Reboilers amine

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. 

Aluminum was tried in the reboiler of an aqueous amine plant but it was found to pit very quickly. 

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 ... 

If I ever have to design an amine plant I will know, for example, that the temperature of the lean amine solution entering the absorber should be about 10°F higher than the inlet gas temperature to prevent hydrocarbon condensation and subsequent foaming, that the reboiler tube bundle should be placed on a slide about six inches above the bottom of the shell to provide good circulation, that about two percent of the total circulating flow should pass through the carbon towers, and many other necessary requirements. 

The reboiler provides the heat input to an amine stripper, which reverses the chemical reactions and drives off the acid gases. Amine reboilers may be either a kettle reboiler (see Chapter 3) or an indirect fired heater (see Chapter 5). 

The heat duty of amine reboilers varies with the system design. The higher the reboiler duty, the higher the overhead condenser duty, the higher the reflux ratio, and thus the lower the number of trays required. The lower the reboiler duty, the lower the reflux ratio will be and the more trays the tower must have. 

The typical stripper consists of a tower operating at 10-20 psig w ith 211 trays, a reboiler, and an overhead condenser. The rich amine feed is introduced on the third or fourth tray from the top. The lean amine i.s removed at the bottom of the stripper and acid gases are removed from the top. 

For most field gas units it is not necessary to specify a stripper size. Vendors have standard design amine circulation packages for a given amine circulation rate, acid-gas loading, and reboiler. These concepts can be used in a preliminary check of the vendor s design. However, lor detailed design and specification of large units, a process simulation computer model should be used. 

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. 

To preclude thermal degradation of the amine solution, the reboiler pressure must be limited to 10 mm Hg absolute pressure. Total allowable pressure drop is 3 mm Hg. 

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. 

In large and extensive industrial process plants, it is not unusual to find unvented condensate receivers or reboilers at the end of a long steam-condensate line. These vessels tend to act as collection and storage points for carbon dioxide, which may redissolve in condensate. These satellite stations should be vented and receive an amine booster feed. 

In the amine stripper, the MEA solution is regenerated by stripping the solution of CO2 and H2S using hot vapors from the reboiler. The hot liquid from the stripper is cooled before returning to flie absorber by first preheating the feed stream to the still in an interchanger and then by air cooling. An accumulator in the line dampens the solution flow rate to the absorber. 

The principle of post-combustion capture is shown in Figure 11.9. The exhaust gas from the NGCC plant is sent to the C02 capture unit, which typically utilizes chemical solvents such as amines or alcohols.7"13 Chemical absorption of C02 using solvent is preferred because of the low concentration of C02 ( 5%) and low pressure in the flue gas. The solvent loaded with C02 is regenerated typically in a reboiler using low-quality steam. The C02 released from the solvent can be sent to a sequestration plant. 

The raw sour gas capacity of each train is 162 million std.ft per day (MMSCFD) or 4.6 million std.m per day for a sulfur production of over 2000 tons per day. The reboilers duty for each amine train was 135 MW (460MMBtuh or 116 Gcal h ), which is roughly equivalent to the heat energy produced by the downstream Claus unit as LP steam. 

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. 

Fig. 2.13. Split flow amine sulfur ronoval process, (a) Absorber, (b) regenerator (c) lean/rich solution heat exchanger (d) cooler, (e) reboiler, (f) reclaimer, (g) condenser...

Whenever the occurence of amines has to be expected - for instance due to the presence of nitrous oxides or ammonia in the synthesis gas - a cation exchanger is normally provided in the predegassed raw methanol. Raw methanol is fed to the bottom half - usually between trays 8 and 10 counting from the top - of the prerun column which is equipped with a total of some 40 trays. Valve trays are normally used as they are characterized by a much better partial load behaviour than the cheaper sieve trays. The column is heated by a reboiler... 

Solvent contaminated] carryover from upstream equipment example oil from compressor brines, corrosion inhibitors, sand, [corrosion products, see Section 1.3] /oxygen leaks into storage tank/inadequate corrosion control, example low pH causing corrosion/degradation via overheating, ex hot spots in reboiler tubes or fire tubes/ineffective filters/ineffective cleaning before startup/for amine absorbers corrosion products/FeS/chemicals used to treat well. 

In the low-pressure amine absorption system, a low stripper pressure is used to keep stripper reboiler duty as small as possible. In the high-pressure TEG absorption system, there is a smaller dependence of reboiler energy on pressure. A higher pressure in the stripper reduces the compression costs to raise the recovered carbon dioxide gas up to the required pipeline pressure for sequestration. Therefore, there is an optimum economic stripper pressure (ISOpsia) that balances compression costs with stripper reboder energy cost. The stripper distillate is cooled to 110 °F to minimize the amount of water in carbon dioxide gas product from the stripper reflux drum. Diameters of the columns are very large due to the enormous throughput. 

Reflux-drum temperature in the stripper is controlled by manipulating stripper reboiler duty (temperature controller TCdrum in Fig. 14.19). A 1 min deadtime is inserted in the loop, and relay-feedback testing and Tyreus-Luyben tuning give Kc = 0.26 and tj = 66 min. The set point of this temperature controller is 110 F. This should be compared to the 363 K (193 °F) used in the low-pressure amine process. 

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