Optimizing Heat Rate in Thermal Power Plants: The Role of Early Coal Mill Activation

Effective management of coal mills and understanding the heat rate in thermal power plants are crucial for enhancing overall efficiency and reducing operational costs. This article explores the significance of activating coal mills as early as possible during the loading process, while considering the heat rate optimization in thermal power plants.

Understanding Heat Rate in Thermal Power Plants

The heat rate in a thermal power plant is a measure of fuel efficiency, defined as the amount of heat energy required to produce one kilowatt-hour (kWh) of electricity. In the context of coal-based power plants, the heat rate is highly dependent on the fuel quality and combustion efficiency.

During the start-up phase of a thermal power plant, there are several critical considerations that must be addressed to ensure an optimized heat rate. One of the key factors is the ignition temperature of the coal, which is a significant parameter during the light-up process. Activating the coal mill immediately can lead to unburnt coal and increased unburnt carbon, thereby decreasing the overall heat rate.

The Importance of Calorific Value and Cost Efficiency

The calorific value of the fuel plays a crucial role in determining the cost efficiency of the power plant. In this context, light oil diesel (LDO) is often used for light-up due to its high calorific value. However, the high cost of LDO compared to coal can significantly impact the overall operational expenses.

Typically, LDO has a calorific value of around 10,700 kcal/kg, while E or F grade coal has a calorific value of approximately 3,000 to 4,000 kcal/kg. Considering these values, LDO is about three to four times more calorifically efficient than coal. However, the cost of LDO is also disproportionately higher—often ranging from 45 to 55 times the cost of coal. Coal is typically priced between 1 to 1.2 Rs/kg, while LDO can cost between 50 to 55 Rs/kg.

During the light-up process, the consumption of LDO is relatively low, but when it’s used, it significantly impacts the overall operational costs. Therefore, it is essential to use LDO judiciously, primarily for critical start-up phases when the boilers are not yet firing coal.

Optimizing the Loading Process

The optimal strategy involves balancing the activation of coal mills and the use of cut oil guns. Cutting down the oil pressure and increasing coal input based on the loading curve can help in achieving a more efficient heat rate. Different boilers and equipment may respond differently under varying circumstances, making it crucial to tailor the approach based on the specific characteristics of the plant.

One effective way to manage the process is by closely following the boiler loading curve, which is typically established based on the calorific value of the fuel and the pressure-temperature relationships. This approach allows for a more precise control over the combustion process, leading to better heat rate optimization.

Real-World Application: Case Studies

A practical example is provided where a substantial reduction in oil consumption can be achieved by activating the coal mill earlier. This early activation not only reduces the pressure in the oil gut but also lowers the overall oil consumption. By following a calculated light-up strategy, the plant can switch from LDO to coal more efficiently, thereby reducing operational costs.

Moreover, the use of multi-level burner configurations and the strategic placement of coal guns can further enhance the combustion efficiency. By carefully monitoring the loading curve and adjusting the parameters accordingly, the plant can achieve a more consistent and efficient heat rate.

In conclusion, the optimization of heat rate in thermal power plants involves a meticulous balance between fuel efficiency and operational costs. Early activation of coal mills, along with careful monitoring and adjustment, can significantly contribute to improved heat rate and cost savings.