Non-Renewable Energy Resources
Coal is a combustible black or brownish-black sedimentary rock composed mostly of carbon and hydrocarbons. The energy in coal comes from the energy stored by plants that lived hundreds of millions of years ago, when the earth was partly covered with swampy forests.
During the formation of coal, carbonaceous matter was first compressed into a spongy material called "peat," which is about 90% water. As the peat became more deeply buried, the increased pressure and temperature of earth turned it into hard coal.
Types of Coal
Graphite is technically the highest rank/grade of coal. But, it is difficult to ignite graphite and thus it is not used as fuel. It is mostly used in pencils lead and can be used as lubricant when in powdered form.
Anthracite: It is the highest quality of hard coal
Bituminous: This coal has been buried deep in earth and subjected to increased temperatures and pressure. It is the most popular coal in commercial use. This grade of coal has high sulfur content. The category is further divided into sub-bituminous coal.
Lignite: It is a low grade brown coal, which is soft with high moisture content.
Peat: this type of coal is only 10% carbon and 90% moisture therefore cannot be used as fuel. Decaying plants in swamps produce peat, which has low carbon content and high moisture contents with the result low heating capacity. Peat is a highly effective absorbent for fuel and oil spills on land and water. It is also used as a conditioner for soil to make it more able to retain and slowly release water.
The table given below gives a brief idea about the carbon content and calorific value of coal
Just to revise; Heating Value/Calorific Value is the amount of heat produced when unit mass of fuel is burned (1kg of solid/ 1 lt of liquid/ 1 cubic meter of gas).
The commercial usage of type of coal in thermal power plants is subjected to its heating value, ash content and sulfur content etc parameters.
Point to remember:-
India is bestowed with high coal reserves mainly concentrated in Bihar, Jharkhand, Orissa, Madhya Pradesh, Chhattisgarh and West Bengal. The Indian coal produces excess of fly ash as well as bottom ash with lower calorific value.
Before going further to other fossil fuels, it is important to know briefly the mining process of coal.
Types of Coal Mining-
- Surface Mining/Open pit mining – this type of mining is done when coal is prsent in upper layer of soil generally at 200 ft depth. The activity spoils the fertile top layer of soil and produce lot of dust and erosion in surrounding areas.
- Underground Mining/Shaft Mining - this type of mining is done when coal is prsent in deep layer of soil generally at 1000 ft depth. The mining is done by making underground passages/tunnels. The risks to workers is much more in this type of mining as they are subjected to underground fires (due to methane trapped inside) and land subsidence.
General law that applies to mining activity is -
Hilt’s Law : is a geological term that states that, in a small area, the deeper the coal, the higher its rank (grade). The law holds true if the thermal gradient is entirely vertical, but metamorphism may cause lateral changes of rank, irrespective of depth.
Point to remember:-
As Coal mining is a major industry in India so Government have stringent rules for approval process for its mining. Environment Impact Assessment (EIA) for getting Environmental Clearance (EC) has different set of thresholds for mining. The screenshot of Government Notification for EIA states that if the mine lease area for coal mining is more than 150 hactares then the proponent needs to get EC from Central Government (MoEFCC) and if the area is from 5 hactares to 150 hactares then the EC will be given by respective State Government (SEIA).
Coal as a fuel
Approximately 60% of electricity production in India is through thermal power plants which uses coal as a fuel.
When coal is used for electricity generation, it is usually pulverized (powwdered) and then combusted (burned) in a furnace with a boiler. The furnace heat converts boiler water to steam, which is then used to spin turbines which turn generators and create electricity.
The process in thermal power plant thus converts heat energy into mechanical energy (fuel burned produce steam which spin turbine) and to electrical energy (the shaft of the turbine spins a magnet inside coils of conductor which induces current)
Thermal efficiencies of old coal fired plants are 25%. It means if we burn 100 kg coal we actually get energy equivalent to 25kg coal rest all the energy go waste. The efficiency depends on fuel, engine and many other factors. Research is continously been done to increase the efficiency of thermal power plant but most of the research till date are not applied on commercial scale.
Approaches to increase efficiency of Coal Fired Thermal Power Plants
An alternative approach of using coal for electricity generation with improved efficiency is the Integrated Gasification Combined Cycle (IGCC) power plant. Instead of pulverizing the coal and burning it directly as fuel in the steam-generating boiler, the coal can be first gasified to create syngas, which is burned in a gas turbine to produce electricity . This technique can increase the thermal efficiencies of plants to a range of 39-42%.
Coal Liquefaction (CTL technology) – In this technique coal is liquified by applying high temprature or pressure to burn it as clean fuel with higher burning efficiceny. But the process increases the energy consumption of plant thus not economically efficient and also have high carbon footprints.
Point to remember:-
Here, we can also go through the Indian Government clearance (EIA) requirment for thermal power plants.
Clearance from Center; if the coal fired thermal power plant will generate more than or equal to 500MW of electricity and if it generate energy in range 50 – 500 MW then the clearnce shall be taken by State Govt.
Non-renewable energy resources
As the name suggest the resources that cannot be renewed. These sources are called non-renewable because they cannot be renewed or regenerated quickly enough to keep pace with their use.
They are also known as conventional energy resources because they are been conventionally used from so many decades.
The term pace is very important here as many people have confusion about the renew concept. For example coal will take another millions of years to get renewed as it’s a natural process but the usage will be much faster then it.
On the other hand trees; have a life cycle of 5-7 years and if used up then can be renewed again in this duration. This makes biomass a renewable resource.
Over 85% of the energy used in the world for various purposes is from non-renewable supplies. Fossil fuels are the most commonly used types of non-renewable energy.
Petroleum / Crude Oil
Crude oil or liquid petroleum, is a fossil fuel that is refined into many different energy products (e.g., gasoline, diesel fuel, jet fuel, heating oil). It is formed when large quantities of dead organisms, usually zooplankton and algae, are buried underneath sedimentary rock and undergo intense heat and pressure. Vast quantities of these remains settled to sea or lake bottoms, mixing with sediments and being buried under anoxic conditions. As further layers settled to the sea or lake bed, intense heat and pressure build up in the lower regions. This process caused the organic matter to change, first into a waxy material known as kerogen, and then with more heat into liquid and gaseous hydrocarbons.
The elemental composition of petroleum is-
- Carbon : 83-87%
- Hydrogen : 11-16%,
- Oxygen plus Nitrogen : 0-4%
- Sulfur : 0-4%
Because petroleum is a fluid, it is able to migrate through the earth as it forms. The crude oil is extracted by drilling down the earth / sea surface. As you can see in the diagram, oil is trapped over the brine layer (salty water) just above the impervious rock surface. Natural gas is found just above the oil surface and is needed to be trapped first before exploring oil.
Petroleum is a preferred fuel source over coal; because equivalent amount of oil produces more kilowatts of energy than coal. It also burns cleaner, producing about 50 percent less sulfur dioxide. However, the availability of crude oil is limited in India and we depend on other nations to import oil from, thus Indian energy sector is dependent on coal/thermal power plants.
Oil recovery process
Primary Stage – Primarily, the oil is extracted by the normal reservoir pressure, which gush out naturally. 30% oil recovery is done by this method
Secondary Stage – in secondary stage hot water, natural gas and steam is injected to increase the pressure into the reservoir around the well which force oil to come out due to capillary action. This water forces the remaining oil toward the area of the well. Additional 10-15% of oil can be extracted by this method
Tertiary Stage – the tertiary stage involves pumping super heated steam or combustion to reduce the viscosity of oil, which generally remain adhered to the impervious stone surface. Additional 10-15% of oil can be recovered at this stage of extraction.
The injection tubes and process can be well understool through the diagrams given with the text. In total 50-60% oil recovery can be done by primary, secondary or tertiary process.
Natural gas production is often a by-product of oil recovery, as the two commonly share underground reservoirs. It is a mixture of gases, the most common being methane (95%). It also contains some ethane, propane and butane. Natural gas is usually not contaminated with sulphur and is therefore the cleanest burning fossil fuel.
Most natural gas was created over time by two mechanisms: biogenic and thermogenic.
Biogenic gas is created by methanogenic organisms in marshes, bogs, landfills, and shallow sediments. Thermogenic gas is created deeper in the earth, at greater temperature and pressure from buried organic material
After recovery, propane and butane are removed from the natural gas and made into liquefied petroleum gas (LPG). In developed countries, natural gas is used primarily for heating, cooking, and powering vehicles. It is also used in fertilizer industry for process of making ammonia fertilizer.
Oil shale and tar sand
Thes are some lesser used crude oil products. Oil shale is a rock, and it doesn’t contain oil. It’s a solid organic compound Kerogen which is tightly packed in clay, mud and silt.
Tar sands are grains of sand containing thick, viscous, soluble organic liquids called bitumen
Calorific Value of different non-renewable energy resources
The table give the approximate calorific value of different conventional fuels used by us in our day to day life. The unit given in K Cal per Kg is given for solid fuels; can be used as Kcal / lt for liquid fuel (petroleum) and K Cal/m3 for gaseous fuels(natural gas).
The calorific value of coal can varie from 3500 – 7000 K Cal / kg for different variety of coals. But, only energy value is not our concern; one of the biggest concern is the green house effect (GHG) of these fuels and also the pollution from respective fuel. For example coal gives oxides of sulphur, wood gives smoke, carbon monoxide and soot particle which all have negative effect on human health and environment.
GHG Impact of Energy Resources
Green House Gas Impact of Energy Resorces
The fuels give specific amount of CO2 on combustion that helps in calculating its carbon footprints. The amount of CO2 produced when a fuel is burned depends on the carbon content of the fuel. The heating value mainly depends on C and H content of fuel which combine with Oxygen during combustion. Water and various elements like sulfur and other non-combustible elements reduce the heating value and increase the CO2 to heat content of fuel. For example coal (anthracite) produce 228 pounds of CO2 per million BTU of energy however coal (bituminous) emit 205 due to variation in sulfur content. Gasoline produce 157 and natural gas produce 117 pound of CO2 per million BTU of energy.
EIA related to Oil and natural gas projects
Petroleum projects go through lot of processing starting from exploration to distillation and then pipeline for transport process. Most of the projects need approval from Central Government due to massive impact on environment; sometimes multi State approval is required when the pipeline goes through the premises of various States. The details of the same are given in the figures from EIA notification, Govt. of India.