Generation of Eco-friendly Steam in Power Plants P M V Subbarao Professor Mechanical Engineering Department Generation of Entropy to Generate Most Eligible Steam …..

Cost to Benefit Ratio Analysis of Rankine Cycle

Heat Rate: An International Standard The term “heat rate” simply refers to energy conversion efficiency, in terms of “how much energy must be expended in order to obtain a unit of useful work.” In a combustion power plant, the fuel is the energy source, and the useful work is the electrical power supplied to the grid. Because “useful work” is typically defined as the electricity, engineers tend to work with the net plant heat rate (NPHR). Units: kJ/kW-hr or kCal /kW-hr

Method of Calculation Net Plant power output : Pnet in kW Fuel consumption rate: mfuel kg/hr Higher heating value or higher calorific value: HHV in kJ/kg

Economics of Flow Steam generation

Economics of Flow Steam generation Supercritical Steam Generation Subcritical Flow Boiling Pump Exit

Natural Circulation Boiler Dry Steam to Super heaters Pump Exit Wet Steam Hot Water

Forced Circulation Boiler Dry Steam to Super heaters Pump Exit Wet Steam Hot Water Recirculation Pump

Once Through Boiler Dry Steam to Super heaters Hot Water Pump

Once Through Subcritical Steam Generator Once-through tangential fired Max. continuous rating: 520 kg/s Max.Steam temperature outlet: 540°C Live steam pressure outlet: > 18.3 MPa

Super Critical Nuclear Reactor

Ranking Cycle using Solar Thermal Energy Steam at a pressure of 23.5 MPa and 570° C

Clues to Generate High Economy and Eco-friendly Steam

Constant Pressure Steam Generation Process Theory of flowing Steam Generation

Selection of Steam Generation Pressure in A Rankine Cycle T C v, m3/kg

Entropy, x=s : A Measure of State of Matter So (J/K•mol) H2O(liq) 69.95 H2O(gas) 188.8 For a given substance S (gaseous state) > S (liquid state) > S (solid state)

Entropy and Order of Molecules of Matter S˚(Br2 liq) < S˚(Br2 gas) S˚(H2O solid) < S˚(H2O liquid)

Entropy, S : Molecular Complexity Increase in molecular complexity generally leads to increase in S.

Standard Molar Entropies

Entropy and Temperature S increases slightly with T S increases a large amount with phase changes

Entropy Change during a Reversible Process From the definition of the entropy, it is known that Q=TdS during a reversible process. The total heat transfer during this process is given by Qreversible =  TdS Therefore, it is useful to consider the T-S diagram for a reversible process involving heat transfer T S On a T-S diagram, the area under the process curve represents the heat transfer for a reversible process A reversible adiabatic process

Process : h-s Diagram : Mollier Diagram Enthalpy-entropy diagram, h-s diagram: it is valuable in analyzing steady-flow devices such as turbines, compressors, etc. Dh: change of enthalpy from energy balance (from the first law of thermodynamics) Ds: change of entropy from the second law. A measure of the irreversibilities during an adiabatic process. Ds Dh h s

Enthalpy Vs Entropy Diagram

Constant Pressure Steam Generation Process Theory of flowing Steam Generation Constant Pressure Steam Generation: A clue to get high temperature with same amount of burnt fuel

Steam Generation : Expenditure vs Wastage Vapour h mfuel Liquid +Vapour Liquid x

Steam Generation At High Pressure x=s

Analysis of Steam Generation at Various Pressures Specific Pressure Enthalpy Entropy Temp MPa kJ/kg kJ/kg/K C 1 3500 7.79 509.9 2 5 7.06 528.4 3 10 6.755 549.6 4 15 6.582 569 20 6.461 586.7 6 25 6.37 602.9 7 30 6.297 617.7 8 35 6.235 631.3

Fuel Savings during Steam Generation   Specific Temp Pressure Enthalpy Entropy C MPa kJ/kg kJ/kg/K 575 5 3608 7.191 10 3563 6.831 12.5 3540 6.707 15 3516 6.601 17.5 3492 6.507 20 3467 6.422 22.5 3441 6.344 25 3415 6.271 30 3362 6.138 35 3307 6.015

Law of Nature Behavior of Vapour at Increasing Pressures Reversible nature of substance at a given temperature All these show that the irreversible behavior of a fluid decreased with increasing pressure.

Reduction of Wastage

Less Fuel for Creation of Same Temperature

The Training for High Altitude Trekking

Classification of Rankine Cycles

Parametric Study of Rankine Cycle h P max

Specific Volume vs Temperature @15MPa @35MPa

Parametric Study of Rankine Cycle 23.5MPa 22MPa 18MPa 10MPa 6MPa 3MPa h 1MPa Tmax

Reheating : A Means to implement High Live Steam Pressure Supercritical 593/6210C 593/5930C 565/5930C 565/5650C 538/5650C Improvement in Efficiency, % 538/5380C