A Simplified Design Method for a Parallel Fixed-Bed Chemical-Looping Combustion Device

Abstract

The present invention belongs to the technical field related to fixed-bed chemical-looping combustion, and discloses a simplified design method for a parallel fixed-bed chemical-looping combustion device. The method includes: presetting RE period parameters, OX period parameters, and oxygen carrier parameters, and obtaining the reactor volume, cross-sectional area, and height without a gas slip region according to the RE period parameters; obtaining the moving speeds of the thermal front and reaction front during the OX period and RE period based on mass conservation and energy conservation; obtaining the operation duration of the OX period by dividing the reactor height by the moving speed; checking the preset operation duration of the RE period; obtaining the moving speed of the thermal front during the P period; obtaining the upward moving distance during the HR period by subtracting the sum of the upward moving distances during the OX period, RE period, and P period from the reactor height, and obtaining the operation duration of the HR period; and checking the preset temperature based on energy conservation. The present application can realize the design of the size and operation scheme of a parallel fixed-bed chemical-looping combustion device.

Description

Technical Field

[0001] The present invention belongs to the technical field related to chemical looping combustion in a fixed bed, and more specifically, relates to a simplified design method for a parallel fixed bed chemical looping combustion device. Background Art

[0002] In the past few decades, chemical looping combustion (CLC) has gradually become a promising low-carbon energy utilization technology. The CLC technology splits the traditional one-step combustion process of fuel into two independent processes of oxidation and reduction occurring in different regions, and has the advantages of cascaded energy utilization and in-situ CO2 separation. So far, the research focus in the CLC field has mainly been concentrated on the development of high-performance oxygen carriers (OCs), the design and operation of reactors, etc. Among them, the rational design of CLC reactors is the main bottleneck restricting the development of this technology. Currently, the CLC technology mainly uses dual circulating fluidized bed reactors (DCFBRs) and packed bed reactors (PBRs). These two technologies each have their own advantages and both have the potential for commercial applications. Compared with the former, the PBR has a more compact structure and lower operating costs, and thus has received extensive attention. However, due to its significant dynamic characteristics, it cannot be effectively designed only relying on the design and calculation methods of traditional combustion devices.

[0003] A reasonable design scheme is the basis for realizing parallel fixed bed CLC, but no systematic design calculation method has been proposed yet. Most research works simulate and predict the operating state by establishing a one-dimensional dynamic model of the PBR, but the calculation cost of this method is relatively high, which is not conducive to the progress of the design process, and the design parameters are limited and cannot comprehensively design the parallel fixed bed chemical looping combustion device. Therefore, there is an urgent need for a simple and comprehensive design method for parallel fixed bed chemical looping combustion devices. Summary of the Invention

[0004] Aiming at the above defects or improvement requirements of the prior art, the present invention provides a simplified design method for a parallel fixed bed chemical looping combustion device, which can realize the design of the size and operating scheme of the parallel fixed bed chemical looping combustion device.

[0005] To achieve the above object, according to one aspect of the present invention, a simplified design method for a parallel fixed-bed chemical-looping combustion device is provided. The method includes: S1: Presetting RE period parameters, OX period parameters, and oxygen carrier parameters, such as the particle size, density, bulk porosity, mass fraction of active ingredients, oxygen content, etc. of the oxygen carrier. Among them, the RE period parameters include the composition of the gaseous fuel in the RE period, the flow rate of the gaseous fuel in the RE period, the in-bed temperature at the start and end of the RE period, and the operating duration τ of the RE period RE ; The OX period parameters include the composition of the gaseous fuel in the OX period, the flow rate of the gaseous fuel in the OX period, and the in-bed temperature at the start and end of the OX period; S2: Obtaining the reactor volume and cross-sectional area without the gas slip region according to the RE period parameters, and obtaining the reactor height without the gas slip region based on the reactor volume and cross-sectional area; S3: Obtaining the moving speeds of the thermal front and reaction front in the OX period and RE period based on the mass conservation on the reaction front and the energy conservation on the thermal front; S4: Dividing the reactor height without the gas slip region by the moving speed of the reaction front in the OX period to obtain the operating duration of the OX period; S5: Using the oxygen carrier reduction reaction kinetics model to obtain the characteristic duration τ required for the complete conversion of the oxygen carrier m , if τ m >τ RE , then update the operating duration τ of the RE period RE , and re-execute steps S1 to S4 until τ m <τ RE ; S6: Setting the ventilation volume in the P period to a preset multiple of the reactor volume and presetting the operating duration of the P period, and obtaining the moving speed of the thermal front in the P period according to step S3 based on the ventilation volume and the operating duration of the P period; S7: Multiplying the operating durations of the OX period, RE period, and P period by the corresponding moving speeds of the thermal front to obtain the upward moving distances of the OX period, RE period, and P period; S8: Subtracting the sum of the upward moving distances of the OX period, RE period, and P period from the reactor height to obtain the upward moving distance of the HR period, and obtaining the operating duration of the HR period based on the operating durations of the OX period, RE period, and P period; S9: Obtaining the in-bed temperature at the end of the OX period and RE period based on energy conservation, calculating the error between the temperature and the preset temperature in step S1, if it is greater than 0.1%, then setting the calculated temperature as the preset temperature and re-executing the above steps S1 to S8.

[0006] Preferably, step S1 further includes obtaining the lattice oxygen content ρ0 contained in the oxygen carrier in the packed state per unit volume according to the oxygen carrier parameters:

[0007]

[0008] Among them, ε is the bulk porosity of the oxygen carrier, and its value ranges from 0.41 to 0.54; ρ s is the density of the oxygen carrier, and its value depends on the type of oxygen carrier, generally ranging from 2500 to 3600 kg / m 3 ; w act is the mass fraction of the active ingredient in the oxygen carrier, and its value depends on the type of oxygen carrier and its oxidation and reduction intervals, generally ranging from 0.1 to 0.5; R o is the oxygen-carrying capacity of the oxygen carrier; MW o is the molar amount of oxygen element.

[0009] Preferably, the calculation formula for the reactor volume V0 without the gas slip region in step S2 is:

[0010]

[0011] Among them, F RE is the flow rate of the gaseous fuel during the RE period; y g，N is the molar fraction of component N; ρ0 is the lattice oxygen content contained in the oxygen carrier in the packed state per unit volume;

[0012] The cross-sectional area A without the gas slip region is:

[0013]

[0014] Among them, MW RE is the molar amount of the gas introduced into the reactor during the RE period; U g，RE is the superficial gas velocity of the gas introduced into the reactor during the RE period; ρ g，RE is the density of the gas introduced into the reactor during the RE period, which is determined by the preset inlet average pressure during the RE period. Let the average pressure be the average of the pressure at the start time and the pressure at the end time of the RE period;

[0015] The calculation formula for the reactor height H0 without the gas slip region is:

[0016]

[0017] Preferably, the parameters in the RE period in step S1 further include the starting pressure and the ending pressure in the RE period; the parameters in the OX period further include the starting pressure and the ending pressure in the OX period; the method further includes step S10: S10: Use the Ergun equation to check the pressure drop in the RE period and the OX period. If the pressure drop error is greater than 5%, then readjust the preset starting pressure and ending pressure. The specific pressure drop calculation formula is:

[0018]

[0019] Among them, Δp jis the pressure drop during period j, where j is OX or RE; ε is the bulk porosity of the oxygen carrier; η g，j is the gas density during period j, U g，j is the inlet gas velocity of the reactor during period j, d p is the oxygen carrier particle size, ρ g，j is the gas density during period j, H is the height of the reactor. When the superficial gas velocity during the RE period is less than or equal to 0.1 m / s, H is equal to H0. When the superficial gas velocity during the RE period is greater than 0.1 m / s, H = H0+(1 - X)L slip , X is the average conversion degree of the oxygen carrier in the gas slip region during the RE period, L slip is the length of the gas slip region.

[0020] Preferably, the moving speed w of the thermal front during the OX period and the RE period 1，j is:

[0021]

[0022] where, w 1，j is the moving speed of the thermal front during period j, where j is OX or RE; U g，j is the reactor inlet gas velocity during period j, ρ g，j is the gas density during period j, ε is the bulk porosity of the oxygen carrier, and its value ranges from 0.41 to 0.54; ρ s is the oxygen carrier density, C p，eq is the equivalent specific heat capacity of the bed, C p，j is the specific heat capacity of the inlet gas during period j;

[0023] The moving speed w of the reaction front during the OX period and the RE period 2，j is:

[0024]

[0025] where, w g，i，j is the mass fraction of gas i at the inlet during period j, W act is the molar amount of the active ingredient in the oxygen carrier, w act is the mass fraction of the active ingredient in the oxygen carrier (such as Fe2O3, CuO, NiO, etc. during the OX period and FeO, Fe, Cu, Ni, etc. during the RE period), MW i is the molar amount of gas i, ξ i is the gas-solid molar ratio of gas component i reacting with the oxygen carrier.

[0026] Preferably, in step S4, the operation duration τ of the OX period OX is calculated as

[0027]

[0028] Among them, H0 is the reactor height without a gas slip region; w 2，OX is the moving speed of the reaction front edge during the OX period;

[0029] When the height of the gas slip region in the reactor during the OX period is greater than the height of the gas slip region during the RE period:

[0030]

[0031] Among them, X OX is the average conversion degree of the oxygen carrier in the gas slip region during the OX period, L slip，OX is the length of the gas slip region during the OX period.

[0032] Preferably, the steps for obtaining the lengths of the slip regions during the OX period and the RE period are as follows:

[0033] Obtaining the length L of the slip region of any gas i slip，i is:

[0034]

[0035] Among them, U g，fro，j is the average apparent gas velocity on the reaction front edge during the j period; γ i is the gas conversion rate of gas i at the outlet of the gas slip region, and can take 0.7 - 0.9; C in，i is the gas concentration at the reactor inlet; n i is the chemical reaction order; R OC，i satisfies the formula:

[0036]

[0037] Among them, μ i is the reaction coefficient of gas i, η i is the intraparticle diffusion efficiency, and can take 0.2 - 0.5, τ i is the characteristic conversion time of the oxygen carrier shrinking core conversion model;

[0038] The length L of the gas slip region during the j period slip，j is:

[0039]

[0040] Preferably, in step S2, when the apparent gas velocity during the RE period is greater than 0.1 m / s, the slip region during the RE period cannot be ignored, and the reactor height H including the gas slip region is:

[0041] H = H0 + (1 - X RE )L slip，RE

[0042] Among them, is the reactor height without the gas slip region, X RE is the average conversion degree of the oxygen carrier in the gas slip region during the RE period, L slip，RE is the length of the gas slip region during the RE period.

[0043] Preferably, the upward movement distance L during the HR period 1，HR is:

[0044]

[0045] Among them, L 1，j = w 1，j τ j , τ j is the operation duration of the j period, w 1，j is the moving speed of the thermal front during the j period;

[0046] The operation duration τ during the HR period HR is:

[0047] τ HR = (N r - 1)τ RE - τ OX - τ P

[0048] Among them, is the number of parallel fixed beds, τ P is the operation duration of the P period.

[0049] Preferably, based on the law of conservation of energy, the temperature T in the bed at the end of the OX period and the RE period is obtained τ，j The calculation formula is:

[0050]

[0051] Among them, A is the cross-sectional area without the gas slip region, T 0，j is the starting temperature of the j period, ΔH i is the heat of chemical reaction, Q loss，j is the heat dissipation loss during the j period.

[0052] Generally speaking, compared with the prior art through the above technical solutions conceived by the present invention, the simplified design method of the parallel fixed bed chemical looping combustion device provided by the present invention mainly has the following beneficial effects:

[0053] 1. The method describes the dynamic heat and mass transfer process inside the device based on the law of the spread of the reaction front and the heat front during operation. By calculating the moving speeds of the reaction front and the heat front through mass and energy conservation at each time period, the operation and size scheme of the device are further calculated. This method establishes the design criteria for a parallel fixed bed, accurately describes the dynamic operation law of the device, and the design scheme obtained accordingly has a high credibility.

[0054] 2. The present application realizes the reasonable design of each parameter by means of iterative verification of the preset temperature, pressure, and operation duration. The scheme is simple and highly operable. Description of the Drawings

[0055] Figure 1 is a dual-reactor parallel fixed-bed CLC device;

[0056] Figure 2 is the operation diagram of the dual-reactor parallel fixed-bed CLC device;

[0057] Figure 3 In [the figure], a is a schematic diagram of the dynamic evolution process of the reaction front and the heat front in the bed during the OX and RE periods under ideal conditions, and b is a schematic diagram of the dynamic evolution process of the reaction front and the heat front in the bed during the RE period under ideal conditions. Detailed Embodiments

[0058] In order to make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0059] For the fixed-bed CLC technology of multiple parallel-running PBRs, oxygen carrier particles are packed in the bed. During the movement, each reactor cycles and switches in turn among operation periods such as Reduction (RE, introducing gaseous fuel), Heat Removal (HR, introducing N2, CO2, or H2O), Oxidation (OX, introducing O2), and Purge (P, introducing N2, CO2, or H2O), and the operation periods of different reactors alternate with each other. To ensure the continuity of the operation of the entire device, it should be ensured that there is always one reactor continuously introducing fuel during operation. Therefore, the parallel fixed-bed CLC device is at least used for two PBRs, and the arrangement of the operation periods of these two reactors must conform to certain principles to meet the requirements of continuous operation. Figure 1 is a dual-reactor parallel fixed-bed CLC device, Figure 2It is the operation diagram of a dual-reactor parallel fixed-bed CLC device. At this time, the operation time of the RE period is equal to the sum of the operation times of the OX, P, and HR periods. For one reactor, the switching of operation periods is mainly completed by solenoid valves. Solenoid valves need to be installed at both the inlet and outlet of the reactor and are controlled by a program to avoid gas cross-leakage.

[0060] The fixed-bed CLC reactor has relatively significant dynamic characteristics during operation because there are movements of reaction fronts and heat fronts. The reaction front and heat front are respectively thin layers where gas-solid reactions and heat transfer occur in the reactor (the thickness of this thin layer is related to the rates of chemical reactions and gas-solid heat transfer. The greater the heat transfer coefficient, the thinner the reaction front and heat front). As time goes by, they continuously move upward, that is, the bed materials in the reactor are gradually transformed from bottom to top. Usually, the reaction front moves faster. On the reaction front, the gaseous fuel or oxygen reacts with the oxygen carrier, and the reaction heat changes the temperatures of the solids and gases at this position; on the heat front, the oxygen carrier is cooled by the low-temperature gas at the inlet, and the heat stored in the bed is transferred from the solid to the gas until they reach the same temperature. The lattice oxygen content and heat-carrying capacity of the oxygen carrier in the reactor change periodically between the maximum and minimum values during the cycle. For the CLC process where the oxidation reaction is exothermic and the reduction reaction is endothermic, after the OX period ends, the oxygen carrier is completely oxidized, and the temperature in most areas of the bed reaches the maximum value (usually between 900 and 1100 °C) from the initial temperature (for easy control, usually the initial temperature of the oxygen carrier in the bed during the OX period is the same as the inlet gas temperature, between 300 and 500 °C). However, at the same time, a small area near the reactor inlet will be cooled to the inlet gas temperature. After the RE period ends, the oxygen carrier in the bed is completely / partially reduced and the temperature decreases (usually between 800 and 1000 °C). Ideally, the dynamic evolution processes of the reaction front and heat front in the bed during the OX and RE periods are as shown in Figure 3 Figures a and b. At this time, it is considered that the gas-solid mass transfer rate on the reaction front is infinite, and the gas-solid heat transfer rate on the heat front is infinite. Therefore, the reaction front and heat front are shown as infinitely thin layers in the figure. It should be noted that usually, after the RE period ends, there is still a certain distance between the heat front and the reactor outlet, indicating that the oxygen carrier between them still stores a large amount of heat. To prevent the oxygen carrier at this position from overheating during the next OX period, it is necessary to cool down this part of the oxygen carrier before the OX period. The simplest method is to introduce a gas with a temperature of Tin to remove this part of the heat. This period can therefore be called the HR period. After the HR period ends, the temperatures at different positions in the bed become Tin. At this time, the lattice oxygen and heat output in the bed "return to zero", and they will return to the maximum value during the next OX period.

[0061] Based on the above periods, this application proposes a simplified design method for a parallel fixed-bed chemical-looping combustion device, and this method includes the following steps S1 to S9.

[0062] S1: Preset the parameters for the RE period, the OX period, and the oxygen carrier parameters, such as the particle size, density, bulk porosity, mass fraction of the active ingredient, oxygen carrying capacity, etc. of the oxygen carrier particles. The parameters for the RE period include the composition of the gaseous fuel in the RE period, the flow rate of the gaseous fuel in the RE period, the bed temperature at the start and end of the RE period, and the operating duration τ of the RE period RE ; The parameters for the OX period include the composition of the gaseous fuel in the OX period, the flow rate of the gaseous fuel in the OX period, and the bed temperature at the start and end of the OX period.

[0063] The preset temperature parameters affect the physical property parameters of the gaseous fuel, and can be determined by methods such as looking up tables. The composition of the gaseous fuel in the RE period is generally gaseous fuels such as syngas and CH4, and the composition of the gaseous fuel in the OX period is air.

[0064] The oxygen carrier parameters mainly include the bulk porosity of the oxygen carrier, the density of the oxygen carrier, the mass fraction of the active ingredient in the oxygen carrier, the oxygen carrying capacity of the oxygen carrier, etc. The active ingredient of the oxygen carrier can be selected according to needs, such as Fe2O3, CuO, NiO, etc.

[0065] The lattice oxygen content ρ0 contained in the oxygen carrier in the packed state per unit volume can be obtained through the oxygen carrier parameters:

[0066]

[0067] where ε is the bulk porosity of the oxygen carrier, and its value ranges from 0.41 to 0.54; ρ s is the density of the oxygen carrier, and its value depends on the type of oxygen carrier, generally between 2500 and 3600 kg / m 3 ; w act is the mass fraction of the active ingredient in the oxygen carrier, and its value depends on the type of oxygen carrier and its oxidation and reduction intervals, generally between 0.1 and 0.5; R o is the oxygen carrying capacity of the oxygen carrier; MW o is the molar amount of oxygen element.

[0068] Specifically, for the bulk porosity ε of spherical oxygen carriers, it can also be calculated through an empirical correlation formula:

[0069]

[0070] where D is the bed diameter, which can be obtained by inverse calculation of the volume according to the following text, and d p is the particle size of the oxygen carrier.

[0071] In step S1, assume the reactor temperature in each operating period, including the bed temperature T at the start and end of the OX period and the RE period 0，j、T τ，j and the change in in-bed temperature ΔT during this period τ，j , and these temperatures are mainly used to calculate the reaction heat of oxidation and reduction reactions and the kinetic parameters on the reaction front (taking the average value of T 0，j and T τ，j ). To simplify the calculation, it can be considered that T 0，OX = T in , T τ，OX = T 0，OX +ΔT τ，OX , T 0，RE = T τ，OX , T τ，RE = T 0，RE +ΔT τ，RE .

[0072] S2: Obtain the reactor volume and cross-sectional area without the gas slip zone according to the RE period parameters, and obtain the reactor height without the gas slip zone based on the reactor volume and cross-sectional area.

[0073] Calculate the reactor volume without the gas slip zone according to the flow rate, molar composition, and preset operating duration of the gas fuel introduced during the RE period. Here, it should be explained that when the gas-solid reaction rate is limited, the reaction front is a bed layer with a certain height, rather than an infinitely thin layer. As the height increases, the conversion rate of the gas fuel in the reaction front gradually changes from 0 to 1, that is, the gas fuel has not been converted at the bottom of the reaction front, but is completely converted at the top of the reaction front after flowing through a certain bed layer. When the reaction front reaches the top outlet of the reactor, if a sufficiently high conversion rate of the gas fuel is to be ensured, a bed layer with a certain height should be reserved at the top of the reactor, and its height is slightly less than the reaction front, which is called the gas slip zone, and the conversion rate of the oxygen carrier in it is between 0 and 1.

[0074] The calculation formula for the reactor volume V0 without the gas slip zone is:[[]]

[0075]

[0076] where F RE is the flow rate of the gas fuel during the RE period; y g，N is the molar composition of component N; ρ0 is the lattice oxygen content contained in the oxygen carrier in the packed state per unit volume.

[0077] The cross-sectional area A without the gas slip zone is:[[]]

[0078]

[0079] where MW RE is the molar amount of the gas introduced into the reactor during the RE period; U g，REis the superficial gas velocity of the gas introduced into the reactor during the RE period; ρ g，RE is the density of the gas introduced into the reactor during the RE period, which is determined by the preset average inlet pressure during the RE period. The preset average pressure is the average of the pressure at the start time and the pressure at the end time of the RE period. The superficial gas velocity is specified manually.

[0080] The calculation formula for the reactor height H0 without the gas slip region is:

[0081]

[0082] Similarly, for the parameters in the OX, P, and HR periods, the gas flow rate, superficial gas velocity, and gas density in this period can be substituted into formula (4) for calculation.

[0083] S3: Obtain the moving speeds of the thermal front and reaction front in the OX period and the RE period based on the mass conservation on the reaction front and the energy conservation on the thermal front.

[0084] The moving speed w of the thermal front in the OX period and the RE period 1，j is:

[0085]

[0086] where, w 1，j is the moving speed of the thermal front in the j period, j is OX or RE; U g，j is the gas inlet velocity at the reactor inlet in the j period, ρ g，j is the gas density in the j period, ε is the bulk porosity of the oxygen carrier, and its value ranges from 0.41 to 0.54; ρ s is the density of the oxygen carrier, C p，eq is the equivalent specific heat capacity of the bed (mainly the specific heat capacity of the oxygen carrier, and can also include the specific heat capacity of parts such as the reactor wall and the thermocouple inserted into the bed. Whether to include the specific heat capacity of these parts can be determined according to the specific situation), C p，j is the specific heat capacity of the inlet gas in the j period;

[0087] The moving speed w of the reaction front in the OX period and the RE period 2，j is:

[0088]

[0089] where, w g，i，j is the mass fraction of gas i at the inlet in the j period, W act is the molar amount of the active ingredient in the oxygen carrier, w act is the mass fraction of the active ingredient in the oxygen carrier, MW i is the molar amount of gas i, ξ i is the gas-solid molar ratio of the reaction between gas component i and the oxygen carrier.

[0090] Similarly, for the P period and the HR period, the moving speed of the internal heat front can also be calculated by the above formula.

[0091] S4: Divide the reactor height without the gas slip region by the moving speed of the reaction front in the OX period to obtain the operation duration of the OX period.

[0092] The operation duration τ of the OX period OX is calculated by the formula

[0093]

[0094] where H0 is the reactor height without the gas slip region; w 2，OX is the moving speed of the reaction front in the OX period. The above formula (8) is only suitable for the case when the gas velocity in the OX period is low and the height of the gas slip region in the reactor is less than that in the RE period; but when the gas velocity is high and the height of the gas slip region in the reactor in this period is greater than that in the RE period, the phenomenon of oxygen slip will occur at the end of the OX period, that is, an excessive amount of oxygen needs to be introduced to completely oxidize the oxygen carrier in the bed. At this time, the operation duration of the OX period is calculated by the following formula:

[0095]

[0096] where X OX is the average conversion degree of the oxygen carrier in the gas slip region in the OX period, and L slip，OX is the length of the gas slip region in the OX period.

[0097] The steps to obtain the lengths of the slip regions in the OX period and the RE period are as follows:

[0098] Obtain the length L of the slip region of any gas i slip，i as:

[0099]

[0100] where U g，fro，j is the average apparent gas velocity on the reaction front in the j period; γ i is the gas conversion rate of gas i at the outlet of the gas slip region, and can take 0.7 - 0.9; C in，i is the gas concentration at the reactor inlet; n i is the chemical reaction order; R OC，i satisfies the formula:

[0101]

[0102] where μ i is the reaction coefficient of gas i, ηi is the intraparticle diffusion efficiency, which can take values from 0.2 to 0.5 for oxygen carriers with a particle size of 2 - 6 mm, and τ i is the characteristic conversion time of the shrinking core transformation model of the oxygen carrier. η i can also be calculated according to the following formula:

[0103]

[0104] Th i is the Thiele modulus, and its calculation formula is related to the reaction kinetic model of the oxygen carrier. For the shrinking core model, it can be calculated according to the following formula:

[0105]

[0106] where d p is the particle size of the oxygen carrier, b i is the stoichiometric ratio of the chemical reaction, k i is the pre - exponential factor, E i is the activation energy, R is the ideal gas constant, and T re，j is the average temperature at the reaction front, n i is the order of the chemical reaction, X is the conversion degree of the oxygen carrier at the reaction front, r g is the grain size of the oxygen carrier, D eff，i，j is the effective diffusion coefficient of gas i in the oxygen carrier particle during the j - th period.

[0107] Finally, the length L of the gas slip region during the j - th period slip，j is:

[0108]

[0109] Then in step S2, when the apparent gas velocity during the RE period is greater than 0.1 m / s, the slip region during the RE period cannot be ignored, and the height H of the reactor including the gas slip region is:

[0110] H = H0+(1 - X RE )L slip，RE (15)

[0111] where is the height of the reactor without the gas slip region, X RE is the average conversion degree of the oxygen carrier in the gas slip region during the RE period, and L slip，RE is the length of the gas slip region during the RE period.

[0112] S5: Obtain the characteristic duration τ m consumed for the complete conversion of the oxygen carrier using the oxygen carrier reduction reaction kinetic model. If τ m > τ RE then update the operating duration τ RE, and re - execute steps S1 - S4 until τ m <τ RE 。

[0113] This step is mainly used to check the preset operation duration of the RE period. Since the intake air cools the oxygen carriers in a section of the bed layer at the reactor inlet, the temperature of this part of the oxygen carriers is low and the reaction rate with the gaseous fuel is slow. To ensure the continuous and stable operation of the device, it is necessary to completely or mostly convert this part of the oxygen carriers within the operation duration, that is, the duration τ m required to completely convert the oxygen carriers is less than the operation duration τ RE of the RE period, otherwise the bed temperature will gradually decrease in successive oxidation - reduction cycles. The calculation method of τ m is related to the kinetic model of the oxygen carrier reduction reaction. For oxygen carriers with hematite, ilmenite, copper oxide, and nickel oxide as the active components, the shrinking core model is most commonly used to describe their conversion process.

[0114] In a mixed atmosphere of CH4, CO, and H2, there is:

[0115]

[0116] τ i is the characteristic reaction duration of the oxygen carrier only under gas i:

[0117]

[0118] where ρ m 、r g 、b i 、k i 、E i 、R、C i 、n i are the molar density, grain radius, reaction coefficient, pre - exponential factor, activation energy, ideal gas constant, gas concentration, and reaction order of the oxygen carrier, respectively.

[0119] S6: Set the ventilation volume in the P period to a preset multiple of the reactor volume and preset the operation duration of the P period, and obtain the moving speed of the thermal front in the P period according to step S3 based on the ventilation volume and the operation duration of the P period.

[0120] Based on operation experience, the ventilation volume in the P period is about 5 times the reactor volume, and the operation time can be 10 - 60 s. Then, the moving speed of the thermal front in this period can be calculated according to the purging gas volume and purging duration (formula 6).

[0121] S7: Multiply the operation durations of the OX period, RE period, and P period by the corresponding moving speeds of the thermal front to obtain the upward moving distances of the OX period, RE period, and P period.

[0122] L 1，j = w 1，j r j (18)

[0123] L 1，j is the upward movement distance in the j-th period.

[0124] S8: Subtract the sum of the upward movement distances in the OX period, RE period, and P period from the reactor height to obtain the upward movement distance in the HR period, and obtain the operation duration of the HR period based on the operation durations of the OX period, RE period, and P period.

[0125] The upward movement distance L in the HR period 1，HR is:

[0126]

[0127] where L 1，j is the upward movement distance in the j-th period, L 1，j = w 1，j τ j , τ j is the operation duration of the j-th period, w 1，j is the moving speed of the thermal front in the j-th period.

[0128] The operation duration τ of the HR period HR is:

[0129] τ HR = (N r - 1)τ RE - τ OX - τ P (20)

[0130] where is the number of parallel fixed beds, τ P is the operation duration of the P period.

[0131] S9: Obtain the in-bed temperatures at the end of the OX period and the RE period based on energy conservation, calculate the error between the temperature and the preset temperature in step S1. If the error is greater than 0.1%, set the calculated temperature to the preset temperature and re-execute the above steps S1 - S8.

[0132] The in-bed temperature T at the end of the OX period and the RE period obtained based on energy conservation τ，j The calculation formula is:

[0133]

[0134] where A is the cross-sectional area excluding the gas slip region, T 0，j is the starting temperature of the j-th period, ΔH i is the heat of chemical reaction, Qloss，j is the heat dissipation loss during period j.

[0135] The parameters during the RE period in step S1 further include the starting pressure and the ending pressure of the RE period; the parameters during the OX period further include the starting pressure and the ending pressure of the OX period; the method further includes step S10:

[0136] S10: Use the Ergun equation to check the pressure drop during the RE period and the OX period. If the pressure drop error is greater than 5%, re-adjust the preset starting pressure and ending pressure. The specific pressure drop calculation formula is:

[0137]

[0138] where, Δp j is the pressure drop during period j, j is OX or RE; ε is the packing porosity of the oxygen carrier; η g，j is the gas viscosity during period j, U g，j is the reactor inlet gas velocity during period j, d p is the particle size of the oxygen carrier particles, ρ g，j is the gas density during period j, H is the height of the reactor. When the superficial gas velocity during the RE period is less than or equal to 0.1 m / s, H is equal to H0. When the superficial gas velocity during the RE period is greater than 0.1 m / s, H = H0 + (1 - X)L slip , X is the average conversion degree of the oxygen carrier in the gas slip zone during the RE period, L slip is the length of the gas slip zone.

[0139] The design scheme of a parallel fixed-bed chemical-looping combustion device designed based on the above method is shown in Table 1 below.

[0140]

[0141]

[0142] Table 1

[0143] It is easy for those skilled in the art to understand that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A simplified design method for a parallel fixed-bed chemical-looping combustion device, characterized in that The method includes: S1: Preset the RE period parameters, OX period parameters, and oxygen carrier parameters. Among them, the RE period parameters include the composition of the gaseous fuel in the RE period, the flow rate of the gaseous fuel in the RE period, the in-bed temperature at the start and end of the RE period, and the operating duration τ of the RE period RE ; the OX period parameters include the composition of the gaseous fuel in the OX period, the flow rate of the gaseous fuel in the OX period, and the in-bed temperature at the start and end of the OX period; the oxygen carrier parameters include one or more of the oxygen carrier particle size, density, bulk porosity, mass fraction of active components, and oxygen carrying capacity; S2: Obtain the reactor volume and cross-sectional area without the gas slip region according to the RE period parameters, and obtain the reactor height without the gas slip region based on the reactor volume and cross-sectional area; S3: Obtain the moving speeds of the thermal front and reaction front in the OX period and RE period based on the mass conservation on the reaction front and the energy conservation on the thermal front; S4: Divide the reactor height without the gas slip region by the moving speed of the reaction front in the OX period to obtain the operation duration of the OX period; S5: Obtain the characteristic duration τ consumed for the complete conversion of the oxygen carrier by using the oxygen carrier reduction reaction kinetic model m , if τ m > τ RE , then update the operation duration τ of the RE period RE , and re - execute steps S1 - S4 until τ m < τ RE ; S6: Set the aeration volume in the P period to a preset multiple of the reactor volume and preset the operation duration of the P period, and obtain the moving speed of the thermal front in the P period according to step S3 based on the aeration volume and the operation duration of the P period; S7: Multiply the operation durations of the OX period, RE period, and P period by the corresponding moving speeds of the thermal front to obtain the upward moving distances of the OX period, RE period, and P period; S8: Subtract the sum of the upward moving distances of the OX period, RE period, and P period from the reactor height to obtain the upward moving distance of the HR period, and obtain the operation duration of the HR period based on the operation durations of the OX period, RE period, and P period; S9: Obtain the temperature in the temperature bed at the end of the OX period and RE period based on energy conservation, calculate the error between the temperature and the preset temperature in step S1, and if it is greater than 0.1%, set the calculated temperature to the preset temperature and re-execute the above steps S1 - S8.

2. The method according to claim 1, characterized in that Step S1 further includes obtaining the lattice oxygen content ρ0 contained in the oxygen carrier in the packed state per unit volume according to the oxygen carrier parameters: Among them, ε is the stacking porosity of the oxygen carrier, and its value ranges from 0.41 to 0.54; ρ s is the density of the oxygen carrier, and its value ranges from 2500 to 3600 kg / m 3 ; w act is the mass fraction of the active ingredient in the oxygen carrier, and its value ranges from 0.1 to 0.5; R o is the oxygen carrying capacity of the oxygen carrier; MW o is the molar amount of oxygen element.

3. The method according to claim 1 or 2, characterized in that, The calculation formula for the reactor volume V0 without the gas slip region in step S2 is: Among them, F RE is the flow rate of the gaseous fuel during the RE period; y g，N is the molar fraction of component N; ρ0 is the content of lattice oxygen contained in the oxygen carrier in the packed state per unit volume. The cross-sectional area A without the gas slip region is: Among them, MW RE is the molar amount of the gas introduced into the reactor during the RE period; U g，RE is the superficial gas velocity of the gas introduced into the reactor during the RE period; ρ g，RE is the density of the gas introduced into the reactor during the RE period, which is determined by the preset inlet average pressure during the RE period, and the preset average pressure is the average of the pressure at the start time and the pressure at the end time of the RE period; The calculation formula for the reactor height H0 without the gas slip region is:

4. The method according to claim 3, characterized in that, The RE period parameters in step S1 further include the RE period start pressure and RE period end pressure; the OX period parameters further include the OX period start pressure and OX period end pressure; the method further includes step S10: S10: Check the pressure drop in the RE period and OX period using the Ergun equation. If the pressure drop error is greater than 5%, re-adjust the preset start pressure and end pressure. The specific pressure drop calculation formula is: where Δp j is the pressure drop in the j-th period, where j is OX or RE; ε is the bulk porosity of the oxygen carrier; η g，j is the gas viscosity in the j-th period, U g，j is the inlet gas velocity of the reactor in the j-th period, d p is the particle size of the oxygen carrier, ρ g，j is the gas density in the j-th period, H is the height of the reactor. When the superficial gas velocity in the RE period is less than or equal to 0.1 m / s, H is equal to H0. When the superficial gas velocity in the RE period is greater than 0.1 m / s, H = H0+(1 - X)L slip , where X is the average conversion degree of the oxygen carrier in the gas slip region in the RE period, L slip is the length of the gas slip region.

5. The method according to claim 1, characterized in that The moving speed w of the thermal front in the OX period and the RE period 1，j is as follows: where, w 1，j is the moving speed of the thermal front in the j-th period, and j is OX or RE; U g，j is the gas velocity at the reactor inlet in the j-th period, ρ g，j is the gas density in the j-th period, ε is the packed porosity of the oxygen carrier, and its value ranges from 0.41 to 0.54; ρ s is the density of the oxygen carrier, C p，eq is the equivalent specific heat capacity of the bed, C p，j is the specific heat capacity of the inlet gas in the j-th period; The moving speed w of the reaction front in the OX period and the RE period 2，j is as follows: where, w g，i，j is the mass fraction of gas i at the inlet in the j-th period, W act is the molar amount of the active component in the oxygen carrier, w act is the mass fraction of the active component in the oxygen carrier, MW i is the molar amount of gas i, ξ i is the gas-solid molar ratio of the reaction between gas component i and the oxygen carrier.

6. The method according to claim 5, characterized in that In step S4, the running duration τ of the OX period OX is calculated by the formula wherein, H0 is the reactor height without a gas slip region; w 2，OX is the moving speed of the reaction front edge during the OX period; When the height of the gas slip region in the reactor during the OX period is greater than the height of the gas slip region in the RE period: Among them, X OX is the average conversion degree of the oxygen carrier in the gas slip region during the OX period, and L slip，OX is the length of the gas slip region during the OX period.

7. The method according to claim 6, wherein The steps for obtaining the lengths of the slip regions in the OX period and RE period are: Obtain the slip region length L of any gas i slip，i It is as follows: Among them, U g，fro，j is the average apparent gas velocity at the reaction front edge in the j-th period; γ i is the gas conversion rate of gas i at the outlet of the gas slip region, which can take 0.7 - 0.9; C in，i is the gas concentration at the reactor inlet; n i is the chemical reaction order; R OC，i satisfies the formula: where, μ i is the reaction coefficient of gas i, η i is the intraparticle diffusion efficiency, which can take values from 0.2 to 0.5, and τ i is the characteristic conversion time of the shrinking core conversion model of the oxygen carrier; The length L of the gas slip region in the j-th time period slip，j is as follows:

8. The method according to claim 1 or 7, characterized in that In step S2, when the superficial gas velocity in the RE period is greater than 0.1 m / s, the gas slip region in the RE period cannot be ignored, and the reactor height H including the gas slip region is: H = H0+(1 - X RE )L slip，RE where is the reactor height without the gas slip region, X RE is the average conversion degree of the oxygen carrier in the gas slip region during the RE period, L slip，RE is the length of the gas slip region during the RE period.

9. The method according to claim 1 or 5, characterized in that, The upward movement distance L of the HR period 1，HR is as follows: Among them, L 1，j = w 1，j τ j , where τ j is the running duration in the j-th period, and w 1，j is the moving speed of the thermal front in the j-th period; The running duration τ of the HR period HR is as follows: τ HR = (N r - 1)τ RE - τ OX - τ P where is the number of parallel fixed beds, and τ P is the running duration of period P.

10. The method according to claim 7, wherein Obtain the temperature T of the temperature bed at the end of the OX period and the RE period based on the law of conservation of energy τ，j The calculation formula is as follows: Among them, A is the cross-sectional area excluding the gas slip region, T 0，j is the starting temperature at the j-th time period, ΔH i is the heat of chemical reaction, Q loss，j is the heat dissipation loss at the j-th time period.

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