The present invention relates to a process and a plant de sign for the reduction of the content of carbon monoxide in the feed for steam reformers in a hydrogen production plant .

In steam reforming, generation of CO, CO2 and ¾ from hy drocarbons takes place. Steam reforming is often used to produce hydrogen for hydrotreating in refinery technology, and the steam reforming process will typically handle a number of different kinds of feedstock that can contain high amounts of CO (>5 mole%) and ¾S (>500 ppm) .

The CO is reactive when passed over Ni-based catalysts, which are also used for removal of trace amounts of sulfur in a pre-reformer. CO will be converted to methane (CH ₄₎ which causes undesirable increases in temperature, making operation of the catalysts less favorable. Furthermore, a desired product is converted back to a reactant. Finally, a high content of CO can make plant construction materials more expensive because metal dusting is likely to occur, and Ni can be removed from the catalyst because of nickel carbonyl formation. So it is desirable to reduce the CO content in the feed for steam reformers in a hydrogen pro duction plant.

CO in a sulfur-containing stream can be converted to CO2 and ¾ in the water-gas shift (WGS) reaction by a sour shift catalyst, thereby reducing the adverse effects of CO in the steam reforming process. The CO2 produced needs to be removed, which is done by using an amine wash unit. An amine unit will be needed with or without the sour shift unit to remove H ₂ S and C0 ₂ . Removing more C0 ₂ as in the sour shift case is possible with only a little additional cost on the OPEX (operating expense) side. This is shown by com paring a gas composition according to the state of the art with the sour shift solution according to the present in vention. Such comparison is made as illustrated in the ta bles below.

Table 1

Gas composition, state of the art

Table 2

Gas composition, after sour shift

So the present invention relates to a process for the re duction of the content of carbon monoxide in sulfur con taining feeds for steam reformers in a hydrogen production plant, comprising the following main unit operations in se ries :

- treatment of a process gas in a sour shift step,

- removal of carbon dioxide and hydrogen sulfide from the shifted gas by an amine wash,

- passage of the gas from the amine wash to a hydrogenator fed with natural gas and with hydrogen,

- adsorption of the hydrogen sulfide, which is formed in the hydrogenator, in a subsequent absorber, - pre-reforming the thus treated gas,

- splitting the pre-reformed gas into two sub-streams, one of which being passed to a heat exchange reformer and the other being subjected to steam reforming in a fired steam reformer and further steam reforming in the heat exchange reformer together with the pre-reformed sub-stream,

- shifting the effluent from the heat exchange reformer in a water gas shift unit,

- separating the shifted gas in a membrane unit, such as a pressure swing adsorption (PSA) unit, to obtain the hydro gen product and

- combining the hydrogen product with hydrogen from

methanation of the hydrogen-containing purge gas from the hydrotreater purge gas loop.

The hydrogen to be fed into the hydrogenator is preferably separated from a hydrotreater purge gas loop, but in some cases hydrogen from the sour shift step is enough.

Preferably the process gas is a permeate gas from a biomass gasifier. Furthermore, it is preferred that the membrane unit is a pressure swing adsorption (PSA) unit.

Regarding prior art, WO 2014/012023 A1 describes a method for producing renewable hydrogen from biomass derivatives using steam reforming technology. More specifically, the biomass derivative is decomposed and introduced directly into a steam reformer.

A process for increasing the hydrogen content of a synthe sis gas containing one or more sulfur compounds is de scribed in WO 2010/013026 A1. The process comprises the steps of heating the synthesis gas and passing at least part of the heated synthesis gas and steam through a reac tor containing a sour shift catalyst, where the synthesis gas is heated by passing it through a plurality of tubes disposed within the catalyst in a direction co-current to the flow of the synthesis gas through the catalyst. The re sulting synthesis gas may be passed through one or more ad ditional reactors containing a sour shift catalyst in order to maximize the hydrogen production yield.

WO 2009/124019 A2 discloses a sour shift process for the removal of carbon monoxide from a gas stream produced by gasification. The sour shift reaction provides an efficient and cost-effective means of elimination carbon monoxide from the gas stream, and it also generates additional hy drogen, thus increasing the amount of hydrogen produced from the gasification process. It is mentioned that the method is useful in integrated gasification processes for converting biomass.

EP 2 540 663 A1 concerns a method for adjusting the hydro- gen-to-carbon monoxide ratio in a synthesis gas comprising carbon monoxide, hydrogen, 10-40 vol% carbon dioxide and one or more sulfur derivatives as impurities. The method involves a water gas shift (WGS) reaction. Because of the presence of sulfur impurities, the WGS reaction should be implemented as a sour gas shift, but it provides good re sults by using a non-sulfided catalyst. Some embodiments provide conditions which contribute to further enhanced CO- conversion in said reaction.

US 2017/0073227 A1 relates to a process for the production of liquid hydrocarbons by Fischer-Tropsch synthesis, in which the reforming section of the plant comprises a pro cess line for autothermal reforming (ATR) or catalytic par tial oxidation (CPO) and a separate process line for steam methane reforming (SMR) .

In US 2008/0142408 Al, the treatment of a raw synthesis gas in a sour water gas step, followed by an acid gas removal, is described, resulting in a crude hydrogen stream. These steps lead to a reduction of the CO content.

Finally, EP 2 872 597 Al concerns a process comprising de composing a biomass derivative in a temperature range from 100 to 500°C to produce a gaseous product with less than 0.5 wt% of coke precursors and at least 1 wt% of gaseous hydrogen, and introducing the gaseous product into a steam reformer. The problem to be solved according to this docu ment is the increased coking activity on the steam reformer catalyst caused by feedstocks with high CO content when processing biomass-derived feeds in a steam reformer. This coking activity will cause premature degradation of the steam reformer catalyst. So, a process which can reduce the coking activity inside a steam reformer catalyst is needed.

This problem is solved by the process according to the in vention by having a sour shift and pre-reforming reaction upstream the steam reformer. Furthermore, reducing the CO content and increasing the ¾ content will make it possible to use less expensive material and minimize the risk of carbonyl formation and temperature run-away.

In accordance with the present invention, the hydrogen plant is subjected to the following successive main unit operations as shown in the appended figure:

The process gas p, preferably a permeate gas from a biomass gasifier, is treated in a sour shift step A. Then CO ₂ and ¾S in the shifted gas are removed using an amine wash B.

The gas from the amine wash is passed to a hydrogenator hg fed with a gas stream gs consisting of natural gas and hy drogen separated from a hydrotreating purge loop. The ¾S formed in the hydrogenator is absorbed in a subsequent sul fur absorber SA.

The treated gas is subjected to pre-reforming in the re former PR, and then the pre-reformed gas is split into two sub-streams. One of the sub-streams is passed to a heat ex change reformer HTER, while the other sub-stream is sub jected to steam reforming, first in a fired steam reformer (SMR) and then in the heat exchange reformer together with the pre-reformed sub-stream.

The effluent from the heat exchange reformer is shifted in a WGS unit. The shifted gas is subsequently separated, preferably in a PSA unit, into hydrogen product and com- bined with hydrogen obtained from methanation of the hydro gen-containing purge gas from the hydrotreater purge gas loop in a methanator (M) .