Reboiler corrosion

The use of iodine-containing species to reduce suction chiller reboiler corrosion (Section 9.1.6.4A) has an added advantage. This iodine that forms reacts as below ... 

Direct reheat bypass line, 127 Dirty amine cleanup, 94-95 corrosion inhibitors, 94—95 reboiler corrosion, 95 regenerator feed temperator, 95... 

Reactor vapor, 184, 186 Reboiler circulation, 272-273 Reboiler corrosion, 109 Reboiler leaks, 92 Reboiler problems (distillation lowers), 271-275, 280, 388 Irapoul pans, 271-272 plugged reboilers, 272-273 trapout pan repair, 273 steam-side problems, 273 blown condensate seal, 273-275 distillation, 388... 

Formex pro-cess, Snam-progetti /V-formyl-morph o-line (FM) water is added to the FM to increase its se-lectivity and also to avoid high reboiler temperatures during solvent recovery by distillation 40 perforated-tray ex-tractor, FM density at 1.15 aids phase separation low corrosion allows use of carbon steel equipment... 

Primary alkanolamine solutions require a relatively high heat of regeneration. Also excessive temperatures or localized overheating in reboilers cause the MEA to decompose and form corrosive compounds. An inhibitor system, such as the Amine Guard system developed by Union Carbide, is an effective method of corrosion control (52). Inhibitors permit the use of higher (25—35%) concentration MEA solutions, thus allowing lower circulation rates and subsequendy lower regeneration duty. 

Stressed, such as heat-affected zones near welds, in areas of high acid-gas concentration, or at a hot gas-liquid interface. Therefore, stress-relieving all equipment after manufacturing is necessary to reduce corrosion, and special metallurgy in specific areas such as the still overhead or the reboiler tubes may be required. 

Rich/lean amine exchangers are usually shell-and-tube exchangers with the corrosive rich amine flowing through the tubes. The purpose of these exchangers is to reduce the reboiler duty by recovering some of the sensible heat from the lean amine. 

A common case where intense general corrosion is experienced in a very restricted section of plant is where an acidic vapour is condensing. As a vapour the acid is usually non-corrosive, but when condensed it can only be handled in expensive materials. Another variation on this theme is that only at the region of initial condensation is there a corrosion problem, either the condense/reboil condition being particularly corrosive or else corrosion only takes place at or near the boiling point. Several variations in design are possible to cope with these situations ... 

Where the corrosion problem is limited to the condense/reboil situation, i.e. where, due to variations in vapour temperature (or temperatures of the surfaces with which the condensate can come into contact), the condensate reboils, the answer may be to use resistant material at... 

That is, carbonic acid, will be formed. Carbonic acid is quite corrosive to carbon steel. Reboiler tube leaks, associated with steam-side corrosion, are almost certainly due to carbonic acid attack. 

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. 

The hardness deposits coat the inside of the boiler s tubes, interfere with heat transfer, and overheat the tubes. The carbon dioxide, which is also generated from the dissolved solids, creates more serious corrosion problems in downstream heat exchangers. When the steam condenses, the carbon dioxide may remain trapped in the reboiler or preheater as a noncondensable gas. Actually, there is no such thing as a noncondensable gas. Even C02 is somewhat soluble in water. As the C02 dissolves in the condensed steam, it forms carbonic acid, a relatively weak acid (pH typically between 5 and 6). Strong acids will have pH values of 1 to 2. Pure water has a pH of seven. Carbonic acid is particularly corrosive to carbon steel heat-exchanger tubes. 

Water in reflux tends to get trapped in the tower, if the tower-bottom temperature is above the boiling point of water, at the tower s operating pressure. The water trickles down the tower and revaporizes off of the hot reboiler tubes. As the water may be saturated with corrosive salts and gases, reboiler tube corrosion can be rapid. In almost every petroleum refinery service, refluxing water is a quick route to reboiler tube leaks. 

Coking in reboilers and rerun columns is caused in many cases by operating at excessive temperatures. In these cases, the difficulty can be reduced and sometimes be eliminated by reducing the temperature of the reboiler. Temperatures of 400°F. and above should be avoided. The breakdown of esters and other sulfur compounds in the rerun reboiler usually results in the production of corrosive alkylate and corrosion in the rerun column. A reduction in the reboiler temperature is sometimes sufficient to clear up this situation, but in some cases, an injection of mono- or triethanolamine into the feed is required. 

Zirconium is used in nitric acid service for cooler condensers, tail gas preheaters and reboilers. It rivals tantalum in its corrosion resistance to nitric acid at all concentrations up to the boiling point. Its resistance extends up to 230°C and 65 wt %. However it is susceptible to stress corrosion cracking, which can be prevented by avoiding high, sustained tensile stresses104. 

The nitric acid was added to the reboiler since HNO3 forms a low-boiling azeotrope with diacetyl, so that the HNO3 went upwards with the diacetyl, thereby protecting the entire column. After this simple measure, the corrosion problem was a specter of the past. 

The absorber and stripper shown in Fig. 9 can be combined into a single reboiled absorption column however water condensed internally will cause bottom column corrosion and plugging, whereas in the scheme of Fig. 9, the water is removed at the feed drum. Tray efficiencies in absorption columns are much lower than in distillation columns because of the presence of noncondensible gases. Furthermore, there is a tendency to... 

Safety, environmental protection, and equipment protection (see Section 16.7 this could include redundant temperature sensing and alarms on reactors and reboilers handling corrosive chemicals such as HF), smooth operation, product quality, profit, monitoring, diagnosis, and troubleshooting. Identify the objective and select a pertinent variable. Direct measurement of the variable is preferred. If direct measurement is impractical, select an inferential or calculated variable. For example, temperature can infer conversion and composition. 

Problems that may be manifested in the operation of evaporators and reboilers are numerous (1) corrosion and erosion, (2) flow maldistribution, (3) fouling, (4) flow instability, (5) tube vibration, and (6) flooding, among others. The final design must take into account some or all of these problems in addition to the thermal and mechanical design. 

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