Functions of the Startup System in Supercritical Circulating Fluidized Bed Once-Through Boilers

The startup of a supercritical circulating fluidized bed once-through boiler represents a complex and critical process that ensures the safe and efficient operation of the entire system. This article delves into the key functions of the startup system in such boilers, highlighting its significance for various aspects of the boiler's operation.

1. Establishing Starting Pressure and Flow

The initial phase of the startup process is the establishment of the starting pressure and flow. Accurate control of these parameters is essential for preventing operational failures and ensuring a smooth transition into full operation. The fluidized bed boiler begins by pressurizing the system to the operational requirements. The fluidized bed itself needs to maintain a consistent flow to maintain the bed's dynamics. This is achieved through the controlled introduction of heating and pressure, which is managed via the startup system's components such as the burner and the primary air supply.

2. Boiler Cold and Hot Cleaning Conditions

During the startup process, maintaining the cold and hot cleaning conditions is vital for extending the life and operational efficiency of the boiler. In the cold condition, the startup system ensures that the bed is properly heated and that any debris or residues from previous operations are removed. This is accomplished through a systematic process that may involve hot-treating the bed to raise it to operational temperatures before introducing the combustion gases. In the hot condition, the cleaning process continues by removing any post-combustion residues that could otherwise affect heat transfer and reduce efficiency. This is typically achieved through specialized cleaning cycles that are integrated into the startup and operational phases of the boiler.

3. Recovering Heat and Working Fluid

One of the critical functions of the startup system in a supercritical circulating fluidized bed once-through boiler is the recovery of heat and working fluid. During the startup, the system must capture and reuse as much heat as possible to minimize energy losses and enhance overall efficiency. This is achieved through heat exchangers and heat recovery steam generators (HRSG) which capture the residual heat from the combustion gases. Additionally, the working fluid, often water or a high-pressure fluid, is recycled through the system to maintain thermal stability and efficiency. Proper heat recovery ensures that the startup process is as efficient as possible, reducing both the time and the amount of energy required to reach full operating temperatures.

4. Auxiliary Treatment of Working Fluid Expansion

Another critical function of the startup system is the auxiliary treatment of working fluid expansion. As the system transitions from a cold to a hot state, the working fluid expands, and this expansion must be managed to prevent pressure surges and potential damage to the system. The startup system is equipped with expanders, accumulators, and relief valves that manage the pressure changes. These systems ensure that the fluidized bed remains at the optimal operating pressure, allowing for safe and controlled expansion of the working fluid. Proper management of this process is crucial for both safety and efficiency, reducing the risk of failures and optimizing the performance of the boiler.

5. Meeting Requirements for Steam Flow Pressure and Temperature in Steam Turbine

Perhaps the most critical function of the startup system is its role in ensuring the steam flow pressure and temperature meet the requirements of the steam turbine. The steam turbine is a key component in the power generation process, and its performance relies heavily on the quality and quantity of the steam supplied by the boiler. The startup system must precisely control the steam temperature and pressure, ensuring that the steam is stable and meets the turbine's specifications. This is achieved through a series of valves, steam drums, and control systems that regulate the steam flow, allowing for smooth and efficient operation during the startup process.

6. Security Protection

The startup system also plays a crucial role in ensuring the security and safety of the boiler and its operation. Safety is a primary consideration during the startup process, as any errors or mishaps can lead to significant damage or even explosions. The startup system is designed with multiple safety features, such as interlocks, relief valves, and alarms that detect and respond to potential issues. These functions help prevent runaway conditions, ensuring that the boiler operates within safe parameters. Regular maintenance and testing of these safety systems are essential for maintaining the safety of both the startup process and the entire boiler system.

Conclusion

In conclusion, the startup system in a supercritical circulating fluidized bed once-through boiler is a complex and multifaceted component that serves several critical functions. From establishing starting conditions to ensuring the safety and security of the system, the startup system plays a pivotal role in the efficient and reliable operation of the boiler. Understanding and optimizing these functions can lead to significant improvements in the performance and efficiency of the entire system, enhancing both economic and environmental benefits.