Steam stripper /stripping side-stream

Whether or not a variable is independent may be more difficult to determine in other cases. For example, a distillation column with a side stripper is shown in Fig. 1. The side stripper in Fig. 1(a) has a reboiler and that in Figure 1 (b) is stripped with steam. Under the program, the liquid side stream which feeds the side stripper must be set. Also, in the column arrangement of Fig. 1(b) the amount and enthalpy of the steam fed must be set, since it constitutes an external feed. For illustration, we assume that the bottom product from the reboiler of the main column has... 

Many side-stream steam strippers, of the type shown in Fig. 10.1, do not work very well. Operating personnel report that the stripping steam is not effective in removing undesirable lighter components from the stripper feed. Why could this be so ... 

Crude oil fractionators are an example of a more elaborate system. They make several products as side streams and usually have some pumparound reflux in addition to top reflux which serve to optimize the diameter of the tower. Figure 3.13 is of such a tower operating under vacuum in order to keep the temperature below cracking conditions. The side streams, particularly those drawn off atmospheric towers, often are steam stripped in external towers hooked up to the main tower in order to remove lighter components. These strippers each have four or five trays, operate... 

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. 

Figure 12.8 shows a model of a main column and a side-stripper. Vapor feed F goes to the bottom of the main column, which is steam-stripped with stream 51, using no reboiler. The column has a partial condenser with vapor distillate D. Side draw SD is taken from around the middle of the main column and steam-stripped in the side-stripper, with the overhead vapor, OH, returned to the draw tray in the main column. The side-stripper is steam-stripped with stream 52. 

Unreacted NH3 and CO2 are separated from the urea solution in the high-pressure separator and in two to three steam-heated carbamate strippers at successively lower pressures. The off-gas from the separator and the first-stage stripper is absorbed in the high-pressure absorber by a side stream of partially stripped reactor effluent from the high-pressure separator. Heat evolved in the absorber reaction is removed (to increase absorption capacity) by the addition and expansion of part of the liquid ammonia feed at this point. Pure gaseous ammonia from the top of the absorber is also recycled to the urea reactor after being condensed. 

Lube distillates are sent at their bubble points to side stream strippers. Steam is injected, reducing the partial pressure of hydrocarbons which effectively removes lighter hydrocarbons improving volatility beyond that obtainable without side stripping. Ten to thirty percent of the stream may be removed in the stripper. If the heavier streams are not stripped this will reduce the yield of lighter lubes. Stripping is an important part of the overall operation to achieve the best separation and produce the desired products. A stripper typically consists of 4 to 6 sieve trays but packing may also be used. 

Set stripping steam to the atmospheric gas oil stripper at 10 pounds per barrel stripped product and estimate the stripout from Figure 2.13. Since the other side-streams are to be reboiled, set their vaporizations equivalent to the amount which would be stripped out by steam at a rate of 10 pounds per barrel stripped product. Plot these stripout points, i.e., minus vaporization, on the product EFV curves. These are the 14,7 psia bubble points of the unstripped sidestream products and will be used later to calculate draw tray temperatures. 

An inefficiency in the original configuration of the case study is shown where the product of the AGO side stripper is spht into two streams one of is cooled and introduced again in the main column. This sub-cooled returned liquid performs the function of a pump around. This separation and remixing is clearly inefficient because of the higher amount of stripping steam required. 

One way to remove this inefficiency is done where the side draw from the main column is split first and returned as sub-cooled stream while the other stream is stripped in the side stripper. Therefore, the required stripping steam is reduced tremendously as the feed is reduced. The total savings in operating cost are 40,000/ for this simple modification in the piping connections. Another example of inefficiency is mixing two vapour streams with a big difference in their composition causes this inefficiency. The returned vapour from the KE side stripper is mixed with the vapour inside the main column which resulting in mixing losses. 

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