In the present scenario, due to the integration of Solar PV on large scale to the grid, thermal power plants are forced to run at part load. It is also important to understand that thermal power plant operations at part load operates close to its design performance parameters at partial loads using simulation. This can be done by using simulation tools for optimum operation and compares with actual measurements.
Amongst various energy-intensive sectors, thermal power plants rank first in terms of total energy consumption and its percentage cost. Improving energy efficiency has become an extremely economical option and an intensely focused drive for profitability. That means, operating a power plant at the lowest heat rate and optimum self-consumption ensures high returns. At the same time viability of future power plants with reduced emissions can meet environmental regulations. For sustainable economic development of the power sector, the availability of reliable and affordable power is critical.
The National Mission for Enhanced Energy Efficiency (NMEEE) is a powerful initiative of the Government of India in meeting the global challenge of climate change. The NMEEE derived regulatory instrument Perform, Achieve and Trade (PAT) aims to reduce specific energy consumption in energy-intensive industries. The PAT cycle 1 covered 144 thermal power plants which accounted for the energy consumption of 104.5 million tonnes of oil equivalent, while the end of cycle achievement in a reduction in energy consumption is 3.06 million tonnes of oil equivalent (3%). The majority of thermal power plants implemented the use of quality coal (blending or washed coal) and the use of variable speed drives to minimize auxiliary power consumption. Subsequent PAT cycles added another 80 thermal power plants under the PAT scheme.
There are numerous methods for improving the efficiency of thermal power plants to bring down the generation cost and maximize power generation levels. One example is of Integrated Gasification Combined Cycle (IGCC) technology, where coal is converted into synthetic gas (or syngas) instead of being combusted as done in conventional pulverized coal-fired power plants. Thermal efficiency is the main factor that puts IGCC above the conventional pulverized coal technology (it could go up to 60%). This is a substantial improvement over the 35% efficiency of pulverized coal plants. Furthermore, with the continuing drive to reduce power plant emissions, coal-fired power plants have been moving to ultra-supercritical (USC) steam conditions. Advanced ultra-supercritical pulverized coal combustion (Advanced USC or A-USC) is a further development of USC. By using A-USC steam conditions of 700°C to 760°C at pressures of 30 MPa to 35 MPa, manufacturers and utilities are working to achieve efficiencies approaching 50% (LHV) and higher.
In the existing conventional power plants, based on steam condition and site location, the overall efficiency can be improved by increasing the efficiency of various components (both stationary and rotating) through which the steam flows. Such analysis can be carried out using a computational Fluid Dynamics (CFD) technique, which is a cutting-edge tool to improve the overall efficiency of turbo-machines. In general, a variety of fluid flow related analysis relevant to power plants such as pressure drop and energy losses in steam turbine components (e.g., casings, blades, cross-over pipes, exhaust hoods, valve chests, inlet sections), efficiency and discharge characteristics of pumps, head and efficiency for various discharge and speeds for compressors, discharge characteristic and power consumption of industrial fans (induced and forced draught), the pressure drop across pressure reduction stations and control valve, will help in identifying operational efficiency of equipment and steam cycle components.
The individual thermal power plant units are designed for a specific heat rate (kCal/kWh), it is essential to run the unit close to its design heat rate. One of the vital methods to monitor the key performance parameters is by simulation tool. The simulation of the heat balance thermodynamic cycle model can be used to calculate the operating parameters at various stages of the power plant. The operating parameters obtained through simulation results indicate the plant condition concerning the original design. A comparison of calculated values and measured values will allow a deeper understanding and depending on the quality of the model used, it will allow identifying problems either in the cycle or in individual components. It is also possible to verify individual measurements or readings from the station instruments with simulation model values.
To achieve this, energy performance mapping of each plant using a simulation tool must have an effective performance monitoring of various parameters for operations. Monitoring should be in real-time and the key controllable parameters must provide more timely and rapid feedback for effective decision making. The performance of the controllable parameters not only helps in optimizing the power plant but also provides sensitive information on the technical condition of the power station. Some examples of monitoring such key parameters are cylinder efficiencies, turbine backpressure, cooling water flow, re-heater temperatures which will determine the optimum heat rate of the plant.
An even more sophisticated approach is to validate the existing set of data collected by the distributed control systems (DCS) of the thermal power plant. Data validation is a mathematical method to correct the measured values in a way that the full set of measured values fulfills all conservation laws like mass balances, energy balances, performance balances, or phase equilibrium. This comparison of measured values through station instruments and the calculated values through simulation can be used for calibration of station instruments and helps the quality of measurements.
In the present scenario, due to the integration of Solar PV on large scale to the grid, thermal power plants are forced to run at part load. It is also important to understand that thermal power plant operations at part load operates close to its design performance parameters at partial loads using simulation. This can be done by using simulation tools for optimum operation and compares with actual measurements. It is essential to utilize such tools to monitor the performance continuously with reliable data. This process helps in the identification of “hot spots” (causes for higher heat rate) in the operation of the power plant and downsizing existing higher capacity equipment with appropriate requirements in part load condition as this would be a more attractive and practical solution in terms of auxiliary optimisation and terms of profitability.
In conclusion, thermal power plants are heavily affected by downward revisions in electricity demand, and its use in industry is tempered by lower economic activity. Coal phase-out policies, the rise of renewables, and competition from natural gas lead to part-load operating and the retirement of 275 gigawatts (GW) of coal-fired capacity worldwide by 2025 (13% of the total). To limit global warming to 1.5°C above pre-industrial levels, the world would need to transform in several complex and connected ways. The ever-growing cost of fuel reduction in heat rate and auxiliary power consumption of existing power plants will lead to better resource utilization and reduced emissions.
- Dr G R Narsimha Rao, Director - Industrial Energy Efficiency Division, TERI Bengaluru
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