Energy Management :: 2007/2008

Transcription

1 :: 2007/2008 Class # 08 Energy balances Prof. Miguel Águas miguel.pn.aguas@igmail.com g g

2 Class objectives Summary The Climaespaço plant Energy balances Class # 08 :: Energy Balances Slide 2 of 53

3 Climaespaço plant Equipment Complete system: Production + Distribution ib ti + Consumption Gas turbine: 4,7 MWe Heat recover steam generator: 10 MWt (10 t/h at 10 bar -> kj/kg x kg / 3600 s) 2 Absorption chillers: 2 x 4,8 MWc (doble effect, COP=~1) 3 Compression chillers: 3 x 5,5 MWc 1 boiler: 15 MWt ELECTRICITY: 5 MW HOT WATER: 25 MW CHILLER WATER: 26 MW Class # 08 :: Energy Balances Slide 3 of 53

4 Recent news Layout Class # 08 :: Energy Balances Slide 4 of 53

5 Climaespaço plant Gas turbine Class # 08 :: Energy Balances Slide 5 of 53

6 Climaespaço plant Building heat exchanger Class # 08 :: Energy Balances Slide 6 of 53

7 Climaespaço plant Energy consumption Vendas de Frio Ano ,0 4,0 Vendas de Energia Térmica 100,0 80,0 60,0 0 40,0 30 3,0 2,0 1,0 0,0 GWh Jan Fev Mar Abr Mai Jun Jul Ago Set Out Nov Dez GWh 20,0 0,0 Vendas de Calor Ano ,5 2, Frio Calor 15 1,5 1,0 GWh 0,5 0,0 Jan Fev Mar Abr Mai Jun Jul Ago Set Out Nov Dez Class # 08 :: Energy Balances Slide 7 of 53

8 CASE STUDY 1: BOILER Consider a boiler represented in the figure. Combustion air Flue gases Steam Heat losses Natural gas Water Purge Is known the following data: Fuel: natural gas Combustion air: temperature Gases: temperature: O2 volume composition Steam: mass flow a) Identify mass and energy flows in an energy balance of a boiler. b) Identify requested data and the way to get it. Class # 08 :: Energy Balances Slide 8 of 53

9 CASE STUDY 1: BOILER The first step is to draw the control volume: Combustion air Flue gases Steam Heat losses Natural gas Water Purge The second step is to write mass and energy balances. Is possible to define 3 mass balances (gases, water and oxygen in gases). b) Identify requested data and the way to get it. First step is to analyze the equations in order to identify unknowns: Equation (1) has 3 unknowns: mcomb air, mnatural gas, mflue gases Equation (2) has 2 additional unknowns: mwater, mpurge Equation (3) has no new unknowns (the percentage of oxygen in air is 21% v/v, and the mass of oxygen per kg Class # 08 :: Energy Balances Slide 9 of 53 f t l i l t t)

10 CASE STUDY 1: BOILER b) Identify requested data and the way to get it. First step is to analyze the equations in order to identify unknowns: Equation (1) has 3 unknowns: mcomb air, mnatural gas, mflue gases Equation (2) has 2 additional unknowns: mwater, mpurge Equation (3) has no new unknowns (the percentage of oxygen in air is 21% v/v, and the mass of oxygen per kg of natural gas is also a constant) Equation (4) has 1 new unknown: Qheat losses The result is: 6 unknowns in 4 equations. This means that is necessary to make more measurements or identify technical equations. Regarding additional measurements, the easiest way would be the measure the combustion air flow and flue gases flow. Regarding additional technical equations, is common practice to consider that heat losses represents around 2% of the heat release and power for purges represents 1% of heat release. Class # 08 :: Energy Balances Slide 10 of 53

11 CASE STUDY 2: ALUMINUM FURNACE Consider a aluminum furnace represented in the figure. Gases Is known the following data: Aluminum: flow and temperatures Air: temperature Combustion air: flow and temperature Gases: temperature, % O2 Surfaces: temperature and areas Ventilator: electrical power Air Aluminum Propane Comb. air Melted alumin a) Identify mass and energy flows in an energy balance of the aluminum furnace. b) Identify requested data and the way to get it. Class # 08 :: Energy Balances Slide 11 of 53

12 CASE STUDY 2: ALUMINUM FURNACE a) Identify mass and energy flows in an energy balance of the aluminum furnace. The first step is to draw the control volume: Gases Heat losses Air Aluminum Propane Comb. air The second step is to write mass and energy balances. Is possible to define 3 mass balances (gases, aluminum and oxygen in gases). Melted aluminum m m& m & m& & Q comb air aluminum in + m& oxygen in comb air propane propane = m& + m& + m& air aluminum out = m& oxygen in air (2) m& flue gases oxygen (1) for propane = m& + W& = Q& + Q& + Q& (4) ventilator aluminum heat losses oxygen in flue gases flue gases (3) Class # 08 :: Energy Balances Slide 12 of 53

13 CASE STUDY 2: ALUMINUM FURNACE b) Identify requested data and the way to get it. First step is to analyze the equations in order to identify unknowns: Equation (1) has 3 unknowns: mnatural gas, mflue gases Equation (2) has 2 additional unknowns: mwater, mpurge Equation (3) has no new unknowns (the percentage of oxygen in air is 21% v/v, and the mass of oxygen per kg of natural gas is also a constant) Equation (4) has 1 new unknown: Qheat losses The result is: 6 unknowns in 4 equations. This means that is necessary to make more measurements or identify technical equations. Regarding additional measurements, the easiest way would be the measure the combustion air flow and flue gases flow. Regarding additional technical equations, is common practice to consider that heat losses represents around 2% of the heat release and power for purges represents 1% of heat release. Class # 08 :: Energy Balances Slide 13 of 53

14 CASE STUDY 3: REFRIGERATION TOWER a) Identify mass and energy flows in an energy balance of the following refrigeration tower b) Identify the request data and the way to get it. c) Calculate dissipated thermal power for: Outside air: Dry temp.=19ºc; RH=33%, Enthalpy=29 kj/kg, mass flow=35 kg/s Exhaust air: Dry temp.=17ºc; RH=80%, Enthalpy=40 kj/kg d) Considering that fun power of 11 kw, compare results with a refrigerator cycle (chiller) Class # 08 :: Energy Balances Slide 14 of 53

15 a) Identify mass and energy flows in an energy balance of the following spring furnace b) Identify requested data and the way to get it. Energy Management CASE STUDY 4: SPRING FURNACE Gases Surfaces Combustion air Propan e Propane Comb. air Losses Spring entrance Air Spring exit b) Define mass and energy balance c) Considering access to the following data (given or measured), what are the unknowns? Springs: flow and temperatures Combustion air: flow and temperature Surfaces: temperature and areas Air: temperature Gases: Temperature, % O2 Fun: electrical power Class # 08 :: Energy Balances Slide 15 of 53

16 a) Identify mass and energy flows in an energy balance of the following spring furnace b) Identify requested data and the way to get it. Energy Management CASE STUDY 5: TEXTILE DRYER Ar chaminé + água evaporada Condensados Perdas pelas paredes Malha (seca) Malha (seca) Malha (água) Malha (água) Ar pelas aberturas Vapor Ventiladores b) Define mass and energy balance c) Considering access to the following data (given or measured), what are the unknowns? Springs: flow and temperatures Combustion air: flow and temperature Surfaces: temperature and areas Air: temperature Gases: Temperature, % O2 Fun: electrical power Class # 08 :: Energy Balances Slide 16 of 53