Steam pressure grade at the bottom of the acidic water stripping unit
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Dear colleagues, I would like to ask what steam pressure is used in the acidic water stripping unit (single tower under pressure with full extraction at the tower top)? Normally, 1.0 Mpa steam is used; I’ve heard that 0.5 Mpa steam is also employed. Are there any differences between these two types of steam in terms of flow rate consumption, reboiler size, and stripping efficiency? What are their respective advantages and disadvantages?
With 1.0 Mpa steam, after passing through the control valve, the pressure normally drops below 0.4 MPa; therefore, there is not much difference compared to using 0.5 Mpa steam. Furthermore, since steam utilizes mainly latent heat rather than sensible heat, there are no significant differences between these two types of steam in terms of flow rate consumption, reboiler size, and stripping efficiency. Also, the key point is that your factory has steam at 0.5 MPa, and there must be suitable users for it.
Thank you, Engineer Yu, for your answer. The current design is to feed 1.0 Mpa into the reboiler, with a pressure of 0.9 Mpa at the outlet of the reboiler. The temperature was reduced from 250 degrees to 180 degrees, which clearly takes advantage of the latent heat of vaporization of steam. As you said, given the large surplus of 0.5MPa steam, it is certainly preferable to use 0.5MPa steam first. Some design institutes believe that using 1.0 MPa steam (without pressure reduction) as the gas source yields a better stripping effect compared to 0.5 MPa steam, as the upper limit for temperature adjustment is higher; however, corrosion of the reboiler may be more severe. It is not clear whether this claim has any theoretical basis.
Our reboilers use steam at 1.0 MPa, and the condensate is also designed based on the saturation temperature at 1.0 MPa; however, this is not the case in actual operation, as the pressure of the actual condensate is only 0.38 MPa. The saturation temperature of the condensate is approximately 20 degrees lower than the bottom temperature of the tower.