Distillation Troubleshooting. Henry Z. Kister. Distillation Troubleshooting Henry Z. Kister Troubleshooting pdf · Read Online Distillation Troubleshooting pdf. Kister Henry Z. Distillation Troubleshooting. Файл формата pdf; размером 32,28 МБ. Добавлен пользователем Serega Oil THIS is the third book on distillation by the renowned Henry Kister. It is a highly impressive piece of work, but readers may be slightly disappointed considering.
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Distillation Troubleshooting. Author(s). Henry Z. Kister. First published April Print ISBN |Online ISBN |DOI/. Henry Z. Kister. C. F. Braun Strategy for Troubleshooting Distillation Problems. Dos and Using this Book: A Troubleshooting Directory a I WAN -. THE FIRST BOOK OF ITS KIND ON DISTILLATION TECHNOLOGY The last half- century of research on distillation has tremendouslyimproved our understanding .
Distillation - Wikipedia ; Distillation is the process of separating the components or substances from a liquid mixture by In industrial chemistry, distillation is a unit operation of practically universal importance, but it is a physical Kister, Henry Z. Distillation operation. Henry Z. Braun, Inc. McGraw-Hill, Inc.
The plug location was found by using radio- demethanizer active spot density measurements along the pipe. The ice plug was melted by external heat. Natural floods were often C2 splitter mistaken for hydrates and were countered by methanol injection, which aggravated them.
Installing separate dP recorders over the top and bottom sections permitted distinguishing natural floods from hydrates, and allowed early corrective action, reducing flood episodes to once a year. The top temperature was too cold, the bottom too hot, so the water was trapped and hydrocarbons concentrated near the feed.
The cure was to upgrade the tray metallurgy. The water peaked at the side reboiler in the middle of the stripping section, forming carbonic recovery acid and corrosion. Increasing solvent circulation, or surges in inlet gas, pushed the water up, causing column hydrates in the chilled condenser, with off-spec product for up to a week. Extensive methanol injection ERC and column thawing dissolved the hydrates.
This led to water accumulation. The deethanizer bottom trays in the absorber and most of the stripper trays experienced severe corrosion and required frequent repair and replacement. The rate of corrosion failure was greatly depropanizer reduced by adopting an effective dehydration procedure at startup.
To dehydrate, acid-free butane was total-refluxed, while drains were intermittently opened until all water was removed. The purge rate, adjusted per daily alkylation lab analysis, was minimized to minimize iC4 loss. An insufficient purge led to nC4 buildup.
This and deiso- variable C5 in the feed impeded temperature control and destabilized the unit. Stabilization was butanizer achieved by inferential model control. Depending on the draw tray temperature and composition, the cooled distillation side draw did not form two liquid phases.
The problem was diagnosed with the help of process simula- tion, and was solved by adding water to the decanter to ensure phase separation. The water problem was solved by decanting the organic phase and returning the aqueous phase to the column.
It decayed into radioactive lead and contaminated the debutanizer towers and auxiliaries, as well as polymer deposits on trays and wastewater from reboiler cleaning. This caused problems with waste disposal and personnel entry into the towers. Under the high-pressure, low-temperature condi- Trapping of lights tions in the tower, the water combines with the light hydrocar- In many hydrocarbon towers, where water is an impurity, bons to form solid ice-like crystalline molecules known as the reflux drum has a boot to remove the water Figure 6.
The hydrates. The hydrates precipitate, plugging tray holes and heavier water phase descends to the boot, from where it is valves and eventually restricting flow through the tray. Liquid removed, typically on interface level control. If the amount of accumulates above the plugged tray and the tower floods. A water is small, an on-off switch is sometimes used.
If the boot common cure is to dose the tower with methanol, which acts level control malfunctions, water can be refluxed to the tower, like anti-freeze and dissolves the hydrates. In the system in Figure 5 Case Plugging may be a problem in the water outlet line from the , the methanol and dissolved water were trapped by the boot because of low flowrates and because solids and corrosion interreboiler.
Over time, the water batch-distilled back into the products tend to become entrapped in the boot and the water tower, causing the hydrate to return. A blowdown from the stream. The converse problem is leakage rates across the water reboiler removed the methanol and dissolved water. This makes maintaining the level inside the boot difficult minor as a few ppm, has caused major corrosion problems in and causes loss of product in the water stream.
Both the plugging and leakage problems are most trouble- It is common in refinery reboiled deethanizer absorbers Figure some when there is a high pressure difference across the water- 2.
In a well-designed tower, the entering hydrocarbons are satu- outlet control valve. A high pressure difference promotes valve rated with dissolved water. Any concentration or water entry leakage; it also tends to keep the valve opening narrow, which beyond that will lead to a free water phase.
If it persists, it will promotes plugging. Both problems can be overcome by adding dissolve acidic components, resulting in weak acid circulating an external water stream which may be a circulating stream through the tower, which is death to carbon steel.
A typical to the boot outlet Figure 6. This stream boosts velocity 21, symptom is corrosion in the middle of the tower sometimes 24 and safeguards against a loss of liquid level. The external also further down , fouling with corrosion products in the lower water flowrate should be low enough to prevent excessive part, while the upper trays remain in good condition. It is also important to pay attention to good level monitoring. In some columns, the overhead is totally condensed and then 1 decanted to form an aqueous stream and an organic product.
The product is sent to a stripper to remove traces of the aqueous 6 phase. The stripper overhead is recycled to the condenser inlet. Reflux When a light condensable organic enters the column, it will Drum end up in the organic phase. In the stripper, it will be stripped C2 Splitter and returned to the condenser.
Thus, it will become entrapped in the system, traveling back and forth between the condenser and 99 Ethylene the stripper. Reflux drum boot arrangement. Experiences of lights trapping. Column Brief Description 21 Refinery Column internals and reboiler tubes severely corroded after the water draw-off control valve on the debutanizer reflux drum boot plugged.
Manual draining was too inconsistent to prevent water saturated with H2S refluxing to the tower. Continuous flushing of the water draw line with an external water source prevented recurrence. Water refluxing to the fractionator over time caused cavitation and damage to the reflux pump, fractionator and deposited salts that plugged the top internals.
Water in the naphtha destabilized the gas plant. The problem was eliminated by blowing the level tap. The stripper bottoms was the propane product, HF alkylation while the stripper overhead was recycled to the depropanizer overhead.
When ethane entered the depropanizer depropanizer due to an upstream unit upset, it became entrapped in the overhead system and could not get out. The depropanizer pressure climbed and excessive venting was needed. This was cured by dropping the stripper bottom temperature to allow ethane into the propane product.
Two snapshot samples had concentrations of the accu- input. Unfortunately, To provide an outlet for the light, either venting from the safety, environmental and equipment constraints often pre- reflux drum or reducing the stripper heat input thus allowing clude drawing internal samples.
Reducing Tracking and closely monitoring temperature changes is stripper heat input is more effective when the light is only also invaluable for diagnosing component accumulation. In Case , Temperature changes reflect composition changes. Since the reducing the stripper heat input effectively provided an outlet accumulation is that of an intermediate key component, it for ethane trapped in the overhead of an alkylation unit tends to warm the top of the tower and cool the bottom of depropanizer, where venting was relatively ineffective.
This tendency will be countered or augmented by the control system and by the rise in tower pressure drop, Trapping by recycle and these interactions need to be considered when interpret- Table 4 reports cases of component trapping due to recy- ing temperature trends. In any case, one symptom is com- cling of product to the feed, usually to improve product recov- mon.
At the initiation stage, temperature deviations from ery. There are two solutions — adding some removal facilities normal are small, often negligible. As the accumulation pro- to take out the component, or increasing the purge rates. Close Diagnosing component trapping to the hiccup point, temperature excursions become large. Key to the diagnosis, especially where hiccups are encoun- The solvent recovery tower in Figure 4 was well-instru- tered, is the symptom.
With hiccups, the symptom is cycling mented, with a temperature indicator every five trays. The that tends to be self-correcting, taking place over a long time tower experienced two types of cycles: a cold cycle, predomi- period. This is seldom less than 1 h, which distinguishes hic- nantly due to the accumulation of n-propanol, and a warm cups from other, shorter-period cycles, such as those associat- cycle, mainly due to the accumulation of CS.
The deviations were largest on tray 20, diminishing from about once every 2 h to once every week.
The cycles are toward the bottom of the tower. Over a 2—3-h period, initially often regular, but if the tower feed or product flows and com- the deviations on tray 20 were small, but they became larger. Then, suddenly the column showed flooding signs and the Drawing internal samples from a tower over the cycle temperatures dropped throughout. Even a single snapshot analysis can show ing the steam flowrate, which allowed the accumulated com- accumulation of a component.
In the tower in Figure 4, a ponent to be purged from the top. Trapping by recycle. Column Brief Description 25 Natural gas Modifications to recover the deethanizer overheads previously sent to fuel compressed, chilled, then DT2. Small quantities of water, previously going to fuel, returned to the deethanizer absorber feed. The absorber top was too cold, and the deethanizer bottom too hot, to allow the water to in series escape. The water built up until freezing at the recycle chiller.
For years, the chiller was thawed to flare once per shift. This was cured by adding a small glycol dryer at the compressor discharge. The recovered materials concentrated in the process.
Corrective action was routing some water away from the process and stripping some with fuel gas into a waste gas burner. Every 2—3 days the product alcohol developed an undesirable smell due to buildup of an impurity.
This was cured by cutting the feed rate, while keeping the fusel oil and heads rates the same. During the warm cycle, the temperatures near the bottom lematic; the temperatures on Trays 4 and 16 did not change rose.
The initial rise was slow. Then the bottom temperature much. In most situations, this is time, the bottom pressure went up by 2—4 psi, indicating readily achievable even if thermocouples are not present, since flooding.
This occurred regardless can be reliably measured At the the accumulation, so the swings stopped. The temperature in same time, the bottom flowrate did not change much. The this case was set high enough to push the accumulation up the operators tackled that by cutting the steam flow by about half tower.
This provided temporary relief only. Eventually the and diverting the bottoms to an off-spec tank. This emptied buildup returned, requiring a further increase in steam. The the accumulation from the bottom rather than from the top, only way to clear the buildup in the long term was to make preventing problems in the dehydration system downstream drastic changes analogous to those described for the Figure 4 and reducing product losses.
Steady-state bulges can be readily simulated bon entrainer. The hydrocarbon is more volatile than the organ- and recognized on a plot of component concentration against ics, so once the water is gone, it distills up, leaving an organic stage numbers Figure 1. But since most accumulation prob- bottom stream. In this system, water descended stable steady-state solution. The main trick to overcome this is to study a related sys- Figure 8 is based on actual operating charts for the system tem that can converge.
One example is to reduce the concen- in Figure 7. The steam flowrate to the reboiler was tempera- tration of accumulating component in the feed to the point ture controlled.
Initially, there was a good temperature gap where convergence is readily reached. Then the concentration between Trays 8 and 12, which is typical of the region where of the accumulating component in the feed is gradually the second liquid phase disappears.
As the accumulation pro- increased, and the changes tracked by means of a tower con- ceeded, the second liquid phase descended toward Tray 8. It centration versus stages diagram for each step. With time, the movement became more intense. In simulation may alternate between a single liquid phase and this case, only the temperatures on Trays 8 and 12 were prob- two liquid phases, making convergence problematic.
There, 30 www. If enough nozzles are available on the tower, dP transmitters can be just as informative.
Finally, sight Organics Water glasses are extremely useful when safety requirements permit. In each specific situation, one of the above techniques can be particularly valuable. For instance, Case DT The hydrates were encountered below the feed, in a 8 tower section that was not operated at maximum load, so a rise in dP of the bottom section signified hydrates, while a dP 4 rise in the loaded top section signified regular flooding.
Azeotropic distillation system that experienced hiccups. This can be done either by raising the top temperature or lowering the bottom temperature, or both. This enables the Tray 4 1 Initiation accumulating component to escape with a product stream. It was successfully applied in several of the experiences reported in Table 1.
In some of these DT2.
In the others Tray 16 , , DT2. Here, the feed Tray 8 temperature is often lowered to prevent accumulation of the component in the top section or raised to prevent accumula- Tray 12 tion in the bottom section. Similarly, a feed point change may Tray 16 encourage the component to leave the column at one end or Tray 4 3 Temperature Control on Manual another. Proper bypasses around preheaters and precoolers are invaluable for this purpose e.
Temperature changes accompanying component purified side stream to the column. If purification is not eco- accumulation in an azeotropic dehydration tower. The side stream drawn purge rate is required.
Often the side draw contains good should be large enough to remove the amount of the compo- product that needs to be recycled after the accumulating nent entering in the feed. Since at the draw-off location the impurity is removed. If most of the good product is recov- component is normally far more concentrated than in the feed, ered from the side draw, there is little issue with drawing a the stream drawn is usually small.
But if some of the A typical example of this technique is using an external product cannot be recovered from the side draw, there is an boot for removing water from inside a hydrocarbon distillation incentive to minimize the side draw flowrate. This is column Figure 2. Only a small portion of the tray liquid goes achieved at the risk of not removing enough to fully mitigate to the boot.
This portion must be large enough to prevent the accumulation. Good control can play an important role water accumulation in the tower, but small enough to permit here, as shown in Case Proper Cases 2.
As with the reflux drum boot, an external water supply may be desirable. Cases , , experienced no hiccups. The problem started when the sol- and 2. During the initial operation, the from deethanizers. Unless lation far less. Fusel oil is commonly hydrated ethylene and was lean in heavier alcohols like removed by a similar scheme to that in Figure 2, except that propanol and butanol.
Occasionally, the plant processed a the side stream is usually cooled prior to phase separation and low-cost feedstock from fermentation rich in the heavier alco- the aqueous phase rather than the organic phase is returned hols. With this feedstock, severe hiccups were experienced. Cases DT2.
Removal of a small benzene- feed or the reflux drum. This is also the cure contemplated rich side stream out of the bottom section effectively increased for Case The component removal technique need not be confined Modifying the tower and internals to gravity settling. Other separation techniques, such as strip- A large number of stages is conducive to accumulation.
Skip to Main Content. Distillation Troubleshooting Author s: Henry Z. First published: Print ISBN: All rights reserved. High-speed computers have taken over the design, control, and operation of towers. Invention and innovation in tower internals have greatly enhanced tower capacity and efficiency. With all these advances, one would expect the failure rate in distillation towers to be on the decline. In fact, the opposite is the case: Distillation Troubleshooting collects invaluable hands-on experiences acquired in dealing with distillation and absorption malfunctions, making them readily accessible for those engaged in solving today's problems and avoiding tomorrow's.
The first book of its kind on the distillation industry, the practical lessons it offers are a must for those seeking the elusive path to trouble-free distillation.
Distillation Troubleshooting covers over 1, case histories of problems, diagnoses, solutions, and key lessons. Coverage includes: Reviews "…an extensive compilation of problems, solutions, and lessons learned…Kister is probably the world's foremost authority on the subject…" CHOICE , September "The third book on distillation by the renowned Henry Kister. Author Bios Henry Z. Kister is a Senior Fellow and director of fractionation technology at Fluor Corporation.
He has 30 years of experience in troubleshooting, revamping, field consulting, design, control, and startup of fractionation processes and equipment.