US-20260125813-A1 - USE OF CO2-RICH FLUE GAS AS A SWEEPING GAS IN AN ELECTROLYSIS UNIT

US20260125813A1US 20260125813 A1US20260125813 A1US 20260125813A1US-20260125813-A1

Abstract

A gas heating section and a reforming section are provided, in which flue gas is used as an anode (oxygen) sweeping gas in an electrolysis unit. The resulting combined gas stream is fed to the gas heating section/reforming section as combustion gas stream. By continuously feeding the combined gas stream to said at least one burner and combusting it, a flue gas stream of high purity CO 2 can be obtained. A chemical plant, and a process for providing a syngas stream are also provided.

Inventors

Steffen Spangsberg CHRISTENSEN

Assignees

TOPSOE A/S

Dates

Publication Date: 20260507
Application Date: 20231214
Priority Date: 20221221

Claims (14)

1 . A gas heating section, said gas heating section comprising a combustion chamber comprising at least one burner; a heating chamber arranged in thermal communication with said combustion chamber, an electrolysis unit; a reactant feed to said electrolysis unit; a fuel supply to said at least one burner; a combustion gas stream to said at least one burner; a first gas feed to said heating chamber; wherein the combustion chamber is arranged to receive said fuel supply and said combustion gas stream and combust them in said at least one burner and thereby outlet a flue gas stream rich in carbon dioxide, wherein said heating chamber is arranged to receive thermal energy from said combustion chamber and output a heated first gas stream, wherein said electrolysis unit is arranged to electrolyse the reactant feed into at least an anode product gas; wherein at least a first portion of said flue gas stream from the combustion chamber is arranged to be supplied to the anode of the electrolysis unit as a sweeping gas for said anode product gas, so as to output a combined gas stream comprising carbon dioxide and the anode product gas from said electrolysis unit; and wherein at least a portion of said combined gas stream is arranged to be supplied to at least one burner of the combustion chamber as at least a portion of the combustion gas stream.
2 . The gas heating section according to claim 1 , wherein the electrolysis unit comprises one or more solid oxide electrolyser cells.
3 . The gas heating section according to claim 1 , wherein a second portion of said flue gas stream is exported from the gas heating section.
4 . The gas heating section according to claim 1 , wherein an oxygen-rich top-up feed is also arranged to be supplied to the at least one burner.
5 . The gas heating section according to claim 1 , wherein the reactant feed is a water-rich feed and wherein said electrolysis unit is arranged to electrolyse the reactant feed into oxygen as anode product gas and hydrogen as cathode product gas.
6 . The gas heating section according to claim 1 , wherein the reactant feed is a CO 2 -rich feed and wherein said electrolysis unit is arranged to electrolyse the reactant feed into oxygen as anode product gas and carbon monoxide as cathode product gas.
7 . The gas heating section according to claim 1 , wherein a third portion of the flue gas stream is arranged to be provided as CO 2 -rich feed to the electrolysis unit.
8 . The gas heating section according to claim 1 , wherein a fourth portion of the flue gas stream is arranged to be mixed with the combined gas stream prior to said combined gas stream being supplied to at least one burner of the combustion chamber.
9 . A reforming section comprising the gas heating section according to claim 1 , in which said first gas stream is a first hydrocarbon feed, and in which said heating chamber is a reforming reactor comprising a reforming catalyst, arranged to convert said first hydrocarbon feed into a syngas stream.
10 . The reforming section according to claim 9 , wherein said reforming reactor is a steam methane reforming reactor, and wherein a water-rich co-feed is supplied to the SMR reactor.
11 . A chemical plant comprising the gas heating section according to claim 1 .
12 . The chemical plant according to claim 11 , wherein the reactant feed is a water-rich feed and wherein said electrolysis unit is arranged to electrolyse the reactant feed into oxygen as anode product gas and hydrogen as cathode product gas, and wherein the hydrogen cathode product gas is supplied as feed to at least one reactor in the chemical plant.
13 . A process for providing a syngas stream in a reforming section according to claim 9 , said process comprising the steps of: providing the fuel supply and the combustion gas stream to the combustion chamber and combusting them in said at least one burner and thereby outletting a flue gas stream rich in carbon dioxide, electrolysing the reactant feed in said electrolysis unit into at least an anode product gas; supplying at least a first portion of said flue gas stream from the combustion chamber to the anode of the electrolysis unit as a sweeping gas for said anode product gas, so as to output a combined gas stream comprising carbon dioxide and anode product gas from said electrolysis unit; supplying at least a portion of said combined gas stream to at least one burner of the combustion chamber as at least a portion of the combustion gas stream; and allowing thermal energy to flow from the combustion chamber to the reforming reactor and converting said first hydrocarbon feed to a syngas stream, in said reforming reactor.
14 . The process according to claim 13 , wherein the flue gas stream is continuously recycled as sweeping gas for the oxygen, and fed as the combined gas stream to said at least one burner and combusted, until a flue gas stream comprising >99% CO 2 is obtained.

Description

TECHNICAL FIELD The present invention relates to a gas heating section and—in particular—a reforming section, in which flue gas is used as an anode (oxygen) sweeping gas in an electrolysis unit. The resulting combined gas stream is fed back to the gas heating section/reforming section as combustion gas stream. By continuously feeding the combined gas stream to said at least one burner and combusting it, a flue gas stream of high purity CO2 can be obtained. A chemical plant, and a process for providing a syngas stream are also provided. BACKGROUND There is increasing interest in the use of electrolysis in industrial chemical plants and processes, to produce gas streams such as oxygen or hydrogen, especially in view of environmental concerns, and the increasing opportunities for using electricity from renewable sources. The oxygen stream from industrial-scale electrolysis processes, such as those which take place in a solid oxide electrolyser cells (SOEC), is often considered as a waste product, and is simply vented to the atmosphere. If oxygen streams from such industrial-scale electrolysis processes are to be effectively used, a so-called “sweeping gas” (also called a “flushing gas” or “sweep gas”) is typically employed. The sweeping gas is passed into the anode-side of the electrolysis unit, where it mixes with the oxygen produced at the anode. The resulting combined gas stream containing oxygen is then outputted from the electrolysis unit. Use of a sweeping gas provides a combined gas stream at a pressure higher than that of the oxygen stream produced in the electrolysis unit, and can be used e.g. to adjust the chemical and physical composition of the oxygen stream, for a particular use. Use of a sweeping gas also improves safety by dilution of the oxygen gas. Atmospheric air has typically been used as sweeping gas, and has the advantage of being readily-available. However, if the combined oxygen-containing gas stream from the electrolysis unit is recycled, the use of atmospheric air as sweeping gas leads to a build-up of inert nitrogen in the flue gas. Thus, when atmospheric air is used as sweeping gas in an electrolysis unit, it is required to subject the resulting flue gas to a CO2 removal step, which is undesired, because a CO2 removal unit is expensive. Thus, CO2 to be sequestered must have a high level of purity to comply with governmental rules. The use of carbon dioxide as a flushing gas is known from US2015038741 and WO2013/164172. U.S. Pat. No. 8,496,908 discloses a steam methane reforming process for producing a hydrogen product while capturing CO2 from the process. It is an object of the invention to provide effective re-use of flue gas streams from fired reformers and gas heaters, with the aim of reducing or removing the need for flue gas purification/scrubbing. It is also an object to provide effective sweeping of gases from electrolysis units. These and other objects are addressed by the present invention. SUMMARY It has been found by the present inventor(s) that generation of pure oxygen in an electrolysis unit, and use of the flue gas from combustion as a sweeping gas provides synergy between the gas heating section/reforming section and the electrolysis unit. At the same time, a flue stream can be provided, being a high purity CO2 stream. Thus, the present invention has provided a possibility of avoiding a step of subjecting the flue gas to a CO2 removal step. So, in a first aspect the present invention relates to a gas heating section, said gas heating section comprising a combustion chamber comprising at least one burner; a heating chamber arranged in thermal communication with said combustion chamber,an electrolysis unit;a reactant feed to said electrolysis unit;a fuel supply to said at least one burner;a combustion gas stream to said at least one burner;a first gas feed to said heating chamber;wherein the combustion chamber is arranged to receive said fuel supply and said combustion gas stream and combust them in said at least one burner and thereby outlet a flue gas stream rich in carbon dioxide,wherein said heating chamber is arranged to receive thermal energy from said combustion chamber and output a heated first gas stream,wherein said electrolysis unit is arranged to electrolyse the reactant feed into at least an anode product gas;and whereinat least a first portion of said flue gas stream from the combustion chamber is arranged to be supplied to the anode of the electrolysis unit as a sweeping gas for said anode product gas, so as to output a combined gas stream comprising carbon dioxide and said anode product gas from said electrolysis unit;and wherein at least a portion of said combined gas stream is arranged to be supplied to at least one burner of the combustion chamber as at least a portion of the combustion gas stream. A reforming section is also provided, which comprises the gas heating section described herein, in which said first gas stream is a first hydrocarbon feed,