Here is an essay on ‘Energy Conversion’ for class 8, 9, 10, 11 and 12. Find paragraphs, long and short essays on ‘Energy Conversion’ especially written for school and college students.
Essay on Energy Conversion
- Essay on the Introduction to Energy Conversion
- Essay on the Electricity Generation
- Essay on the Transport Energy
- Essay on the Rural Energy
- Essay on the Direct Energy Conversion Devices
- Essay on the Limitations of Current Power Generation Systems
Essay # 1. Introduction to Energy Conversion:
The energy available in natural form is not directly usable. The fossil energy is chemical energy of fuels or nuclear energy of fissile materials. The hydro energy and wind energy are available as kinetic energy or potential energy of water and air streams. Solar energy is available as photon energy of thermal energy. The usable forms of energy are electricity for heating, lighting and motive power for industries, transport, domestic and commercial activities. Therefore, the natural forms of energy are to be converted into usable forms with the aid of suitable plants and technologies.
Essay # 2. Electricity Generation:
Electrical energy is most convenient form of usable energy and is produced in a power plant.
There are many types of power plants:
a. Utility Plants or Central Power Plants:
These are large capacity power plants usually located near the natural source of energy. The power generated is transmitted over long distances to the consumers. Depending upon the input natural energy sources these plants may be thermal power plants, nuclear power plants or hydro power plants.
The flow diagram of thermal power plants is shown in Fig. 3.1. The flow diagram of a nuclear power plant is shown in Fig. 3.2 along with various stages of energy conversion. Similarly, different stages of hydro power plant are shown in Fig. 3.3.
In a steam power plant, pulverised coal or lignite is burned in the furnace of a steam generator. The chemical energy of fuel is released as thermal energy during combustion and hot flue gases are used to generate steam. The enthalpy of high pressure steam is converted into mechanical energy in a steam turbine which in turn rotates an electric generator. The electricity thus produced is transmitted over long distances and distributed to the consumers for industrial, domestic and commercial applications.
In a gas turbine plant, natural gas or furnace oil is combusted in a combustion chamber to heat compressed air. The enthalpy of hot air is converted into mechanical energy is a gas turbine, which in turn rotates an electric generator. The electricity thus produced is transmitted over long distances and distributed to the consumers. In a diesel engine plant both combustion and energy conversion of heat into mechanical energy takes place inside the cylinder of the engine. The electrical generator is rotated by the engine to produce electricity.
The nuclear power plant is similar to steam power plant where nuclear fission takes place in a nuclear reactor and thermal energy produced is used to raise steam in a steam generator which is further used in running a steam turbine as in a steam power plants.
In a hydro-electric power plant, water streams in hills/mountains are collected behind a dam. The potential energy of stored water is conducted to a hydro turbine where potential energy of water is used to rotate the turbine. The mechanical energy of rotation of turbine is used to run an electrical generator to produce electricity. The electricity generated is transmitted over distances and distributed to consumers of electric energy.
b. Captive Power Plants:
Certain metallurgical and other industries are very sensitive to even short interruption in power supply. Similarly, hospitals and hotels cannot afford power failure even for a very short duration. These manufacturing and service industries are allowed to install their own power plants to meet their total power requirement. Such plants are called capture power plants. These are thermal power plants of smaller capacity. Long transmission lives are not required.
c. Cogeneration Plants or Total Energy Plants:
There are many industries especially process industries like refineries, fertilizer plants, pharmaceuticals, organic and inorganic chemical plants, sugar mills, paper mills, etc. which require bulk of heat energy along with electrical power. Similarly, hospitals, hotels and other community centres need electricity as well as heat energy for various processes. The present system of buying power from the grid and installing a low pressure boiler is not efficient. The total energy requirements can be met from a single plant called co-generator plant at a very high thermodynamic efficiency.
The most common cogeneration plants use a high efficiency, high pressure boiler to generate steam for running a steam turbine. The required heat energy is supplied by medium or low pressure steam extracted from the turbine at suitable points A schematic diagram is shown in Fig. 3.4.
The cogeneration plant can also be based on a gas turbine (Fig. 3.5) where air exhausted from the turbine is utilized for process heating. Similarly in a diesel engine co-generation plant, exhaust gases from the engine and jacket cooling water can be used for meeting the heat requirements.
d. Autonomous Power Plants:
These are small capacity power plants which normally work on local sources of energy. These plants generate electricity for local use and transmission losses are avoided.
These plants can be:
(i) Wind Power Plants,
(ii) Solar Power Plants,
(iii) Biomass Power Plants, and
(iv) Mini and Micro Hydro Power Plants.
These plants are normally conceived as hybrid system. The intermittency of solar energy and wind energy is compensated by standby power plants. The plant uses the solar energy or the wind energy as the main source of energy when available and sufficient, a diesel engine or small hydro power plant is used at other times. In such hybrid schemes, there is no need of storage of energy.
e. Combined Cycle Power Plants:
The gas turbine power plants working on Brayton cycle are high temperature plants. The temperature at inlet to gas turbine may be of the order of 1200 – 1300 K. The exit temperatures of air are also very high of the order of 700-900K. In order to utilize this high grade energy the outlet gases may be used to raise steam in a boiler to run a steam turbine power plant.
Such arrangements are called combined cycle power plants. Due to high temperature range of utilization of heat for the combined plant, the thermal efficiencies of gas turbine plant and steam turbine plant are almost added resulting in very high thermal efficiency of the combined cycle power plant. There can be many arrangements but a schematic diagram of a typical combined-cycle plant is shown in Fig. 3.7.
Essay # 3. Transport Energy:
There are more than 500 million vehicles in the world. Cars and trucks alone consume one-third of world’s oil production. There are aero-engines, marine engines, automobile engines, engines for earthmoving and material handling machines. The total capacity of these mobile engines or power packs is many times the total installed capacity of the power plants used for electricity generation.
The engines used for transport vehicles are gas turbines for ships and aircrafts and piston-cylinder internal combustion engines using petrol, diesel and compressed natural gases fuel for other vehicles. In addition to consumption of these hydrocarbons, these engines emit greenhouse gas causing thermal pollution and adversely affecting, the global climate. In addition, nitrous oxides are also emitted which are primary components of tropospheric ozone. The emission of carbon by vehicles cannot be absorbed by the present forests.
Essay # 4. Rural Energy:
India is essentially an agricultural country with 78% of its population living in rural countryside and 70% of its gross domestic product emanating from rural agricultural sector. There are more than 5 lakh villages scattered all over the country about 95% of these villages are small villages with population less than 2000.
On the average, the villages consume 150 kWh of energy per day for energising irrigation pumps, for lighting, for cooking, etc. As the demand factor is very low and because these villages are widely dispersed, it is most uneconomical to electrify them from power grids. Transportation of commercial fuels like coal, diesel and petrol over long distances is very difficult.
The development, welfare and prosperity of rural villages depend upon the availability of the following services:
1. Cooking energy is 80% of the basic rural energy needs. This amounts to 0.5 to 1 kWh per person per day.
2. Water for irrigation, drinking and washing 25 m3/hectare-day for drip irrigation of corn, wheat, cotton, millets; 50-60 m3/hectare-day for flood irrigation for rice and sugarcane; 40-50 liters/head-day for livestock,
3. Domestic amenities cooking, drinking and wash water, lighting and heating as per Table 3.1.
4. Community services Radio and T.V. sets, street lighting and cooperative milk chilling as per Table 3.2.
5. Utilities for village industries: Power, water and steam as per Table 3.3.
6. Food supply system.
Table 3.4. For Imperishable Food supply system.
Table 3.5. For Perishable Food supply system.
Table 3.6. For Animal Husbandry Food supply system.
Local Energy Resources in Villages:
The following renewable sources of energy are generally available in the villages which can be tapped and converted into usable energy:
1. Solar Energy:
4.5-7.0 kWh/m2 for 250-300 days/year.
2. Water Current Energy:
Water current energy in the rivers and irrigation canals: Low/zero head turbines of 200 kW – 1000 kW for power generation and lift irrigation. Total potential of Indian villages: 5000 MW.
Agricultural residues 200 million tone/year plus wood 130 million tones/year for power generation of 75,000 MW by combustion or gasification.
4. Animal Wastes:
13.5 kg/day cow-dung per cattle to produce 0.46 nm3 biogas which can be used to generate 1 kWh of electricity
5. Wind Energy:
100 kWh/m2 to 500 kWh/m2 of turbine swept area to generate 20,000 MW of electricity or use for irrigation water.
Alternative Available Technologies:
The following conversion devices have been developed and are available for use in rural areas:
1. Solar Cookers:
Box type solar cookers; Hot plate type solar cookers, solar ahara, bio-gas plates.
2. Water Pumping:
(i) NPL Abhimanyu solar water pump of 1 kW rating using Freon R-114 priced at Rs. 37,000/-.
(ii) CEL solar photovoltaic water pumping system. 30-40m3/day of water capacity, total head 10m, priced at Rs. 40,000/-.
(iii) NAL wind mill water pumping system of 5m diameter to lift 23m3/day of water from a depth of 20m at wind speed 10m/s, priced at Rs. 11,750/-.
(iv) Bharat Biogas engine of 3.7 kW/1500 rpm, 100 × 100 mm centrifugal pump, priced at Rs. 16,500/-.
(v) Jyoti 5 kW/1500 rpm, biogas engine with 100 × 100 mm centrifugal pump priced at Rs. 37,000/-.
(vi) Micro-hydro pumping system as per site conditions.
3. Solar Devices:
Photovoltaic solar system for street lighting TV sets. Solar dryers, kilns, air and water heaters, distillation plants, solar refrigerator, milk cooler, vaccine freezer.
4. Hot Water, Steam and Electricity Generation Plants:
Thermal solar, photovoltaic, biogas engines; biomass plants, windmills; micro-hydro plants.
Essay # 5. Direct Energy Conversion Devices:
Many of the disadvantages of current power generation system can be overcome by small power packs not subject to Carnot limitation, free from rotating prime movers and generators installed locally at the consumer point’s not needing transmission and distribution systems or cooling water.
a. Fuel Cell:
If an electric current is passed through a dilute solution of an acid or an alkali by means of two platinum electrodes, hydrogen is produced at the cathode and oxygen is evolved at the anode. It this process is reversed by removing the power supply and connecting the two electrodes through a suitable resistance, the presence of hydrogen at one electrode and oxygen at the other will produce a small current in the external circuit, water being produced as a by-product.
This reverse process of electrolysis is the essence of the fuel cell technology as chemical energy stored in hydrogen and oxygen has been combined to produce electricity. The fuel cells do not have moving components and it is quieter; require less maintenance and attention in operation. Fuel cells convert chemical energy directly to electrical energy at room temperatures. These are very efficient and are not subject to Carnot limitation.
Hydrogen and oxygen were selected as reactants for the fuel cells used for spacecraft power supplies because of relatively high reactivity of hydrogen. The reactants for commercial fuel cells can be cheap and readily available natural gas or petroleum derivatives as fuel and air as oxidants.
The fuel cells can be installed at individual apartments, commercial buildings as on-site power units. The local trains and buses, trucks or personal cars can be propelled by methanol fuel cells.
b. Solar Cell:
The solar cell utilizes energetic photons of the incident solar radiations directly on a p-n junction to produce electricity at high conversion efficiencies. The technology of solar cell is well developed as a part of satellite and space- travel technology. It is also a direct conversion technology and does not use a working fluid like steam or gas and is not subject to Carnot limitation.
It is simple, convenient and, lacking moving parts, dependable. The solar cell is modular, so that arrays of identical modules can be assembled to meet various power needs ranging from small residential systems installed on roof tops to relatively large central systems. Efforts at reducing costs include search for lower-cost cell-manufacturing techniques and new and cheaper materials than silicon.
c. Thermoelectric Power Units:
When two dissimilar materials are joined together to form a loop and the two junctions are maintained at different temperatures, an emf will be developed around the loop. This is called See-back effect. This principle is used in thermocouples to measure temperatures.
The electricity produced by the device is proportional to the temperature difference between hot junction and cold junction and therefore is subject to Carnot limitation. But the device is very simple, without any moving part and hence very dependable without much need of operation and maintenance attention. Due to material constraints, the present conversion efficiencies are very low of the order of 3%.
With the development of new materials in the field of ceramics and semi-conductors, the thermoelectric generator is projected with high potential in the field of base load and peak load power generation. The present applications are restricted to small units operating in remote areas as signaling and navigational device.
The cold junction is maintained either by cooling water or atmospheric air and the source of heat can be oil or gas burner, direct solar radiators by paraboloidal concentrator, heat of radio-active decay of isotopes.
d. Thermionic Converter:
A Thermionic generator converts heat directly into electricity by using thermionic emission. An emitter which is a metallic cathode is heated till electrons cross the surface Fermi barrier and are collected at the opposite colder anode. The container holding the two electrodes is filled with ionized cesium vapour to minimize energy losses of the electrons crossing the gap between the electrodes.
The emitter is positively charged and the collector is negatively charged. It is a low-voltage high current device limited by Carnot’s law. Thermal efficiencies of 10 – 20% have been realized and higher efficiencies are possible in future. This device is being designed for space power applications. For the time being it is used to supply power to boats’, power tools and irrigation pumps.
e. Magneto-Hydro-Dynamic Generator:
MHD is a direct heat-to-electricity conversion technique based on Faraday Law that when an electric conductor moves across a magnetic field, a voltage is induced in it which produces an electric current. Here the conductor is an ionized gas which is passed at high velocity through a powerful magnetic field; a current is generated and can be extracted by placing electrodes in a suitable position in the stream. It produces d.c power directly.
MHD is the most promising direct conversion technology where the mechanical link can be by past. It can overcome some of the limitations of conventional power generation. By hybridization of MHD and thermal power plants, the efficiency can be raised from 40% to 55%, thus better utilizing the fuel resources and reducing the conventional pollution.
Essay # 6. Limitations of Current Power Generation Systems:
The current power generation systems of large capacities suffer from some serious disadvantages and price of electricity from the power grid is high. The power supply at the same time is not reliable.
i. Carnot Limitation:
The steam turbine power plants based on coal or nuclear fuels, gas turbine plants and diesel engine plants work on the principle of conversion of thermal energy into electrical energy. The maximum possible cycle efficiency is limited by Carnot efficiency of Tmax – Tmin/Tmax. Specific heat rates of most modern thermal power stations is in the range of 8400 – 10,000 kJ/kWh generated and about 65-70% of the heat available from the fuel is lost to the cooling water in the condensing plant and boiler stacks. The overall achievable efficiency of 40% of a modern central power station is called Carnot limitation.
ii. Metallurgical Limitation:
Tmin is site specific and depends upon the temperature of cooling water available. Tmax is limited by the availability of technical materials for boiler tubes and turbine blades. This is called metallurgical limitation.
iii. Reliability and Mechanical Links:
There are many mechanical links in modern thermal and hydro power plants in the form of boilers, penstocks, turbines, pumps, generators. There is loss of reliability and mechanical Tosses get added up with every additional component specially rotating systems. The energy output in India is only 3600 kWh/kW installed capacity.
iv. Ecological Balance:
The modern power plants are large size plants and disturb the ecological balance of the site. The need of a large dam in a hydro power plant results in submergence of large fertile areas under the water reservoir, displacement of huge population, loss of crops and forests, adverse effect of high water table of very large areas damaging the corps. The thermal discharges from a thermal power plant into rivers or lakes serving as source of cooling water and fly ash discharges from the stacks can adversely change the environment.
v. Plant Costs:
Huge capital requirement (Rs. 5000/kW installed) on boilers, turbines, generators, cooling water treatment and supply system, cooling towers, etc., and availability of fuel and cooling water are main constraints in siting thermal power plants. The construction costs of a dam for a hydro power plant are very high (Rs. 40,000-50,000/kW installed). The gestation period is many years.
vi. Transmission and Distribution:
One of the most expensive forms of energy transmission is that of electric power from power plants. A huge investment in procuring rights of way, installing towers, erecting lines and providing protection against lighting and other problem is required. The erection and repair costs for overhead lines are very high and overhead lines are prone to breakdown disrupting power supply on a large scale.
In addition to high investment costs, considerable power losses occur during transmission. In India, the transmission losses are as high as 18 to 20% against 8 to 10% in developed countries. This is due to high pilferages and voltage drops. The investment costs on transmission lines in India constitute 30% of power generation plant costs whereas in developed countries it is 100% of power generation plant cost.
The power distribution system can be very complex for a metropolitan city or industrial estate. In addition to huge investments, the erring distribution system causes frequent disruptions in power supplies resulting in production losses.