Method for calculating semi-closed blast furnace flue gas volume based on fire simulation

Abstract

The application discloses a calculation method for calculating smoke gas volume of a large semi-closed ore-heating furnace by using a thought suitable for citing a fire model, and comprises the following steps: obtaining average fire load density per unit time when a semi-closed ore-heating furnace is subjected to smelting, and then is subjected to furnace ramming and material ramming operation; obtaining theoretical time for complete combustion of CO released by the semi-closed ore-heating furnace during the furnace ramming and the material ramming operation and reducing agent participating in combustion at a furnace mouth; obtaining maximum heat release rate of a flashover stage after the furnace ramming and the material ramming operation; and obtaining smoke gas volume flow of the semi-closed ore-heating furnace. The method is combined with production operation, and worst working conditions of the semi-closed ore-heating furnace are selected and fitted with the case that maximum fire heat release rate is generated in a flashover stage of fire occurrence, so that a smoke gas volume multiple relationship under the worst working conditions of the semi-closed ore-heating furnace and stable and continuous production is obtained, and maximum smoke gas volume flow of the semi-closed ore-heating furnace is obtained. The method provides an optimal reference for reasonably selecting the smoke gas volume of the semi-closed ore-heating furnace by using an air excess coefficient method.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical process technology, and specifically relates to a calculation method for the flue gas volume of a large semi-enclosed submerged arc furnace, which is applicable to the use of fire models. Background Technology

[0002] Submerged arc furnaces are mainly used for the reduction and smelting of ores, carbonaceous reducing agents, and solvents. Inside the furnace, oxides in the ore are reduced by carbon, continuously generating CO which escapes from the furnace opening and burns stably in contact with air. Additionally, some of the reduced agent lost at the furnace opening also participates in the combustion reaction.

[0003] Currently, the main method for calculating the flue gas volume of semi-enclosed submerged arc furnaces is the excess air coefficient method. This method uses the ratio of the actual air mass supplied for combustion of combustible gas at the furnace opening to the theoretical air mass required for combustion, i.e., the excess air coefficient λ, to control the amount of flue gas.

[0004] Based on the material balance of the reaction inside the semi-enclosed submerged arc furnace, the amount of combustible gas (mainly CO) produced by reduction is calculated. The value of λ is then selected based on the air volume required for combustion and the system leakage of the semi-enclosed submerged arc furnace. The system leakage mainly depends on the furnace conditions and smelting operating habits, and is difficult to predict accurately during the design phase, mostly relying on the experience of equipment manufacturers. Therefore, the final value of λ is generally between 18 and 25 Nm. 3 The range of / h varies, resulting in different calculated flue gas volumes. Moreover, the larger the capacity of the submerged arc furnace, the greater the difference in the selection of flue gas volume, and the different system configurations. To ensure the operational capability of the submerged arc furnace's supporting facilities, equipment manufacturers mostly tend to directly select the largest process parameter.

[0005] Taking industrial silicon submerged arc furnaces as an example, the flue gas volume of the first batch of 33MVA capacity submerged arc furnaces built after 2010 was approximately 160,000 to 180,000 Nm³. 3 / h. Subsequent operation revealed that the flue gas volume was too low, the system configuration was inadequate, and the exhaust system was not entirely reasonable. In actual production, various problems were observed, including smoke and leakage from the equipment, excessive flow velocity near the air intake, and the phenomenon of "material being sucked through."

[0006] With the rapid development of the industrial silicon industry in recent years, a new batch of 33MVA industrial silicon furnaces has been built and put into operation at an alarming rate. Looking at the configuration of most 33MVA industrial silicon submerged arc furnace production lines, the system process parameters for flue gas treatment have generally exceeded 200,000 Nm³. 3 / h, most are selected as 220,000 to 230,000 Nm 3 / h, with some reaching 250,000 Nm 3 / h flue gas volume. Furthermore, system configuration must consider the system's operating rate and operating coefficient in addition to the above process parameters. As system configurations become increasingly larger, construction investment increases, and operating costs remain high. Summary of the Invention

[0007] The purpose of this invention is to address the aforementioned problems by providing a method for calculating the flue gas volume of a semi-enclosed submerged arc furnace based on fire simulation. This method calculates the flue gas volume based on a fire simulation under conditions of stable and continuous production of combustible gas. The flue gas volume is then verified by combining the worst-case operating conditions of production to obtain the flue gas volume calculation result of this invention. This result is then compared with the calculation results of many existing methods using the excess air coefficient, providing an optimal reference for rationally selecting the flue gas volume of a semi-enclosed submerged arc furnace using the excess air coefficient method.

[0008] This invention is achieved through the following technical solution: a method for calculating flue gas volume in a semi-enclosed submerged arc furnace based on fire simulation, characterized by: setting the average combustible product generation and combustion conditions during submerged arc furnace production as the stable stage of combustion at the furnace mouth; setting the furnace tamping and charging conditions as the flashover stage of combustion at the furnace mouth; selecting the period from the stable stage to the flashover stage as the research interval for combustion at the furnace mouth of the semi-enclosed submerged arc furnace; and using the combustion conditions at this furnace mouth as the basic model, the specific process for calculating the flue gas volume during the production process of the semi-enclosed submerged arc furnace is as follows:

[0009] Step 1: Obtain the average fire load density Q per unit time during the furnace tamping and material handling operations after the semi-enclosed submerged arc furnace has been quenched. Pmax The unit is MJ / ㎡.

[0010]

[0011] In the formula: n is the simmering time coefficient, which is the ratio of simmering time t1 to unit time;

[0012] ω represents the percentage of Si element content in the product produced by the semi-enclosed submerged arc furnace, in %;

[0013] Q h The output of a semi-enclosed submersible arc furnace is expressed in t / h.

[0014] H ico This refers to the calorific value of CO combustion, expressed in MJ / kg.

[0015] H ic This represents the calorific value of carbonaceous reducing agents, expressed in MJ / kg.

[0016] d is the diameter of the combustion surface at the furnace opening, d = Φ + 0.7, in meters;

[0017] Step 2: Obtain the theoretical time t0 for the complete combustion of CO released during the tamping and charging operations of the semi-enclosed submerged arc furnace and the reducing agent participating in combustion at the furnace opening, in minutes.

[0018]

[0019] In the formula: q t Design fire load density for the room, MJ / ㎡;

[0020] D is the inner diameter of the fume hood, in meters (m).

[0021] H represents the net height of the fume hood, in meters (m).

[0022] Φ is the furnace diameter, in meters (m).

[0023] h represents the equivalent height of various ventilation openings in the semi-enclosed electric arc furnace hood, in meters.

[0024] A v The area of ​​various ventilation openings in a semi-enclosed electric arc furnace fume hood is shown in square meters.

[0025] Step 3: Calculate the maximum heat release rate Q during the flashover stage of the semi-enclosed submerged arc furnace after the furnace tamping and charging operations. max The unit is kW.

[0026]

[0027] To obtain the calculated value of the maximum flue gas volume, it is assumed that the total heat release rate Q in the furnace is... max All the corresponding heat is carried away by the flue gas, and a steady state is reached at 600℃. Based on the specific heat capacity and density of the flue gas at this point, the mass flow rate M (kg / h) and volumetric flow rate G (m³) are calculated. 3 The relationship for / h is:

[0028]

[0029] In the formula: M is the mass flow rate of flue gas from a semi-enclosed submerged arc furnace, in kg / h;

[0030] ρ is the density of flue gas at 600℃, in kg / m³. 3 ;

[0031] C is the specific heat capacity of the flue gas, expressed in J / (kg·℃);

[0032] The calculated G is the maximum flue gas flow rate of the semi-enclosed submerged arc furnace. By converting the maximum flue gas flow rate to standard conditions, the upper limit of the optimal value for selecting the flue gas flow rate of the semi-enclosed submerged arc furnace using the excess air coefficient method is obtained.

[0033] The method for calculating flue gas volume in a semi-enclosed submerged arc furnace based on fire simulation described in this invention, in step one, is based on the reaction equation where the carbonaceous reducing agent in the semi-enclosed submerged arc furnace is mainly used for the reduction of SiO2 in the raw ore. It derives that during production in the semi-enclosed submerged arc furnace, the CO generated by the reaction uniformly overflows from the furnace opening, and the amount of CO generated is:

[0034] q co =2.22H ico ·ω·Q h

[0035] During production in a semi-enclosed submerged arc furnace, there is a direct combustion loss of carbonaceous reducing agent at the furnace opening. Taking 10% of the fixed carbon as the loss, the amount of carbonaceous reducing agent participating in combustion is:

[0036] When coal is used as a reducing agent, q c1 =0.2H ic ·ω·Q h ;

[0037] When coke is used as a reducing agent, q c2 =0.13H ic ·ω·Q h ;

[0038] Based on obtaining the maximum Q max If q is the target, then select q directly. c1 The value of the expression, that is:

[0039] q c =0.2H ic ·ω·Q h

[0040] The generated CO and the burned-out reducing agent are assumed to be completely combusted, i.e., the combustion factor is set to 1.

[0041] Among them, the flame burning area is That is, 0.785(Φ+0.7) 2 The formula for calculating the average design fire load density per unit time within the combustion space is as follows:

[0042]

[0043] Based on the objective of calculating the maximum flue gas volume, this study assumes that no reducing gas overflows from the material surface during the smoldering period, and that the reducing gas released after smoldering is concentrated and burned at the furnace mouth until flashover occurs. This is considered the combustion research phase. The amount of CO produced during the maximum smoldering period is used in the calculation to obtain the maximum combustible heat release rate during flashover, i.e., the maximum fire load density Q during flashover. max Calculate using the following formula:

[0044]

[0045] Finally, q co and q c Substituting the calculation formula into the above, we obtain Q in step one. max The calculation formula.

[0046] The method for calculating flue gas volume in a semi-enclosed submerged arc furnace based on fire simulation described in this invention, in step two, uses the following formula for calculating the theoretical time t0:

[0047]

[0048] In the formula q t Fire load density for a semi-enclosed submerged arc furnace, in MJ / m²; η is the ventilation coefficient, in m³. 1 / 2 ;

[0049] Since a higher fire load density per unit furnace leads to a higher fire heat release rate and a greater volume of flue gas produced, t0 should also be at its maximum. Therefore, q t =Q pmax ;

[0050] in,

[0051] In the formula: A v The area of ​​all ventilation openings inside a semi-enclosed electric arc furnace is shown in square meters.

[0052] h is the equivalent height of the ventilation opening inside the semi-enclosed electric arc furnace, in meters.

[0053] A t This is the sum of the areas of the side walls and top of the fume hood, in square meters (㎡).

[0054] The ventilation openings of the semi-enclosed submerged arc furnace include: furnace doors A located around the furnace for furnace operation. v1 The area of ​​the gap in the smoke hood is A v2 A ring-shaped vent at the top of the fume hood v3 and the annular gap A between the furnace opening and the inner wall of the fume hood v4 The area A of the furnace perimeter air inlets evenly distributed along the lower part of the outer perimeter of the fume hood v5 ;

[0055] The equivalent heights of the ventilation openings in a semi-enclosed submerged arc furnace are as follows: h is the height of the furnace door around the furnace for tamping operation. v1 The width of the gap in the smoke hood is h v2 The width h of the annular vent at the top of the fume hood v3 and the width h of the annular gap between the furnace opening and the inner wall of the fume hood v4 Furnace perimeter air inlet height h v5 ;

[0056] Right now:

[0057] The sum of the sidewall and top areas of the fume hood of a semi-enclosed electric arc furnace, A t The calculation formula is:

[0058]

[0059] In the formula: D is the inner diameter of the fume hood, in meters;

[0060] H represents the net height of the fume hood, in meters (m).

[0061] The formula for calculating the ventilation coefficient η during flashover in a semi-enclosed submerged arc furnace after ramming and charging is as follows:

[0062]

[0063] The ventilation coefficient η and the maximum fire load density during flashover are used. pmax Substituting the calculation formula into the above, we get:

[0064]

[0065] Finally, the formula for calculating the theoretical time t0 in step two is obtained.

[0066] The method for calculating flue gas volume of a semi-enclosed submerged arc furnace based on fire simulation described in this invention, in step three, the combustion at the furnace opening of the semi-enclosed submerged arc furnace can be measured using t. 2 This can be expressed using a fire simulation model: Q = αt 2 ,

[0067] In the formula: Q is the heat release rate of the fire, in kW;

[0068] α is the growth coefficient of fire heat release rate, with units of kW / s. 2 Take 0.04689;

[0069] t is the time when the fire occurs, in seconds. To obtain the maximum fire heat release rate, it is set that all combustibles at the furnace opening are burned out within the heat release time t, i.e., t = t0.

[0070] In step one, Q max q co q c Substituting the calculation formulas for t and t0 in step two into the formulas for t... 2 From the fire simulation model described, we can summarize as follows:

[0071]

[0072] Based on preliminary calculations using current heat balance data for semi-enclosed submerged arc furnaces, it is assumed that the heat loss rate carried away by the circulating water system is Q. S Then QS The maximum value is less than 1 / 4 of Q. Since the goal is to obtain the calculated value of the maximum flue gas volume, Q is set as follows: S = 1 / 4Q, the total heat release rate Q in the furnace max =Q+Q S Therefore, the formula for calculating the total heat release rate inside the furnace is as follows:

[0073]

[0074] The maximum heat release rate Q during the detonation stage in step three is obtained by sorting. max The calculation formula.

[0075] The method for calculating flue gas volume in a semi-enclosed submerged arc furnace based on fire simulation described in this invention, in step three, the critical heat release rate at the point of flashover can be verified using the following formula:

[0076]

[0077] At this point, the fire heat release rate is set to its maximum value, and after flashover in the space, combustion continues stably without any external spread. The data calculated based on this is then used to derive the flue gas volume calculation value of the semi-enclosed submerged arc furnace by applying the relationship between the flue gas mass flow rate M and the volume flow rate G. The calculation results of the two methods are basically consistent.

[0078] The method for calculating flue gas volume of a semi-enclosed submerged arc furnace based on fire simulation described in this invention, in step three, calculates the flue gas volume G as the flue gas volume of the semi-enclosed submerged arc furnace under operating conditions without considering pressure differences. The conversion to standard flue gas volume G0 is based on the calculation formula: The unit is Nm 3 / h.

[0079] This method calculates flue gas volume based on fire simulation under stable and continuous combustible gas production conditions. It combines the worst-case operating conditions of a semi-enclosed submerged arc furnace with the maximum fire heat release rate during the initial burst of a fire, deriving the ratio of flue gas volume between the worst-case operating conditions and stable, continuous production conditions. This leads to the calculation method for the maximum flue gas volumetric flow rate of the semi-enclosed submerged arc furnace. The results are then verified against other fire heat release rate calculation formulas, and are found to be within a reasonably selected range. The flue gas volume calculation results of this invention are compared with the values ​​obtained using numerous existing air excess coefficient methods, providing an optimal reference for selecting the appropriate flue gas volume for semi-enclosed submerged arc furnaces using the air excess coefficient method.

[0080] Based on the mechanical smoke prevention and exhaust theory of the semi-enclosed submerged arc furnace flue gas volume calculation value under fire simulation and the corresponding fire situation proposed in this invention, optimization concepts and design ideas are put forward for the rational design of the existing semi-enclosed submerged arc furnace collection and exhaust system, providing a reference for the overall improvement of the effect of the semi-enclosed submerged arc furnace exhaust system in the current production stage. Detailed Implementation

[0081] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0082] Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the claims, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other.

[0083] A method for calculating flue gas volume in a semi-enclosed submerged arc furnace based on fire simulation is disclosed. First, the combustion type within the semi-enclosed submerged arc furnace and the initial parameters for fire simulation are set. Combustion at the furnace opening is considered as the diffusion combustion of gaseous combustibles and combustion-supporting molecules. Based on the analysis of fire development stages within a building (referring to a confined space with a ceiling, furnace body, and openings; in this invention, it refers to the interior of the submerged arc furnace hood), the phenomenon of uniform generation and release of combustibles within the furnace per unit time, and continuous combustion at the furnace opening, conforms to the stable combustion stage of a fire, i.e., continuous fuel supply, good ventilation, and sustained combustion development.

[0084] The semi-enclosed submerged arc furnace production process involves operations such as simmering, furnace tamping, and material binding. During simmering, no material surface maintenance is performed, and CO gas generated by reduction accumulates below the material surface. After reaching a certain level, furnace tamping and material binding operations are required to release and burn the reducing gas in the furnace. Therefore, the production process of a semi-enclosed submerged arc furnace is a process of periodic accumulation and release of reducing gas inside the furnace.

[0085] This invention defines the stable combustion stage of a semi-enclosed submerged arc furnace as the condition where combustibles are uniformly generated and released per unit time during production, and continuously burn at the furnace mouth. The furnace conditions during stoking and charging are defined as the flashover stage. The study interval between the stable and flashover stages is selected as the combustion study range for the semi-enclosed submerged arc furnace, where unsteady-state combustion characteristics exist. Specifically, this invention studies and analyzes the worst-case scenario of semi-enclosed submerged arc furnace production to reflect the main combustion characteristics, flue gas volume, and smoke control requirements under the most extreme conditions. Using this combustion condition at the furnace mouth as the basic model, the specific process for calculating the flue gas volume during the semi-enclosed submerged arc furnace production process is as follows:

[0086] Step 1: Obtain the average fire load density Q per unit time during the furnace tamping and material handling operations after the semi-enclosed submerged arc furnace has been quenched. Pmax The unit is MJ / ㎡.

[0087]

[0088] In the formula: n is the simmering time coefficient, which is the ratio of simmering time t1 to unit time;

[0089] ω represents the percentage of Si element content in the product produced by the semi-enclosed submerged arc furnace, in %;

[0090] Q h The output of a semi-enclosed submersible arc furnace is expressed in t / h.

[0091] H ico The value is the calorific value of CO combustion, expressed in MJ / kg, and is taken as 1.18 MJ / kg.

[0092] H ic The calorific value of the carbonaceous reducing agent is expressed in MJ / kg, and is taken as 31 MJ / kg.

[0093] d is the diameter of the combustion surface at the furnace opening, in meters, and is taken as the empirical value of furnace diameter Φ+0.7.

[0094] Semi-enclosed submerged arc furnaces are mainly used to produce industrial silicon, ferrosilicon alloys, silicon-chromium alloys, and other products. The carbonaceous reducing agent inside the furnace is primarily used for the reduction of SiO2 in the raw ore. The main chemical reaction equations are as follows:

[0095] SiO₂ + 2C = Si + 2CO↑

[0096] Based on the above reaction equation, it can be deduced that during the production of a semi-enclosed submerged arc furnace, the CO generated by the reaction overflows uniformly from the furnace opening, and the amount of CO produced is:

[0097] q co =2.22H ico ·ω·Q h

[0098] During production in a semi-enclosed submerged arc furnace, there is a direct combustion loss of carbonaceous reducing agent at the furnace opening. Taking 10% of the fixed carbon as the loss, the amount of carbonaceous reducing agent participating in combustion is:

[0099] When coal is used as a reducing agent, q c1 =0.2H ic ·ω·Q h ;

[0100] When coke is used as a reducing agent, q c2 =0.13H ic ·ω·Q h ;

[0101] Based on obtaining the maximum Q max If q is the target, then select q directly. c1 The value of the expression, that is:

[0102] q c =0.2H ic ·ω·Q h

[0103] The generated CO and the lost reducing agent are assumed to be completely combusted, i.e., the combustion factor is set to 1. Combustion is considered only for the two fuels mentioned above; other combustibles such as wood blocks, charcoal, and electrode oxidation are ignored.

[0104] Among them, the flame burning area is That is, 0.785(Φ+0.7) 2 The formula for calculating the average design fire load density per unit time within the combustion space is as follows:

[0105]

[0106] Because the fume hood of an industrial silicon submerged arc furnace is in a state of thermal equilibrium and stability, it contains not only combustible materials but also a temperature field in thermal equilibrium, with the heat exchange between the large-area hot material and the leaking air entering the furnace being the most significant. Therefore, the thermal radiation load density between the material surface and the amount of leaking air cannot be ignored.

[0107] The coefficient 1.25 in the above formula is the radiation coefficient considered when the heated walls and material surface inside the furnace radiate heat to the air initially entering the furnace at t'=40℃ at a stable temperature of T=600℃, and the upper limit value of 1.25 is taken. That is, the temperature field inside the fume hood is stable at 600℃, that is, the temperature of the inner wall of the fume hood, the temperature of the flue gas, and the temperature of the introduced ambient air after heating are all equal.

[0108] Semi-enclosed submerged arc furnaces are most typically used in industrial silicon production, and the production process involves operations such as simmering, furnace tamping, and material handling. Simmering is a routine operation in semi-enclosed submerged arc furnace production; all furnace doors except the air inlet are closed, and no material surface maintenance is performed during this period. During simmering, a crust forms on the material surface inside the furnace, hindering the uniform escape of gas. At this time, the thermal efficiency, electrical efficiency, and reaction rate below the material surface are optimal, which is beneficial for smelting. When the CO gas generated by reduction accumulates to a certain level inside the furnace, furnace tamping and material handling equipment are used to periodically break up the material layer to release the reducing gas. Therefore, the production process of a semi-enclosed submerged arc furnace is a process of periodic accumulation and release of reducing gas inside the furnace.

[0109] After the initial smoldering, during the furnace tamping and material handling operations, the reducing gas CO produced by the reaction is burned relatively concentratedly at the furnace opening. The flue gas during the initial smoldering process mainly consists of a small amount of overflowing CO combustion products and ambient air entering through the door gaps. The flue gas volume differs significantly between the two operating conditions, indicating different combustion rates of the combustibles. The heat release rate during the concentrated combustion process is much greater than Q. P .

[0110] This invention aims to calculate the maximum flue gas volume. It assumes that no reducing gas overflows from the material surface during the smoldering period, and that the reducing gas released after smoldering is concentrated and burned at the furnace mouth until flashover occurs. This is considered the combustion research stage. The amount of CO produced during the smoldering period is used in the calculation to obtain the maximum combustible heat release rate during flashover, i.e., the maximum fire load density Q during flashover. max Calculate using the following formula:

[0111]

[0112] Finally, q co and q c Substituting the calculation formula into the above, we obtain Q in step one. max The calculation formula.

[0113] Step 2: Obtain the theoretical time t0 for the complete combustion of CO released during the tamping and charging operations of the semi-enclosed submerged arc furnace and the reducing agent participating in combustion at the furnace opening, in minutes.

[0114]

[0115] In the formula: q t Design fire load density for the room, MJ / ㎡.

[0116] Specifically, the formula for calculating the theoretical time t0 is:

[0117]

[0118] In the formula q tFire load density for a semi-enclosed submerged arc furnace, in MJ / m²; η is the ventilation coefficient, in m³. 1 / 2 .

[0119] According to fire combustion theory, the higher the fire load density per unit furnace, the greater the fire heat release rate, and the more flue gas produced, the greater t0 should be. Therefore, q t =Q Pmax .

[0120] According to formula (6.1.3-2) in the "Technical Specification for Fire Protection of Steel Structures in Buildings",

[0121] The formula in the aforementioned specification uses a coefficient of 0.53, which refers to the actual ventilation opening data under conditions of window breakage during flashover, taking into account the relative coefficient of the irregular hole generated by the window explosion to the window size under the destructive force of the fire. However, for industrial silicon production, the ventilation opening size and location are fixed, and the actual area of ​​the ventilation opening during combustion is the effective ventilation area. Therefore, this formula converts the 0.53 coefficient to 1, i.e.,

[0122]

[0123] In the formula: A v The area of ​​all ventilation openings inside a semi-enclosed electric arc furnace is shown in square meters.

[0124] h represents the height of the ventilation opening inside the semi-enclosed electric arc furnace, in meters (m).

[0125] A t This is the sum of the areas of the side walls and top of the fume hood, expressed in square meters (㎡).

[0126] The ventilation openings of the semi-enclosed submerged arc furnace include: furnace doors A located around the furnace for furnace operation. v1 The area of ​​the gap in the smoke hood is A v2 A ring-shaped vent at the top of the fume hood v3 and the annular gap A between the furnace opening and the inner wall of the fume hood v4 The area A of the furnace perimeter air inlets evenly distributed along the lower part of the outer perimeter of the fume hood v5 ;

[0127] The equivalent heights of the ventilation openings in a semi-enclosed submerged arc furnace are as follows: h is the height of the furnace door around the furnace for tamping operation. v1 The width of the gap in the smoke hood is h v2 The width h of the annular vent at the top of the fume hood v3 and the width h of the annular gap between the furnace opening and the inner wall of the fume hood v4 Furnace perimeter air inlet height h v5 ;

[0128] Right now:

[0129] The ignition range of the semi-enclosed submerged arc furnace almost covers the entire area of ​​the furnace opening, except in A. v4 Since there is no combustible material burning, the ignition surface of the furnace opening inside the electric arc furnace hood is not included in A. t A t This is the sum of the areas of the sidewalls and top of the fume hood of a semi-enclosed submerged arc furnace, calculated using the following formula:

[0130]

[0131] In the formula: D is the inner diameter of the fume hood, in meters;

[0132] H represents the net height of the fume hood, in meters (m).

[0133] The formula for calculating the ventilation coefficient η during flashover in a semi-enclosed submerged arc furnace after ramming and charging is as follows:

[0134]

[0135] The ventilation coefficient η and the maximum fire load density during flashover are used. Pmax Substituting the calculation formula into the above, we get:

[0136]

[0137] Finally, the formula for calculating the theoretical time t0 in step two is obtained.

[0138] Step 3: Calculate the maximum heat release rate Q during the flashover stage of the semi-enclosed submerged arc furnace after the furnace tamping and charging operations. max The unit is kW.

[0139] Specifically, the combustion at the furnace opening of a semi-enclosed submerged arc furnace is a relatively small ignition space compared to a fire of similar scale, exhibiting characteristics of unsteady-state combustion. Therefore, a t (likely referring to a specific method or technique) can be used. 2 This can be expressed using a fire simulation model: Q = αt 2 ,

[0140] In the formula: Q is the heat release rate of the fire, in kW;

[0141] α is the growth coefficient of fire heat release rate, with units of kW / s. 2 This calculation takes into account the characteristics of the substances involved in combustion and selects the rapid fire growth coefficient in the fire development stage, which is taken as 0.04689.

[0142] t is the time when the fire occurs, in seconds. To obtain the maximum fire heat release rate, it is set that all combustibles at the furnace opening are completely burned within the heat release time t, i.e., t = t0.

[0143] In step one, Q max q co qc Substituting the calculation formulas for t and t0 in step two into the formulas for t... 2 From the fire simulation model described, we can summarize as follows:

[0144]

[0145] Because the semi-enclosed submerged arc furnace is in a stable state of heat flow balance, the sum of the heat release rate of the combustible material at the furnace opening, the heat carried away by the equipment cooling medium, and the heat loss rate carried away by the heat exchanger on the outer surface of the equipment is needed to maintain balance with the sum of all the electrical and reactive heat inputs into the furnace. The outer surface temperature of the submerged arc furnace equipment is very low, and the heat radiated to the outside is negligible compared to the large base heat input. The circulating cooling water system of the submerged arc furnace equipment is centrally located at the furnace opening and the core reaction zone, which will carry away a certain amount of heat Q. S .

[0146] Based on preliminary calculations using current heat balance data for semi-enclosed submerged arc furnaces, it is assumed that the heat loss rate carried away by the circulating water system is Q. S Then Q S The maximum value is less than 1 / 4 of Q. Since the goal is to obtain the calculated value of the maximum flue gas volume, Q is set as follows: S = 1 / 4Q, the total heat release rate Q in the furnace max =Q+Q S Therefore, the formula for calculating the total heat release rate inside the furnace is as follows:

[0147]

[0148] The maximum heat release rate Q during the detonation stage in step three is obtained by sorting. max The calculation formula, namely

[0149]

[0150] Similarly, in order to obtain the calculated value of the maximum flue gas volume, it is assumed that the total heat release rate Q in the furnace is... max All the heat is carried away by the flue gas, and a steady state is reached at 600℃. Based on this, the specific heat capacity of the flue gas at this point is approximately 1214 J / (kg·℃) and the flue gas density is approximately 0.40 kg / m³. 3 Then the flue gas mass flow rate M, in kg / h, and the volumetric flow rate G, in m³ / h, are given. 3 The relationship for / h is:

[0151]

[0152] In the formula: D is the inner diameter of the fume hood, in meters;

[0153] H represents the net height of the fume hood, in meters (m).

[0154] h represents the equivalent height of various ventilation openings in the semi-enclosed electric arc furnace hood, in meters.

[0155] A v The area of ​​various ventilation openings in a semi-enclosed electric arc furnace fume hood is shown in square meters.

[0156] n is the simmering time coefficient;

[0157] ω represents the percentage of Si element content in the product produced by the semi-enclosed submerged arc furnace, in %;

[0158] Q h The output of a semi-enclosed submersible arc furnace is expressed in t / h.

[0159] φ is the furnace diameter, in meters.

[0160] The calculated flue gas volume G is the flue gas volume under the operating condition of a semi-enclosed submerged arc furnace without considering pressure differences. The conversion to the standard flue gas volume G0 is based on the calculation formula: The unit is Nm 3 / h. This yields the upper limit of the optimal value for selecting the flue gas volume of a semi-enclosed submerged arc furnace using the excess air coefficient method.

[0161] The relationship between flue gas mass flow rate M and volumetric flow rate G shows that the flue gas volume of a semi-enclosed submerged arc furnace based on the combustion angle is directly related to the product positioning, operating habits, and design parameters of the fume hood. Specifically, the fume hood design must ensure that the flue gas volume obtained using the fire simulation calculation method based on the combustion angle described above can be effectively collected and discharged.

[0162] Furthermore, the critical heat release rate at the time of flashover, based on the calculation results in step three, can be verified using the following formula:

[0163] At this point, the fire heat release rate is set to its maximum value. After flashover within the space, combustion continues stably without any external spread. Flashover combustion is ventilation-controlled, meaning the ventilation and smoke extraction systems have no impact on combustion within the space. The heat release rate remains at its maximum value. The data calculated using this method is then used to apply the relationship between flue gas mass flow rate M and volumetric flow rate G to derive the flue gas volume of the semi-enclosed submersible arc furnace. The calculation results from both methods are essentially consistent.

[0164] The following is an example of smoke volume calculation based on fire simulation:

[0165] Semi-enclosed submerged arc furnaces are most typically used for producing industrial silicon products. This calculation example uses a 33MVA industrial silicon semi-enclosed submerged arc furnace, currently the largest capacity in the industry, to calculate the flue gas volume.

[0166] Step 1:Obtain the average fire load density Q per unit time for a 33MVA industrial silicon semi-hermetic arc furnace. Pmax .

[0167] The Si element content percentage (ω) in industrial silicon products is 99%.

[0168] Production Q h It is 2.08 t / h.

[0169] The furnace diameter Φ is 7.1m.

[0170] The amount of CO produced per hour q c0 Approximately 4.58 t / h.

[0171] The reducing agent is selected as whole coal, and the coal combustion rate is q. c Approximately 0.42 t / h.

[0172] The flame burning area is A = 51.5m². 2 .

[0173] The average design fire load density Q of combustibles per unit time inside the smoke hood P =442.2MJ / m 2 .

[0174] The simmering time coefficient n is set to 1, and the simmering time t1 is 1 hour.

[0175] The maximum fire load density Q during flashover occurs when a 33MVA industrial silicon submerged arc furnace undergoes furnace tamping and charging operations. Pmax =798.0 MJ / m 2 Flashover occurs after 1 hour of simmering in an industrial silicon submerged arc furnace. It is assumed that during the simmering stage, all combustible gases accumulate below the material layer without overflow. The heat release rate of the combustibles is at its maximum when flashover occurs. It is worth noting that in actual production, the rate of CO overflowing from the material surface during simmering is relatively low, and it does not all accumulate below the material layer. The above assumptions are only to obtain the maximum amount of combustible material participating in combustion, thereby calculating the maximum fire load density.

[0176] Step Two: The theoretical time t0 (min) for the complete combustion of CO released during the tamping and charging operations of a 33MVA industrial silicon semi-enclosed submerged arc furnace and the reducing agent participating in combustion at the furnace mouth was obtained.

[0177] Design fire load density q inside the electric arc furnace t =Q pmax =798.0MJ / ㎡.

[0178] The parameters of the ventilation opening for a 33MVA semi-enclosed submerged arc furnace include:

[0179] The furnace doors around the furnace for operation are approximately 3.6 × 1.7 m in size, totaling 3 doors, A.v1 =18.36㎡, the height h of the furnace door for furnace operation around the furnace is 18.36㎡. v1 =1.7m.

[0180] The gap in the fume hood only considers the gap at the small furnace door, which is approximately 2.9m x 1.2m in size. The area of ​​the gap is A. v2 =0.11㎡, width of the smoke hood gap h v2 =0.04m.

[0181] A ring-shaped vent at the top of the fume hood v3 = 52.82㎡, ventilation opening width h v3 =1.77m.

[0182] Annular gap A between furnace opening and inner wall of fume hood v4 = 12.98㎡, annular gap width h v4 =0.38m.

[0183] The area of ​​the furnace perimeter air inlets A is evenly distributed along the lower part of the outer perimeter of the fume hood. v5 =10.61㎡, height h of the furnace perimeter air inlet v5 =0.3m.

[0184] The space where the combustion takes place is the cylindrical space of the fume hood, with D = 11.26m and H = 3.35m.

[0185] The sum of the wall surfaces of the semi-enclosed electric arc furnace hood, A t =217.97㎡.

[0186] The ventilation coefficient η was calculated to be 0.5 when the semi-enclosed electric arc furnace experienced flashover after tamping and packing.

[0187] The above ventilation coefficient η and the design fire load density Q inside the electric arc furnace are used as examples. pmax Substituting into the formula for the theoretical time t0, the flashover phenomenon generated by the tamping and packing operations of the industrial silicon submerged arc furnace is calculated, and the theoretical burnout time of all combustibles is t0 = 16.6 min = 996 s.

[0188] Step 3: The maximum heat release rate during the flashover stage of a 33MVA industrial silicon semi-enclosed submerged arc furnace after ramming and charging operations was calculated.

[0189] Substitute t0 into t above 2 Fire simulation model, calculate t 2 The fire growth heat release rate of the fire simulation model is Q = 46504kW, which is equivalent to Q = 167416MJ / h.

[0190] Considering that the 33MVA industrial silicon semi-enclosed submerged arc furnace is in a stable state of heat flow balance, the sum of the heat release rate of the combustible material at the furnace opening, the heat carried away by the equipment cooling medium, and the heat loss rate carried away by the heat exchanger on the outer surface of the equipment is needed to maintain balance with the sum of all the electrical heating and reaction heat input into the furnace. The heat loss rate carried away by the circulating water system of the submerged arc furnace is Q. S Then Q S The maximum value is taken as 1 / 4 of Q. Calculate Q. max =209270MJ / h.

[0191] Similarly, for the purpose of obtaining the calculated value of the maximum flue gas volume, it is assumed that the total heat release rate Q in the furnace is... max All the heat is carried away by the flue gas, and a steady state is reached at 600℃. Based on this, the specific heat capacity of the flue gas at this point is approximately 1214 J / (kg·℃), and the flue gas density is approximately 0.40 kg / m³. 3 The volumetric flow rate G of the flue gas from a 33MVa industrial silicon semi-enclosed submerged arc furnace is 760934 m³. 3 / h.

[0192] Furthermore, the calculation results for G above are further verified, specifically, the critical heat release rate Q at the time of flashover is verified. fo =153203MJ / h, Q fomax =191503MJ / h, then the volumetric flow rate of flue gas from a 33MVA industrial silicon semi-enclosed submerged arc furnace is G' = 760934m³. 3 / h, the results of the two calculation methods are consistent.

[0193] Converting the flue gas volume of a semi-enclosed submerged arc furnace to standard flue gas volume G without considering pressure differences. O Therefore, the flue gas volume of a single 33MVA industrial silicon submerged arc furnace is approximately 218,000 to 238,000 Nm³ under standard conditions. 3 The result, calculated at / h, is consistent with the traditional method for calculating the peroxide coefficient of flue gas volume and represents the maximum flue gas volume during production. This indicates that applying combustion theory to calculate the flue gas generation at the furnace mouth of an industrial silicon submerged arc furnace has a certain degree of accuracy.

[0194] As can be seen from the above calculation process, all parameters were selected to obtain the maximum flue gas volume calculation result and to take into account production fluctuations. Therefore, the flue gas volume of 225,000 Nm3 / h is preferred as the upper limit of the flue gas volume of a single 33MVA industrial silicon submerged arc furnace. Due to different natural conditions at the construction site, the flue gas volume will be less than this calculated value due to factors such as altitude and temperature.

[0195] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for calculating flue gas volume in a semi-enclosed submerged arc furnace based on fire simulation, characterized in that: The average combustible product generation and combustion conditions during the production of the submerged arc furnace are defined as the stable stage of combustion at the furnace mouth. The furnace conditions of stoking and charging are defined as the flashover stage of combustion at the furnace mouth. The period from the stable stage to the flashover stage is selected as the research interval for combustion at the furnace mouth of the semi-enclosed submerged arc furnace. Using the combustion conditions at this furnace mouth as the basic model, the specific process of calculating the flue gas volume during the production process of the semi-enclosed submerged arc furnace is as follows: Step 1: Obtain the average fire load density Q per unit time during the furnace tamping and material handling operations after the semi-enclosed submerged arc furnace has been quenched. Pmax The unit is MJ / ㎡. In the formula: n is the simmering time coefficient, which is the ratio of simmering time t1 to unit time; ω represents the percentage of Si element content in the product produced by the semi-enclosed submerged arc furnace, in %; Q h The output of a semi-enclosed submersible arc furnace is expressed in t / h. H ico This refers to the calorific value of CO combustion, expressed in MJ / kg. H ic This represents the calorific value of carbonaceous reducing agents, expressed in MJ / kg. d is the diameter of the combustion surface at the furnace opening, d = Φ + 0.7, in meters; Step 2: Obtain the theoretical time t0 for the complete combustion of CO released during the tamping and charging operations of the semi-enclosed submerged arc furnace and the reducing agent participating in combustion at the furnace opening, in minutes. In the formula: q t Design fire load density for the room, MJ / ㎡; D is the inner diameter of the fume hood, in meters (m). H represents the net height of the fume hood, in meters (m). Φ is the furnace diameter, in meters (m). h represents the equivalent height of various ventilation openings in the semi-enclosed electric arc furnace hood, in meters. A v The area of ​​various ventilation openings in a semi-enclosed electric arc furnace fume hood is shown in square meters. Step 3: Calculate the maximum heat release rate Q during the flashover stage of the semi-enclosed submerged arc furnace after the furnace tamping and charging operations. max The unit is kW. To obtain the calculated value of the maximum flue gas volume, it is assumed that the total heat release rate Q in the furnace is... max All the corresponding heat is carried away by the flue gas, and a steady state is reached at 600℃. Based on the specific heat capacity and density of the flue gas at this point, the mass flow rate M (kg / h) and volumetric flow rate G (m³) are calculated. 3 The relationship for / h is: In the formula: M is the mass flow rate of flue gas from a semi-enclosed submerged arc furnace, in kg / h; ρ is the density of flue gas at 600℃, in kg / m³. 3 ; C is the specific heat capacity of the flue gas, expressed in J / (kg·℃); The calculated G is the maximum flue gas flow rate of the semi-enclosed submerged arc furnace. By converting the maximum flue gas flow rate to standard conditions, the upper limit of the optimal value for selecting the flue gas flow rate of the semi-enclosed submerged arc furnace using the excess air coefficient method is obtained.

2. The method for calculating flue gas volume of a semi-enclosed submerged arc furnace based on fire simulation according to claim 1, characterized in that: In step one, based on the reaction equation where the carbonaceous reducing agent in the semi-enclosed submerged arc furnace is mainly used for the reduction of SiO2 in the raw ore, it is deduced that during the production of the semi-enclosed submerged arc furnace, the CO generated by the reaction overflows uniformly from the furnace opening, and the amount of CO generated is: what co =2.22H ico ·ω·Q h During production in a semi-enclosed submerged arc furnace, there is a direct combustion loss of carbonaceous reducing agent at the furnace opening. Taking 10% of the fixed carbon as the loss, the amount of carbonaceous reducing agent participating in combustion is: When coal is used as a reducing agent, q c1 =0.2H ic ·ω·Q h ; When coke is used as a reducing agent, q c2 =0.13H ic ·ω·Q h ; Based on obtaining the maximum Q max If q is the target, then select q directly. c1 The value of the expression, that is: what c =0.2H ic ·ω·Q h The generated CO and the burned-out reducing agent are assumed to be completely combusted, i.e., the combustion factor is set to 1. Among them, the flame burning area is That is, 0.785(Φ+0.7) 2 The formula for calculating the average design fire load density per unit time within the combustion space is as follows: Based on the objective of calculating the maximum flue gas volume, this study assumes that no reducing gas overflows from the material surface during the smoldering period, and that the reducing gas released after smoldering is concentrated and burned at the furnace mouth until flashover occurs. This is considered the combustion research phase. The amount of CO produced during the maximum smoldering period is used in the calculation to obtain the maximum combustible heat release rate during flashover, i.e., the maximum fire load density Q during flashover. max Calculate using the following formula: Finally, q co and q c Substituting the calculation formula into the above, we obtain Q in step one. max The calculation formula.

3. The method for calculating flue gas volume of a semi-enclosed submerged arc furnace based on fire simulation according to claim 1, characterized in that: In step two, the formula for calculating the theoretical time t0 is: In the formula: q t Fire load density for design of semi-enclosed submerged arc furnace, MJ / m²; η is the ventilation coefficient, in meters. 1 / 2 ; Since a higher fire load density per unit furnace leads to a higher fire heat release rate and a greater volume of flue gas produced, t0 should also be at its maximum. Therefore, q t =Q pmax ; in, In the formula: A v The area of ​​all ventilation openings inside a semi-enclosed electric arc furnace is shown in square meters. h is the equivalent height of the ventilation opening inside the semi-enclosed electric arc furnace, in meters. A t This is the sum of the areas of the side walls and top of the fume hood, in square meters (㎡). The ventilation openings of the semi-enclosed submerged arc furnace include: furnace doors A located around the furnace for furnace operation. v1 The area of ​​the gap in the smoke hood is A v2 A ring-shaped vent at the top of the fume hood v3 and the annular gap A between the furnace opening and the inner wall of the fume hood v4 The area A of the furnace perimeter air inlets evenly distributed along the lower part of the outer perimeter of the fume hood v5 ; The equivalent heights of the ventilation openings in a semi-enclosed submerged arc furnace are as follows: h is the height of the furnace door around the furnace for tamping operation. v1 The width of the gap in the smoke hood is h v2 The width h of the annular vent at the top of the fume hood v3 and the width h of the annular gap between the furnace opening and the inner wall of the fume hood v4 Furnace perimeter air inlet height h v5 ; Right now: The sum of the sidewall and top areas of the fume hood of a semi-enclosed electric arc furnace, A t The calculation formula is: In the formula: D is the inner diameter of the fume hood, in meters; H represents the net height of the fume hood, in meters (m). The formula for calculating the ventilation coefficient η during flashover in a semi-enclosed submerged arc furnace after ramming and charging is as follows: The ventilation coefficient η and the maximum fire load density during flashover are used. pmax Substituting the calculation formula into the above, we get: Finally, the formula for calculating the theoretical time t0 in step two is obtained.

4. The method for calculating flue gas volume of a semi-enclosed submerged arc furnace based on fire simulation according to claim 1, characterized in that: In step three, the combustion at the furnace opening of the semi-enclosed submersible furnace can be carried out using t 2 This can be expressed using a fire simulation model: Q = αt 2 , In the formula: Q is the heat release rate of the fire, in kW; α is the growth coefficient of fire heat release rate, with units of kW / s. 2 Take 0.04689; t is the time when the fire occurs, in seconds. To obtain the maximum fire heat release rate, it is set that all combustibles at the furnace opening are burned out within the heat release time t, i.e., t = t0. In step one, Q max q co q c Substituting the calculation formulas for t and t0 in step two into the formulas for t... 2 From the fire simulation model described, we can summarize as follows: Based on preliminary calculations using current heat balance data for semi-enclosed submerged arc furnaces, it is assumed that the heat loss rate carried away by the circulating water system is Q. S Then Q S The maximum value is less than 1 / 4 of Q. Since the goal is to obtain the calculated value of the maximum flue gas volume, Q is set as follows: S = 1 / 4Q, the total heat release rate Q in the furnace max =Q+Q S Therefore, the formula for calculating the total heat release rate inside the furnace is as follows: The maximum heat release rate Q during the detonation stage in step three is obtained by sorting. max The calculation formula.

5. The method for calculating flue gas volume of a semi-enclosed submerged arc furnace based on fire simulation according to claim 4, characterized in that: In step three, the critical heat release rate at which flashover is achieved can be verified using the following formula: At this point, the fire heat release rate is set to its maximum value, and after flashover in the space, combustion continues stably without any external spread. The data calculated based on this is then used to derive the flue gas volume calculation value of the semi-enclosed submerged arc furnace by applying the relationship between the flue gas mass flow rate M and the volume flow rate G. The calculation results of the two methods are basically consistent.

6. The method for calculating flue gas volume of a semi-enclosed submerged arc furnace based on fire simulation according to claim 1, characterized in that: In step three, the calculated flue gas volume G is the flue gas volume under the operating conditions of a semi-enclosed submerged arc furnace without considering pressure differences. The conversion to the standard flue gas volume G0 is based on the following formula: The unit is Nm 3 / h.

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