Designed System for the Reduction of CO2 Emission Case ICoal Fired Power Plants

A designed system for the reduction of CO2 emission from coal-fired power plants is presented (28). Microalgal cultivation using CO2 in gas emitted from power plants has been described. In this system, CO2-fixed product by mi-

Table 3. Desired Properties of Microalgae for CO2 Fixation

1. High pCO2 tolerance

2. Low pH tolerance

3. Stable and high growth rate in the linear growth phase

4. Capacity to grow at high cell densities

5. Acidic gas (NOx, SOx) tolerance

6. Thermotolerance croalgal culture is used as biomass fuel, which will substitute for fossil fuel (Fig. 3). CO2 recycling in coal-fired power plants will achieve the reduction of CO2 emission from power plants.

Cost of microalgae CO2 mitigation using the designed system has been estimated based on several designed specifications:

1. Plant size: emission gas from a 500 MW power plant

2. Gas condition: 30.85 kg C/S (CO2) concentration in dry flue gas: 14.2% (vol)

3. Biofixation conditions a. One hundred percent of the CO2 produced by the power plant is fed to biological systems, and 90% of the CO2 fed to the system is utilized during daylight summer hours.

b. Direct biofixation of CO2 is applied where CO2 in emission gas from the power plant is directly fed to algal ponds for photosynthesis.

c. Both 10% (case 1) and 20% (case 2) of photosyn-thetic efficiency based on visible light are studied as are 4.5% (case 1) and 9.0% (case 2) based on total light.

d. The average solar radiation should be greater than 200 W/m2.

4. Operation of the plant: The power plant is operated at 70% operation factor. That is to say, the plant is operated at 100% of rated capacity for 18.8 h (70% of 24 h) during the day and is shut down for 7.2 h (30% of 24 h) during the night.

5. CO2 production rate a. Hourly CO2 production: 407 tCO2/h b. Annual CO2 production: 2,495,724 tCO2/year

8. Algal Strain: NANNP2 (Nannochloropsis sp. from the DOE/NREL/ASP culture collection) The expected productivities of algal biomass: 42 g/m2/day (case 1) and 84 g/m2/day (case 2)

Table 4 presents preliminary cost estimates for a large-scale (over 1,000 ha) microalgal system for biomass fuel production. Two different productivities, 42 and 84 g/m2/ day, were assumed to correspond to about 10 and 20% solar conversion efficiencies, based on visible light, and 4.5 and

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