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T213/SEP ENERGY AND SUSTAINABILITY Answer FIVE questions

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T213/SEP ENERGY AND SUSTAINABILITY
Answer FIVE questions. Showing all your reasoning can gain marks, and may help to ensure that you use the right method of calculation. References and book page numbers are not required in your answers for this exam. There is a data sheet with useful numerical values at the end of the question paper. (a) Figure 1 shows UK emissions of sulfur dioxide between 1970 and 2019. Figure 1 UK Sulfur dioxide emissions 1970-2019 (i) Give the chemical equation for the complete combustion of one atom of sulfur in air. (2 marks) (ii) If the atomic weight of sulfur is 32 and that of oxygen in 16 calculate the mass of sulfur dioxide produced by the combustion of 1.0 kg sulfur. (2 marks) (iii) UK coal consumption in 1970 was 150 Mt. Using the data in Figure 1, and assuming that the combustion of coal was the only significant source of UK SO2 emissions, show that the average sulfur content of the coal was about 2%. (2 marks) (b) State two forms of pollution damage that result from SO2 emissions. (2 marks) (c) (i) Figure 1 shows a large reduction in UK SO2 emissions from electricity generation and energy industries between 1990 and 2000. Express this fall as a percentage. (2 marks) (ii) Give two reasons for this reduction that relate to electricity generation. (4 marks) Question 1 SPECIMEN T213/SEP TURN OVER 3 (d) Describe the most common process for flue gas desulfurisation. Identify the key mineral that has to be mined for this process and one useful product that can be made from the waste product. (6 marks) SPECIMEN T213/SEP 4 (a) (i) One option for heating a small building is a propane gas heater with a heat output of 2.0 kW. Given that the combustion of 1.0 kg of propane gas produces 50.4 MJ of heat, and assuming an efficiency of 70%, show that the heater uses about 0.2 kg of propane per hour. (4 marks) (ii) An alternative to the propane heater would be a 2.0 kW electric heater. Using the data below, compare the CO2 emissions in kilograms per hour of the two systems. Carbon dioxide emissions The combustion of 1.0 kg of propane gas releases 3.0 kg of CO2. The UK grid releases an average of 0.19 kg of CO2 per kWh of electricity. (2 marks) (iii) A typical propane storage tank is 1.2 cubic metres in size. The density of liquid propane is 493 kg per cubic metre. Calculate the total number of hours that this tank can supply the propane heater in part (a) of this question if it is running at full power. (3 marks) (b) Table 1, below, shows data for three power stations: a small coal-fired plant, a combined cycle gas turbine (CCGT) plant and a biomass-fired plant. For each of these the table gives the rate of fuel input needed for an electrical output of 100 MW, the energy content per tonne of fuel, and the mass of CO2 emitted in producing one gigajoule of heat. Table 1 Plant type Electrical output / MW Fuel input rate / tonnes per hour Energy content of fuel / GJ t–1 CO2 released / kg GJ–1 Coal-fired 100 42 24 90 CCGT 100 16 45 57 Biomass-fired 100 70 15 4.0 (i) Use the appropriate data from the table to calculate the overall fuel-to[1]electricity generation efficiency of each plant. (7 marks) (ii) Calculate the emissions of CO2 per kilowatt-hour generated for each plant. (3 marks) (iii) Show that the CO2 emission factor for the coal-fired plant is over twice that of the CCGT plant. (1 mark) Question 2 SPECIMEN T213/SEP TURN OVER 5 (a) (i) One constituent of crude oil is octane, a hydrocarbon in which the molecules have eight carbon atoms and eighteen hydrogen atoms (C8H18). Show the equation for the combustion of two molecules of octane in an excess of air. (4 marks) (ii) The relative atomic masses of C, H and O are 12, 1 and 16 respectively. Explaining your reasoning, show that the combustion of 1 kg of octane will produce slightly more than 3 kg of CO2. (4 marks) (b) (i) Explain what is meant by the ‘octane rating’ of petrol. (2 marks) (ii) Name the chemical that was added to petrol in the past to improve its octane rating and state why its use for this purpose is now banned in most countries. (2 marks) (c) List five reasons why oil and gas are considered ‘special’ (i.e. particularly attractive) sources of primary energy as explained in this module. (5 marks) (d) (i) List two hydrocarbons commonly sold as ‘liquefied petroleum gas’ (LPG). (2 marks) (ii) State the main difference between the storage conditions required for LPG and those for liquefied natural gas (LNG). (1 mark) Question 3 SPECIMEN T213/SEP 6 Table 2 below gives data for two electricity generation schemes: a proposed large offshore wind farm and a combined cycle gas turbine (CCGT) plant with the same rated output. Table 2 Wind farm CCGT Rated output (MW) 225 225 Capital cost (£ million) 300 120 Annual O&M costs (£ million) 18 10 Annual fuel cost (£ million) nil 65 Average annual capacity factor 40% 80% (a) (i) Suppose that, for both schemes, the annual capital repayment rate is £102 per year for each £1000 of capital cost. Calculate the annual capital repayment for each scheme, in £ million. Add the other annual costs shown in Table 2 to obtain a total annual cost in £ million for each scheme. (4 marks) (ii) Using further data from Table 2, calculate the annual output of each plant, in millions of kWh. (Note that there are 8760 hours in a year.) (2 marks) (iii) Use the results of (a)(i) and (ii) above to show that the cost per kWh of electricity from the wind farm would be just over 10% more than that from the CCGT. (3 marks) (b) What assumption does this simple kind of calculation make about the construction time of both schemes? (2 marks) (c) What environmental cost element is missing from Table 2 that might help balance the difference in the cost of electricity from these two schemes? (2 marks) (d) Calculate the cost per kWh of electricity derived from gas if the annual fuel cost doubles to £ 130 million. (3 marks) (e) If the CCGT plant is in competition with other forms of electricity generation and its fuel cost rises significantly as suggested above, then explain what is likely to happen to the CCGT’s average annual capacity factor. (2 marks) (f) Why might the annual capital repayment rate for other technologies such as wave and tidal power be higher than that used here for the wind turbines and CCGT plant? (2 marks) Question 4 SPECIMEN T213/SEP TURN OVER 7 In many countries, personal transport accounts for a significant contribution to greenhouse gas emissions as well as local urban air pollution. (a) (i) A medium-sized petrol car has a fuel consumption of 6.30 litres per 100 km travelled. If the specific CO2 emissions of petrol are 2.30 kg per litre, calculate the CO2 emissions of the car in grams per kilometre travelled. (1 mark) (ii) How many tonnes of CO2 will it emit if it travels 12 000 km per year? (1 mark) (iii) A petrol car is also likely to emit nitrogen oxides (NOx). Explain briefly how these are produced, given that petrol contains almost no nitrogen. (2 marks) (iv) Describe briefly the two main methods for reducing the emissions of NOx from petrol engines. (4 marks) (v) The 2015 European Euro 6 legislation stipulates a maximum NOx emission level of 0.080 g km−1 for cars. If the pollutant damage done by NOx is given a value of £6385 per tonne, calculate the annual NOx damage done by a car meeting this specification and travelling 12 000 km per year. (2 marks) (b) Name and describe two technological advantages that hybrid vehicles may have over conventional cars. (4 marks) (c) One alternative to the petrol engine is the fuel cell, which may run on hydrogen. Briefly explain how a fuel cell works and its basic efficiency and pollution advantages over an internal combustion engine. (6 marks) Question 5 SPECIMEN T213/SEP 8 (a) (i) List the three main mechanisms of heat loss through a double-glazed window. (3 marks) (ii) Early sealed double glazing units were filled with air. Name two heavy gases that can be used instead to improve the thermal performance. (2 marks) (iii) Low-emissivity coatings can be added to the glass in double glazing units to improve their thermal performance. List the two general types of coating that can be used. (2 marks) (iv) Windows are now sold with Window Energy Ratings on a scale A–G. List the three properties of a window used to calculate the rating. (3 marks) (b) (i) Table 3, below, gives the U-values and the areas of the elements of a two[1]storey detached house. Use these values to calculate the total fabric heat loss in W K–1. Table 3 Element Net area / m2 U-Value / W m–2 K–1 Windows and doors 25 1.80 Floor 50 0.25 Roof 50 0.30 External walls 125 0.32 (5 marks) (ii) The building has a volume of 250 m3 and an air change rate of 0.70 ACH. Calculate the ventilation heat loss coefficient in W K–1 given that the heat capacity of air is 0.33 Wh m–3 K–1. (2 marks) (iii) Calculate the house total heat loss coefficient in W K–1. (1 mark) (iv) If the internal temperature is 20 °C and the external temperature 8 °C, show that the heat loss rate from the building is just over 2 kW. (2 marks) Question 6 SPECIMEN T213/SEP TURN OVER 9 (a) Table 4 shows the atomic number and mass of four different nuclear isotopes. For each of the examples in the table, list the numbers of protons and neutrons in the nucleus. Table 4 Isotope Atomic number Atomic mass Uranium-235 92 235 Uranium-238 92 238 Xenon-138 54 138 Strontium-90 38 90 (4 marks) (b) (i) Explain the meaning of the term ‘fissile nucleus’. (2 marks) (ii) State the fissile element that can be produced when Uranium-238 absorbs a free neutron. (2 marks) (iii) Give the full name of ‘MOX’ and state what fissile isotopes it contains. (3 marks) (c) Give two advantages and three disadvantages of the reprocessing of spent nuclear fuel. (5 marks) (d) (i) Explain what is meant by the half-life of a radioactive substance. (2 marks) (ii) Tritium has a half-life of 12 years. State how many years it will take for the activity of a sample to fall to one sixteenth of its original value. (2 marks) [END OF QUESTIONS] Question 7 SPECI