Reboiler steam

The fractionator shell itself should often have some extra trays. Conventional instrumentation alone cannot always be expected to handle all the things that can happen to a fractionation system, such as changes in feed composition, reboiler steam pressure, or coolant temperature (especially for an air condenser during a sudden cold front). Experience for a given service is the best guide for extra trays. 

Note Alarms and shutdowns as shown are not to be considered as meeting any minimum safety requirement but are shown as representative of types used for controi systems. Schematic Alarm/Shutdown Hydrocarbon Low Pressure Hot oil or Glycol Amine Label Description Line Heater Reboiler Steam Heater Salt Heater Reboiler Reboiler ... 

It) High column pressures in both columns pinch reboiler steam. 

The reboiler steam valve has linear installed characteristics and passes 30,000 Iboi/h when wide open. Steam latent heat is 1000 Btu/lb . 

There is a first-order dynamic lag of t minutes between a change in the signal to the steam valve and vapor boilup. The low base-level override controller pinches the reboiler steam valve over the lower 25 percent of the level transmitter span. 

Figure 1.10 illustrates this point, from plant test data obtained in a Texas refinery. Point A is called the incipient flood point, that point in the towers operation at which either an increase or a decrease in the reflux rate results in a loss of separation efficiency. You might call this the optimum reflux rate, that would be an alternate description of the incipient flood point, neglecting the energy cost of the reboiler steam. 

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. 

While these specially designed exchangers may be the solution to a process problem, construction costs tend to be higher than those of "standard" engineered shell-and-tube equipment. Common TEMA designations include BKU, BJM, BFM and DED. Specially designed exchangers are often called for in such applications as reboilers, steam heaters, vapor condensers, and feedwater heaters. 

In these types of heat exchangers the two fluids are separated by the tube walls. As one fluid flows through the shell— the region outside the tubes — the other fluid flows through the tubes. Heat transfer occurs so as to cool, and perhaps even condense, the hotter fluid, and heat, and even vaporize, the cooler fluid. Heat exchangers are called by various names depending on their function such as chillers, condensers, coolers, heaters, reboilers, steam generators, vaporizes, waste heat boilers, and so on. 

The low exergetic efficiency is typical for distillation systems with close boiling mixtures and with high energy requirements in the reboiler. An alternative is to use reboiler-liquid flashing. A compressor is used to return the reboiled vapor to the bottom of the column. The required reboiler duty is somewhat larger than the required condenser duty, and so an auxiliary steam-heated reboiler is needed. Thus, a trade-off is made between the power used in the compressor and the large reduction in reboiler steam. 

Step 5. Reboiler steam controls product purity. Now the fresh feed Ftf cannot be used to control pressure. The purge stream is so small that effective pressure control is unlikely. Reactor cooling water flow is used to control reactor temperature. Therefore, the logical choice for pressure control is the cooling water flow to the condenser CWc. The controller gain of this loop was empirically set at 25 (with a pressure transmitter span of 3000 kPa). 

Four alternative control schemes are commonly used for distillation column control, as shown in Figure 3.15 through Figure 3.18, respectively. Scheme 1 directly adjusts the material balance by manipulation of the distillate flow. If the distillate flow is increased, then the reflux accumulator level controller decreases the reflux flow. As less liquid proceeds to flow down to the sump, the sump level controller decreases the bottoms flow a like amount. The separation is held constant by manually setting the reboiler steam flow to maintain a constant energy per unit feed. 

Heavy naphta molar flow rate 8 N703 reboiler steam flow rate... 

Rich Oil Steam steam Reboiled steam Reboiled... 

To avert high-pressure blow-outs of plumbing and equipment, pressure gauges and pop-off valves should be installed in the following places (1) in the condenser to sense product pressure, (2) near the base of the stripping and rectifying column sections to sense internal column pressure, and (3) in the reboiler steam chamber or the steam injector nozzle to sense steam pressure being applied. 

F (10.5 psia) to the tower top temperature of 111°F (1.3 psia). To transfer this heat through the reboilers, steam at 233°F (22 psia) was required. Because this heat is needed only at relatively low temperatures, it is very inefficient to obtain it by burning fuel under boilers, without making use of the heat at higher temperatures first. Two possible ways of providing low-temperature heat more efficiently are these ... 

The use of cold feed, case (it), requires the smallest number of plates but the greatest amount of reboiler steam. The total energy requirement for the reboiler and the preheater is about the same for all three cases. The reasons for preheating the feed, in most cases, are to keep the vapor flow rate about the same in both... 

Case Reboiler steam n> kg/h Number of ideal plates... 

A fixed-gain relay is to be used as a low base-level override controller on a distillation column. The column is 7 ft in diameter and has a base-level transmitter span of 3 ft. The density of the liquid in the base is 50 lbn,/ft. Its heat of vaporization is 200 Btu/lbm-The reboiler steam valve has linear installed characteristics and passes 30,000 Ibm/hr when wide open. Steam latent heat is 1000 Btu/lbm. 

When reboiler steam flow is unmetered, it can often be measured by running a hose to a 45-gallon drum and timing it Check whether this technique can be used. Remember that steam condensate flashes unless it is cooled, giving rise to incorrect readings. It may be necessary to cool the condensate or run it into a drum partially... 

Radiotracer techniques. These involve ipjection of a radioactive tracer into sections of the plant and monitoring its movement with the aid of radiation detectors. Depending on the application, the tracer may be injected either as a pulse or at a constant rate. These techniques are often applied for leak detection and for flow measurement. For instance, a tracer can be injected into the reboiler steam line, and a detector on the process side will determine whether any of it found its way into the process fluid. A case where this technique successfully diagnosed a reboiler leak and measured the rate of leakage has been reported (71). Radiotracer techniques are discussed in detail elsewhere (71, 72, 229, 424). 

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