Geothermal Energy Sources

Hot Spring

Geothermal energy is clean and sustainable source of energy. Heat obtained from the earths crust can be used in many ways, from large power station to relatively small pumping system.Resources of geothermal energy is found in shallow ground to hot water and hot rock found few miles beneath the earth.
The energy present in the earth's crust which is in the form of heat such energy is called geothermal energy.
The uppermost crust up to 10 km or so of the earth's crust constitutes a potentially useful and almost inexhaustible source of energy.

Heat Extraction

In the above  representation of geothermal energy, at depth of 5-10 km or so lies impermeable magma and the magma are impermeable crystalline rocks which are overloaded by pockets of permeable rock . This localized pockets are founded by the fracture zone or faults around which some relative motion of rock has occurred.
Water is circulated along with the fault lines and moves in the earth's interior path. It is heated by permeable rock or layer which is in term heated by conduction of heat from the magma. The hot water comes out through another fault and forms a hot spring.
Availability of Geothermal Energy:-

Depending on the temperature and depth of the the permeable rock the natural hydro thermal systems can be divided into three categories:

1. Dry Steam System:- The temperature of permeable rock is very high. The whole of the water is converted into steam which is converted into steam which gets superheated by the time comes out on surface.
2. Wet Steam System:- The temperature of permeable rock is not very high.By the time water comes out on the surface only a part of it is get converted into steam therefore the eruption gives a water-steam mixture. 
3. Hot water System:- The temperature of permeable rock is rather low, therefore the surface eruption provides hot water. 

Vapour Turbine Cycle

Vapour Turbine Cycle

Recently in Geothermal plants heat exchanger and vapour turbine cycle have been proposed for generation. The geothermal hot water is used to heat for low boiling point fluids (Propane/Freon). This fluid expands in turbine which drives the generator. The fluid is condensed and reused to form a closed circuit system in vapour turbine cycle system. The low enthalpy geothermal water can also be profitably used.
It should be noted that electricity generated by California based Geothermal Power Plants(USA) is almost half of electricity generated by Geothermal Power Plants.

Geothermal Electricity Plant - California (USA)

Geothermal energy is also used for heating purposes.There are many examples of direct using of geothermal energy for heating purposes as for drying out fish, to heat greenhouses, for improving oil recovery, fish farms, etc. Around the world, people also used hot spring for relaxation and rest.

Advantages:

Geothermal energy has many advantages as follow:

1. Reliability:- Unlike other Non Conventional energy sources such as Wind, Tidal and Solar, Geothermal energy is reliable as it provides constant power.
2. Geothermal energy is environment-friendly. There is a very less or we can say no pollution is produced by Geothermal Plant. Although fumes are not produced while drilling the earth. Therefore there is no adverse effect on environment.
3. The pollution can be reduced somewhat by increasing use of Geothermal as well as other non conventional energy sources which is caused by use of many conventional fuels like oil, coal, etc.
4. Geothermal energy has many application. For instance it can be used to generate electricity as well as for providing heat to home and businesses. 

Magneto Hydrodynamic Generation (MHD)

Magnetohydrodynamic is the branch of science which deals with the study of physics background of conducting plasma.The electrical energy is obtained from high temperature conducting plasma, highly intense magnetic field.

MHD Generator

Suppose  charge particle "q" moves with a velocity of "v" right angle to the magnetic field, it means two plates p as shown, then magnetic force is given by,

If this charged particle q is replaced by a mass of ionized gas with same velocity v then positive ions accelerates toward upper plate and negative ions to the lower plate.

If this plates are connected externally through resistance  then current start flowing through resistance thus electrical power is generated by extracting the mechanical power of ionized gas.

This is the principle of Magnetohydrodynamic generation called direct form of generation  from heat without the necessity of any accessories as in Steam Power Plant.

Working principle of Magnetohydrodynamic Generation

There are two types of cycle in Magnetohydrodynamic generation:

1. Open cycle MHD generation
2. Closed cycle MHD generation.

1. Open Cycle MHD generation

Open Cycle MHD Generation

In above figure you can see that open cycle MHD generation consisting of a MHD generator resembles shape of a  rocket engine. Coal or natural gas is burned into combustor to produce hot gases. The hot gases is then seeded with alkaline metals ( cesium or potassium ) to increase electrical conductivity of of the gas. This gas then enters into a MHD generator which is rocket engine shaped in which gas expands and electrical power is generated by accelerating gas ions towards electrode and strong magnet. 

          Air preheater is used to preheat the air which is used as input hot air to the combustor. Later on seed material is recovered from the gas and next on Nitrogen and Sulphur is extracted from the gas to avoid air pollution and then flue gases are exhausted to the atmosphere with the help of stack. The output of MHD generator which is surrounded by the huge magnet is in the form of DC and then that DC is converted into AC with the help of inverter.

2. Closed Cycle MHD generation         

         

Closed Cycle MHD Generation

• HX1& HX2 - Heat exchanger 1 & 2
• S.T. - Steam Turbine
• CP - Compressor Product
• P - Removal of Nitrogen and Sulphur
• CS - Cessium injection

          Closed cycle MHD generation consist of three distinct part but interlocked with each other. In figure, at very left side heating loop in which air, coal and steam is used to be converted into gasifier form at a temperature of 520℃ and this heated gas is then fed to the combustor in which Argon gas is heated. The combustor product passes through the air preheater which preheats the air and then fed as input to the combustor. After air preheater removal of Nitrogen and Sulphur from the flue gases to decrease the air pollution and then this gas is exhausted to the atmosphere through stack.

         Heated Argon gas is fed to the MHD generator which resembles rocket engine shape surrounded by the huge magnet.

         During the expansion of the Argon gas into MHD generator, conversion of mechanical energy into electrical energy take place and then converted into 3Ø AC with the help of inverter. The speed of the gas is slowed down with the help of diffuser and then heat of the gas is utilized in heat exchanger 2 and water get get converted into steam. Steam is partially used to drive compressor and partially used to generate electrical power with the help of alternator. The Argon gas is recycled and fed back to heat exchanger 1 through the compressor and intercooler.

Thermal Power Station

In thermal power station the heat energy of coal is converted into mechanical energy and then this mechanical energy is converted into electrical energy.It is also known as Steam Power Station. Boiler is the heart of thermal power station. The main equipment of thermal power station is boiler and it has three main inputs namely: coal (fuel of thermal power station), air (for combustion of coal) and water for producing steam.
This topic will cover:-

Thermal Power Station

• Selection criteria of site for thermal power station
• Coal Handling Plant
• Working
• Condenser 
• Cooling Tower
• Ash Handling Plant

Selection criteria of site for thermal power station:- 

While installing the thermal  power station this point should be taken in consideration.

1. Availability of Coal :The power station should be installed near coal mines. Coal is the primary requirement of thermal power station for the generation of electricity. A thermal power station of 400 MW capacity requires 5000 to 6000 tons of coal per day. Nearer to coal mines reduces the transportation cost. 
2. Space requirement :Quite large space is required by the thermal power station up to 3 to 5 acres per MW for installing equipment, machinery, coal storage, ash disposal, staff colony etc. And the land available for power plant must be available at low cost also it should have sufficient bearing capacity for holding the heavy equipment's, to withstand the load of machinery.  
3. Availability of water :Water is the secondary requirement of thermal power station. In thermal power station water is required for many purpose. But the two main purposes are, firstly for conversion into steam for steam turbine and secondly for condenser. It is also required for drinking purpose for staff colony. Therefore the plant should be located near the resources of water such as rivers, ponds, lake, canal, etc.
4. Ash disposal facilities:20 to 40% of ash is produced of total weight of coal i.e. 1500 to 2000 tons per day. So it becomes a problem for handling ash. It becomes a more serious problem as it comes out in the hot condition and is highly corrosive. Therefore, large space is required for the disposal of large quantity of coal. Nowadays the ash from the power plants is used for many industrial process such as for making bricks, cement and more. Therefore disposal problem does not arise.
5. Transportation facilities:We can say this point is not very important and also important. Because every power plant is built near coal, water resources. Power plants should have the transportation facility such as road and rail for transportation of materials and machinery. ( But nowadays the materials and machinery are built on site.)  
6. Away from populated area:Due to burning of huge amount of coal thermal power plant produces smoke and fumes.This pollutes the environment. Hence plant should be located at considerable distance from populated area.
7. Near to load center:This is a common point for all the power station. Power station should be located near to load center to minimize the transmission cost of electrical energy. 

Coal Handling Plant: 

Coal Handling Plant

As huge amount of coal is required for the generation of electricity; it is required to store coal in storage plant. Storage of coal avoids the shortage in case of failure of failure of transportation and other abnormal conditions.

Working :

Working is same. Firstly, in the boiler the coal is burnt and heat is utilized to convert the water into steam. Flue gases after the combustion of coal are released to atmosphere through chimney. Flue gases are passed through the super heater, economizer and air preheater before releasing to atmosphere.

Working Thermal Power Plant

• Superheater: The steam produced in the boiler is impure. That means it contains some impurities in it such as moisture. Hence wet steam is passed through superheater to dry and superheat. Superheater also helps to increase the efficiency of the plant.     
• Economizer: The heat lost in the process is recovered in economizer to heat the feed water.
• Air preheater: In economizer the heat lost is not entirely recovered. Therefore air preheater is employed to recover some of heat in the flue gases. This helps to increase the steam capacity per square meter of the boiler.
• Steam Turbine: The superheated steam obtained from the superheater is fed to the low pressure steam turbine. The steam expands in the high pressure turbine. Therefore steam attains higher velocity. The potential energy of steam is converted into kinetic energy due to pressure and internal energy.
• Alternator: The mechanical/kinetic energy obtained from steam turbine is converted into electrical energy.

Condenser:

Condenser

The cooling water is generally passes through number of closed tubes and steam surrounds the tube called condenser. Non mixing type of condenser is generally used universally.

Cooling System:

Natural Draft Cooling Tower

1. Cooling Tower:- In cooling tower the amount of water which is large is divided in smaller quantities practically of the size of drops.These water droplets fall from a height of 8 to 10 meters to the bottom of cooling tower. The splitting of water helps to cool water quickly. The water from the base of cooling tower is pumped back to the condenser and same cycle is repeated.There are two types of cooling tower: a) Natural Draft Cooling b) Forced draft cooling
2. Spray Pond:- In this system water is circulated in closed loop and is used again and again. The water is cooled by both convection and evaporation.

Ash Handling Plant:

Ash Handling Plant

The ash storage plant is located 15 KM away from the power station. In ash handling plant the ash is removed from the coal and then delivered to the ash storage plant. Also ash is distributed to industries for various purposes such as for making bricks and cement.

In this way electricity is generated in Thermal Power Station.

 

Transmission

After the electrical power is been generated it is needed to transfer the electrical energy  for utilization. But the generated electrical energy can not be directly utilized at consumer level as the power generated is of very high magnitude around 15 kV or 17.5kV in general . So we employ, Transmission and Distribution system. In this post we will cover the basics of Transmission system.

Transmission System

Transmission line

The transmission system is simply defined as the transfer/transportation of electrical power generated in generating station to substation over a long distance. "Transmission System" is a broad term which directly refers to "Transmission Line." The basic remains same that electrical energy is transported from one place to another. Although "transmission line" is precisely defined as, " the transfer of electrical energy from generating station to substation in bulk." Generated electricity is in the form of 3Ø supply which is step up in power substation. Then it is stepped down in distribution substation to utilization level. 

Standard transmission voltages are:

400kV, 220kV, 132kV, 66kV, 33kV, 11kV.

Normal voltages of primary transmission are:

132kV, 220kV, 400kV.

Different transmission system:

1. Overhead transmission system
2. Underground cable system

Overhead transmission System:

Overhead Transmission line

We can easily view this system around us. This system is mostly used transmission system. Its consist of a bare conductor supported by the supporting structure and insulator. The high voltage conductors are not covered with any type of insulation. The supporting structure maintain clearance between ground and conductor and the insulator provide insulation between conductor and supporting structure. As the transmission voltage level increases, the height of supporting structure has to be increased to provide more clearance between ground and conductor.

Underground cable transmission system:

Underground Transmission line

Electrical power is also transmitted by underground cables but it is not widely used. In underground cable system one or two or more conductors are bunched together but are properly insulated from each other. Underground cables are provided with lead sheet and armouring, this helps to prevent the cable from moisture and mechanical damage. The thickness of insulation among the conductors and between conductors and earth is increased if the voltage of transmission system increases.