmental tone set by the US House of Representatives and the EPA – and ultimately established as a law. Also of strong interest is the usage of algae as a source of feedstock material for biodiesel, and perhaps fermentation. CO2 is an ingredient used by algae for normal growth, during photosynthesis, and of course, the challenge for a strong reduction of atmospheric CO2 content is one of today's greatest challenges. Algae can be a partial means to an end in this quest for greenhouse gas reduction, and at the same time serving as an essential ingredient required for algae cultivation. The driver in algae based CO2 fixation or sequestration has been CO2 sourcing from coal fired power plants. The coal fired power plants yield ½ of the power produced, and at the same time some 83% of the CO2 emitted from all power sources. For each Kwh of electricity, about 2.1 pounds of CO2 are produced, and sent out as flue gas, on average, from the coal fired power plants.
A range of 1.5 to 3.0 pounds of CO2 are required for one pound of algae cultivated. Power plant projects are under the greatest amount of pressure to reduce airborne CO2 emissions today, however, larger fermentation projects are also viable CO2 source targets; plus a number of commercial energy production and chemical manufacturing sources as well. Most of the testing for CO2 fixation by algae has been via the coal fired power plant, which is a lean CO2 content v. a fermentation project. The difference in CO2 content can make for a broad range in capital expense and production cost, as well as the raw gas specifications – that being nitrogen oxides (NO x) and sulfur oxides (SO x) are major culprits when defining which algae strains will accept the use of a raw flue gas with lots of the sulfur and nitrogen compounds v. a generally cleaner by-product from select chemical manufacturing processes; which may or may not require purification in this application. Therefore, hurdles via flue gas include selection of a viable algae for cultivation, assuming little or no purification takes place; plus the application of large volumes of raw gas could be problematic, from an application point of view.
Algae cultivation as a carbon sink is a popular consideration among those in the power generating business. In this scenario, generally DOE or industry sponsored demo projects have produced most of the headlines in the press as of late. In such settings, generally the algae project is located around or near the power facility, chemical manufacturer, or other projects which have a significant CO2 output. The difference among various CO2 emitters, in terms of the amount of CO2 available per pound or ton can be a day v. night scenario, and this would then create a range of requirements for capital investment, application technology, and results achieved. In real world terms, it is not always possible or convenient to allow an 'across the fence' algae production site, in part, since adjacent real estate is not always conveniently available.
As to algae fuel, this can represent up to 30 times more energy value per acre than a common crop, such as soybean. Other examples, include the difference with palm oil can average one – fifteenth the energy value when compared with algae. Given the high oil yield from algae, it is estimated that about one percent of today's one billion acres used in the United States for farming and grazing would be sufficient (as land, pond, or ocean space) to produce enough algae to replace all petro – diesel fuel used in the United States today. That is a significant number, and algae should be utilized and developed to take advantage of opportunities such as this.
Numerous challenges lie in this successful application of algae as a medium in the biofuels world, when considering CO2 applications, which include distance from the CO2 source to the algae production site, the nature of the CO2 source – and how it impacts the cost and feasibility in this application. All of this is highly sensitive to the increasing requirement to reduce carbon emissions.
Application of CO2 and Sources
Many of the projects which have been evaluated or are under a test today are electric power projects, generally coal – fired projects. Since coal – fired electric generating plants account for about 40% of today's CO2 emissions, and if CO2 emissions are reduced from this sector, a major impact on greenhouse gases would occur. In the United States, CO2 is now being recovered from the flue gas produced from coal fired cogeneration plants; and the economic model worked due to a prior energy law which fostered the use of cogenerated steam which is used in an amine (MEA) solvent recovery process – a method of concentrating the CO2 from a lean content in the flue gas. Further, when considering relatively large CO2 emitters, the ethanol industry has been in the spotlight due to a substantial amount of CO2 emitted in a concentrated form as a direct by-product of fermentation. As to fermentation by-product, anhydrous ammonia by-product, and the by-product of certain hydrogen reformer processes found in oil refineries, to name a few - would have CO2 raw gas content (often in a water saturated state) of 97 to 99% by volume.
When comparing this to emissions from combustion of various fossil fuels, such as coal, this can often range within the 12 - 15% by volume order of magnitude. Gas fired turbine exhaust in cogeneration can be below 3%; and heavier hydrocarbons have higher concentrations of CO2 accordingly. Some consider the need to concentrate the CO2 via traditional processes, such as MEA, which is quite expensive. If using MEA, this would represent between three and five times the cost of applying CO2 from a concentrated source, such as those named above – let's say fermentation. Other novel or test applications are underway with so-called proprietary processes, including membrane and refrigeration systems. In my experience, however, new and novel means of concentrating the CO2 are not commercially proven thus far.
Therefore, the economics behind what type of CO2 source is used, is driven by the raw CO2 content in the gas – source type, as well as the impurities found in this CO2 source. If the source is relatively clean, and well concentrated, direct application for CO2 fixation by certain algae strains is entirely feasible. Separately, when concentrating a flue gas v. using a highly concentrated source (chemical manufacturing by-product for example), the economics are like night and day.
On the other hand, if these projects are DOE sponsored, or within the forthcoming greenhouse gas laws and CO2 emissions regulations call for economic considerations, perhaps the need for concentrating or refining is a viable possibility.
It has been found that select strains of algae might be able to endure a more harsh environment when applying directly a power plant based flue gas. It has been found that a broad spectrum of algae will not endure the SO x and NO x content of raw power plant flue gas; however, algae strains specifically defined as NANNO2 grew after a lag period of time when under 300 PPM of nitrogen oxide. Other results when applying direct power plant flue gas in this application of algae growth, specifically NANNP-2 and PHAEO-2 algae proved to be successful with the harsh power plant flue gas in an untreated state.
Some of the above findings have proven well in a raceway type setting for algae cultivation, when diffusing power plant flue gas v. using a refined and / or liquefied CO2. The other consideration, beyond algae type and growth tolerance in the direct flue gas setting, would be the availability of real estate or physical space for algae cultivation. This thought precipitates the question of transporting the CO2 source to the algae cultivation site.
CO2 Transportation and Algae Cultivation Sites
Traditionally, CO2 has been transported (via pipeline, truck and rail) in a liquid form; always purified when used in the merchant markets. The exception to much or any purification has been for EOR – enhanced oil recovery. It is important to remember that liquid CO2 would represent a great deal more carbon dioxide presence v. simply trying to transport a gaseous, dilute, power plant product. The construction of a liquid carbon dioxide pipeline can easily run $1million per mile; and when transported as a liquid via pipeline, this distance can be substantial, these CO2 pipelines which transport liquid to enhanced oil recovery (EOR) sites are often long distance lines, up to one hundred , and even hundreds of miles; this would require sufficient compression on the front end and compression sub-stations in route. As to the case when considering algae fixation as a means of sequestering CO2, and a further means of producing a substantial raw material for the manufacture of biodiesel, it is entirely technically feasible to transport CO2 via pipeline. Consideration has been given to projects which use high pressure from enriched sources of CO2, such as fermentation for various destinations such as EOR. This concept could be applied to biodiesel in the fixation of algae with the CO2 by-product. As to transport of raw flue gas long distances, I would say this may be entirely new for a project such as this. First, the question is whether or not the algae will endure the SO x and NO x, plus other constituents; however there is evidence, as outlined before, this is possible with select strains of algae. Next, capital cost considerations for compression and pipeline as the basic infrastructure would be necessary. In the end, since massive quantities of CO2 from fossil fuel combustion in the power sector can amount to 20 million tons daily on a global scale – this is from a total amount emitted by all sources as 75 million tons of CO2 daily. When taking this into consideration, all means of containing, sequestering, or fixing CO2 via a environmentally friendly and extremely useful product such as algae is an extraordinary opportunity. The end result is twofold – the production of an extremely useful and rich in energy value v. grain and other organic matter feedstock materials such as soy and palm oil. Many of the test or small scale algae cultivation sites have occurred in a series of tubes, and bags, which have provided proof of growth capabilities. Larger scale cultivation of algae for energy sources, would probably occur in ponds, or captive seaside facilities. Please see caption number 1 as a conceptual flue gas from power plants for supply of carbon dioxide to the algae project.
Ethanol – Algae – Biodiesel loop
An interesting concept, in coordination with the production of ethanol, or other enriched CO2 sources, could be via a loop system, whereby CO2 from the enriched source could supply algae the ever-important carbon dioxide ingredient, in conjunction with sunlight, water and nutrients; thus producing algae and the high energy oil from a specific algae for biodiesel. The same algae could be a feedstock for fermentation as well; thus creating a full loop system. Please see diagram number 1 to view this concept.
Summary
The greatest level of CO2 content would be found among select by-product streams in the chemical manufacturing industry; and the larger scale plants are probably those to be targeted in the planned new legislation and EPA directives. The first 25,000 tons per year are exempt from any cap and trade, or other mechanism proposed by the House of Representatives and floating around in the EPA; however, other mechanisms beyond cap and trade may take place with the new CO2 related directives. Therefore, the focus for greenhouse gas reduction as carbon dioxide alone will apply to larger industrial projects, power plants, chemical manufacturing, oil refining, cement plants, etc. If the source is enriched, such as fermentation, then a higher quality stream of CO2 is available up to 99% by volume, with lower levels of impurities. If this stream is flue gas from power plants, the CO2 content would probably not exceed 12 – 15% by volume. In either case, we are working with a raw gas. If the CO2 is liquefied and or purified, then a further investment is required; such as concentrating the weak CO2 content in the flue gas off a power project or other large fossil fuel combustion project. The transportation of this raw gas would most likely take place as a pipeline operation; however, within a reasonable distance from the source to the algae fixation site would make the most sense – but long distance transportation is possible, at a price. The concepts surrounding the application of various forms of raw CO2 feedstock for the algae project are entirely possible. However the more complex the treatment of the raw stream is, and the more distant the algae site is from the source; the economic feasibility becomes more challenging. Since such a large focus on (fossil fuel) based power plants is now underway, and since this is the largest single source type for global CO2 emissions, the payback against the investment for the infrastructure surrounding CO2 treatment and transportation, in the form of revenues from the sale of algae for biodiesel may well outweigh the challenges. This form of sequestering CO2 is unique, since it represents carbon fixation in plant life, and it also is an ingredient essential for the growth of an energy rich product for the biofuels industry.
About the author
Sam A. Rushing is a chemist, and a consultant, as well as president of Advanced Cryogenics, Ltd., with decades long CO2 and cryogenic gas expertise with the merchant sector and as an international cryogenic gas and CO2 consultant, serving the biofuels, energy, and chemical industries. Advanced Cryogenics is celebrating a 20 year anniversary this year. e-mail: rushing@terranova.net , phone 305 852 2597.
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