BioDieselNow - Renewable biodiesel fuel

While racetracks in the desert would minimize the cost per acre of growing algae, the problem of contamination means 'weak' species of algae genetically modified for fuel yield would succumb to more aggressive species. Sealing the racetracks or growing the algae in photobioreactors can minimize contamination issues, but its my understanding that you'd run into massive heat issues. The biosphere 2 was built out in the Arizona desert, and has a huge electric bill from air conditioning. Without the air conditioning, the plants inside would quickly die. 

I guess some form of thermal storage could store the heat in the daytime, and then use that heat to warm the algae during the cold nights. Or if we managed to properly insulate the reactors, perhaps we could use photosynthesizing thermophillic bacteria instead. Too bad thermophilic bacteria contain so little phospholipids.

hi young scientist..

 heres some suggestions... there is a reflective mesh that reflecxts 10% of the heat that can be put over the system that you use to grow the algae, ,

 the proper placement of circulating fans will also bring down the heat load.

dig the ponds deep so as to take advantage of geotherman heating-cooling

 the use of eutectic salts for heat storage would work to store the heat load through phase change.

 heat exchangers to  take up the solar insolation with water or ethylene glycol coolant running through radiators, in a geo thermal cell will cool both the air and the water.

a lot of the water that is heated may also be used to pre heat mash to a low delta t so that itc an be cooked and then fermented and in addition, the heated water could preheat  distillation columns or produce the optimal temps for a methane digestor. the idea is to devise ways to utilize the heat in such a way as to turn it from a problem into usefull energy.

 

marc

Temp control at an affordable cost is one of the limiting factors in growing algae - no doubt about that.

I am working on an idea of using geothermal control to maintain water temp at around 24 degrees.

For a rough overview of how it works check this site :-

http://geothermal.marin.org/GEOpresentation/sld101.htm

 

The world's largest algae farm is in the desert and does not use any of this expensive equipment.

Their secret - they shut down in the winter.

 

An open system in the desert will have a huge waterloss in evaporation, so a fresh water source is needed, even when growing marine algae. On the other hand, a closed reactor in The Netherlands, not a country know for its warm climate, needs to be cooled 9 months per year, so a temperature of a reactor in the desert must be a major bottleneck

liberty1:

 

The world's largest algae farm is in the desert and does not use any of this expensive equipment.

Their secret - they shut down in the winter.

 

Yeah, but Bobby,

If we can maintain an even temperature we score increased production by staying in operation 24/7/365.

 

Slippery,

The increased production may not be worth the cost.

 

Many algae grow preferrently faster at higher temperatures, some in the range of 40 degrees C (104 degrees F) and possibly as high as 45 degrees C (113 degrees C).  This being said, exactly how hot are some of these reactors reporting they get?  Not sealing the culture effectively allows your culture to lose heat due to evaporation, basically "sweating" in the same way people do, correct?  What maximum temperatures are we looking at in a closed and in an open design?

davtuner:

Many algae grow preferrently faster at higher temperatures, some in the range of 40 degrees C (104 degrees F) and possibly as high as 45 degrees C (113 degrees C). 

  The higher the temp swing, the less optimal time of growth temp. There turns out to be a whole lotta loss due to respiration at sub-optimal temps. Night time is brutal enough on a PBR, temps swinging at night are a 2x whammy.

I dont have an cites off hand but I know you can find many stating that the interface between cold water and morning sunlight is a real production killer.

Ground-coupled heat exchangers could be used to limit temperature swings for the PBR both for the day/night cycle, and for the winter/summer seasons. During the day the earth would help cool the algae by absorbing the heat, and in the night using the heat stored to keep the PBR warm. Over the summer the ground would slowly increase in temperature, providing additional heating for the winter months. Insulating the PBRs is going to add significant cost, but I don't see any other way to avoid major temperature control costs.  

I have been doing some more thinking on the Geothermal idea and think it may be feasable to plumb directly into an underground pipe work system and simply pump the growing medium directly through the pipes. This will give the algae a certain amount of dark time(really dark time) as well.

youngscientist:

  Ground-coupled heat exchangers could be used to limit temperature swings   

  Sure can. We can engineer anything. But quite quickly you will find out that trying to control the temp of your system will be a thermodynamic loser. This means that you will spend more energy pumping than what comes out of your system.

Geothermal is ~ 350% efficient. But making KWH's is only ~ 33% efficient to run the pumps. Thus... lets say for sake of example that 100% of harvested biomass can be turned into 100% efficient changes in delta.  

This is not an easy calculation because it is based on many assumptions but remember that it takes ~ 4200joules to change 1kg of water 1C. Or ~ 4BTU's. Lets say you have 1 cuft of water (12x12x12") = ~ 28kg.  Thus 112BTU/sqft of water for Delta 1C.

There is ~ only 430BTU/sqft/hr called the solar constant. Algae can only use PAR = ~ 27% of total solar constant = 116BTU of usable energy coming into the system /sqft/hr. Lets say the you have super duper efficient algae that =10% solar yield efficient = 11.6/BTU/hr x 12 hr = 140BTU/sqft/day of harvested energy in the form of biomass within that 1sqft of water.

So if you need to raise or lower that 1 sq ft of water even 1 Delta 1C, you will only have 28BTU/sqft/day left to pay for the drying/crushing/filtering/pressing/pumping/etc.

This simple exercise shows that is a thermodynamic folly to try and control the temp of your system by active heating/cooling. Passive (using the sun) is different.

This is a wonderful post, however I don't understand why being a thermodynamic loser would be so bad. The goal of algae cultivation is finding a cost effective way of convert solar energy into a form with a high energy density, and is easy to both store and transport. How much energy I need to make a barrel of biodiesel should be irrelevant, so long as the process is cost effective. 

My primary interest in active temperature control would be to minimize the temperature fluctuations of the night/day cycle and the summer/winter cycle. For a PBR insulated glazing could be used to passively control the temperature, with the glaze reflecting excess infrared during the day and a double pane design minimizing heat loss at night. 

If a way to cost effectively grow biofuels on arid land cannot be found, we will still grow biofuels. But in solving the oil crisis we will create an ecological crisis and a food crisis, as forests are destroyed and farmland converted in order to grow biofuels. An alternative must be found.

 

 

 

youngscientist:

I don't understand why being a thermodynamic loser would be so bad.

Because when making energy, thermodynamics are the king.

When making a head of lettuce, themrodynamics are damned.

Young,

You are right.  Cost is what matters.  If you invent a process that wastes 99% of the sunlight falling on it, but it produces vegetable oil for $1.00 per gallon, you have a winner.

Thenmodynamic efficiency is important because it can help you lower cost, but the real criterion is cost.

Slippery:

I am working on an idea of using geothermal control to maintain water temp at around 24 degrees. 

  Because the PBR prevents the free evaporation of water, there is no doubt that some sort of cooling unit will need to be implemented. Someone much smarter than me can figure out how much actual BTU's need to be let loose/lb of water within the PBR... regardless of what this number is, it almost exclusively means using KWH's to do the work.

There are 2 easy answers... Geothermal and Compressor. Compressor is out of the question because of thermodynamics. Again, someone much smarter than myself will have to prove this but I am fairly confident with the theory that a aircond unit couldnt do the job. We are then left with Geo heat pump. Again, someone much smarter than me needs to do the math... anyone willing?

But if you have to use Coal to make KWH's to make algae... IMO, your missing the point. And if people are willing to make that sacrifice, then coal2liquid is for you... going thru algae would be a huge in-efficiency of the yield.

 If you can use a series of black poly pipes on the roof of the house/shed/factory to produce hot water - thermosyphone    - would you be able to do the same using a geothermal system?

Not sure what temperature differneces you would need to make the water flow however, if it worked you would not be using E to heat or cool the PBR.

Hello all. I came across this site today and I like what I see. There is very interesting dialogue  here. If I can ask this maybe someone can answer: what about utilizing current power plants (nuclear or fossill) in as far as their cooling tower or whatnot in the process of stabilizing temps. for algae growth?

Slippery:

But if you have to use Coal to make KWH's to make algae... IMO, your missing the point. And if people are willing to make that sacrifice, then coal2liquid is for you... going thru algae would be a huge in-efficiency of the yield.

I agree entirely. While I am not worried about the energy effiency of biodiesel production, I am greatly concerned about exposure to higher future energy costs. If passive systems provide insufficient environmental control and an active system is needed, the power for it should idealy be generated on site. One scenario I have is using a small number of Heliostats to heat a sterling engine, which would be directly linked to the pumps of the geothermal system.

masjimmn:

Hello all. I came across this site today and I like what I see. There is very interesting dialogue  here. If I can ask this maybe someone can answer: what about utilizing current power plants (nuclear or fossill) in as far as their cooling tower or whatnot in the process of stabilizing temps. for algae growth?

Cooling Towers provide cooling by evaporating large volumes of water, while you could use a salt-water powered cooling tower to cool a fresh water algae culture you'd quickly run into corrosion issues and the formation of brine. 

In some sense, what I'm interested in doing is using algae to create a large scale mechanical cacti. Most land based plants actively control their temperature by opening and closing their stomata to control the rate of evaporation. A plant could keep its stomata closed all the time to conserve water, but it wouldn't be able to expel oxygen or intake more carbon dioxide. Cacti keep their stomata closed during the daytime in order to store water, and then open the stomata at night. In order to hold all of the CO2 needed for the next day of photosynthesis, cacti actually store the CO2 in their roots during the night.