Boiler drum level measurement system

The following 3D diagram is from the process engineer of Sissen Automation. The boiler drum level measurement analysis comes from the joint explanation of the field service engineer and the production technology department. I hope it can help everyone in boiler drum level measurement.

Keeping the boiler drum liquid level within the normal range is an important safety indicator for boiler operation. The drum liquid level will change frequently due to changes in load, combustion conditions and feed water flow. As we all know, excessively high or drastic fluctuations in the liquid level will cause deterioration of steam quality and water carryover, resulting in salt deposition on the heating surface. In severe cases, it will cause water shock vibration of the turbine and damage to the blades. A low liquid level will cause sewage discharge failure, and the addition of chemicals into the steam in the furnace may even cause steam carryover in the downcomer, affecting the boiler water circulation condition and causing large-scale explosion of the boiler tube. The above-mentioned vicious accidents caused by problems in the measurement and control of the drum liquid level occur from time to time, seriously affecting the safety of the operation of thermal power plants.

During boiler operation, we monitor and control the drum liquid level through the liquid level measurement system. When the drum liquid level exceeds the normal operating range, the alarm system will send out an alarm signal, and the protection system will immediately take necessary protective measures to ensure the safety of the boiler and steam turbine. Therefore, the boiler drum liquid level measurement system is an extremely important system for the safe operation of the unit.

Schematic diagram of boiler drum level measurement system

 

 

Factors Affecting Drum Liquid Level Change

The liquid level of the boiler changes frequently during operation. The main reasons for the change in liquid level are external and internal disturbances of the boiler. When external and internal disturbances occur, the material balance relationship of the evaporation equipment (i.e., the balance relationship between evaporation amount and feed water amount) will be destroyed, or the working fluid state will change (when the boiler pressure changes, the specific volume of water and steam changes), thus causing the drum liquid level to change. The severity of the change in the drum liquid level is not only related to the size of the disturbance, but also to the disturbance speed.

Basic requirements for boiler drum level measurement system

According to the importance of boiler drum level measurement and the characteristics of measurement technology, the boiler drum level measurement system should at least meet the following basic requirements:

1. Good accuracy

As we all know, the boiler drum level is not a parameter that needs to be precisely controlled compared to parameters such as main steam pressure and temperature. Under normal circumstances, the deviation of the two drum level measurement indications within 30mm is acceptable. And it is not very difficult to maintain such accuracy under normal conditions. However, since the drum water level measurement object is very complex, and the drum water level measurement adopts the connecting tube or differential pressure measurement principle, when the drum pressure and measurement reference conditions change, it will cause a very large error that far exceeds the above requirements. Therefore, for a long time, ensuring the accuracy of drum water level measurement has always been a difficult and key issue before us. Guangzhou Xisen Automation Control Equipment Co., Ltd. has solved this difficulty through the differential pressure measurement principle!

2. Good maintainability

The maintenance of the boiler drum liquid level measurement system should be simple, the maintenance workload should be as little as possible, and it should be convenient to carry out protection linkage tests of online actual water level signals, etc.