Illinois Energy Enterprise Energy Balance 4 2 textbook 1 Energy is conserved 2 Energy Balance change in internal plus external energy energy flux in energy flux out per unit time dE Ein Eout dt For steady state Ein Eout Energy can neither be created not destroyed Energy may be changed from one form to another chemical to work potential to mechanical etc Eout includes energy that heats up the system or causes phase change 3 Energy is released or absorbed in phase change mass x heat of phase change 4 Energy Unit J N m kg m 2 W s s s3 kJ kW s heat flux for evaporation m Cvap heat flux for melting m C fusion heat flux to increase temperature m C T C specific heat capacity m mass flow rate mass time 5 6 1 Water Use A thermoelectric power plant Efficiency of Energy Conversion efficiency output power input power http ga water usgs gov edu powerplant html 7 1000 MW 8 First find how much energy is required to cool water the total energy produced by the plant 1000 MW x 100 33 3 3000 MW of fuel energy Energy loss 3000 1000 2000 MW Energy goes to smoke stack 2000 x 15 300 MW Energy goes to cooling water 2000 300 1700 MW 33 3 energy from coal burning produces 1000 MW electrical energy 67 energy from coal burning is heat waste 15 heat waste goes up the smoke stack 85 heat waste is taken away by cooling water that is drawn from a nearby river How much is heat waste taken away by cooling water 9 Specific heat of water 4 184 kJ kg C How fast does the cooling water need to be pumped to remove 1700 MW of heat Specific heat of water 4 184 kJ kg C 10 Energy added from the power plant E in 1700MW E out The rate of change in internal energy for cooling water m C T m is the mass flow rate of cooling water 1000 MW E in E out E in m c T m E in 1700MW 40 6 103 kg s c T 4184 J kg C 10 C 1MW 106 J s Mass flow rate m can be converted to flow rate Q 11 m kg s 40 6 103 kg s 40 6m3 s kg m3 1000kg m3 12 2 What will be the temperature of the river receiving 1700 MW of heat m is the mass flow rate of river water 0 E in m C T E in Q C T We need to assume negligible loss of water during cooling 1000 MW so that the flow rate of the river is still 100m3 s T E in Q C 106 J s 1700 MW MW T 4 C 100m3 s 103 kg m3 4184 j kg C 13 14 Find emission of C SO2 and particulate matter EPA Mercury and Air Toxics Standards to atmosphere 130 g S or 260g SO2 per 106 kJ 13 g particulate per 106 kJ coal with 62 C 2 S 10 ash and 24kJ g energy content 70 fly ash Efficiency of emission control for S and particulate 30 bottom ash Cooling water To produce 1 kWhr electricity by this plant how much coal is needed 15 16 Find emission of C SO2 and particulate matter To produce 1 kWhr electricity by this plant how much coal is needed to atmosphere 130 g S or 260g SO2 per 106 kJ 13 g particulate per 106 kJ the heat input for 1 kWhr electricity 1kWhr 1kJ s s input energy 3600 10800kJ kWhr 0 33 kW hr coal with 62 C 2 S 10 ash and 24kJ g energy content Amount of Coal to produce this amount of heat electricity energy concent 10800kJ kWhr 450 g coal kWhr 24kJ g coal coal input 70 fly ash Efficiency of emission control for S and particulate 30 bottom ash Cooling water To produce 1 kWhr electricity by this plant we need to burn 450 g of coal How much S is emitted 17 18 3 Find emission of C SO2 and particulate matter To produce 1 kWhr electricity by this plant we need to burn 450 g of coal How much S is emitted to atmosphere 130 g S or 260g SO2 per 106 kJ 13 g particulate per 106 kJ Amount of Coal to produce this amount of heat coal input electricity 10800kJ kWhr 450 g coal kWhr energy concent 24kJ g coal Coal has 2 S S emission 0 02 g S g coal 450 g coal kWhr 9gS kWhr 19 the maximum sulfur emission is S 130 gS 10800kJ kWhr 1 4 gS kWhr 106 kJ S emission from burning 450 g coal kWhr 9gS By law we cannot emit more than 1 4 g S the removal efficiency should be 1 1 4 9 0 85 coal with 62 C 2 S 10 ash and 24kJ g energy content 70 fly ash Efficiency of emission control for S and particulate 30 bottom ash Cooling water To produce 1 kWhr electricity by this plant we need to burn 450 g of coal and we emit 9 g of S The Clean Air act only allow 130 g of S emitted per 106 kJ of heat input How efficiency is the S emission control 20 system should be for this plant A typical coal fired electric power plant produces 1 000 MW of electricity by burning fuel with an energy content of 2 800 MW Three hundred and forty MW are lost as heat up the smokestack leaving 2 460 MW to produce electricity However the thermal efficiency of the turbine is only 42 The other 58 is wasted heat that must be removed by cooling water with flow rate of 100m3 s Find the change in temperature of the cooling water The heat capacity of water c 4 184 J kg 1 C 1 21 22 Renewable Energy in China Heat taken up by cooling water 2 460 MW 0 58 1 430 MW This amount of heat will heat up the cooling water m water c T 1430MW T 1430MW m water c 1430 106 J s 3 4o C J m3 kg 4 184 1000 3 100 kg o C s m 23 24 4
View Full Document
Unlocking...