Heat exchangers reflux drums

Fig. 1. ASPEN-Plus PFD of carbonic acid pretreatment process as analyzed in this study. Bl, pretreatment reactor (Rstoic) B2, screw mixer B3, blowdown tank and screw conveyor B4, slurrying tank and tank agitator B5, cooler B6, reflux drum and condenser B7, feed pump B8, in-line C02 mixer B9, heater BIO, pneumapress filter Bll, heat exchanger B12, loading pump B13, C02 compressor B14, primary filtrate pump.

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. 

A double drum system operates with a high tower top temperature that is above the dew point of the water-hydrogen chloride solution. A heat exchange with crude or another stream condenses only hydrocarbon in the first drum. This hydrocarbon, usually called heavy naphtha, is a hot reflux that controls... 

A dynamic model of a distillation column can be assembled from simpler units, as trays, heat exchangers (condenser, reboiler), reflux drum, valves and pumps (Fig. 4.5). Tray modelling has to answer two issues (1) accurate description of material and energy holdup, and (2) accurate pressure drop calculation. 

The column shell plus auxiliary pumps, heat exchangers, boilers, and reflux drum cost anywhere from three to six times as much as the trays or packing in a typical installation that is outdoors and operating under pressure or vacuum. Specific cases can vary by orders of magnitude Sawistowski and Smittf present a cost analysis for a column where the shell plus auxiliary equipment costs less than the plates. 

Figiue 21.34 shows the monochlorobenzene separation process introduced in Section 4.4. The process involves a flash vessel, V-100, an absorption column, T-lOO, a distillation column, T-101, a reflux drum, V-101, and three utility heat exchangers. As shown in Figure 4.23, most of HCl is removed at high purity (96 mol% by design) in the vapor effluent of T-100. However, rather than use the treater to remove the residual HCl, it is removed in the small vapor purge from T-101. The benzene by-product and monochlorobenzene product are obtained at high purity as distillate (99 mol% benzene) and... 

After the parameters for estimating equipment sizes and the utility parameters are adjusted, and a new steam utility is defined, the simulation units (blocks, modules, or subroutines) are mapped into Aspen IPE. In this case, there is only one distillation unit, Dl, to be mapped. The default mapping results in (1) a tray tower, (2) a shell-and-tube heat exchanger with a fixed tube sheet for the condenser, (3) a horizontal drum for the reflux accumulator, (4) a centrifugal reflux pump, and (5) a kettle reboiler with U tubes. 

A reasonable differential temperature-driving force is about 20 K. If the AT is too small, the heat-transfer area of the condenser/reboiler heat exchanger becomes quite large. The pressure in the second column is adjusted to give a reflux drum temperature of 367 - - 20 = 387 K. The pressure in C2 is 5 atm. The base temperature in C2 at this pressure is 428 K, which will determine the pressure of the steam used in this reboiler. 

In normal control studies, these assumptions are reasonable because the composition dynamics of the column trays, column base, and reflux drum are typically much slower than the dynamics of the heat exchangers. However, for predicting rapid responses to safety scenarios, the dynamics of the heat exchangers should not be neglected. 

Stripper. Absorber bottoms at 322 K is preheated to 380 K in a heat exchanger using the hot stripper bottoms at 400 K and fed to the top of a stripping column with 10 stages and operating at 2 atm in the column and 1.5 atm in the reflux drum. Reboiler heat input is 54.12 MW to maintain a reflux-drum temperature of 363 K, as suggested by Desideri and Paolucci as a balance between stripper reboiler energy and water losses in the vapor from the reflux dmm. 

The tower was limited by condensing capacity that is, the heat exchangers used to condense the reflux and distillate were marginally inadequate. Whenever the propane content of the overhead would increase, the bubble-point temperature of the liquid in the reflux drum would drop. This made it more difficult to condense the tower overhead vapors. As the splitter was only equipped to make liquid products, the inability to condense even a small fraction of the overhead vapors upset the tower. Here is the way this happened ... 

At this point, the heat duty in the condenser/reboiler is known. All the temperatures throughout both columns are also known. Therefore, the heat-transfer area of this heat exchanger can be determined by using the difference between the reflux drum temperature... 

Figure 12.2 gives the flowsheet with stream conditions, heat duties, reflux ratios, and column diameters. Both columns operate at 1.1 atm. Reflux drum temperatures are 332 and 337 K, which permit the use of cooling water in the condensers. The reflux ratios are fairly small (0.802 and 0.628), which indicates that the separations are not difficult and columns with relatively few trays are required. Notice that a heat exchanger is installed to cool the solvent from the bottom of the solvent recovery column before introducing it into the extractive column. Figure 12.6 gives temperature and composition profiles for the two columns. 

The sizing of process equipment should be conpleted and the approximate location on the plot plan determined. Referring to Table B.1.3 for equipment specifications gives some idea of key equipment sizes. For example, the data given for the reflux drums V-202 and V-203, reactor R-201, and towers T-201 and T-202 are sufficient to sketch these units on the plot plan. However, punp sizes must be obtained from vendors or previous jobs, and additional calculations for heat exchangers must be done to estimate their required footprint on the plot plan. Calculations to illustrate the estimation of equipment footprints are given in Example 1.11. 

The distillate stream from a distillation column (flowrate 35 m /h, density of water) is recycled. The destination of the recycle stream is at a location 3 m below the fluid level in the reflux drum. First, the recycle passes through a pump to supply sufficient head to overcome frictional losses (20 kPa) and reach the pressure of the stream with which it is mixed (250 kPa above distillate stream). Then it is heated from 90°C to 120°C using low-pressure steam at 140°C. Assume that all resistance is on the process-stream side of the exchanger (tube side). 

HYDROCYANIC ACID. HCN. In laboratoty tests, all( 3003. 5052, and 6053 were resistant to a 77% solution of hydrocyanic acid at ambient temperature. Hydrocyanic acid has been processed in aluminum distillation towers, reflux condensers, final condensers. adsorption towers, heat exchangers, tankage, shipping drums, and piping. See also Ref (1) p. 134,... 

Condensers are usually conventional tubular heat exchangers, generally arranged horizontally with the coolant inside the tubes, but also vertically with the coolant on either side of the tubes [27]. The condenser may be placed above the tower for gravity flow of the condensed reflux to the top tray, but it is usually more convenient for purposes of construction and cleaning to place the condenser nearer the ground and to return the reflux from an accumulator drum [55] to the top tray by pumping. This procedure also provides more pressure drop for operation of control valves on the reflux line. 

When protecting a column that has a reboiler, condenser, and overhead reflux drum, a single relief valve is frequently used, as long as there are no block valves or other means of creating flow restrictions between the equipment items. (The heat exchangers may need their own relief valve on the utility side if a hazards analysis shows that a leak from the process into the utility stream could cause unacceptable overpressure.)... 

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