Why is there water at the boiler outlet?

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Years of field research have shown that too many steam users suffer from severe water in the boiler outlet, which significantly impacts production. What exactly is the reason? Today, Fred will share points one and two with everyone. 1) Large fluctuations in steam demand: Among industrial steam users, there are significant fluctuations in steam demand, with the amount of steam used sometimes increasing by more than 15% in an instant. For example, situations such as the rapid opening of the steam supply valves for starting up machines or equipment in a workshop, or the sudden activation of additional production lines in that workshop, can cause a sudden increase in steam volume of over 15%. For those enterprises that operate during the day and stop at night, the problem becomes more severe every time they turn the equipment on and supply steam. When the steam consumption increases by more than 15% suddenly, first, since the boiler’s combustion system is unable to respond quickly enough to meet this sudden increase in steam demand, the steam pressure inside the boiler drops rapidly, resulting in water being carried in the outlet steam. Secondly, when the pressure inside the furnace decreases, part of the saturated water vaporizes rapidly, resulting in the formation of numerous bubbles in the boiler water. The level of the boiler water rises quickly, which causes a large amount of boiler water to be drawn into the steam pipeline, leading to steam containing a significant amount of water at its outlet. The rapid decrease in boiler water increases the steam content in the vapor mixture within the boiler tubes, which can lead to excessive heating of these tubes and affect their lifespan. Furthermore, since a large amount of boiler water is carried away by the steam, an increase in boiler make-up water is actually required. However, the level sensor detects an increase in liquid level, which causes the control unit to issue an incorrect command to reduce the amount of boiler make-up water. As a result, the boiler’s water level drops sharply, leading to a low-level alarm and the shutdown of the boiler. For modern, compact, and efficient boilers, the problem is even more severe. This is because these boilers have a smaller steam space; even a slight increase in the steam load can cause a significant drop in pressure inside the furnace. Additionally, since the water level in the furnace is close to the steam outlet, compared to older large-scale boilers, an instantaneous increase in the steam load leads to more severe steam carrying water. 2) When the boiler operates at low pressure, bubbles rising from the boiler water surface carry along some of the boiler water. First, when the bubble ruptures, or in other words, when the water film surrounding the bubble breaks, the steam inside will carry that broken water film along at high speed into the steam space. At the same time, the bursting of bubbles creates voids on the liquid surface instantly, and the water surrounding it rushes into these voids from various directions, resulting in water impacts and splashes; these splashed water droplets can easily enter the steam space. The size of the bubbles is directly related to the pressure inside the boiler. When the boiler operates at low pressure, the specific volume of steam increases, resulting in more and larger bubbles forming on the boiler water surface, and causing more intense fluctuations in the water level. As these bubbles burst and rise away from the water surface, they carry with them more water from the surface layer; this inevitably leads to the formation of more and larger voids, which in turn causes more intense water impact and splashing, with more water droplets entering the vapor space. Furthermore, when the boiler operates at low pressure, it increases the steam flow rate, causing more water droplets to fail to return to the surface due to gravity and instead be carried into the steam system. There are other reasons as well that cause water to be present at the outlet of steam boilers; Fred will share more details with everyone in the future.