Sidestream strippers

Steam used in the sidestream strippers and in the stripping section of the main column is condensed in the overhead condenser. This water settles to the bottom of the distillate dmm and is drawn off through a small water pot in the bottom. In most installations, ammonia gas is injected into the overhead line to raise the pH of this water and reduce corrosion. 

Alatiqi presented (I EC Process Design Dev. 1986, Vol. 25, p. 762) the transfer functions for a 4 X 4 multivariable complex distillation column with sidestream stripper for separating a ternary mixture into three products. There are four controlled variables purities of the three product streams (jCj, x, and Xjij) and a temperature difference AT to rninirnize energy consumptiou There are four manipulated variables reflux R, heat input to the reboiler, heat input to the stripper reboiler Qg, and flow rate of feed to the stripper Lj. The 4x4 matrix of openloop transfer functions relating controlled and manipulated variables is ... 

Sidestream stripper a device used to perform further distillation on a liquid... 

Example The dew point is defined an all-vapor system except for one very small increment of liquid. Now take the feed again, and consider the fact that this is a flash-off crude still sidestream vapor at 20 psig (34.7 psia). The dew point is to be determined to set the proper sidestream stripper overhead temperature for this desired product. This problem is worked similarly to the bubble point. Simply hold the pressure (34.7 psia) constant, and vary the temperature. Note that when you find the temperature at which just a small amount of liquid is formed, the sign SYSTEM IS ALL VAPOR goes off and the flash component summary appears. Note also that the previous flash summary will remain on the screen (if you had a previous run) until you input a flash zone temperature and click on Run Prog. 

Fractionation Section. A typical fractionation section includes the coker fractionator and attendant heat exchange equipment, the light gas oil side stream stripper and the overhead system. The coke drum overhead vapors enter the fractionator under shed trays which are located below conventional wash trays. Hot induced gas oil reflux is pumped to the wash trays to condense recycle and to wash the product vapors. The light and heavy gas oil products are condensed as sidestream products. The light gas oil product is usually steam stripped in a sidestream stripper. The overhead vapors from the fractionator are partially condensed and the gas and gasoline products are directed to the vapor recovery unit. 

Fig. 18.14. Crude distillation—Foster Wheeler. Includes exchanger heaters (1,3), desalter process (2), fired heater (4), main fractionator (5), overhead gas accumulator (6), sidestream strippers (7,8,9,10), second fired heater (11), and vacuum fractionator (12). (Source Hydrocarbon Processing, 2004 Refining Process Handbook. CD-ROM. September 2004 copyright 2004 by Gulf Publishing Co., all rights reserved.)...

Glinos, K. and M.F. Malone, Minimum vapor flows in a distillation column with a sidestream stripper. Industrial Engineering Chemistry, Process Design and Develop menu 1985, 24 1087 1090. 

Figure 10.20 gives design parameters and equipment sizes of this process. The reboiler heat input in the main column is 1.38 MW. It is interesting to compare this with the energy requirements of the sidestream/stripper flowsheet shown in Figure 10.15 (1.20 + 0.022 = 1.22 MW). The two processes produce essentially the same three product streams with the same purities. The energy consumptions of the two flowsheets are quite similar.

The vapor leaving the top of the column is condensed in a water- or air-cooled condenser. The liquid distillate is a heavy naphtha stream, which is used for the production of gasoline. It has ASTM 5% and 95% boiling points of 195 and 375 °F, respectively. In some refineries, it is sent to a reforming unit to produce aromatics (benzene, toluene, and xylenes) and hydrogen. The condensed water is decanted off the reflux drum. Note that this water stream is quite large (17,180 Ib/h) because of all the open stripping steam that is used in the column base and sidestream strippers. 

Use of stripping steam in all product strippers rather than in only the first sidestream stripper will decrease draw tray temperatures of the second sidestream and all others above. 

Calculate the reflux heat, at Tray Dl. Reflux heat is defined as the apparent heat imbalance between external heat quantities at the point in question in the tower. These external heat quantities are denoted as Q with appropriate subscripts to signify their location. External heat input quantities are defined as the heat contained in the feed plus all heat to the system at product strippers either directly as steam or indirectly throu reboilers. External heat output quantities at a given tray are defined as the heat contained in liquid products leaving the system from points lower in the towier, the heat contained in the internal vapors of products plus steam and the heat contained by a product liquid flowing to the sidestream stripper. If the tray is nbt a sidestream draw tray, this latter quantity does not enter into the heat balance. 

The liquid which is to be revaporized in the sidestream stripper falls from Tray 9 at 603 F and, in passing across Tray 8 is heated to 610 F, thus absorbing 0.016 MMBTU/hr. 

Using Figure 2.13, set a steam rate to the sidestream strippers and estimate the material balance around these towers. For design purposes, a steam rate of 10 pounds per barrel of stripped liquid is recommended. At the indicated vaporization, find the EFV temperatures of the sidestreams at the appropriate minus vaporization percentages. These are the 14,7 psia bubble points of the product liquids on the draw trays and will be used later in calculating draw tray temperatures. 

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