Steel mill offgas separation and purification
A method comprising contacting an offgas stream comprising H2, H2O, CO, CO2, and at least one impurity comprising COS with at least one metal oxide to catalyze a reaction of H2O and COS to form H2S and CO2 in the offgas stream; contacting the offgas stream with an H2S-adsorbent to remove H2S from the offgas stream to produce a treated gas stream; and separating the treated gas stream to produce a carbon dioxide-enriched stream and a carbon dioxide-depleted stream.
1 . A method comprising:
contacting an offgas stream comprising H2, H2O, CO, CO2, and at least one impurity comprising COS with a pretreating adsorbent in a pretreating adsorbent bed to catalyze a reaction of H2O and COS to form H2S and CO2 in the offgas stream and remove H2S from the offgas stream to produce a treated gas stream; and
separating the treated gas stream to produce a carbon dioxide-enriched stream and a carbon dioxide-depleted stream;
wherein the pretreating adsorbent comprises particles with a combination of an H2S-adsorbent and at least one metal oxide.
2 . The method of claim 1 , wherein the at least one metal oxide comprises at least one of alumina, titania, MnO2, CuO, CaO, MgO, and NiO.
3 . The method of claim 1 , wherein the H2S-adsorbent comprises zinc oxide.
4 . The method of claim 1 , wherein the at least one impurity further comprises H2S, SOx, NOx, HCN, NH3, and/or BTEX.
5 . The method of claim 4 , further comprising contacting the offgas stream with an HCN hydrolysis catalyst to catalyze a reaction of HCN and H2O to form NH3 and CO in the offgas stream.
6 . The method of claim 1 , wherein the absolute value of the total concentration of water in the offgas stream minus the total concentration of water in the treated gas stream is less than 500 ppmv.
7 . The method of claim 1 , wherein the absolute value of the total concentration of oxygen in the offgas stream minus the total concentration of oxygen in the treated gas stream is less than 500 ppmv.
8 . The method of claim 1 , further comprising contacting the treated offgas stream with a water gas shift catalyst prior to separation to produce carbon dioxide-enriched stream and the carbon dioxide-depleted stream.
9 . The method of claim 1 , wherein the offgas stream has a temperature ranging from 230 to 300° C. when contacted with the at least one metal oxide.
10 . The method of claim 1 , further comprising:
separating the carbon dioxide-depleted stream or a stream derived from the carbon dioxide-depleted stream to produce a hydrogen product stream and a hydrogen-depleted tail gas stream;
contacting the carbon dioxide-enriched stream with a dehydrating adsorbent to produce a dry carbon dioxide product and a spent dehydrating adsorbent; and
regenerating the spent dehydrating adsorbent with a regeneration gas stream to produce the dehydrating adsorbent and a spent regeneration gas stream;
wherein the regeneration gas stream comprises at least a portion of the hydrogen-depleted tail gas stream or a stream derived from the hydrogen-depleted tail gas stream.
11 . The method of claim 10 , further comprising recycling at least a portion of the hydrogen product stream to a blast furnace; wherein the hydrogen product stream has a purity ranging 50% to 95%.
12 . The method of claim 10 , further comprising separating a carbon monoxide product from the carbon dioxide-depleted stream prior to separating the carbon dioxide-depleted stream or a stream derived from the carbon dioxide-depleted stream to produce a hydrogen product stream and a hydrogen-depleted tail gas stream.
13 . The method of claim 12 , further comprising removing oxygen from the carbon dioxide-depleted stream prior to separating the carbon monoxide product from the carbon dioxide-depleted stream.
14 . The method of claim 10 , further comprising separating the hydrogen-depleted tail gas stream by selective permeation prior to regenerating the spent dehydrating adsorbent to produce a hydrogen-enriched permeate stream and a hydrogen-depleted retentate stream;
wherein the regeneration gas stream comprises at least a portion of the hydrogen-depleted retentate stream.
15 . The method of claim 14 , further comprising combining the hydrogen-enriched permeate stream with the offgas stream.
16 . The method of claim 10 , wherein the dehydrating adsorbent also removes NH3 and BTEX from the carbon dioxide-enriched stream.
17 . The method of claim 10 , further comprising reacting the spent regeneration gas stream with an oxidant to produce a vent stream;
wherein the vent stream comprises at least 85% N2 by volume.