Question

Estimate the area of forest (in hectares) needed to absorb the carbon dioxide produced by a 1 GWe coal-fired power plant with a capacity factor of 80% and efficiency of 35%. Is this a practical method of counteracting carbon emissions? Explain how you got your number for absorption amount.

Answer 1

Step 1:

Total heat input in a year = plant output * plant capacity factor * 365 * 24 * 3600 / plant efficiency

                                     = 10⁹* 0.8*365*24*3600 / 0.35

                                      = 72082285.7 * 10⁶ kJ per year

Step2:

Assume this required heat is obtained by combustion of coal (75% carbon containt and lower heating value of 32500 kJ / kg) with 100% combustion efficiency

amount of coal used for combustion per year = Total heat input per year / lower heating value of coal

                                                                  = 72082285.7 * 10⁶ / 32500

                                                                  = 2218 * 10⁶ kg

amount of CO₂ produced on combustion of 1 kg of coal = % of carbon in 1 kg of coal * 44 / 12

                                                                                = 0.75 * 44 / 12

                                                                                 = 2.75 kg

total amount of CO₂ produced per year from plant = 2.75 * amount of coal used for combustion per year

                                                                         = 2.75 * 2218 * 10⁶ kg

                                                                         = 6100 * 10⁶ kg

Step 3 :

assume that one mature tree absorbs 20 kg of carbon dioxide per year.

number of required tree = total amount of CO₂ produced per year from plant / 20

                                   = 6100 * 10⁶ / 20

                                   = 305 * 10⁶   trees

step 4:

Assuming one tree takes 4 meter * 4 meter of land

number of tree in one hectare of land = 10000 / (4*4)   = 625 trees

step 5:

total land required for counteracting carbon emissions = number of required tree / number of tree in one hectare

                                                                              = 305 * 10⁶ / 625 hectare

                                                                               = 488000 hectare

                                                                               = 4880 km²

...................................................................................................................................................................

tree plantation requires high amount of land area . therefore, it is not a practical method of counteracting carbon emissions .