General calculation method suitable for sludge smoldering temperature and smoldering speed prediction

Abstract

The invention relates to the field of sludge thermochemical treatment, in particular to a general calculation method suitable for sludge smoldering temperature and smoldering speed prediction.The general calculation method comprises the steps that sludge sample characteristic parameters are obtained, and reaction conditions of the sludge smoldering process are determined; on the basis of the sludge sample characteristic parameters and the reaction conditions, sludge intrinsic smoldering kinetic parameters are obtained through an isothermal smoldering weightlessness method; according to the sludge intrinsic smoldering kinetic parameters, a heat and mass transfer conservation equation in the sludge smoldering process is solved through a large activation energy asymptotic method, and therefore a sludge smoldering universal model is constructed; and based on the sludge smoldering general model, predicting the sludge smoldering temperature and the sludge smoldering speed under different air velocities. According to the method, accurate prediction of the smoldering temperature and the smoldering speed of the multi-source high-humidity sludge can be realized.

Description

Technical Field

[0001] The invention relates to the field of sludge thermochemical treatment, and more specifically, to a general calculation method suitable for predicting sludge smoldering temperature and smoldering speed. Background Art

[0002] With the continuous advancement of urbanization and industrialization in my country, the treatment rates of municipal and industrial sewage have increased year by year, and the output of sludge, as a by-product of sewage, has also increased year by year. According to statistics, from 2018 to 2022, China's sludge production has rapidly climbed from 13.77 million tons to 47.38 million tons, of which municipal sludge accounted for 88% and industrial sludge accounted for 12%. At present, the main methods of sludge disposal are land use and incineration. Among them, land use is often subject to many restrictions due to the complex nature of sludge (such as organic matter, heavy metals) and other reasons, and incineration, as a high-temperature disposal method, often requires the addition of a large amount of high calorific value fuel when facing high-water sludge. At the same time, the complexity of equipment and processes also limits its large-scale industrial application.

[0003] In recent years, self-sustaining smoldering technology has attracted much attention due to its potential in the treatment of organic solid waste with high water content. In general, the smoldering process can achieve self-sustaining operation by stimulating the energy of the fuel itself, and has a natural advantage in the treatment of sludge with high water content. Unlike traditional incineration technology, self-sustaining smoldering technology does not require a pre-drying process, and no additional high calorific value fuel needs to be added during the operation stage, which can greatly reduce the construction and operation costs. As a surface oxidation reaction occurring in the porous medium space, smoldering involves heat and mass transfer processes under complex atmospheric conditions. The smoldering temperature and smoldering speed during the reaction can often explain the smoldering state under these conditions. It is affected by multiple parameters, which is crucial for the development and application of smoldering equipment and technology. However, there is currently no unified theoretical model to describe the smoldering propagation process and analyze the changes in smoldering characteristics with key parameters. At the same time, for sludge from different sources, the fuel properties are often very different. How to ensure the adaptability of the smoldering model to sludge from different sources is the premise for promoting the large-scale and efficient application of sludge smoldering. Therefore, it is necessary to establish a universal smoldering mechanism model and based on it, predict the sludge smoldering temperature and smoldering speed. Summary of the invention

[0004] In view of the above defects and improvement needs of the prior art, the present invention provides a general calculation method suitable for the prediction of sludge smoldering temperature and smoldering speed. Starting from the heat and mass transfer principles in the sludge smoldering process, combined with different sludge sample characteristic parameters and reaction conditions, the accurate prediction of multi-source high-humidity sludge smoldering temperature and smoldering speed can be achieved.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A general calculation method for predicting sludge smoldering temperature and smoldering speed comprises the following steps:

[0007] Obtain characteristic parameters of sludge samples and determine reaction conditions of sludge smoldering process;

[0008] Based on the characteristic parameters of the sludge sample and the reaction conditions, obtaining the intrinsic smoldering kinetic parameters of the sludge by an isothermal smoldering weight loss method;

[0009] According to the intrinsic smoldering kinetic parameters of the sludge, the heat and mass transfer conservation equations of the sludge smoldering process are solved by the large activation energy asymptotic method, thereby constructing a general sludge smoldering model;

[0010] Based on the sludge smoldering general model, the sludge smoldering temperature and smoldering speed under different air flow rates are predicted.

[0011] In the general calculation method as described above, further, the sludge sample characteristic parameters include:

[0012] Industrial analysis data of dried sludge samples;

[0013] Elemental analysis data of dry sludge samples;

[0014] Specific heat capacity of dry sludge samples;

[0015] True density of dry sludge sample;

[0016] Particle size of dry sludge samples; and,

[0017] Calorific value of dried sludge samples and porosity of mixed fuels.

[0018] The general calculation method as described above, further, the reaction conditions include:

[0019] Air oxygen concentration;

[0020] Specific heat capacity of air;

[0021] Air density;

[0022] Air temperature;

[0023] Smoldering reactor diameter;

[0024] Smoldering reactor height; and,

[0025] Thermal conductivity of smoldering reactor.

[0026] In the above general calculation method, further, the industrial analysis data includes:

[0027] the volatile matter content of the dry sludge sample;

[0028] ash content; and,

[0029] Fixed carbon content.

[0030] The general calculation method as described above, further,

[0031] The elemental analysis data include:

[0032] The carbon element of the dry sludge sample;

[0033] Hydrogen;

[0034] Nitrogen;

[0035] elemental sulfur; and,

[0036] Oxygen element.

[0037] The general calculation method as described above further utilizes the final sludge to obtain the sludge sample after drying, crushing and screening steps.

[0038] In the general calculation method as described above, further, the intrinsic smoldering kinetic parameters of the sludge include:

[0039] smoldering reaction activation energy; and,

[0040] Smoldering reaction pre-exponential factor

[0041] The general calculation method as described above, further, the intrinsic smoldering kinetic parameters of sludge are obtained by isothermal smoldering weight loss method, specifically including:

[0042] Conduct smoldering experiments to obtain the smoldering temperature and corresponding smoldering weight loss law at different air flow rates;

[0043] The smoldering weight loss law is monitored by a weighing balance, and the mass loss occurring during the isothermal smoldering process is analyzed by the Arrhenius equation. The relationship between the smoldering reactivity and the temperature is expressed as:

[0044]

[0045] Where α is the dimensionless conversion rate of the smoldering reaction, A, E, T, and t are the pre-exponential factor, activation energy, reaction temperature, and reaction time of the smoldering process, respectively, and R is the ideal gas constant, R = 8.314 J·mol -1 ·K -1 , f(α) is the reaction mechanism function, f(α)=(1-α) n , where n is the reaction order;

[0046] Performing logarithmic operations on the above formula, we get:

[0047]

[0048] The intrinsic smoldering kinetic parameters of the sludge were obtained by drawing a fitting straight line of ln(dα / dt) and 1 / T and calculating the slope and intercept of the fitting straight line.

[0049] The general calculation method as described above, further, solves the heat and mass transfer conservation equations of the sludge smoldering process by the large activation energy asymptotic method, thereby constructing a general sludge smoldering model, specifically including:

[0050] Use a single-step oxidation process to represent the smoldering reaction:

[0051] 1g Fuel+n O O2→n A Ash+n gp Gas products+Q

[0052] Where n O 、n A 、n gp are the mass-weighted stoichiometric coefficients of oxygen, ash and gaseous products in the single-step reaction, respectively;

[0053] The reaction rate of a single-step reaction is written in the form of the Arrhenius equation:

[0054]

[0055] In the formula, A is the pre-exponential factor of the chemical reaction, E is the activation energy of the reaction, R is the universal constant of ideal gas, and ρ g , s are the air flow density and solid fuel density, is the mass fraction of oxygen in the air flow, T f is the sludge smoldering temperature;

[0056] The smoldering in the porous medium space is assumed to be a gas-solid two-phase flow process accompanied by chemical reactions. According to the local thermal equilibrium theory, the gas phase and the solid phase are expressed at the same temperature. The mass conservation equation and energy conservation equation of the process are simplified to the following form:

[0057]

[0058] In the formula, c g , g are the specific heat capacity and density of the gas, c f is the specific heat capacity of the fuel, ρ s Taking both solid fuel and ash into account, Y O 0 is the oxygen concentration of the gas, v g is the air flow rate, A s is the shape factor of spherical particles, φ is the porosity, λ eff is the effective thermal conductivity, nO is the mass-weighted stoichiometric coefficient of oxygen in the single-step reaction, Q is the calorific value of the fuel, D is the oxygen diffusion coefficient, and u s is the smoldering rate;

[0059] Assuming that the smoldering wave in the fixed bed propagates stably, the above equations are simplified using the large activation energy asymptotic method to obtain the sludge smoldering model:

[0060]

[0061] Compared with the prior art, the present invention has the following beneficial effects: the present invention adopts an isothermal smoldering weightlessness method to obtain the intrinsic smoldering kinetic parameters of sludge, which can take into account the reaction characteristics of sludge from different sources and effectively eliminate the kinetic compensation effect existing in the fitting process of the intrinsic smoldering kinetic parameters of sludge; the present invention conducts a mechanism analysis on the heat and mass transfer process in sludge smoldering, and approximately solves the conservation equation of the smoldering process based on the large activation energy asymptotic method, and obtains a general mechanism model of sludge smoldering; based on the established general mechanism model of smoldering, the present invention can carry out sensitivity analysis on the smoldering process under different fuel characteristics and operating conditions, and can quickly and effectively predict the sludge smoldering temperature and smoldering speed under different air flow rates, which provides theoretical guidance for the industrial application of sludge smoldering technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0063] Figure 1 It is a flow chart of a general calculation method of sludge smoldering temperature and smoldering speed according to an embodiment of the present invention;

[0064] Figure 2 is a sensitivity analysis diagram of the smoldering characteristics of an embodiment of the present invention to key parameters;

[0065] Figure 3 The figure is a comparison chart of the experimental value and the calculated value of the smoldering temperature and smoldering speed of the embodiment of the present invention. DETAILED DESCRIPTION

[0066] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0067] Example:

[0068] It should be noted that the terms "including" and "having" and any variations of the embodiments of the present invention are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0069] See also Figure 1 This embodiment provides a general calculation method for predicting sludge smoldering temperature and smoldering speed, comprising the following steps:

[0070] Step 1: Obtain the characteristic parameters of the sludge sample and determine the reaction conditions of the sludge smoldering process.

[0071] In this step, the sludge sample is mainly dry sludge. In specific implementation, the sludge sample can be obtained by using the final sludge after drying, crushing and screening steps, so that all test samples can be guaranteed to be in the same state. In the field of sewage treatment and environmental protection, the final sludge refers to the sludge obtained after a series of treatment processes and meeting specific treatment standards or final disposal requirements.

[0072] The characteristic parameters of the sludge sample include industrial analysis data of the dry sludge sample, elemental analysis data of the dry sludge sample, specific heat capacity of the dry sludge sample, true density of the dry sludge sample, particle size of the dry sludge sample, calorific value of the dry sludge sample and porosity of the mixed fuel.

[0073] Wherein, the reaction conditions include air oxygen concentration, air specific heat capacity, air density, air temperature, smoldering reactor diameter, smoldering reactor height and smoldering reactor thermal conductivity.

[0074] Among them, the industrial analysis data include the volatile matter content, ash content and fixed carbon content of the dry sludge samples, and the elemental analysis data include the carbon element, hydrogen element, nitrogen element, sulfur element and oxygen element of the dry sludge samples.

[0075] It should be noted that since the smoldering reaction is a surface reaction occurring in the porous medium space, the porosity of the mixed fuel in this step is crucial to the oxygen diffusion in the smoldering process and can directly affect the propagation of the smoldering front. The porosity of the mixed fuel can be quickly measured by the water drainage method.

[0076] Step 2: Based on the characteristic parameters of the sludge sample and the reaction conditions, the intrinsic smoldering kinetic parameters of the sludge are obtained by an isothermal smoldering weight loss method.

[0077] In this step, the intrinsic smoldering kinetic parameters of the sludge include the activation energy of the smoldering reaction and the pre-exponential factor of the smoldering reaction. The intrinsic smoldering kinetic parameters of the sludge can be measured by the isothermal smoldering weightlessness method. The smoldering reaction process is complex enough, and multiple physical and chemical reactions (evaporation, pyrolysis and oxidation) occur simultaneously. The weightlessness characteristics of the real smoldering process of the sludge are used to solve the intrinsic smoldering kinetic parameters of the sludge. The reaction characteristics of sludge from different sources can be taken into account, and the kinetic compensation effect existing in the fitting process of the intrinsic smoldering kinetic parameters of the sludge can be effectively eliminated.

[0078] Among them, the isothermal smoldering weightlessness method is intended to be carried out by obtaining the smoldering temperature and the corresponding smoldering weightlessness law in the smoldering experiment under different air flow rates. The smoldering temperature refers to the reaction temperature in the self-sustaining stage of smoldering, which is in a constant temperature mode during the entire self-sustaining stage, thus reflecting the reaction state of the entire sludge smoldering process.

[0079] Then, the smoldering weight loss law is monitored by a weighing balance. The mass loss occurring during the isothermal smoldering process can be analyzed by the Arrhenius equation. The relationship between the smoldering reactivity and temperature can be expressed as:

[0080]

[0081] Where α is the dimensionless conversion rate of the smoldering reaction, A, E, T, and t are the pre-exponential factor, activation energy, reaction temperature, and reaction time of the smoldering process, respectively, and R is the ideal gas constant, R = 8.314 J·mol -1 ·K -1 , f(α) is the reaction mechanism function, f(α)=(1-α) n , where n is the reaction order;

[0082] Next, we can perform logarithmic operations on the above formula and obtain:

[0083]

[0084] Then, the ln(dα / dt) and 1 / T fitting lines are drawn, and the intrinsic smoldering kinetic parameters E and A of the sludge can be calculated through the slope and intercept of the fitting line;

[0085] Step 3: Based on the intrinsic smoldering kinetic parameters of the sludge, the heat and mass transfer conservation equations of the sludge smoldering process are solved by the large activation energy asymptotic method, thereby constructing a general sludge smoldering model.

[0086] In this step, the sludge smoldering reaction has similar structural characteristics to the diffusion flame, that is, the fuel and the oxidant converge from opposite directions of the reaction front respectively. At the same time, the smoldering reaction zone can be considered to be infinitely thin. Therefore, the large activation energy asymptotic method is used to solve the heat and mass transfer conservation equations of the smoldering process, and a general sludge smoldering model is established.

[0087] Among them, the large activation energy asymptotic method assumes that the smoldering oxidation reaction occurs in a very narrow area and is very sensitive to temperature. In order to simplify the calculation, the following assumptions are introduced into the model:

[0088] (1) The propagation of gas and solid in porous media space is one-dimensional and upward;

[0089] (2) The thermophysical properties of the gas and solid phases are isotropic in the reactor, and the chemical properties remain unchanged during the smoldering process;

[0090] (3) The heat transfer between the gas phase and the solid phase is fast enough, so the gas phase and the solid phase are in local thermal equilibrium and the same temperature can be used to describe the gas phase and the solid phase;

[0091] (4) In the smoldering stable stage, the heat transfer layer moves faster than the combustion layer, forming a reaction tail structure.

[0092] Then, the mechanism of sludge smoldering process is analyzed. When the air flow rate is relatively large, the smoldering process is mainly controlled by reaction kinetics. At this time, the smoldering speed is strongly dependent on the smoldering temperature, which in turn is highly dependent on the air flow rate. The smoldering reaction process involves multiple physical and chemical reactions (pyrolysis and oxidation) occurring simultaneously. However, considering that the pyrolysis process only increases the width of the front and has no qualitative effect on the structure of the smoldering characteristic solution, a single-step oxidation process is used to represent the smoldering reaction:

[0093] 1g Fuel+n O O2→n A Ash+n gp Gas products+Q

[0094] Where n O 、n A 、n gp are the mass-weighted stoichiometric coefficients of oxygen, ash and gas products in the single-step reaction, respectively.

[0095] The reaction rate of a single-step reaction can be written in the form of the Arrhenius equation:

[0096]

[0097] In the formula, A is the pre-exponential factor of the chemical reaction, E is the activation energy of the reaction, R is the universal constant of ideal gas, and ρ g , s are the air flow density and solid fuel density, is the mass fraction of oxygen in the air flow, T f is the sludge smoldering temperature;

[0098] Next, the smoldering in the porous medium space can be regarded as a gas-solid two-phase flow process accompanied by chemical reactions. According to the local heat balance theory, the gas phase and the solid phase can be expressed at the same temperature, and the mass conservation equation and energy conservation equation of the process can be simplified to the following form:

[0099]

[0100] In the formula, c g , g are the specific heat capacity and density of the gas, c f is the specific heat capacity of the fuel, ρ s Taking both solid fuel and ash into account, is the oxygen concentration of the gas, v g is the air flow rate, A s is the shape factor of spherical particles, φ is the porosity, λ eff is the effective thermal conductivity, n O is the mass-weighted stoichiometric coefficient of oxygen in the single-step reaction, Q is the calorific value of the fuel, D is the oxygen diffusion coefficient, and u s is the smoldering rate;

[0101] Finally, the smoldering wave in the fixed bed propagates stably. The above equations are simplified using the large activation energy asymptotic method to obtain the sludge smoldering model:

[0102]

[0103]

[0104] Step 4: Based on the sludge smoldering general model, predict the sludge smoldering temperature and smoldering speed under different air flow rates.

[0105] In this step, there are only two target parameters in the simplified sludge smoldering model, namely, the smoldering temperature T f and smoldering speed u s , and the remaining variables involve characteristic parameters of different sludge samples, reaction conditions and kinetic parameters. According to the sludge smoldering model, the sensitivity analysis of the influence of different fuel characteristics and operating conditions on the smoldering process can be carried out, and the accurate prediction of sludge smoldering temperature and smoldering speed under different air flow rates can be achieved.

[0106] As an example: First, the sludge sample is dried in a 105°C oven at a constant temperature for 24 hours to obtain a dry sample, and then the dry sample is crushed and sieved into uniform particles of 150-270 μm to ensure that all test samples are in the same state. According to the national standard GB / T2122008, the industrial analysis of the dry sludge sample is carried out in a program temperature-controlled muffle furnace. The element analysis of the dry sludge sample is carried out in an element analyzer. The true density and calorific value of the dry sludge sample are measured by a true density meter and a bomb calorimeter, respectively. The porosity of the mixed fuel is measured by the drainage method. The sludge sample characteristic results are shown in Table 1:

[0107] Table 1 Sludge sample characteristics

[0108]

[0109] a Calculated by difference method.

[0110] In this embodiment, the air oxygen concentration and air temperature in the reaction conditions are the initial air oxygen concentration and the initial air temperature, which are 0.21 and 300K, respectively. The air specific heat capacity and air density are the parameter values ​​at the reaction temperature (such as 900K), which are 0.3868 kg / m 3 and 1121 J / (kg·K). The smoldering reaction occurs in a cylindrical quartz reactor with a height of 0.4 m and a diameter of 0.15 m, and its effective thermal conductivity is 0.074 W / (m·K).

[0111] Subsequently, the intrinsic smoldering kinetic parameters of the sludge were obtained by the isothermal smoldering weight loss method. This method considers the smoldering self-sustaining stage as an isothermal weight loss stage, which can reflect the overall state of the smoldering process. Therefore, the intrinsic smoldering kinetic parameters of the sludge can be solved based on the mass loss data under different working conditions.

[0112] More specifically, in the smoldering experiments under three different air flow rates, the temperature data and mass loss data under different air flow rates were monitored, and the smoldering temperature in the self-sustaining stage under different working conditions was extracted. The mass loss data can be converted into the relationship between the smoldering conversion rate and time, which can be expressed by the Arrhenius equation:

[0113]

[0114] Where α is the dimensionless conversion rate of the smoldering reaction, A, E, T, and t are the pre-exponential factor, activation energy, reaction temperature, and reaction time of the smoldering process, respectively, and R is the ideal gas constant, R = 8.314 J·mol -1 ·K -1 , f(α) is the reaction mechanism function, f(α)=(1-α) n , where n is the reaction order;

[0115] Performing logarithmic operations on the above formula, we can obtain:

[0116]

[0117] Draw the ln(dα / dt) and 1 / T fitting straight lines, and the intrinsic smoldering kinetic parameters E and A of the sludge can be calculated through the slope and intercept of the fitting straight line;

[0118] Next, the mechanism of sludge smoldering process is analyzed. When the air flow rate is relatively large, the smoldering process is mainly controlled by reaction kinetics. At this time, the smoldering speed is strongly dependent on the smoldering temperature, which in turn is highly dependent on the air flow rate. The smoldering reaction process involves multiple physical and chemical reactions (pyrolysis and oxidation) occurring simultaneously. However, considering that the pyrolysis process only increases the width of the front and has no qualitative effect on the structure of the smoldering characteristic solution, a single-step oxidation process is used to represent the smoldering reaction:

[0119] 1g Fuel+n O O2→n A Ash+n gp Gas products+Q

[0120] Where n O 、n A 、n gp are the mass-weighted stoichiometric coefficients of oxygen, ash and gas products in the single-step reaction, respectively.

[0121] The reaction rate of a single-step reaction can be written in the form of the Arrhenius equation:

[0122]

[0123] In the formula, A is the pre-exponential factor of the chemical reaction, E is the activation energy of the reaction, R is the universal constant of ideal gas, and ρ g , s are respectively the air flow density and the solid fuel density, Y O 0 is the mass fraction of oxygen in the air flow, T f is the smoldering temperature of sludge.

[0124] Smoldering in porous media space can be regarded as a gas-solid two-phase flow process accompanied by chemical reactions. According to the local thermal equilibrium theory, the gas phase and the solid phase can be expressed at the same temperature. The mass conservation equation and energy conservation equation of the process can be simplified to the following form:

[0125]

[0126] In the formula, c g , g are the specific heat capacity and density of the gas, cf is the specific heat capacity of the fuel, ρ s Taking both solid fuel and ash into account, is the oxygen concentration of the gas, v g is the air flow rate, A s is the shape factor of spherical particles, φ is the porosity, λ eff is the effective thermal conductivity, n O is the mass-weighted stoichiometric coefficient of oxygen in the single-step reaction, Q is the calorific value of the fuel, D is the oxygen diffusion coefficient, and u s is the smoldering rate.

[0127] Assuming that the smoldering reaction occurs in a very small area and the smoldering wave propagates steadily, the above equation can be simplified using the large activation energy asymptotic method to obtain:

[0128]

[0129] There are only two target parameters in the simplified smoldering model, namely the smoldering temperature T f and smoldering speed u s , and the remaining variables involve characteristic parameters of different sludge samples, reaction conditions and kinetic parameters.

[0130] In the above smoldering mechanism model, different variables have different effects on the smoldering characteristics. Therefore, the sensitivity of multiple parameters to smoldering temperature and smoldering speed can be clarified according to the smoldering mechanism model. The values ​​of all parameters in the model will be changed by ±50% around the baseline value to analyze the sensitivity of different parameters. The baseline value is determined by experiment. The calculation results are as follows: Figure 2 As shown in the figure, the porosity φ and activation energy E have the most significant influence on the smoldering characteristics. The porosity φ determines the oxygen supply and thus determines the smoldering propagation speed. The activation energy E characterizes the difficulty of the chemical reaction and determines the internal heat balance of the fuel, which proves the rationality of the smoldering mechanism model.

[0131] Since the sludge smoldering process occurs under oxygen-limited conditions, oxygen supply and heat loss are two key factors in controlling the spread of smoldering. In fixed-bed smoldering equipment, adjusting the air flow rate can directly affect these two key factors, providing a practical and reliable means for controlling high-humidity sludge treatment. Based on the above-mentioned sludge smoldering general model, the sludge smoldering temperature and smoldering speed prediction under different air flow rates can be achieved. The experimental and calculated values ​​of smoldering temperature and smoldering speed are compared. Figure 3 shown.

[0132] It can be seen that the present invention adopts the isothermal smoldering weightlessness method to obtain the intrinsic smoldering kinetic parameters of the sludge. This method can take into account the reaction characteristics of sludge from different sources and effectively eliminate the kinetic compensation effect existing in the fitting process of the intrinsic smoldering kinetic parameters of the sludge; the present invention conducts a mechanism analysis on the heat and mass transfer process in the sludge smoldering, and approximately solves the conservation equation of the smoldering process based on the large activation energy asymptotic method, and obtains a general mechanism model of sludge smoldering; based on the established general mechanism model of smoldering, the present invention can carry out sensitivity analysis on the smoldering process under different fuel characteristics and operating conditions, and can quickly and effectively predict the smoldering temperature and smoldering speed of sludge under different air flow rates, which provides theoretical guidance for the industrial application of sludge smoldering technology.

[0133] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0134] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable ordinary technicians in the field to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made based on the essence of the content of the present invention should be included in the protection scope of the present invention.

Claims

1. A general calculation method, characterized in that: The method is used to predict the smoldering temperature and smoldering speed of sludge, including the following steps: Obtain characteristic parameters of sludge samples and determine reaction conditions of sludge smoldering process; Based on the characteristic parameters of the sludge sample and the reaction conditions, obtaining the intrinsic smoldering kinetic parameters of the sludge by an isothermal smoldering weight loss method; According to the intrinsic smoldering kinetic parameters of the sludge, the heat and mass transfer conservation equations of the sludge smoldering process are solved by the large activation energy asymptotic method, thereby constructing a general sludge smoldering model; Based on the sludge smoldering general model, the sludge smoldering temperature and smoldering speed under different air flow rates are predicted.

2. The general calculation method according to claim 1, characterized in that: The sludge sample characteristic parameters include: Industrial analysis data of dried sludge samples; Elemental analysis data of dry sludge samples; Specific heat capacity of dry sludge samples; True density of dry sludge sample; Particle size of dry sludge samples; and, Calorific value of dried sludge samples and porosity of mixed fuels.

3. The general calculation method according to claim 1, characterized in that: The reaction conditions include: Air oxygen concentration; Specific heat capacity of air; Air density; Air temperature; Smoldering reactor diameter; Smoldering reactor height; and, Thermal conductivity of smoldering reactor.

4. The general calculation method according to claim 2, characterized in that: The industrial analysis data include: the volatile matter content of the dry sludge sample; ash content; and, Fixed carbon content.

5. The general calculation method according to claim 2, characterized in that: The elemental analysis data include: The carbon element of the dry sludge sample; Hydrogen; Nitrogen; elemental sulfur; and, Oxygen element.

6. The general calculation method according to claim 1, characterized in that: The sludge sample is obtained by using the final sludge through drying, crushing and screening steps.

7. The general calculation method according to claim 1, characterized in that: The intrinsic smoldering kinetic parameters of the sludge include: smoldering reaction activation energy; and, Smoldering reaction pre-factor.

8. The general calculation method according to claim 1, characterized in that: The method of obtaining the intrinsic smoldering kinetic parameters of sludge by the isothermal smoldering weight loss method specifically includes: Conduct smoldering experiments to obtain the smoldering temperature and corresponding smoldering weight loss law at different air flow rates; The smoldering weight loss law is monitored by a weighing balance, and the mass loss occurring during the isothermal smoldering process is analyzed by the Arrhenius equation. The relationship between the smoldering reactivity and the temperature is expressed as: Where α is the dimensionless conversion rate of the smoldering reaction, A, E, T, and t are the pre-exponential factor, activation energy, reaction temperature, and reaction time of the smoldering process, respectively, and R is the ideal gas constant, R = 8.314 J·mol -1 ·K -1 , f(α) is the reaction mechanism function, f(α)=(1-α) n , where n is the reaction order; Performing logarithmic operations on the above formula, we get: The intrinsic smoldering kinetic parameters of the sludge were obtained by drawing a fitting straight line of ln(dα / dt) and 1 / T and calculating the slope and intercept of the fitting straight line.

9. The general calculation method according to claim 1, characterized in that: The heat and mass transfer conservation equations of the sludge smoldering process are solved by the large activation energy asymptotic method, thereby constructing a general sludge smoldering model, which specifically includes: Use a single-step oxidation process to represent the smoldering reaction: 1g Fuel+n O O2→n A Ash+n gp Gas products+Q Where n O 、n A 、n gp are the mass-weighted stoichiometric coefficients of oxygen, ash and gaseous products in the single-step reaction, respectively; The reaction rate of a single-step reaction is written in the form of the Arrhenius equation: In the formula, A is the pre-exponential factor of the chemical reaction, E is the activation energy of the reaction, R is the universal constant of ideal gas, and ρ g , s are respectively the air flow density and the solid fuel density, Y O 0 is the mass fraction of oxygen in the air flow, T f is the sludge smoldering temperature; The smoldering in the porous medium space is assumed to be a gas-solid two-phase flow process accompanied by chemical reactions. According to the local thermal equilibrium theory, the gas phase and the solid phase are expressed at the same temperature. The mass conservation equation and energy conservation equation of the process are simplified to the following form: In the formula, c g , g are the specific heat capacity and density of the gas, c f is the specific heat capacity of the fuel, ρ s Taking both solid fuel and ash into account, Y O 0 is the oxygen concentration of the gas, v g is the air flow rate, A s is the shape factor of spherical particles, φ is the porosity, λ eff is the effective thermal conductivity, n O is the mass-weighted stoichiometric coefficient of oxygen in the single-step reaction, Q is the calorific value of the fuel, D is the oxygen diffusion coefficient, and u s is the smoldering rate; Assuming that the smoldering wave in the fixed bed propagates stably, the above equations are simplified using the large activation energy asymptotic method to obtain the sludge smoldering model:

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