What are the signs of uneven heating in a steam boiler?

What are the signs of uneven heating in a steam boiler??

Steam boilers are one of the commonly used boiler equipment in modern industry. The principle of a boiler is to heat water to a certain temperature, producing high-pressure steam to provide effective production power. Here are some basic facts about steam boilers.

The heating surface of a steam boiler is composed of parallel pipes. The ratio of the enthalpy increase of the working substance in a single coil to the overall average enthalpy increase is known as the thermal deviation. The thermal deviation of a boiler is mainly caused by uneven heat absorption and flow.

The reasons for the imbalance are as follows:

1.Steam boilers exhibit uneven heat absorption.

The reasons for uneven heat absorption are closely related to the burner arrangement, operating methods, and fuel type. Uneven temperature distribution in the furnace can lead to low thermal load intensity in the water-cooled walls inside the furnace. Generally speaking, when the fuel type is the same, the thermal load distribution in a liquid slag discharge furnace is much more uneven than in a solid slag discharge furnace. The thermal load in an oil furnace is more uneven than in a coal-fired furnace, and the thermal deviation in vertical tube panels is greater than in horizontal tube panels.

The uneven heat absorption of a once-through steam boiler differs from that of a natural circulation steam boiler. Natural steam boilers possess a heat compensation feature that can play a major role in reducing heat discrepancies. However, in the evaporative heating surface of a once-through steam boiler, the tubes with greater heat absorption produce more steam, leading to increased capacity and resistance, which in turn reduces the flow rate of the steam tubes. Conversely, the flow rate in weakly heated pipes increases. Therefore, the uneven heat absorption in the evaporative heating surface of a once-through steam boiler not only causes heat discrepancies but also amplifies them through the influence of uneven flow rates.

2.The steam boiler's flow is uneven.

Flow resistance varies among parallel heated surface pipes, pressure changes along the length of the distribution header, and different head pressures between pipes can all lead to uneven flow distribution.

The impact of flow resistance on thermal deviation varies due to the differing structure, quality, length, diameter, roughness, and curvature of steam pipes, resulting in varying flow resistance. Under the same pressure difference, resistance can cause uneven flow distribution.

The impact of head pressure on thermal bias in vertical riser bundles is significant. Due to the large height of the bundles, when the parallel tubes are heated unevenly, there is a considerable density difference. Therefore, the influence of head pressure must be considered. When the heat load on an individual tube is high, the flow velocity of the tube decreases. However, due to the reduction in both the working fluid density and head pressure, the flow rate increases. Consequently, high head pressure aids in reducing thermal bias.