Methods and Apparatuses for Removal of Hydrogen Sulfide and Carbon Dioxide from Biogas

Abstract

Methods, systems and apparatuses herein provide a unique and novel process to remove H 2 S from biogas. Methods, systems and apparatuses herein provide a unique and novel process to remove H 2 S from biogas with ease of operation and reduced operating and capital costs. Methods, systems and apparatuses herein provide a unique and novel process to remove H 2 S over CO 2 from biogas.

We claim: 
     
         1 . A method for removing contaminants in a biogas comprising:
 (a) heating and aerating anaerobic digester effluent in an aeration reactor to produce an alkaline effluent;   (b) contacting the alkaline effluent from step (a) with an input biogas in a reactor to produce a treated biogas and a resulting effluent with a lower pH as compared to the pH of the alkaline effluent; and   (c) recovering the treated biogas from step (b), wherein the treated biogas has less H 2 S as compared to the input biogas.   
     
     
         2 . The method of  claim 1  further comprising:
 (d) aerating the resulting effluent of step (b) to produce a regenerated effluent with an alkaline pH. 
 
     
     
         3 . The method of  claim 2  further comprising:
 (e) contacting the regenerated alkaline effluent of step (d) with the recovered biogas of step (c) to remove CO 2  in the biogas. 
 
     
     
         4 . The method of  claim 1 , wherein heating the anaerobic digester effluent comprises using a heat exchanger with the exhaust from a biogas engine as the heated air stream. 
     
     
         5 . The method of  claim 1 , wherein heating the anaerobic digester effluent comprises heating the effluent to a temperature from about 140° F. to about 170° F. 
     
     
         6 . The method of  claim 1 , wherein aerating the anaerobic digester effluent is accomplished using micro-aerators that aerate the effluent at a rate from 5 gallons/cfm to 25 gallons/cfm. 
     
     
         7 . The method of  claim 1 , wherein contacting the alkaline effluent with an input biogas comprises using an alkaline effluent with a pH from about 9.0 to about 12.0. 
     
     
         8 . The method of  claim 1 , wherein contacting an input biogas with the alkaline effluent comprises using a bubble column reactor. 
     
     
         9 . The method of  claim 8 , wherein the bubble column reactor has an inlet orifice sparger. 
     
     
         10 . The method of  claim 8 , wherein the bubble column has a churn-turbulent flow regime. 
     
     
         11 . The method of  claim 1 , wherein contacting the alkaline effluent with an input biogas comprises a gas:liquid ratio selected from the group consisting of: 20:1, 21:1, 22:1, 23:1, 24:1, 25:1, 26:1, 27:1, 28:1, 29:1, and 30:1. 
     
     
         12 . The method of  claim 1 , wherein contacting the alkaline effluent with an input biogas comprises a gas:liquid ratio of 21-25:1. 
     
     
         13 . A method for removing contaminants in a biogas comprising:
 (a) heating and aerating an anaerobic digester effluent in an aeration reactor to produce an alkaline effluent;   (b) contacting the alkaline effluent from step (a) with an input biogas in a reactor to produce a treated biogas and a resulting effluent with a lower pH as compared to the pH of the alkaline effluent;   (c) recovering the treated biogas from step (b), wherein the treated biogas has less H 2 S as compared to the input biogas;   (d) aerating the resulting effluent of step (b) to produce a regenerated effluent with an alkaline pH; and   (e) contacting the regenerated alkaline effluent of step (d) with the recovered biogas of step (c) to remove CO 2  in the biogas.   
     
     
         14 . A system comprising:
 an aeration reactor for heating and aerating anaerobic digester effluent, wherein heating and aerating the effluent produces an alkaline effluent;   a reactor for contacting the alkaline effluent with an input biogas to produce a treated biogas and a resulting effluent with a lower pH as compared to the pH of the alkaline effluent; and   a vessel for collecting treated biogas, wherein the treated biogas has less H 2 S than the input biogas.   
     
     
         15 . The system of  claim 14 , wherein the aeration reactor comprises micro-aerators for aerating the effluent. 
     
     
         16 . The system of  claim 14  further comprising an anaerobic digester for digesting waste material, wherein effluent from the digested waste material is provided to the aeration reactor. 
     
     
         17 . The system of  claim 14  wherein the reactor for contacting the alkaline effluent with an input biogas also can be used to aerate the resulting effluent. 
     
     
         18 . The system of  claim 14 , wherein the reactor comprises a bubble column reactor. 
     
     
         19 . The system of  claim 18 , wherein the bubble column reactor has an airstone or inlet orifice sparger. 
     
     
         20 . The system of  claim 18 , wherein the bubble column reactor has a gas:liquid ratio selected from the group consisting of: 20:1, 21:1, 22:1, 23:1, 24:1, 25:1, 26:1, 27:1, 28:1, 29:1, and 30:1.