Design method of heating temperature of coal powder gas flow

Abstract

The present application belongs to the technical field of coal powder boiler combustion, and discloses a design method of coal powder airflow heating temperature. ignition The present application adopts the thermal gravimetric analysis method to obtain the TG curve of the change of the weight of the coal powder sample with temperature, and the intersection of the tangent of the inflection point of the TG curve and the initial baseline is the coal powder ignition temperature T ignition ; the relationship between the powder pipe safe operation temperature and the coal powder ignition temperature is T 粉管 =T ignition -100; the initial temperature of the coal powder airflow corresponding to the ignition distance of 0.5 m of the coal powder airflow is selected as the burner safe operation temperature T 燃烧器 by adopting the field measurement method; the powder pipe safe operation temperature T 粉管 is compared with the burner safe operation temperature T 燃烧器 , and the smaller one of T 粉管 and T 燃烧器 is taken as the coal powder airflow heating temperature. The present application gives the determination method of the initial temperature of the coal powder airflow, and has strong guiding significance for the selection of the coal powder airflow heating temperature.

Description

Technical Field

[0001] This invention relates to the field of pulverized coal boiler combustion technology, and in particular to a method for designing the heating temperature of pulverized coal airflow. Background Technology

[0002] In the operation of a coal-fired power plant's pulverizing system, high-temperature primary air and raw coal enter the coal mill together. The primary air serves to dry the raw coal and carry the pulverized coal. After exiting the coal mill, the pulverized coal gas flows through the pulverized coal pipes into the boiler furnace. Inside the furnace, the pulverized coal heats up by entraining the surrounding high-temperature flue gas and receiving heat from the flame radiation, thus meeting the ignition conditions. The higher the initial temperature of the pulverized coal gas flow, the easier it is to ignite and burn, which is more beneficial for improving the boiler's coal adaptability and combustion stability. However, an increased initial temperature of the pulverized coal gas flow can also easily cause deflagration in the pulverizing system and burn-out of the burner nozzles.

[0003] Currently, to ensure the safe operation of coal mills, the outlet pulverized coal gas temperature is strictly limited. For example, for commonly used bituminous coal, the outlet temperature is typically controlled below 90℃. In recent years, with the deterioration of coal quality and the prevalence of low-load operation, higher requirements have been placed on the coal type adaptability and combustion stability of coal-fired boilers. To increase the initial temperature of the pulverized coal gas flow, a technology for directly heating the pulverized coal gas flow on the pulverized coal pipe has emerged. This avoids the limitations of safe operation of the coal mill and can significantly increase the initial temperature of the pulverized coal gas flow. However, there is no clear regulation on the maximum temperature that the pulverized coal gas flow can be heated to. Summary of the Invention

[0004] The purpose of this invention is to provide a method for designing the heating temperature of pulverized coal gas flow, thereby solving the problems existing in the prior art.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for designing the heating temperature of pulverized coal gas flow, comprising the following steps:

[0007] (1) Determine the safe operating temperature T of the powder pipeline 粉管

[0008] Thermogravimetric analysis (TGA) was used to obtain the weight change curve of the pulverized coal sample as a function of temperature (TG curve). Differentiating the TG curve yielded the rate of change of the pulverized coal sample's weight as a function of temperature (DTG curve). The inflection point of the TG curve was determined based on the maximum value of the rate of change of the pulverized coal sample's weight on the DTG curve. The intersection of the tangent line at the inflection point of the TG curve and the initial baseline was taken as the pulverized coal ignition temperature T. ignition ; Safe operating temperature of powder pipe T 粉管 With the ignition temperature T of pulverized coal ignition The relationship is:

[0009] T粉管 =T ignition -100;

[0010] The initial baseline is a horizontal baseline with a weight of 100%;

[0011] (2) Determine the safe operating temperature T of the burner 燃烧器

[0012] Using on-site measurement methods, the initial temperature of the pulverized coal gas flow corresponding to an ignition distance of 0.5m was selected as the burner's safe operating temperature T. 燃烧器 ;

[0013] (3) Determine the pulverized coal gas flow heating temperature T 煤粉

[0014] The safe operating temperature T of the powder pipe 粉管 With the burner's safe operating temperature T 燃烧器 For comparison, T 粉管 With T 燃烧器 The smaller of the median values ​​is used as the heating temperature of the pulverized coal gas flow, i.e.:

[0015] T 煤粉 =min(T) 粉管 T 燃烧器 ).

[0016] Preferably, in the above-mentioned method for designing the heating temperature of pulverized coal gas flow, the heating rate in the thermogravimetric analysis method in step (1) is 1 to 10 °C / min.

[0017] Preferably, in the above-mentioned method for designing the heating temperature of pulverized coal gas flow, step (2) involves determining the safe operating temperature T of the burner. 燃烧器 The specific process is as follows: After a pulverized coal gas flow with a certain initial temperature enters the furnace through the burner nozzle, a thermocouple is inserted into the furnace through the burner. Taking the burner nozzle as the zero point, a temperature measuring point is set every 10cm forward. The temperature of the pulverized coal gas flow at different distances from the burner nozzle is measured, and then a curve is plotted. The distance represented by the point where the slope of the curve is 1 is the ignition distance of the pulverized coal gas flow. Then, the initial temperature of the pulverized coal gas flow is changed, and the above process is repeated. The initial temperature of the pulverized coal gas flow corresponding to an ignition distance of 0.5m is selected as the safe operating temperature T of the burner. 燃烧器 .

[0018] The principles involved in this invention are as follows:

[0019] (1) The initial temperature rise of the pulverized coal gas flow affects the safe operation of the pulverized coal pipe and the burner, and may cause deflagration of pulverized coal accumulation in the pulverized coal pipe and burnout of the burner nozzle. Therefore, from the perspective of the safe operation of the pulverized coal pipe and the burner, the safe operating temperature T of the pulverized coal pipe should be determined respectively. 粉管and the safe operating temperature T of the burner 燃烧器 The two temperatures are compared, and the lower one is selected as the upper limit of the initial temperature of the pulverized coal gas flow.

[0020] (2) Coal powder, carried by the primary airflow, enters the boiler furnace through the pulverized coal pipe. The carrying capacity of the airflow for coal powder is closely related to the airflow velocity. When there are bends, dead angles, or other corners inside the pulverized coal pipe that cause a decrease in airflow velocity, or when the overall coal powder airflow velocity is low, the coal powder will detach from the airflow and deposit, forming accumulated powder. The accumulated powder undergoes slow oxidation, releasing heat and volatile gases. Once a certain temperature is reached, ignition and explosion may occur. This temperature is closely related to the coal quality. Generally, coals with lower coalification and higher volatile content have lower ignition temperatures, while coals with higher coalification and lower volatile content have higher ignition temperatures. In addition, the heat released by the oxidation of the accumulated powder gradually raises the coal powder temperature above the coal powder airflow temperature. To prevent the coal powder from burning inside the pulverized coal pipe, a safe operating temperature T is required. 粉管 It should be related to the ignition temperature T of pulverized coal. ignition There is a certain safety margin. Based on operating experience, this safety margin is set at 100℃ in this method. When the safety margin is less than 100℃, it will cause the pulverized coal to spontaneously combust in the pulverized coal pipe.

[0021] (3) According to the different heating rates, thermogravimetric analysis can be divided into rapid thermogravimetric analysis and slow thermogravimetric analysis. The heating rate of rapid thermogravimetric analysis can reach 10 to 1000℃ / min, while the heating rate of slow thermogravimetric analysis is 1 to 10℃ / min. Since the deflagration of pulverized coal in the pulverized coal conveying pipeline is usually caused by the slow oxidation and spontaneous combustion of the accumulated pulverized coal, the pulverized coal ignition temperature measured by slow thermogravimetric analysis should be used to determine the safe operating temperature of the pulverized coal pipeline in this method.

[0022] (4) The pulverized coal gas flow enters the furnace through the pulverized coal pipe and passes through the burner. After entering the furnace through the burner nozzle, the pulverized coal gas flow is heated by the surrounding high-temperature flue gas and flame, and ignites and burns after reaching the ignition temperature. If the pulverized coal ignites too quickly, the ignition point will be too close to the nozzle, causing burner nozzle damage; if the pulverized coal ignites too slowly, the ignition point will be too far from the nozzle, causing unstable combustion and flameout. It is generally believed that an ignition distance of 0.5 to 1.5 m can maintain the safety of the burner nozzle and the stability of ignition. This invention proposes to use a field measurement method to determine the ignition distance of the pulverized coal gas flow, measure the ignition distance of the pulverized coal gas flow corresponding to different initial temperatures, select the initial temperature of the pulverized coal gas flow when the ignition distance is 0.5 m, and determine it as the safe operating temperature T of the burner. 燃烧器 .

[0023] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects:

[0024] This invention addresses the problem of uncertain initial temperature limits for pulverized coal gas flow during coal-fired boiler operation by proposing a method to design the maximum heating temperature of the pulverized coal gas flow from the perspective of the operational safety of the pulverized coal pipe and burner. The invention introduces methods for obtaining the safe operating temperatures of the pulverized coal pipe and burner, with the upper limit of the initial temperature of the pulverized coal gas flow being the minimum of the safe operating temperatures of the pulverized coal pipe and burner. This method provides a way to determine the initial temperature of the pulverized coal gas flow, offering significant guidance for selecting the heating temperature of the pulverized coal gas flow. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0026] Figure 1 The ignition temperature T of pulverized coal ignition Determine the diagram;

[0027] Figure 2 This is a curve showing the ignition distance test of pulverized coal gas flow. Detailed Implementation

[0028] This invention provides a method for designing the heating temperature of pulverized coal gas flow, comprising the following steps:

[0029] (1) Determine the safe operating temperature T of the powder pipeline 粉管

[0030] Thermogravimetric analysis (TGA) was used to obtain the weight change curve of the pulverized coal sample as a function of temperature (TG curve). Differentiating the TG curve yielded the rate of change of the pulverized coal sample's weight as a function of temperature (DTG curve). The inflection point of the TG curve was determined based on the maximum value of the rate of change of the pulverized coal sample's weight on the DTG curve. The intersection of the tangent line at the inflection point of the TG curve and the initial baseline was taken as the pulverized coal ignition temperature T. ignition ; Safe operating temperature of pulverized coal pipe (T); Ignition temperature of pulverized coal pipe and pulverized coal (T) ignition The relationship is:

[0031] T 粉管 =T ignition -100;

[0032] The initial baseline is a horizontal baseline with a weight of 100%;

[0033] (2) Determine the safe operating temperature T of the burner 燃烧器

[0034] Using on-site measurement methods, the initial temperature of the pulverized coal gas flow corresponding to an ignition distance of 0.5m was selected as the burner's safe operating temperature T. 燃烧器 ;

[0035] The initial temperature of the pulverized coal gas flow is the temperature of the pulverized coal gas flow in the pulverized coal pipe;

[0036] (3) Determine the pulverized coal gas flow heating temperature T 煤粉

[0037] The safe operating temperature T of the powder pipe 粉管 With the burner's safe operating temperature T 燃烧器 For comparison, T 粉管 With T 燃烧器 The smaller of the median values ​​is used as the heating temperature of the pulverized coal gas flow, i.e.:

[0038] T 煤粉 =min(T) 粉管 T 燃烧器 ).

[0039] In this invention, the heating rate in the thermogravimetric analysis method in step (1) is preferably 1 to 10 °C / min, more preferably 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 °C / min, and more preferably 1 °C / min.

[0040] In this invention, step (2) involves determining the burner's safe operating temperature T. 燃烧器 The specific process is as follows: After a pulverized coal gas flow with a certain initial temperature enters the furnace through the burner nozzle, a thermocouple is inserted into the furnace through the burner. Taking the burner nozzle as the zero point, a temperature measuring point is set every 10cm forward. The temperature of the pulverized coal gas flow at different distances from the burner nozzle is measured, and then a curve is plotted. The distance represented by the point where the slope of the curve is 1 is the ignition distance of the pulverized coal gas flow. Then, the initial temperature of the pulverized coal gas flow is changed, and the above process is repeated. The initial temperature of the pulverized coal gas flow corresponding to an ignition distance of 0.5m is selected as the safe operating temperature T of the burner. 燃烧器 .

[0041] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] Example 1

[0043] (1) Determine the safe operating temperature T of the powder pipeline 粉管

[0044] The pulverized coal sample was placed in a thermogravimetric analyzer and heated at a rate of 1℃ / min. Simultaneously, the weight change of the pulverized coal sample was measured, resulting in the weight change curve (TG curve). Differentiating the TG curve yielded the weight change rate curve (DTG curve). The inflection point of the TG curve was determined based on the maximum value of the weight change rate on the DTG curve. The intersection of the tangent line at the inflection point of the TG curve and the initial baseline was taken as the pulverized coal ignition temperature T. ignition ,like Figure 1 As shown; safe operating temperature T of the powder pipe 粉管 With the ignition temperature T of pulverized coal ignition The relationship is:

[0045] T 粉管 =T ignition -100;

[0046] (2) Determine the safe operating temperature T of the burner 燃烧器

[0047] After a pulverized coal gas flow with a certain initial temperature enters the furnace through the burner nozzle, a thermocouple is inserted into the furnace through the burner. Using the burner nozzle as the zero point, a temperature measuring point is established every 10 cm forward from the nozzle. The temperature of the pulverized coal gas flow at different distances from the burner nozzle is then measured, and a curve is plotted, as shown below. Figure 2 As shown, the distance represented by point D when the slope of the curve is 1 is the ignition distance of the pulverized coal gas flow. Then, by changing the initial temperature of the pulverized coal gas flow and repeating the above process, the initial temperature of the pulverized coal gas flow corresponding to an ignition distance of 0.5m is selected as the burner's safe operating temperature T. 燃烧器 .

[0048] (3) Determine the pulverized coal gas flow heating temperature T 煤粉

[0049] The safe operating temperature T of the powder pipe 粉管 With the burner's safe operating temperature T 燃烧器 For comparison, T 粉管 With T 燃烧器 The smaller of the median values ​​is used as the heating temperature of the pulverized coal gas flow, i.e.:

[0050] T 煤粉 =min(T) 粉管 T 燃烧器 ).

[0051] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for designing the heating temperature of pulverized coal gas flow, characterized in that, Includes the following steps: (1) Determine the safe operating temperature T of the powder pipeline 粉管 Thermogravimetric analysis (TGA) was used to obtain the weight change curve of the pulverized coal sample as a function of temperature (TG curve). Differentiating the TG curve yielded the rate of change of the pulverized coal sample's weight as a function of temperature (DTG curve). The inflection point of the TG curve was determined based on the maximum value of the rate of change of the pulverized coal sample's weight on the DTG curve. The intersection of the tangent line at the inflection point of the TG curve and the initial baseline was taken as the pulverized coal ignition temperature T. ignition ; Safe operating temperature of powder pipe T 粉管 With the ignition temperature T of pulverized coal ignition The relationship is: T 粉管 =T ignition -100; The initial baseline is a horizontal baseline with a weight of 100%; (2) Determine the safe operating temperature T of the burner 燃烧器 Using on-site measurement methods, the initial temperature of the pulverized coal gas flow corresponding to an ignition distance of 0.5m was selected as the burner's safe operating temperature T. 燃烧器 ; (3) Determine the pulverized coal gas flow heating temperature T 煤粉 The safe operating temperature T of the powder pipe 粉管 With the burner's safe operating temperature T 燃烧器 For comparison, T 粉管 With T 燃烧器 The smaller of the median values ​​is used as the heating temperature of the pulverized coal gas flow, i.e.: T 煤粉 =min(T 粉管 ,T 燃烧器 )。 2. The method for designing the heating temperature of pulverized coal gas flow according to claim 1, characterized in that, The heating rate in the thermogravimetric analysis method in step (1) is 1 to 10 °C / min.

3. The method for designing the heating temperature of pulverized coal gas flow according to claim 1 or 2, characterized in that, In step (2), the safe operating temperature T of the burner is determined. 燃烧器 The specific process is as follows: After a pulverized coal gas flow with a certain initial temperature enters the furnace through the burner nozzle, a thermocouple is inserted into the furnace through the burner. Taking the burner nozzle as the zero point, a temperature measuring point is set every 10cm forward. The temperature of the pulverized coal gas flow at different distances from the burner nozzle is measured, and then a curve is plotted. The distance represented by the point where the slope of the curve is 1 is the ignition distance of the pulverized coal gas flow. Then, the initial temperature of the pulverized coal gas flow is changed, and the above process is repeated. The initial temperature of the pulverized coal gas flow corresponding to an ignition distance of 0.5m is selected as the safe operating temperature T of the burner. 燃烧器 .

Images