Author: by R. G. Boothroyd Ph.D., C.Eng.*, author contact email: [annboothroyd]@[bigpond].[com] – remove  for email address.
Oilgae thanks the author/s for their kind contribution to this database.
*The contributor is a retired professional engineer and the Author of Flowing Gas-Solids Suspensions, (Chapman and Hall, 1971) but claims no specialist expertise in the fields of exploiting algae, flash pyrolysis and industrial scrubbers.
ABSTRACT This communication seeks to raise discussion related to finding a low capital cost algae treatment process where one basic design can be applicable to a wide variety of industrial waste effluent situations. The emphasis is on economy of scale derivable from a large market and by seeking design simplicity. It is suggested that this industry has future potential for multibillion dollar economic activity worldwide. This justifies more detailed consideration than is given in the present communication. The approach suggested is to combine open racecourse algae ponds with on-site flash pyrolysis. Waste materials, including CO2, can be recycled to produce pyrolytic oil, combustible gas and char. The latter two components would appear to be sufficient to provide enough useable energy for the entire plant which can also be easily fully automated except for normal routine maintenance work.
The concept may have considerable application in future municipal planning of industrial estates on the periphery of large temperate coastal cities particularly in Australia and the United States. For “stand alone” industries such as cement production and coal-fired power stations, where location is dictated by access to input bulk materials, the concept also appears to be attractive as these plant are sufficiently large. The concept of converting existing power station cooling towers to bio-scrubbers feeding algae production ponds leading to pyrolitic oil production is outlined. It appears that this approach may contribute, in a reasonably inexpensive way, to significantly reducing green-house gas emission by recycling and using waste CO2 instead of sequestering it. It is also expected to contribute significantly to offsetting the effects of the forthcoming shortage of petroleum feedstccks. The concept also seems to be a more logical way of using waste heat discharged from power stations (presently an environmental nuisance) to increase algae production in cooler climates.
1. INTRODUCTION AND BACKGROUND (N.B. in this discussion paper, complicated and detailed questions are shown in italics and important suggestions and proposals are in bold type)
The more conventional approach to producing Biodiesel from algae is in the closely-controlled and enclosed photobioreactor. In such systems great care must be taken to exclude wild algae and bacteria. These are more vigorous and would compete with the specially chosen algae strains selected to optimize oil production.
It is suggested that an exactly opposite design approach may also have some merit. Why not allow the more aggressive algae to compete and overwhelm weaker rivals and simply aim to maximize crude biomass production? This approach would allow the open race-course method of algae production to be used which has much lower capital costs. This method also dictates the need for well-designed low energy input for handling the resulting biomass and its treatment. It is suggested that on-site flash pyrolsis may be the best approach and this would produce a reasonably consistent by-product (oil content approaching 70%of the original biomass). It is suggested that the rotating-cone flash pyrolyser ( PyRos design) may be the most suitable plant. The rotating cone pyrolyser has many advantages. It is simple, inexpensive, robust, works at atmospheric pressure and it can be easily scaled to the size required by using multiple units on the same drive. It uses ordinary sand which is also recyclable .
In the proposed process it is necessary that all nutrient for the algae ponds shall be reduced to liquids, be this dissolved CO2, sewage or any other waste. This keeps pumping and pipeline costs to minimum levels. In industry these gaseous pollutants would normally be reduced to a liquid by passing them through a scrubber. This is a normal part of a modern plant producing gaseous waste..
2 OUTLINE DESIGN OF A TYPICAL SYSTEM
Fig (1) illustrates the suggested general design principles involved in organizing part of a municipal industrial site. The race-course ponds are not necessarily identical in size or shape. The reason for this is that, in an advanced system, they would be emptied and replenished automatically under computer control. The control system would log input data, such as climate conditions, continuously. The ponds follow the natural contours of the land, thus minimizing earthworks. The ends of adjacent pairs of ponds discharge into a channel (B1-B2) which leads to one of several flash pyrolysis units (C). The channel (B1-B2) is at right angles to the contours of the land. De-watering of the algae biomass starts at B2 using a porous belt-conveyor, followed by a variable pitch screw conveyor/elevator (the last de-watering stage) thence to the pyrolysis unit C. A final water content of 10% is reasonable with an acceptable upper limit of 15% for flash pyrolysis. Some systems, in warmer climates, may, perhaps, use a final Solar drying stage, which is why C is shown enlarged and circular. It is envisaged that such a solar dryer would probably use a circular rail system supporting a slowly-rotating beam which distributes the damp biomass at its trailing edge with an auger and recollects it when dried at its leading edge.
The water from the de-watering may be recirculated back to the ponds or it may pass to other ponds downhill. Cross-contamination of algae for ponds receiving waste from different industries is not important in the crude biomass approach. In fact, in the absence of practical experience in optimizing such systems, cross contamination of ponds should be encouraged .Detailed design decisions here are likely to be based on nutrient availability.
The industrial plant D is located on ‘inconvenient’ sloping land. Obviously there is some conflict of interest here. Everyone wants flat land for cheap housing, factories, agriculture etc but, in an overcrowded world some compromise is necessary.
In the design of a municipal industrial site, there is much to be said in favour of incorporating adjacent compact primary industries such as market gardening, aquaculture, intensive livestock rearing and, perhaps, even recreational areas. One long term objective would be to reduce transport costs of these basic consumer commodities which are needed in the city.
3 ‘STAND ALONE’ INDUSTRIES/APPLICATION TO LARGE COAL-FIRED POWER STATIONS
For illustrative purposes, let’s consider, as an example, the largest coal-fired power station in the U.K., the 4GW Drax complex. Drax emits a huge 2x107 tonnes of CO2 annually. Assuming a CO2 conversion efficiency of 90%, which seems easily achievable from current technical data, this equates to a pyrolytic oil production of about 107 tonnes annually. If it was retro-fitted as a CO2 converter, Drax would clearly justify its own adjacent oil refinery. In principle this is a chemical engineer’s dream: we have three freely available resources, CO2, waste low grade heat, and solar energy and these can be converted into pyrolytic oil which is a marketable product. Also two of these inputs, namely CO2 and waste heat are an environmental nuisance!
From web photographs, Drax appears to be located on flat terrain, which is well-suited for algae ponds. Why not retrofit the cooling towers at Drax to become giant bio-scrubbers? Why not redirect the flue gases through the cooling towers which would be fed with recirculated water from the algae ponds? There are a number of details in such a scheme which merit attention. For example, would it be advantageous to seed this cooling water with a suitable (perhaps genetically engineered) thermophilic algae to enhance CO2 uptake? Should this warmed CO2-carrying water then be reseeded with another algae to promote high biomass conversion, together with a nitrogen-fixing algae? One complication with the pyrolyis approach is that nitrogen-containing nutrients are destroyed in the pyrolysis process, necessitating nitrogen fixing in the biomass production. Conversely mineral nutrients can be recycled continuously after the pyrolysis.
It is suggested that, as a first step, we should decommission just one of the cooling towers at Drax in order to use it for experimental conversion to a full-scale bioscrubber., Perhaps the cooling tower in the worst state of repair could be selected for these experiments? This should allow the existing power station to continue to function normally without interruption. The remaining cooling towers should be able to accommodate the extra heat disposal load while this developmen work is being carried out.
It is suggested that this experimental cooling tower/scrubber be fitted with a shutter system at its top. During winter months the efflux from the top of the tower would be restricted to boost the waste heat supplied to the ponds. During summer, more evaporative heat disposal may be allowed by opening the shutters. The intention here is to prolong the growing season of the algae and make it more uniform seasonally. There are other approaches, (which could be applied simultaneously) to seasonal climate change such as altering the spectrum of algae species on a seasonal basis so as to make biomass production suit the desired power station output.
It has to be admitted that there are likely to be problems associated with converting cooling towers in this way. Anti-corrosion and anti-fouling would need to be considered. It is of interest that algicide is normally used in power station cooling towers. It is also of interest that two German power stations use the cooling tower as a chimney to discharge Flue Gas but in these cases, the flue gas is merely cleaned prior to discharge into the tower. One other factor which needs serious consideration is Legionnaires Disease. Presumably sulphur dioxide would need to be removed prior to CO2 conversion. The use of SO2 scrubbers is normal practice in power stations today and these are used at Drax. Biofuels have the great advantage of low sulphur content. Nutrient considerations are important and the possibility of developing adjacent industries such as market gardening, fertilizer production and Aquaculture may merit consideration. Can fly-ash be useful as part of the nutrient?
Two factors may be problematical for retro-fitting Drax as a CO2 converter. Firstly, is the climate too cold in this place? Secondly is there sufficient space for such a large area of algae ponds? Lack of space is likely to be an inhibiting factor in using any form of renewable energy in countries such as U.K. Conversely, bearing in mind the digression in section (7) which suggests that applied research should become a matter of international cooperation, perhaps there is a strong argument for using Drax to obtain experience of local microclimate control; increasing photosynthetic conversion in colder climates and finding a design best suited where land availability is limited. Use of land for both algae production and other purposes such as transport corridors and isolation of hazardous industries has been identified as an important area of future study in its own right. All forms of renewable energy production are cursed by their fundamental need for large areas of land. The use of algae is by far the most promising approach in this respect but its future widespread adoption is likely to depend critically on using the land for multiple purposes, perhaps even for recreation.
4 PYROLYTIC OIL
Unfortunately pyrolitic oil is very different from petroleum feedstock. It is denser (1250kg/m3) and is immiscible with petroleum fuels. As produced, it is an emulsion containing water. This, in itself, is not perceived as a serious problem as far as combustion in a diesel engine is concerned. The recently marketed ‘Aquadiesel’ is also an emulsion (13% water) and it is claimed to be a superior and cleaner fuel compared to straight diesel. Pyrolytic oil has been used in stationary diesel engines but in its raw state is completely unsuitable for transport and the modern high speed diesel engine unless the technology for refining and reforming it becomes available. Relatively little determined research in this area seems to have been carried out. Perhaps this area of research needs a clear incentive for further work such as oil production of 107 tonnes annually from a single coal-fired power station!
It seems reasonable to draw comparison with the vast previous expenditure which has been invested in giving us present day high quality petroleum fuels. As produced, the pyolytic oil has a low viscosity which aids pumping but this viscosity tends to increase with time due to polymerization caused by contamination from carry-over char. There are certainly several problems to be solved in using pyrolytic oil as a substitute for petroleum but these do not appear to be intractable. Much the same can be said also for problems associated with algae production and processing itself. A large enough market should be able to provide the necessary funding for this future research.
5 ADDITIONAL INFORMATION NEEDED
There seems to be a huge amount of very useful basic scientific information about the many different species of algae. However, plant design engineers often need some very specific data which seem sometimes to be difficult to locate. Our future need will for ‘goal-orientated’ research but for this we need to first find and define our goals. Essentially this is the ‘raison d’etre’ of this discussion paper. The following are typical examples of questions which come to mind.
a)Exactly what is the basic mechanism of Photosynthesis in algae? Is there any significant difference compared with other forms of plant life? Do different algae vary in this respect?
b) Presumably some algae in a race-course pond would exude an oily film on the surface of the water? Can this be exploited to reduce evaporation which is so significant in the economics of this process? Are there likely to be any detrimental effects in reducing evaporation in this way? Quantitative data on cross-film mass transfer would be of interest.
c) Related to (b) is the problem of ensuring adequate turbulent mixing for optimizing biomass production. This is because photosynthesis may be limited to the top few millimeters of the pond and photosaturation inhibition may be a problem. Many algae species would be expected to dampen turbulence (a common phenomenon in some multiphase fluids) Turbulent mixing will restricted by the shallow depth in ponds which would be used. Evaporation losses suggest that wind-induced turbulent mixing should be avoided by using shelterbelts. Would the use of suitably- chosen fish be the best way to optimize mixing in the system? It should be easy enough to harvest the fish mechanically and concurrently with the algae when it is harvested.
6 AN OVERVIEW WITH COMPARISONS
One of the most difficult problems facing the senior engineer is when he has to develop a new technology. It is hard to identify the most profitable line of design from a number of alternatives because the concept designer is working with limited practical experience.
“Back-of-envelope guesstimates” suggest that the algal biomass/flash pyrolysis approach presents no fundamental problem which would inhibit its development. Yet we have to ask ourselves the question: “is this the best way to go? What are the competing alternatives and how do they al measure up?” Once such a firm decision can be made, only then can we (indeed, we should!) “go for it”.
We can derive some encouragement from the history of other big industries such as nuclear power fission reactors, automobile manufacture, PCs, and the petroleum industry itself.. It took many years for each of these industries to slowly develop the sophisticated and reliable products we have today. The first of these industries had the advantage of a kick-start from military interests and the other three had the advantage of being able to market an undeveloped product so as to finance further applied research. Biomass liquid fuels from waste CO2 has neither of these advantages. Yet we are probably facing impending catastrophe for humanity and our civilization because of the drying up of petroleum supplies and environmental pollution. Sadly it is simply human nature to just close our eyes to a difficult problem and hope that it will go away. We can’t do this anymore.
It takes just one serious scientific or economic limitation to make a good idea impractical. Yet sometimes one of those little quirks of nature can give us the breakthrough we need. For example, few people realize that it would be impossible to manufacture safe nuclear fission reactors without a little, hardly known, quirk of nature. This ‘quirk’is the tiny fraction of fission products which are delayed neutron emitters which enable us to control nuclear reactors . Again, quoting from the nuclear industry, the writer knows of two very promising nuclear reactor designs which had to be abandoned after much expenditure in research. In one case, it was just a single intractable safety problem which was the source of trouble.
Perhaps not all the necessary components of the algal biomass/flash pyrolysis approach will click into place as is hoped. If not, then perhaps, at least, this discussion paper may help to inspire my younger professional engineering colleagues to seek an answer elsewhere.
7 THE BIG PICTURE
The general consensus of opinion is that we need to apply every alternative available to us if we are to offset the effects of declining petroleum reserves and the consequences of excessive greenhouse gas emission. This discussion paper would be deficient if it failed to mention that it is unreasonable for Society to expect technology to always find a cure for every problem we make for ourselves. We are all aware of the likely consequences of our greed and wastefulness. Yet the biggest factor in our problem hardly ever gets a mention, probably because the topic is so distasteful and is shunned by our politicians. With the exception of mainland China no country has yet faced up to consequences of an irresponsible and untenable increase in human population.
Some people have said that our society is hooked on its addiction to cheap energy. It seems equally true to suggest that we are addicted to ever-increasing and denser human population. Most of our institutions are affected by this addiction. >From the smallest shopkeeper to the largest corporation, ‘more people’ is perceived as ‘more business and more profit’. The reality in a finite world is very different: more people equates to more stress and competition and an ever diminishing share of resources for us all. Even our other institutions, which are non-profit making, such as all levels of government and organized religion itself, can be accused of self-interest in their addiction to overpopulation..
8 GOVERNMENT AND INTERNATIONAL RESPONSIBILITY
Can private enterprise and venture capital develop algae technology? The answer to this question seems to be a very resounding no. It is not reasonable to expect private investment to carry the risk of developing a field where such a high level of innovation is required. This is because any new marketable system would be rendered technically obsolete almost immediately in the light of improvements gained from its own operational experience. It seems, therefore, that initial responsibility for this field of research must rest firmly on the shoulders of the tax-payer and our governments. Moreover, the term tax-payer in this context is the international community of developed wealthy nations. This is an international issue and it needs international cooperation not competition. It is considered that an unnoticeable fraction of our present military expenditure would be enough to get this technology really moving. In particular it would be tragic if the few private entrepreneurs in this field were to be allowed to ‘wither on the vine’ simply because their first attempts were not successful financially-speaking. We will need to use their experience and their knowledge.
No references are included
as all the input data for this paper are readily available on the Internet.
The Author expresses particular appreciation for the large amount of data
available from oilgae.com.
R. G. B. , January 5, 2007
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