Segmented electric heating system

Abstract

The utility model discloses a segmented electric heating system which comprises a mixer, a steam supply system, a primary electric heater, a secondary electric heater, a gas concentration online detection device and a control system, wherein the gas concentration online detection device is used for detecting the gas concentration of a key point; and the control system is used for outputting a control signal according to a detection result of the gas concentration online detection device so as to control the steam supply quantity of the steam supply system. According to the utility model, the carbon deposition phenomenon generated in the heating process of the CO-containing feed gas can be effectively inhibited, the smooth switching of the electric heating system is realized, and the stability of the heating system is greatly improved.

Description

TECHNICAL FIELD

[0001] The utility model relates to a kind of heating method for the high-temperature reducing gas required in direct reduced iron (DRI) production process, more particularly to a kind of subsection electric heating system of CO reduction gas rich. BACKGROUND

[0002] Direct reduced iron (DRI) is prepared by the reaction of iron ore and high-temperature raw material gas (gas containing hydrogen and carbon monoxide) in a gas-based shaft furnace. The core process requires that the raw material gas be heated to 1000℃-1050℃ to ensure high raw material gas utilization. The current heating technology mainly includes traditional tube heating and new electric heating systems.

[0003] The traditional tube heating furnace uses a combustion system to supply heat, which transfers heat energy to the material inside the tube to achieve heating. This heating method has many shortcomings: low heating efficiency, uneven gas heating; in a high-temperature operating environment, the furnace tube is easily oxidized, which shortens the service life of the equipment and reduces its reliability; temperature regulation response lag, affecting process stability. These problems make it difficult for tube heating furnaces to meet the needs of direct reduced iron processes for high-temperature raw material gas heating.

[0004] In contrast, electric heaters have become a more ideal heating method due to their significant technical features. Electric heaters exhibit high and stable heating capacity, enabling high-precision temperature control and flexible real-time temperature adjustment according to actual needs. They have fast heating speed and good temperature uniformity, effectively avoiding the uneven heating problem of traditional tube heaters. In addition, electric heaters have the advantages of compact structure, easy installation and maintenance, and no pollution emissions. These characteristics make them have great application potential and market value in industrial applications, especially in scenarios requiring precise control and efficient heating.

[0005] Currently, electric heaters used for raw material gas heating are mostly designed in one stage. Although one-stage design simplifies the heating process, it has exposed a series of problems in actual application:

[0006] 1) High material selection cost: One-stage electric heaters need to heat raw material gas from room temperature to 1000℃-1050℃, which requires the material selection of one-stage heaters to meet the use requirements at all temperatures within the heating range, significantly increasing the material selection cost.

[0007] 2) Insufficient heating efficiency: In production scenarios with high demand for raw material gas, the heating efficiency of one-stage heaters is difficult to meet production requirements.

[0008] 3) Maintenance and repair are complex: for a one-stage electric heater, maintenance and repair work often need to stop the furnace operation, which will undoubtedly affect the continuous and stable operation of the system and the production efficiency. If you want to avoid stopping the furnace, you need to configure a standby one-stage heater, which will greatly increase the operating cost.

[0009] In addition, the safety problem in the process of heating raw gas is also noteworthy. Since the raw gas is generally prepared by methane steam reforming, carbon dioxide reforming, blast furnace gas or chemical by-product gas, etc., it often contains a high proportion of carbon monoxide (CO) and hydrogen (H2). Studies have shown that when the CO concentration in the raw gas is high, especially when the volume fraction exceeds a certain proportion (15-35%), CO is prone to dismutation reaction in the temperature range of 400-700℃, and the presence of H2 will further promote the occurrence of the reaction, and the reaction equation is:

[0010] 2CO=C+CO2

[0011] This reaction not only leads to carbon deposition, reduces heating efficiency, and increases energy consumption, but also clogs the heating equipment, causing production interruption. More seriously, carbon deposition can cause short circuit and rupture of the resistance tube, causing gas leakage, causing more serious explosion consequences, and posing a great safety threat to the life and property of the production device and the operator. Practical new type content

[0012] In order to overcome the above defects, the purpose of the present application is to provide a segmented electric heating system and method for raw gas rich in CO, which uses segmented electric heating technology, takes CO dismutation reaction temperature as the critical point, and uses multi-stage (two-stage or more) segmented heating.

[0013] In order to achieve the above purpose, the segmented electric heating system of the present application comprises: a mixer, a steam supply system, a first-stage electric heater, a second-stage electric heater, a gas concentration online detection device and a control system; wherein,

[0014] The mixer is used to mix the treated furnace top gas and fresh raw gas and output to the mixing pipe;

[0015] The steam supply system is used to generate water vapor and output to the mixing pipe;

[0016] The first-stage electric heater is used to heat the mixed gas input by the mixing pipe;

[0017] The second-stage electric heater is used to heat the mixed gas after the first-stage heating and output;

[0018] The gas concentration online detection device is used to detect the gas concentration at the key point;

[0019] A control system is used to output a control signal according to the detection result of the gas concentration online detection device to control the steam supply amount of the steam supply system.

[0020] Further, the primary electric heater is composed of two primary electric heaters in parallel, one of which is a main primary electric heater and the other is a standby primary electric heater; controlled valves are arranged on the inlet and outlet pipelines of the two primary electric heaters;

[0021] The control system controls the switching of the two primary heaters by controlling the controlled valves.

[0022] Further, the gas concentration detection device is composed of two CO concentration detection points, one of which is arranged in the mixer to detect the input CO concentration data and feed back to the control system; the other is arranged on the pipeline before the inlet of the secondary heater to detect the CO concentration data and feed back to the control system, and the control system dynamically controls and adjusts the steam output amount of the steam supply system according to the detection results before and after heating.

[0023] Further, the steam supplied by the steam supply system is superheated steam with a pressure of 1.0 MPa and a temperature of 200-250 DEG C.

[0024] To achieve the above purpose, the segmented electric heating method for CO reduction gas rich in the utility model, comprising the following steps:

[0025] The treated top gas and fresh raw gas are mixed in the mixer and then output to the mixing pipeline;

[0026] The water vapor generated by the steam supply system is output to the mixing pipeline;

[0027] The mixed gas input into the mixing pipeline is heated by the primary electric heater;

[0028] The mixed gas after the primary heating is output after being heated by the secondary electric heater;

[0029] The CO concentration in the mixed gas before and after heating entering the primary electric heater is detected in real time;

[0030] The steam supply amount of the steam supply system is controlled according to the detection result.

[0031] Further, the following steps are further included: the CO decay coefficient K is calculated according to the detection result, and the steam supply amount of the steam supply system is controlled through the decay coefficient K.

[0032] Further, the calculation includes the following steps:

[0033] (1) Calculate the concentration of CO a1 in the mixed gas at the outlet of the mixer and the flow rate b1 of the mixed gas; calculate the water vapor demand flow rate b2 according to the CO concentration and control the steam generator to add water vapor;

[0034] (2) Detect the CO concentration a2 of the gas at the inlet pipeline of the secondary heater, calculate the decay coefficient K of CO according to the detected data, and the calculation formula is: K=(b1+b2)a2 / b1a1.

[0035] When 100%>K≥70%, control the steam generator to increase the amount of added water vapor, and when K<70%, switch the primary heater, open the control valve of the outlet and inlet of the standby primary electric heater, and close the control valve of the outlet and inlet of the primary electric heater in use, to realize smooth switching of the primary heater.

[0036] Further, the primary electric heater heats the CO-rich gas from room temperature to 700 DEG C, and the secondary or multi-stage electric heater continues to heat the gas to 1000 DEG C-1050 DEG C.

[0037] The utility model divides the heating process into two stages (primary heating: room temperature to 700 DEG C; secondary heating: 700 DEG C to 1050 DEG C) with CO disproportionation reaction temperature as the critical point, dynamically adjusts the amount of added water vapor and the use of the primary electric heater by calculating the CO decay coefficient K before and after primary heating, effectively suppresses the carbon deposition phenomenon generated in the heating process of the CO-containing raw gas, realizes smooth switching of the electric heating system, and greatly improves the stability of the heating system. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 It is the flow chart of the process

[0039] In the figure: 1-steam generator, 2-primary electric heater system, 3-secondary electric heater, 4-gas-based shaft furnace body, 5-gas concentration detection and control system.

[0040] Figure 2 It is the structure diagram of the primary electric heater system

[0041] In the figure: 201-primary heater inlet control valve, 202-primary heater, 203-primary heater outlet control valve, 204-backup primary heater inlet control valve, 205-backup primary heater, 206-backup primary heater outlet control valve. DETAILED DESCRIPTION

[0042] The embodiments of the utility model will be described in detail below with reference to the drawings.

[0043] In the description of the utility model, it is necessary to understand that the orientation or positional relation indicated by the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like is the orientation or positional relation shown based on the drawings, and is only for the convenience of describing the utility model and simplifying the description, and does not indicate or imply that the indicated device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the utility model.

[0044] The terms "first", "second" are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features. In the description of the utility model, unless otherwise specified, the meaning of "a plurality of" is two or more.

[0045] In the description of the utility model, it should be pointed out that, unless otherwise specified and limited, the terms "mounting", "connection", "connection" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected, it can be directly connected, or indirectly connected through an intermediate medium, it can be the communication inside two elements. For ordinary skilled in the art, the specific meaning of the above terms in the utility model can be understood according to the specific circumstances.

[0046] The utility model relates to a kind of segmented electric heating system, for the direct reduction of iron oxide in gas-based shaft furnace.The system integrates steam supply system, primary electric heater system (parallel, standby switching), secondary electric heater and gas concentration on-line detection and control system, realize the efficient, safe heating and flexible control of CO reduction gas rich, meet the production requirement of gas-based shaft furnace.

[0047] Workflow: The processed top gas of shaft furnace and fresh raw material gas (rich in CO) are mixed in the pipeline, pass through the first CO concentration detection point, and the detected data are transmitted to the steam supply system after calculation by the control system. According to the calculation result, appropriate amount of water vapor is added to the mixed gas. The mixed gas and water vapor enter the primary heater for mixing and heating, and then pass through the pipeline into the secondary heater for the second CO concentration detection. According to the detection result, the CO attenuation coefficient K is calculated, and the addition amount of water vapor and the use of the heating furnace are dynamically adjusted through the attenuation coefficient K. Subsequently, the mixed gas is heated in the secondary heater to meet the requirements of the shaft furnace and then enters the gas-based shaft furnace. The utility model takes the CO disproportionation reaction temperature as the critical point to divide the heating process into two stages (primary heating: normal temperature to 700 DEG C; secondary heating: 700 DEG C to 1050 DEG C). The addition amount of water vapor and the use of the primary electric heater are dynamically adjusted through the calculation of the CO attenuation coefficient K before and after the primary heating, which effectively inhibits the carbon deposition phenomenon generated in the heating process of the CO-containing raw material gas, realizes the smooth switching of the electric heating system, and greatly improves the stability of the heating system.

[0048] Embodiment

[0049] As shown in Figure 1 , Figure 2 , the segmented electric heating system and method for CO-containing raw material gas of the embodiment comprise a steam generator (1), a primary electric heater system (2) (comprising a primary heater inlet control valve (201), a primary heater (202), a primary heater outlet control valve (203), a standby primary heater inlet control valve (204), a standby primary heater (205), and a standby primary heater outlet control valve (206)), a secondary electric heater (3), a gas-based shaft furnace body (4), and a gas concentration detection and control system (5).

[0050] The processed top gas of shaft furnace and fresh raw material gas are mixed (the flow rate is b1), and the CO concentration a1 is measured before entering the primary heater. Based on this data, the water vapor generator injects appropriate amount of water vapor (the flow rate is b2) (calculated according to H2O / CO=0.6-1.5) into the mixed gas, aiming to inhibit the carbon deposition phenomenon. In addition, in order to monitor the internal situation of the heater in all directions, the CO concentration a2 is measured for the second time before the gas enters the secondary heater. The CO attenuation coefficient K is calculated, and the calculation rule is as follows:

[0051] K=(b1+b2)a2 / b1a1

[0052] The water vapor adding amount is dynamically adjusted by the attenuation coefficient K, and the furnace condition is evaluated. When 100%>K≥70%, the water vapor injection amount is appropriately increased; when K<70%, the control system opens the control valves (204, 206) at the outlet and inlet of the standby first-stage electric heater, closes the control valves (201, 203) at the outlet and inlet of the first-stage electric heater, and after cooling, the first-stage electric heater (202) is overhauled and maintained. Finally, the gas is heated to the target temperature by the second-stage heater and then introduced into the gas-based shaft furnace.

[0053] The utility model has been described in detail above in combination with the drawings, but the utility model is not limited to the above-mentioned embodiments, and various changes can be made within the knowledge range possessed by those skilled in the art without departing from the purpose of the utility model. Many other changes and modifications can be made to the concept and range of the utility model without departing from the concept and range of the utility model, and should be regarded as the protection range of the utility model.

[0054] In the description of the present specification, specific features, structures, materials or characteristics can be combined in any one or more embodiments or examples in a suitable manner.

[0055] The above is only a specific implementation manner of the utility model, but the protection range of the utility model is not limited to this, and any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the utility model, which should be covered in the protection range of the utility model. Therefore, the protection range of the utility model should be subject to the protection range of the claims.

Claims

1. A segmented electric heating system, characterized in that, The system comprises a mixer, a steam supply system, a first-stage electric heater, a second-stage electric heater, a gas concentration on-line detection device and a control system, wherein The mixer is used for mixing the processed top gas and fresh raw material gas and outputting to a mixing pipe; The steam supply system is used for generating water vapor and outputting to the mixing pipe; The first-stage electric heater is used for first-stage heating of the mixed gas inputted by the mixing pipe; The second-stage electric heater is used for second-stage heating of the mixed gas after the first-stage heating and outputting; The gas concentration on-line detection device is used for detecting the gas concentration at key points; The control system is used for outputting a control signal to control the steam supply amount of the steam supply system according to the detection result of the gas concentration on-line detection device.

2. The segmented electrical heating system of claim 1, wherein, The first-stage electric heater is composed of two first-stage electric heaters in parallel, one of which is a main first-stage electric heater and the other is a standby first-stage electric heater; controlled valves are arranged on the inlet and outlet pipes of the two first-stage electric heaters; The control system controls the switching of the two first-stage electric heaters by controlling the controlled valves.

3. The segmented electrical heating system of claim 1, wherein, The gas concentration on-line detection device is composed of two CO concentration detection points, one of which is arranged in the mixer and is used for detecting the input CO concentration data and feeding back to the control system; the other is arranged at the pipe before the inlet of the second-stage heater and is used for detecting the CO concentration data and feeding back to the control system, and the control system dynamically controls and adjusts the steam output amount of the steam supply system according to the detection results before and after the heating.

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