CN115143455A - Novel chemical looping combustion method comprising hydrogen production process - Google Patents

Abstract

The invention belongs to the technical field of heat supply, and particularly relates to a novel chemical looping combustion method comprising a hydrogen production process, which comprises the following steps: natural gas and water are reformed under the condition of reforming catalyst and then are subjected to chemical looping combustion with air. The chemical looping combustion method of the invention reduces the natural gas into hydrogen and carbon monoxide in advance, thus fundamentally solving the problem of carbon deposition caused by sintering of the oxygen carrier.

Description

Novel chemical looping combustion method comprising hydrogen production process

Technical Field

The invention relates to the technical field of heat supply, in particular to a novel chemical looping combustion method comprising a hydrogen production process.

Background

The description of the background of the invention pertaining to the related art to which this invention pertains is given for the purpose of illustration and understanding only of the summary of the invention and is not to be construed as an admission that the applicant is explicitly or implicitly admitted to be prior art to the date of filing this application as first filed with this invention.

With the rapid development of economy, people enjoy the increasingly improved living standard and consume a large amount of energy, and pollutants discharged by the energy in the using process influence the ecological environment on which people live. It is anticipated that for a long period of time in the future, fossil energy such as natural gas, coal, petroleum and the like is still the main energy used by people. Carbon dioxide (CO) released by its combustion ₂ ) Nitrogen oxides (NOx), sulfides (SO) ₂ ) And atmospheric pollutants such as particulate matters are increasing. People should pay attention to the influence on the environment while considering energy efficiency.

CO emitted by people in the process of consuming energy ₂ Can cause greenhouse effect; NOx, SO ₂ Has toxic effect on human body and is one of the main reasons for forming acid rain and acid mist; particulate matter is the primary cause of haze weather, while NOx is an important precursor to the more harmful secondary particles in PM 2.5. In addition, under the irradiation of sunlight, NOx can generate a series of complex photochemical oxidation reactions with Volatile Organic Compounds (VOC) in the atmosphere after reaching a certain concentration, photochemical smog can be formed, ozone can be generated to enhance atmospheric oxidation, the atmosphere oxidation is very harmful to human health like haze, and the harmful effect on plants is also achieved. Natural gas, as a relatively clean energy source, has much less impact on the environment than petroleum and coal, but the combustion of natural gas still generates a certain amount of pollutants in the flue gas, so that countries put forward increasingly strict limiting standards on the emission of NOx in the combustion of natural gas. For small gas boilers on the order of tens to hundreds of kilowatts, the NOx emission levels are typically required to be between 100ppm and 200ppm, while the latest standards in California in the United states are even required to be below 18 ppm. Local standards are also established in Beijing, and the emission limit of nitrogen oxides of a newly-built boiler is regulated to be 30mg/m < 3 > from 4/1 in 2017, so that people pay enough attention to the emission reduction of NOx, and the low-nitrogen combustion technology of fossil fuels becomes a research hotspot. At present, the energy consumption of China is huge, and the country already sets the total energy consumption in the future to improve the energy utilization rate and realize the clean utilization of energy, so thatThere is a need to develop a new generation of clean gas utilization technology to further improve the energy utilization efficiency of the gas and realize zero emission of pollutants and resource utilization of emissions.

Chemical-Looping Combustion (CLC) is a clean, efficient new-generation Combustion technology, breaking through the traditional Combustion mode, and becoming an innovative breakthrough to solve energy and environmental problems. The existing chemical looping combustion technology mainly uses coal and natural gas as fuels, the main application object is thermal power generation, the temperature of an oxygen carrier reduction process is required to be above 900 ℃, and the temperature of an oxidation regeneration process is higher and reaches 1300 ℃. In order to maintain the heat balance of the reduction process and strengthen the heat and mass transfer between the reaction gas and the oxygen carrier, serial fluidized beds are mostly adopted in the system. The existing chemical-looping combustion process mainly has the problems of short service life of an oxygen carrier, complex system, poor air tightness and the like caused by high-temperature sintering, carbon deposition and serious abrasion.

Disclosure of Invention

It is an object of embodiments of the present invention to provide a novel chemical looping combustion method involving a hydrogen production process.

A novel chemical looping combustion method comprising a hydrogen production process, comprising the steps of:

reforming natural gas and water under the condition of reforming catalyst and then carrying out chemical looping combustion with air.

Further, the natural gas and the water are reacted in the presence of a reforming catalyst to generate hydrogen and carbon monoxide, the hydrogen and the carbon monoxide are subjected to reduction reaction with an oxygen carrier, and the oxygen carrier is obtained by oxidation reaction of the air and the reduced oxygen carrier.

Further, reforming of natural gas and water over a reforming catalyst is coupled with a chemical looping combustion process.

The embodiment of the invention has the following beneficial effects:

the invention provides a chemical looping combustion process flow based on a double fixed bed reactor, which is characterized by being provided with a CH4 pre-reforming step. The process converts CH4 into H2 and CO with stronger reduction capability in advance, so that the reduction process of the oxygen carrier can work at lower temperature, and the problem of carbon deposition caused by sintering of the oxygen carrier is fundamentally overcome.

Drawings

FIG. 1 shows an embodiment of the present invention with CH ₄ A chemical looping combustion process schematic diagram of prereformed natural gas;

FIG. 2 shows a CH with a burner not included in the embodiment of the present invention ₄ A schematic diagram of a prereformed natural gas chemical looping combustion process;

FIG. 3 shows an embodiment of the present invention in which CH is coupled ₄ A natural gas chemical looping combustion process diagram which is characterized by a reforming link;

FIG. 4 is a schematic diagram of a natural gas chemical looping combustion process applied to a 100kW grade prototype in an embodiment of the present invention;

FIG. 5 is a system diagram of a 100KW prototype in the embodiment of the invention;

FIG. 6 is a schematic diagram of a chemical looping combustion process of natural gas applied to a 500kW grade prototype in an embodiment of the invention;

FIG. 7 is a schematic diagram of a 100KW reactor in an example of the present invention;

FIG. 8 is a schematic illustration of the main body of a 100KW reactor in an example of the present invention;

FIG. 9 is a schematic illustration of a 100KW chemical chain set in an example of the present invention;

FIG. 10 is a system diagram of a 500KW prototype in the embodiment of the invention;

FIG. 11 is a schematic view of a 500KW chemical chain set in an example of the present invention;

FIG. 12 is a schematic view of a 500KW reactor in an example of the present invention;

FIG. 13 is a schematic view of a 500KW reactor set in an example of the present invention;

FIG. 14 is a sectional view of a 500KW reactor stack in accordance with an embodiment of the present invention.

Detailed Description

The present application is further described below with reference to examples.

In the following description, different "one embodiment" or "an embodiment" may not necessarily refer to the same embodiment, in order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art. Various embodiments may be replaced or combined, and other embodiments may be obtained according to the embodiments without creative efforts for those skilled in the art.

The CLC has the main principle that the combustion reaction in the mixed gas of fuel and air is divided into two gas-solid reactions which are separately carried out through the oxygen carrier, namely the reduction reaction of the fuel and the oxygen carrier in an oxidation state and the oxidation regeneration reaction of the air and the oxygen carrier in a reduction state. The oxygen carrier plays a role of taking oxygen in the air as lattice oxygen in the reaction process

(O2 ^- ) The form of the oxygen carrier is transferred to the action of the fuel, so that the direct contact between the fuel and air is avoided, the direct open flame combustion of the air and the fuel is converted into indirect reaction combustion, the oxygen carrier is in a core position in the whole chemical chain reaction system, and the oxidation-reduction performance, the cycle life, the carbon deposition resistance, the mechanical stability and the like of the oxygen carrier are directly related to the success or failure of the whole CLC system.

The CLC system consists of an oxidation reactor, a reduction reactor and an oxygen carrier. Oxygen carriers generally consist of transition metal oxides, which are active components and participate in redox reactions and transport lattice oxygen, and supports, which are inert components, for supporting and dispersing the metal oxides and improving their mechanical properties and stability in chemical reactions. The fuel and the oxygen carrier in the oxidation state are firstly subjected to reduction reaction in a reduction reactor, the fuel obtains lattice oxygen from the oxygen carrier in the oxidation state in the reaction to form reaction products of CO2 and H2O, the H2O is removed through condensation to obtain high-purity CO2, and the oxygen carrier in the oxidation state loses the lattice oxygen and is converted into the oxygen carrier in the reduction state. The reaction formula of the reduction reaction between the oxidation state oxygen carrier and the fuel in the reduction reactor is shown as the formula 1-1:

(2x+y/2)MeO+C _x H _y ＝xCO ₂ +y/2H ₂ O+(2x+y/2)Me (1-1)

then the reduced oxygen carrier contacts with air in an oxidation reactor to generate oxidation reaction, so that the reduced oxygen carrier is regenerated into an oxidized oxygen carrier, molecular oxygen in the air is fixed in a form of lattice oxygen, and a large amount of reaction heat is released at the same time. The reaction formula of the oxidation reaction between the reduced oxygen carrier and oxygen in the oxidation reactor is shown as formula 1-2:

(2x+y/2)Me+(x+y/4)O ₂ the total reaction formula of the two reactions of = (2x + y/2) MeO (1-2) is the same as that of the ordinary combustion reaction, as shown in formulas 1-3:

C _x H _y +(x+y/4)O ₂ ＝xCO ₂ +y/2H ₂ O (1-3)

CLC has

The characteristic of small loss is mainly reflected in that the concentration of N2 in the oxidation product gas and the concentration of CO2 and water vapor in the reduction reaction product are greatly improved, thereby endowing the combustion product with the utilization value. In addition, because the operating temperature of the reduction reactor and the oxidation reactor is relatively low, generally between 900 ℃ and 1300 ℃, and the fuel is not directly contacted with the air and belongs to flameless combustion, the generation of fuel type NOx can be inhibited, and the generation of rapid type and thermal type NOx can not be generated in the oxidation reactor, so that no NOx exists in the flue gas. The chemical looping combustion technique has two distinct advantages over traditional direct combustion:

zero energy consumption for CO2 separation: the fuel is not directly contacted with the air, the flue gas in the reduction reaction only contains CO2 and water vapor, and only high-purity CO2 is left after the water vapor is condensed by cooling, and compared with the traditional CO2 capturing technology, the method does not need to additionally increase energy consumption;

low emission of NOx: since the fuel does not directly contact with the air, rapid NOx is not generated, and in addition, since the chemical looping combustion temperature is significantly lower than that of direct combustion, thermal NOx generation is also suppressed;

a novel chemical looping combustion method comprising a hydrogen production process, comprising the steps of:

reforming natural gas and water under the condition of reforming catalyst and then carrying out chemical looping combustion with air.

Further, generating hydrogen and carbon monoxide from natural gas and water under the condition of a reforming catalyst, then carrying out reduction reaction on the hydrogen and the carbon monoxide and an oxygen carrier, and carrying out oxidation reaction on air and the reduced oxygen carrier to obtain the oxygen carrier.

Further, reforming of natural gas and water over a reforming catalyst is coupled with a chemical looping combustion process.

A novel natural gas chemical looping combustion device, comprising:

the chemical looping combustion reactor comprises a first reactor and a second reactor, wherein the first reactor and the second reactor respectively discharge carbon dioxide, condensed water and nitrogen after exchanging heat with a heat exchanger.

In some embodiments of the invention, comprising: and a pipeline for discharging condensed water is communicated with the inlet of the chemical-looping combustion reactor.

In some embodiments of the present invention, the inlet and outlet pipes of the first reactor and the second reactor are communicated by a three-way valve.

In some embodiments of the present invention, the chemical looping combustion reactor is a cylinder, a reforming reactor is disposed in the chemical looping combustion reactor, the reforming reactor and the chemical looping combustion reactor are concentric cylinders, the reforming reactor is filled with a reforming catalyst, a combustion chamber is formed between the chemical looping combustion reactor and the reforming reactor, and the combustion chamber is filled with an oxygen carrier.

In some embodiments of the invention, the chemical looping combustion reactor in which natural gas reforming is coupled to the chemical looping combustion process is mixed with a packed oxygen carrier and a reforming catalyst.

In some embodiments of the invention, the reactor comprises a reactor main body, wherein the upper end of the reactor main body is provided with an upper end socket assembly welding part, and the lower end of the reactor main body is provided with a lower end socket assembly welding part; the reactor main body in be equipped with the soaking pipe, the reactor main body in the bottom laid the corundum ball layer, corundum ball layer top pack and have the mycoplasma filler.

A zero-carbon heating system is characterized in that a natural gas chemical-looping combustion device provides heat energy, a first reactor of the natural gas chemical-looping combustion device exchanges heat through a first plate heat exchanger to provide a heat source for a heating water supply pipe, and a heating water return pipe enters the first plate heat exchanger through a reduction flue gas shell-and-tube heat exchanger and is communicated with the heating water supply pipe; the second reactor exchanges heat through a second plate heat exchanger, and the hot water source enters the second plate heat exchanger through the oxidized flue gas shell-and-tube heat exchanger to exchange heat with the second reactor and then outputs cooling water;

the first plate heat exchanger forms a loop with the first reactor through a first cooling water tank; the second plate heat exchanger and the second reactor form a loop through a second cooling water tank;

outlets of the first reactor and the second reactor are communicated with the reducing flue gas shell-and-tube heat exchanger, and an inlet of the oxidizing flue gas shell-and-tube heat exchanger is communicated with natural gas;

outlets of the reduction flue gas shell-and-tube heat exchanger and the oxidation flue gas shell-and-tube heat exchanger are connected with a gas-water separator;

the outlets of the first reactor and the second reactor are connected with a heating burner;

a water separator is arranged between the first plate heat exchanger and the heating water supply pipe, and a water collector is arranged between the heating water return pipe and the reduction smoke pipe shell type heat exchanger.

Oxygen carrier

An oxygen carrier can also be considered as a solid catalyst, generally consisting of an active ingredient and an inert carrier. The active ingredients are used as oxygen carriers and reaction media and are circulated between the two reactors to realize the transfer of oxygen and continuously transfer heat generated by oxidation-reduction reaction in the two reactors. Therefore, the performance of the oxygen carrier is very critical to the application of the chemical looping combustion technology, the performance directly influences the operation effect of the whole chemical looping combustion system, and the chemical looping combustion needs to be applied on a large scale, and a matched oxygen carrier needs to be found.

The performance of the oxygen carrier required in the chemical looping combustion process can be evaluated from the aspects of oxygen transfer capacity, oxidation-reduction reaction rate, mechanical properties (sintering resistance, agglomeration resistance, abrasion resistance and breakage resistance), carbon deposition resistance, production cost, environmental influence and the like, and meanwhile, the oxygen carrier does not have obvious attenuation after being cycled for many times. Oxygen carriers studied at present are mainly: metal oxygen carriers, sulfate oxygen carriers, perovskite oxygen carriers, and the like.

(1) Metal oxygen carrier

The metal oxygen carriers which are currently being studied more include Ni, fe, cu oxides of metals such as Mn and particles prepared by mixing these metal oxides with an inert carrier.

Metallic Ni has a melting point of 1453 c, a common oxide form of NiO, and a melting point of 1990 c. The nickel-based oxygen carrier has the advantages of high activity, low high-temperature volatility, strong high-temperature resistance, large oxygen carrying capacity and the like, and is widely concerned by people. But it is harmful to the environment and expensive, and the carbon deposition phenomenon is very serious because CO and H2 are generally generated in the reaction process.

The Cu-based oxygen carrier has higher activity and larger oxygen carrying capacity, is not easy to react with the carrier, and is more expensive because the oxidation and the reduction of copper oxide of the Cu-based oxygen carrier are exothermic reactions, so that heat is not required to be provided for the reduction process to maintain the reaction temperature unlike other oxygen carriers, the continuous heat release of the oxidation and the reduction process can be realized, and the only defect of the Cu-based oxygen carrier is that the low melting point of the copper metal makes the copper metal easily agglomerate and sinter at high temperature, and the use at high temperature is limited.

The Fe-based oxygen carrier has relatively high activity, and can maintain good reactivity at high temperature due to the high melting point, so that the Fe-based oxygen carrier has the advantages of difficult occurrence of carbon deposition, good stability and the like, has the advantages of wide sources, environmental protection and the like compared with the oxygen carriers such as Ni, co and the like, and is an oxygen carrier which is very economic and has application prospect. The disadvantage is that the reactivity is inferior compared to several other commonly used metal oxygen carriers.

Therefore, the single metal oxide has respective advantages and disadvantages, and if the composite metal oxide is formed, the respective advantages can be effectively exerted, and the disadvantages are avoided.

(2) Non-metallic oxygen carrier

Most of the researches on non-metal oxide oxygen carriers at present mainly include sulfate non-metal oxygen carriers such as CaSO4, baSO4 and SrSO4, and the sulfate non-metal oxygen carriers have the advantages of high oxygen carrying capacity, high quality and low price and the like, and are widely concerned recently. The disadvantage is that decomposition reaction is easy to occur in the high-temperature reaction process to generate harmful gases such as SO2 and the like. Moreover, its low mechanical strength is also an important limiting factor.

(3) Preparation method of oxygen carrier

The preparation method of the oxygen carrier is an important research content in the screening process of the oxygen carrier, and factors such as inert carriers, active components, mixing proportion, preparation process, sintering temperature and the like have obvious influence on the performance of the oxygen carrier, wherein the preparation method mainly comprises the following steps: mechanical mixing, dipping, dispersion, spray drying, freeze granulation, sol-gel combustion synthesis, and the like.

Mechanical mixing method: mixing metal oxide with certain particle size and inert carrier (adding graphite or starch with the mass percent of 10% as an additive) according to a set mass ratio, crushing, adding a proper amount of water to obtain a paste with proper fineness, then pressing and molding, drying at a milder temperature, sintering in a muffle furnace at a high temperature, and finally crushing and sieving to obtain the oxygen carrier with certain particle size.

The dipping method comprises the following steps: dissolving metal nitrate (such as Ni (NO 3) 2, cu (NO 3) 2 and the like) in H2O to obtain a saturated solution, adding an inert carrier into the solution, continuously stirring to enable metal nitrate ions to be adsorbed on gaps and surfaces of the inert carrier, then removing the H2O, and calcining at a certain temperature to decompose the nitrate so as to achieve the loading purpose (the loading amount can be increased by multiple times of impregnation), wherein the obtained particles can be used as an oxygen carrier.

A dispersion method: dissolving metal oxide and nitrate of an inert carrier in water according to a certain proportion, stirring for a period of time, drying in sections under different temperature gradients, finally roasting to obtain a raw material for preparing the oxygen carrier, and treating the raw material according to the same procedure of a mechanical mixing method to obtain the oxygen carrier.

Spray drying method: the raw materials for preparing the oxygen carrier are obtained by the dispersion method, the raw materials are crushed and added with water to form slurry, and then the slurry is dried by a spray drier and roasted to obtain the oxygen carrier.

A freeze granulation method: mixing metal oxide, inert carrier and a small amount of dispersant with water (adding starch with volume fraction of 10% as additive), obtaining slurry by a ball mill, atomizing the slurry by a nozzle, spraying liquid nitrogen to obtain frozen spherical particles, removing water in the particles by a freeze drying method, removing organic matters in the particles by a pyrolysis method, roasting at a certain temperature, and finally obtaining the oxygen carrier with a certain particle size by screening.

Sol-gel method: taking the preparation of a NiO/YSZ oxygen carrier as an example, zirconium tetra-n-butoxide (C16H 36O4 Zr) and yttrium nitrate hexahydrate (Y (NO 3) 3.6H 2O) were dissolved in isopropanol (C3H 8O) (the molar ratio of ZrO2 to Y2O3 was 92, the alkoxide concentration was 25mol/m 3), nitric acid was added so that the molar ratio of nitric acid to alkoxide was 4. So as to obtain NiO/YSZ powder, and the NiO/YSZ oxygen carrier can be prepared after the powder is processed by the same procedure as the mechanical mixing method.

The synthesis method of sol-gel combustion comprises the following steps: taking preparation of Fe2O3/Al2O3 as an example, accurately weighing Fe (NO 3) 3.9H 2O, al (NO 3) 3.9H 2O and urea according to a stoichiometric proportion, then adding a certain amount of deionized water, uniformly stirring in a magnetic stirrer, and continuously heating at a constant temperature of 75 ℃ until a viscous sol is formed. The gel is dried in stages at 80 ℃ and 120 ℃ respectively, the obtained dried gel is burnt in a muffle furnace with the preheating temperature of 600 ℃ for 15min, and finally the dried gel is roasted in the muffle furnace with the temperature of 950 ℃ for 2h.

The key to the engineering of chemical looping combustion technology lies in the oxygen carrier, and the key to the oxygen carrier lies in the reduction reaction performance. The oxygen carrier has the characteristics of large oxygen carrying capacity, high reaction activity, high mechanical strength, sintering resistance, carbon deposition resistance and good pulverization resistance. The oxygen carrier for the fixed bed reactor has two other characteristics, namely, the oxygen carrier is required to have a low enough ignition temperature and a large enough working temperature width because the outer wall of the reaction tube is used as a heat exchange surface and the reaction zone continuously moves towards the downstream of the reaction tube along with time, so that huge temperature distribution is formed in the radial direction and the axial direction of the reaction tube; secondly, if the reduction reaction of the oxygen carrier is not exothermic or endothermic, the temperature of the oxygen carrier is continuously reduced during the reduction reaction to cause flameout, and in addition, the combustion heat is concentrated in the oxidation regeneration process of the oxygen carrier to be released, so that overheating of the oxygen carrier, especially local overheating, is inevitably caused to cause degradation, and therefore the reduction reaction of the oxygen carrier in an oxidation state and the oxidation reaction of the oxygen carrier in a reduction state are required to be exothermic reactions.

The temperature required by the reduction reaction can be greatly reduced by arranging a CH4 pre-reforming step to convert CH4 into CO and H2 with stronger reduction capability, and the applicant inserts the steam reforming of CH4 into the reduction reaction process of an oxygen carrier by mixing a partial reforming catalyst with the oxygen carrier. Taking a Cu-Fe-Al based oxygen carrier as an example, the reaction performance when the reforming catalyst is not mixed and the reforming catalyst is mixed is compared. By steam reforming with CH4 embedded in the reduction reaction process, the light-off temperature and the complete conversion temperature can be reduced by about 100 ℃, and the method has remarkable effect.

Referring to fig. 1, a system for a pre-reforming process includes a combustor 101, a reforming reactor 102, a first chemical looping combustion reactor 103, a second chemical looping combustion reactor 104, and a tank 105.

With CH ₄ Pre-reformed natural gas chemical looping combustion process

Reforming reaction of natural gas: CH4+ H2O = =3H2+ CO

Reduction reaction of oxygen carrier: 3CuO +3H2= =3Cu +3H2O

CuO+CO＝＝＝Cu+CO2

Oxidation reaction of oxygen carrier: 4Cu +2O2= =4CuO

The overall reaction of chemical looping combustion: CH4+2O2= = CO2+2H2O

However, the provision of a CH4 pre-reforming process complicates the process flow. In order to simplify the prereforming process, a process flow is provided in which a burner for supplying heat to the reforming reactor is omitted by arranging the reforming reactor in a concentric cylinder of a chemical looping combustion reactor, and the heat required for the reforming reaction is provided by the chemical looping combustion reactor. As shown in fig. 2, compared with fig. 1, a burner for supplying heat to the reforming reactor is omitted, the reactor comprises an oxygen carrier 201 and a reforming catalyst 202 positioned in the center, a heat exchange jacket 203 is arranged outside the reactor, and a heat exchanger 204 is arranged between the heat exchange jacket and a tank 205.

However, the process flow suffers from the problem that the reactor is relatively complex and not easily scalable. Therefore, the applicant proposes a new chemical looping combustion process in which a reforming catalyst is mixed in a reactor and a CH4 reforming link is coupled to a chemical looping combustion process, and the experimental result of oxygen carrier reduction reaction performance evaluation shows that 25% of Ni-based oxygen carrier serving as the reforming catalyst is mixed to obtain a remarkable effect of reducing the reduction reaction ignition temperature by 120 ℃ when the S/C is 1.0. In the system shown in fig. 3, the reactors 301 and 302 are provided with heat exchange jackets 303 at the outside and heat exchangers 304 are still provided between the tank 305 and the reactors.

In order to further optimize the chemical-looping combustion process flow and simplify a prototype system, the process flow is provided. The improvement point comprises that two groups of plate heat exchangers and a cooling water tank are combined into a whole, and a hot water heat exchange loop is simplified. In addition, in order to avoid the loss of thermal efficiency caused by the fact that CH4 introduced air remained in the reduction reactor is blown out of the N2 discharge pipeline when the reactor is switched, the process is provided with an electric three-way valve and a circulating pipeline connected with an air introduction pipeline on the N2 discharge pipeline, and the three-way valve is tangential to the circulating pipeline within seconds after the switching, so that the CH4 and the air enter the oxidation reactor together to be utilized. A system for a natural gas chemical looping combustion process applied to a 100kW class prototype is shown in figure 4 and comprises a first reactor 401 and a second reactor 402.

The operation and control method of the prototype system comprises the steps of firstly mixing fuel gas and water vapor, then leading the mixture into a first chemical-looping combustion reactor (on the left) through a first electric three-way valve in a descending flow mode to carry out a reduction reaction process, enabling the reduction reaction product gas to enter a reduction product gas heat exchanger through a second electric three-way valve to exchange heat with return water, enabling sensible heat of the reduction reaction product gas and latent heat of most of the water vapor to be recycled and then enter a gas-water separator, capturing high-purity CO2 after the separation from condensed water, and enabling a part of the condensed water to be heated and vaporized to be added into the fuel gas as a reforming agent of the fuel gas.

Meanwhile, air is upward-flowed and guided into a second chemical-looping combustion reactor (right side) through an air pump and a third electric three-way valve to carry out an oxidation regeneration reaction process, and oxidation reaction product gas enters an oxidation product gas heat exchanger through a fourth electric three-way valve to exchange heat with return water and is then discharged through a fifth electric three-way valve.

When the CH4 concentration in the reduction product gas indicated by the CH4 detector on the reduction product gas line was gradually increased from zero to a set value (0.5%), the first to fourth electric three-way valves were simultaneously switched so that the fuel gas was introduced into the second chemical looping combustion reactor and the air was introduced into the first chemical looping combustion reactor. At the same time, the fifth electric three-way valve is switched, and after about 10 seconds, the state is switched back.

When the three-way valve switching is performed, if the O2 concentration in the oxidation product gas indicated by the O2 detector on the oxidation product gas line is 0%, the flow rate of air is appropriately increased by the air pump, and when the O2 concentration in the oxidation product gas indicated by the O2 detector is greater than the set value (2%), the flow rate of air is appropriately decreased by the air pump.

When the temperature sensor provided in the reaction tube indicates a temperature exceeding 750 deg.c, the flow rate of the cooling water is increased by the cooling water shield pump, and when the temperature sensor provided in the reaction tube indicates a temperature below 650 deg.c, the flow rate of the cooling water is decreased by the cooling water shield pump.

The 100kW prototype system mainly comprises a reactor, a reactor cooler, a combustion preheating system, a flue gas heat exchanger, a gas compressor, an air blower and a control system.

1) A reactor:

19 DN125 reaction tubes are arranged in a vertical barrel with the diameter of 800mm of the reactor, a soaking tube with the diameter of 76mm is concentrically arranged in each reaction tube, oxygen carriers and corundum balls are filled in an annular area between the reaction tubes and the soaking tubes, the upper end and the lower end of each soaking tube are respectively filled with the corundum balls with the diameter of 240mm, 5 layers of 200mm oxygen carriers with the total diameter of 1000mm are filled in the middle of each soaking tube, and each layer is supported by a material supporting plate; a distributor is arranged at the position 70mm away from the upper end of each reaction tube, so that cooling water is uniformly distributed on the outer wall of each reaction tube;

two reactors are switched between reduction and oxidation, one is in the reduction process, and the other is in the oxidation process; in the reduction process, natural gas enters from the upper end of the reactor, is reduced in a pipe and an oxidation state oxygen carrier, and then is discharged from the lower end of the reduction flue gas and enters a reduction flue gas heat exchanger; air is fed from the lower end of the reactor in the oxidation process, and after the air is oxidized in the pipe and by the reduced-state oxygen carrier, the air is discharged from the lower end of the oxidation flue gas and enters the oxidation flue gas heat exchanger; a 100kw chemical chain system diagram is shown in fig. 5, and comprises a first reactor 501 and a second reactor 502 which are respectively communicated with a reduction flue gas shell-and-tube heat exchanger 503 and an oxidation flue gas shell-and-tube heat exchanger 504; a heating water return pipe 508 is communicated with the shell-and-tube heat exchanger 503 of the reduction flue gas through a water collector 506; a heating water supply pipe 507 is communicated with the first reactor 501 through a water separator 505; the blower unit 509 is communicated with the reduction flue gas shell-and-tube heat exchanger 503 through a steam-water separator 514; the natural gas compressor 510 is respectively communicated with the first reactor 501 and the second reactor 502; in the figure, 512 shows the hot water inlet direction, and 511 shows the cold water outlet direction. The 100kw reactor is shown in fig. 7, and comprises an upper end socket assembly welding 701, a 100kw reactor main body 702, a lower end socket assembly welding 703, a soaking pipe 704, a carrier filler 705 and a corundum ball layer 706, and the specific positions are shown in fig. 7. The reactor main body is shown in FIG. 8 and comprises a reactor cylinder 802, a flange 801 is arranged at the end part of the cylinder, and a reactor heat exchange pipe 803 and a temperature measurement guide pipe 804 are arranged in the reactor main body; the internal reactor cooling water distribution tubes 805 and reactor cooling water distribution plates 806 and heat exchanger end plates are shown in fig. 8. FIG. 9 is a schematic diagram of the structure layout of a 100KW chemical chain set, wherein 901 and 902 are the first reactor and the second reactor, respectively; 903 is a reducing flue gas shell-and-tube heat exchanger, 904 is an oxidizing flue gas shell-and-tube heat exchanger, 905 is a blower (roots blower), 906 is a first reactor cooling water tank, 907 is a second reactor cooling water tank, and the reducing flue gas steam-water separator is shown as a graph 908.

2) Reactor cooling system

The heat-exchange water tank consists of a circulating water pump, a plate heat exchanger, a water storage tank and a heat-radiating system. The circulating water pump conveys water in the water storage tank to a shell layer of the reactor, the outer wall of the reaction tube is cooled through the liquid distribution plate, steam generated by vaporization enters the plate heat exchanger, water which is not vaporized returns to the water storage tank, the other side of the plate heat exchanger is cooled through circulating water of an external heat dissipation system, and steam condensate water flows back to the water storage tank;

3) A combustion preheating system:

preheating a gas burner, cooling the burner combustion chamber by using air to generate high-temperature gas, and entering the reactor from the lower end of the reactor to preheat an oxygen carrier in the reactor;

4) A flue gas heat exchanger:

5) The reduction flue gas heat exchanger and the oxidation flue gas heat exchanger are arranged; high-temperature reduction flue gas enters a tube pass from the upper end of a reduction flue gas heat exchanger, external circulating water enters a shell layer of the reduction flue gas heat exchanger to perform countercurrent heat exchange with the reduction flue gas, and low-temperature reduction flue gas is mixed with air and then enters a reactor from the lower end of the reactor; high-temperature oxidation flue gas enters a tube pass from the upper end of the oxidation flue gas heat exchanger, external circulating water enters a shell layer of the oxidation flue gas heat exchanger to perform countercurrent heat exchange with the oxidation flue gas, and low-temperature oxidation flue gas is discharged;

6) A gas compressor:

after a gas compressor is added with a frequency converter, controlling the flow and the pressure of gas entering a reactor;

7) An air blower:

combustion air of a natural gas burner, cooling air and air in an oxidation process during preheating;

8) A control system;

the system is composed of a PLC module, kingView software, a gateway control module, automatic operation and data acquisition and storage.

When the steam pressure of the shell layer of the reactor is too high during operation, the inlet and outlet temperature of cooling water of the plate heat exchanger is not obviously increased, the pressure of the shell layer of the reactor is equalized with that of the water storage tank according to condition analysis, condensed water is stored at the heat exchange side of the plate, and only a small amount of steam enters, so that the plate exchange efficiency is not high, and the steam pressure rises; in addition, the flange bolt of the reactor runs at high temperature for a long time, and the stretched flange of the bolt has the phenomenon of air leakage; and in addition, the temperature measurement result before the steam enters the plate and is changed shows that the superheat degree of the steam is high, and the superheated steam is cooled.

500kW prototype system composition: as shown in fig. 6, the reactor comprises two reactors 601 and 602, and a tank 603 respectively communicating with the reactors 601 and 602, and the specific connection relationship is shown in fig. 6. The 500kw chemical chain system diagram is shown in fig. 10, where 1008 is shown as reactor number one and 1002 is reactor number two. The reference numeral 1001 denotes a reducing flue gas shell-and-tube heat exchanger, 1007 denotes an oxidizing flue gas shell-and-tube heat exchanger, 1006 denotes a blower (roots blower), 1003 denotes a water separator, 1004 denotes a water collector, and a reducing flue gas steam-water separator is shown in a drawing 1005. Fig. 11 shows a 500kw chemical train diagram, where 1101 shows an oxidation flue gas heat exchanger, 1002 shows a reduction flue gas heat exchanger, 1103 shows a reduction flue gas water separator, 1104 and 1105 show two 500kw reactors, 1106 shows a roots blower, and 1107 shows a reactor cooling water tank. FIG. 12 shows that 1202 is reactor assembling and welding, an upper end enclosure 1201 and a lower end enclosure 1203, 1204 are respectively provided with a flow guider, 1205 is provided with a carrier filler. FIG. 13 shows a reactor barrel 1301, a reactor leg 1302, a reactor cooling water return port 1303, a center tube retainer 1304, a center tube and a reaction tank 1305 and 1306, respectively, and a cooling water distributor 1307. In FIG. 14, reference numerals 8 to 10 denote reactor cooling water distribution pipes, reference numeral 11 denotes a reactor water tank, reference numeral 12 denotes a center pipe cooling water distribution pipe, and reference numeral 13 denotes a reactor wall cooling water distribution pipe.

The 500kW prototype machine mainly comprises a reactor, a reactor cooling and combustion preheating system, a flue gas heat exchanger, an air blower and a control system.

1) Reactor with a reactor shell

217 DN65 reaction tubes are arranged in a vertical barrel with the diameter of 1600mm of the reactor, a liquid distribution plate is arranged at 158mm of the upper end of each reaction tube, so that cooling water is uniformly distributed on the outer wall of each reaction tube, and 6 cooling water distribution tubes are arranged between an upper end plate and the liquid distribution plate because the area of the liquid distribution plate of the reactor is too large, so that the uniform distribution of the cooling water is optimized; the heat efficiency is improved, the heat loss is reduced, the temperature of the cylinder body of the reactor is reduced, and a cooling water pipe for the cylinder body is arranged below the liquid distribution plate on the inner side of the cylinder body; in order to prevent the central temperature of the reactor from being overhigh, a reaction tube is not arranged in the center, a steel tube with the diameter of 158mm is arranged, and the central steel tube is independently cooled; and 3 layers of 180mm oxygen carriers are filled at the position 228mm from the bottom of the reaction tube, each layer is supported by a material supporting plate, 50mm is reserved between the two layers of the oxygen carriers, and the thermal expansion and gas redistribution of the oxygen carriers are considered.

Two reactors are switched by reduction and oxidation, one is in the reduction process, and the other is in the oxidation process; in the reduction process, natural gas enters from the upper end of the reactor, is reduced in a pipe and an oxidation state oxygen carrier, and then is discharged from the lower end of the reduction flue gas and enters a reduction flue gas heat exchanger; in the oxidation process, air is fed from the lower end of the reactor, and after the air is oxidized in the pipe and the reduced oxygen carrier, the lower end of the oxidized flue gas is discharged and enters the oxidized flue gas heat exchanger.

2) Reactor cooling system:

the heat-exchange water tank consists of a circulating water pump, a plate heat exchanger, a water storage tank and a heat-radiating system. The circulating water pump conveys water in the water storage tank to a shell layer of the reactor, the outer wall of the reaction tube is cooled by the liquid distribution plate, steam generated by vaporization enters the plate heat exchanger, the steam is considered to be steam with high superheat degree, the superheat degree of the steam is reduced for protecting the heat exchanger and heat exchange efficiency, the steam enters the heat exchanger after being cooled by cooling water spraying, the water which is not vaporized returns to the water storage tank, the other side of the plate heat exchanger is cooled by circulating water of an external cooling system, and steam condensate water flows back to the water storage tank through the steam trap; the two reactors share one water storage tank and plate heat exchanger and reduce the spray of superheated steam;

3) A combustion preheating system:

the gas burner is provided with a gas burner 2 sleeve, high-temperature gas is generated by cooling a burner combustion chamber with air, enters the reactor from the lower end of the reactor, and preheats an oxygen carrier in the reactor;

4) A flue gas heat exchanger:

a reduction flue gas heat exchanger and an oxidation flue gas heat exchanger are arranged; high-temperature reduction flue gas enters a tube pass from the upper end of a reduction flue gas heat exchanger, external circulating water enters a shell layer of the reduction flue gas heat exchanger to perform countercurrent heat exchange with the reduction flue gas, and low-temperature reduction flue gas is mixed with air and then enters an oxidation process reactor from the lower end of the reactor;

high-temperature oxidation flue gas enters a tube pass from the upper end of the oxidation flue gas heat exchanger, external circulating water enters a shell layer of the oxidation flue gas heat exchanger to perform countercurrent heat exchange with the oxidation flue gas, and low-temperature oxidation flue gas is discharged;

5) An air blower:

providing combustion-supporting air during preheating, and oxidizing in the oxidation process;

6) A control system;

the system is characterized by comprising a PLC module and KingView software; on-off control, automatic operation and data acquisition and storage;

the 500kW prototype revealed several engineering problems in debugging and simulated heating operations:

(1) 217 DN65 reaction tubes of 1000mmL are distributed in the cylinder of the reactor with the diameter of 1600mm of the sample machine, and oxygen carriers are filled in the reaction tubes in a layered manner. During debugging operation, the temperature rise amplitude of the reaction tube close to the center is obviously larger than that of the reaction tube at the outer side when gas is introduced, which shows that the gas flow distribution among the reaction tubes is uneven, so that the temperature distribution among the reaction tubes is uneven and the CH4 escape starting time is advanced. This should be due to the fact that the flow resistance of the gas in the reaction tubes is too low (about 0.3kPa at full load) for a flow rate of only one tenth of the air flow rate, so that the gas flow tends to concentrate in the relatively short reaction tubes near the center of the cylinder. In fact, as a countermeasure for alleviating the flow rate distribution unevenness between the reaction tubes, the present prototype has taken a measure to provide a closed cylinder having a diameter of 150mm at the center of the reactor cylinder. As a further measure to be taken in the future, there are a method of increasing the length of the reaction tubes to reduce the diameter of the reactor cylinder and the number of the reaction tubes, and a method of providing orifice plates having different diameters at the inlet ends of the respective reaction tubes to increase the flow resistance of the fuel gas in the reaction tubes appropriately to reduce the flow distribution between the reaction tubes. However, the cost of this measure is that the air flow resistance will also increase, resulting in an increase in the power consumption of the fan.

(2) The prototype adopts a reaction heat exchange mode as follows: the cooling water passing through the shell pass forms a falling film on the outer wall of each reaction tube through the cooling water distributor and absorbs reaction heat to generate steam, the steam is guided into a plate heat exchanger arranged outside the reactor to exchange heat with a heating medium, and formed condensed water is pumped to the cooling water distributor through the shielding pump. However, during debugging operation, the phenomenon that when the shield pumping water quantity is too much and the drain valve cannot drain water in time, so that the shell side accumulated water reaches a certain degree, a large amount of steam is generated, the shell side pressure is increased rapidly, and the shell is deformed. As a future improvement measure, an electric water discharge valve is additionally arranged and used for monitoring the water level in the shell, and when the water level reaches a preset value, the electric valve is opened for discharging water. Meanwhile, from the safety perspective, an automatic pressure relief valve for connecting the shell and the smoke exhaust pipeline is arranged, when the pressure in the shell reaches a certain value, the valve is opened, the steam in the shell is discharged to the outside through the smoke exhaust pipeline, and when the pressure is reduced to a safety value, the pressure relief valve is automatically closed.

(3) Because the temperature rise amplitude of the reactor shell is obviously smaller than that of the reaction tube during operation, the thermal expansion of the reaction tube is restrained by the reaction shell and the end plate to generate larger thermal stress in the axial direction, so that the reaction tube is deformed and even cracked. Therefore, it is considered to provide an expansion joint in the reactor shell.

1) Reactor preheating

The purpose of preheating the reactor is to heat the oxygen carrier in the reactor to above 650 c so that it can undergo the normal reduction reaction with CH 4. The reactor of this experiment was filled with reforming catalyst, corundum balls and oxygen carrier particles. The preheating of the reactor is carried out according to the following scheme:

a) Heating the filler in the reactor to above 500 ℃ by using high-temperature flue gas generated by a combustion burner;

b) Decomposing CH4 into H2 and CO by using a reforming catalyst, reacting the decomposed gas with an oxygen carrier, and heating to above 650 ℃;

c) Introducing natural gas from the top of the reactor directly to carry out normal oxidation-reduction reaction, and continuously heating to over 900 ℃;

d) The temperature in the reaction is controlled between 650 ℃ and 900 ℃ by utilizing a reactor condensed water system.

2) Oxidation reduction reaction

After the temperature in the reactor can be controlled between 650 ℃ and 900 ℃, normal oxidation-reduction reaction can be carried out, thereby generating heat. At the moment, the top of the natural gas enters a reduction reactor to carry out reduction reaction with an oxygen carrier, and the reaction formula is shown as formula 3-4-1:

4CuO+CH ₄ ＝CO ₂ +2H ₂ O+4Cu (3-4-1)

the generated CO2 and water vapor enter the oxidation reactor together with air from the bottom after being condensed, and the O2 in the air and the oxygen carrier are subjected to oxidation reaction to release heat, wherein the reaction formula is shown as a formula 3-4-2:

2Cu+O ₂ ＝2CuO (3-4-2)

the generated tail gas is discharged into the atmosphere through a chimney, and the main content of the tail gas is CO2 and N2. If CO2 capture is performed, only N2 is present in the exhaust. In addition, a CH4 and O2 real-time detector is arranged at the flue, and whether the reactor needs to be switched is judged according to the detection result: normally, the flue gas does not contain CH4 and O2, and if CH4 is detected, the oxygen carriers in the reduction reactor are all reduced to a reduced state, so that CH4 escapes, and the reactor needs to be switched at this time. Similarly, if O2 is detected, it is indicated that the oxygen carriers in the oxidation reactor are all oxidized to the oxidation state, and the reactor needs to be switched at this time.

A100 kW-level chemical looping combustion prototype is provided with 2 fixed bed reactors for oxidation-reduction reactions respectively, and a series of valves are utilized for switching the oxidation-reduction reactions. In the aspect of oxygen carrier, cu-based oxygen carrier is selected, because the Cu-based oxygen carrier has higher activity and larger oxygen carrying capacity and is not easy to react with the carrier. On the other hand, the oxidation reaction of the metal Cu of the Cu oxygen carrier and the reduction reaction of the CuO are exothermic reactions, so that the continuous heat supply in the oxidation and reduction processes can be realized.

In the cold starting stage, the oxygen carrier in the reactor needs to be heated by high-temperature flue gas generated by combustion of the preheating burner, and normal oxidation-reduction reaction can be carried out when the temperature of the oxygen carrier reaches above 650 ℃. The main components of the flue gas from the reduction reactor are CO2 and H2O, and the CO2 gas with higher purity is obtained after the reduction flue gas heat exchanger condenses water vapor and removes condensed water through a gas-liquid separator. The main component of the flue gas from the oxidation reactor is N2, and the heat in the flue gas is recovered by an oxidation flue gas heat exchanger and then is discharged into the atmosphere. The reaction heat generated by oxidation-reduction reaction in the fixed bed reactor is replaced by a circulating heat exchange system consisting of a plate-and-frame heat exchanger, a condensate water tank and a condensate water pump and is conveyed to a heat supply system.

In addition, a set of experiment platform is also set up to perform heat supply demonstration operation experiment so as to detect the concentration of the flue gas emission and the concentration of reduced flue gas CO2, and simultaneously verify whether the oxygen carrier performance and the design of the reactor and the process flow are reasonable.

The instrumentation used for this experiment is shown in Table 1. TABLE 1 Main instruments and equipment for experiment

(3) Operating conditions

This run was run from 11 days 4/2016 to 17 days 6/2016, and the total run time for the reactor reached 404 hours. Certain achievements are achieved in the aspects of preheating, oxidation-reduction reaction, heat supply operation effect and the like.

The two previous running debugging experiments are carried out according to the steps of burner combustion temperature rise, catalytic reforming temperature rise and oxidation-reduction temperature rise. The combustion temperature rise of the burner only needs to preheat the oxygen carrier to 500 ℃, then the temperature rise is carried out by catalytic reforming, the reforming catalyst decomposes CH4 into CO and H2, and the oxygen carrier is continuously preheated by utilizing the reaction heat generated by the reduction reaction of the CO and the H2 and the oxygen carrier until the temperature of the oxygen carrier reaches above 650 ℃. At the moment, normal oxidation-reduction reaction is carried out, and the temperature of the oxygen carrier is raised to about 900 ℃. The later two running and debugging experiments remove the temperature rise stage of catalytic reforming, and the oxygen carrier is directly preheated to more than 650 ℃ through the combustion temperature rise of the burner. Under the condition of catalytic reforming temperature rise, the preheating time is short, and the oxygen carrier temperature is preheated to 650 ℃ only within 410 minutes and 603 minutes for the 1 st running debugging and the 2 nd running debugging respectively. And under the condition of removing the temperature rise of the catalytic reforming, the preheating time is longer, and the 3 rd running debugging and the 4 th running debugging respectively take 1454 minutes and 1438 minutes to preheat the temperature of the oxygen carrier to 650 ℃. The reason why the preheating time of the several running and debugging experiments is different and gradually increased is mainly analyzed by the following points:

a) When the 1 st operation debugging is carried out, the heat preservation effect of the equipment is the best, and some parts are inevitably transformed or disassembled along with the experiment, so that the whole heat preservation effect is damaged correspondingly, and the preheating time is prolonged;

b) In the stage of catalytic reforming temperature rise at about 500 ℃, the CH4 is easy to generate carbon deposition, once the carbon deposition is formed, oxygen carrier particles are wrapped, the heat transfer effect of the oxygen carrier particles is influenced, and the preheating time of subsequent operation debugging experiments is prolonged;

c) The oxygen carrier is heated and cooled vigorously for many times, which inevitably causes sintering or pulverization of part of the oxygen carrier, increases the resistance of the reactor, and also influences the heat transfer effect of the oxygen carrier.

1) Demonstration operation effect of heating

Since the 100kW chemical chain prototype was commissioned and preheated to a temperature at which normal redox reactions could take place, the heating season of beijing has passed. Therefore, the heating condition can be simulated only by the air-cooled radiator, under the condition of 60% load, the water supply temperature is between 46.6 and 64.3 ℃, the water return temperature is between 43.1 and 60.1 ℃, and the temperature difference is not very large. The reasons for this are mainly:

a) The circulating water system has large circulating amount, according to the initial design, the circulating amount of the system under the condition of full load is 10m3/h, the circulating amount of the system actually running according to 60% load is 12m3/h, and when the circulating amount is large, the temperature difference of supply and return water is possibly small;

b) In 6 th of months, the outdoor temperature reaches above 30 ℃, and under the condition, the heat dissipation effect of the air radiator is poor, so that the temperature difference between the supplied water and the returned water is small.

2) Problems encountered during operation and solutions

During the prototype experiments, the applicant also encountered a number of engineering problems, mainly focusing on the preheating and reactor condensation systems, mainly:

a) During the preheating process, the resistance of the reactor is increased due to the carbon deposition of the oxygen carrier, the sintering of the reforming catalyst and the like. The measures are mainly that air and natural gas are alternately passed through during preheating, and the phenomenon of carbon deposition is avoided as much as possible.

b) The creep of the lower end socket bolt caused by the long-time high-temperature heating of the reactor influences the sealing performance of the reactor. The measure taken against the problem is to replace a high-temperature resistant stainless steel bolt, so that the sealing performance of the bolt is improved.

c) The flow of the reaction gas is unevenly distributed inside the reactor, resulting in uneven temperature distribution inside the reactor. The distribution of the gas flow in the reactor needs to be optimized for the problem, the gas flow distribution in the reactor is difficult to change in a 100kW model machine, and a gas flow distribution device is added at a gas flow inlet of a 500kW model machine, so that the reaction gas flow can be uniformly distributed in each reaction tube.

d) The condensing system has poor heat exchange effect, resulting in the pressure rise of the reactor. The applicant also takes a series of measures against the problem, including replacing the plate-frame heat exchanger with larger heat exchange capacity, and increasing the spraying tank in front of the plate-frame heat exchanger so as to increase the pressure difference between the front and the back of the heat exchanger, and the like, so that the heat exchange effect of the condensing system can basically meet the requirement.

3.4.1.2 prototype run test

The applicant entrusts a product quality supervision and inspection station of gas and gas appliances in Beijing to carry out operation tests on the operation process of a 100kW prototype.

(1) Test protocol

The quality supervision and inspection station for gas and gas appliance products in Beijing City detects a 100kW prototype according to GB/T10820-2011 'test method for thermal efficiency and thermal engineering of domestic boilers' and GB/T10180-2003 'test procedure for thermal engineering performance of industrial boilers', and the detection items and frequency are shown in Table 2:

TABLE 2 100kW model machine operation detection project

(2) Test results

Because some engineering problems are encountered in the debugging and running process of a 100Kw chemical chain prototype, particularly the problem of carbon deposition causes the pressure resistance in a reactor to rise, so that the gas flow is reduced, the prototype cannot run at full load according to the original plan, and can only run to 60% of load at most, in this case, the quality supervision and inspection station of gas and gas appliance products in Beijing market only detects the smoke emission and the thermal efficiency of 25%, 50% and 60% of load, each load detects 6 groups of data, and the result is shown in Table 3:

TABLE 3 detection station detection data

As can be seen from the table 3, no matter under any output state, the flue gas of the chemical-looping combustion prototype does not contain NOx and SO2, and the advantages of the chemical-looping combustion prototype are obvious compared with those of the conventional gas-fired boiler. In addition, the lower heating value heat efficiency and the higher heating value heat efficiency are increased to a certain extent along with the increase of the load.

Conclusion of the experiment

This experiment basically achieves the established experimental goals, but many engineering problems are encountered during the experiment, which is also an unavoidable problem of the technology from the laboratory to the engineering. The experience lessons in the experimental process are summarized to facilitate the development and experiments of subsequent 500kW chemical chain prototypes. The experiment has the following main conclusions:

(1) From the actual measurement result, after the normal oxidation-reduction reaction is carried out, the chemical looping combustion technology can realize zero nitrogen and zero sulfur emission, and compared with a conventional boiler, the reduction rate of NOx and SO2 can reach 100%;

(2) For CCS, CO2 capture refers to the recovery of high concentrations of CO2 from combustion flue gases. In the process flow, from the time of reactor switching to the time of next reactor switching, because CH4 fully reacts with excessive oxidation state oxygen carrier all the time, CH4 detected by a CH4 sensor on a reduction product gas pipeline is always kept at 0%, namely, high-concentration CO2 gas containing little water vapor is discharged out of the system and is trapped. The next reactor switch was made when the CH4 concentration detected by the CH4 sensor rose to 0.5% and continued in cycles. According to the actual measurement result, the concentration of the dry gas of the CO2 recovered by the process flow reaches more than 99.5 percent, and the CO2 emission reduction rate reaches more than 95 percent;

(3) From the view of preheating effect, the preheating time is too long and unstable, and a series of problems of oxygen carrier carbon deposition, reforming catalyst sintering and the like are encountered in the preheating process. Needs to be optimized and solved in the subsequent development process of a 500kW prototype;

(4) From the design of the reactor, although the whole experimental process is completed, two problems exist, namely, the high-temperature creeping phenomenon of the upper and lower end socket bolts of the reactor causes the reduction of the sealing effect; secondly, the gas flow of the reaction gas is unevenly distributed in the reactor, so that the temperature distribution in the reactor is uneven, the degree of the oxygen carrier participating in the reaction is also uneven, and the problems need to be optimized and solved in the subsequent development process of a 500kW prototype;

(5) From the process flow of a prototype, the continuous operation of the prototype can be realized by alternately carrying out the oxidation-reduction reaction by two reactors, but the problem of pressure rise caused by poor heat exchange effect of a condensing system also exists, the problem is solved by measures such as a better plate frame heat exchanger, a spraying tank and the like in the later period of an experiment, but the problem is not stable and needs to be optimized and solved in the subsequent development process of a 500kW prototype.

3.4.2 500kW prototype simulation operation

On the basis of solving a series of engineering problems in the trial operation process of a 100kW double-row double-pipe sample machine, the applicant designs and optimizes a 500kW chemical looping combustion system, and takes measures including changing a reactor sealing mode, adding a combustion burner, optimizing a condensed water system and the like, so that the safety and the reliability of the 500kW chemical looping combustion system are improved to a certain degree.

The purpose of this experiment is to carry out installation debugging and simulated operation to the novel natural gas chemical chain model machine of 500kW, makes equipment reach basic stable operation, verifies the performance of 500kW model machine, detects technical indexes such as its thermal efficiency and exhaust emission. The 500kW prototype system achieves the research and development target and meets the following index requirements:

(1) The heat supply efficiency of the high calorific value is not lower than 93 percent, and the heat supply efficiency of the low calorific value is not lower than 100 percent;

(2) The heat supply load can be adjusted (30-100%), and the water supply temperature is not lower than 90 ℃ in a full load state;

(3) Flue gas emission index: the NOx and SOx emission concentration of the prototype is not higher than 10ppm and 5ppm respectively, and zero emission of CH4 is realized.

Simulation operation scheme and implementation situation

(1) Experimental protocol

The 500kW chemical chain model machine used in this experiment also consisted of two reactors, with redox reactions alternately taking place between the two reactors by switching of the valve group. Thereby realizing continuous operation. The heat generated by the reaction is transferred to a water cooling tower on the top of the building through a circulating water system for heat dissipation.

The experiment mainly comprises the following contents:

preheating an oxygen carrier, wherein the temperature of the oxygen carrier is preheated to be more than 650 ℃;

debugging a condensation system of the reactor to ensure that the condensation system can exchange reaction heat to a circulating water system in time;

carrying out oxidation-reduction reaction experiments according to different loads, and verifying the reliability and safety of the oxidation-reduction reaction experiments;

detecting flue gas generated in the experimental process, and analyzing the content of NOx and SO2 in the flue gas;

the 500kW prototype test experiment was performed in steps, with the detection of smoke emissions being performed in a continuous operating phase.

1) Step of Cold Start

The method comprises the steps of preheating an oxygen carrier in a reactor through high-temperature flue gas generated by a burner, monitoring the temperature change condition of the oxygen carrier in the reactor through a temperature sensor in the process, closing the burner when the temperature of the oxygen carrier at the bottom of the reactor reaches above 650 ℃, alternately introducing natural gas and air at the bottom of the reactor to perform oxidation reduction heating, heating the oxygen carrier through reaction heat generated by the burner until the temperature of the oxygen carrier at the top of the reactor also reaches above 650 ℃. At the end of the cold start, the oxygen carriers in both reactors should be kept in the reduced state, and a blind plate should be inserted at the burner outlet.

2) Step of Hot Start

And introducing air to the bottom of the reactor for oxidation reaction, heating the oxygen carrier by reaction heat, and introducing natural gas from the top of the reactor for reduction reaction when the temperature of the oxygen carrier reaches above 650 ℃. And (4) timely starting a condensate pump to control the temperature in the reactor to be between 650 and 900 ℃. One reactor is always kept to carry out reduction reaction and the other reactor is kept to carry out oxidation reaction under the control of the valve group, so that the continuous operation is realized.

3) Continuous operation

After the cold start and the hot start are both debugged, the device is continuously operated for 72 hours at the load of 30 percent, 50 percent and 100 percent respectively so as to meet the requirement of the heat supply load in the assessment index on adjustability, and the detection of the smoke emission of a prototype is completed in the process.

(2) System building

The applicant further optimizes and amplifies the design of a 500 kW-grade fixed bed chemical looping combustion prototype on the basis of a 100 kW-grade chemical looping prototype, establishes a set of experiment platform, and performs a heat supply demonstration operation experiment so as to detect the concentration of the smoke emission and the concentration of reduced smoke CO2, and simultaneously verifies whether the oxygen carrier performance and the design of a reactor and a process flow are reasonable. The 500 kW-level chemical looping combustion prototype is provided with 2 fixed bed reactors, and the fixed bed reactors are respectively subjected to oxidation-reduction reaction and are periodically switched by utilizing a valve control system. In the aspect of oxygen carrier, the Cu-based oxygen carrier is still selected, and two preheating burners are arranged for preheating the oxygen carrier.

In the cold start stage, the oxygen carrier in the reactor needs to be heated by high-temperature flue gas generated by combustion of the preheating burner, and normal oxidation-reduction reaction can be carried out when the temperature of the oxygen carrier reaches above 650 ℃. The main components of the flue gas from the reduction reactor are CO2 and H2O, and the CO2 gas with higher purity is obtained after the reduction flue gas heat exchanger condenses water vapor and removes condensed water through a gas-liquid separator. The main component of the flue gas from the oxidation reactor is N2, and the heat in the flue gas is recovered by an oxidation flue gas heat exchanger and then is discharged into the atmosphere. The two reactors are alternately used for carrying out oxidation-reduction reaction through a series of valve groups, and the generated reaction heat is replaced by a circulating condensation system and is conveyed into a water cooling tower for heat dissipation.

The equipment used in the experiment is based on a 500 kW-level fixed bed chemical-looping combustion prototype and comprises a set of circulating water system for heat dissipation. See table 4.

TABLE 4 Main instruments and equipment for experiment

(3) Operating conditions

This run was run from 5/25/2017 to 6/1/2017 for a total reactor run time of 52 hours. Certain achievements are obtained in the aspects of preheating, oxidation-reduction reaction, heat supply operation effect and the like, but certain problems also exist.

1) Preheating effect

We performed 2 run-and-debug experiments on a 500kW total chemical chain prototype.

The 1 st operation debugging experiment is carried out from 25 days to 26 days in 5 months in 2017, the operation is carried out for 31 hours, wherein the combustion heating of a burner is carried out from 10 points to 21 points in 25 days for about 11 hours, the preheating speed is greatly increased due to the adoption of two high-power combustion burners, the temperature of an oxygen carrier at the lowest layer of the reactor is increased to 650 ℃ after preheating for about 6 hours, and then the temperature of all the oxygen carriers is preheated to more than 650 ℃ after preheating for 5 hours, so that the condition for carrying out the oxidation-reduction reaction is met. In order to allow the redox reaction to proceed on day 2, the temperature was maintained at 650 ℃ or higher by the redox reaction during 25 days and night.

The 2 nd running debugging experiment is carried out from 31/5/6/1/2017 for 22 hours, wherein the burner preheating temperature rise is carried out from 18 o 'clock in 31/6/1/12 o' clock for about 18 hours, in order to ensure that the oxidation-reduction reaction can be carried out in the daytime, the running experiment selects to carry out the temperature rise at night, in order to control the temperature rise speed, the used gas quantity is less, the temperature rise is relatively stable, and after about 8 hours of preheating, the oxygen carrier at the bottom layer of the reactor is preheated to more than 650 ℃. After that, all the oxygen carriers are preheated to above 650 ℃ for another 10 hours.

From the effect of the two-time combustion burner heating, the heating speed is obviously improved when compared with 100kW after the two burners are used for heating. And the sealing performance of the upper and lower end enclosures of the reactor is obviously improved after the upper and lower end enclosures are changed into welding and sealing, and the engineering problems of the sealing performance reduction of the sealing gasket caused by long-time high-temperature heating, the high-temperature creeping of the sealing bolt and the like are solved.

2) Effect of oxidation-reduction reaction

When the oxygen carriers in the two reactors of the 500kW chemical chain model machine reach more than 650 ℃, the normal redox reaction can be carried out. In the experimental process, the degree of the oxidation-reduction reaction in the reactor is mainly judged by observing the change condition of the temperature of the oxygen carrier in the reactor and detecting the content of CH4 in the reduction flue gas and the content of O2 in the oxidation flue gas. Under the condition of closing the burner, the temperature of the oxygen carrier is still maintained above 700 ℃ and is steadily increased just by alternately introducing natural gas and air into the reactor, which indicates that the oxygen carrier and the natural gas or the air can perform normal oxidation-reduction reaction, so that reaction heat is generated to heat the oxygen carrier and the natural gas or the air. On the other hand, a CH4 online detector is arranged at a reducing flue gas outlet, CH4 can be detected in the CH4 online detector when natural gas is introduced into the reactor at first, which indicates that the temperature of part of oxygen carriers in the reactor cannot reach the reduction reaction degree, more and more oxygen carriers reach the reduction reaction temperature along with the increase of the temperature, so that the oxygen carriers can react with more natural gas, the CH4 online detector cannot detect CH4 at this time, most of the oxygen carriers escape from the reaction after the reduction reaction is completed along with the reaction, the CH4 can be detected in the CH4 online detector, and the process is probably within 20-30 min.

(1) Test protocol

The quality supervision and inspection station for gas and gas appliance products in Beijing City detects a 500kW prototype according to GB/T10820-2011 'test method for thermal efficiency and thermal engineering of domestic boilers' and GB/T10180-2003 'test procedure for thermal engineering performance of industrial boilers', and the detection items and frequency are shown in Table 5:

TABLE 5 500kW model machine operation detection project

(2) Test results

As the debugging running time of the 500KW chemical chain prototype is shorter, the product quality supervision and inspection station of gas and gas appliances in Beijing is only used for detecting the smoke emission and the heat efficiency under the condition of 100 percent of load, as shown in Table 6

Shown in the specification:

table 6 inspection station inspection data

As can be seen from Table 6, the flue gas of the chemical looping combustion prototype contains no NOx and SO2 no matter what the power state is.

Conclusion of the experiment

The 500kW chemical chain model machine is optimized on the basis of summarizing the 2kW, 50kW and 100kW model machines, the technical level is greatly improved, and the stability and the safety of the model machines are greatly improved. The experiment is carried out according to the preset steps and contents, the related experiment and detection tasks are smoothly completed, but some engineering problems still exist in the actual operation process and need to be optimized in subsequent research. The experiment has the following main conclusions:

(1) From the smoke detection result, after the normal oxidation-reduction reaction is carried out, NOx and SO2 can hardly be detected in the reduction smoke and the oxidation smoke of the chemical-looping combustion technology, and the smoke emission level is obviously superior to that of a conventional boiler;

(2) From the viewpoint of the preheating effect, although the preheating time is improved as compared with 100kW, however, the preheating time is long, so that the cold start time is not superior to that of the conventional boiler;

(3) From the design of the reactor, although the problems of high-temperature creeping, uneven distribution of reaction gas flow and the like of the bolts of the upper end socket and the lower end socket of the reactor are solved, the problems of poor processing technology of the reactor, inconvenience in replacing the oxygen carrier and the like also exist;

(4) From the overall process design of a prototype, although the redox reaction can be alternately carried out by two reactors, the prototype has low automation level and is relatively complicated to operate, and unattended automatic operation cannot be realized.

It should be noted that the above embodiments can be freely combined as necessary. The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made to the present invention by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (3)

1. A novel chemical looping combustion method comprising a hydrogen production process, characterized by comprising the steps of:

reforming natural gas and water under the condition of reforming catalyst and then carrying out chemical looping combustion with air.

2. A zero-carbon heating method as claimed in claim 1, wherein the oxygen carrier is obtained by subjecting natural gas and water to reforming catalyst to generate hydrogen and carbon monoxide, and then subjecting the hydrogen and carbon monoxide to reduction reaction with the oxygen carrier and oxidation reaction of air and the reduced oxygen carrier.

3. A zero carbon heating process according to claim 3, wherein reforming of natural gas and water over a reforming catalyst is coupled with a chemical looping combustion process.

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