Amine scrubbing

When both HjS and mercaptans are to be removed in the light ends treating plant, the amine scrubbing tower precedes the caustic washing step. If the order were reversed, the large quantity of HjS present would "fix" the caustic. Also, the caustic will act to remove any final traces of HjS when it follows the scrubbing tower. 

Refiners can address the sulfur issue in stages, but decisions should be made that will leave the door open for further reductions. If hydrotreating is selected, the design can include oversized reactors, connections for a spare compressor, or connections for adding amine scrubbing inside the recycle loop. Some process or catalyst changes can buy time, some can solve the problem. 

Figure 7.4 Air Liquide/Medal membrane unit replacement of amine scrubbing towers (used with permission).

The major problems in the current liquid amine scrubbing process are the following ... 

Even the methane present in natural gas is not without its sulfur gas polluting potential if burned directly in the form obtained from the wellhead. This potential is removed by thorough desulfurization using an amine scrub before it is piped to industrial and domestic consumers (Section 7.5). This is another example of a precombustion cleaned fuel. 

SO2 reduction with H2S + catalyst (Claus) SO2 reduction with CH4 + catalyst to H2S, then amine scrub (e.g.. none s... 

Or the sulfur dioxide may be reduced catalytically with methane or other hydrocarbons to hydrogen sulfide. The hydrogen sulfide produced by this method is captured by amine scrubbing of the reduced gas stream (Eqs. 3.18-3.20). 

A minor variant to the amine scrubbing process described above is the Sulfinol process, which still uses an alkanolamine base, diisopropanolamine (35%), but in a solvent consisting of a mixture of sulfolane (40%), tetramethy-lene sulfone (CH2)4S02, a good hydrogen sulfide solvent) and water [29]. Other processes are based on hydrogen sulfide absorption in aqueous alkaline carbonate solutions, such as the Catacarb and Benfield systems (Eqs. 9.16 and 9.17). 

Hydrogen sulfide separated from natural gas by amine scrubbing is a highly odorous, toxic, low boiling gas and for these reasons is difficult to store or ship in large quantities. Hence, a Claus unit is closely associated with each amine scrubber to convert the hydrogen sulfide gas product of the scrubber to elemental sulfur. This is much easier and safer to store and ship in large quantities. 

Iron casting (core production) For core production, the cold-box and Croning processes are used. Scrubbing concentrates are generated in amine scrubbing... 

Where there is carbon dioxide mixed with methane from natnral gas wells, its separation is well proven. Several processes are nsed, inclnding hot potassium carbonate which is energy-intensive and requires a large plant, an olamine process which yields high-purity carbon dioxide, amine scrubbing, and membrane processes (Mokhatab et al., 2006 Speight, 2007a,b). 

Oxyfuel combustion, where coal is burned in oxygen rather than air, means that the flue gas is mostly CO2 and hence it can more readily be captured by amine scrubbing—at about half the cost of capture from conventional plants. 

We also accoimt for emissions associated with the operation of amine scrubbing in the case of Barnett gas. Amine scrubbing is not required for Marcellus gases, as the CO2 content is within pipeline specifications. 

Several post-combustion technologies are under development, such as amine scrubbing, membrane separation, adsorption. Among these technologies, an interesting option is the cryogenic CO2 separation as reported in the following section. 

The aim of the work described in this chapter is to evaluate the cryogenic packed bed (CPB) concept, both on technical aspects and on economic performance. Furthermore, the economics of the CPB concept are compared to other post-combustion technologies, namely, amine scrubbing and membrane technology, investigating the importance of various process assumptions. 

The chapter is organized as follows first a base case is defined and the costs per ton of CO2 emissions avoided are calculated. Subsequently, a sensitivity analysis of some key process parameters is discussed. Finally, the results are compared to the results of economic studies on CO2 capture via amine scrubbing [23] and membrane technology [20]. 

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