Condensate drum installation

To determine if this problem exists on a reboiler, establish a definite condensate seal by restricting the condensate effluent line. If the tower bottom s temperature increases, the reboiler has a blown condensate seal. This wastes steam and reboiler capacity. The correction is the same for condensate backup installation of a steam condensate seal drum. 

Option Five—Install a condensate pump and condensate drum. Pump the condensate out under level control. The drum must be immediately next to and underneath the reboiler. Also, the drum must be high enough above the new condensate pump to provide sufficient net positive suction head (NPSH) for the pump. This is, of course, the preferred, if not the typical way of handling this very common design problem. 

The fix for the erratic reflux drum pressure problem was to provide for separate pressure control of the fractionator column and the reflux drum. A new pressure control valve was installed upstream of the condenser and the old condenser outlet control valve was removed. A hot gas bypass, designed for 20% vapor flow, was installed around the pressure control valve and condenser. A control valve was installed in the hot gas bypass line. The column pressure was then maintained by throttling the new control valve upstream of the condenser. The reflux drum pressure w as controlled by the hot gas bypass control valve and the psv saver working in split range. The new system is shown in the figure below. 

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 drum and is drawn off through a small water pot in the bottom. In most installations, ammonia gas is injected into the overhead line to... 

Install a knock-out drum immediately upstream of the flare seal drum, to remove material condensed in the flare header. 

It is important to note that in some installations where local pollution regulations would not permit venting a condensible blowdown tank in toxic service to the atmosphere, a pressure drum or sphere, vented to a flare, may be necessary. 

Piping to Burners - First and second stage piping and headers, as well as the burner lines themselves, are sized to minimize pressure drop and velocity effects. Thus, maldistribution of flow to the burners will be minimized. The burner lines are fabricated from standard 1(X) mm pipe, and are arranged in a split grid layout with distribution headers and split feed lines on opposite sides, for both first and second stage burners. First and second stage headers must be sloped so that any condensate will drain back to the seal drums. However, the burner lines must be accurately installed in a horizontal plane. 

The bypassed vapor heats up the liquid there, thereby causing the pressure to rise. WTien the bypass is closed, the pressure falls. Sufficient heat transfer surface is provided to subcool the condensate, (f) Vapor bypass between the condenser and the accumulator, with the condenser near ground level for the ease of maintenance When the pressure in the tower falls, the bypass valve opens, and the subcooled liquid in the drum heats up and is forced by its vapor pressure back into the condenser. Because of the smaller surface now exposed to the vapor, the rate of condensation is decreased and consequently the tower pressure increases to the preset value. With normal subcooling, obtained with some excess surface, a difference of 10-15 ft in levels of drum and condenser is sufficient for good control, (g) Cascade control The same system as case (a), but with addition of a TC (or composition controller) that resets the reflux flow rate, (h) Reflux rate on a differential temperature controller. Ensures constant internal reflux rate even when the performance of the condenser fluctuates, (i) Reflux is provided by a separate partial condenser on TC. It may be mounted on top of the column as shown or inside the column or installed with its own accumulator and reflux pump in the usual way. The overhead product is handled by an alter condenser which can be operated with refrigerant if required to handle low boiling components. 

Blown condensate seal. When this occurs, uncondensed vapor blows and channels right through the reboiler and out the condensate drain line. Heat transfer slumps and water hammer may follow. Experience shows that as much as half the reboiler duty is lost by a small amount of vapor blowing (239). Throttling the reboiler outlet reestablishes the seal. Installation of a condensate seal drum can cure this problem. Additional discussion is in Sec. 17.1.2. 

Some troublesome experiences with liquid carryover fi om these condensers have been reported (381). The author had an experience with liquid carryover from a vent condenser mounted on top of a Cg splitter reflux drum (similar to Fig. 15.14c). Carryover occurred whenever the vent control valve opened excessively, and was recognized by "watering or icing up of the line downstream of the valve (due to liquid flashing). The author is familiar with other similar experiences. Installing a valve limiter was sufficient to prevent carryover in the above case. 

To overcome this problem, a submerged condensate pot is often installed instead of the steam trap (Fig. 17.le) as described earlier (item 5 above). An alternative remedy is replacing the steam trap by a level condensate pot (Fig. 17.1/). By varying the level control set point, the surface in the reboiler can be adjusted so that the reboiler operates at a pressure high enough to ensure condensate removal at all times without a pump. Note that the bottom of this drum is located below the bottom of the condensing side of the reboiler (189) otherwise, "dry reboiler operation at high rates will not be possible, and reboiler capacity will be reduced. 

After leaving the autoclaves the ammonia gas is washed and dried by being passed through a series of mud drums and an installation of 7 ammonia columns each 9 feet in diameter by 19 feet high connected by 14 inch pipe to 7 de-phlegmators each 7 feet 2 inches in diameter by 8 feet 3 inches high and 7 condensers similar In size to the dephleg-mators. P rom the condensers, the ammonia gas is stored in two 60,000 cubic feet gas holders. 

Some distillation columns with partial condensers are constructed with the condenser installed at the top of the column inside the shell. There is usually no reflux drum. Vapor flows upward through the tubes of the condenser. The condensate liquid flows downward and drops into a liquid distributor above the top tray. These dephlegmatoi systems are frequently used when very toxic or dangerous chemicals are involved because it avoids potential leak problems with pumps and extra vessels and fittings. 

I have spent many fruitless hours trying to set such a control valve. In practice, operating personnel will not be able to put such a control valve in a proper position routinely. Even if the control valve is set correctly, a small increase in the condenser operating temperature will cause vapor to start blowing through the throttle valve again. The only permanent solution is to install an accumulator drum between the condenser and the throttle valve. The throttle valve will then be controlled by the accumulator drum liquid level. 

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. 

Conversion of any existing scheme to flooded condenser is more than just a change in control configuration. It requires a full process design check and is likely to result in changes to relief valves and other safety-related systems. There are also a number of ways in which it can be configured. For example the drum can also be flooded thus avoiding the need to install a valve on its inlet. The pressure controller can then either manipulate either the reflux flow or the distillate flow directly. 

In units treating sour hydrocarbon gases at high pressure, it is customary to flash the rich solution in a flash drum maintained at an intermediate pressure to remove dissolved and entrained hydtocaibons before add gas stripping (see Chapter 3). When heavy hydrocarbons condense frmn die gas stream in the absorber, die flash drum may be used to skim off liquid hydrocarbons as well as to remove dissolved gases. The flashed gas is often used locally as friel. A small packed tows with a lean amine wash may be installed on top of the flash drum to remove HjS from die flashed gas if sweet fuel gas is required (Manning and Thompson, 1991). 

The distillation column operates at its optimum pressure and temperature for separation (320 K in the reflux drum). The column is fed with two pure reactant fresh feedstreams Fqa and Fob- The column has three zones. There are Ns trays and a partial reboiler in the stripping section and a rectifying section with Nr trays and a total condenser. As shown in Figure 16.1, a number of total liquid trap-out trays are installed at several intermediate trays between these two zones. There are Nm trays in the middle of the column. No reaction occurs anywhere in the column. Reaction only occurs in the external side reactors. 

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