energy and environment Energy Balance

Energy Balance Energy balance must be performed when dealing with thermal pollution from coal fired power plants and nuclear reactors. Potential climate changes resulting from the discharge of greenhouse gasses and combustion of fossil fuel ( coal, natural gas and gasoline) to produce energy.

Energy Balance Thermodynamics : is the study of energy changes resulting from physical and chemical processes. Changes in energy associated with biological and chemical processes are very important in environmental engineering.

Energy Balance Enrgy : the capacity for doing work. Many forms of energy such as, chemical, electrical, kinetic, potential, and thermal(heat). Heat and work are related forms of energy. Thermal energy can be converted into work and work can be converted into heat energy. Various units are used for measuring energy such as: BTU, Cal, J,

Energy Balance British Thermal Unit (BTU) is energy required to raise the temperature of one pound of water one degree Fahrenheit oF. The Calorie: is the amount of energy required to raise the temperature of one gram of water by one degree Celsius. Celsius = 1.8 Fahrenheit 1 BTU= 252 calories. Joule : the amount of work done by a force of one newton to raise an object one meter.

Energy Balance Work : is transferring energy to an object by applying force and causing motion. (N.m) Power: the rate of doing work. So has unit of energy per unit of time. Watt (W)= 1 J/s and = 3.412 BTU/h Therefore, Chemical energy is a form of internal Energy(U), Kinetic Energy (KE) can produce electricity through windmills or water flowing through turbines. Potential Energy(PE) results from change in elevation a

Energy Balance Total Energy (E) is the sum of internal , kinetic, and potential energies E= U+KE+PE So the first law of thermodynamic states that the energy cant be created or destroyed (excluding nuclear reactors). Only the form of energy will change. So similar to material and mass balance. [energy accumulated]= [energy input]-[energy output] +[energy generated].

Energy Balance Energy generated is usually comprised two terms: [energy generated]= [energy produced]-[energy consumed] During energy conversion some loss of useful energy will occurs, normally through waste heat. Second law of thermodynamics states that there will always be some waste heat released during energy conversions.

Energy Balance Heat is a form of internal energy expressed as the thermodynamic property enthalpy (H), which is function of temperature, pressure, and volume. H=U+PV Where: U= the internal energy of the substance P= pressure of the system V= volume of the system

Energy Balance When a process occurs without a change in volume, the change in internal energy can be calculated as follow: ΔU= mcv ΔT Where: m: mass of the substance Cv: specific heat or heat capacity of the substance at constant volume ΔT: Temperature change

Energy Balance For constant pressure systems, thermal or heat energy changes can be estimated by using the following equation: ΔH= mcp ΔT Where: ΔH: change in enthalpy or thermal (heat) energy m: mass of the substance Cp: specific heat or heat capacity of the substance at constant Pressure

Energy Balance For incompressible substances, such as solids and most liquids. Cv and cp are nearly the same and they replaced with c. therefore, ΔU= ΔH and this yield to: ΔU= mc ΔT Where: c: specific heat or heat capacity of the substance

Energy Balance For most environmental applications, we are concerned with the rate of energy change. [the rate of change in stored energy]= mc ΔT And m here account for the mass flow rate . At 15oC the specific heat of water is 4.18kJ/kg. oC, 1.0 kcal/kgoC or 1.0 BTU/ib. OF. The density of the water also equal to 1000 kg/m3 under the same Temp.

Energy Balance In any water plant the output Energy over the plant efficiency will equal to the input energy. Enrgy heat = EnergyIN – consumed Energy

Energy Balance EX1Calculate the minimum rate at which 15°C make-up water from a river must be pumped to evaporative cooling towers for a 1000 MW nuclear power plant. The efficiency of the plant is 32% and all of the waste heat is assumed to be dissipated through evaporative cooling with no direct heat lost to the atmosphere.

Energy Balance Ex2 : An industrial WWTP discharges approximately 7560 cubic meter per day of treated effluent to the river at an average Temperature of 27oC. If the temperature and flow rate of the river upstream of the discharge are 10 o C and 2 cubic meter per second respectively. Determine the temperature in the river downstream of the industrial discharge.

Energy Balance Ex3 : A 1000 MW coal-burning power plant is burning West Virginia bituminous coal with 8% ash content. The power plant is 33% efficient with 35% of the ash settling out in the firing chamber as bottom ash. A simplified schematic diagram is shown below. Draw an energy diagram for the facility and calculate the rate of heat emitted to the environment in kJ/s;

Energy Balance Ex4 : A textile dryer is found to consume 4 m3/hr of natural gas with a calorific value of 800 kJ/mole. If the throughput of the dryer is 60 kg of wet cloth per hour, drying it from 55% moisture to 10% moisture, estimate the overall thermal efficiency of the dryer taking into account the latent heat of evaporation only.

Energy Balance

Energy Balance Ex5 : One gallon of gasoline has an energy value of 126000 BTU. Express this in calories, joules and Kwh.

Energy Balance Ex6 : A coal fired power plant uses 1000 Mg of coal per day. The energy value of the coal is 28000kJ/kg. the plant produces 2.8x106 kwh of electricity each day. What is the efficiency of the power plant?

Energy Balance Ex7 : A coal fired power plant discharge 3 m3/s of cooling water at 80 oC in a river that has a flow of 15 m3/s and a temperature of 20 oC. What will be the temperature in the river immediately below the discharge?

Electric power production

Energy Balance Ex8 : A 2000 MW coal fired power plant is only 33.5% efficient at converting coal energy into the electrical energy. Assume that the coal has an energy content of 25 kJ/g and contains 60% carbon, 2% sulfur, and 9% ash. Perform a material and energy balance around the coal fired power plant. Assume that 65% of the ash is released as fly ash and 35% of the ash settles outside of the firing chamber and is collected as bottom ash. Approximately 15% of the waste heat is assumed to exit in the stack gasses, and the cooling water dissipates the remaining heat. Air emission standard restrict sulfur and particulate quantities to 260 g SO2 per 106 Kj of heat input and 13 g particulates per 106 kJ of heat input into the coal fired power plant.

Calculate the quantity of heat loss to the cooling tower (MW) Calculate the quantity of cooling water (kg/s) and flow (m3/s) assuming 10oC increase in the temperature of the cooling water Calculate the efficiency of the sulfur-dioxide removal system to meet air emission standards. Calculate the efficiency of the particulate removal system to meet air emission standards.