Method for automatic regulation of a turbo-feed pump in the vicinity of the critical point of opening the recirculation valve

Abstract

The application discloses an automatic adjusting method of steam-driven feed water pumps near a critical point of opening a recirculation valve, and comprises the following steps: when reaching the critical point of simultaneously opening the recirculation valves of two steam-driven feed water pumps, setting a rotating speed offset amount for one of the steam-driven feed water pumps, slowly increasing the corresponding steam pump inlet flow, and moving away from the critical point of opening the corresponding recirculation valve, only slowly opening the corresponding recirculation valve of the other steam-driven feed water pump. The automatic adjusting method of steam-driven feed water pumps near a critical point of opening a recirculation valve provided by the application can realize that, by opening a single recirculation valve, the supercritical coal-fired unit will not cause too large main feed water flow fluctuation when near the critical point of opening the recirculation valve during unit load change, and is particularly suitable for supercritical coal-fired units with two steam-driven feed water pumps with 50% capacity.

Description

Technical Field

[0001] This invention belongs to the field of industrial automation technology, specifically relating to an automatic adjustment method for a steam-driven feedwater pump near the critical point of opening the recirculation valve. Background Technology

[0002] In recent years, my country's thermal power units have developed rapidly, with supercritical and ultra-supercritical coal-fired units becoming the main power generation type in the country. For ultra-supercritical coal-fired units, the load (BD) versus feedwater flow target curve is as follows: Figure 1 As shown, by Figure 1 It can be seen that the feedwater flow rate around 500MW is approximately 1240t / h. When both steam pumps are simultaneously operating automatically, the average outlet flow rate of each steam pump is approximately 620t / h. Figures 2-3 As shown, when the inlet flow rate of the steam pump is less than 620 t / h, the recirculation valve of the steam-driven feedwater pump needs to be opened to its maximum opening degree (100%), and the inlet flow rate of the steam pump is 380 t / h. When the recirculation valves of the two steam-driven feedwater pumps are opened at the same time, it will cause a large disturbance to the main feedwater flow rate, which may lead to a low main feedwater flow rate and a potential MFT (Main Fuel Turbine Flow).

[0003] The information disclosed in the background section is only for enhancing the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0004] To address the technical problems existing in the prior art, the present invention aims to provide an automatic adjustment method for a steam-driven feedwater pump near the critical point of opening the recirculation valve.

[0005] To achieve the above objectives and technical effects, the technical solution adopted by this invention is as follows:

[0006] An automatic adjustment method for a steam-driven feedwater pump near the critical point of opening the recirculation valve includes the following steps:

[0007] When the critical point is reached where the recirculation valves of both steam-driven feedwater pumps open simultaneously, a speed offset is set for one of the steam-driven feedwater pumps to slowly increase the inlet flow rate of the corresponding pump, moving it away from the critical point of opening the corresponding recirculation valve, so that only the other steam-driven feedwater pump slowly opens the corresponding recirculation valve.

[0008] Furthermore, to set a speed offset for one of the steam-driven feedwater pumps, allowing only the other steam-driven feedwater pump to slowly open the corresponding recirculation valve, the following conditions must be met simultaneously:

[0009] 1) Both the boiler main control command and the unit load command are less than the critical value;

[0010] 2) two steam-driven feed water pumps corresponding to the steam pump inlet flow is less than a certain value, at the critical point near the opening of the recirculation valve;

[0011] 3) two steam-driven feed water pumps corresponding to the recirculation valve are not opened;

[0012] 4) the speed of the two steam-driven feed water pumps is in automatic control mode;

[0013] 5) the recirculation valve capable of slow opening is in automatic control mode.

[0014] Further, a speed offset is set for one of the steam-driven feed water pumps, and only the other steam-driven feed water pump slowly opens the corresponding recirculation valve, which needs to meet the following conditions:

[0015] 1) the boiler main control instruction and the unit load instruction are less than 500MW;

[0016] 2) the steam pump inlet flow corresponding to the two steam-driven feed water pumps is less than 660t / h, at the critical point near the opening of the recirculation valve;

[0017] 3) the maximum value of the recirculation valve opening degree corresponding to the two steam-driven feed water pumps is less than 3%, at this time, the recirculation valve corresponding to the two steam-driven feed water pumps is not opened;

[0018] 4) the speed of the two steam-driven feed water pumps is in automatic control mode;

[0019] 5) the recirculation valve capable of slow opening is in automatic control mode.

[0020] The speed offset is 50r / min, and the rising rate is 2-3rpm / s.

[0021] When the unit load instruction is greater than 520MW, the feed water flow target value is far away from the critical point of the opening of the recirculation valve of the two steam-driven feed water pumps, and the steam-driven feed water pump recovers from the speed offset to 0 offset at a rate of 2-3rpm / s, so that the two steam-driven feed water pumps restore output balance.

[0022] The boiler main control instruction is less than 500MW, the feed water flow instruction is 1240t / h, and the two steam-driven feed water pumps are in the critical point near the opening of the recirculation valve when they are running simultaneously.

[0023] Compared with the prior art, the beneficial effects of the present application are:

[0024] The application discloses an automatic adjusting method of steam-driven feed water pump near a critical point of opening a recirculation valve, and comprises the following steps: when reaching the critical point of simultaneously opening the recirculation valves of two steam-driven feed water pumps, setting a rotating speed offset amount for one of the steam-driven feed water pumps, slowly increasing the corresponding steam pump inlet flow, and far from the critical point of opening the corresponding recirculation valve, only slowly opening the corresponding recirculation valve of the other steam-driven feed water pump. The automatic adjusting method of steam-driven feed water pump near the critical point of opening the recirculation valve provided by the application can realize that, when the supercritical coal-fired unit is in the process of changing the unit load, the steam-driven feed water pump can be opened to prevent the main feed water flow from being excessively fluctuated near the critical point of opening the recirculation valve, and is particularly suitable for the supercritical coal-fired unit with two steam-driven feed water pumps with a capacity of 50%. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a load and feed water flow target value graph;

[0026] Figure 2 is a steam-driven feed water pump recirculation valve double-fold line control strategy graph;

[0027] Figure 3 is a double-fold line graph of the steam-driven feed water pump recirculation valve double-fold line control strategy graph;

[0028] Figure 4 is a flowchart of the application. DETAILED DESCRIPTION

[0029] The application will be described in detail below so that the advantages and features of the application can be more easily understood by those skilled in the art, and the protection scope of the application can be more clearly and explicitly defined.

[0030] The following presents a simplified summary of one or more aspects in order to provide a basic understanding of such aspects. This summary is not an extensive overview of all contemplated aspects, and is intended to neither identify key or critical elements of all aspects nor delineate the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that is presented later.

[0031] As Figure 4 shown, the application discloses an automatic adjusting method of steam-driven feed water pump near a critical point of opening a recirculation valve, which can realize that, when the supercritical coal-fired unit is in the process of changing the unit load, the steam-driven feed water pump can be opened to prevent the main feed water flow from being excessively fluctuated near the critical point of opening the recirculation valve, and is particularly suitable for the supercritical coal-fired unit with two steam-driven feed water pumps with a capacity of 50%. The method specifically comprises the following steps:

[0032] When the critical point of the two steam-driven feed water pumps is reached, in order to reduce the disturbance, a speed bias is set for one of the steam-driven feed water pumps, so that the corresponding steam pump inlet flow is slowly increased at a certain rate, and the critical point of opening the corresponding recirculation valve is slowly stabilized away, under the control of the steam pump feed water flow regulation loop, only the other steam-driven feed water pump slowly opens the corresponding recirculation valve, the opening of a single recirculation valve causes less disturbance to the steam pump outlet flow, and the main feed water flow will not fluctuate greatly due to the simultaneous opening of the two recirculation valves.

[0033] The above adjustment method needs to meet the following five conditions:

[0034] 1) The boiler master control command and the unit load command are both less than the critical value;

[0035] 2) The steam pump inlet flow of the two steam-driven feed water pumps is less than a certain value, near the critical point of opening the recirculation valve;

[0036] 3) The corresponding recirculation valves of the two steam-driven feed water pumps are not opened;

[0037] 4) The speed of the two steam-driven feed water pumps is in automatic control mode;

[0038] 5) The recirculation valve that can be slowly opened is in automatic control mode;

[0039] It should be particularly pointed out that when the unit load command is greater than the critical value, condition 1) is not met, at this time, the speed bias needs to be restored to 0 bias at a rate of 2-3 rpm / s, so that the two steam-driven feed water pumps restore the output balance and restore the state before automatic adjustment; wherein the speed bias is 50 r / min;

[0040] When the unit load command is greater than the critical value, the feed water flow target value is away from the critical point of opening the recirculation valve of the two steam-driven feed water pumps, and the two steam-driven feed water pumps can restore to the state before automatic adjustment.

[0041] The above adjustment method can effectively avoid the instability of the main feed water flow caused by the opening of the recirculation valve during the unit load variation.

[0042] It should be noted that if the speed of any steam-driven feed water pump is in manual control mode, it cannot be adjusted by the present application because it cannot meet condition 4).

[0043] Example 1

[0044] As shown in Figure 1 and 4 , an automatic adjustment method for a steam-driven feed water pump near the critical point of opening the recirculation valve, comprising the following steps:

[0045] When the critical point of the two steam-driven feed water pumps is reached, in order to reduce the disturbance, a speed bias of 50 r / min is set for one of the steam-driven feed water pumps (referred to as steam-driven feed water pump A), so that the corresponding steam pump inlet flow (referred to as steam-driven feed water pump A inlet flow) is slowly increased at a certain rate, and the critical point of the slowly stable opening of the recirculation valve (referred to as A steam pump recirculation flow valve) is far away. Under the control of the steam pump feed water flow regulation loop, only the other steam-driven feed water pump (referred to as steam-driven feed water pump B) slowly opens the corresponding recirculation valve (referred to as B steam pump recirculation flow valve). The opening of a single recirculation valve causes less disturbance to the steam pump outlet flow, and the main feed water flow will not fluctuate greatly due to the simultaneous opening of the two recirculation valves.

[0046] The above adjustment method needs to meet the following conditions:

[0047] 1) The boiler main control command and the unit load command are both less than 500 MW;

[0048] 2) The steam pump inlet flow corresponding to the two steam-driven feed water pumps is less than 660 t / h, which is near the critical point of opening the recirculation valve;

[0049] 3) The maximum opening of the recirculation valve corresponding to the two steam-driven feed water pumps is less than 3%, at which time the recirculation valve corresponding to the two steam-driven feed water pumps is not opened;

[0050] 4) The speed of the two steam-driven feed water pumps is in automatic control mode;

[0051] 5) The recirculation valve that can be slowly opened is in automatic control mode;

[0052] When the unit load command is greater than 520 MW, condition 1) above is not met. At this time, the speed bias needs to be restored to 0 bias at a rate of 2 rpm / s, so that the two steam-driven feed water pumps restore the output balance and return to the state before automatic adjustment;

[0053] When the unit load command is greater than 520 MW, the feed water flow target value is far from the critical point of opening the recirculation valve of the two steam-driven feed water pumps, and the two steam-driven feed water pumps can restore the state before automatic adjustment;

[0054] Through the above adjustment method, the instability of the main feed water flow caused by the opening of the recirculation valve near the critical point of the steam pump inlet flow during the unit load variation process (near 500 MW) can be effectively avoided.

[0055] When the boiler main control command is less than 500 MW, the feed water flow command is 1240 t / h, and the two steam-driven feed water pumps are simultaneously operated near the critical point of opening the recirculation valve.

[0056] The parts or structures not specifically described in the present application can be realized by using the prior art or existing products, and will not be described here.

[0057] The above is only an embodiment of the present application, and does not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation using the content of the present application specification, or direct or indirect application in other related technical fields, is also included in the patent protection scope of the present application.

Claims

1. A method of automatic regulation of a turbo-feed water pump in the vicinity of the critical point of opening the recirculation valve, characterized by, The method comprises the following steps: When reaching the critical point of simultaneously opening the recirculation valves of the two steam-driven feed water pumps, a speed offset is set for one of the steam-driven feed water pumps to slowly increase the corresponding steam pump inlet flow, to move away from the critical point of opening the corresponding recirculation valve, and only slowly open the corresponding recirculation valve of the other steam-driven feed water pump; The following conditions are met when setting the speed offset for one of the steam-driven feed water pumps and only slowly opening the corresponding recirculation valve of the other steam-driven feed water pump: 1) The boiler main control instruction and the unit load instruction are both less than 500 MW; 2) The steam pump inlet flows corresponding to the two steam-driven feed water pumps are both less than 660 t / h, and are near the critical point of opening the recirculation valve; 3) The maximum values of the recirculation valve openings corresponding to the two steam-driven feed water pumps are both less than 3%, and at this time, the recirculation valves corresponding to the two steam-driven feed water pumps are not opened; 4) The speeds of the two steam-driven feed water pumps are both in the automatic control mode; 5) The recirculation valve that can be slowly opened is in the automatic control mode; The speed offset is 50 r / min, and the rising rate is 2-3 rpm / s; When the unit load instruction is greater than 520 MW, the feed water flow target value moves away from the critical point of opening the recirculation valves of the two steam-driven feed water pumps, the steam-driven feed water pump recovers from the speed offset to 0 offset at a rate of 2-3 rpm / s, and the two steam-driven feed water pumps restore the output balance; The boiler main control instruction is less than 500 MW, the feed water flow instruction is 1240 t / h, and when the two steam-driven feed water pumps are simultaneously operated, they are near the critical point of opening the recirculation valve.

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