๐ฅ
Module 3 ยท Thermal Plant Continuation: Cooling Water & Fuels
The steam circuit converts water to superheated steam via the boiler and superheater, drives the turbine, then condenses back via the cooling water circuit. Fuels (coal, oil, gas) provide the input thermal energy.
Steam Circuit Recap
$$\text{Boiler: water} \rightarrow \text{high-pressure wet steam}$$
$$\text{Wet steam} \xrightarrow{\text{Superheater}} \text{Superheated steam}$$
$$\text{Superheated steam} \rightarrow \text{Main valve} \rightarrow \text{Turbine}$$
$$\text{After turbine: steam} \rightarrow \text{Condenser} \rightarrow \text{Feed water}$$
Cooling Water Circuit
$$Q_{cooling} = \dot{m}_w c_p (T_{out} - T_{in}) = Q_{condenser} = \dot{m}_s(h_2 - h_3)$$
$$\text{Sources: River / Canal / Sea / Cooling tower}$$
$$\text{Water passed through screens to remove debris}$$
Fuels Used in Thermal Plants
| Type | Examples | Calorific Value |
|---|---|---|
| Solid | Coal, wood, peat | 15,000โ35,000 kJ/kg |
| Liquid | Fuel oil, diesel | โ 43,000 kJ/kg |
| Gas | Natural gas, producer gas | โ 55,000 kJ/mยณ |
๐ฅ Cooling Water & Fuel Comparison
COOLING WATER SOURCE
River: Once-through cooling. Water drawn from river, passed through screens, used in condenser, returned at higher T. Cheapest but limited by river flow & thermal pollution limits.
FUEL COMPARISON
Solid (Coal)
15โ35 MJ/kg
๐ฎ๐ณ Most used in India
Liquid (Oil)
โ 43 MJ/kg
Gas (NG)
โ 55 MJ/mยณ
Q COOLING CALCULATOR
โ๏ธ
Module 3 ยท Classification of Coal
Coal is classified into grades based on carbon content, moisture, volatile matter, and calorific value. Grades progress from Peat (lowest) to Super Anthracite (highest). India mostly uses Bituminous coal (Gondwana coal fields).
Coal Grade Ranking (Worst โ Best)
$$\text{Peat} < \text{Lignite} < \text{Sub-bituminous} < \text{Bituminous} < \text{Semi-bituminous}$$
$$< \text{Semi-anthracite} < \text{Super anthracite}$$
Enthalpy of Combustion by Grade
$$\text{Peat: } 3{,}000\;\text{kJ/kg} \quad (\text{moisture } 60\text{โ}90\%)$$
$$\text{Lignite: } 13{,}800\text{โ}17{,}600\;\text{kJ/kg} \quad (\text{moisture } 30\text{โ}50\%)$$
$$\text{Sub-bituminous: } 18{,}000\text{โ}23{,}000\;\text{kJ/kg} \quad (\text{volatile } 35\text{โ}45\%)$$
$$\text{Bituminous: } 23{,}000\text{โ}34{,}000\;\text{kJ/kg} \quad (\text{low moisture})$$
$$\text{Semi-bituminous: } 27{,}000\text{โ}35{,}000\;\text{kJ/kg}$$
$$\text{Semi-anthracite: } 33{,}500\text{โ}34{,}750\;\text{kJ/kg} \quad (\text{highest C\%})$$
$$\text{Super anthracite: Very hard, shiny black surface}$$
Rankings
$$\%C:\;\text{Peat} < \text{Lignite} < \text{Sub-bit} < \text{Bituminous} < \text{Anthracite}$$
$$\%H_2O:\;\text{Peat}(60\text{โ}90\%) > \text{Lignite}(30\text{โ}50\%) > \text{Anthracite}(\sim3\%)$$
โ๏ธ Coal Grade Visualization
CALORIFIC VALUE COMPARISON (kJ/kg)
COAL GRADE IDENTIFIER