A control method for preventing primary fan overcurrent protection from triggering boiler MFT

Abstract

The application discloses a control method for preventing overcurrent protection of a primary air fan from triggering boiler MFT, and comprises the following steps: 1, primary air fan tripping judgment; 2, protection action after primary air fan tripping: after one-side primary air fan tripping is monitored, the tripped fan is automatically released, the outlet baffle door of the tripped fan is closed, and the unit control mode is switched from the coordination mode to the unit following mode; meanwhile, corresponding response is made according to the unit load, so that the boiler MFT is prevented from being triggered. The control method for preventing overcurrent protection of a primary air fan from triggering boiler MFT aims at preventing the boiler MFT from being triggered due to overcurrent protection of the fan caused by improper adjustment of the primary air fan on the other side after one-side primary air fan tripping, and effectively ensuring stable and safe operation of the unit.

Description

Technical Field

[0001] This invention belongs to the field of thermal automatic control and protection technology, specifically relating to a control method for preventing the primary air fan overcurrent protection from triggering the boiler MFT. Background Technology

[0002] In actual operation, it was found that the primary air blower of thermal power generator unit B would shut down due to hydraulic cylinder failure, causing the RB (RUNBACK) protection of the unit to activate. The primary air blower of unit A would automatically open its blades. During the adjustment process, the current of the primary air blower of unit A exceeded the rated current. The primary air blower of unit A would trip due to the inverse time protection of the 6kV switch. All coal mills would trip due to low primary air flow, resulting in the loss of all fuel and causing the boiler to fail. Summary of the Invention

[0003] To address the technical problems existing in the prior art, the purpose of this invention is to provide a control method to prevent the primary air fan overcurrent protection from triggering the boiler MFT.

[0004] To achieve the above objectives and technical effects, the technical solution adopted by this invention is as follows:

[0005] A control method for preventing boiler MFT triggered by primary air fan overcurrent protection is provided to prevent boiler MFT caused by improper adjustment of the primary air fan on the other side after a trip of a single primary air fan. The control method includes the following steps:

[0006] 1. Perform a test to determine if the fan has tripped;

[0007] II. Protection actions after primary fan trip:

[0008] When a single primary air fan trips, the automatic tripping of the tripped fan is deactivated, the outlet damper of the tripped fan is closed, and the unit control mode is switched from coordinated mode to machine-following mode. At the same time, the corresponding response is made according to the unit load level to avoid triggering the boiler MFT.

[0009] Furthermore, the criteria for determining the primary turbine trip include:

[0010] A primary fan is considered to have tripped if it meets all of the following conditions:

[0011] (1) The primary air fan has been running for more than 10 minutes;

[0012] (2) The primary air fan current is less than 5A;

[0013] (3) The differential pressure between the inlet and outlet of the primary air blower is less than 1 kPa.

[0014] Furthermore, the formula for calculating the differential pressure between the inlet and outlet of the primary air fan is as follows:

[0015] The differential pressure between the inlet and outlet of the primary air blower = the total pressure at the outlet of the primary air blower - the total pressure at the inlet of the primary air blower.

[0016] Furthermore, the steps to respond accordingly based on unit load levels to avoid triggering a boiler MFT include:

[0017] When the actual unit load is greater than Y, the unit load is automatically reduced to Y. The forced draft fan and induced draft fan adjust automatically according to the load. The primary fan automatically increases its output to the fan opening degree X and then the automatic fan operation is deactivated. The coal mills automatically jump from top to bottom to maintain the operation of the bottom Z coal mills and automatically put two oil guns into stable combustion.

[0018] When the actual unit load is less than or equal to Y, the unit load is kept constant, the forced draft fan and induced draft fan are kept under automatic control, the number of coal mills in operation remains unchanged, the primary air fan is automatically increased to the primary air pressure set value under the current load, and the two oil guns are automatically put into stable combustion.

[0019] Among them, the fan opening degree X when the primary fan reaches the rated current, the unit load Y, and the number of coal mills in operation Z are determined through testing.

[0020] Furthermore, the test steps for determining the fan opening degree X, unit load Y, and number of coal mills operating when the primary air fan reaches its rated current include:

[0021] Start the primary air fan on one side, and put the forced draft fan and induced draft fan on both sides into operation. Gradually increase the unit load and gradually increase the number of coal mills in operation according to the unit load. When the primary air fan current reaches the rated current, keep the unit load unchanged and record the fan opening degree X, unit load Y, and number of coal mills in operation Z at this time.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] This invention discloses a control method to prevent boiler MFT triggered by primary fan overcurrent protection. The purpose is to prevent boiler MFT caused by improper adjustment of the primary fan on the other side after the primary fan on one side trips, thereby effectively ensuring the stable and safe operation of the unit. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of the present invention. Detailed Implementation

[0025] The present invention will now be described in detail so that its advantages and features can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0026] The following provides a brief overview of one or more aspects to offer a basic understanding of them. This overview is not an exhaustive summary of all conceived aspects, nor is it intended to identify key or decisive elements of all aspects, nor to define the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form to prepare for the more detailed descriptions that follow.

[0027] like Figure 1 As shown, a control method for preventing the primary air fan overcurrent protection from triggering the boiler MFT includes the following steps:

[0028] I. Primary air fan tripping judgment:

[0029] A single primary air fan is considered to have tripped if all of the following conditions are met:

[0030] (1) The primary air fan has been running for more than 10 minutes;

[0031] (2) The primary fan current is less than 5A. The fan current signal can be obtained through the DCS control system;

[0032] (3) The differential pressure between the inlet and outlet of the primary air fan is less than 1 kPa. Pressure measuring points are installed at the inlet and outlet of the primary air fan respectively. The differential pressure between the inlet and outlet of the primary air fan = the total pressure at the outlet of the fan - the total pressure at the inlet of the fan.

[0033] II. Protection actions after primary fan trip:

[0034] Upon detecting a single primary air fan trip, the automatic control of the tripped fan is deactivated, the outlet damper of the tripped fan is closed, and the unit control mode is switched from coordinated mode to follow-up mode. The current unit load is assessed.

[0035] When the actual unit load is greater than Y, the unit load is automatically reduced to Y. The forced draft fan and induced draft fan adjust automatically according to the load. The primary fan automatically increases its output to the fan opening degree X and then the automatic fan operation is deactivated. The coal mills automatically jump from top to bottom to maintain the operation of the bottom Z coal mills and automatically put two oil guns into stable combustion.

[0036] When the actual unit load is less than or equal to Y, the unit load is kept constant, the forced draft fan and induced draft fan are kept under automatic control, the number of coal mills in operation remains unchanged, the primary air fan is automatically increased to the primary air pressure set value under the current load, and the two oil guns are automatically put into stable combustion.

[0037] The fan opening degree (X), unit load (Y), and number of operating coal mills (Z) when the primary air fan reaches its rated current can be determined through testing. The test steps are as follows:

[0038] Start the primary air fan on one side, and put the forced draft fan and induced draft fan on both sides into operation. Gradually increase the unit load and gradually increase the number of coal mills in operation according to the unit load. When the primary air fan current reaches the rated current, keep the unit load unchanged and record the fan opening degree X, unit load Y, and number of coal mills in operation Z at this time.

[0039] Example 1

[0040] like Figure 1 As shown, Unit 4 of a power plant is a 660MW ultra-supercritical unit equipped with two dual-stage adjustable axial-flow primary air fans, namely primary air fans A and B. In 2018, Unit 4 had a load of 640MW, operating in coordinated mode with AGC (Automatic Guided Vehicle) in operation. Coal mills A, B, C, D, E, and F were running, with a coal flow rate of 237t / h. Primary air fans A and B were operating with automatic blade operation, current of 126 / 133A, blade actuator feedback of 50 / 44%, and primary air main pipe pressure of 8kPa. Due to a hydraulic cylinder failure, the blades of primary air fan B in Unit 4 were completely shut off, triggering the unit's RB (Remote Protection Unit) protection. The blades of primary air fan A automatically opened, but during the adjustment process, the current of primary air fan A exceeded the rated current. Primary air fan A tripped due to the inverse time protection of the 6kV switch. All coal mills tripped due to low primary air flow, resulting in total fuel loss and a boiler MFT (Main Fuel Troubleshooting).

[0041] According to the judgment criteria of this invention, since the primary air blower B's moving blades are all closed, the current is less than 5A, and the differential pressure between the inlet and outlet of the primary air blower is less than 1kPa, it is judged that the primary air blower B has tripped. Therefore, the controller releases the automatic operation of the primary air blower B and closes the outlet damper of the primary air blower B. At this time, the unit load is high, and the output of the primary air blower on one side cannot meet the current load requirements. The controller automatically reduces the unit load to the maximum load of 350MW that the primary air blower can reach with the rated current. The controller automatically reduces the size of the forced draft fan and induced draft fan to track the load. The controller controls the primary air blower A to automatically open the moving blade opening to 93% of the maximum opening with the rated current and then releases the automatic operation of the primary air blower A, keeping the moving blade opening of the primary air blower A unchanged. The controller causes the upper coal mills D, E, and F to trip automatically, while maintaining the operation of the three coal mills A, B, and C at the bottom. The controller also controls the No. 1 and No. 3 oil guns to maintain stable combustion, avoiding the inverse time protection tripping due to the fan operating current exceeding the rated current, which would cause the boiler to MFT.

[0042] Any parts or structures not specifically described in this invention can be made using existing technologies or products, and will not be elaborated upon here.

[0043] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A control method for preventing boiler MFT triggered by primary air fan overcurrent protection, characterized in that, To prevent a boiler MFT (Main Fuel Trip) caused by improper adjustment of the primary air fan on one side due to overcurrent protection of the fan after a trip of the primary air fan on the other side, the control method includes the following steps:

1. Perform a test to determine if the fan has tripped; II. Protection actions after primary fan trip: When a single primary air fan trips, the automatic tripping of the tripped fan is deactivated, the outlet damper of the tripped fan is closed, and the unit control mode is switched from coordinated mode to machine-following mode. At the same time, the unit responds accordingly based on the unit load level to avoid triggering the boiler MFT. The steps to respond accordingly to the unit load level and avoid triggering a boiler MFT include: When the actual unit load is greater than Y, the unit load is automatically reduced to Y. The forced draft fan and induced draft fan adjust automatically according to the load. The primary fan automatically increases its output to the fan opening degree X and then the automatic fan operation is deactivated. The coal mills automatically jump from top to bottom to maintain the operation of the bottom Z coal mills and automatically put two oil guns into stable combustion. When the actual unit load is less than or equal to Y, the unit load is kept constant, the forced draft fan and induced draft fan are kept under automatic control, the number of coal mills in operation remains unchanged, the primary air fan is automatically increased to the primary air pressure set value under the current load, and two oil guns are automatically put into stable combustion. Among them, the fan opening degree X when the primary fan reaches the rated current, the unit load Y, and the number of coal mills in operation Z are determined by test; The test steps for determining the fan opening degree X, unit load Y, and number of coal mills in operation Z when the primary air fan reaches its rated current include: Start the primary air fan on one side, and put the forced draft fan and induced draft fan on both sides into operation. Gradually increase the unit load and gradually increase the number of coal mills in operation according to the unit load. When the primary air fan current reaches the rated current, keep the unit load unchanged and record the fan opening degree X, unit load Y, and number of coal mills in operation Z at this time.

2. The control method for preventing primary air fan overcurrent protection from triggering boiler MFT as described in claim 1, characterized in that, The criteria for determining the primary air turbine trip include: A primary fan is considered to have tripped if it meets all of the following conditions: (1) The primary air fan has been running for more than 10 minutes; (2) The primary air fan current is less than 5A; (3) The differential pressure between the inlet and outlet of the primary air blower is less than 1 kPa.

3. The control method for preventing primary air fan overcurrent protection from triggering boiler MFT according to claim 2, characterized in that, The formula for calculating the differential pressure between the inlet and outlet of the primary air fan is: The differential pressure between the inlet and outlet of the primary air blower = the total pressure at the outlet of the primary air blower - the total pressure at the inlet of the primary air blower.

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