How is the outlet pressure of a steam boiler controlled?
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How is the outlet pressure of a steam boiler controlled? Is evaporation rate related to outlet pressure?
The pressure at the outlet is controlled, first, by the main pipeline network, and second, by calculating the calorific value
With constant pipeline resistance, the evaporation rate is proportional to the outlet pressure.
It doesn’t seem to be proportional; at most it’s inverse proportional! This issue has indeed not been considered in detail. Logically, without taking the conditions of the piping system into account, the evaporation rate should be inversely proportional to the outlet pressure – and this holds true under the condition that the heating load of the boiler remains constant. But conversely: if a boiler rated at 2.45 MPa is used at a reduced pressure, say 1.25 MPa, can the excess heat load be converted into an increase in evaporation volume? But there are requirements regarding the design of boilers; they can only operate at 110% of their rated capacity. So if a boiler designed for high pressure is used at low pressure, the excess energy generated must surely exceed 110% of its rated capacity! Looking forward to others' insights.
Whether it is proportional or not should be related to the gas consumption, that is, the load. When the boiler’s output remains constant, the greater the load, the lower the pressure. Conversely, when the load is constant, the greater the evaporation rate, the higher the boiler’s output and the higher the outlet pressure as well
I’m sorry, but I don’t think it has anything to do with the pipeline resistance or the heating load.
Same question: is the pipeline network pressure the pressure at the boiler outlet after passing through the pressure reducing valve?
The boiler outlet pressure is not a control parameter, but an adjustment parameter. As the evaporation rate increases, the valve opens wider, the resistance decreases, and the pressure drop from the boiler outlet to the user is reduced ； If the steam parameters are insufficient, the boiler needs to add more fuel to raise the steam pressure to an acceptable level. When the amount of steam used by the user decreases, the boiler outlet valve is closed, resulting in a reduction in flow rate and an increase in resistance; consequently, the pressure at the boiler outlet rises. By adjusting (reducing) the fuel supply, the boiler pressure will gradually drop back to the normal level for the given load. The specific adjustment process requires a lead time for load adjustment.
Boilers generally use three-shot control. However, the export pressure depends on the consumption of the steam network. This post was last edited by julius6054 on 2008-10-17 00:35.]
When the gas consumption in the steam network remains constant, the pressure at the boiler outlet depends only on the boiler’s output – that is, its evaporation rate.
The outlet pressure of the boiler is related to the heat absorbed by the heating elements (which can also be referred to as the evaporation rate), the resistance in the piping system, the amount of steam consumed by the users, and the stability of the feedwater temperature. When the evaporation rate is greater than the consumption rate, and subject to ensuring the needs of the users, the steam vent valve of the drum can be used to control the drum pressure. If the system is shut down and no external steam is required, the main steam valve can be closed and control can be achieved directly using the vent valve.