In conventional industrial technologies for gas purification, impurities, such as H2S, CO2 and/or COS are removed from a gas stream such as flue gas, natural gas, syngas or other gas streams by absorption in a liquid solution, e.g. in a liquid solution comprising an amine compound.
Used liquid solution is subsequently regenerated in a regenerator column to release the impurities comprised in the solution, typically by countercurrent contacting with steam. The steam needed for regeneration is typically produced by boiling the regenerated liquid solution in a reboiler, located at the bottom at the regenerator column. In addition, reboiling may provide further release of impurities comprised in the liquid solution.
In conventional absorption-regeneration processes as described above, regenerated and reboiled liquid solution is typically re-used in another absorption cycle. The reboiled solution may however have a temperature as high as 100-150° C. To enable efficient absorption, liquid solutions based on amine compounds typically requires cooling before being passed to another round of absorption. Cooling has conventionally been accomplished by heat-exchange with used liquid solution from absorption.
The energy produced by the reboiler is not only required for regeneration, but also at other locations in an absorption-regeneration process. In general, the energy requirements of a conventional gas purification process are of three types: binding energy, stripping energy and sensible heat. Binding energy is required for breaking the chemical bond formed between the impurities and the liquid solution, whereas stripping energy is required for production of the steam needed for releasing the impurities from the liquid solution. Sensible heat is in turn needed for heating of the liquid solution prior to regeneration. In conventional systems and processes, part of the produced energy may be lost for example in the system coolers, which reduce the temperature at specified locations in the system, e.g. the cooler located near the absorber inlet for cooling return wash solution before feeding it to the absorber. Moreover, energy may be lost in condensers located at the top of the absorber, regenerator etc, and in the form of water vapor exiting the process, mostly at the top of the regenerator where water vapor is present in the purified CO2 gas.
Thus, gas removal, and in particular regeneration, is an energy intensive process. Reduction of energy requirements at different parts of a gas purification process could potentially reduce the total energy required by the process.
U.S. Pat. No. 4,152,217 discloses an absorption-regeneration process with reduced overall heat energy requirements. The process comprises a split-flow arrangement in that the spent impurity-enriched solution, resulting from absorption, is split into two streams. The first stream is directed to the top of the regenerator column without being heated. The second stream is, after being heated by heat-exchange with the hot lean stream from the bottom of the regenerator column, fed to a lower, intermediate point in the regenerator column.
In WO09/112518, a process for removal of CO2 is disclosed wherein the absorbing liquid enriched in CO2 is heated by heat-exchange prior to being fed to a regenerator column. Before being subjected to heat-exchange, the absorbing liquid is split into two streams. The first stream is heated by heat-exchange with regenerated liquid, and the second stream is heated by heat-exchange with stripping gas enriched in CO2 from the top of the regenerator column.
EP 1 759 756 discloses a CO2 recovery process wherein a solution rich in CO2 is regenerated in a regenerator tower comprising a heating member. The heating member heats the rich solution in the regenerator tower with steam generated when regenerating the rich solution in the regenerator tower.
Although various improvements of conventional gas purification technologies are known, there is an ever-existing desire to further improve these technologies, in particular in respect of energy consumption.