RU2521632C1 - Method of producing hydrogen from water - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention can be used in chemical industry and when producing fixed and mobile fuel sources. Iron oxide is reduced by thermolysis while heating with an inert gas to obtain oxygen at temperature higher than 1200°C and pressure higher than 0.1 MPa. Iron is then oxidised with a stream of steam which is heated by the inert gas in a container which is alternately filled with the hot inert gas and the steam. Absorption or membrane separation or electrochemical separation is used to separate hydrogen as an end product from the steam of stream, as well as oxygen from the stream of inert gas. The cycle for oxidising and reducing iron oxide is carried out in parallel switched sections connected via inert gas and steam.

EFFECT: high efficiency of the method.

9 cl, 1 dwg

Description

The invention relates to a method for producing hydrogen from water and can be used in the chemical industry, as well as in energy storage and transport systems and as a fuel source in transport and stationary power plants.

Since the beginning of the 20th century, the basic technology for the production of hydrogen from water has been based on the so-called iron-steam method, in which steam at 500-1000 ° C is passed over iron: 3Fe + 4Н ₂ О → Fe ₃ O ₄ + 4Н ₂ +160.67 kJ. Hydrogen obtained by this method is usually used for the hydrogenation of fats and oils. The composition of iron oxide depends on the process temperature; at <560 ° С Fe ₃ O ₄ prevails, above 560 ° С the proportion of FeO increases. Since the reduction of the initial iron from the formed iron oxides was usually carried out with coke, coal or water gas (a mixture of CO and H ₂ ), a small admixture of CO in the hydrogen produced was removed by passing a heated mixture of H ₂ + CO over the catalyst. In this case, CO is converted to methane CH ₄ .

A known method of producing hydrogen, including the interaction of water vapor with elemental iron and / or with its lower oxide in a fluidized bed at 500-650 ° C, a pressure of 0.1-0.4 MPa, the regeneration of the formed iron oxides by contacting them with solid carbon-containing material at 800-1100 ° With obtaining regeneration gases and reduced iron oxides and returning them to the interaction stage, the regeneration gases are returned to the regeneration stage [RF patent No. 1125186, IPC С01В 3/10, publ. 11/23/1984, BI No. 43, “Method for producing hydrogen”, authors V. Lebedev and etc.]. The disadvantages of the method are the complexity of the process, low productivity, high energy consumption, as well as the consumption of solid carbon-containing material.

There is also known a method of producing hydrogen, which consists in the conversion of superheated saturated water vapor in a reactor with electrodes, characterized in that an iron wire is periodically introduced into the reactor, which is passed between the electrodes in an environment of superheated saturated water vapor, an electric discharge of 45 kV is periodically supplied to the electrodes and periodically produce a wire explosion on the smallest liquid metal particles that react with water vapor, forming iron oxides and hydrogen gas [RF patent No. 2424973, IPC С01В 3/10, publ. 07/27/2011, Bull. No. 21, “Method for the production of hydrogen”, authors Nosyrev D.Ya., Pletnev A.I. - prototype]. The disadvantages of the method are the complexity of the process, low productivity, high energy consumption, as well as the need for the production of iron wire and high voltage electricity.

In patent RU 2415072, publ. November 27, 2010, a method for producing hydrogen gas from a composition intended to produce hydrogen gas is described, comprising by weight 40-70% calcium oxide (CaO) in the form of a powder, 2-20% calcium chloride (CaCl ₂ ), magnesium chloride ( MgCl ₂ ) or sodium bicarbonate (NaHCO ₃ ) in the form of a powder, 6.7-30% of aluminum or aluminum oxide (Al ₂ O ₃ ) in the form of a powder and 0.001-10% of iron or magnesium in the form of a powder, in which 56 grams of calcium oxide ( CaO) and 2 moles, i.e. 36 grams, of water (H ₂ O) are reacted to produce 2 grams of hydrogen gas (H ₂ ). The volume of 2 grams of hydrogen gas is 22.4 liters at a temperature of 0 ° C and 1 atmosphere (normal state), and therefore, 35.7 grams (approximately 400 liters) of hydrogen gas will be generated from 1 kg of calcium oxide. The disadvantages of the method are the complexity of the process, low productivity, high energy consumption, as well as the consumption of solid material - calcium oxide (CaO). Various solar furnaces have been proposed for the decomposition (reduction) of metal oxides (calcium, zinc, manganese, iron, cerium), see, for example, Thermodynamic Analysis of Cerium-based Oxides for Solar Thermochemical Fuel Production, Scheffe J., Steinfeld A. Energy & Fuels, Vol.26, pp.1928-1936, 2012, however, the disadvantage of such furnaces is the extremely low volumetric productivity associated with the decomposition reaction, mainly on the surface illuminated by the sun, which limits the scope of this technology. The disadvantage is the need to maintain extremely low pressure in the furnace due to the need to use quartz glass to pass solar energy into the furnace.

The objective of the present invention is to create a new method that allows to reduce the heat costs of the process of decomposition of water, as well as to increase the productivity and efficiency of hydrogen production technology.

The problem is solved in that:

The proposed method for producing hydrogen from water, in which the oxidation and reduction of iron oxide is carried out to produce hydrogen during the oxidation of iron by water vapor, hydrogen is isolated as a final product from the stream of water vapor, while the reduction of iron oxide is carried out by thermolysis when heated with an inert gas to obtain oxygen, after which iron is oxidized by a stream of water vapor heated by an inert gas, and its oxidation by water vapor is carried out in a container alternately filled with heated inert gas and water vapor.

Besides:

- inert gas is heated in a plasma jet, or by electric heaters, or by the method of induction heating, or by heating solar or nuclear energy, or by the combustion products of fossil fuels,

- reduction of iron oxide is carried out at a temperature above 1200 ° C and a pressure above 0.1 MPa, after which oxygen is released from the inert gas stream by adsorption, or by membrane or electrochemical separation,

- water vapor pressure is selected in the range from 0.1 to 1.0 MPa,

- part of the heat necessary for heating the inert gas is removed from the reduced iron oxide,

- the separation of hydrogen from water vapor after iron oxidation is carried out by adsorption, or condensation of water vapor, or membrane separation, or by an electrochemical process,

- by means of regenerative heat exchange, the temperatures of the inert gas and water vapor flows at the inlet and outlet of the oxidation and reduction cycle of iron oxide are changed,

- the cycle of oxidation and reduction of iron oxide is carried out in parallel switchable sections of homogeneous design, connected by an inert gas and water vapor,

- helium, or argon, or nitrogen, or krypton, or mixtures thereof, are selected as the inert gas.

The drawing shows one of the possible schemes for the implementation of this method, where 1 is heated helium, 2 is a thermolyzer, 3 is a helium-oxygen mixture, 4 is an oxygen separator, 5 is oxygen, 6 is cooled helium, 7 is water vapor, 8 is a mixture water vapor and hydrogen, 9 - a regenerative heat exchanger for heating water vapor, 10 - a hydrogen separator, 11 - hydrogen, 12 - a regenerative heat exchanger for heating helium, 13 - heat removal from metal oxide.

An example implementation of the invention is the method of producing hydrogen from water, described below.

In the described embodiment of the invention, it is proposed, as an example, to use helium 1 as an inert gas and the process of thermolysis of iron oxides: Fe ₂ O ₃ ⇒ 2FeO + 1 / 2O ₂ (thermolysis above 1300-1400 ° C) to produce oxygen 5.

As is known, for reactions of the type FeO _x + H ₂ O⇒Fe ₂ O ₄ (or Fe ₂ O ₃ ) + H ₂ (technology like HyGas), the oxidation of Fe (or FeO _x ) proceeds according to:

w ² t ^-1 = 2.4 · 10 ¹⁴ exp (-84300 / RT), where

w is the increment of the weight of the metal due to its oxidation (g / m ² ).

Heterogeneous reactions limited by diffusion in the condensed phase are of such parabolic nature. The dependence of the decomposition of hematite is of a similar nature, which allows us to characterize the features of the invention as applied to the oxidation of wustite to hematite in thermolizer 2 to obtain a mixture of water vapor and hydrogen 8 from water vapor 7 supplied to thermolizer 2.

In the first stage of the process, helium 1, heated to a temperature of 1500 ° C, enters thermolyser 2, filled with iron oxide mainly in the form of hematite, and, heating the hematite to a temperature of 1300-1400 ° C, decomposes it to wustite and oxygen, which is mixed with helium and is removed from the thermolizer 2 in the form of a helium-oxygen mixture 3 cooled to 1000-1100 ° C, which enters, for example, a high-temperature electrochemical oxygen separator 4, in which oxygen 5 is separated from the helium stream through oxygen diffusion through a ceramic electrolyte 6 supplied to reheating (not shown in the drawing). In the high-temperature electrochemical oxygen separator 4, a helium-oxygen mixture 3 is supplied to the input of the cathode space of the high-temperature electrochemical process when electric energy is supplied, while oxygen is released in the anode space separated from the cathode by an electrolytic layer made of oxygen-conducting ceramic, for example, SrFeCo _0.5 O _3.25-δ , as described in the Department of Chemistry, University of Houston, Houston, TX 77204-5641, USA, Solid State lonics DOI: 10.1016 / S0167-2738 (98) 00106-4, i.e. a material that has a high level of ionic conductivity and a comparable (or greater) level of electronic conductivity. The acceptor doping of the cationic sublattice provides the appearance of oxygen vacancies and, therefore, provides high values of oxygen-ion conductivity, and the presence in the structure of an element capable of easily changing the oxidation state ensures high electronic conductivity. Some promising compositions of solid solutions can also be proposed as promising materials, for example, CaTi _0.8 Fe _0.2 O _3-δ . The evolution of oxygen 5 from the flow of helium-oxygen mixture 3 is also advisable to carry out adsorption, membrane separation, however, in these embodiments, the temperature of the helium-oxygen mixture 3 should be lowered to 200-300 ° C, which can be achieved either by regenerative heating of helium 1 entering thermolizer 2, or by heating water vapor 7. Regenerative heat exchangers 12 and 9 of heating the incoming flows of helium 1 and water vapor 7, respectively, conduct heating due to the outgoing flows of helium-oxygen mixture 3 and a mixture of hydrogen and water vapor and 8 respectively. In addition, partially the flow of incoming helium 1 can be heated by heat 13 from the section of the thermolizer 2, in which the metal oxide is reduced.

In the second stage, the flow of helium 1 to the thermolizer 2 is stopped, into which a stream of water vapor 7 is heated, heated to a temperature of 400-800 ° C. Water vapor 7, when interacting with iron oxide mainly in the form of wustite, oxidizes the latter to hematite with the formation of hydrogen, which mixes with the stream of water vapor removed from the thermolizer 2 in the form of a mixture of hydrogen with the stream of water vapor 8 supplied to the hydrogen separation 11, for example, a high-temperature electrochemical hydrogen separator 10, in which, when supplying electric energy, a mixture of hydrogen with a stream of water vapor 8 is supplied to the input of the anode space of the high-temperature electrochemical process meat, while a mixture of hydrogen is isolated in the cathode compartment separated from an anode electrolytic layer made of a proton-conducting ceramics, for example, SrCeO ₃ having high proton conductivity as an electrolyte dominant characteristic. High proton conductivity values were obtained for SrCeO ₃ doped with Y, Sc, In, REE at 600-1000 ° С [Uchida H., Maeda N., Iwahara H. Relation between proton and hole conduction in SrCeO ₃ - based solid electrolytes under watercontaining atmospheres at hift temperatures // Solid State lonics. 1983. V.11. N2. P.117-124]. Electrolytes were tested in cells, which form the basis of a number of high-temperature electrochemical devices, and showed good characteristics. The separation of hydrogen from water vapor 7 can also be carried out by adsorption, condensation of water vapor or membrane separation of a mixture of hydrogen with a stream of water vapor 8 in a hydrogen evolution apparatus 10 to produce production hydrogen 11.

The heating of helium 1 is carried out in a plasma jet, either by electric heaters, or by the method of induction heating, or by heating solar or nuclear energy, or by the combustion products of organic fuel, not shown in the drawing. In addition to iron oxides in thermolizer 2, alloys based on metals selected from the group of tin, indium, gallium, manganese, chromium, titanium, copper, cerium, zinc, aluminum, zirconium, lead, vanadium, ruthenium, and mixtures thereof can also be used as a metal. or compounds. Iron oxides, hematite (FeO _1.5 ), magnetite (FeO _1.33 ) and wustite (FeO _1.1 ) have the features of a close-packed structure of oxygen ions, can form spinels, in particular for wustite, various Fe / O ratios can differentiate, which is usually denoted by Fe _{1 -δ} O (with 0.05 <δ <0.17). Wustite may contain 23.1-25.6% of the mass. oxygen. The hydrolysis of wustite (FeO) is limited due to the formation of magnetite Fe ₃ O ₄ , which plays the role of a diffusion barrier. Components such as Mn, Cr, Ti, Cu, Pb, V and Al can be added to increase productivity, and additives Al, Cr , Zr, Ga, and V have a positive effect on the redox behavior of iron oxides, probably because hydrogen is activated by additives or increases the diffusion of oxygen in iron (oxides).

In addition to regenerative heating in the heat exchanger 9, the heating of water vapor 7 with a pressure in the range from 0.1 to 1.0 MPa before supplying metal for oxidation to thermolysis 2 is also carried out using, for example, heated inert gas 6 exiting separator 4 to temperatures of 400-800 ° C using a separate heat exchanger (not shown in the drawing) through sealed heat transfer surfaces.

The oxidation and reduction cycle of metal oxide is carried out in parallel switchable sections of thermolizer 2, homogeneous in design, connected by helium 1 and water vapor 7 so that the helium stream 1 alternately switches to supply to neighboring sections of thermolizer 2, in which the oxidation of metal oxide is completed, namely, in the described embodiment, the oxidation of wustite to hematite. In addition to helium 1, argon, nitrogen, krypton, or mixtures thereof are also selected as an inert gas.

Below is the calculation of the heat balance of the implementation of the method:

1. Q thermolysis of hematite (before wustite: Fe ₂ O ₃ ⇒2FeO + 1 / 2О ₂ ): 342.8 kJ / mol Fe ₂ O ₃

2. Q of heating / cooling of hematite / wustite (900 → 1500 ° С): With _r.hem ^average × ΔТ = 1 kJ / kg · K × 600 K = 0.6 MJ / kg Fe ₂ O ₃ /

From the _{river Vyust} ^average × ΔТ = 0.73 kJ / kg · K × 600 K = 0.44 MJ / kg FeO

3. Q for evaporation and heating of water vapor (1 MPa) to 1100 ° С: 2.26 + 2.17 × (1100-180) = 4.26 MJ / kg H ₂ O

4. Taking the consumable mass of hematite and water vapor per 1 kg of hydrogen produced, equal to:

mFe ₂ O ₃ = 100 kg, which, respectively, is 1.25 times greater than the stoichiometric flow rate (conversion rate for thermolysis is 80%), wustite mass: mFeO = 72 kg and wustite / hematite mixture (after thermolysis): mFe _x O _y = 92 kg, mH ₂ O = 13.5 kg, which, in turn, is 1.5 times the stoichiometric flow rate, in accordance with the expected degree of steam conversion (60-70% according to Production of Synthesis Gas and hydrogen by the Steam-Iron Process: Pilot Plant Study of Fluidized and Free-Falling Beds, Gasior, SJ, Fomey, AJ, Field, JH, Bienstock, Daniel, Benson, HE, US DoI, Bureau of Mines, RI 5911.1961), we obtain the total heat consumption (in reduction to 1 kg of hydrogen):

- to conduct the thermolysis reaction: 171.2 MJ,

- for hematite heating: 0.6 × 100 = 60 MJ,

- to receive and heat water vapor: 4.26 × 13.5 = 57.5 MJ.

Of these, the costs of production and heating of water vapor are covered by cooling wustite from the hematite thermolysis temperature (1500 ° С) to the working temperature of hydrogen generation (1100 ° С), which gives 0.76 × 600 × 92 = 41.7 MJ, as well as due to cooling the flow of water vapor (4.5 kg) and hydrogen (1 kg) from 1100 ° C to 180 ° C, which gives 2 × 4.5 + 14.55 × 0.92 = 21.88 MJ and cooling the oxygen flow (8 kg) from the thermolysis temperature (1500 ° C) up to 180 ° C (in the version of the thermolizer with heat transfer through the wall), which gives 1520 × 1 × 8 = 12.16 MJ, of which 4.8 MJ can be used to heat hematite before the term Lees, with a corresponding decrease heat losses covered heated helium.

Thus, the heat consumption from the energy source using helium heat carrier will be 171.2+ (60-4.8) = 226.4 MJ.

The corresponding overall efficiency of the process for producing hydrogen from water will be: 143 / 226.4 = 63%.

This indicator of the efficiency of hydrogen production from water exceeds all known thermochemical technologies.

With the achieved volumetric rate of water vapor in the reaction volume of 300 1 / h and calculated on a power of 1 MW, the volume of the reactor thermolizer takes at a water vapor density of 0.5 kg / m ³ :

1 MW / 226.4 MJ × 3600 × 9 / 0.5 / 300 = 0.95 m ^3.

The total process of decomposition of water in the proposed invention is described by the reaction (H ₂ O → 1 / 2O ₂ + H ₂ ), in which it is possible to obtain hydrogen and oxygen of high purity from water with pressure necessary for further use. Thus, in the proposed invention, it was possible to reduce the heat costs of the process of water decomposition, as well as to increase the productivity and efficiency of hydrogen production technology, to effectively use the energy potential of high-temperature energy sources, including nuclear ones, which allows us to count on high economic efficiency. The resulting water decomposition products - gaseous hydrogen and oxygen can then be used in the chemical industry and metallurgy for hydrocarbon processing, as well as in energy storage and transport systems and as fuel in transport and stationary power plants.

Claims (9)

1. A method of producing hydrogen from water, in which a cycle of oxidation and reduction of iron oxide is carried out to produce hydrogen during the oxidation of iron by water vapor, hydrogen is isolated as a final product from a stream of water vapor, characterized in that the reduction of iron oxide is carried out by thermolysis when it is heated by inert gas to produce oxygen, after which iron is oxidized by a stream of water vapor heated by an inert gas, and its oxidation by water vapor is carried out in a container alternately filled with heated inert gas and water vapor. 2. The method according to claim 1, characterized in that the inert gas is heated in a plasma jet, or by electric heaters, or by the method of induction heating, or by heating solar or nuclear energy, or by the combustion products of organic fuel. 3. The method according to claim 1, characterized in that the reduction of iron oxide is carried out at a temperature above 1200 ° C and a pressure above 0.1 MPa, after which oxygen is released from the inert gas stream by adsorption, or by membrane or electrochemical separation. 4. The method according to claim 1, characterized in that the water vapor pressure is selected in the range from 0.1 to 1.0 MPa. 5. The method according to claim 1, characterized in that part of the heat necessary for heating the inert gas is removed from the reduced iron oxide. 6. The method according to claim 1, characterized in that the separation of hydrogen from water vapor after oxidation of iron is carried out by adsorption or condensation of water vapor, or membrane separation, or by an electrochemical process. 7. The method according to claim 1, characterized in that by means of regenerative heat exchange, the temperatures of the inert gas and water vapor flows at the inlet and outlet of the oxidation and reduction cycle of iron oxide are changed. 8. The method according to claim 1, characterized in that the cycle of oxidation and reduction of iron oxide is carried out in parallel switchable sections of uniform design, connected by an inert gas and water vapor. 9. The method according to claim 1, characterized in that helium, or argon, or nitrogen, or krypton, or mixtures thereof, are selected as the inert gas.

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