Condensate drum

There is no process reason to use the condensate drum shown in Fig. 13.2 rather than a steam trap. In a modern refinery with large steam flows, the convention is to design systems with condensate 

Which is ridiculous, as the reboiler is only 5 ft in diameter. Even a 1 psi AP would submerge half the tubes with water. The operators will respond to this design error by draining the channel head directly to the sewer. Thus, the correct balance Hne coimection location to use is through valve B, and never valve C. That is, leave C closed and B open. I learned about this from Sandy Lani. 

As steam condensate flows through process piping, it loses pressure due to frictional losses. Alternately, condensate draining from a reboiler outlet nozzle will accelerate and lose pressure according to the following formula  

For example, condensate draining through a nozzle at 10 ft per second would undergo a AP of 1% psi. As the condensate is presumed to be draining out of the reboiler at its saturated liquid temperature (or boiling point or bubble point) as it loses the IVi psi, you might think it would have a tendency to partially vaporize to steam. But this is not the case. 

The consequences of vapor lock on the performance of a vertical thermosyphon steam reboiler, with steam on the shell side, is shown in Fig. 13.3. 

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Select a condensible blowdown drum for condensible releases, rather than the non-condensible type. If a condensible blowdown drum is not suitable for handling the total blowdown service (e.g., if cold liquids are involved), then a combination of a condensible and a non-condensible drum may be used. 

Liquid circulation from the reactor to the heat exchanger is flow-controlled. Condensate level in the condensate drum is controlled by manipulating BFW (boiler feed water). 

A better design is shown in Fig. 8.6. In this scheme, a condensate drum is used to monitor the level in the channel head. As the drum level is drawn down, the number of tubes in the reboiler exposed to the condensing steam is increased. However, when the water level drops to... 

One important feature of Fig. 8.6 is the condensate drum balance line. Note, that this line is connected below the channel head pass partition baffle. This ensures that the pressure in the channel head, below the pass partition baffle, and the pressure in the condensate drum, are the same. If these two pressures are not identical, then the level in the condensate drum cannot represent the level in the channel head. For this reason, never connect the condensate drum vapor space to either the steam supply line or the top vent of the reboiler s channel head. 

Venting the channel head through the balance line shown in Fig. 8.6 will prevent an excessive accumulation of C02. This is done by continuous venting from the top of the condensate drum. For every 10,000 lb/h of steam flow, vent off 50 lb/h of vapor through a restriction orifice, placed in the condensate drum vent. This is usually cheaper than controlling reboiler steam-side corrosion, with neutralizing chemicals. 

One such turbine, in a refinery near London, would not drain properly, In order to push the condensate out of the turbine case, the operators were forced to raise the surface condenser pressure from 100 to 250 mm Hg (i.e., 20 in of mercury vacuum, in the American system). Note that the balance line shown in Fig. 8.11 keeps the pressure in the turbine case and the condensate drum, into which the turbine case is draining, both equal at the same pressure. 

An alternative control strategy fixes the reactor-inlet toluene flow rate [16]. Fresh toluene is fed into the condenser drum of the last distillation column, on level control. Production-rate changes can be achieved by changing the setpoint of the toluene reactor-inlet flow, or the setpoint of the reactor-inlet temperature controller. When this control structure is used, the whole range of conversion becomes stable. Drawing of this control structure is left as an exercise to the reader. 

The task of the lights column is to remove the light components from the recycled EDC, with chloroprene and tri-chloroethylene being the most important impurities. Therefore, a concentration-cascade scheme was implemented, with chloroprene concentration and reboiler duty as controlled and manipulated variables, respectively. The distillate to feed ratio was kept constant using feedforward control. This ratio can be used to adjust the level of tri-chloroethylene in the bottom product. The level in the condenser drum was controlled by the reflux. Note that fixing the reflux and controlling the level by distillate does not work, because the distillate rate is very small. 

Minimum Stages A column operating at total reflux is represented in Fig. 13-28(1. Enough material has been charged to the column to fill the reboiler, the trays, and the overhead condensate drum to their working levels. The column is then operated with no feed and with all the condensed overhead stream returned as reflux (Lf/+i = Vf/ and D = 0). Also all the liquid reaching the reboiler is... 

In steam reboilers, a small atmospheric vent should be provided on top of the condensate drum and always left cracked open (234) (except when steam chest pressure dips below atmospheric). This will... 

Condenser drum no chemical reaction takes place de to the absence of catalyst a vapor phase stream enters the compartment and a liquid stream leaves it heat... 

Figure 8.8. Entropy production rate profile for a 15 stage RD column for MTBE synthesis. Legend 5m entropy produced by interfacial mass diffusion S entropy produced by interfacial energy transfer Srx. entropy produced by chemical reaction Remarks stages are numbered from top to bottom reboiler and condenser drum are not depicted MeOH feed stream is fed at 9 tray and iCt stream at 10 tray. The operational and design variables are listed in table 8.4.

The steam trap neither aids nor retards condensate drainage, unless it is mechanically malfunctioning, meaning it is sticking either open or closed. Also, replacing the steam trap with a condensate drum and LRC also neither retards nor aids drainage. Condensate drainage is a function of system hydraulics, as discussed in subsequent sections. 

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. 

Figure 13.4 illustrates a condensate drum that is elevated above the reboiler steam trap. For simplicity, let s assume that 15 psi of pressure (i.e., 1 atmosphere) equates to 35 ft of hot water head pressure. 

Figure 13.4 Elevating a condensate drum above the reboiler, regardless of the steam supply pressure, will result in loss of reboiler capacity.

Condensate drum balance line Used to connect the channel head of a steam reboiler to the condensate drum for pressure balance. 

One important feature of Fig. 11.6 is the condensate drum balance line. 

Operators who have problems with loss of reboiler capacity often attribute these problems to condensate backup. This is usually true. To drop the level of water out of channel head, either the steam trap or the condensate drum is bypassed by putting the condensate to the sewer. Sometimes the float of the trap is sticking, but mostly the difficulty is an erratically high pressure in the condensate collection... 

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