Algae Concept

8/8/2019 Algae Concept

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MICROALGAE CULTIVATION FOR BIODIESEL PRODUCTION USINGEXHAUST GASES FROM VEHICLES

Concept

The concept basically involves installing a collection cylinder within the vehicle (say bus) andstoring all the exhaust gases in it using a compressor pump. This cylinder is emptied wheneverthe vehicle is getting refueled and starts its next cycle. At the fuel station the exhaust gases aretransferred to a gas-transporting truck after temporary storage or a pipeline which eventuallytakes the exhaust gases to a centralized CCS (Carbon dioxide Capture and Storage). The CCScan either store the CO2 in geological formations or it can be microalgae based biodiesel plantwhich can directly function using the exhaust gas composition including CO, NOx and SO2.

The costs for installing the set up are incurred by 1. Compressor, 2. Collection tank, 3. Safetyvalve & controls and for transporting to the CCS. The electrical energy required for thecompressor to run can be obtained from the lead acid accumulators in the vehicle itself. Whenimplementing this on smaller vehicles like cars, storage space will be an issue. This issue (ifarises) can be overcome by modifying the fuel tank itself wherein the space created as the fuel is

getting used up is used for the pressurized storage of the exhaust gas without affecting anyintermediate fuel fillings. The expansion of the gases can be done with turbo expanders toregenerate some percentage of energy lost during compression.

Micro-algae for CCS

Micro-algae cultivation for the production of biodiesel is envisioned as the suitable technology tofix the CO2 at the Carbon capture and storage (CCS) site. The various considerations for thisdesign are as follows

1. One major advantage of algae cultivation over fuel crops and agriculture in general, is theability of many algae to tolerate saline water. Fresh water is scarce in many parts of theworld, and agriculture uses 70% of the total global fresh water consumption. This

characteristic of algae allows the installation of the plant at sea so that it can draw itsrequired water requirements easily.

2. Algae can grow directly on combustion gas (typically containing 4-15 percent CO 2),whereas plants take up CO2 from the atmosphere (open air concentration 0.036 percent).This makes a way to utilize the collected exhaust gas effectively.

3. Micro algae have the ability to fix CO2 using solar energy with an efficiency 10 times

greater than that of terrestrial plants, with numerous additional technological advantages.

4. The amount and kind of nutrients needed for algal growth depends very heavily on the

species, but as an indication for the most important nutrients, about 5 percent (typically is7-8 percent) of algal dry matter consists of nitrogen (N) and 1 percent of phosphorus(P).The most convenient form to supply nutrients is through chemical fertilizer, but fromsustainability point of view this is undesirable since nitrate production has a very highenergy input and phosphorus is mined, thus a fossil resource that will be depleted. Aunique solution is to use nutrient source as nitrogen oxides (NOx) and to a lesser extentsulphur dioxide (SO2, has a large pH effect) from combustion gas. The gasses dissolveinto the water phase (together with CO2), where they are used for algae as a nutrientsource.


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5. Previous studies have shown that there are strains of green algae capable of growingrapidly under high CO2 concentrations (50%) and also in the presence of SOx and NOxwhich are common contaminants in exhaust gas from fossil fuel combustion. Exposure tohigh CO2 concentrations have shown to increase the production of high valuebiomolecules.

6. Chlorella sp. UK001, a type of micro-algae, has a mean rate of CO 2 fixation 0.0318 gCO2/l/day. The efficiency of conversion of energy to biomass is estimated as 4.3%. Thisspecies of micro-algae can grow in an atmosphere containing 340% CO2 with pHbetween 5.5 and 6.0 and temperature of around 30 C. It was found that Chlorella sp. T-1is highly resistance to temperature and high concentrations of CO2. The strain was testedat 35 C and 15% CO2, making this particular strain ideal for biological fixation of CO 2exhausted from coal fired plants. The cultivation of this strain was satisfactory even whenactual flue gas was used. This demonstrated the strains resistance not only to CO 2, SOXand NOX , but also to chlorine, fluorine and dust.

7. Calculations of economics for commercial production of algal biomass showed that thecost of CO2 purchased from the market constitutes 40% of the raw material expenses of

the production.

The following processing steps has to be implemented on the collected combustion gas is toremove particulates, CO and unburnt hydrocarbons. These can be done as follows:

The particulates have to be removed using electrostatic precipitators and filters.

The NOX, CO and unburnt hydrocarbons are treated using a single continuous catalytic converter

at the CCS site. Its tasks are as follows:

1. Reduction of nitrogen oxides to nitrogen and oxygen: 2NOx xO2 + N2

2. Oxidation of carbon monoxide to carbon dioxide: 2CO + O2 2CO2

3. Oxidation of unburnt hydrocarbons (HC) to carbon dioxide and water: CxH2x+2 +

[(3x+1)/2]O2 xCO2 + (x+1)H2O

Requirement to produce 1ton Dry algae mass

Maximum valuesCarbon requirements (mass) 786 kg / Day-1

CO2 requirements (mass) 2881 kg / Day-1

Maximum valuesCO2 requirements (volume - PTN)1467 m3 / Day-1

(0.8% dw) Nitrogen requirements 81 kg / Day-1(0.6% dw) Phosphorus requirements 11 kg / Day-1

The phosphorus requirement for the algal growth can be supplemented using processed poultry

litter


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Model for biodiesel production and conversion integration


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Similar concept:

How it differs: The GREENBOX is replaced by a simple collection tank and the processing of

the exhaust emissions to remove particulates is done solely at CCS.

Benefits:

Bring about zero emission status in existing vehicles without heavy investment. This

makes it comparable with electric vehicle technology wherein the emissions are made at

a centralized location (Power plants), battery waste etc.

No need to install costly catalytic converters in each cars/buses.

Long term biodiesel production costs can be brought down using the exhaust gases

which are free.

Improve the air quality in urban areas and hence the health of the people.


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This can be a simple and a firm stepping stone towards implementing large scale micro

algae cultivation for the future.

Cultivation setup:

Open raceway ponds are considered for the microalgae cultivation. The following are theconsiderations for this set up.

The biggest advantage of these open ponds is their simplicity, resulting in low productioncosts and low operating costs.

While this is indeed the simplest of all the growing techniques, it has some drawbacksowing to the fact that the environment in and around the pond is not completely undercontrol.

Bad weather can stunt algae growth. Contamination from strains of bacteria or otheroutside organisms often results in undesirable species taking over the desired algaegrowing in the pond.

The water in which the algae grow also has to be kept at a certain temperature, whichcan be difficult to maintain. Another drawback is the uneven light intensity and distributionwithin the pond.

The NRELs Aquatic Species Program (ASP) used open ponds for its experiments andhas also favoured the same for the future primarily owing to its economic value.
http://www.oilgae.com/ref/glos/aquatic_species_program.htmlhttp://www.oilgae.com/ref/glos/aquatic_species_program.html


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Race way ponds for Microalgae cultivation

Potential risks and solutions:

Open ponds have higher risk of contamination, evaporation of water and loss of thescrubbed carbon dioxide - This can be overcomed by layering oil over the water surfaceof the pond. The dissolved oxygen requirements can be met by the oxygen derived fromNOx dissociation in the catalytic converter further the exhaust gases themselves have alow load of pathogenic microbes.

Micro algae production has waste streams, Green House Gas (GHG) emission of thesestreams need to be prevented. At night algae consume oxygen which may causeanaerobic conditions that can lead to the emission of N2O and CH4 gas. Also, whencultivation conditions become toxic, mass algae death can occur, which in turn can resultin GHG emissions. Hence a proper collection of these toxic gases and their efficientreuse has to be adopted.

Carbon Dioxide Stripping from Diesel Exhaust Gases

The carbon dioxide from the exhaust gases would be scrubbed with pond water to absorb as

much of the carbon dioxide as would be economically feasible. A simple bubble column in feeding

vessel, a pit with downward media flow and upward carbon-dioxide containing gas flow, would be


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appropriate for this scrubbing operation. Note that the system is sized for 12 hours per day

operation, a seasonal average for the duration of the photosynthesis period.

Basis: 40 kg carbon required per day for the 1 acre growth pond (algae assumed to be 50 wt%

carbon), diesel exhaust is 20 mole % carbon dioxide

Basis: comparable to 1 acre pond, ~ 4000 m2

Carbon Dioxide Concentration required 0.35 kg CO2/m3 exhaust:

Gas Flow Rate: 0.0096 m3/s

Height of Column Required: 3 m

Minimum Cross-sectional Area of Column Required: 0.32 m2

Bubble rise velocity of 0.3 m/s

Note: The terminal velocity of the gas bubbles is 0.3 meters per second, which means that this

liquid velocity would create gas holdup problems. We therefore need to reduce the liquid

velocity in the column, perhaps by a factor of ten, to 0.042 meters per second, by

increasing the column area by a factor of ten, to 3.2 m2 (2 meters or 6.6 feet in diameter).

This is for a 1-acre pond.

Liquid Pumping Power: 1,330 W (for12 hours)

Gas Pumping (Compression) Power (PG ): 380 W (for12 hours)

Pit Volume: 3,300 gal

Water Residence Time (): 2d

Energy requirements:

It is estimated that the total electrical load for the farm would be 100 kW, 5 kW for the front-end

equipment, 20 kW for the back end equipment, 30 kW for the ponds, and the remainder for the

various electrical loads on the farm.

Drying the algae requires about 2400 kW of energy which can be got using some portion of theproduced biodiesel itself.

170 kWh would be required to dry the daily production of 1 acre, which computes to 710 kW for a

24-hour drying period. The excess available thermal power would be more than 1700 kW.

This would be used to control the temperature of the pond.


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Economics:

Indicative cost/Revenue structure for a standalone micro-algae system.

Specifications:

Algae Approx 30 g/day/sq. mPrice t/CO2 Rs. 1278 ($27)Oil market price Rs. 3151 per barrel ($67)Algae Oil produced 35000 L/ha/pa

Cost item (hectare/annum) High cost (ha/pa) Low cost (ha/pa)Land (5% pa) Rs. 315000 ($6714) 0Pond investment (capitalcharge from 15% to 25% over20 years)

Rs. 1654000 ($35255) Rs. 1063000 ($22658)

Operation and Maintenance Rs. 630000 ($13428) Rs. 315000 ($6714)CO2 compression and

transport

Rs. 252000 ($5371) 0

Risk premium Rs. 284000 ($6054) 0Net cost Rs. 31,35,000 ($66822) Rs. 13,78,000 ($29372)

Specification Revenue for 1hectare/annum

Oil revenue Rs. 693000 ($14771)Carbon credit Rs. 118000 ($2515)Net revenue Rs. 8,11,000 ($17286)

From the net revenue and the net costs it can be inferred that the pay back period is about4years.

Assuming the investment for CO2 (Rs. 2,52,000/ha/annum) is now complemented with theproposed strategy; the economics of the system can be established. Considering 1 hectareproduce is devoted for a single metro bus using (90 L diesel per day).

Cost for the bus operation per annum: Rs. 35 X 90L X 365 days = Rs. 11,49,750 ($24507)using conventional diesel

Approximate costs:

Cost of onboard compressor: Rs. 5000Cost for catalytic converter at CCS: Rs. 5000Cost of the compressed gas storage tank: Rs. 100000

CO2 Transport from fuel station to CCS (R): Rs. 200 X 365 = Rs. 73,000Total cost: Rs. 1,83,000 ($3901)

(R) Recurring every year;

R cost incurred for CO2 requirements by the CCS = Rs. 73,000 ($1556)

Now, the net savings in meeting the CO2 requirements for the CCS = 252000 73000 = Rs.1,79,000 ($3815)


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Further to get the biodiesel revenue of Rs. 693000, it can be sold to the transport corporation atthe cost of Rs. 22 X 90L X 365 days = Rs. 722,700 ($15404) per annum

The savings for the transport corporation per litre of diesel is Rs.35-Rs.22 = Rs.7 ($0.15)

Net savings (per bus) in using the microalgalBiodiesel: 7 X 90 L X 365 days = Rs. 2,29,950 ($4901) per annum

Thus both CCS and the Transport corporations are benefited from this concept.

Though this profit is small in terms of business, the basis for the idea is to free the peoplefrom pollution which is more worth than this amount.

Reference:

www.llbc.leg.bc.ca/public/pubdocs/bcdocs/454478/microalgae_report.pdfwww.adb.org/documents/papers/.../adb-wp09-transport-co2-emissions.pdf

sequestration.mit.edu/pdf/2009_CO2_Capture_and_Storage_Ch13_book.pdf

www.climatebabes.com/documents/Algae_biodieselTSDec06.pdf
http://www.llbc.leg.bc.ca/public/pubdocs/bcdocs/454478/microalgae_report.pdfhttp://www.adb.org/documents/papers/.../adb-wp09-transport-co2-emissions.pdfhttp://sequestration.mit.edu/pdf/2009_CO2_Capture_and_Storage_Ch13_book.pdfhttp://www.climatebabes.com/documents/Algae_biodieselTSDec06.pdfhttp://www.llbc.leg.bc.ca/public/pubdocs/bcdocs/454478/microalgae_report.pdfhttp://www.adb.org/documents/papers/.../adb-wp09-transport-co2-emissions.pdfhttp://sequestration.mit.edu/pdf/2009_CO2_Capture_and_Storage_Ch13_book.pdfhttp://www.climatebabes.com/documents/Algae_biodieselTSDec06.pdf

Algae Concept

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