EA023934B1 - Process and reactor system for production of methane rich product gas - Google Patents

Abstract

A process is disclosed for production of a methane rich product gas comprising the steps of: (a) providing a feed comprising carbon oxide such as carbon monoxide and/or carbon dioxide, hydrogen and at least 1% C2+ hydrocarbons. (b) adding a flow comprising steam to said feed forming a reacting feed mixture, (c) reacting said reacting feed mixture in the presence of a catalyst forming a product gas rich in methane (d) withdrawing the methane rich product gas wherein the ratio of water molecules to carbon atoms in higher hydrocarbons, S/HHC, is below 25, the maximum catalyst temperature T is at least 460°C, preferably at least 480°C, and even more preferably 500°C, and the maximum catalyst temperature is less than the critical carbon formation temperature for the S/HHC value for said catalyst. In a preferred embodiment the recycle is driven by an ejector with steam feed as motive gas.

Description

This invention relates to a method for producing a natural gas substitute (CG) from carbon-containing materials. In particular, the invention relates to a method for producing HMO from a carbon-containing material, in which the carbon-containing material is converted to synthesis gas and mixed with a certain amount of water vapor and reused stream before the methane production reaction and the addition of water vapor is carried out in an ejector returning the reused a stream separated from a methane-rich product stream.

The lower availability of fossil liquid and gaseous fuels, such as oil and natural gas, has led to a reassessment of the attitude towards the development of technologies capable of producing synthetic combustible gases from widely available sources, such as coal, biomass, as well as exhaust gases from coke ovens. The resulting gas, called natural gas substitute (LNG) or synthetic natural gas (LNG), contains methane as its main component.

Coke is a solid fuel obtained from coal by burning coal in a furnace without air. During the production of coke, the volatile components of coal remove, purify and produce an exhaust gas containing, among others, one or both carbon dioxide and carbon monoxide, as well as hydrogen and hydrocarbons. This flue gas from a coke oven is rich in energy and is often used as a combustible gas to produce heat, for example to heat a coke oven when coke is produced for steel production. However, especially when coke is produced for use as solid fuel in plants without other energy requirements, an excess of off-gas may be useful.

With regard to gasification of biomass or waste, similar gases containing carbon monoxide, hydrogen and hydrocarbons can also be obtained.

In this regard, there is a prejudice towards the use of gases rich in C2 + hydrocarbons to produce methane, and even under operating conditions with the presence of minimal amounts of C2 + hydrocarbons, and a substantial safety margin has been laid down due to the size of the reactor.

Reactors with noble metal catalysts for producing methane at high temperatures have long been known. On such a more expensive catalyst, the formation of carbon antennae does not occur, and this makes it possible to work at elevated temperatures with a limited possibility of carbon formation.

The process of producing methane from carbon oxides and hydrogen is exothermic, so after the process is activated, the process will continue towards equilibrium with significant heat. The increased temperature permissible for the catalyst thus allows for an increased concentration of carbon monoxide in the reactor feed and thus a reduced reactor volume.

We unexpectedly found that with a careful analysis of thermodynamics and reaction conditions, it is possible to identify the optimal reaction window by combining temperature control and adding water vapor.

Further, we found that the use of an ejector to drive reused product gas is particularly advantageous in the presence of C2 + hydrocarbons, since the effect of increasing the addition of water vapor through the ejector has an effect on the increase in reuse, and the combined increase in the addition of water vapor and reuse is manifested in the synergistic effect of reducing the formation of carbon material.

We also found that the operating interval for the process unexpectedly expands as a result of choosing a temperature in the region close to the carbon formation curve, if the ratio between water vapor and higher carbons is kept in the intermediate interval.

The temperature of the reactants and products will increase as they pass through the catalyst bed in an adiabatic reactor. On the other hand, such an increase in temperature tends to shift the equilibrium toward a lower methane concentration. Consequently, a complete or near complete reaction is possible only if the temperature increase is limited by cooling the reacting gas in one way or another, for example, by reusing the cooled product gas, as described in I8 4130575.

It is well known that the reaction temperature of methane production can be controlled by adding water vapor to the synthesis gas, as described, for example, in patent application EP 2110425. Such an addition of water vapor, in particular in the case of a feed containing higher hydrocarbons (C> 1), has the consequence of less carbon tendril formation, which could potentially harm the catalyst.

We have found that feeding steam through an ejector moving a reused stream of methane-rich product gas into a synthesis gas feed containing CO and / or CO ₂ and H ₂ requires a reduced amount of water vapor for this kind of reuse.

The outstanding effect of the combination of steam addition, gas reuse and the use of a steam-driven ejector to ensure gas reuse is that the use of the ejector not only uses the pressure difference between water vapor and syngas to control gas reuse, but also the same time lowers the outlet temperature and increases the ratio of steam to higher hydrocarbons, which is very important

- 1,023,934 to prevent carbon formation.

As used here, the terms C2 + hydrocarbons and higher hydrocarbons mean any hydrocarbons and / or oxidized products that contain at least 2 carbon atoms.

As used here, the term δ / LHC means the ratio of water vapor to higher hydrocarbons and is calculated as the ratio of the number of moles of water in the form of steam to the number of moles of carbon atoms C2 + hydrocarbons, both taken into account at the entrance to the catalytic reactor. The term ratio of water vapor to carbon atoms in higher hydrocarbons can be used in the same sense. In fact, a certain amount of water can form in the reactor before the C2 + hydrocarbon reaction, so that the true critical δ / LHV values are determined in practice by the values of the higher hydrocarbon concentrations at the inlet and the concentration of water vapor at the outlet.

As used here, a critical δ / LHV value means a δ / LHV value for a given temperature and a given catalyst for which a δ / HHV value below a critical δ / HHV value leads to a significantly increased risk of carbon formation on the catalyst.

As used here, critical temperature means the temperature for a given ratio δ / LHV and a given catalyst, for which a temperature above the critical leads to a significantly increased risk of carbon formation on the catalyst.

As used here, a critical temperature with respect to a δ / LHC curve or a carbon formation curve means a curve corresponding to temperatures and δ / LHC ratios for a given catalyst at which temperatures and δ / LHC ratios above the critical temperature and / or below δ / LHC ratios result to a significantly increased risk of carbon formation on the catalyst.

In its broadest form, the invention includes a method for producing a methane-rich product gas, which comprises the steps of (a) providing nutrition containing carbon monoxide, such as carbon monoxide and / or carbon dioxide, hydrogen and at least 1% C2 + hydrocarbons, (b) adding a stream comprising water vapor to said feed to form a reactive feed mixture, (c) reacting said reactive feed mixture in the presence of a catalyst to produce methane-rich product gas, (ά) removing products methane-rich gas in which the ratio of water molecules to carbon atoms in higher hydrocarbons, δ / LHC, is less than 25, the maximum temperature of the catalyst T is at least 460 ° C, preferably at least 480 ° C and even more preferably 500 ° C, and the maximum catalyst temperature is less than the critical carbon formation temperature for the δ / LHC value of said catalyst with the advantage of ensuring methane production in the absence of catalyst deactivation by carbon formation.

In another embodiment of the invention, the critical carbon formation temperature for the δ / LHV value of said catalyst is determined experimentally with the advantage of establishing operating conditions that specifically satisfy the analyzed catalyst.

In yet another embodiment of the invention, the critical carbon formation temperature for the δ / LHC value of said catalyst is defined as T _critical . = 425 + 30L / NNS with the advantage of providing a prediction of operating conditions without conducting an experiment.

In yet another embodiment of the invention, the catalyst contains nickel as a catalytically active component, which is a catalyst with good activity at a reasonable price compared to noble metal catalysts such as ruthenium.

In yet another embodiment of the invention, the catalyst is supported, which may include alumina, and in particular a combination of one or more components from the group consisting of alumina, spinel MDA1, alumina-zirconia and calcium aluminates with the advantage of providing large areas of active surfaces, with reasonable price of the metal used.

In another embodiment of the invention, the water vapor stream is added using an ejector driven by a reusable product gas stream with the advantage that no additional energy is needed for the reused stream.

In another embodiment of the invention, additional carbon dioxide is added to the feed with the advantage that the stoichiometric balance of the feed is optimized, in which there is an excess of hydrogen.

In another embodiment of the invention, the ratio of water vapor to higher hydrocarbons is maintained above 1.5, which is manifested in a decrease in the formation of carbon from C2 + hydrocarbons.

In another embodiment of the invention, the feed gas is generated from a carbon-containing material selected from the group consisting of coke, coal, petroleum coke, biomass, oil, black liquor, animal fat, and combinations thereof, the advantage of which is that methane-rich gas is obtained from such a gas , which in another way is unproductive gas.

Another aspect of the invention relates to a reactor system for producing methane-rich product gas from a synthesis gas feed obtained from a coke oven configured to combine said feed line with a second feed line to a reactor inlet line configured to power a reactor containing a catalyst for the production of methane, characterized in that the said second feed line includes an ejector configured to supply water vapor as a driving gas and reused atogo methane product gas as a movable gas associated with the advantage of re-use the gas without the need of energy costs for pumping or pump without the need for moving parts.

In another embodiment of the invention, such a reactor system is configured to operate at the highest catalyst temperature in the range of 460-750 ° C, preferably 500-700 ° C, and more preferably at a temperature in the range of 550-650 ° C. The temperature range balances the fact that the increased temperature of the catalyst creates the advantages of minimizing the required inert and product flow and thereby increases the conversion to the volume of the reactor, with the fact that the low temperature shifts the product mixture in the direction of increasing methane concentration.

In such processes, the formation of methane from carbon oxides and hydrogen occurs rapidly with respect to equilibrium in the presence of a catalyst and in accordance with one or both reaction schemes

СО + ЗН ₂ <=> СН ₄ + Н ₂ О (1),

СО ₂ + 4Н ₂ <=> СН ₄ + 2 Н ₂ 0 (2).

These reactions are related to the equilibrium between carbon monoxide and carbon dioxide, as shown below

СО + Н ₂ О <=> СОг + Нг (3).

The pure methane formation reaction, either during reaction (1), or (2), or both, is highly exothermic.

From the field of water vapor reforming, it is known that catalysts and equipment exposed to a synthesis gas atmosphere can form carbon if certain elements, such as nickel or precious metals, are present in the material. The most common types of carbon are tendrils of carbon, resin or encapsulated carbon, and pyrolytic carbon. The type of carbon is highly dependent on the operating temperature and ultimately the formation of carbon is determined by a combination of material composition, raw materials, temperature and water vapor content. The possibility of the formation of solid carbon (C (k)) from simple molecules can be established by considering thermodynamics for the following reactions:

CH ₄ <=> C (s) + 2H ₂ (4),

2CO <=> C (h) + CO ₂ (5),

CO + H ₂ <=> C (s) + H ₂ O (6).

While the possibility of carbon formation from higher hydrocarbons is associated with kinetic competition between carbon formation and water vapor reforming according to the reaction below:

C _p N _t => olefins => C (5) (7),

C _p N _t + pH ₂ O => pCO + (p + UH) H ₂ (8).

The carbon formation that occurs after the expiration of the induction period ίο is reflected by the kinetics and subsequent carbon growth at a constant speed

The risk of carbon formation can be assessed by the critical ratio of water vapor to C2 + hydrocarbons (§ / LHF) _critical , which increases with temperature and depends on the type of hydrocarbon and the type of catalyst used. So, in order to avoid the formation of carbon, the possibility should be evaluated from all points of view, using thermodynamics for simple molecules and for higher hydrocarbons, the ratio of water vapor and higher hydrocarbons should be maintained above the critical ratio of water vapor and higher hydrocarbons for operating temperature at any point the reactor.

For the purposes of methane production, the same principles should be applied to assess the possibility of carbon formation as described above for water vapor reforming applications, however, the controls for the operation window will vary significantly. Due to the fact that the reforming reaction of methane and water vapor (reverse (1)) is highly endothermic, heat is supplied from the outside and the reaction occurs at excessive temperatures, which can lead to the formation of carbon - 3 023934 yes, this can be avoided by supplying external heat , the methane formation reaction (see (1) above) is highly exothermic, and the heat release during the reaction should be controlled so as not to exceed the critical combination for the maximum working temperature and the minimum ratio of water steam and higher hydrocarbons when higher hydrocarbons are present in the feed. Alternatively, the water vapor content should be adjusted in order to maintain the ratio of water vapor to higher hydrocarbons above a critical value for a given operating temperature.

There are several ways to control the temperature increase: working in a cooled reactor, diluting the reagents, working under stoichiometric conditions, and reusing the product stream.

Re-use of the product stream can be achieved by using rotary equipment or static installations such as an ejector.

In particular, the reuse of the product stream by adding water vapor through the ejector is tempting, since water vapor can be used to drive the ejector reusing the product stream without additional energy use. Thus, the use of an ejector makes it possible to combine the temperature and water vapor content in the food in order not to exceed the critical ratio of water vapor and higher hydrocarbons when higher hydrocarbons are present in the feed.

The optimal operating window for the process of producing methane from raw materials containing higher hydrocarbons was determined and established using the ratio between the operating temperature and the critical ratio of water vapor and higher hydrocarbons, which depends on the catalyst and requires a certain protective limit, and also has an upper temperature limit , which is determined by the decomposition of methane (4).

These conditions are the main achievements of the known conditions under which operating temperatures above 500 ° C are associated with δ / LHV ratios significantly higher than 30, and thus, for synthesis gases with a content of C2 + hydrocarbons outside of secondary pollution, according to the requirements, they are practically excessive.

In one embodiment of the invention illustrated in FIG. 2, coke oven gas 4 originating from the coke oven 2 is optionally purified in 6, if necessary mixed with raw materials from secondary sources of raw materials 8, if necessary, further purified in 10, before the formation of the raw materials, which are combined with a stream including water vapor 13, and sent as a reacting feed mixture 12 to the inlet of a reactor 14 containing a catalyst in the presence of which a methane formation reaction takes place. Methane-rich product gas 20 is removed from the reactor. The gas composition and temperature are determined so that the conditions indicated in FIG. 1, possibly by cooling, for example, in a heat exchanger 22.

In a preferred embodiment of the invention, the reused product gas stream 24 is recovered from the cooled methane-rich product gas.

In another preferred embodiment of the invention, the reused product gas stream is directed to an ejector 26, in which water vapor 28 can be used as a driving gas, and the reused product gas stream is a movable gas forming a stream 13 that includes water vapor and a reused stream grocery gas.

Methane-rich product gas that is not reused can be sent to the final production of methane 30 to form synthetic natural gas 32.

For commercial catalyst A, the following experimental procedure is used to determine the upper level of the operating interval.

1. The catalyst is loaded into a 35 mm reactor with a total layer height of 200 mm and maintained with a gas mixture containing 59% CH ₄ , 43% H ₂ O, 5.8% C ₂ + and a balance containing CO, CO ₂ and H ₂ at 30 bar gauge, resulting in a ratio of water vapor to carbon atoms in higher hydrocarbons of 2.38. The inlet linear velocity was 8.2 cm / s and the inlet temperature of the reactor was raised to 500 ° C. for more than 500 hours. The reactor was maintained pseudo-adiabatically by compensating for the heating. Subsequent analysis of the catalyst showed no signs of carbon tendrils. Thus, the conditions were found to be within an acceptable operating range.

2. The catalyst is loaded into a 21 mm reactor with a total layer height of 550 mm and incubated with a gas mixture containing 67% CH ₄ , 24% H ₂ O, 6.6% C ₂ + and a balance containing CO, CO ₂ and H ₂ at 30 bar gauge pressure, leading to a ratio of water vapor and carbon atoms in higher hydrocarbons of 1.43. The linear inlet velocity was 19.5 cm / s and the temperature at the inlet to the reactor was raised to 460 ° C for more than 700 hours. The reactor was maintained pseudo-adiabatically by compensating for the heating. Subsequent analysis of the catalyst showed no signs of carbon tendrils. Thus, the conditions were found to be within an acceptable operating range.

3. The catalyst is loaded into a 21 mm reactor with a total layer height of 550 mm and maintained with a gas mixture containing 52% CH ₄ , 40% H ₂ O, 5.6% C ₂ + and a balance containing CO, CO ₂ and H ₂ at 30 bar excess pressure, leading to a ratio of water vapor and carbon atoms in higher hydrocarbons of 2.82. The linear inlet velocity was 26.8 cm / s and the temperature at the inlet to the reactor was raised to 521 ° C. for more than 850 hours. The reactor was maintained pseudo-adiabatically by compensating for the heat. Subsequent analysis of the catalyst showed no signs of carbon tendrils. Thus, the conditions were found to be within an acceptable operating range.

4. The catalyst is loaded into a 13.5 mm reactor with a total layer height of 10 mm and kept with a gas mixture containing 38% CH ₄ , 59% H ₂ O, 3.3% C ₂ + and a balance containing CO, CO ₂ and H ₂ at 20 bar gauge pressure, leading to a ratio of water vapor and carbon atoms in higher hydrocarbons of 3.94. The inlet linear velocity was 15.9 cm / s and the inlet temperature of the reactor was raised to 535 ° C. for more than 200 hours. The reactor was maintained pseudo-adiabatically by compensating for the heat. Subsequent analysis of the catalyst showed no signs of carbon tendrils. Thus, the conditions were found to be within an acceptable operating range.

5. The catalyst is loaded into a 39 mm reactor with a total layer height of 1,500 mm and maintained with a gas mixture containing 53.8% CH ₄ , 39.9% H ₂ O, 3.3% C ₂ + and a balance containing CO, CO ₂ and H ₂ at 36 bar gauge, resulting in a ratio of water vapor and carbon atoms in higher hydrocarbons of 2.75. The inlet linear velocity was 18.8 cm / s and the inlet temperature of the reactor was raised to 525 ° C. for more than 1600 hours. The reactor was maintained pseudo-adiabatically by compensating for the heat. Subsequent analysis of the catalyst showed a significant presence of carbon tendrils formed.

Thus, the conditions were defined as being outside, but close to an acceptable operating interval.

The above experiments can be summarized as follows:

No antennae there is antennae Temperature 460 [500 521 535 525 5 / NVS 1.43 2.38 2.82 3.94 2.75

By linear regression of the upper limit, the working temperature limit T = 30-8 / NNS + 425 was determined. In specific examples, linear regression of the experimental points was calculated, however, more complex equations, such as 88H = A + B / T, can be determined approximately, which depends on the amount of experimental data.

The operating window is determined by the operating temperature T obtained at equilibrium of the feed gas according to the methane production reaction and the molar ratio of water vapor to higher hydrocarbons is 8 / LHC of the equilibrium gas to produce methane with unconverted higher hydrocarbons. The broadest form of the new and operational window for methane production according to the invention covers operation in the presence of at least 1% C2 + hydrocarbons at a temperature above 460 ° C, a ratio of 8 / HHC below 25 and a temperature below T = 30-8 / HHC + 425. The experimental results are shown in table. 1 are denoted by Δ during operation without formation of carbon antennae and during operation with formation of carbon antennae, together with an indication of the declared interval in FIG. one.

Table 1

Typical coke oven flue gas composition ranges

The following three examples show the production of methane-rich gas. Operating points are also shown in FIG. one.

In the first example, shown with the □ symbol in FIG. 1, obtaining methane-rich gas with temperature control when reusing the stream according to the previous type of process, the operation (reaction) occurs at a temperature of 450 ° C. To carry out the operation at a temperature of 450 ° C with gas reuse, reuse of 446.110 Um ³ / h is required, in this case the water vapor present in the reused stream for the operation has an 8 / LHF ratio of 21 at the inlet to the reactor. The total output stream is 546.512 Ohm ³ / h and get 19.084

- 5,023,934

Νμ ^3/4 methane. The disadvantage of this example is the large overall flow and high energy requirements for driving the reused stream.

In the second example, indicated by ◊ in FIG. 1, with the addition of water vapor according to the previous type of process for producing methane-rich gas, it involves an operation with a ratio of 8 / LHF equal to 33. With the installed feed, this will lead to a temperature of 500 ° C. In this case, 154 tons of water vapor / h are required and 13.558 Νμ ³ Λι methane will be produced.

In the case of the third example indicated by o in FIG. 1, when operating under temperature conditions and in the range of ratios of water vapor and higher hydrocarbons according to this invention and with the combined addition of water vapor and reuse of the gas stream, in which an ejector can be advantageously used, the invention is clearly visible, since it is possible to work at a temperature 600 ° С with a ratio of 8 / NNS equal to 10, for which it is necessary to add 17 tons of water vapor / h, which drives the reused gas in the volume of 88.213 Νμ ³ Λι. This corresponds to the same complete feed stream as in the first two examples, in the production of 15.856 ΝμΧι methane.

From the examples presented, it is clearly seen that the energy required to add water vapor or reuse the gas stream is significantly lower in the third example according to this invention and the production volume increases. In the third example, small losses occurred in the form of CO ₂ production, which are associated with a higher temperature, however this is outweighed by the reduced water vapor consumption.

table 2

Example one 2 3 Target T "FROM 450 500 600 Feed stream Νμ ’/ h 100402 100402 100402 Steam flow t / h 154 17 Reusable flow Ym ³ / h 446110 88213 Output stream 546512 291815 210373 to the reactor t 'FROM 330 330 330 H ₂ 0 Mol% 19.86 65.62 24.30 With Mol% 1.47 2.75 4.10 from ₂ Mol% 0.96 1.72 3.45 sun ₄ Mol% 48,43 7.35 25.45 s ₂ n ₆ Mol% 0.29 0.55 0.76 s, n ₈ Mol% 0.17 0.33 0.45 8 / NNS (NNS input / N ₂ O input) eighteen 32 8 Reactor exit T 'FROM 450 500 600 H ₂ 0 Mol% 24.31 71.75 33.21 with Mol% 0.00 0.06 0.66 from ₂ Mol% 0.05 1.95 2,52 sun ₄ Mol% 54.52 12.65 36.38 C ₂ H ₆ Mol% 0.00 0.00 0.00 Szn ₅ Mol% 0.00 0.00 0.00 5 / NNS (NNS input / N ₂ O output) 21 33 10 Net production of CH ₄ Νμ ’/ h 19084 13558 15856

CLAIM

Claims (13)

1. A method of producing a methane-rich product gas, comprising the steps of: (a) a feed comprising carbon monoxide such as carbon monoxide and / or carbon dioxide, hydrogen and at least 1% C2 + hydrocarbons is fed to the reactor, (b) a steam stream is added to said feed to form a reactive feed mixtures - 6,023,934 (c) interacting the specified reactive starting mixture with the catalyst to produce methane-rich product gas, (ά) methane-rich product gas is removed, and the ratio of water molecules to carbon atoms in higher hydrocarbons is less than 25, the maximum temperature of the catalyst T is at least 460 ° C, and the maximum temperature of the catalyst is less than the critical temperature of carbon formation at the specified ratio of water molecules to carbon atoms in higher hydrocarbons for the specified catal mash. 2. The method according to claim 1, in which the maximum temperature of the catalyst T is at least 480 ° C and even more preferably 500 ° C. 3. The method according to claim 1 or 2, in which the critical temperature of carbon formation for the specified ratio of water molecules and carbon atoms in higher hydrocarbons for the specified catalyst is determined experimentally. 4. The method according to claim 1 or 2, in which the critical temperature of carbon formation for the specified ratio of water molecules and carbon atoms in higher hydrocarbons for the specified catalyst is defined as T _critical = 425 + 30- (the ratio of water molecules and carbon atoms in higher hydrocarbons) . 5. The method according to any one of claims 1 to 4, in which the catalyst contains Nickel as a catalytically active component. 6. The method according to any one of claims 1 to 5, in which the catalyst is on a carrier containing alumina. 7. The method according to claim 6, in which the carrier includes one or more components from the group comprising alumina, spinel MDA1, alumina-zirconia and calcium aluminates. 8. The method according to any one of claims 1 to 7, in which a stream of water vapor is added as a driving gas to the ejector, which drives the reused product gas stream. 9. The method according to any one of claims 1 to 8, in which additional carbon dioxide is added to the feed. 10. The method according to any one of claims 1 to 9, which is carried out at a ratio of water molecules to carbon atoms in higher hydrocarbons of more than 1.5. 11. The method according to any one of claims 1 to 10, in which the feed gas is generated from a carbon-containing material selected from the group consisting of coke, coal, petroleum coke, biomass, oil, black liquor, animal fat, and combinations thereof. 12. The reactor system for producing methane-rich product gas from the feedstock leaving the coke oven for implementing the method according to claims 1-11, including an inlet line to the reactor, which is configured to combine a feed line with a second feed line, the specified line the inlet to the reactor is designed to power a reactor containing a catalyst for producing methane, characterized in that said second feed line includes an ejector that provides water vapor as a driving gas and rich methane product for reuse as a movable gas. 13. The system according to item 12 is configured to operate at the highest temperature of the catalyst in the range of 460-750 ° C, preferably 500-700 ° C and even more preferably 550 650 ° C.