A：Correct control of steam pressure is often critical in steam system design because steam pressure affects steam quality, steam temperature, and steam heat transfer capability. Steam pressure also affects condensate discharge and secondary steam generation.
For boiler equipment suppliers, in order to reduce the volume of boilers and reduce the cost of boiler equipment, steam boilers are usually designed to work under high pressure.
When the boiler is running, the actual working pressure is often lower than the design working pressure. Although the performance is low pressure operation, the boiler efficiency will be increased appropriately. However, when working at low pressure, the output will be reduced, and it will cause the steam to “carry water”. Vapor carryover is an important aspect of steam filtration efficiency, and this loss is often difficult to detect and measure.
Therefore, boilers generally produce steam at high pressure, ie, operate at a pressure close to the design pressure of the boiler. The density of high-pressure steam is high, and the gas storage capacity of its steam storage space will also increase.
The density of high-pressure steam is high, and the amount of high-pressure steam passing through a pipe of the same diameter is greater than that of low-pressure steam. Therefore, most steam delivery systems use high pressure steam to reduce the size of the delivery piping.
Reduces condensate pressure at the point of use to save energy. Reducing the pressure lowers the temperature in the downstream piping, reduces stationary losses, and also reduces flash steam losses as it discharges from the trap to the condensate collection tank.
It is worth noting that energy losses due to pollution are reduced if the condensate is discharged continuously and if the condensate is discharged at low pressure.
Since vapor pressure and temperature are interrelated, in some heating processes, the temperature can be controlled by controlling the pressure.
This application can be seen in sterilizers and autoclaves, and the same principle is used for surface temperature control in contact dryers for paper and corrugated board applications. For various contact rotary dryers, the working pressure is closely related to the rotation speed and heat output of the dryer.
Pressure control is also the basis for heat exchanger temperature control.
Under the same heat load, the volume of the heat exchanger working with low-pressure steam is larger than that of the heat exchanger working with high-pressure steam. Low pressure heat exchangers are less costly than high pressure heat exchangers due to their low design requirements.
The structure of the workshop determines that each piece of equipment has its maximum allowable working pressure (MAWP). If this pressure is lower than the maximum possible pressure of the supplied steam, the steam must be depressurized to ensure that the pressure in the downstream system does not exceed the maximum safe working pressure.
Many devices require the use of steam at different pressures. A specific system flashes high-pressure condensed water into low-pressure flash steam to supply other heating process applications to achieve energy-saving purposes.
When the amount of flash steam generated is not enough, it is necessary to maintain a stable and continuous supply of low-pressure steam. At this time, a pressure reducing valve is needed to meet the demand.
The control of steam pressure is reflected in the lever links of steam generation, transportation, distribution, heat exchange, condensed water and flash steam. How to match the pressure, heat and flow of the steam system is the key to the design of the steam system.