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WO2007107730A1 - Dispositif et procédé de combustion de combustibles solides - Google Patents

Dispositif et procédé de combustion de combustibles solides Download PDF

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Publication number
WO2007107730A1
WO2007107730A1 PCT/GB2007/000961 GB2007000961W WO2007107730A1 WO 2007107730 A1 WO2007107730 A1 WO 2007107730A1 GB 2007000961 W GB2007000961 W GB 2007000961W WO 2007107730 A1 WO2007107730 A1 WO 2007107730A1
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WO
WIPO (PCT)
Prior art keywords
solid fuel
bed
reactor
char
cla
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Ceased
Application number
PCT/GB2007/000961
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English (en)
Inventor
John Dennis
Allan Hayhurst
Stuart Scott
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Cambridge Enterprise Ltd
Original Assignee
Cambridge Enterprise Ltd
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Filing date
Publication date
Application filed by Cambridge Enterprise Ltd filed Critical Cambridge Enterprise Ltd
Publication of WO2007107730A1 publication Critical patent/WO2007107730A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
    • F23C99/00—Subject-matter not provided for in other groups of this subclass

Definitions

  • This invention relates to a method and an apparatus for solid fuel combustion, and in particular to the in situ gasification of a solid fuel, such as coal, and chemical looping.
  • Electricity generation accounts for ⁇ 38% of global anthropogenic carbon emissions to the atmosphere or ⁇ 2,400 Mt/y (carbon basis), projected to exceed 4,000 Mt/y by 2020 1 .
  • To control its environmental impact there is an urgent requirement to sequester CO 2 from the combustion of coal, or fuels derived from it, in the earth 2 .
  • the cost of sequestration is small (e.g. $4-8/t C) compared to the costs of separating CO 2 from typical flue gases ($100-200/t C) 2 , so that disposal approaches viability only if pure CO 2 is available, largely free of nitrogen and other inert gases.
  • One means of obtaining pure CO 2 from a power plant burning a gaseous fuel, e.g. natural gas is to use chemical looping combustion 2 (CLC).
  • CLC chemical looping combustion 2
  • the fuel, in gaseous form is oxidised with a metal oxide, generalised as MeO, in:
  • the invention may advantageously provide a method and an apparatus for combusting a solid fuel, for example for generating power, as defined in the appended independent claims. Preferred or advantageous features of the invention are set out in dependent subclaims.
  • chemical looping may thus be applied to solid fuels.
  • This may be carried out, for example, in a semi-batch mode, involving say a fluidised bed reactor containing a chemical looping agent (CLA) such as a metal oxide (MeO).
  • CLA chemical looping agent
  • the reactor would be operated in a steady cycle of three consecutive periods, t h t 2 and t 3 .
  • the bed would be fluidised by a gasification agent, such as steam or CO 2
  • a solid fuel such as coal-char
  • reaction (1) • the syngas reacts with the surrounding CLA (MeO particles) to give CO 2 and steam by a version of reaction (1):
  • This system can only function down to a certain degree of reduction of the metal oxide.
  • the feed of coal-char ceases and the remaining inventory of bed carbon is allowed to gasify for a further period of time, t 2 , until the inventory is sufficiently small.
  • the bed is fluidised by air instead of steam or CO 2 for a period of time, t 3 , during which reaction (2) regenerates the bed of metal oxide.
  • reaction (2) regenerates the bed of metal oxide.
  • some residual carbon might be burned off, leading to a small release of CO 2 with the regenerating air, but very much less than that from the direct combustion of coal in air.
  • the invention may thus advantageously allow the use of CLC with solid fuels directly, in situ inside a chemical looping reactor. This has not previously been possible for reasons including the problem of separating the solid fuel and the metal oxide for the oxidation (regeneration) phase.
  • This may therefore advantageously provide a technique for isolating the CO 2 from burning a solid fuel.
  • a preferred embodiment may use chemical looping combustion with a solid fuel, such as coal-char, with a gasification agent like steam (or CO 2 ) introduced into the reactor.
  • a gasification agent like steam (or CO 2 ) introduced into the reactor.
  • the gasification agent is believed to transfer solid carbon to gaseous CO, which like H 2 can be reacted with a solid, e.g. Fe 2 O 3 , carrying oxygen, to yield CO 2 and H 2 O.
  • a solid e.g. Fe 2 O 3
  • the reaction of sintered compacts of Fe 2 O 3 appears to be sufficient to make a semi-batch process feasible.
  • the inventors have demonstrated the feasibility of this technique when used with CO 2 or steam as the gasifying agent.
  • Figure 1 is a plot of the rate of production of CO from a bed of sand (i.e. the product of the total molar flow rate and mole fraction of CO) in which a single batch of char (0.0904g) was gasified in 27.5 mol% CO 2 at 900 0 C;
  • Figure 2 illustrates the results of a series of experiments in which successive batches of char were gasified in the active bed of Fe 2 O 3 and silica sand. The bed was regenerated after the fourth batch using 5% O 2 in N 2 . In each case the mass of char in the batch is shown, together with the recovery;
  • Figure 3 illustrates the results of a series of experiments in which batches of coal (+1.4mm, -1.7mm) were gasified in the active bed of Fe 2 O 3 and silica sand. The bed was regenerated after the fourth batch using 5% O 2 in N 2 . The mass of coal used in each experiment is shown;
  • Figure 4 is a plot of the mole fractions of CO, CO 2 and H 2 (dry basis) for an experiment in which 0.0946g of char was gasified in steam and N 2 , in a bed of silica sand at 900 0 C.
  • the mole fraction of H 2 in this case, has been calculated from the reaction's stoichiometry;
  • Figure 5 is a plot of the rate of production of CO and CO 2 for experiments in the active bed containing Fe 2 O 3 .
  • the fluidising gas was either 27.6 mol % steam in N 2 or 5.2 mol% O 2 in N 2 .
  • the triangles in the plot show the ratio of the yields of CO and CO 2 produced during each experiment.
  • the mass of char (in grams) added for each experiment is indicated.
  • the temperature of the bed was 900 0 C; and
  • Figure 6 is a plot of measured mole fractions of H 2 , CO, CO 2 in the off-gases for the last two experiments in Figure 5. The concentrations shown are on a dry basis.
  • the first embodiments involve preliminary experiments to test the feasibility of the above technique using iron oxide (Fe 2 O 3 ) as the CLA, and a lignite fuel gasified by CO 2 .
  • the chemical looping agent was produced from Fe 2 O 3 powder (Aldrich > 99% purity), which was mixed with a small amount of distilled water, in a food mixer.
  • the resulting particles were sieved to +300, -710 ⁇ m (i.e. to a range between approximately 300 and 710 ⁇ m particle size), and any larger lumps broken up. The procedure was repeated until a sufficient quantity of particles was in this size range.
  • the agglomerated particles of Fe 2 O 3 were then placed in a furnace, heated to 900 0 C and maintained at this temperature for 5h. The resulting particles were then sieved into two size ranges, 300 to 425 ⁇ m and 425 to 71 O ⁇ m.
  • the fuels used were a lignite (Hambach) and its char.
  • the char was manufactured in a bed of silica sand (sieved to 355-425 ⁇ m) contained in a quartz reactor, initially at 900 0 C, fluidised by N 2 .
  • the lignite (1.4 to 1.7mm) was added slowly; ⁇ 15g was added over a time period of ⁇ 30min.
  • the bed was then allowed to regain a temperature of 900 0 C, and then cooled (whilst fluidised by N 2 ) until the char could be recovered.
  • the off-gases were sampled continuously into two NDIR (non-dispersive infrared) analysers, one measuring [CO 2 ] and [CO] (with ranges of 20mol% and 1 mol%, respectively) and the other [CH 4 ] and [CO] (with ranges of 6mol% and 11mol%, respectively), via a trap at 0 0 C (to remove tars etc) with a glass wool filter and a PermapureTM membrane drier (MD 070 44P), which was purged at 5L min '1 with dry nitrogen. Each analyser received 1 L min "1 of sample gas.
  • NDIR non-dispersive infrared
  • the first experiments used the bed of silica sand alone and served as a control. With the hot bed fluidised by the mixture of N 2 and CO 2 , a batch ( ⁇ 0.1 g) of the char was added to the bed. The char was allowed to gasify until completion in every experiment. The experiment was repeated several times.
  • the second set of experiments used the bed containing the particles of Fe 2 O 3 mixed with silica sand. As in the first experiments, a batch of char (-0.1 g) was added to the bed and gasified to completion. Further batches of char were added, until it was clear that the chemical looping agent (Fe 2 O 3 ) had been used up.
  • FIG. 2 shows the results of experiments in which a batch of char was gasified in CO 2 , in a bed initially of sand and Fe 2 O 3 particles.
  • reaction (4) again produces CO, which is subsequently oxidised in reaction (6) by the solid particles of Fe 2 O 3 .
  • the recovery is here defined as the number of moles of CO actually produced in the off-gases to the amount which would have been produced had all the carbon in the char been gasified to CO.
  • the bed was not regenerated between the first four experiments; consequently, the ability of the Fe 2 O 3 particles to react with CO was gradually reduced.
  • the largest peak concentration in Figure 2 corresponds to 1.9mol%; it occurs when the Fe 2 O 3
  • the second embodiments involve preliminary experiments to test the feasibility of the technique using iron oxide (Fe 2 O 3 ) as the CLA, and a lignite fuel gasified by steam.
  • the reactor was placed in a tube furnace and the bed was heated to 900 0 C; the temperature of the bed was monitored by a K-type thermocouple within the bed.
  • the off-gases were continuously sampled into two NDIR analysers, one measuring [CO] and [CO 2 ] (with ranges of 20mol% and 1mol%, respectively), the other [CH 4 ] and [CO] (with ranges of 6mol% and 11mol%, respectively).
  • the samples were passed through two traps maintained at 0 0 C (to condense the water), a glass wool filter and a PermapureTM membrane drier (MD 070 44P), purged at 5L min "1 with dry nitrogen. Each analyser received 1 L min "1 of sample gas.
  • a mass spectrometer Hiden HPR-20 was used to detect H 2 in the off-gases.
  • the first set of experiments used the bed of silica sand without Fe 2 O 3 and served as a control. With the bed fluidised by the mixture of N 2 and H 2 O a batch (0.1g) of the char was added to the bed. The char was allowed to gasify to completion in all experiments. The experiment was repeated several times.
  • the second set of experiments used the bed containing the particles of Fe 2 O 3 . As in the first experiments, a batch of char (0.1g) was added to the bed and allowed to gasify to completion. Subsequent batches of char were added, until it was clear that the chemical looping agent had been depleted. At this point, the bed was re-oxidised with the mixture of air and N 2 , after which, the gasification experiment was repeated.
  • Figure 4 shows the mole fractions of H 2 , CO and CO 2 in the off-gas (dry basis) for an experiment in which a batch of char was added to the (inert) bed of silica sand, when fluidised by steam and N 2 .
  • the average yield of carbon recovered in the off-gas as CO and CO 2 was between 103 to 108% of the amount of carbon added in the char, for five repetitions of this experiment.
  • H 2 can only be produced either by gasifying the char with steam in reaction (3), or by the water-gas shift equilibrium:

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Industrial Gases (AREA)

Abstract

La présente invention concerne un procédé de combustion de combustibles solides, lequel procédé consiste à utiliser un réacteur contenant un agent de bouclage chimique. Pendant une première période, un combustible solide et un agent de gazification sont amenés dans le réacteur puis, lors d'une seconde période, un oxydant est amené dans le réacteur. Ces étapes peuvent être répétées de manière cyclique.
PCT/GB2007/000961 2006-03-22 2007-03-19 Dispositif et procédé de combustion de combustibles solides Ceased WO2007107730A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB0605762.4 2006-03-22
GB0605762A GB0605762D0 (en) 2006-03-22 2006-03-22 Solid fuel combustion method and apparatus

Publications (1)

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WO2007107730A1 true WO2007107730A1 (fr) 2007-09-27

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WO (1) WO2007107730A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2009138595A3 (fr) * 2008-04-30 2010-02-18 Ifp Masse active d'oxydo-reduction et procédé de combustion en boucle chimique

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5447024A (en) * 1992-06-03 1995-09-05 Tokyo Electric Power Co., Inc. Chemical-looping combustion power generation plant system
US20050175533A1 (en) * 2003-12-11 2005-08-11 Thomas Theodore J. Combustion looping using composite oxygen carriers
US20060024221A1 (en) * 2004-08-02 2006-02-02 Etienne Lebas Device for producing a hot gas by oxidation using a simulated rotary reactor

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5447024A (en) * 1992-06-03 1995-09-05 Tokyo Electric Power Co., Inc. Chemical-looping combustion power generation plant system
US20050175533A1 (en) * 2003-12-11 2005-08-11 Thomas Theodore J. Combustion looping using composite oxygen carriers
US20060024221A1 (en) * 2004-08-02 2006-02-02 Etienne Lebas Device for producing a hot gas by oxidation using a simulated rotary reactor

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2009138595A3 (fr) * 2008-04-30 2010-02-18 Ifp Masse active d'oxydo-reduction et procédé de combustion en boucle chimique

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