Calculation of steam heat exchangers
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Operating conditions: Shell side steam: 3 MPa, 420°C; Tube side: Medium to be heated, inlet temperature 130°C, outlet temperature 180°C. 1. Normally, heat exchangers should use saturated vapor, but due to the site conditions, only this superheated vapor can be used. If one wants to improve heat transfer efficiency, it is necessary to make use of latent heat. If there are no restrictions at the steam outlet, simply making full use of the heat will suffice – how should this be considered? 2. In locations with similar operating conditions, the following process was observed: a drain device is installed after the heat exchanger, and then the fluid enters the flash tank. I’m not quite sure about the principle behind this; could it be that latent heat is being utilized for heat exchange? How is this process calculated?
“If there are no restrictions on the steam outlet, you must limit the operating pressure of the heat exchanger, that is, the condensation pressure of the steam within the heat exchanger – this is controlled by the outlet valve.
3 MPa is the operating pressure; a control valve is installed before the heat exchanger； ”If there are no restrictions at the steam outlet – I’m referring to the outlet of the heat exchanger. What is the process involved in calculating the parameters of the heat exchanger? Please give me some guidance. Thank you
It is likely to meet the requirements for steam balance in subsequent processes.
This post was last edited by wiseboy on 2018-4-28 at 14:32. “If there are no restrictions on the steam outlet,” then there must still be some condition; just because you haven’t set any conditions doesn’t mean there are none. For example, if there is no pressure buildup at the outlet, that means \"the outlet is open to the atmosphere\", which in other words means the outlet pressure is at atmospheric pressure; this is also a condition. If there is no pressure buildup at the outlet, then the operating pressure in the heat exchanger will be close to atmospheric pressure, rather than 3 MPa. The operating pressure in the middle of the heat exchanger is controlled (held in place) by the outlet valve, rather than by the control valve installed before the heat exchanger. . . . . . . . . . . . . . . . . . . . .
Of course, a valve is installed at the outlet of the heat exchanger; I just don’t understand how to use this valve to control the heat exchange time of the steam within the heat exchanger, so as to ensure that the latent heat can be fully utilized.
The latent heat must definitely be utilized. For superheated steam at 3 MPa, if the latent heat is not used, it means steam enters and exits without any benefit, which is a great waste. The entire heat exchange process can be described as follows: Superheated steam enters the shell side; after heat exchange, its temperature drops to the saturation temperature, followed by condensation heat exchange. The condensed water, being saturated water, is discharged into the flash tank through a trap. The shell-side condensation pressure is 3 MPa minus the pressure drop due to superheated steam heat exchange.
How is this heat exchange area reflected in the transformation of superheated steam into saturated steam? How should this step be calculated? Please give some guidance. Also, what is the impact of the steam trap on the flow rate?
Also, is it standard practice to use a steam trap after the heat exchanger, regardless of whether the inlet steam is superheated or saturated? For 30 kilograms of steam, which type of steam trap would be suitable?
For full-condensation heat exchange under pressure, a steam trap must be installed, and a water seal should be provided between the outlet on the shell side of the heat exchanger and the buffer tank, to prevent steam from entering the buffer tank directly. Regarding the process in which superheated steam turns into saturated steam, you can refer to the high-pressure heaters in power plants; it seems you asked me about this before.
This post was last edited by wiseboy on 2018-4-29 07:13. I don’t recommend learning *this stuff here, because as long as the concept of \"time\" is mentioned, it shows that there’s no basic knowledge of heat exchangers at all. Since the residence time of the fluid in the heat exchanger is reflected in the length of the tubes (the flow channels in the shell side) and the flow velocity, and does not directly involve the concept of time, you seem to be thinking about heat exchangers in too simplistic a way. Therefore, it is not appropriate for you to try to learn the basics here. Additionally, the pressure in the heat exchanger is definitely controlled through the outlet. If you leave it uncontrolled, pressure will be released: think of any container – no matter how high the pressure at the inlet is, if the pressure at the outlet isn’t controlled, then there will be no pressure inside the container; it’s basic common sense. For example, if the factory building is airtight (with no control), and you introduce high-pressure gas at 100 MPa into it, the pressure inside the building remains at normal levels. . . . . . .