Reboilers steam

When considering the steam side of steam heated reboilers, it is best to think about the reboiler as a steam condenser. The steam, at least for a conventional horizontal reboiler, is usually on the tube side of the exchanger, as shown in Fig. 8.1. The steam is on the tube side, because the shell side was selected for the process fluid. If the reboiler is a thermosyphon, or natural-circulation reboiler, then low-process-side pressure drop is important. For a horizontal reboiler, it is easiest to obtain a low pressure drop for the fluid being vaporized by placing it on the shell side. 

The steam enters through the top of the channel head of the reboiler. Any superheat in the steam is quickly lost to the tubes. Superheated steam does very little in increasing heat-transfer rates in a reboiler. Actually, when considering the temperature difference between the steam and the process fluid, it is best to use the saturated steam temperature, as the real temperature at which all the heat in the steam, is available. For example, assume the following steam flow to a reboiler  

The 100-psig steam condenses at approximately 320°F. The heat available from the steam is 

This calculation is typical, in that 94% of the heat is liberated at the 320°F condensing temperature of the saturated steam. Another way of stating the same idea is that a steam reboiler depends on latent-heat transfer, and not on sensible-heat transfer. 

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Capacity cause Steam reboiler flow set above column jet flood limit... 

In the amine regenerator, the rich amine solution is heated to reverse the acid-base reaction that takes place in the contactor. The heat is supplied by a steam reboiler. The hot, lean amine is pumped from the bottom of the regenerator and exchanges heat with the rich amine in the lean-rich exchanger and a cooler before returning to the contactor. 

When a vapor condenses to a liquid, we say that the latent heat of condensation of the vapor is liberated. In a steam reboiler, this liberated heat is used to reboil the distillation tower. When a vapor, or more commonly a liquid, cools, we say that its sensible heat is reduced. For a small or slight temperature change, the change in latent heat might be large, while the change in sensible heat will be very small. 

What would happen to a steam reboiler if the float in the steam trap became stuck in a partly closed position, or if the steam trap were too small Water—that is, steam condensate—would start to back up into the channel head of the reboiler, as shown in Fig. 8.3. The bottom tubes of the reboiler bundle would become covered with water. The number of tubes exposed to the condensing steam would decrease. This would reduce the rate of steam condensation, and also the reboiler heat duty. 

We can see, then, that either condensate backup, or blowing the condensate seal, will cause a steam reboiler to lose capacity. If you think either of these two problems could cause a loss in reboiler duty, try opening the bypass around the steam trap. If the reboiler duty goes up, the problem was condensate backup. If the reboiler duty goes down, then the problem might be a blown condensate seal. If it looks like a blown condensate seal problem, close the steam trap bypass. Then, partially close the valve downstream of the steam trap. If this increases the reboiler duty, a blown condensate seal failure is proved. 

Backpressure from the condensate collection lines creates control difficulties in steam reboilers or heaters. 

Many water strippers are initially designed with steam reboilers, rather than with open stripping steam. The amount of steam required is the same in either case. The great advantage of the reboiled stripper is that the steam condensate is recovered, and recycled back to the boilers. When open stripping steam is used, the steam condensate is added to the stripped water, thus increasing the plant s water effluent. Hence, the use of open stripping steam is environmentally unfriendly. 

Condensation in shell-and-tube heat exchangers. If what you have just read seems to be a repetition of the discussion on steam reboilers in... 

Chap. 8, your analysis is correct. A steam reboiler has the same problems, and works on the same principles as a process condenser. The only difference is that a steam reboiler s heat is removed by the shell-side process fluid, and a process condenser s heat is removed by cooling water. 

It is probably best to consume steam generated in small waste-heat boilers, locally, in steam reboilers and preheaters. Turbine drivers are... 

Rich Oil Steam steam Reboiled steam Reboiled... 

The sweetened gas goes overhead and is sent to the fuel gas system. The rich amine exits the bottom of the scrubber and is heated in the lean—rich exchanger. It then enters the amine regenerator, where a steam reboiler is used to heat the amine to 225—250 °F. At these temperatures, the salts are thermally dissodated to regenerate the amine. The add gas, composed primarily of H2S, is sent to a sulfur recovery unit that generates elemental sulfur. 

Failure of steam controller. A common practice with steam reboilers (293) is to assume the steam valve is wide open, the steam pressure in the reboiler is the same as in the steam supply line, and that reboiler area remains constant (condensate is removed as soon as it is formed). The process side is usually assumed to have the same temperature rise (outlet minus inlet) as in usual operation. 

Inerts. Accumulation of inerts can drastically reduce heat transfer, particularly in steam reboilers. Accumulation of acidic or oxidizing inerts such as CO2 is also known to have caused severe corrosion (234, 253, 254). Numerous troublesome case histories of inert accumulation in the heating side of reboilers have been reported (28, 96, 232, 239). Inert venting facilities must be adequate. The following guidelines have recommended for venting inerts (28, 377, 381) ... 

It is good practice to provide tubesheet vents (134, 254, 358 Fig. 15.106) opposite the top vapor inlet nozzle in a vapor-heated vertical reboiler (condensing on the shell side). This is essential in steam reboilers, where a small steam purge should be continuously vented to atmosphere. Shell corrosion due to CO2 accumulation is known to have occurred in steam reboilers that had no such vent (234, 254). 

Typical examples are steam reboilers and refrigeration vapor reboilers. The control valve may be located either in the reboiler inlet line (Fig. 17.1c) or in the reboiler condensate outlet line (Fig. 17.16). 

The vapor inlet scheme may be troublesome when there is a small pressure difference between the reboiler heating medium and the condensate header (e.g., with steam reboilers using 15 to 35-psig steam). The problem is identical to that described in item 8 above, but it is caused by insiifficient AP rather them oversizing or clean siuface. In this case, the condensate outlet scheme of Fig. 11.Id is often preferred (234). The vapor inlet scheme shown in Fig. 17.1c can also be used and will provide better control, but at the expense of the additional pmnp. 

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... 

Loop seal. In some low-pressure steam reboilers the condensate pot is replaced by a loop seal (Fig. 17.Ih). In this arrangement, increasing the flow to the reboiler raises the pressure in the reboiler shell, which in turn lowers the liquid level in the reboiler and exposes more tube area. The dynamics of this system are similar to that of the condensate outlet scheme. The height of liquid in the loop is typically 5 to 10 ft. The system can be troublesome when the reboiler heat load or the steam mains pressure tend to fluctuate, and it is usually best avoided. 

Wild (426) described a horizontal steam reboiler ceise history which is analogous to the problem above. A high liquid level in the reboiler shell (Fig. 15.10/) caused liquid heimmer. The remedy was to inject inerts when the level rose excessively. 

As a general rule, sources of heat such as fired heaters and steam reboilers should be shut down as an emergency develops. Cooling systems should continue to operate because they remove heat from the system. Utilities, such as the steam and air supplies, should remain in operation in order to retain control of the equipment that is still in operation. 

Steam reboiler duty and efficiency can be estimated directly from steam rates and conditions. We can also estimate furnace reboiler duty and efficiency. The amount of fuel fired in the reboiler can be measured from the meter. The heat delivered by fuel combustion can be estimated from both fuel rate and heating value of the fuel. 

The same method is used to choose the method of stripping with the help of steam, reboiler, or a combination of steam and reboiler. Application of reboilers compared with steam stripping, on the one hand, requires additional investment cost and heat expenditures, but on the other hand, it leads to a decrease of vapor flow in the column (i.e., to a decrease of necessary diameter and to an increase of the temperature of stripping product used for heating the crude oil). Besides that, the application of reboilers is inadmissible for heavy products because the resulting increase of the product s temperature may lead to its chemical decomposition. In the case when apphcation of reboilers is admissible, the choice between reboilers. 

A much improved ORC-process can be obtained with heat recovery steam (HR-steam) from the TMP-steam reboilers. An integrated mill with a TMP-plant combined with a paper machine is taken here as an example. Paper grade is newsprint with a basis weight of 40 g absolute dry web/m. With a machine speed of 1700 m/min and a sheet width of 10 m the production of paper is 12.3 kg/s air-dry paper with 92 % dry solids. The paper... 

If the steam from the TMP-refiners is used directly in ORC, instead of the HR-steam, the overall investment cost could be reduced. The steam reboiler for that part of the TMP-steam is replaced with the ORC-evaporator. The construction of the ORC-evaporator is close to the reboiler construction. 

On one gas plant, this difficulty was overcome by providing a supplementary trim steam reboiler. Referring to Figure 3-7, the steam flow to this... 

The majority of refinery light-ends distillation lowers are reboiled with steam. Likely, the use of steam reboilers predates the petroleum industry. 

Steam balance (energy savings), 218 Steam condensers, 121 Steam drivers (compressor problem diagnosis), 230-231 Steam nozzle, 289 Steam reboilers, 273-275, 382-383 ... 

Trim gas oil, 284, 293, 299 Trim steam reboiler, 88 Trimming burner operation (combustion air supply), 318 Trip elimination, 359—361 Troubleshooting problems. See specific process. 

Steam reboilers are subject to a wide variety of serious capacity problems. The most common is steam condensate backup into the channel head. This is checked by manually draining the steam condensate to a nearby sewer and observing if the reboiler duty increases or the steam inlet control valve closes. 

FIGURE 18-10 Steam reboiler condensate drainage system is improperly designed. 

Nothing could be further from the truth. Steam reboilers are a major cause of tower instability, and the problems seem related to one function draining the condensed steam out of the reboilers channel head (see Fig. 18-10). Either the condensate does not drain freely from the reboiler and backs up over the tubes, or the condensate seal is blown and heat-transfer efficiency is impaired. 

When a vent is left cracked open, CO2 accumulations on the steam side of an exchanger will be eliminated. This practice effectively has reduced corrosion in many refinery steam reboilers. 

A vertical steam reboiler, when operated at 20% of its design load, emitted bangs loud enough to awaken the dead. At 50% of design heat duty, it ran smoothly and quietly. A kettle reboiler produced a terrific steam hammer when it was first brought on-line. Once the contents had started boiling, it immediately quieted down. 

Finding the condensate level in the channel head of a steam reboiler. 

Rich Oil Steam Steam Reboiled Steam Reboiled... 

The accumulation of non-condensables on the tube side of horizontal steam reboilers has an extremely detrimental effect on heat transfer. I have observed reboiler duty drop by well over one-half. The origins of the non-condensable vapors are ... 

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