Method of manufacturing polysilicon particles

Abstract

This invention relates to a method for manufacturing polycrystalline silicon particles in a fluidized bed reactor, wherein seed particles are continuously supplied and fluidized in a fluidized bed by means of an airflow, wherein the fluidized bed region is heated by a heating device, wherein elemental silicon is deposited on the seed particles to form polycrystalline silicon particles by supplying a feed airflow comprising hydrogen and silane and / or halosilane, and wherein, in a continuous process, the silicon particles are discharged from the fluidized bed reactor as a product stream, wherein the fluidized bed temperature T is a response variable. WS The temperature T of the waste gas flow (Equation (I)) from the fluidized bed region is determined by the mass and energy balance of equilibrium range I and / or equilibrium range II. Abgas,WS The equilibrium range I is composed of the following: the enthalpy of the supply gas stream (Equation (III)) (Equation (II)), the enthalpy of the seed particle stream entering the fluidized bed region (Equation (V)) (Equation (IV)), the enthalpy of the product stream (Equation (VII)) (Equation (VI)), the enthalpy of the waste gas mass stream from the fluidized bed (Equation (IX)) (Equation (VIII)), and the reaction enthalpy Δ. R H 23 The heat output Q of the heating device 20 The energy Q removed from the reactor in the fluidized bed region of the reaction zone 24 Furthermore, the enthalpy of the waste gas flow in equilibrium range I (Equation (VIII)) is given by equation (Equation (IX)). Equilibrium range II consists of the following components: the enthalpy of the seed particle flow (Equation (V)) entering the fluidized bed region (Equation (IV)), the enthalpy of the seed particle flow (Equation (XI)) entering the reactor (Equation (X)), the enthalpy of the waste gas mass flow (Equation (I)) from the fluidized bed region (Equation (VIII)), the enthalpy of the waste gas flow (Equation (XIII)) from the reactor (Equation (XIII)), and the energy Q removed from the reactor in the region above the fluidized bed. 25 Furthermore, the enthalpy of the waste gas flow in the equilibrium range II (Equation (VIII)) is given by equation (Equation (XIV)). The temperature T of the fluidized bed WS The equation (XV) gives the result, where (I) = exhaust gas mass flow rate, c p,22 = The heat capacity of the exhaust gas flow, wherein according to the response variable T WS At least the heat output Q 20 It is controlled as a manipulated variable, so that Q is achieved per kilogram of silicon in the fluidized bed. 20 In the range of 0.5 to 3 kW.

Description

Technical Field

[0001] This invention relates to a method for manufacturing polycrystalline silicon particles in a fluidized bed reactor, wherein the fluidized bed temperature T is a response variable. WS The waste gas flow from the fluidized bed region was determined by the mass and energy balance of equilibrium range I and / or equilibrium range II. Temperature T offgas,WS .

[0002] Polycrystalline silicon particles (hereinafter referred to as particles) are generated in a fluidized bed reactor (also known as a moving bed reactor). This is achieved by fluidizing the silicon seed particles with an airflow in a fluidized bed, which is heated to a high temperature by a heating device. The addition of silicon-containing reactive gases causes a deposition reaction on the surface of the heated particles, thereby depositing elemental silicon onto the seed particles. This results in an increase in the diameter of the seed particles. Periodically removing the particles with increased diameter and adding more seed particles allows the process to run continuously. Silicon-containing reactive gases that can be used include, for example, halogen compounds (e.g., chlorosilanes or bromosilanes), silanes (SiH4), and mixtures of these gases with hydrogen. The deposition of elemental silicon produces waste gases consisting of unconverted reactive gases and gaseous byproducts, particularly halosilanes.

[0003] Deposition processes and apparatus for performing these processes are well known. Reference may be made herein to, for example, EP 1 990 314A2 and EP 2 662 334 A1.

[0004] The temperature in a fluidized bed (fluidized bed temperature) typically defines fundamental product and process parameters. Precise control of the fluidized bed temperature is essential for optimized product quality and economical process management.

[0005] Furthermore, an ideal, constant low chlorine content is generally crucial for particle performance in subsequent applications. For example, good performance can be achieved when the splashing effect during the single-crystal pulling process can be minimized or avoided. In principle, chlorine is the primary impurity in particle manufacturing. The chlorine content generated in the particles depends on the process conditions of the fluidized bed reactor, particularly the fluidized bed temperature.

[0006] Fluidized bed temperature also affects dust formation, specific energy consumption, and reactor operating time, thus seeking precise and ideal instantaneous temperature control.

[0007] However, directly measuring fluidized bed temperature using thermocouples, for example, is disadvantageous because the presence of thermocouples typically has a negative impact on process and / or product quality. Silicon can be continuously deposited on thermocouples, thus limiting process run time. Products can also be contaminated by physical and chemical processes on the thermocouple surface. For example, a fluidized bed reactor with encapsulated pyrometers or thermocouples disposed in the reaction space is described in EP 2 514 521 A1.

[0008] EP 2 653 446 A2 describes a method for particle manufacturing in which the concentration of HCl in the exhaust gas is measured as a response variable and the introduction rate of fresh seed particles and the output of the heating device are controlled as manipulated variables. A pyrometer can also be used to measure the temperature.

[0009] Measuring fluidized bed temperature using a pyrometer is often problematic because the beam path is disrupted by dust formation. This makes precise temperature-dependent reactor control impossible.

[0010] Therefore, the object of the present invention is to provide a method that allows for the undisturbed measurement of fluidized bed temperature.

[0011] This objective is achieved by a method for producing particles in a fluidized bed reactor, wherein in a fluidized bed region, continuously supplied seed particles are fluidized by means of an airflow, wherein the fluidized bed region is heated via a reactor wall by a heating device, wherein the supply of a feed airflow comprising hydrogen and silanes and / or halosilanes causes elemental silicon to deposit on the seed particles to form particles, and wherein, in a continuous process, the particles are discharged from the fluidized bed reactor as a product stream, wherein the fluidized bed temperature T is a response variable. WS The waste gas flow from the fluidized bed region was determined by the mass and energy balance of equilibrium range I and / or equilibrium range II. Temperature T offgas,WS .

[0012] The equilibrium range I is formed by the following

[0013] -Feed airflow enthalpy

[0014] - Seed particle flow entering the fluidized bed region enthalpy

[0015] -Product Flow enthalpy

[0016] -Exhaust gas mass flow from fluidized bed enthalpy

[0017] - enthalpy of reaction Δ R H 23 ,

[0018] -Heat output Q of the heating device 20 ,

[0019] - Energy Q removed from the reactor in the fluidized bed region 24 ,

[0020] Enthalpy of exhaust gas flow in equilibrium range I It is given by equation (10).

[0021]

[0022] Balance range II is formed by the following:

[0023] - Seed particle flow entering the fluidized bed region enthalpy

[0024] - Seed particle stream entering the reactor enthalpy

[0025] -Exhaust gas mass flow from the fluidized bed region enthalpy

[0026] - Exhaust gas flow from the reactor enthalpy

[0027] - Energy Q25 removed from the reactor in the region above the fluidized bed.

[0028] Enthalpy of exhaust gas flow in equilibrium range II It is given by equation (11).

[0029]

[0030] Fluidized bed temperature T WS Therefore, equation (12) gives the result.

[0031]

[0032] c p，22 It is the heat capacity of the exhaust gas flow.

[0033] Based on the response variable T determined in this way WS Therefore, at least the heat output Q 20 It is controlled as a manipulated variable, so that Q of silicon per kilogram in the fluidized bed 20 Within the range of 0.5 to 3 kW, preferably 1 to 2 kW, and particularly preferably 1.3 to 1.6 kW. Typically, when below the target temperature T...WS When the temperature exceeds the target temperature T, the heat output increases, and when the temperature exceeds the target temperature T... WS At that time, heat output decreases.

[0034] The goal of control is economically optimal process management to ensure constant product quality, particularly regarding chlorine content. The reactor may be affected by disturbance variables (e.g., variations in fluidization of the fluidized bed due to changes in particle size) and T. WS The chlorine content in the product may change due to the influence of the product.

[0035] The main manipulated variable used for control is T. WS Its control is based on the energy balance corresponding to the exhaust gas temperature from the fluidized bed (primary control). In case of deviation, control is achieved by changing the manipulated variable. Q 20 Used as a manipulation variable. If T is not reached... WS If the target value is reached, then Q is increased. 20 If T WS If the target value is exceeded, reduce Q. 20 .

[0036] To explain equilibrium ranges I and II, Figure 1 The general structure of the fluidized bed reactor 200 is shown first. It includes a reaction vessel 1 containing a reaction tube 2, which may optionally be segmented internally. The reactor tube 2 is sandwiched between the reactor top 13 and the reactor bottom 15. A gap 5 is located between the inner wall 4 of the reaction vessel 2 and the outer wall 3 of the reaction tube 2. This gap 5 typically contains insulating material and may be filled with an inert gas. The pressure in the gap 5 is typically higher than the pressure inside the reaction tube 2. The reactor interior contains a fluidized bed region 6 and a region 28 above the fluidized bed region 6, which contains the fluidized bed during operation. The fluidized bed region 6 is heated by a heating device 7. Region 28 is an unheated expansion zone, where its cross-sectional area is enlarged compared to the fluidized bed region 6 to prevent particle discharge. A conduit 8 and a nozzle 9 supply fluidizing gas to the reaction tube 2. A conduit 10 and a nozzle 11 supply a reaction gas mixture (feed gas stream) containing hydrogen and silanes and / or halosilanes. The height of the nozzle 11 for supplying the reaction gas mixture may differ from the height of the nozzle 9 for supplying the fluidizing gas. Device 12 supplies seed crystals to reaction tube 2 at the top 13 of the reactor. Finished product particles are removed through product discharge conduit 14 located at the bottom 15 of the reactor. Additionally, at the top 13 of the reactor, waste gas is removed through waste gas discharge conduit 26. Sample streams used for gas chromatography are typically extracted through waste gas discharge conduit 26.

[0037] The reactor operates as follows: Feed gas is supplied to the reactor. The raw material, in the form of silicon particles, is loaded into the reactor and fluidized. During the heating phase, the heat output entering the fluidized bed is increased. Energy is increased until the target value T is reached. WS The reactor is in a steady state. Under this state, the reactor provides optimal product quality while ensuring controlled production over long-term operation. Stable product quality is characterized by a chlorine content in the product within the desired range. If the response variable T... WS If the threshold is exceeded, the reactor may shut down prematurely, for example, due to the sintering of granular particles on the walls. If T WS If the content is below the threshold, it may result in excessively high chlorine content in the product.

[0038] Controlling fluidization in a fluidized bed is essential for effective process management, aiming for longer uptime and lower dust formation. Fluidization is determined by the gas velocity u in the fluidized bed and the minimum fluidization velocity umin. mf The ratio is determined by, and can be adjusted based on pressure and T. WS The Sotter diameter, air intake and composition of particles in the fluidized bed, and the initial fluidization porosity Ψ mf Perform calculations. If the gas velocity is related to u... mf If the gas velocity is too low, the fluidized bed will not be sufficiently fluidized and may form local hot spots, leading to sintering in the fluidized bed. mf If the concentration is too high, the bubble size in the fluidized bed will increase, leading to a higher dust formation rate during the process. For optimal process management, the gas volume and particle size in the fluidized bed are varied by introducing seed particles. S , make u / u mf The ratio remains constant.

[0039] Fluidized bed temperature T WS Calculated using the reactor's energy and mass balance.

[0040] Figure 2 The equilibrium range of the mass balance is shown (dashed rectangle), which forms with... Figure 1 The reactor's equilibrium ranges I and II are based on this. For clarity, conduit 8 and nozzle 9 are omitted. Renaming of reactor components is also avoided. The following material flow rates are in equilibrium:

[0041] -Feed airflow 16:

[0042] - Seed particle stream entering reactor 17:

[0043] -Product Flow 18:

[0044] - Waste gas flow from reactor 19:

[0045] The mass flow rates of the feed gas, seed crystals, and products (particles) are measurable (e.g., by mass flow meter) and therefore known. The composition (silane / chlorosilane mass fraction) of the exhaust gas from the reactor can be measured using gas chromatography. The measurement result is the mass fraction of chlorosilanes (y) based on the total chlorosilane mass flow rate in the exhaust gas. i *([mol i / mol chlorsilane The analysis will be described in detail below.

[0046] The mass flow rates in the product and waste gas streams are calculated using key components and key reactions. The three elements Si, Cl, and H are in equilibrium. If the feed gas contains not only H2 but also SiCl4, SiHCl3, and / or SiH2Cl2, then seven related substances (i = 7) will appear: Si, H2, HCl, SiCl4, SiHCl3, SiH2Cl2, and SiH3Cl. To fully describe the system, four independent reaction equations (j = 7 – 3 = 4) are necessary.

[0047] (I) 4SiHCl3 → 3SiCl4 + 2H2 + Si

[0048] (II) SiHCl3 + H2 → Si + 3HCl

[0049] (III) 2SiHCl3-->SiCl4+SiH2Cl2

[0050] (IV) 2SiH₂Cl₂ --> SiHCl₃ + SiH₃Cl

[0051] Corresponding to these four independent reaction equations, there are four independent key components: SiCl4, SiCl3, SiH2Cl2, and SiH3Cl.

[0052] Degree of reaction ξ i This indicates the progress of partial reactions (I) to (IV). Changes in the amount of substances in the components can be determined by the extent of the reaction.

[0053] Through reactions (IV) and (II), the mass flow rate of chlorosilanes in the waste gas decreases. The mass flow rate of chlorosilanes in the waste gas can be calculated using the degree of reaction and the mass flow rate of chlorosilanes in the feed gas as follows:

[0054] (1)

[0055] The change in the amount of SiCl4 is given by the following formula:

[0056] (2)

[0057] The mass flow rate of SiCl4 in the exhaust gas can be calculated by the mass fraction of SiCl4 in the exhaust gas and the degree of reaction.

[0058] (3)

[0059] For SiCl4, equations (2) and (3) yield the following:

[0060] (4)

[0061] The components SiHCl3, SiH2Cl2, and SiH3Cl can be derived similarly from this equation. This yields a well-defined solvable system of four equations and the calculable extent of four unknown reactions.

[0062] The degree of reaction makes it possible to calculate the mass flow rates of all key components in the exhaust gas. For example, for SiCl4:

[0063] (5)

[0064] Therefore, the individual reaction conversion rate and mass flow rate of all components in the exhaust gas can be calculated.

[0065] Figure 3 Showing about Figure 1 The energy balance of the reactor is divided into balance range I (BI) and balance range II (BII).

[0066] To calculate the energy balance, calculate the mass and energy flows, as well as the enthalpy of reaction, across all equilibrium boundaries. Calculate the fluidized bed temperature T using equilibrium boundaries I and / or II. WS .

[0067] The balance range I (BI) includes:

[0068] -Feed airflow 16:

[0069] -Product Flow 18:

[0070] - Cooling flow 24 (energy removed from the reactor in the fluidized bed region): Q 24

[0071] - Enthalpy of reaction 23: Δ R H 23

[0072] -Heat output of heating device 20: Q 20

[0073] -The stream of seed particles entering fluidized bed 21:

[0074] - Waste gas flow from fluidized bed 22:

[0075] Balance Range II (BII) includes:

[0076] -The stream of seed particles entering fluidized bed 21:

[0077] - Waste gas flow from fluidized bed 22:

[0078] - Seed particle stream entering reactor 17:

[0079] - Waste gas flow from reactor 19:

[0080] - Cooling flow (energy removed from the reactor in the region above the fluidized bed) 25: Q 25

[0081] The enthalpy of the mass flow across the equilibrium boundary as Heat capacity c p,i and temperature T i Function calculation:

[0082] (6)

[0083] The reactor is cooled by a cooling medium (e.g., at the bottom of the reactor) and the surrounding environment. The cooling output through the cooling medium is calculated using the enthalpy change of the cooling medium. If sufficient insulation is available, heat loss to the surrounding environment is negligible. Heat loss to the surrounding environment through convection and radiation can optionally be estimated.

[0084] (7)

[0085] In the case of electric heating, the electrical output is captured. In the case of heating with a heating medium (e.g., combustion gas), the enthalpy change of the heating medium is calculated.

[0086] (8)

[0087] The enthalpy of reaction is calculated by summing the standard enthalpies of formation of the reactants and products. The composition of the reactants and products can be determined by the mass balance described above.

[0088] (9)Δ R H 23 =∑ΔH B,Products-∑ΔH B,reactants

[0089] To calculate T WS The temperature of the waste gas stream from the fluidized bed is calculated through energy balance. Due to the thermal equilibrium in the fluidized bed, the waste gas stream has the same temperature as the fluidized bed. It is also assumed that the waste gas stream from fluidized bed 22 and the waste gas stream from reactor 24 have the same composition. For the seed particle stream entering fluidized bed 21, it is assumed that the stream has the same temperature as the waste gas stream from fluidized bed 22. For simplicity, a quasi-stationary isobaric process can be assumed. The sum of the energy flow, entropy flow, and reaction enthalpy across the equilibrium boundary is 0.

[0090] For equilibrium range I, analyze the enthalpy of the exhaust gas mass flow from the fluidized bed. Conclusion:

[0091] (10)

[0092] For equilibrium range II, analyze the enthalpy of the exhaust gas mass flow from the fluidized bed. Conclusion:

[0093] (11)

[0094] For the exhaust gas mass stream from fluidized bed region 22, the energy balance is analyzed. The composition of the exhaust gas mass stream is known through gas chromatography measurements. The exhaust gas mass stream can be calculated from the degree of reaction of the key reactions. The temperature of the exhaust gas mass stream from the fluidized bed is calculated from the enthalpy of the exhaust gas mass stream based on the energy balance using the average specific heat capacity of the exhaust gas stream.

[0095] (12)

[0096] Heat capacity is calculated as a function of temperature.

[0097] (13)c p,i (T)=a0+a1T+a2T 2 +a3T 3 +a4T 4

[0098] Equation (12) can therefore be solved iteratively.

[0099] In a preferred embodiment of the method, the apparent gas velocity u and the minimum fluidization velocity u can be controlled as another manipulated variable. mf The ratio is used to control the fluidization in the fluidized bed, so that u / u mf Within the range of 1 to 6, 2 to 5 are preferred, and 3 to 4 (secondary regulation) are especially preferred.

[0100] Apparent gas velocity u and minimum fluidization velocity u mfThe ratio is used as a parameter for fluidization in the fluidized bed. It is assumed that the gas composition in the fluidized bed is the same as the exhaust gas composition from the reactor, which is known through mass balance. Mass balance allows for the calculation of the average mass weight. and exhaust gas material flow It became possible.

[0101] The density of the gas in the fluidized bed is calculated using the ideal gas law:

[0102]

[0103] Gas density is used to calculate the apparent gas velocity u in the fluidized bed. u is given by equation (14):

[0104] (14)

[0105] in,

[0106] = Average molar mass of gas in the fluidized bed [kg / mol]

[0107] =Material flow rate of exhaust gas from the fluidized bed [mol / s]

[0108] A = Cross-sectional area of ​​the fluidized bed [m] 2 ]

[0109] ρ Gas = Density of gas in fluidized bed [kg / m³] 3 ]

[0110] And u mf Given by equation (15):

[0111] (15)

[0112] in

[0113] ψ = Fixed bed porosity

[0114] v = viscosity of the gas in the fluidized bed [m 2 / s]

[0115] d S =Souter diameter of particles in a fluidized bed [m]

[0116] Ψ mf = Initial fluidized porosity

[0117] ρ particle = Density of particles in a fluidized bed [kg / m³] 3 ]

[0118] g = 9.81 m / s2 .

[0119] Preferably, in this process, the ratio u / u mf Keep constant. u / u mf The ratio typically depends on temperature, pressure, gas quantity and composition, and particle size in the fluidized bed. At excessively low ratios, u / u... mf To reduce the particle size in a fluidized bed, the feed gas flow rate can be increased and / or the particle size can be reduced by increasing the addition of seed crystals. At excessively high ratios u / u... mf This can reduce the amount of feed gas in the fluidized bed and / or increase the particle size in the fluidized bed by reducing the amount of seed particles added.

[0120] The density of particles in the fluidized bed is preferably between 2.250 and 2.330 g / cm³. 3 Within the range of 2.280 to 2.330 g / cm³, it is particularly preferred. 3 Within the range, especially between 2.320 and 2.330 g / cm³. 3 Within the range.

[0121] The density of silicon particles in a fluidized bed can be determined using helium gas adsorption (specific gravity bottle), preferably using a Porotec Pycnomatic ATC instrument. For example, the sample volume can be 60 mL.

[0122] The density ρ of the gas in the fluidized bed gas Preferably between 0.5 and 2 kg / m 3 Within the range of 0.7 to 1.2 kg / m³, it is particularly preferred. 3 Within the range.

[0123] The porosity ψ of the fixed bed is preferably between 0.3 and 0.36 kg / m³. 3 Within the range, ψ is particularly preferred to be 0.33.

[0124] The casting density ρ of a fixed-bed casting system can be determined according to ISO 967, for example using an apparatus for determining casting density from Landgraf LaborsystemeHLL GmbH. The casting density ρ can be used to calculate the fixed-bed porosity ψ according to formula (16).

[0125] (16)

[0126] Initial fluidized porosity Ψ mf Preferably, it is in the range of 0.33 to 0.4, and particularly preferably 0.37.

[0127] Initial fluidized porosity Ψ mf This can be determined experimentally (see VDI-). [VDI Heat Atlas], version 11, L3.2 und Druckverlust in Wirbelschichten[Forms of flow and pressure loss in fluidized beds]). Ψ mf The initial fluidization point can be determined using the Ergen equation (17):

[0128] (17)

[0129] in,

[0130] Δp: Fluidized bed pressure difference at the initial fluidization point [bara],

[0131] L: Fluidized bed height at the initial fluidization point [m].

[0132] The Sotter diameter of particles in a fluidized bed reactor is preferably in the range of 150 to 10,000 μm, particularly preferably in the range of 500 to 5,000 μm, and especially in the range of 850 to 2,000 μm.

[0133] d S The determination can be performed using silicon particles (particles) obtained as a product, by image analysis using a particle analyzer with dynamic image analysis (e.g., Retsch Technology's CAMSIZER P4, according to ISO 13322-2 dynamische Bildanalyse, measurement range: 30 μm to 30 mm, analysis type: dry measurement of powders and particulates).

[0134] In another embodiment of the method, the amount of seed particles introduced per kilogram of silicon in the fluidized bed (in kilograms) can be controlled as an operating variable, such that it is in the range of 0.01 to 0.05, preferably in the range of 0.02 to 0.03.

[0135] mass flow rate m of seed particles and product flow i Bulk materials can be measured using a continuous online flow system (e.g., Mütec Instruments' MF3000).

[0136] The quality of silicon in the fluidized bed can be continuously measured. For this purpose, the pressure difference Δp between the bottom and top of the reactor is continuously measured (e.g., using an Endress+Hauser electronic differential pressure system Deltabar FMD72).

[0137] Δp=p Bottom -p top

[0138] This pressure difference corresponds to the pressure drop in the fluidized bed. The pressure drop is related to the bed weight (m). bed They are directly proportional. This can be calculated using the following formula:

[0139] in

[0140] m Bed Mass of silicon in the fluidized bed [kg]

[0141] A: Cross-sectional area of ​​the fluidized bed [m] 2 ].

[0142] The temperature T of the fluidized bed WS Preferably, the temperature is in the range of 700°C to 1200°C, particularly preferably in the range of 800°C to 1150°C, and especially in the range of 850°C to 1100°C.

[0143] The chlorine content of the particles is preferably 10-70 ppmw, and particularly preferably 15-40 ppmw.

[0144] The chlorine content in large-volume particles can be determined using instrumental neutron activation analysis (INAA; SEMI PV10). The chlorine content in large-volume particles is measured in ppmw. Alternatively, it can be measured using X-ray fluorescence analysis.

[0145] The composition of the exhaust gas mass flow 22 can be determined using a gas chromatograph.

[0146] All components of the deposition reaction can be detected and quantified in the exhaust gas via online analysis. These components are particularly chlorosilanes, hydrogen chloride, and hydrogen. Available measuring devices include gas chromatographs equipped with flame ionization detectors and thermal conductivity detectors. The composition of chlorosilanes in the exhaust gas required for mass balance is determined. It can be output as the mass fraction i of chlorosilanes based on the total chlorosilane mass flow rate in the exhaust gas.

[0147] The temperatures of cooling, feed gas, and exhaust gas can typically be measured using thermocouples (e.g., type K thermocouples according to DIN EN60584-1, with a measurement range up to 1250°C).

[0148] Mass flow rates (m) of feed gas and cooling stream i It can be determined using a Coriolis mass flow meter (e.g., Endress+Hauser, Promass 83F).

[0149] The preferred mass flow rate of the specific silicon-containing feed gas is 400 to 6500 kg / (h*m). 2 The preferred hydrogen volumetric flow rate is 800 to 4000 Nm³.3 / (h*m 2 ) Specific fluidized bed weight m bed Preferably 500 to 2000 kg / m 2 The preferred rate of introducing specific silicon seed particles is 1 to 40 kg / (h*m). 2 The preferred reactor heating power is 800 to 3000 kW / m³. 2 .

[0150] Electric heating output P electric The output of the secondary side of the factory transformer can be measured according to DIN EN 60076.

[0151] The measurement of these parameters is preferably performed continuously throughout the entire process.

[0152] As the feed gas, trichlorosilane or dichlorosilane and H2 are preferred. The fluidizing gas is preferably hydrogen, argon, nitrogen, or mixtures thereof.

[0153] The feed gas can be introduced into the fluidized bed through one or more nozzles. The local gas velocity at the nozzle outlet is preferably 0.5 to 200 m / s. Based on the total gas volume flowing through the fluidized bed, the concentration of the silicon-containing feed gas component is preferably 5 to 50 mol%, and particularly preferably 15 to 40 mol%.

[0154] The concentration of the silicon-containing feed gas component based on the total feed gas volume before entering the reactor is preferably 5 to 80 mol%, particularly preferably 14 to 60 mol%.

[0155] The absolute reactor pressure is preferably in the range of 1 to 10 bar, and particularly preferably 1.5 to 5.5 bar.

[0156] Figure 1 The structure of the fluidized bed reactor is shown.

[0157] Figure 2 The equilibrium range of mass balance is shown.

[0158] Figure 3 The energy balance ranges I and II are shown. Example

[0159] according to Figure 1 In addition to H2, the fluidized bed reactors are also operated with trichlorosilane or dichlorosilane (see Table 1).

[0160] The examples were conducted in a reactor with a diameter of 400 mm. Table 1 shows the steady-state operating points of the reactor, i.e., the data that remained constant over several hours.

[0161]

[0162] Table 1

[0163] The amounts of chlorosilanes and H2 in the feed gas are based on the cross-sectional area of ​​the reaction zone (fluidized bed). WS (This invention) is based on the fluidized bed temperature calculated according to the invention based on energy balance (see Table II for example).

[0164] T WS The pyrometer measures the fluidized bed temperature. It is installed at the top of the reactor, directly above the fluidized bed. Due to dust formation, the measurement signal is interfered with, and the measured temperature is significantly lower than the temperature T calculated according to the present invention. WS (This invention).

[0165] EP 2 653 446 A2 discloses that the HCl value in exhaust gas can be used to control the Cl value in particulate matter. The HCl value in exhaust gas is obtained based on the chemical equilibrium in a fluidized bed. This chemical equilibrium is a function of pressure, temperature, and the composition of the feed gas.

[0166] Table 1 shows that the Cl value in the particles depends largely on T. WS (This invention), rather than the HCl value in the exhaust gas. Therefore, based on T WS The process control in this invention is linked to improved product quality. If reactor control based on the HCl value in the exhaust gas is affected by changes in reactor pressure, the amount of chlorosilanes entering the reactor or the amount of feed gas can lead to unacceptable enrichment of Cl in the particles.

[0167] The T here WS (In this invention) is determined by the equilibrium range I (normalized to the cross-sectional area of ​​the reactor) (see Table 2).

[0168]

[0169] Table 2

Claims

1. Process for producing polysilicon particles in a fluidized bed reactor, wherein in a fluidized bed region continuously supplied seed particles are fluidized in the fluidized bed by means of a gas stream, wherein the fluidized bed region is heated with a heating device, wherein a feed gas stream comprising hydrogen and silane and / or halosilane is supplied, which leads to the deposition of elemental silicon on the seed particles to form polysilicon particles, and wherein in a continuous process the silicon particles are discharged as product stream from the fluidized bed reactor, wherein as a response variable the fluidized bed temperature T WS is determined by means of a mass and energy balance of the equilibrium range I and / or the equilibrium range II for the offgas stream from the fluidized bed region offgas,WS , wherein the equilibrium range I consists of: - the feed gas stream the enthalpy of the feed gas stream - a stream of seed particles entering the fluidized bed region the enthalpy - the product stream the enthalpy - said exhaust gas mass flow from said fluidized bed the enthalpy - reaction enthalpy Δ R H 23 , - the thermal output Q of the heating device 20 , - energy Q removed from the reactor in the fluidized bed region 24 ; and the enthalpy of the exhaust gas stream of the balance range I is given by equation (10) and wherein the balancing space II consists of the following parts: - the stream of seed particles into the fluidized bed region the enthalpy - the flow of seed particles into the reactor the enthalpy of - the exhaust gas mass flow from the fluidized bed region the enthalpy - a waste gas stream from the reactor the enthalpy - energy Q removed from the reactor in the upper region of the fluidized bed 25 , and the enthalpy of the exhaust gas stream of the balance range II is given by equation (11) wherein the temperature T of the fluidized bed is WS is given by equation (12) c p,22 = the heat capacity of the exhaust gas stream, and wherein the response variable T WS In the range from 700 °C to 1200 °C, and according to T WS , at least the thermal output Q 20 is controlled as a manipulated variable, so that in the fluidized bed Q 20 per kg of silicon is in the range from 0.5 to 3 kW.

2. The method of claim 1, wherein The heat output Q per kilogram of silicon in the fluidized bed 20 In the range of 1 to 2 kW.

3. The method according to claim 1 or 2, characterized in that, As a manipulated variable, the fluidization in the fluidized bed is controlled as a ratio of the superficial gas velocity u to the minimum fluidization velocity u mf wherein u is given by equation (14) mf in the range of 1 to 6 A = cross-sectional area of the fluidized bed [m2] 2 ] p Gas = density of gas in the fluidized bed [kg / m 3 ] and where u mf Given by equation (15): wherein ψ = fixed bed porosity v = viscosity of the gas in the fluidized bed [m 2 / s] d S = the Sauter diameter of the particles in the fluidized bed [m] Ψ mf = initial fluidized porosity p particle = density of the particles in the fluidized bed [kg / m 3 ] g = 9.81 m / s2 2 .

4. The method of claim 3, wherein u / u mf In the range of 2-5.

5. The method according to claim 3 or 4, characterized in that, During the method, u / u mf is kept constant.

6. The method according to claim 3 or 5, characterized in that ρ particle In the range of 2.250 to 2.330 g / cm 3 .

7. The method according to any one of claims 3 to 6, characterized in that ρ gas In the range of 0.5 to 2 kg / m 3 .

8. The method according to any one of claims 3 to 7, characterized in that Ψ is in the range of 0.3 to 0.36 kg / m 3 of 0.3 to 0.36 kg / m 9. The method according to any one of claims 3 to 8, characterized in that Ψ mf In the range of 0.33 to 0.

4.

10. The method according to any one of claims 3 to 9, characterized in that d S in the range of 150 to 10 000 μm.

11. The method according to any of the preceding claims, characterized in that, As operating variable, the seed particle introduction in kg per kg of silicon in the fluidized bed is controlled in the range of 0.01 to 0.

05.

12. The method according to any of the preceding claims, characterized in that, The temperature T of the fluidized bed WS in the range of 800 to 1150 °C.

13. The method according to any of the preceding claims, characterized by The silicon particles have a chlorine content of 10-70 ppmw.

14. The method according to any of the preceding claims, characterized by The composition of the off-gas stream is determined with gas chromatography.

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