Discussion on the pressure of waste boiler drums
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When the boiler feedwater flow suddenly stops or decreases significantly, the drum pressure rises greatly. What are the possible reasons for this?
When the boiler feed water stops suddenly or is significantly reduced, the drum loses its source of cooling, which results in the generation of a much larger amount of steam than usual; as a consequence, the pressure rises considerably.
I believe a loss of water in the drum will cause a short-term increase in pressure; if the steam discharge valve of the drum is not closed promptly, the pressure will gradually decrease. The pressure rises because no water is supplied, and the water inside the drum is continuously heated, which causes the pressure to increase. The pressure drops because a large amount of water evaporates and is removed from the drum, resulting in a decrease in pressure. Personal opinion
What are the three or four reasons why the drum pressure rises significantly when the feedwater flow to the furnace stops suddenly or decreases only slightly? 1. The heat source is not interrupted; 2. The cold source is interrupted or its flow is reduced; 3. The control valve fails to adjust to the required opening degree due to process changes within a short time period. 4. It is difficult to achieve pre-adjustment and delayed adjustment. If the feed water to the steam drum is interrupted, it must be restored within three to four minutes; otherwise, an emergency shutdown must be initiated
When the boiler feedwater supply is suddenly stopped or reduced, the drum loses its source of cooling, and the increased evaporation rate generates a much larger amount of steam than usual, resulting in a significant rise in pressure. It would be good if it can recover in a short time; if not, it’s best to reduce the parking duration.
Cold shock interruption causes the temperature in the waste boiler to rise, gas production increases, and the pressure in the steam drum goes up; it cannot be restored in a short time, so shutdown is required! Is it related to the saturated vapor pressure? I’m not sure; please advise!
If the water supply to the drum is interrupted or is very limited, the pressure in the drum increases for the following reasons: 1. An interruption or insufficient water supply to the drum can be caused by a pump that fails to generate sufficient pressure, or by a malfunctioning water supply control valve; in such cases, it is necessary to reduce the load promptly and identify the cause. 2. The increase in drum pressure is also due to a reduction in water supply, which leads to a decrease in cooling capacity and rapid evaporation of the water inside the drum, thereby increasing the pressure. In this situation, it is important to adjust the drum pressure so that it remains within the specified range. If these issues cannot be resolved within a short time, an emergency shutdown must be carried out.
There are two reasons: 1. The feedwater temperature is generally lower than the saturation temperature; therefore, the feedwater must first go through a heating process before it can boil. A disruption in water supply means reduced cooling, which leads to an increase in steam production and a rise in pressure ； 2. After the water supply is interrupted, the liquid level in the drum drops; the saturated steam is heated by some of the heating surfaces to become superheated steam, causing its volume to expand and its pressure to rise.
It’s best to quickly find out the cause and top up the fluid; otherwise, stop the vehicle right away~ For safety reasons~
When saturated steam is heated to superheated steam, its volume expands and the pressure rises?
When the boiler feedwater supply is suddenly stopped or reduced, the drum loses its source of cooling, and the increased evaporation rate within the drum generates a much larger amount of steam than usual, resulting in a significant rise in pressure. It can be controlled through a control valve in the short term, but if the liquid level drops to such an extent that it poses a safety risk, it is still necessary to stop the operation
The steam vessel itself does not generate steam; it is merely a container for storing boiler water and for separating and concentrating steam. It is the waste boiler that actually produces steam. In cases of water supply interruption or a significant reduction in the amount of water supplied, the pressure in the steam vessel rises sharply while the liquid level drops rapidly and can no longer be maintained. The time available for handling such situations is usually only about 2 minutes. If normal operation cannot be restored, an emergency shutdown is necessary; otherwise, overheating of the waste boiler and overpressure in the steam vessel can cause serious damage to the equipment or even lead to catastrophic accidents.
A sudden interruption in boiler feed water does not immediately cause pressure fluctuations, as the pressure is determined by the heat exchange capacity of the boiler; moreover, the addition of water to the air tank has little effect on the boiler water temperature. If the operating time is long and the water volume in the boiler decreases, less steam is produced, and the pressure inevitably drops. However, in terms of safety, attention should be paid to tube dry burning and the risk of tube explosion caused by high-temperature feed water.
Is it related to the low inlet pressure of the boiler water?
Low inlet pressure is a superficial symptom; the cause of the low feed water pressure must be identified. If it cannot be found promptly, an emergency shutdown should be carried out.
Does our company’s methanol synthesis tower rely on the steam generated directly by the steam drum? Why do we still need a boiler?
Your synthesis tower is actually just a waste heat boiler
The gas heat exchanger that comes out must be a waste heat boiler, right?
Heat exchange is inevitable. You suddenly reduced the water supply. There must be too much waste steam
This is also greatly influenced by the synthesis load and the components involved; these components and the load determine the reaction rate, which in turn relates to the amount of heat released. The impact of this on the temperature and liquid level of the steam drum is easy to imagine. Of course, this is an analysis under the assumption that all other conditions are normal