A method for low nox combustion control in a heating furnace

Abstract

The present application belongs to the field of metallurgical industrial furnace, and relates to a low-NOx combustion control method for a heating furnace. The method comprises a heating furnace, a burner, an air pipeline, a circulating flue gas pipeline, and an exhaust gas pipeline. The circulating flue gas pipeline is communicated with the air pipeline, and a circulating fan and an adjusting valve are arranged on the circulating flue gas pipeline. An oxygen detection device and a combustion-supporting gas flow detection device are arranged on the pipeline where the air is mixed with the circulating flue gas. A NOx detection device is arranged on the exhaust gas pipeline. A furnace temperature detection device is arranged on the heating furnace. The NOx detection value, the combustion-supporting gas flow detection value, the furnace temperature detection value, the residual oxygen detection value, and the heating process are taken as input values to jointly control the circulating flue gas adjusting valve. The present application increases the control means of the heating furnace, greatly improves the flexibility and control precision of the heating furnace, and most significantly, can perform advanced control on NOx, and can intervene in the working conditions that are prone to cause NOx exceeding the standard, such as too small flow, too high residual oxygen, and heat preservation rolling, thereby greatly reducing the NOx emission of the heating furnace.

Claims

1. A method for controlling low NOx combustion in a heating furnace, characterized in that, The system includes a furnace (1) with at least one burner (2), an air pipe (3) connected to the burner (2), and an exhaust pipe (5) connected to the furnace (1). The exhaust pipe (5) is connected to the air pipe (3) via a circulating flue gas pipe (4). The furnace (1) is equipped with a furnace temperature detection device (11), and a flue gas residual oxygen detection device (12) is provided between the furnace (1) and the exhaust pipe (5). A NOx detection device (52) is provided at the outlet end of the exhaust pipe (5). The circulating flue gas pipe (4) is installed along the flue gas flow direction. The system is equipped with a circulating fan (41) and a circulating flue gas regulating valve (42); the air pipeline (3) is equipped with a combustion gas flow detection device (31) and an oxygen detection device (32) in sequence along the air flow direction; it also includes a control module (6) for controlling the opening of the circulating flue gas regulating valve (42); the control module (6) is electrically connected to the furnace temperature detection device (11), the flue gas residual oxygen detection device (12), the combustion gas flow detection device (31), the oxygen detection device (32), the circulating flue gas regulating valve (42), and the NOx detection device (52); The circulating flue gas regulating valve is controlled by multiple input parameters, including NOx detection value, combustion gas flow rate detection value, furnace temperature detection value, residual oxygen detection value, and heating process parameters. Specifically, these include: The circulating flue gas regulating valve (42) is controlled by the NOx detection value: the NOx emission standard value is A, the NOx detection value on the flue gas pipeline (5) is NOx-1, when NOx-1 < NOx-a, the NOx detection value does not participate in the control of the circulating flue gas regulating valve (42); when NOx-a ≤ NOx-1 ≤ NOx-b, the opening of the circulating flue gas regulating valve (42) is gradually increased; when NOx-1 > NOx-b, the opening of the circulating flue gas regulating valve (42) is rapidly increased until the oxygen concentration of the combustion-supporting gas reaches the lower limit of the set value, where NOx-a < NOx-b < A; NOx-a is the preset lower limit value of the detection value on the flue gas pipeline (5), and NOx-b is the preset upper limit value of the detection value on the flue gas pipeline; The circulating flue gas regulating valve (42) is controlled by the combustion gas flow detection value: the preset air flow value is Q, the combustion gas flow detection value is Q1, and when Q1 < c When Q, increase the opening of the circulating flue gas regulating valve (42), when Q1≥c When Q is reached, the opening of the circulating flue gas regulating valve (42) is reduced, and the value of c is in the range of 0.3~0.5; The circulating flue gas regulating valve (42) is controlled by furnace temperature: the preset value of the furnace temperature of the heating furnace (1) is T, and the furnace temperature detection value is T1; when the difference between T1 and T is less than the preset temperature difference range, the furnace temperature does not participate in the control of the circulating flue gas regulating valve (42); when the difference between T1 and T is greater than or equal to the preset temperature difference range, if T1 < T, the opening of the circulating flue gas regulating valve (42) is reduced, and if T1 > T, the opening of the circulating flue gas regulating valve (42) is increased. The circulating flue gas regulating valve (42) controls the residual oxygen in the flue gas: the preset value of residual oxygen in the flue gas is B, and the detected value of residual oxygen in the flue gas is B1. When B1 < d When B, reduce the opening of the circulating flue gas regulating valve (42), when B1 > e When B, increase the opening of the circulating flue gas regulating valve (42), where the value of d ranges from 0.8 to 1.0 and the value of e ranges from 1.0 to 1.2; The circulating flue gas regulating valve (42) is controlled by the heating furnace operation process: when the heating furnace (1) is about to enter the heat preservation and rolling stage, the opening of the circulating flue gas regulating valve (42) is increased; If multiple inputs affect the circulating flue gas regulating valve (42) at the same time, the input with higher priority covers the input with lower priority; the priority order of the inputs controlling the circulating flue gas regulating valve (42) is: NOx detection value control > combustion gas flow detection value control > furnace temperature detection value control > flue gas residual oxygen detection value control > heating furnace operation process control.

2. The low-NOx combustion control method for a heating furnace according to claim 1, characterized in that: The oxygen concentration for combustion after air and circulating flue gas are mixed ranges from 10% to 21%.

3. A low-NOx combustion control method for a heating furnace according to claim 1 or 2, characterized in that, For the high-temperature section, medium-temperature section and low-temperature section of the heating furnace (1), the lower limit of the oxygen concentration of the combustion-supporting gas meets the following condition: high-temperature section < medium-temperature section < low-temperature section.

4. The low-NOx combustion control method for a heating furnace according to claim 1, characterized in that: The value range of NOx-a is 0.

6. A~0.8 The values ​​of A and NOx-b range from 0.

8. A~1.0 A.

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