METHOD FOR THE REMOVAL OF OXYGEN FROM AN INDUSTRIAL GAS FEED

Abstract

Oxygen is removed from a gas feed such as a landfill gas, a digester gas or an industrial CO.sub.2 off-gas by heating the feed gas, optionally removing siloxanes and silanols from the heated feed gas, optionally removing part of the sulfur-containing compounds in the heated feed gas, injecting one or more reactants for oxygen conversion into the heated feed gas, carrying out a selective catalytic conversion of any or all of the volatile organic compounds (VOCs) present in the gas, including sulfur-containing compounds, chlorine-containing compounds and any of the reactants injected, in at least one suitable reactor, and cleaning the resulting oxygen-depleted gas. The reactants to be injected comprise one or more of H.sub.2, CO, ammonia, urea, methanol, ethanol and dimethyl ether (DME).

Claims

1. A method for the removal of oxygen from an industrial gas feed, said method comprising the following steps: (a) heating the feed gas, (b) optionally removing siloxanes and silanols from the heated feed gas, (c) optionally removing part of the sulfur-containing compounds in the heated feed gas, (d) injecting one or more reactants for oxygen conversion into the heated feed gas, (e) carrying out a selective catalytic conversion of any or all of the volatile organic compounds (VOCs) present in the gas, including sulfur-containing compounds, chlorine-containing compounds and any of the reactants injected in step (d), in at least one suitable reactor, and (f) cleaning the resulting oxygen-depleted gas.

2. Method according to claim 1, wherein the reactor in step (e) is divided into two or more reactors with inter-bed cooling in between.

3. Method according to claim 1, wherein the gas feed, from which oxygen is to be removed, is a landfill gas, a digester gas or an industrial CO.sub.2 off-gas.

4. Method according to claim 1, wherein the cleaning in step (f) comprises removal of CO.sub.2 in a separation unit, removal of N.sub.2 and drying of the cleaned gas.

5. Method according to claim 1, wherein the gas has a high content of nitrogen and oxygen.

6. Method according to claim 2, wherein the energy recovered after each reactor is used in a re-boiler in the CO.sub.2 separation unit.

7. Method according to claim 1, wherein the feed gas is heated to a temperature of between 150 and 450 C.

8. Method according to claim 1, wherein the feed gas is heated to a temperature of between 150 and 450 C. and thereafter fed to the units for sulfur, siloxane and silanol removal.

9. Method according to claim 8, wherein the feed gas to the sulfur, siloxane and silanol removal units is heated through heat exchange with the effluent gas from the oxygen removal step.

10. Method according to claim 1, wherein the components to be injected comprise one or more of H.sub.2, CO, ammonia, urea, methanol, ethanol and dimethyl-ether (DME).

11. Method according to claim 3, wherein the landfill gas contains H.sub.2S and organic sulfur along with siloxanes, silanols, CO.sub.2, H.sub.2O, methane, chlorinated compounds, freon compounds and various VOC (volatile organic carbon) compounds.

12. Method according to claim 1, wherein the catalyst comprises a metal selected among vanadium, tungsten, chromium, copper, manganese, molybdenum, platinum, palladium, rhodium and ruthenium in metallic or metal oxide form supported on a carrier selected from alumina, titania, silica and ceria.

13. Method according to claim 1, wherein the sulfur components are converted to SO.sub.2 through selective catalytic conversion and the SO.sub.2 is removed in a scrubber.

14. Method according to claim 13, wherein the SO.sub.2 is removed in a wet caustic or H.sub.2O.sub.2 scrubber or in a dry scrubber using a caustic sorbent.

Description

[0039] The invention is illustrated further with reference to the figure, where the present invention is combined with Applicant's GECCO technology for digester and landfill gas conditioning. The feed gas is heated to 200-450 C. and fed to a siloxane and silanol absorption bed comprising alumina, alumina with nickel, silica or combinations thereof. After siloxane and silanol removal, one or more components suitable for catalytic oxidation, i.e. H.sub.2, CO, ammonia, urea, methanol, ethanol, DME etc., is/are injected into the main gas stream containing oxygen. Then the gas is fed to a catalytic reactor for both selective oxidation of sulfur components and selective catalytic oxygen conversion. Said catalytic reactor contains one or more catalysts converting the sulfur compounds to SO.sub.2 and the VOC compounds (not methane and light [i.e. C3 and lower] hydrocarbons) to CO.sub.2 and water and also hydrogen halides if some of the VOCs are halogenated. The catalyst(s) also effect(s) selective oxidation to H.sub.2O and CO.sub.2, while the valuable hydrocarbons, such as methane and light [i.e. C3 and lower] hydrocarbons, are substantially not converted. It is preferred that the catalyst comprises tungsten, vanadium, molybdenum, platinum or palladium in metallic or metal oxide form supported on a TiO.sub.2 carrier.

[0040] The catalyst(s) can be selected from tungsten, vanadium, molybdenum, platinum and palladium in metallic or in metal oxide form supported on a TiO.sub.2 carrier or from vanadium, tungsten, chromium, copper, manganese, molybdenum, platinum, palladium, rhodium or ruthenium in metallic or metal oxide form supported on a carrier selected from alumina, titania, silica and ceria or combinations thereof.

[0041] The hot reactor exit gas can be utilized to heat the reactor inlet gas by using a feed-effluent heat exchanger.

[0042] The additional heat generated in the oxygen removal step will provide a higher temperature difference for the feed-effluent heat exchanger, which reduces the CAPEX.

[0043] Downstream from the heat exchanger, the SO.sub.2 is removed in a wet caustic or H.sub.2O.sub.2 scrubber or a dry scrubber using a caustic sorbent. After the SO.sub.2 removal, CO.sub.2 is removed by using amine-based technology, solvent-based CO.sub.2 removal technology, water-based CO.sub.2 removal technology or alternatively PSA and/or membrane technology.

[0044] Nitrogen removal can be accomplished using membrane or PSA based technology. Then water is removed by using cooling and condensation followed by a molecular sieve, alternatively in a TSA configuration. Alternatively, the nitrogen removal unit is positioned downstream from the water removal unit.

[0045] It is further preferred that the catalyst is monolithic to decrease the power consumption for transport of the landfill gas through the cleaning section.