How to achieve ethical energy and How to achieve ethical energy and environmental sustainability to satisfy future environmental sustainability to satisfy future

energy demands energy demands ……

The Use Of The Use Of AlgaeAlgae

Adam A MarshAdam A Marsh04043040404304

MSc Sustainable Energy and EnvironmentMSc Sustainable Energy and Environment

Different AlgaeDifferent Algae

ProcessesProcesses

PossibilitiesPossibilities

LimitationsLimitations

Chlorella sp.Chlorella sp.

ChlamydomonasChlamydomonas reinhardtiireinhardtii

Botryococcus brauniiBotryococcus braunii

Chlorella Chlorella sorokinianasorokiniana::Very fast growing Very fast growing --

(doubling time of 2.5 h)(doubling time of 2.5 h)Tolerant to high temperatures Tolerant to high temperatures --

((optimumoptimum 4040ooC) C) Tolerant to highTolerant to high

COCO22

concentrations concentrations --

(5 (5 --

40%CO40%CO22

))Found in hot springsFound in hot springs

High concentration of lipid hydrocarbons (<70%)High concentration of lipid hydrocarbons (<70%)At 50% concentration (dry weight), HHV ~ 34MJ/kgAt 50% concentration (dry weight), HHV ~ 34MJ/kgCan grow in brackish waterCan grow in brackish waterSlow growing Slow growing ––

(doubling time of a few days)(doubling time of a few days)Can form bio filmsCan form bio films

Can produce pure Hydrogen gas when deprived of SCan produce pure Hydrogen gas when deprived of SRapid growing Rapid growing ––

(doubling time of 6.4 h achieved)(doubling time of 6.4 h achieved)Limited growth during HLimited growth during H22

productionproduction

Chlorella vulgaris:Chlorella vulgaris:Fast growingFast growingFound all over the world in lakes and pondsFound all over the world in lakes and pondsHuge amount of literatureHuge amount of literature

COCO22

+ H+ H22

O +O + (CH(CH22

O) + OO) + O22

++light light energyenergy

chemicalchemicalenergyenergy

ChlorophyllChlorophyll

WavelengthWavelength

IntensityIntensity

PhotoperiodPhotoperiod

ConcentrationConcentration

Flow rateFlow rate

Retention timeRetention time

TemperatureTemperature

Nutrients Nutrients

SalinitySalinity

LightLight

Chlorophyll mainly absorbs light at Chlorophyll mainly absorbs light at approximately 450 and 650 nm, perceived as approximately 450 and 650 nm, perceived as blue and red respectively.blue and red respectively.

6.3 W/m2 47.3 W/m2

Different species have individual characteristics. Different species have individual characteristics. However, similar triHowever, similar tri--region growth curve fits all.region growth curve fits all.

1.1.

Light dependant region;Light dependant region;increased light = increased growth rate. increased light = increased growth rate.

2. Light independent region;2. Light independent region;constant growth rate between saturation constant growth rate between saturation (A)(A)

and photo inhibition and photo inhibition (B)(B)

light levels.light levels.

3. Light dependant region;3. Light dependant region;increased light = reduced growth rate.increased light = reduced growth rate.

Botryococcus Braunii

W/m2

WavelengthWavelength

IntensityIntensity(A) (B)

LightLightPhotoperiodPhotoperiod

Botryococcus BrauniiPhotoperiod is the ratio of light and dark, typically measured out of a maximum 24 hour period.

If NADPH and ATP compounds are available, the remaining processes of photosynthesis can take place without the necessity of light.

It can be seen above that algae does not utilise much more than 12 hours of light in a 24 hour period.

The maximum growth rate of a Chlorella sp. can be maintained in 9s of darkness if each cell has been exposed to 20 W.m-2

for 0.5s.

1 hour ~ 3.2 minutes

12h

30W/m2

LightLight

TemperatureTemperature

Temperature affects the rate of photosynthesis by Temperature affects the rate of photosynthesis by changing the rates of enzyme reactions involved in changing the rates of enzyme reactions involved in systems of the photosynthetic complex.systems of the photosynthetic complex.

The maximum growth rate will occur at the optimum The maximum growth rate will occur at the optimum temperature, with declining rates either side of the temperature, with declining rates either side of the optimum.optimum.

The optimum temperature will vary for individual The optimum temperature will vary for individual species.species.

Typical values for algae range from 20 Typical values for algae range from 20 --

3535ooCC

Botryococcus Braunii

Botryococcus Braunii

When utilising species for a byWhen utilising species for a by--product, the product, the optimum temperature for growth may not be the optimum temperature for growth may not be the same as that for optimum production. same as that for optimum production.

COCO22 SupplySupplyConcentrationConcentrationCurrent atmospheric CO2 concentrations of dry air Current atmospheric CO2 concentrations of dry air are in the order of 0.038%are in the order of 0.038%

Typical CO2 concentrations emitted from a 1500MWe Typical CO2 concentrations emitted from a 1500MWe coal power station will be in the order of 13%coal power station will be in the order of 13%

Optimum growth rate of Optimum growth rate of Chlorella vulgarisChlorella vulgaris occurs at occurs at 2% CO2% CO22

concentrationconcentration

Highest COHighest CO22

reduction efficiency also occurs at 2% reduction efficiency also occurs at 2% COCO22

concentration at 58%concentration at 58%

Highest COHighest CO22

reduction occurs at optimum growth reduction occurs at optimum growth rate.rate.

Chlorella Chlorella SorokinianaSorokiniana will grow well at concentrations will grow well at concentrations of 13% COof 13% CO22

..

Adding further volumes of bioreactors increases the Adding further volumes of bioreactors increases the volume sequestration linearly with similar volume sequestration linearly with similar

efficiencies. efficiencies.

Chlorella Chlorella SorokinianaSorokiniana

COCO22 SupplySupplyFlow Rate and Flow Rate and Retention TimeRetention TimeIn small reactors, the capacity of COIn small reactors, the capacity of CO22

fixation fixation (and O(and O22

evolution) decreases with an evolution) decreases with an increasing gas flow rate as the retention time increasing gas flow rate as the retention time is dramatically reduced.is dramatically reduced.

Increasing the retention time enables more Increasing the retention time enables more sufficient contact between algae and COsufficient contact between algae and CO22

resulting in better absorption.resulting in better absorption.

However, larger reactors will increase the However, larger reactors will increase the retention time by increasing the distance for retention time by increasing the distance for which the gas must pass through the culture, which the gas must pass through the culture, allowing higher gas flow rates to be used.allowing higher gas flow rates to be used.

A faster gas flow rate will increase turbulence. A faster gas flow rate will increase turbulence. Turbulence will improve the mass transfer Turbulence will improve the mass transfer coefficient and will induce mixing of the cells, coefficient and will induce mixing of the cells, allowing each cell time in the light intense allowing each cell time in the light intense areas of the reactor.areas of the reactor.Lihai

Fan et al., 2007. Optimization of Carbon Dioxide Fixation by Chlorella vulgaris Cultivated in a Membrane Photobioreactor, Chem. Eng. Technol.; Volume 30, Issue 8, pg. 1094-1099

Chlorella sp.

Chlorella vulgaris

COCO22 ReductionReduction

This paper claimed the optimum gas flow rate This paper claimed the optimum gas flow rate was 1.25 L/min.was 1.25 L/min.

Membranes were used to enhance the gasMembranes were used to enhance the gas--

liquid mass transfer rate.liquid mass transfer rate.

At the rather low luminous intensity of 8W/mAt the rather low luminous intensity of 8W/m22, , and COand CO22

concentration of 1%, the COconcentration of 1%, the CO22

fixation fixation rate was approximately rate was approximately 0.14g/L.h0.14g/L.h

Original cell density was 5x10Original cell density was 5x1077

cells/mlcells/ml

Lihai

Fan et al., 2007. Optimization of Carbon Dioxide Fixation by Chlorella vulgaris Cultivated in a Membrane Photobioreactor, Chem. Eng. Technol.; Volume 30, Issue 8, pg. 1094-1099

Chlorella Vulgaris

T = 25oC; Density; 5x107 cells/mL; Irradiance ~ 8 W/m2; CO2 concentration; 1%

~8W/m2

1500MWe4300MWthη=35%

Coal HHV Coal HHV ≈≈

30MJ/kg30MJ/kg

Coal Coal ≈≈

143.3kg/s143.3kg/s

C C ≈≈

80%80%O O ≈≈

13%13%H H ≈≈

6%6%S S ≈≈

1%1%

CC

≈≈

114.6 kg/s114.6 kg/s

C + OC + O22

= CO= CO22

(12) + 2(16) = (44)(12) + 2(16) = (44)

1 : 2.67 : 3.671 : 2.67 : 3.67

COCO22

≈≈

420 kg/s420 kg/s

nnCO2 CO2 ≈≈

9.6 9.6 kmol/skmol/s

VVCO2 CO2 ≈≈

235 m235 m33/s/s( @ 25( @ 25ooC )C )

VVTT

≈≈

1815 m1815 m33/s/s

COCO22

≈≈

13%13%SOSO22

≈≈

0.005%0.005%OO22

≈≈

3.8%3.8%NN22

≈≈

82.9%82.9%

1500MWe Power Station1500MWe Power Station

COCO22 ReductionReduction

Using Using Chlorella Chlorella sorokinianasorokiniana;;Φ

130mm120mm1m

0.14 0.14 g/L.hrg/L.hr

::= 2.3 g/m= 2.3 g/m33.s.s

1.25 L/min1.25 L/min

@@

13% CO13% CO22

::= 2.7x10= 2.7x10--66

mm33/s CO/s CO22= 4.8x10= 4.8x10--33

g/sg/s

COCO22

Assuming constant reduction Assuming constant reduction rate, reactor volume required :rate, reactor volume required :

4.8x104.8x10--33

/ 2.3 = 1.77x10/ 2.3 = 1.77x10--33

mm33

Reactor length required :Reactor length required :

1.77x101.77x10--33

/ 0.0133 = 0.133 m/ 0.0133 = 0.133 m

0.14g CO0.14g CO22

/L.hr/L.hr 0% CO0% CO22

Length ?Length ?

CSA = 0.0133 m2

Power plant actually produces Power plant actually produces 1815 m1815 m33/s @ 13% CO/s @ 13% CO22

= 87.3x10= 87.3x1066

times more massivetimes more massive

87.3x1087.3x1066

x 0.133 = 11.61x10x 0.133 = 11.61x1066

m m

11,610 km of pipeline are needed.11,610 km of pipeline are needed.

4 pipes in each metre width4 pipes in each metre width

2.9x102.9x1066mm22

horizontal areahorizontal area

1.7km1.7km22

≈≈

2 km2 km22

1.25 L/min1.25 L/min13% CO13% CO22

Original cell density = 5x10Original cell density = 5x1077

cells/mlcells/ml

= 0.7kg/m= 0.7kg/m33

Original Total Mass = 0.7 x 154.5x10Original Total Mass = 0.7 x 154.5x1033

= 108x10= 108x1033

kgkg

Doubling time of 2.5 hours = 9.6 doublings a dayDoubling time of 2.5 hours = 9.6 doublings a day

Mass grown = 9.6 x 108x10Mass grown = 9.6 x 108x1033

= 1.04x10= 1.04x1066

kg/daykg/day

(dry weight)(dry weight)

= 12 kg/s= 12 kg/s

Cell GrowthCell Growth

Chlorella Chlorella SorokinianaSorokiniana

has a HHV of 15.6MJ/kghas a HHV of 15.6MJ/kgThis is too low for combustion.This is too low for combustion.

However, would provide 187MWthHowever, would provide 187MWthThis is about 4% of power stationThis is about 4% of power station

Anaerobic DigestionAnaerobic DigestionAnaerobic digestion is a process carried out by micro organisms Anaerobic digestion is a process carried out by micro organisms that can degrade that can degrade carbon based matter without the presence of oxygen.carbon based matter without the presence of oxygen.

The main products are Carbon Dioxide and Methane. (60% CHThe main products are Carbon Dioxide and Methane. (60% CH4 4 and 40% COand 40% CO22

))

Biomass is a suitable source for anaerobic digestion.Biomass is a suitable source for anaerobic digestion.

1.7 kg VS/m1.7 kg VS/m33.day.day

FeedstockFeedstockReactor

35oC20-30days 0.68 kg /m0.68 kg /m33.day.day

60% reduction in organic matter60% reduction in organic matter

COCO2 2 CHCH44

Methane has a HHV of 55.5 MJ/kgMethane has a HHV of 55.5 MJ/kg

Therefore :Therefore :

266.4 266.4 MWthMWth

could be produced.could be produced.(~6% of power plant)(~6% of power plant)

Bioreactor can take 1.7 kg/mBioreactor can take 1.7 kg/m33.day.dayTherefore : Therefore :

245x10245x1033

mm33

reactors would be neededreactors would be needed= 311, 10m high, 10m diameter reactors= 311, 10m high, 10m diameter reactors

3.2 m3.2 m33/s CO/s CO22

(~1.3% of plant)(~1.3% of plant)

Anaerobic DigestionAnaerobic Digestion

Kelp can produce biogas at a rate of :Kelp can produce biogas at a rate of :0.4 m0.4 m33/kg VS/kg VS

We are producing :We are producing :1.04x101.04x1066

kg/daykg/day12 kg/s 12 kg/s (dry weight)(dry weight)

This equates to :This equates to :

416x10416x1033

mm33/day/day4.8 m4.8 m33/s/s

ConclusionsConclusionsAlgae can serve to be a natural way for removing COAlgae can serve to be a natural way for removing CO22

emissions.emissions.

98% is a realistic reduction value.98% is a realistic reduction value.

Huge crops of algae will be produced daily.Huge crops of algae will be produced daily.

Using as a fuel for the power plant is not a realistic possibiliUsing as a fuel for the power plant is not a realistic possibility.ty.

Using as a transport fuel will simply reUsing as a transport fuel will simply re--release the COrelease the CO22

..

Alternative uses must be found.Alternative uses must be found.

Research is being carried out in this area.Research is being carried out in this area.

--

BioBio--fuelsfuels--

BioBio--PlasticsPlastics--

Foods Foods --

FertiliserFertiliser

QUESTIONSQUESTIONS??

1500MWe, η=35%

1500 / 0.35 = 4286

≈

4300MWth

Coal HHV ≈

30MJ/kg

4300 / 30 = 143.3

Coal ≈

143.3kg/s

C ≈

80%O ≈

13%H ≈

6%S ≈

1%

143.3 x 0.8 = 114.6

C ≈

114.6 kg/s

C + O2

= CO2

(12) + 2(16) = (44)

1 : 2.67 : 3.67

114.6 x 3.67 = 420.6

CO2

≈

420 kg/s

420 / 44 = 9.55 kmol/s

CO2

≈

9.6 kmol/s

9.6x103

x 24.5x10-3

= 236

VCO2

≈

236 m3/s( @ 25oC )

VT

= 236 / 0.13 = 1815.4

VT

≈

1815 m3/sCO2

≈

13%SO2

≈

0.005%O2

≈

3.8%N2

≈

82.9%

dCkII

o

ln

Where;Where;I = Light intensity at depth of penetration dI = Light intensity at depth of penetration dIo = Incident light intensityIo = Incident light intensityC = Algae concentration (kg.mC = Algae concentration (kg.m--3 or g.l3 or g.l--1)1)d = Depth (m)d = Depth (m)k = Light extinction coefficient (m2.kgk = Light extinction coefficient (m2.kg--1) 1)

PhotoPhoto--limitationlimitation

To make enough fuel To make enough fuel from algae to run from algae to run entire plant :entire plant :

Starting density of Starting density of 11.6kg/m11.6kg/m33

is neededis needed