Cairo University Faculty of Engineering Electrical Power Engineering (EPE) Lectures - Principles of Energy Conversion (EPEG102)

Cairo University Faculty of Engineering Electrical Power Engineering (EPE) Principles of Energy Conversion (EPEG102) Lecture 4 – Fossil Power Plants Dr. Ahmed M. Zobaa Contact email: [email protected] Fossil Power Plants Fuel Storage and Han...

Cairo University Faculty of Engineering Electrical Power Engineering (EPE) Principles of Energy Conversion (EPEG102) Lecture 4 – Fossil Power Plants Dr. Ahmed M. Zobaa Contact email: [email protected] Fossil Power Plants Fuel Storage and Handling Boiler Turbine Generator and Electrical System Combustion Turbine Combined Cycle Plants Fossil Power Plants An assortment of energy sources, including both renewable and nonrenewable Most nonrenewable electricity generating schemes today require a thermal-to-mechanical-to-electrical energy conversion process The renewable forms, including solar, wind, hydroelectric, and ocean-based energy, take a variety of energy conversion paths to produce electric power. Fossil Power Plants The steam boiler burns fuel in a furnace. The heat generates steam that drives the turbine–generator set. The turbine-driven generator converts the mechanical rotational energy to electrical energy. Fossil Power Plants The major components of a thermal power plant are: Fossil Power Plants 1-Fuel Storage and Handling A- Coal The heating value “per-unit mass” Transportation to power plant Coal train Conveyer belts open-air Barge coal yard Additional conveyer belts move the coal into the power plant where the coal is fed through hoppers to large mills The mills pulverize the coal to a fine powder The coal powder is mixed with air and injected into the boiler through burners. The mixture is ignited as it enters the furnace. Fossil Power Plants 1-Fuel Storage and Handling B- Oil and liquefied natural gas The heating value “per-unit volume” Transportation to power plant Rail Pumping System large steel Pipelines tanks The oil is pumped to the burners, which atomize the oil and mix the small oil particles with air. The mixture is injected into the furnace and ignited Note: Natural gas is the easiest of the fossil fuels to burn as it mixes well with air and it burns cleanly with little ash. Fossil Power Plants 2 Boiler * The boiler is an inverted U-shaped steel structure. * Water tubes cover the walls of the boiler. * The major systems of a boiler are the following: Fuel injection system, Water–steam system, Air–flue gas system, and Ash handling system. Fossil Power Plants 2- Boiler Fossil Power Plants Condenser *A deaerator is built in the condenser to remove the air from the condensed water. *This is necessary because the air (oxygen) in the water causes corrosion of the pipes * Heat dissipation techniques include: Once-through cooling to a river, lake, or ocean. Cooling ponds, including spray ponds. Cooling towers. Fossil Power Plants Electrostatic precipitators: Fossil Power Plants Ideally, the hydrocarbon combustion produces water and carbon dioxide gases. The main gaseous pollutants from combustion sulfur oxides (SOX), nitrous oxides (NOX), and CO. Both SOX and NOX can create acid rain composed of sulfuric acid (H2SO4) and nitric acid (HNO3), respectively. The SOX, mostly SO2 and some SO3, can cause respiratory irritation. The NOX contributes to smog and ozone formation and vegetation damage. The CO reduces the oxygen-carrying capability of the blood, referred to as carbon monoxide poisoning Note: Ground-level ozone is a harmful air pollutant that is the main ingredient in “smog”. It is also known as tropospheric ozone or low-level ozone. The stratospheric ozone, on the other hand, is a naturally occurring atmospheric gas that forms the ozone layer that protects the Earth from catastrophic ultraviolet rays produced by the sun Fossil Power Plants *Most fossil plants utilize a Rankine thermal cycle employing steam. The thermal efficiency is defined as: * The maximum thermal efficiency is defined by the Carnot cycle as: Fossil Power Plants 3-Turbine * The heat energy in the steam is converted to mechanical energy Fossil Power Plants 3-Turbine Fossil Power Plants 4-Generator and Electrical System Fossil Power Plants 4- Generator and Electrical System Synchronous machines are principally used as alternating current (AC) generators. They supply the electric power used by all sectors of modern societies: industrial, commercial, agricultural, and domestic. Synchronous generators are built in large units, their rating ranging from tens to hundreds of megawatts. Synchronous generator converts mechanical power to ac electric power. The source of mechanical power, the prime mover, may be a diesel engine, a steam turbine, a water turbine, or any similar device. For high-speed machines, the prime movers are usually steam turbines employing fossil or nuclear energy resources. Low-speed machines are often driven by hydro-turbines that employ water power for generation. Fossil Power Plants 4- Generator and Electrical System Types of Synchronous Machine According to the arrangement of the field and armature windings, synchronous machines may be classified as rotating-armature type or rotating-field type. Rotating-Armature Type: The armature winding is on the rotor and the field system is on the stator. Rotating-Field Type: The armature winding is on the stator and the field system is on the rotor. *According to the shape of the field, synchronous machines may be classified as cylindrical-rotor (non-salient pole) machines and salient-pole machines Fossil Power Plants 4- Generator and Electrical System Generator and Electrical System inside the Power Plant Fossil Power Plants Other types of fossil power plants include: Combustion Turbine. Combined Cycle Plants. Fossil Power Plants Combustion Turbine Petroleum and natural gas can be burned in a furnace boiler- based plant to produce steam for input to a turbine generator. Light fuel oil and natural gas can undergo combustion in a conventional gas turbine that utilizes the Brayton thermal cycle. The figure below shows that a gas turbine plant is significantly simpler in structure than the coal-fired unit described earlier. Fossil Power Plants Combustion Turbine Fuel is added to compressed air, which, upon combustion, creates expansive gases that drive the gas turbine. The compressor and generator are shaft-connected to the turbine. The simplicity and size of these plants permit locating them on small sites, but the thermal efficiency of these simple cycles is low. With the higher cost of fossil fuels and the low thermal efficiency, these conventional gas turbine plants are generally restricted to serving as peaking or reserve units. Fortunately, gas turbines can be taken from a cold start to 100% power within minutes. Fossil Power Plants Combined Cycle Plants Combined cycle plants have become a popular generation scheme in recent years A combined cycle unit utilizes a gas turbine (Brayton) top cycle with the excess heat going to a steam turbine (Rankine) bottom cycle. Fossil Power Plants Combined Cycle Plants * The efficiency of a combined cycle plant without heat augmentation is determined from the efficiencies of the Brayton and Rankine cycles using: Fossil Power Plants Combined Cycle Plants The overall thermal efficiency of combined cycle plants built today is a remarkable 60%. Combined cycle plants are designed for intermediate load since they are relatively quick to start. Additional advantages of these plants are that they can be constructed in a relatively short period (about 2 years) and their use of natural gas, which is an environmentally good choice (except for greenhouse gas emission) and a reasonably priced fuel. Combined cycle plants should not be confused with cogeneration, also known as combined heat and power (CHP), which is the production of electricity in-house along with industrial process steam. Fossil Power Plants Useful Videos: Thermal Power Plants: https://youtu.be/IdPTuwKEfmA?feature=shared Combined Cycle Power Plants: https://youtu.be/bnR-CLpZE9I?feature=shared Fuel Calorific (Heating or Energy) Value The calorific value is a measure of the amount of heat a substance produces after complete combustion. It is also known as the heating value, energy value, or specific energy of combustion. It is usually expressed in energy units / mass units, i.e., kWH/kg or kJ/kg. This energy is the input power to the station and can be expressed as: 𝐸𝑖𝑛 = 𝑚 ∗ 𝐶𝑉 The mass is often expressed as mass flow rate (𝑚), ሶ thus, the power can be expressed as: 𝑃𝑖𝑛 = 𝑚ሶ ∗ 𝐶𝑉 Plant Output Power and Efficiency The station output power can be expressed as: 𝑃𝑜𝑢𝑡 = 3𝑉𝐿 𝐼𝐿 cos(∅) In case of three phase (which is the practical case), where VL is the line voltage and IL is the line current, and ∅ is the phase shift between the phase voltage and phase current waveforms. For simplicity, we may consider the output of the station is DC; hence the output power is: 𝑃𝐷𝐶 𝑜𝑢𝑡 = 𝑉𝐼 Plant Output Power and Efficiency The station efficiency can be expressed as: 𝐸𝑜𝑢𝑡 𝑃𝑜𝑢𝑡 𝑃𝑖𝑛 − 𝑃𝑎𝑢𝑥𝑖𝑙𝑙𝑖𝑎𝑟𝑦 − 𝑃𝑙𝑜𝑠𝑠𝑒𝑠 η= = = 𝐸𝑖𝑛 𝑃𝑖𝑛 𝑃𝑖𝑛