Amine Stripper

Eor use in paint strippers, one of its first appHcations, methylene chloride is blended with other chemical components to maximi2e its effectiveness against specific coatings. Typical additives include alcohols, acids, amines or ammonium hydroxide, detergents, and paraffin wax. Paint stripping formulations without methylene chloride have not as yet been shown to be as effective as those with methylene chloride. 

Tower Internals and Equipment Modification. Tower capacity expansion can be achieved through the use of random or stmctured packing, or through the use of higher capacity trays such as the UOP multiple downcomer tray. Packing has been used in the gasoline fractionator, water quench tower, caustic and amine towers, demethanizer, the upper zone of the deethanizer, debutanizer, and condensate strippers. Packing reduces the pressure drop and increases the capacity. 

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). 

Amine strippers use heat and steam to reverse the chemical reactions with CO2 and H2S. The steam acts as a stripping gas to remove the COo and HjS from the liquid solution and to cairy these gases to the overhead. To promote mixing of the solution and the steam, the stripper is a trayed or packed tower with packing normally used for small diameter columns. 

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. 

Amine-stripper overhead condensers are typically air-cooled, fin-fan exchangers. Their duty can be determined from the concepts in Chapter 3 as required to cool the overhead gases and condense the overhead steam... 

A typical chemical absorption scheme is shown in Figure 4. A low C02 concentrated flue gas is introduced in the absorber in crosscurrent with lean solvent from the stripper at 50-55°C and ambient pressure. C02 reacts with amines in the absorber according to the overall reaction ... 

As C02 is absorbed, rich amine from the absorber bottom is fed into a cross-exchanger with lean amine before it is introduced into the stripper. The stripping temperature varies between 120 and 150°C, and the operating pressure reaches up to 5 bar. A water saturated C02 stream is released from the top and is subsequently ready for transport and storage, while lean amine leaving the stripper is pumped back into the absorber. 

In Europe, the TNO [27] and Kvaerner [19] are both developing contactors to remove water and carbon dioxide from natural gas. Glycol or amines are used as the absorbent fluid. The goal is to reduce the size and weight of the unit to allow use on offshore platforms, so oftentimes only the absorber, the largest piece of equipment in a traditional absorber/stripper, is replaced with a membrane contactor. Kvaerner has taken this technology to the demonstration phase and commercial units are expected to be introduced soon. 

Figure 6 shows a simplified C02 capture process with two major process units absorber and stripper Zhang et al., 2009. A lean amine solvent (low C02 loading) is fed into the top of the absorber and is in counter-current contact with the gas containing C02. The C02 is chemically absorbed by the amine solvent and the treated gas exits the top of the absorber. The rich (high C02 loading) amine leaves the bottom of the absorber and is preheated by a cross heat exchanger before... 

The resulting figure, equal to 18.3 /ton of C02 recovered, is quite interesting and competitive with traditional technologies to capture C02, such as, for example, direct contact strippers using amines (the estimated cost to capture C02 in this case is about 40 /ton) or absorption processes (VPSA) combined with a cryogenic C02 purification unit (the estimated cost to capture C02 in this case is about 30 /ton). 

The cooled process gas that leaves the Syngas Scrubber is fed to the Amine unit. The amine unit consists of an absorption-stripping system plus associated equipment. In this system a circulating amine stream (activated MDEA - or Methyl Diethanolamine) absorbs the C02 in the C02 Absorber. The amine is regenerated in the C02 Stripper with the C02 being recycled to the compressor. 

In this case, carbon dioxide reacts reversibly in the adsorber with aqueous alkaline solutions to form a carbonate adduct (configuration 1). This adduct decomposes in the stripper upon heating. In early ammonia plants, an aqueous solution of 15-20 wt % monoethanolamine (MEA) was always standard for removing CO2. Primary alkanolamine solutions, however, require a relatively high heat of regeneration so that, nowadays, secondary and tertiary ethanol amines are mainly used. 

Chapters 7 and 9 present that stage efficiency prediction and scaleup can be difficult and unreliable. Section 4.1.2 points out that the computational form in which stage efficiencies are often applied, as multipliers to the equilibrium If-values, may inadequately reflect actual equilibrium or column operation. For highly nonideal, polar, and reactive systems, such as amine absorbers and strippers, prediction and... 

Methane is the most common hydrocarbon in acid gas mixtures. Large quantities of other hydrocarbons are probably indicative of problems with the amine plant and should be addressed. For example, foaming will cause carry-over of the hydrocarbons into the stripper. In the regeneration of the amine, the hydrocarbons will end up in the acid gas. 

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 reaction with stronger acidic gases (pKa < 6) leads to the HSAS or inorganic salts, which are difficultly regenerated at stripper conditions, resulting in degradation of the amine solvents. 

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