WO2011048299A1

WO2011048299A1 - Method and device for producing power by means of oxidation of fuel in a chemical loop

Info

Publication number: WO2011048299A1
Application number: PCT/FR2010/052102
Authority: WO
Inventors: Simon Jallais; Bruno Alban; Ivan Sanchez-Molinero
Original assignee: L'air Liquide Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude
Priority date: 2009-10-22
Filing date: 2010-10-06
Publication date: 2011-04-28
Also published as: US20120199054A1; CN102575842A; FR2951807B1; FR2951807A1; EP2491306A1

Abstract

The invention relates to a method (1) for producing power from at least one fuel (4), said method including: a step a) of oxidizing (2a) said fuel (4) by means of placing it in contact with at least one oxygen-loaded solid compound (5a) and of concomitantly reducing (2b) said solid compound; a step b) of recovering said solid compound (9), reduced in step a); an exothermic step c) of oxidizing (3b) a nonzero fraction (9a) of said solid compound, recovered in step b), by means of placing it in contact with at least one oxygen-containing gas (6); and a step d) of recovering said oxidized solid compound from step c) and using, in step a), a nonzero fraction (5a) of said oxidized solid compound (5). The heat released in step c) is at least partially recovered so as to carry out said power production, said method being characterized in that the oxygen-containing gas (6) is alternately, according to the desired power level, air or a gas including a volume concentration of oxygen between 22% and 100%.

Description

Method and device for producing energy by oxidation of a fuel in a chemical loop

The present invention relates to a method and a device for producing energy by oxidation of a fuel in a chemical loop.

Chemical looping techniques have appeared relatively recently in the field of fuel oxidation. They use a solid active compound, generally metallic, which chemically fixes the oxygen of the air and then serves to oxidize a compound, generally carbon, solid, liquid or gaseous. In general, said active compound circulates in a loop, from a reactor where its oxidation takes place in contact with air, to at least one other reactor where it is reduced during the oxidation reaction of the fuel. This oxidation of the compound regenerates it. It can be used again to fix oxygen. The active compound is generally used in the form of a fluidized and circulating bed of particles. It separates easily from gaseous mixtures, for example by a cyclone. Regeneration of the solid active compound is generally very exothermic. The heat released is converted into energy (steam, mechanical or electrical power, for example). In other configurations, the same principle is implemented, not by beds of the fluidized particles of these compounds, but by fixed regenerative beds comprising these compounds. Oxidizing or reducing gases are then alternately passed over these beds. One possible implementation is to use rotating compartments (which are brought into contact alternately with oxidizing or reducing gases).

In particular, mention may be made of WO2007104655 A1, which describes a thermal power station including a thermochemical loop, comprising oxidation and reduction chambers, cyclones for separating solid particles from effluent gases, heat exchangers, and heat transfer means. production of electrical energy from the thermal energy released. The application WO2008036902, "Chemical looping combustion", presents an implementation of the chemical loop principle, in particular thanks to a reactor composed of rotary compartments.

The advantage of chemical looping techniques applied to the oxidation of a fuel is that the products of oxidation (mainly water and carbon dioxide or CO2) are easily suitable for C02 capture. , because they contain little or no nitrogen, provided that the tightness of the system with respect to the ambient is ensured. On the contrary, this nitrogen is found in large quantities in the effluents of a conventional combustion in air. Another specific advantage of chemical loops is that they only require air as an oxidant, compared to other oxidation techniques of fuels facilitating capture of CO2, such as oxy-combustion or pre-combustion, which can use a concentrated oxygen flow rate.

For a power generation installation (electricity, work or heat), the main dimensioning element is the maximum power that must be produced. The size of the chemical loop is deduced therefrom (capacity of the reactors, quantity of oxygen carrier active compound, size of the equipment, etc.). Once this dimensioning has been carried out, the peak power of the installation is set at a value that can not be exceeded. In fact, the installation will generally produce a lower power, that is, it is mostly oversized. It will eventually be pushed to its maximum production at certain times and this maximum will not change over time except to significantly change the installation, with significant investment. An object of the present invention is to overcome all or part of the disadvantages of the prior art, in particular the fixed aspect of the maximum power produced (related to the size of the installed equipment) and the oversizing of the facilities that may result.

The invention relates firstly to a method for producing energy from at least one fuel, comprising:

a step a) of oxidation of said fuel by contact with at least one solid compound loaded with oxygen and concomitant reduction of said solid compound;

a step b) of recovering said reduced solid compound in step a);

a step c), exothermic, of oxidation of a non-zero fraction of said solid compound recovered in step b) by placing in contact with at least one gas comprising oxygen; and

a step d) of recovering said oxidized solid compound at the end of step c) and of implementing in step a) a non-zero fraction of said oxidized solid compound; the heat released in step c) being at least partially recovered to achieve said energy production;

said method being characterized in that the gas 6 comprising oxygen is alternately, depending on the desired energy power, air or a gas comprising a volume concentration of oxygen of between 22% and 100%.

In other words, during a period T of energy production we have: a first production period T1 during which the gas 6 comprising oxygen is air; energy at a power PI is produced during this period T1; and

a second production period T2 during which the gas 6 comprising oxygen is a gas comprising a volume concentration of oxygen of between 22% and 100%; energy at a power P2 is produced during this period T2.

With T = Tl + T2 and P2> Pl

The fuel can be solid, liquid or gaseous, or multiphase. It may be a conventional fuel, such as natural gas or naphtha, or a purge or fumes from another process, or coal, coke, petroleum coke, biomass and its derivatives or petroleum residues .

In step a), the fuel is contacted with at least one oxygen-carrying solid compound. This contacting can be carried out in several times and / or with a sufficient residence time, and / or with a given excess of one of the reactants (fuel or solid carrier compound), until a certain reaction rate is obtained. . This solid compound may in particular be a metal, in a form sometimes oxidized, sometimes reduced. The fuel reacts with an oxidized form of the solid compounds. Here we must give a relative meaning to "oxidized" and "reduced". The bottom line is that at least a fraction of the solid compound can release oxygen to a lower oxidation state. Oxidation-reduction reactions may not be complete. As a result of the oxidation-reduction reaction, the solid compound in a reduced form and, on the other hand, effluents which are the products of the oxidation of said fuel.

In step b), the solid compound is recovered in a reduced form, for example by physical solid-gas separation.

In step c), at least a portion of the reduced solid compound, optionally supplemented with an addition of solid compound, is brought into contact with an oxygen-containing gas. In the prior art, this gas is air. In contact with this gas, the solid compound passes to a higher oxidation state, and thereby sets oxygen. This contacting can be carried out in several times and / or with a sufficient residence time, and / or with a given excess of one of the reagents (oxygen-containing gas or solid carrier compound), until a certain reaction rate. It results from this reaction of a the solid compound in an oxidized form and, on the other hand, effluents which are the oxygen-depleted input gas with respect to its initial content.

At the end of this regeneration, after a recovery which is the subject of step d), it is again ready, possibly with a complement of solid compound, to be used for the oxidation of said fuel (step a)) .

It can be seen that steps a) to d) form a loop from the point of view of the oxygen-carrying solid compound (s). At certain stages they are oxidized and at others reduced. In general, the solid compound (s) is circulated from one reactor to another, so the loop is also physical (the solid compounds are transported). We could also leave them on the spot and circulate the other compounds. Various means known to those skilled in the art can be implemented to ensure sealing during steps a) and d), such as solid siphons, intermediate sealed chambers with alternative opening (in English: lock-hoppers), or other .

The said oxygen-carrying solid compound (s) are generally used in the form of solid particles. These particles consist of the solid compound or compounds, optionally agglomerated with a binder material according to techniques known to those skilled in the art. This one focuses in particular on:

give them a specific capacity (per unit mass) to set and release the highest possible oxygen,

to give them good mechanical strength, especially attrition, promote reaction kinetics between said particles and said fuel, and between said particles and the gas comprising oxygen.

The particles are generally used in the form of a fluidized bed, for example by injecting steam or CO 2 -rich gas or fuel gas or effluents recycled to a reactor (step a)), and injections air or other gas containing oxygen or steam in another reactor (step b)). This steam can be produced in the heat exchangers. This fluidized bed circulates zones where the reduction of said particles takes place, ie the oxidation of said fuel, towards the zones where the regeneration of said particles takes place, ie the oxidation of the active compounds they contain.

The particles are generally separated from the other products of the oxidation of the fuel by physical separation, for example in a cyclone. They are also separated from any other solids resulting from the oxidation of the fuel (ash and / or soot and / or unconverted solid fuel). It is the same during the regeneration of said particles. Other separating elements may be provided for separating any solids from the reactions of the oxygen-carrying active compound so as to recover the carrier material and to increase the conversion efficiency.

In general, the oxidation of the oxygen-carrying solid compound is exothermic, as is that of the fuel. It happens nevertheless at high temperature.

Part of the heat released by the chemical reactions used is recovered by heat exchange. There can be many heat exchanges to recover heat where it is. This can be recovered in particular in or around the reaction media, or in the primary effluent, secondary, and / or regeneration. The heat energy is partly transferred to one or more heat transfer fluids, such as steam or hot oil, according to methods known to those skilled in the art. These fluids, possibly produced at different levels of pressure and / or temperature, can be used as they are or to produce mechanical and / or electrical energy.

During a first period of time when it is desired to produce a given power output, in step c) air, optionally pretreated, is used to regenerate the oxygen-carrying solid compound (s). The delivered power is modulated using other parameters, in particular the flow rate of fuel and solid compound in the loop. The inventors have established that if, during a given second period, it is desired to increase the power produced, it is advantageous to use in step c) at least one gas containing between 22% and 100% oxygen by volume. In this gas, the 100% by volume supplement consists of gases that are non-reactive with the solid compound (s) (nitrogen, argon, CO2, etc.). This gas can be a mixture of air and relatively pure oxygen. In step c), the solid compound can be brought into contact with a plurality of gases comprising oxygen, some of which is air, others being gases containing between 22% and 100% of oxygen by volume. lume.

The first period and second period are not necessarily successive. The second period is not necessarily after the first period. All this requires having a source of gas richer in oxygen than air, which has an investment cost, if we do not have a source, and an operating cost. On the other hand, this makes it possible to increase the maximum power produced, without having to enlarge the installation carrying out the process. Thus, the installation can be dimensioned not on a peak power, but on a lower power. In this way, the initial investment cost of the power generation unit can be reduced.

The gaseous effluents from the fuel oxidation step a) are similar to the fumes of conventional combustion using air as the oxidant, but have little or no nitrogen. Their CO2 concentration is also higher. After condensation of the water (for example by cooling), they are therefore particularly capable of undergoing CO2 capture by all the techniques known to those skilled in the art (washing with amines, adsorption, permeation, cryogenic distillation, etc. etc.).

Moreover, the gaseous effluents resulting from the regeneration of the solid compounds in step c) are depleted of oxygen. By achieving sufficient depletion, the invention has the additional advantage of providing a residual gas that can be used in inerting applications.

According to particular embodiments, the invention may further comprise one or more of the following features:

during said second period of energy production, said gas comprising oxygen has an oxygen volume concentration of between 23% and

40%.

during said first period of energy production, said fuel is of a first given type; and during said second energy generation period, said fuel is of a second type given more reactive in step a) than said first type. To determine if one fuel is more reactive than another, the following calorimetric experiment is performed successively on the two fuels to be tested. In a calorimeter bomb, a quantity of fuel equivalent to LP (lower heating value) is set at a value chosen in advance. A stoichiometric amount is added to the oxygen-carrying compound in the form in which it is used in step a) of the process according to the invention, that is to say an oxidized form. Both reagents are initially at 20 ° C. The temperature rise curve is then measured as a function of time. The curves obtained for the two fuels are compared on the same graph. It will be said that the most reactive is that for which the initial rise in temperature is the fastest, that is to say the one for which the temperature curve is higher for at least a certain time interval. said first type of fuel is sub-bituminous coal and said second type of carbonaceous fuel is lignite or coal or HFO (heavy fuel oil) or LPG (liquefied petroleum gas) or natural gas.

during said first period (Tl) of energy production at said first power (PI), a first flow rate of said solid compound in step a) and a second flow rate of said solid compound in step c) are used; ; and during said second energy generation period (T2) at said second power (P2), a third flow rate of said solid compound in step a) and a fourth flow rate of said solid compound in step c) are implemented. the ratio of said third rate on said first rate and the ratio of said fourth rate on said second rate being greater than or equal to the ratio of said second power (P2) on said first power (PI). The first and second rates generally have close values. If they differ, it is because they have purged solid compound or made a supplement. The same is true for the third and fourth solid compound flow rates.

During said second energy generation period, more energy per unit time is released by the chemical reactions in the oxidation and reduction reactors. Adaptations known to those skilled in the art can be made in the installation to evacuate this additional power. For example, there may be additional heat exchangers that come into operation during this second period, in a heat transfer fluid circuit shared or not with the main circuit. In another example, the mass flow of heat transfer fluid passing through the same heat exchangers can be increased accordingly during this second period. In another example, the control parameters of the coolant circuit change in this second period, so that the heat transfer fluid is hotter at the heat exchanger outlet than during the first period (thus storing more heat energy) . In another example, the pressure of the heat transfer fluid circuit increases during this second period, so as to promote the presence of liquid phase in this circuit, with a higher specific heat, which can better evacuate the additional power produced.

The advantage of using a gas whose volume concentration of oxygen is between 23% and 40% is to limit the risk of a too high rise in temperature during step c). This could necessitate adapting the reactor (s) where the exothermic regeneration (step c) of the solid compound (s) is implemented, with negative consequences for the investment. The invention also relates to a device for producing energy, comprising at least:

a fuel oxidation reactor connected at the inlet to one or more fuel sources and at least one pipe capable of conveying a solid oxygen-carrying compound to said oxidation reactor, said reactor having at least one an outlet for gases resulting from the oxidation of said fuel;

a reactor for regenerating said oxygen-carrying solid compound, connected at the inlet to an air source and at least one pipe capable and intended to convey said oxygen-carrying solid compound from an outlet of said oxidation reactor; to said regeneration reactor, said reactor having at least one outlet for gases from the regeneration of said oxygen-carrying solid compound;

means for recovering said solid compound at the outlet of said oxidation and regeneration reactors; and

heat exchangers adapted and adapted to convert into energy the heat generated in said regeneration reactor;

said pipe adapted and adapted to convey a solid oxygen-carrying compound to said oxidation reactor being connected to an outlet of said regeneration reactor; said device being characterized in that it further comprises:

a source of a gas having a volume concentration of oxygen of between 22% and 100% connected to an inlet of said regeneration reactor; and

means for selectively opening or closing said connections between said regeneration reactor and said air source on the one hand and said regeneration reactor and said source of a gas having an oxygen volume concentration of between 22 % and 100%, on the other hand.

By pipe connection between the reactors, it means that there is connection by a system of pipes capable of transporting a flow of material. This connection system may include valves, intermediate storages, bypasses, heat exchangers, compressors, but not chemical reactors. "Reactor" must be taken in the definition of the invention in the broad sense of "unity". They can therefore have a complex structure known to those skilled in the art and in particular comprise several containers. The device may also comprise means for injecting an extra charge of oxygen-carrying solid compound, or purging means, for example on the pipes connecting the reactors. The recovery means of the oxygen-carrying solid compound can be of any kind capable of isolating solid particles in gaseous flows, for example systems called "cyclones". The means making it possible to select one or the other of the gas sources comprising oxygen to be injected into the regeneration reactor, or to mix the gases originating from these sources, are generally valves that are slaved to a control system. .

According to particular embodiments, the invention may further comprise the following characteristic: said source of a gas having an oxygen volume concentration of between 22% and 100% is suitable and intended to supply a gas whose concentration oxygen volume is between 23% and 40%.

Other features and advantages of the invention will appear on reading the following description, made with reference to the figures, where:

FIG. 1 represents an installation implementing the method according to the invention; FIG. 2 is a diagram illustrating the choice of the gas comprising oxygen implemented in step c).

In the example illustrated in FIG. 1, a fuel 4 and ilmenite 5a are introduced into a reactor 2. The oxidation of the fuel 2a in contact with the ilmenite 2b in the reactor 2 produces primary effluents 8 and Ilmenite in reduced form 9. These primary effluents are conducive to CO 2 capture in that they contain little or no nitrogen. This capture can be done by one or more known techniques for CO 2 separation, possibly preceded by a condensation of the water present in the effluents 8. A non-zero fraction 9a of this ilmenite 9, preferably close to 100%, is introduced into the reactor 3, which is also introduced a gas 6 comprising oxygen. There is a very exothermic oxidation of ilmenite 3b in contact with this gas 3a in the reactor 3. This reaction produces a gas 7 depleted of oxygen with respect to the gas 6 entering the reactor 3. Ilmenite 3b is charged with oxygen and is recovered in an oxidized form 5. A non-zero fraction 5a thereof, preferably close to 100%, is introduced into the reactor 3.

The oxygen carrier compound, here ilmenite, performs a chemical loop through the states 5a, 2b, 9, 9a, 3b, 5. The ilmenite is recovered at the outlet of the reactors 2 and 3 by techniques known to those skilled in the art, for example cyclones (not shown). A supplement of product, or a purge, may be necessary to maintain the quantity (mass) and quality of the oxygen carrier. The heat released by the reactions in the reactor 2 is recovered by heat exchange in the reactor 2. In addition, it can also be recovered in the reactor 2 and / or hot solid or gaseous products circulating between the reactors. In practice, this heat is used to heat water to produce steam, which can then be converted totally or partially into mechanical and / or electrical energy.

The gas 6 comprising oxygen may be prepared from an air source 6a and / or by mixing this air 6a with relatively pure oxygen produced by an air separation unit 6b. The passage of a supply of the reactor 3 to air 6a to a mixture of air and oxygen will regenerate a greater quantity of ilmenite 9a. More oxidized ilmenite is obtained and it is possible to inject a larger quantity 5a into the reactor 2. Thus, all other things being equal, the passage from a supply of the reactor 3 to the air to a feed Oxygen allows you to oxidize more fuel and generate more energy. In a particular configuration of the example illustrated in FIG. 1, the fuel 4 is natural gas, and the volume oxygen content of the flow rate 6 is 30%. Compared to a configuration in which the flow rate 6 would be exclusively air, the invention makes it possible to oxidize 60%> of natural gas in addition, and thus to produce about 60%> more energy in the same installation.

The increase in energy production permitted by the change in nature of the gas 6 comprising oxygen can be further increased by changing the nature of the fuel 4 sent to the reactor 2. FIG. 2 schematically shows an evolution of as a function of time, the volume concentration of oxygen C of the gas 6 sent to the reactor 3 and the power P in kW or MW (amount of energy produced per unit of time) produced by the installation can be determined as a function of time. Thus, for a period of time T1, the gas 6 sent to the reactor 3 is air (C 1) from the source 4a (optionally pre-treated air). The installation then produces a PI power. This period Tl generally corresponds to the normal operation of the installation. If, for one reason or another, it is desired to satisfy a peak of consumption corresponding to a power P2 during a period of time T2, the nature of the gas 6 sent to the reactor 3 is changed. The gases 6 (C2) then come from a oxygen source 6b or a mixture 6a and 6b. During this time T2, the quantity of fuel 4 injected into the reactor 2 is also increased, in order to deliver this power P2 into the system. The period T2 is not necessarily subsequent to the period T1. T2 is simply a period of time during which it is desired to produce a power P2 that is greater than that obtained in an operating regime in air. P2 is often called peak power. Thus, the installation can be sized to meet the need for power P l. The passage to gas comprising between 22% and 100% oxygen by volume makes it possible to satisfy a higher P2 requirement without having to modify the installation. For example, a plant using as fuel 4 natural gas, produced during the period T l a useful thermal power P1 = 200 MWth (thermal megawatts) with the oxidant 6 of the air (Cl = 21%). In this case, the amount of natural gas consumed is 21 635 Nm3 / h (cubic meters per hour taken under normal conditions of temperature and pressure, ie 0 ° C. and 1 atmosphere) as input to the reactor 2. amount of air 6 is 206,049 Nm3 / h, of which 43,270 Nm3 / h of oxygen.

During the period T2, additional oxygen (26 492 Nm3 / h) is added to these 206 049 Nm3 / h of air, so that the oxygen volume concentration of 6 is equal to 30% (C2 = 30% ). In this case, the total flow rate of oxidant 6 is 232,541 Nm3 / h. The quantity 4 of natural gas to be oxidized in the reactor 2 can increase to 34 881 Nm3 / h. The plant will then be able to produce P2 = 322 MWth of useful thermal power.

During the period T2, the flow rates of solid compound used (entering) in the reactors 2 and 3 are increased by 65% with respect to the same flow rates considered during the period T1. This increase is greater than the ratio P2 / P 1 of increase of the power produced, which is about 60%.

Claims

claims

A method (1) for producing energy from at least one fuel (4), comprising:

a step a) of oxidation (2a) of said fuel (4) by placing in contact with at least one oxygen-containing solid compound (5a) and concomitant reduction (2b) of said solid compound;

a step b) of recovering said reduced solid compound (9) in step a);

a step c), exothermic, oxidation (3b) of a non-zero fraction (9a) of said solid compound recovered in step b) by contact with at least one gas (6) comprising oxygen; ; and

a step d) of recovering said oxidized solid compound (5) at the end of step c) and of implementing in step a) a non-zero fraction (5a) of said oxidized solid compound (5); );

the heat released in step c) being at least partially recovered to achieve said energy production;

said method being characterized in that the gas (6) comprising oxygen is alternately, depending on the desired energy power, air or a gas comprising a volume concentration of oxygen of between 22% and 100%.

Process according to Claim 1, characterized in that the gas 6 comprising oxygen is alternately, according to the desired energy power, air or a gas comprising an oxygen volume concentration of between 23% and 40%. .

Process according to either of Claims 1 and 2, characterized in that:

during the period during which the gas (6) comprising oxygen is air, said fuel (4) is of a first given type (4a); and

during the period during which the gas (6) comprising oxygen is a gas comprising an oxygen volume concentration of between 22% and 100%) or 23% and 40%, said fuel (4) is a second given type (4b) more reactive in step a) than said first type (4a).

Process according to claim 3, characterized in that said first type (4a) of fuel is sub-bituminous coal and said second type (4b) of carbonaceous fuel is lignite or coal or HFO (heavy fuel oil) or LPG (liquid petroleum gas) or natural gas. Process according to any one of Claims 1 to 4, characterized in that:

during the period during which the gas (6) comprising oxygen is air, implementing a first flow rate of said solid compound in step a) and a second flow rate of said solid compound in step c ); and

during the period during which the gas (6) comprising oxygen is a gas comprising a volume concentration of oxygen of between 22% and 100% or 23% and 40%, a third rate of said compound is used; solid in step a) and a fourth flow rate of said solid compound in step c), the ratio of said third flow on said first flow and the ratio of said fourth flow on said second flow being greater than or equal to the ratio of said second power (P2) on said first power (PI).

Device (1) for producing energy, comprising at least:

a fuel oxidation reactor (2) connected at input (4) to one or more fuel sources (4a, 4b) and to at least one pipe (5, 5a) suitable for conveying a solid carrier compound oxygen (2b) to said oxidation reactor (2), said reactor (2) having at least one outlet (8) for gases from the oxidation of said fuel;

a regeneration reactor (3) of said oxygen-carrying solid compound (3b), connected at the inlet (6) to an air source (6a) and at least one pipe (9, 9a) adapted and intended to convey said oxygen carrier solid compound (9a) from an outlet of said oxidation reactor (2) to said regeneration reactor (3), said reactor (3) having at least one outlet (7) for gases from the regeneration of said solid oxygen carrier compound; means for recovering said solid compound (3b, 2b) at the outlet of said oxidation (2) and regeneration (3) reactors; and

heat exchangers suitable and for converting into energy the heat generated in said regeneration reactor (2);

said pipe (5, 5a) adapted and intended to convey a solid oxygen-carrying compound (2b) to said oxidation reactor (2) being connected to an outlet of said regeneration reactor (3);

said device (1) being characterized in that it further comprises:

a source (6b) of a gas having an oxygen volume concentration of between 22% and 100% connected to an inlet (6) of said regeneration reactor (3); and

means (10a, 10b) for selectively opening or closing said connections between said regeneration reactor (3) and said air source (6a) on the one hand and said regeneration reactor (3) and said source ( 6b) of a gas pos- sedant having a volume concentration of oxygen of between 22% and 100%, on the other hand.

Device (1) according to claim 6, characterized in that said source (6b) of a gas having an oxygen volume concentration of between 22% and 100% is suitable and intended to supply a gas whose oxygen volume concentration is between 23% and 40%>.