Optimizing Boiler Steam Consolidation: Impact of Boiler Economizer Outlet Water Temperature

Introduction:

Unlocking the full potential of boiler steam consolidation is crucial for efficient and reliable operations. In this report, we delve into the critical aspect of optimizing boiler steam consolidation by examining the impact of boiler economizer outlet water temperature. We explore the challenges posed by decentralized heat down tubes and the absence of recirculation piping, along with the implications for boiler performance. Through careful analysis and practical solutions, we address the control of outlet water temperature, the importance of stable water supply, and the prevention of steam repetition. By mastering these key factors, operators can ensure smooth and efficient steam consolidation, leading to enhanced boiler performance and overall operational success. Join us as we delve into the intricacies of optimizing boiler steam consolidation and unlocking its true potential.

The A/B boiler, a high-pressure steam pulverized coal boiler, is a crucial component of the thermal plant owned by the company. It is designed with a decentralized heat downtube, a membrane water-cooled wall, and a steam bag that enables natural circulation within the system. The combustion mode employed in the A/B boiler involves the formation of an 11/2U-type flame, which is sprayed by the front wall. With a rated output of 225 tons per hour, the A/B boiler operates at a main steam pressure of 10.6 MPa and a main steam temperature of 535°C. The primary fuel utilized in this boiler is lean coal.

The A/B boiler receives qualified demineralized water, which undergoes thorough thermal and chemical deaeration in the deaerator. Subsequently, the deuterated water is efficiently delivered to the boiler economizer through a reliable feed pump. The economizer employed in the A/B boiler is equipped with a non-boiling spiral fins economizer constructed from 20G steel pipe. For a comprehensive understanding of the boiler’s flow dynamics, please refer to Figure 1 in the boiler flow diagram section.

Problems:

One of the challenges faced by the high-pressure steam pipeline network is the integration process after a boiler failure and subsequent shutdown. When the boilers are restarted for merging into the pipeline network, it is common to experience steam surges. Consequently, steam is intermittently introduced into the network only to be promptly expelled. This issue primarily arises due to a significant drop in the high-pressure steam temperature, leading to a sharp decrease in the liquid level within the steam bag.

Cause Analysis:

The root cause of the problem can be attributed to the absence of a recirculation pipe connecting the steam packet and the boiler economizer in the design of the A/B boilers. As a result, during the initial ignition of the boiler, the boiler economizer remains devoid of any flow.

Consequently, when the feedwater in the boiler economizer, which is heated by the flue gas, surpasses the saturation temperature corresponding to the steam ladle’s pressure, steam is generated within the boiler economizer. This steam then flows through the steam pipe of the steam ladle and directly enters the superheater.

During the boiler startup process, as there is no steam flow meter installed on the air-to-air steam exhaust line, the steam production load of the boiler is estimated based on the feedwater flow rate. The feedwater flow rate serves as an indicator for assessing the steam production load.

The steam production load of the boiler is dependent on the flow rate of the boiler feed water, which is adjusted based on the level of the steam ladle. During the initial ignition phase, the thermal expansion of the water in the boiler water-cooled wall leads to a rise and subsequent fall in the liquid level of the steam ladle. Only when the liquid level of the ladle significantly decreases will the boiler commence water makeup. The amount of makeup water must be carefully balanced with the rate of evaporation to stabilize the ladle’s level. Consequently, the feedwater volume experiences fluctuations, causing corresponding fluctuations in the outlet water temperature of the boiler economizer.

Solutions:

4.1 Strictly follow the recommended pressure rise rate during pressurization:

During the boiler start-up process, it is crucial to adhere to the recommended pressurization curve to ensure smooth operations. The pressure should be increased gradually, following the designated rate. In the initial hour, the pressure should not exceed 0.5 MPa. After 3 hours, the rate of pressure increase can be adjusted. By increasing the fuel input, the evaporation rate can be augmented, leading to a stable feedwater flow.

4.2 Proper adjustment of accidental water discharge:

Due to the decentralized heating downtube design of the boiler, changes in boiler load have a significant impact on the liquid level of the steam bag and subsequently influence the makeup water requirement. To prevent excessively high outlet water temperature in the coal boiler economizer, it is advisable to increase the feed water flow as necessary. Additionally, to avoid excessively high steam bag levels, the accidental water discharge can be appropriately opened. This helps maintain a balanced relationship between water intake, evaporation, and steam bag level, ultimately enabling effective control of the coal boiler economizer outlet water temperature.

4.3 Ensure stable water supply prior to steam merging:

Before the steam merging process, it is essential to maintain a stable water supply. It is crucial not to make significant adjustments solely based on the liquid level of the steam bag. Particularly, allowing the liquid level to become excessively low can directly impact the outlet water temperature of the coal boiler economizer. Therefore, maintaining a consistent and stable water supply is imperative to ensure optimal performance and prevent fluctuations in the economizer outlet water temperature.

4.4 Maintain outlet temperature below saturation temperature:

From the moment the boiler is ignited until it is seamlessly integrated into the pipeline network, it is crucial to strictly control the outlet water temperature of the boiler economizer below the saturation temperature corresponding to the pressure of the steam bag. It is essential to adhere strictly to the principle of avoiding steam generation in the non-boiling boiler economizer.

By implementing these measures, the process of incorporating the boiler’s steam into the network will become significantly smoother, minimizing the occurrence of steam surges and repetitions.

Conclusions:

The impact of boiler economizer outlet water temperature on the ramp-up process during boiler ignition and steam consolidation is significant. This effect is particularly pronounced in the A/B boiler due to its decentralized heat downtube design without recirculation piping between the ladle and the boiler economizer.

Recommendations:

1. Recirculation piping for other boilers: For natural circulation steam packet boilers with recirculation lines but without centralized heat descent lines, similar issues may arise, although not as prominently as in the A/B boiler. It is recommended to implement a process of desuperheating water input during ignition and pressurization, followed by unlisting and subsequent reintegration. This can help mitigate adverse effects on the boiler, especially in the vicinity of steam merging.
2. Strict temperature control: Maintain the outlet water temperature of the boiler economizer below the saturation temperature corresponding to the pressure of the steam bag. This will prevent superheater over-temperature and reduce the need for repeated operation of desuperheating water.
3. Attention to boilers with minimal air exhaust vapor: Pay special attention to boilers with relatively small amounts of air exhaust vapor. These boilers may require additional measures to ensure stable operation and avoid issues related to steam repetition.

By implementing these recommendations, it is possible to optimize boiler performance, enhance stability during ignition and steam consolidation, and mitigate adverse effects such as superheater over-temperature and repeated operation of desuperheating water.

During the boiler ignition process and the subsequent merging of main steam into the pipeline network, the boiler undergoes a transition from a cold state to a hot state. It is crucial to adhere to the operating procedures and ensure accurate control of various details throughout this process. By implementing proper control measures and closely following the procedures, the boiler operation can be optimized, resulting in a smoother and more efficient operation overall. Attention to detail and adherence to procedures are key to achieving optimal performance and stability in boiler operations.

 [Source] Fan shijie, Nitrogen Fertilizer & Syngas, #11 2021-11

FAQ

Here are some common questions and their corresponding answers related to the topic of optimizing boiler steam consolidation and the impact of boiler economizer outlet water temperature:

Q: What is boiler steam consolidation?

A: Boiler steam consolidation refers to the process of efficiently integrating the steam produced by boilers into a pipeline network for various industrial applications.

Q: How does boiler economizer outlet water temperature affect steam consolidation?

A: The outlet water temperature of the boiler economizer plays a crucial role in steam consolidation. If not controlled properly, fluctuations in outlet water temperature can lead to steam surges, decreased steam quality, and instability in the steam consolidation process.

Q: What challenges are associated with decentralized heat downtubes and the absence of recirculation piping?

A: Decentralized heat downtubes and the lack of recirculation piping can result in fluctuations in water flow, temperature imbalances, and difficulties in controlling outlet water temperature, thereby affecting steam consolidation efficiency.

Q: How can the outlet water temperature of the boiler economizer be controlled?

A: The outlet water temperature can be controlled by regulating the fuel input, adjusting the feedwater flow rate, and closely monitoring the saturation temperature corresponding to the steam ladle pressure.

Q: Why is stable water supply crucial for steam consolidation?

A: Maintaining a stable water supply is essential for smooth steam consolidation. Fluctuations in water supply can lead to inconsistent steam generation, decreased steam quality, and disruptions in the steam consolidation process.

Q: How can steam repetition be prevented during steam consolidation?

A: Preventing steam repetition requires careful monitoring of water levels, maintaining appropriate water levels in the steam bag, and controlling the water intake and evaporation rates to achieve a balanced system.

Q: What are the benefits of optimizing boiler steam consolidation?

A: Optimizing boiler steam consolidation results in enhanced boiler performance, improved steam quality, increased efficiency, and reduced operational issues such as steam surges and temperature imbalances.

Q: What measures can be taken to optimize boiler steam consolidation?

A: Measures include following recommended pressurization rates, implementing recirculation piping, controlling outlet water temperature, maintaining stable water supply, and closely monitoring and adjusting feedwater flow rates.