In our previous discussion, we explored some controllable parameters for Heat Rate, studying critical factors like fuel quality, main steam pressure, temperature, and reheat steam temperature. Today, let’s shift our focus to another set of vital controllable parameters that demand our attention, such as condenser pressure, cooling water outlet temperature, reheater spray flow, LOI and auxiliary consumption.
- Condenser pressure
Condenser operation controls more than 60% of energy losses in a power station. A key to enhancing the efficiency of a steam power plant lies in improving condenser operation towards reducing condenser pressure. This is because a lower condenser pressure allows the steam turbine to extract more energy from the steam, which results in more electricity being generated.
The condenser serves as a critical heat exchanger, cooling the steam from the turbine, facilitating its transformation back into water. A decreased condenser pressure translates to greater heat extraction from the steam, resulting in a reduced heat rate.
The optimal condenser pressure for a steam power plant will depend on several factors, including the type of power plant, the design of the steam turbine, and the operating conditions. The decision to lower condenser pressure is complex and should consider every specific case. For optimizing condenser pressure the following factors should be consider:
- Lower condenser pressure implies higher construction costs when condenser pressure is decided during prefeasibility state of the power plant. Once the plant is running, the operation should ensure the design conditions to all loads to optimize condenser performance.
- Stronger control over the steam turbine may be required at lower pressure levels.
- Detecting air in-leakages into the turbine lead to condenser common issues.
- Ensuring proper function of vacuum pumps is imperative.
- Cooling Water outlet temperature
This parameter is relevant for units operating with a cooling tower for condenser refrigeration. A lower cooling tower outlet temperature will have a positive impact on the heat rate of a steam power plant. This is because the cooling tower is more efficient to remove the heat in the condenser, having a positive impact of overall efficiency.
However, there are constraints to bear in mind when contemplating a reduction in cooling tower outlet temperature. Lower temperatures can increase the risk of scaling, mineral buildup on cooling tower components. Scaling compromises cooling tower efficiency and increases the Heat Rate. The optimal cooling tower outlet temperature for a steam power plant will depend on several factors as the thermodynamic model, the cooling tower type, and operating conditions.
The reduction of the cooling water outlet temperature should consider the following factors as well:
Here are some additional things to consider:
- Lower cooling tower outlet temperatures heighten scaling risks, routine maintenance and cleaning could solve these problems
- Building a cooling tower with lower outlet temperatures may incur higher costs.
- Vigilant monitoring of cooling tower performance is essential.
- Reheater Spray flow
Effective management of this parameter is critical in preventing turbine failures by regulating the steam temperature entering the turbine. It’s worth noting that an increased spray flow leads to a higher Heat Rate, with every additional ton per hour (t/h) of spray water causing a roughly 5 Btu/kWh rise in Heat Rate.
In some cases, the steady increase of reheater Spay flow increases is easily ignored and there is a hidden increase in Heat Rate. It is vital closely monitor the spray water flow to optimize it, using some possible strategies as follows:
- Maintain a comprehensive record of Reheater Spray Flow and steam temperatures.
Evaluate the soot-blowing procedure. - Undertake thorough cleaning of water wall surfaces during scheduled maintenance shutdowns.
- Monitor coal size in the boiler.
- Strive to align manufacturer conditions for main and reheat steam as closely as possible to mitigate equipment degradation.
- Loss of ignition or unburned carbon in ash
Higher LOI reduces boiler efficiency and increase Heat Rate. It is crucial to monitor combustion performance to optimize the fuel usage within the boiler, parameters such as particle size, primary air and secondary air contribute to optimize this parameter.
LOI, in essence, signifies the weight loss of a material when subjected to high temperatures in an oxygen-depleted environment. In the context of pulverized coal boilers, LOI represents the unburned carbon content in fly ash. A higher LOI translates to a greater presence of unburned carbon in fly ash, which can result in several issues, including: increased emissions, reduced boiler efficiency, increased wear on boiler components.
Efforts to mitigate LOI in pulverized coal boilers include various strategies:
Improving coal preparation: This involves finely milling the coal to increase its surface area, facilitating more efficient combustion. Achieving this can entail employing a more efficient coal mill or adjusting mill settings.
Optimizing combustion conditions: Fine-tuning the fuel-air ratio, air flow rate, and burner configuration is crucial. The fuel-air ratio ensures adequate oxygen for complete combustion, while air flow rate influences fuel-air mixing. Selecting the right burner configuration is equally vital.
Implementing Flue Gas Recirculation: Injecting some flue gas back into the furnace promotes LOI reduction.
Effective boiler maintenance: A well-maintained boiler exhibits superior combustion efficiency, contributing to LOI reduction.
Monitoring and controlling the combustion process: Regular monitoring and control measures help identify and rectify issues leading to elevated LOI, ensuring consistent efficiency.
- Auxiliary consumption can be a vital allied of energy savings and efficiency improvement while save emissions and the plant.
Ensuring proper monitoring and control of key parameter on the Heat Rate benefits the overall performance of the power plant, common strategies to ensure that are:
Ensuring proper monitoring and control of key parameter on the Heat Rate benefits the overall performance of the power plant, common strategies to ensure that are:
- Continues Heat Rate training of operations, maintenance, and manager staff.
- Clear and transparent information about Heat Rate and plant efficiency.
- Start a routine performance testing program for the equipment.