Carbon Emission Calculations

May 2014
ES8910 Energy and the Environment
Assignment 2
Carbon Emission Calculations
1. A flow of steam at 180oC from a geothermal field is supplied to a steam turbine connected to
an electric generator. The steam flow has a power content of 150kW. The power system uses
a cooling tower to reject heat and the ambient temperature is 15oC.
(a) What is the theoretical maximum electrical power output from the generator?
(b) The electricity is sold at a rate of 6 cents per kW-hour. If the average thermal efficiency
of the actual power plant is 0=18%, what is the total revenue generated in one year
(assuming that the plant operates continuously).
2. In Saskatchewan all of the electricity is supplied to a house from a coal-fired power plant with
an overall thermal efficiency of η=33%. The power plant uses low grade coal (lignite) with a
carbon intensity (based on the lower heating value, LHV) of 28gC/MJ. In the summer months the
electricity is used to run a vapour compression air conditioning system, with a coefficient of
performance of β=3.2.
(a) Calculate the CO2 emission intensity of the coal-fired electrical power generation in
gCO2/kW-hr, i.e. grams of carbon dioxide (CO2) emitted to the atmosphere per kW-hr of
electrical energy produced. Assume complete combustion.
(b) Calculate the effective overall carbon intensity of overall system for providing air
conditioning, including the power plant. The overall carbon intensity of the system is the
number of grams of carbon (C) emitted to the atmosphere per MJ of cooling provided to the
house. Express your answer in gC/MJ based on the LHV of the fuel.
3. The attached advertisement from General Electric Corporation appeared in the Toronto Star.
This advertisement makes a claim of savings in greenhouse gas (GHG) emissions through the use
of compact fluorescent light bulbs. Read the assumptions below carefully.
(a) Estimate the annual CO2 emissions (in kg/yr) from one typical Canadian car using the
following assumptions:
-
A litre of gasoline contains 0.611 kg of carbon, which is converted entirely to CO2 during
combustion. (To be generous to General Electric, base the automobile emissions on only
these tank-to-wheel emissions, not the full life cycle fuel emissions.)
The average Canadian passenger car uses 8.6 litres of gas per 100 km traveled (Canadian
Automobile Association, CAA).
The average Canadian passenger car is driven 17,000 km per year (CAA).
(b) The advertisement claims a total annual savings in electricity worth 73 million dollars for each
Canadian household replacing one 60W incandescent bulb with a 13W fluorescent bulb. If the
typical total cost of electricity (averaged across Canada) is 8.0 cents per kW-hr, how many hours
per day must the replacement and original light bulb be left switched on (on average over the
year)? Use the following assumptions:
- There are 13.3 million residential households in Canada (Statistics Canada, 2011).
(c) Using the above result, estimate the annual CO2 emission savings (in kg/yr) associated with
replacing one 60W incandescent bulb with one 13W fluorescent bulb, in one typical Canadian
household. Do this calculation from “first principles” using the following assumptions:
- The GHG savings are entirely CO2 and result from the reduced combustion of fossil
fuels in electric power plants.
- Canada’s electrical power generation mix is 23% from fossil fuels (EIA Country Analysis
Brief, 2010). Assume electricity from other sources (hydro, nuclear and renewable)
have approximately zero carbon emissions.
- Canada’s fossil fuel based electrical generating capacity is comprised of 70% coal and
30% natural gas (EIA, 2010). Use these percentages to compute the weighted-average
carbon intensity, based on the LHV of the three fuel sources given in the class notes.
- Assume the overall efficiency for the fuel energy to electrical power conversion process is
35%. This includes all effects, such as combustion efficiency, plant thermal efficiency,
electrical generation losses and transmission line losses.
- Most light bulbs are located indoors, in an occupied living space. So, for six months of
the year (i.e., in cold weather) the reduced electricity use by the bulb will require an
equivalent amount of additional home heating. So, the net carbon emissions savings
will be approximately zero for six months of the year.
(d) Using the results above, calculate the equivalent number of passenger cars “taken off the road”,
if every Canadian household replaced one 60W incandescent bulb with one 13W fluorescent bulb.
This is done by dividing the carbon emissions calculated from part (c) by the carbon emissions for
one car that you calculated in part (a). How does your estimate compare to the statement by
General Electric? Discuss possible reasons for any difference.
(e) Comment on last assumption in part (c). In the winter months, will the “home heating effect”
always cause the net GHG savings to be zero? In some households, could the replacement of an
incandescent bulb result in more net GHG emissions because of this effect? In some cases, could it
be less? Discuss briefly.
Hint: Think about what would happen to the carbon emissions if the bulb’s electricity supply was
carbon-free e.g. In Quebec, most of the power comes from hydro. What would replace the lost
home heating effect of the bulb?
(f) The simple hand calculation done in part (c) is intended to give some insight into the factors that
influence the carbon intensity of electrical power generation. In practice, this approach is not
necessary. The actual carbon intensity of electricity generation is reported by Environment Canada
in the attached “National Inventory Report”. As shown in the attached table, in 2007 the overall
GHG intensity of Canada’s electricity generation was 210 gCO2 (equivalent) per kWhr. Compare
this intensity to the rough value that you calculated using a simplified procedure in part (c). (The
two values should be reasonably close.)
National
Inventory
Report
1990-2008
Part 3
GREENHOUSE GAS SOURCES
AND SINKS IN CANADA
The Canadian Government`s Submission
to the UN Framework Convention on Climate Change
Table A13-1: Electricity Generation and GHG Emission Details for Canada1
1990
Overall Total4,5
Coal
7
Refined Petroleum Products
Natural Gas
Nuclear
Hydro
Biomass
8
Other Renewables
10
Other
Overall Total
2000
92 500
77 400
13 630
3 900
68 800
262 900
10
30
80
426 700
2001
126 300
107 700
10 810
25 900
68 700
323 500
1 910
260
170
538 900
2002
127 900
107 800
13 250
27 300
72 400
299 600
2 120
370
420
523 200
2003
2004
Greenhouse Gas Emissions3
kt CO 2 eq
123 300
106 900
10 790
26 400
71 300
314 600
2 180
430
490
533 000
128 600
2005
2006
20082
2007
119 300
118 800
110 200
118 000
111 600
Electricity Generation6
GWh
100 400
94 900
12 560
12 800
26 200
25 300
70 700
85 200
302 400
303 600
2 140
2 000
700
970
4 190
4 560
519 300
529 400
99 700
10 040
27 300
86 800
327 200
1 860
1 580
2 600
557 000
93 200
5 420
26 100
92 400
316 100
2 010
2 470
4 120
542 000
99 900
6 470
31 800
88 200
334 200
2 000
3 100
3 660
569 300
97 300
5 060
26 700
90 600
340 100
N/A
9
4,900
4 350
568 500
Greenhouse Gas Generation Intensity3
g GHG / kWh electricity generated
230
246
224
CO 2 intensity (g/ kWh)
216
233
243
212
202
206
195
CH4 intensity (g / kWh)
N2O intensity (g / kWh)
0.004
0.009
0.009
0.009
0.009
0.009
0.008
0.008
0.009
0.008
0.004
0.004
0.005
0.004
0.005
0.004
0.004
0.004
0.004
0.004
220
230
240
230
250
230
210
200
210
200
Overall Intensity (g CO2 eq / kWh)
Notes:
1. Data presented include emissions, generation and intensity for public utilities.
2. Data for 2008 are preliminary.
3. Data taken from Report on Energy Supply and Demand in Canada , Catalogue No. 57-003-XIB, Statistics Canada.
4. Emissions from the flooding of land for hydro dams are not included.
5. Emissions related to the use of biomass for electric power generation are not included.
6. Data taken from Electric Power Generation, Transmission and Distribution (EPGTD), Catalogue No. 57-202-XIB, Statistics Canada with the exception of
data for 2007 and 2008, which are taken from CANSIM Table 127-0007.
7. Includes electricity generated by combustion of light fuel oil, heavy fuel oil and diesel fuel oil.
8. Other Renewables - includes electricity generation by wind and tidal.
9. Other Renewables calculated from totalling provincial sources.
10. Others - includes electricity generation by fuels not easily categorized (i.e. waste).
11. Overall Intensity values are rounded to incorporate uncertainty in the estimates.
N/A - Not Available.
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