WO2020047620A1

WO2020047620A1 - Generation of syngas for hydrogen production by steam reforming of hydrocarbons applying a process of complete combustion of a fuel gas stream in autothermal reforming

Info

Publication number: WO2020047620A1
Application number: PCT/BG2019/050001
Authority: WO
Inventors: Todor Todorov
Original assignee: Todor Todorov
Priority date: 2018-09-03
Filing date: 2019-08-27
Publication date: 2020-03-12
Also published as: BG112796A

Abstract

The invention relates to the processes of steam reforming of hydrocarbons and of the partial or complete oxidation of hydrocarbons. The invention replaces the process of partial oxidation of the feed process gas in the conventional ATP by a process of complete combustion of a fuel gas stream. For the process of ATR with complete combustion, a fuel gas stream (11) separated after the Sulfur Removal Unit is fed into the combustion zone of the ATP reactor (16), mixed with a steam stream (12). A stream of oxidant (8), mixed with a steam stream (13), is also fed into the combustion zone. The complete combustion products deliver their heat by mixing with a (5) feed process gas and steam stream. The gas mixture enters the catalyst zone (16B) of the full combustion ATR reactor (16), where a steam reforming process of the hydrocarbons supplied by stream (5) (a process feed gas and steam mix) takes place.

Description

Generation of Syngas for hydrogen production by steam reforming of hydrocarbons applying a process of complete combustion of a fuel gas stream in Autothermal Reforming

Technical Field of the invention

The invention relates to the production of syngas by steam reforming of hydrocarbons.

Background art of the invention

Current state of hydrogen production technology

There are various hydrogen production technologies. The ones that are the most cost-effective and, therefore, the most wide-spread are those that are based on the production of syngas from hydrocarbons. These include:

• Partial oxidation

• Steam reforming

• Autothermal reforming (ATR)

Syngas is a gas mixture composed of hydrogen and carbon monoxide, as well as carbon dioxide and unreformed hydrocarbons. At the next step of the hydrogen production process, the shift conversion of the carbon oxide, the carbon monoxide reacts with steam to form carbon dioxide, thus yielding additional hydrogen.

According to the intended end product of the industrial process - hydrogen, ammonia, methanol, synthetic fuel, etc, different ratios of hydrogen to carbon monoxide are required within the syngas mixture. The production of hydrogen and ammonia requires the highest possible yield of hydrogen per unit of starting material.

A review of current syngas production process technologies Partial Oxidation (POX)

This is a technology in which hydrocarbons are subjected to partial oxidation with oxygen.

The oxygen source can be air, oxygen-enriched air, or pure oxygen.

Because all the necessary hydrocarbon source is fed to combustion, and the supplied oxygen is limited, it is not completely oxidized to carbon dioxide and water. Instead, partial oxidation takes place, producing carbon monoxide and hydrogen, or carbon monoxide and water, in a process described by the following reactions (here and in the following examples methane is used as the hydrocarbon source).

1. CH₄ + 1.50₂<=> CO + 2H₂0 DH_{298 K} = -519 kJ/mol

2. CH₄ + 0.5O₂<=> CO + 2H₂ DH_{298 k}= -36 kJ/mol

The reactions are exothermic - they release heat, and the process does not need to be supplemented with an external heat source.

At the next step, the shift conversion of carbon monoxide, carbon monoxide reacts with water steam on a catalyst to yield additional hydrogen.

The POX technology has the lowest relative hydrogen yield among the three technologies described here, but in practice it is the only efficient enough for production of syngas from coal, coke and the heavy residues of petroleum refining. Because the POX technology does not use a catalyst, it is less sensitive to the presence of sulfur in the hydrocarbon source or to soot formation and carbon deposition.

Steam reforming of hydrocarbons

Steam reforming of hydrocarbons is based on the oxidation of natural gas or other light hydrocarbons with steam. The process occurs in tubes filled with a catalyst mainly in an endothermic reaction (3)

3. CH₄ + H₂0<=> CO + 3H₂ DH₂₉₈ K = +206 kJ/mol

This process results in the highest relative hydrogen yield; it is endothermic and requires heat, provided by burners outside the tubes.

The catalyst reduces its activity in the presence of sulfur in the feed gas (natural gas or light hydrocarbons), as well as in the case of deposition of soot and / or carbon on it.

To avoid possible sulfur contamination, the natural gas feed undergoes sulfur removal at 350-400°C.

To avoid the formation of soot or carbon, the steam reforming is implemented in the excess of steam, with a typical molar steam to carbon ratio of 3: 1.

When hydrocarbons with more carbon atoms are subjected to steam reforming, the feed process gas can be subjected to pre-reforming at temperatures of 400-550°C, where the heavier than methane hydrocarbons are converted to methane, hydrogen, carbon monoxide and carbon dioxide.

As a unit, steam reforming is a complex technical facility with large investment costs. The implementation of the process in a large number of tubes, the large temperature and pressure differences inside and outside the tubes, and the proximity of the burner flame to the tube walls impose high requirements for tube materials as well as limitations in the process temperature and pressure. Typical values are: outlet temperature around 800 - 850°C, pressure up to 30 - 35 bar.

In order to reduce the size and capital costs of steam reforming, to reduce fuel consumption in furnace burners, and to dose the required amount of nitrogen for synthesis of ammonia, a two-step reforming process is used. First stage - primary tubular steam reforming, and second stage - secondary steam-oxygen (air) reforming.

The secondary reforming consists of two zones. In the first zone enter the oxidant and the syngas coming from the primary reforming (containing hydrogen, carbon monoxide, carbon dioxide and residual unreformed methane. In this zone part of the combustible ingredients of the syngas (hydrogen, carbon oxide, methane) react with the oxygen from the oxidizing agent.

Depending on the desired objectives - a degree of reduction of primary reforming; hydrogen yield; supplementation of nitrogen in a stoichiometric amount for ammonia synthesis or a defined ratio of hydrogen to carbon monoxide, the oxidant may be air, oxygen enriched air, or oxygen.

Besides good combustion conditions, this zone needs to ensure the proper mixing and homogenization of the gas mixture in order to avoid the formation of soot and carbon and their deposition onto the catalyst.

After the first zone, the mixture of singas and combustion products enter a zone with a catalyst bed, where the endothermic process of the steam reforming takes place (equation 3), and the temperature of the gas mixture quickly decreases. The typical temperatures at the exit of the secondary reforming are between 900°C and 1000°C. Secondary reforming reduces both capital and operating costs (fuel for primary reformer burners) but reduces the relative hydrogen (ammonia) yield per unit of hydrocarbon feedstock in the feed gas because of burning of part of the products or the residual methane fed from the primary reforming.

Autothermal reforming (ATR)

In the case of autothermal reforming, all processes take place in a single reactor with two zones. In the first zone is performed the partial oxidation (POX) of the input hydrocarbons (equation 1 and 2), while the second zone contains the catalysts and conducts the process of steam reforming (equation 3).

The hydrocarbon source first passes through a Sulfur Removal Unit at 350- 400°C, and if it contains hydrocarbons heavier than methane, it may also undergo a pre-reforming process at 400-550°C.

Since the hydrocarbons amount is higher than the stoichiometric amount needed for complete oxidation, combustion in the combustion and mixing zone is incomplete POX (Partial Oxidation). In order to provide sufficient heat for the next catalytic, endothermic steam reforming process in the second zone, the oxidant used is usually oxygen, oxygen-enriched air or more air (the last one necessitates subsequent removal of excess nitrogen).

ATR technology allows to design cost-effective reactors with large syngas capacities. The installation of multiple ATR reactors connected with one or more combustion chambers enables the building of syngas production units with practically unlimited capacity. In spite of its lower cost, ATR is not as widely used as the two-step steam reforming due to lower energy efficiency of the ATR and its relatively lower hydrogen output per unit of hydrocarbon material.

In fact, the secondary reforming described above is autothermal reforming, which bums the syngas combustible components incoming from the first reforming.

Different variations of steam reforming and ATR are used worldwide, as well as combinations of these, for example heat exchange reforming, in which the syngas leaving the secondary autothermal reforming heats up the steam reforming tubes placed in a heat exchanger.

The input raw materials can also vary - they can be methane, light hydrocarbons, waste gases and byproducts from refining, or oxygen- containing compounds, such as alcohols or ethers (used in Fuel Cell technology, for example).

The oxidants may differ as well - air, oxygen-enriched air or pure oxygen are used.

Currently the two-stage steam reforming remains the most commonly used method for syngas production.

Disclosure of the Invention

This invention replaces the partial oxidation (POX) process in autothermal reforming and the process of combustion of syngas components in secondary reforming, with a process of complete combustion (oxidation) of a fuel gas stream. The oxidant and a fuel gas flows enter the combustion chamber in amount which allows for maximum approximation to the complete combustion (oxidation) reaction (4).

CH₄ + 20₂<=> C0₂ + 2¾0 DH₂₉₈ = -891 kJ/mol

The oxidant in this process can vary (air, oxygen-enriched air or pure oxygen) depending on the goal of the industrial process - high hydrogen output, energy efficiency, production of a certain product, etc.

Complete oxidation (Eq. 4) produces more heat per unit of fuel and per unit of oxygen than POX (Eq. 1, 2) or combustion of hydrogen to form water, and carbon monoxide to form carbon dioxide that takes place in the secondary reforming. The complete oxidation of the fuel gas flow produces heat that is used for the steam reforming (Eq.3) of more feed process gas and results in higher hydrogen yield per unit of starting material, thus reducing fuel consumption and decreasing cost per unit of output.

Combustion of fuel takes place inside the reactor and, after mixing with the input feed process gas, combustion products come into contact with a catalyst. Thus the fuel gas for this process also needs to be free of sulfur components.

When the autothermal reforming process with complete combustion is used as a secondary reformer, there also is used a hydrocarbon fuel gas stream , bypassed the primary reforming. In this way, all feed process gas flow reacts in both two stages of the steam reforming, maximizing the total hydrogen yield, same as at the primary tubular steam reforming. There is no burning and loss of primary reforming products, which is happens with the conventional secondary reforming of the syngas incoming from the primary reforming. This results in decreased consumption of feed process gas per unit of product . On the other hand, the complete combustion products are mixed with the feed process gas in the same vessel, thus transfering theirs heat into the process gas directly and completely, without losses caused by heat exchange through the walls of the primary reforming tubes and the escaping heat from the exhaust flue gases. This results in decreased fuel consumption for the reforming of feed process gas in comparison with conventional two-step reforming.

The invention decreases production cost by decreasing both the feed process gas and the fuel gas needed for the two-step steam reforming.

Reduced consumption of natural gas from full combustion ATR and steam reforming with full combustion secondary reforming , reduces to the same degree carbon dioxide emissions into the atmosphere.

For two step steam reforming, relatively larger is the reduction of carbon dioxide emissions from primary reforming burners flue gasses, which are at atmospheric pressure, and it is technically complex as well as energy and cost uneffective to capture them. The share of carbon dioxide emissions from syngas after full combustion secondary reforming increases in the total emissions.

Because the process occurs at approximately or above 30 bar pressure, it allows for the capture of more carbon dioxide per product unit through known and widely used technologies for carbon dioxide removal from syngas and its subsequent use for the production of other chemicals (e.g. urea) or its sequestration.

Brief Description of Drawings There are presented four figures.

Fig: 1 Schematic of the conventional two-step reforming Fig: 2 Schematic of the conventional autothermal reforming

Fig: 3 Schematic of the two-step steam reforming with a secondary reforming with complete combustion of a stream of fuel gas - object of the invention

Fig: 4 Schematic of the autothermal reforming with complete combustion of a stream of fuel gas - object of the invention

A list of figure elements

1. Total gas flow - source

2. Feed process gas flow for sulfur removal

3. Fuel gas flow for the burners of the primary steam reforming

4. Sulfur removal unit

5. Process feed gas and steam mixture

6. Primary steam reforming

7. Raw syngas to secondary reforming

8. Oxidant

9. Conventional secondary reforming

9 B. Catalyst zone within secondary reforming

10. Syngas

11. Fuel gas for complete internal combustion within autothermal reforming or secondary reforming - the object of this invention

12. Steam to mix with the process feed gas

13. Steam to mix with the oxidizing agent 14. Conventional auto thermal reforming

14 B. Catalyst zone within the auto thermal reforming

15. Secondary reforming with complete combustion - object of this invention

15 B. Catalyst zone of the secondary reforming with complete combustion.

16. Autothermal reforming with complete combustion - object of the invention

16 B. Catalyst zone within the auto thermal reforming with complete combustion

Notes

1. In all schematics, there is the option of placing pre -reforming after“4.

Sulfur removal unit”

2. In the schematics shown in Fig. 2 and Fig. 4,“3. Fuel gas stream for the burners of the primary steam reforming” is not used. In these figures, the terms“1. Total source gas stream” and“2. Input process gas stream for sulfur removal” refer to the same thing.

Examples for the implementation of the invention. Detailed description 1. Autothermal reforming with complete combustion

Fig. 4, depict a process of autothermal reforming with complete combustion

The reactor of autothermal reforming with complete oxidation, is a high pressure vessel with refractory on the inside of the shell and usually a water jacket on the outer side. The natural gas, consisting primarily of methane is the most commonly used source for syngas production.

The natural gas (1) heated to 350-400°C enters Sulfur Removal Unit (4), where sulfur-containing compounds are removed.

The gas, purified from sulfur compounds, is mixed with a stream of steam

(12).

At the next step the gas-steam mixture is split into two streams - stream (5): the process feed gas which enters ATR (16) to mix with the products of complete combustion, and stream (11): fuel gas for complete combustion, which enters the combustion zone of the ATR reactor (16). Another possible option is to divide fuel gas stream (11) immediately after (4) SRU and before mixing stream (5) and stream (12).

The oxidizing agent (8), mixed with a certain amount of steam (13) is supplied to the oxidation zone of the ATR (16), and complete combustion takes place (Eq.4). Another option is to supply the oxidizing agent (8) without steam (13).

The complete combustion products are mixed with the process feed gas (5), and the gas mixture enters the catalyst zone (16B), where the steam reforming process of the methane takes place (Eq.3).

Depending on the desired final product, the resultant syngas (10), after cooling, is either transferred to a CO shift conversion unit, where the carbon oxide reacts with steam to produce carbon dioxide and hydrogen, or is used for other processes that require carbon oxide as a raw material, for example the production of methanol or of products for the Fischer-Tropsch synthesis. 3. Two-stage steam reforming with secondary reforming with complete combustion (Fig. 3)

Natural gas (1) is split into two streams - stream (3): fuel gas for the burners of the primary reforming, and stream (2): process feed gas, which is heated to 350-400°C and enters a Sulfur Removal Unit (4) for removal of sulfur compounds.

The feed process gas, purified of sulfur contaminants, is mixed with steam

(12).

The gas-steam mixture is then split into two streams

The process feed gas stream(5) enters the tubes of the primary reforming (6), where steam reforming reaction (Eq. 3) takes place. To reduce the amount of fuel gas (3) low thermal load can be maintained, therefore resulting in lower reaction temperature (under 750°C) in the tubes and in higher methane slip in the produced raw syngas (7). This methane can be then reformed in the energetically more loaded secondary reforming (15).

The fuel gas stream (11) for complete combustion enters the combustion zone of the secondary (ATR) steam reforming (15). Another option is to separate stream (11) immediately after the sulfur purification unit (4) and before mixing with steam (12).

The oxidation agent (stream (8)) is supplied to the combustion zone of the secondary reforming (15), mixed with a certain amount of steam (13), and the complete oxidation reaction takes place (Eq.4). Another option is to supply the oxidizing agent (8) without the addition of steam (13). The products of complete combustion are mixed with the process feed gas (5), and the gas mixture enters the catalyst zone (15B), where the steam reforming takes place (Eq.3).

After cooling, the resultant syngas (10) is either transferred to a CO shift conversion unit where the carbon oxide reacts with steam to produce carbon dioxide and hydrogen, or it is used for other processes that require carbon oxide as a raw material, for example the production of methanol or of products for the Fischer-Tropsch synthesis.

Uses of the invention

The invention can be implemented in all processes based on syngas.

The invention is easy to implement. Design changes of ATR and secondary reforming reactors are required only within the combustion and mixing zone.

Conventional reactors for ATR and secondary reforming are currently designed to ensure partial oxidation of the gases entering the reactor and the homogeneous mixing of all components, in high volumes and under high pressure and temperature.

The process of complete combustion in ATR occurs at temperatures and pressure close to those required for partial oxidation, and it does not impose new technical requirements for the design, manufacture, comissioning, process control and operation of ATR and secondary reforming reactors with complete combustion.

All experience and knowledge accumulated using conventional processes and reactors for ATR and secondary reforming can be applied to the new process of complete oxidation and to the reactors for its implementation. For modern process control systems, there is no problem to control with a high level of accuracy, reliability and safety, any ratio between the combustion gas and the oxidant, the other necessary parameters of the flows entering the reactor, and to monitor the processes inside the reactor.

The invention can be applied both in new installations and to revamp existing ones.

Supplying fuel gas for full oxidation in a stoichiometric ratio to the oxidant maximizes the yield of hydrogen per unit of hydrocarbon feedstock. This is the case with the highest efficiency for the production of hydrogen and ammonia.

The supply of fuel gas with a different non- stoichiometric ratio to the oxydant ("partially" conducting partial oxidation), combined with methods for adjusting the composition of the syngas in the downstream steps, allows for the production of syngas with optimal ratio of hydrogen to carbon monoxide to produce the required end product at improved efficiency.

The composition of the syngas and, in particular, the nitrogen content, can be changed by the use of an oxidant with a different nitrogen to oxygen ratio (this ratio in the air is 3.71). The oxidant may be: pure oxygen; oxygen- enriched air; regular air; nitrogen-enriched air.

Higher usage efficiency of raw material and fuel, and a technically simplified scheme facilitate the use of complete combustion autothermal reforming to produce hydrogen for uses in Fuel Cell Technology and for use in local small, combustion, non-combustion and production units.

Advantages of the invention Compared with conventional processes for the production of syngas from hydrocarbons, this invention:

- Increases the yield of hydrogen per unit of raw material, thus decreasing the consumption of raw material.

- Decreases investment cost (CAPEX)

- Decreases operation cost (OPEX)

- Significantly reduces primary steam reforming or, for many applications, eliminates the need for two-stage reforming, leaving only one stage - an autothermal reforming with full combustion of the fuel gas.

- Schemes without primary steam reforming (without reaction tubes) can operate at a higher process pressure - above 40 bar; a lower steam to carbon ratio in the process feed gas around and under 2, with increased capacity for syngas production.

- Schemes without primary reforming are no longer a "bottleneck" and an obstacle to increasing the capacity of syngas plants.

- Reduces carbon dioxide emissions per unit of product.

- Allows for more carbon dioxide capturing and utilization due to the increased carbon dioxide released from syngas (at higher pressure), than the carbon dioxide which is released at atmospheric pressure by the burners in the primary reforming furnace.

- Increases the use of steam reforming process to produce hydrogen for units and "engines" with Fuel Cells. - Enables the production of hydrogen for local, small-scale’boutique" applications.

- Revamping existing units with the replacement of conventional reactors, or with minor changes in their design and with small investments, achieves a significant energy, economic and environmental impact.

References:

1. CnpaBOHHHK A30THHKa H3aaHHe 2-e, nepepa6oTaHHoe MocKBa„XHMHB“ 1986

2. US5595719A Process for steam reforming of hydrocarbons

3. US6936082B2 Very large autothermal reformer

4. US7550215B2 Autothermal reformer-reforming exchanger arrangement for hydrogen production

5. EP 0 440 258 B1 Heat exchange reforming process and reactor system

Claims

1. A process of autothermal reforming with complete combustion for production of syngas from hydrocarbons, characterized by the following: in a combustion zone of a reactor for autothermal reforming with complete combustion, by complete combustion of a stream of fuel gas with oxygen from an oxidant stream, and by mixing of the complete combustion products with process feed gas stream mixed with steam, provides the heat for the endothermic catalytic process of steam reforming of the hydrocarbons in the process feed gas stream, which process takes place in the catalyst zone of reactor for autothermal reforming with complete combustion.

2. Applying the complete combustion process as described in claim 1 to a secondary steam reforming process with complete combustion to produce syngas, characterized by the following: in a combustion zone of a reactor for secondary reforming with complete combustion, by complete combustion of fuel gas stream with oxygen from an oxidant stream and, after mixing the products of complete combustion with a crude syngas stream coming from the primary steam reforming, provides the heat for the endothermic catalytic steam reforming process of the residual methane in the crude syngas, which process takes place in the catalyst zone of reactor for secondary reforming with complete combustion.

3. Applying the processes described in claim 1 and claim 2 for the production of syngas from natural gas, light hydrocarbons, refinery gases, alcohols, ethers.

4. Applying the processes described in claim 1 and claim 2, for revamping of existing conventional syngas plants, by replacing existing conventional reactors with new ones with complete combustion, or by modernizing of existing reactors.

5. Feeding fuel gas in different proportions to the oxygen in the oxidant and / or an oxidant having different oxygen contents to the combustion and mixing zones of the reactors for ATR with complete combustion and the secondary reforming with complete combustion, in order to run both complete and partial oxidation processes, and improved efficiency production of syngas with such a ratio between the syngas components that is required for the production of the final product.

6. Applying the processes described in claim 1 and claim 2 to build ATR constructions with high capacity, characterized by the following: they consist of more than one ATR reactor, connected to one or more combustion chambers for complete combustion of fuel gas.

7. The application of the processes described in Claim 1 and Claim 2 to the production of hydrogen for use in stationary and mobile Fuel Cell units.

8. Applying the processes described in claim 1 and claim 2 to the production of hydrogen in local installations for use as fuel or as fuel additive for combustion in furnaces, boilers, pre-heaters, engines, gas turbines or other fuel-using installations, in which the use of conventional (fossil - based) fuels is undesirable or limited.

9. Applying the processes described in Claim 1 and Claim 2 to the production of hydrogen for use in local stationary or mobile installations for non-combustion applications.