CN105785759A - Separated bunker coal feeding thermal power generating unit coal feeding amount optimized distribution control method - Google Patents

Abstract

A control method for optimizing the distribution of coal supply to a coal-fired thermal power unit in bins, the method adopts an equal-proportion follow-up control system to control the coal supply of each coal mill of the thermal power unit, and in the control logic, the coal supply command of each coal mill Add a speed limit module, and set a speed limit bias value setting module at the control end of each speed limit module, and set the output value of each speed limit bias value setting module separately, so that when the total coal supply changes, the inferior coal The rate of change of the coal supply command is lower than the change rate of the coal supply command of high-quality coal. The present invention adds a speed-limiting module to the traditional coal supply control logic, realizes the individual control of the change rate and change range of the coal supply of each coal mill, and completely solves the problem of low-quality coal corresponding to the coal mill in the process of variable load of the unit. Due to the large fluctuation of the coal supply, the burner has problems such as blockage of the coal mill, vibration of the coal mill, and unstable combustion of the burner, thus ensuring the normal operation of the thermal power unit for coal distribution in bins.

Description

Optimum distribution control method for coal supply of coal-fired power units in sub-bin distribution

technical field

The invention relates to a method for optimizing the distribution of coal supply for a coal-fired power unit in separate bins and belongs to the technical field of power generation.

Background technique

In the coal market, the price of coal with high calorific value is obviously higher. The price of high-quality coal with a calorific value of 22MJ/kg is 2-3 times higher than that of low-quality coal with a calorific value of 15MJ/kg. The cost of coal combustion accounts for more than 70% of the overall operating cost of thermal power units. Under the basic conditions for the safe and stable operation of thermal power unit boilers, blending low-calorie low-quality coal can effectively reduce the fuel cost of thermal power companies and improve their profitability. In addition, due to the single use of low-quality coal and the pollution of the environment when stored and used, it is also in line with national economic and environmental protection policies for thermal power units to preferentially burn low-quality coal.

Thermal power unit boilers are designed for specific coal types. When the coal quality changes significantly, it may cause problems such as changes in the heat load of the boiler section, coking of the high-temperature heating surfaces of the furnace and flue, abnormal exhaust gas temperature, and insufficient output of the pulverizing system. Therefore, when a thermal power unit is blended with low-quality coal, it needs to go through rigorous tests to determine the nature of the blended coal and the proportion of coal blending. At present, thermal power plants mainly adopt two coal blending methods: coal yard coal blending and bin coal blending. Coal blending in the coal yard is to mix all kinds of coal in the coal yard evenly and then send them to the coal bunkers and coal mills. The coal burners of the boilers use the same type of coal; Different types of coal are distributed to different coal bunkers and coal mills, and the types of coal burned by each burner of the boiler are different. Compared with coal blending in coal yards, bin coal blending does not require additional on-site equipment, which is conducive to taking advantage of the advantages of various coal types to organize the combustion process in the furnace, and the operation mode is more flexible, but it also puts forward higher requirements for the control of boiler coal feed.

The vast majority of large-capacity thermal power units adopt the mode of parallel operation of multiple coal pulverizers in the positive pressure direct blowing medium-speed pulverizing system. The coal mill has minimum output and maximum output limitations. If the coal supply is too small, the direct collision between the grinding disc and the grinding roller of the coal mill will easily cause the mill to vibrate violently; when the coal supply is too large, it is difficult for the primary wind to blow out the coal powder in the mill, which may easily lead to blockage Fault. When the power generation load of a typical 600MW unit varies from 50% to 100%, 3, 4, 5, or 6 coal mills may be operated. The higher the unit load, the worse the coal grindability, and the more coal mills are running.

At present, the thermal power unit coal supply control adopts an equal-proportion follow-up control system, which can realize the following functions: (1) adopt closed-loop control to ensure that the total coal supply feedback can quickly follow the coal supply instruction; (2) the operator can set a certain coal mill Adjust the output of a certain coal mill under the condition that the total coal supply remains unchanged; (3) The change in the coal supply command is evenly distributed to each automatic coal feeder.

The coal supply equal-proportion following control system of a typical 600MW unit is shown in Fig. 1. In Fig. 1, "SUM1-1~SUM1-6" are six two-way coal supply summation modules; "SUM3" is a multiple Road coal supply summation module; "PID-1" is the coal supply PID (proportional, integral, differential) control module, "sp" is the set value input terminal, "pv" is the feedback value input terminal; "A1～ A6" is the setting module of the coal feed offset value of the six connected operator screens.

The characteristics of this control system are: the command signal of the total coal feeding amount of the boiler and the total coal feeding amount feedback signal obtained after summing the actual coal feeding amount signals of each coal mill enter into the coal feeding amount PID control module, and the coal feeding amount PID control module The output signal is superimposed with the coal feed bias signal set by the operator to form an automatic coal feed command signal for each coal mill. The working principle of the control system is: when the set value of the total coal feed of the boiler changes, the unbalanced input of the coal feed PID control module generates a corresponding control output signal, which is sent to the coal feed command side of each coal mill, and the actual coal feed of each coal mill The change of the coal supply changes the total coal supply, and finally makes the total coal supply feedback value equal to the coal supply setting value; when the operator modifies the coal supply command offset value corresponding to a certain coal mill, the mill When the coal feed command of the coal machine changes, the actual coal feed also changes and the total coal feed changes. If the input of the coal feed PID control module is unbalanced, the corresponding control output is generated, and the coal feed commands of all coal mills are adjusted. Finally, the feedback value of the total coal feed amount is equal to the set value of the coal feed amount. After the system reaches a new equilibrium state, the coal feed amount of the coal mill with a bias value is set to be different from the coal feed amount of other coal mills.

By setting the offset value, the basic output of each coal mill can be adjusted. For example, the total coal supply is 200t/h, A, B, C, D, a total of 4 coal mills are put into automatic operation, and the B coal mill is set with a bias of -12t/h. After the balance, the coal supply of each coal mill is : A mill 53t/h, B mill 41t/h, C mill 53t/h, D mill 53t/h. When the total coal supply increases by 40t/h, A, B, C, and D mills all increase the coal supply by 10t/h at the same rate. After stabilization, the coal supply of each coal mill is: A mill 63t/h, B mill Grinding 51t/h, C grinding 63t/h, D grinding 63t/h.

This control system has been very mature after long-term application. However, for coal blending in separate bins, the biggest problem is to evenly distribute the change in the coal supply command to each automatic coal feeder. The medium-speed coal mill widely used in thermal power units is very sensitive to changes in coal grindability. When the coal grindability decreases, the output of the coal mill will drop significantly or even blockage failure will occur. Low-quality coal with high ash and moisture content has poor grindability. In many cases, low-quality coal itself is coal gangue, coal slime, etc. left over from washing in the coal mining process, mixed with a large amount of foreign matter such as stones and sand. A lot of operating experience shows that the blockage of coal mill and primary air powder pipeline often occurs during the process of large changes in coal supply. For example, when the coal feed command of the boiler increases significantly, each coal mill will equally share the increase in coal feed. There is no problem with the coal mill feeding high-quality coal, but the coal mill feeding low-quality coal may occur. Jam fault. In addition, the ignition performance of low-quality coal is also very poor, and a large change in the amount of coal fed will lead to a large change in the pulverized coal flow rate of the corresponding burner, which will affect the combustion stability. Thirdly, when a certain coal mill has minor failures such as grinding discs and grinding roller wear and output drop, a large change in coal feed will lead to a rapid deterioration of the mill's operating status and be forced to stop for maintenance.

In order to avoid the above situation, operators often switch the coal feeder corresponding to the pulverizer fed with inferior coal or poor working condition to the manual state to maintain a stable coal supply, or add a negative bias to the command side of the coal supply. The resulting problems are as follows: the coal mill will lose its ability to adjust after manual switching, and the part of the change in the coal supply command is completely borne by other coal mills, resulting in poor operating conditions of other coal mills and burners; When the coal supply of the unit increases, the negative bias coal mill will not be blocked due to excessive coal supply, but when the coal supply decreases, it is prone to vibration due to too low coal supply.

To sum up, the existing coal supply control method cannot ensure the stable operation of the coal mill and the burner when the coal is divided into bins, and there is an urgent need for a method that can set different coal supply according to the coal quality of each coal mill. The control method of the increase and decrease rate and amplitude.

Contents of the invention

The purpose of the present invention is to aim at the drawbacks of the prior art, and provide a method for optimizing the distribution of coal supply to thermal power units in separate warehouses, which can set different coal supply increase and deceleration rates and ranges according to the coal quality of each coal mill , to ensure the stable operation of the coal mill and burner.

Problem described in the present invention is solved with following technical scheme:

A control method for optimizing the distribution of coal supply to a coal-fired thermal power unit in bins, the method adopts an equal-proportion follow-up control system to control the coal supply of each coal mill of the thermal power unit, and the coal supply command of each coal mill in the control logic Add a speed limit module, set a speed limit bias value setting module at the control end of each speed limit module, and set the output value of each speed limit bias value setting module separately, so that when the total coal supply changes, the inferior coal The rate of change of the coal supply command is lower than the change rate of the coal supply command of high-quality coal.

The above-mentioned method for optimal distribution and control of coal supply of thermal power units in bin-divided coal distribution, said method is also provided with a rate balance logic, said rate balance logic includes a total coal supply rate limit value setting module, a rate balance PID control module, a multi-channel The rate summation module and multiple two-way rate summation modules corresponding to each coal mill one by one, the set value input terminal of the rate balance PID control module is connected to the total coal supply rate limit value setting module, and the feedback value The input terminal is connected to the output terminal of the multi-channel rate summation module; one input terminal of each dual-channel rate summation module is connected to the speed limit bias value setting module of the corresponding coal mill speed limit module, and the other input terminal is connected to the rate balance The output terminal of the PID control module and the output terminal of the two-way rate summation module are connected to the input terminal of the speed limiting module of the corresponding coal mill and connected to an input terminal of the multi-channel rate summation module.

In the above-mentioned method for optimal distribution and control of coal supply of thermal power units for coal distribution in bins, the equal-proportion follow-up control system includes a multi-channel coal supply summation module, a coal supply PID control module, and multiple coal mills one-to-one corresponding to each coal mill. A two-way coal supply summation module and a plurality of coal supply offset value setting modules, the multiple input terminals of the multi-channel coal supply summation module are respectively connected to the actual coal supply signals of each coal mill. The output terminal of the coal supply summation module is connected to the feedback value input terminal of the coal supply PID control module; the set value input terminal of the coal supply PID control module is connected to the boiler total coal supply command signal; each two-way One input terminal of the coal supply summation module is connected to the output terminal of the coal supply PID control module, the other input terminal is connected to the coal supply bias value setting module of the corresponding coal mill, and the two-way coal supply summation module The output terminal provides the coal quantity instruction for the corresponding coal mill.

The present invention adds a speed-limiting module to the traditional coal supply control logic, realizes the individual control of the change rate and change range of the coal supply of each coal mill, and completely solves the problem of low-quality coal corresponding to the coal mill in the process of variable load of the unit. Due to the large fluctuations in the amount of coal fed to the burner, problems such as blockage of the coal mill, vibration of the coal mill, and unstable combustion of the burner occur, thereby ensuring the normal operation of the thermal power unit for coal distribution in bins.

Description of drawings

Figure 1 is the existing typical 600MW unit coal supply control system;

Figure 2 is a typical 600MW unit coal feeding control system after improvement.

The labels in the figure are represented as: SUM1-1～SUM1-6, the first two-way coal supply summation module to the sixth two-way coal supply summation module; SUM2-1～SUM2-6, the first two-way speed Summing module ~ the sixth two-way speed summation module; SUM3, multi-way coal supply summation module; SUM4, multi-way speed summation module; A1 ~ A6, the first coal supply offset value setting module ~ the first Six coal supply offset value setting modules; B1~B6, the first speed limit offset value setting module to the sixth speed limit offset value setting module; C, the total coal supply amount speed limit value setting module; PID-1, coal supply PID control module; PID-2, rate balance PID control module; V1<～V6<, first speed limit module to sixth speed limit module.

detailed description

The present invention will be further described below in conjunction with accompanying drawing.

Aiming at the problem that the existing control system of the thermal power unit that implements bin-divided coal distribution cannot allocate the coal feed of each coal mill according to the coal quality, the present invention proposes a control method for optimizing the distribution of coal feed. This method is based on the existing conventional coal supply control system of thermal power units, and adds a change rate limiting function module on the automatic command signal channel of each coal mill coal supply, and adds a balance logic of the total coal supply change rate. Operators can individually set the bias value of the rate limit of coal feed rate change for each coal mill and set the rate limit value of the total coal feed rate limit. Realize the function of low-quality coal corresponding to low-speed and small-scale changes in the coal feed rate of the coal mill, and high-quality coal corresponding to the function of high-speed and large-scale changes in the coal feed rate of the coal mill, effectively reducing the working status of each coal mill and burner under variable load conditions Unstable probability.

When the coal supply changes, the thermal power unit that implements bin coal blending hopes that the low-quality coal will correspond to a low rate and small change in the coal supply of the coal mill. The function of the change rate limiting module (referred to as speed limit module) commonly used in automatic control is: when the change rate of the input signal is lower than the set rate, the output signal is equal to the input signal; when the change rate of the input signal is higher than the set rate, the output signal Follows the input signal at a set rate of change. In the original control logic, the speed limit module is added to the command of the coal supply of each coal mill, and the change rate of the inferior coal supply command is set to be low, which can realize the low rate and small change of the inferior coal supply when the total coal supply changes. function.

For example, the total coal supply is 200t/h, A, B, C, D, a total of 4 coal mills are running in automatic state, B coal mill is set with a bias of -12t/h, and the speed limit value of B mill coal supply is 1( t/h)/s, and the speed limit value of the other grinding coal is 3(t/h)/s. When the total coal feed increases by 40t/h, the coal feed increase rate of B mill is 1(t/h)/s, and that of other mills is 3(t/h)/s. After stabilization, the coal feed of each coal mill is : A is 65t/h, B is 45t/h, C is 65t/h, D is 65t/h, the coal feed to B mill is increased by 4t/h, and the other mills are increased by 12t/h. Adding a speed-limiting module at the coal-feeding command of each coal mill can change the change rate and range of the coal-feeding quantity of each coal-mill when the total coal-feeding quantity changes, and the two are directly proportional.

In order to avoid the situation that the speed limit value of all pulverizer coal supply commands is set too low and the total coal supply feedback cannot quickly follow the total coal supply command, it is also necessary to increase the rate balance logic. The set value of the change rate limit of the total coal supply is set by the operator, and the sum of the change rate limit values of the coal supply of all automatic coal mills is the actual coal supply change rate limit feedback value, which is respectively introduced into the PID controller. At the same time, the coal feed rate limit of each coal mill is introduced in the form of an offset value, which is added to the output of the PID controller to form the actual rate limit value of each coal mill. Closed-loop control can ensure that the actual coal supply change rate limit value is equal to the set value. For example, a total of 4 coal mills A, B, C, and D run in automatic state, and the set value of the speed limit for the total coal supply is 10 (t/h)/s. The speed limit offset value of the coal feeding amount of B mill is -2(t/h)/s, then the actual coal feeding speed limit value of B mill is 1(t/h)/s, and the other mills are 3(t/h) /s, the effect is the same as the previous example.

The following takes 6 coal mills of a 600MW unit as an example to illustrate, as shown in Figure 2, the dotted line box is the new logic added on the basis of the original coal supply control logic. Including the following functional modules: the total coal supply rate limit value setting module C, which is set by the operator on the operator station screen; the rate balance PID control module PID-2, which receives the output of C and SUM4 to ensure the actual coal supply limit The speed value is equal to the set value; the speed limit offset value setting module B1~B6 of the coal feeder coal supply is set by the operator on the operator station screen; the two-way speed summation module SUM2-1~SUM2-6 ;Speed limit module V1<～V6<, receiving the value output by the two-way rate summation module SUM2-1～SUM2-6, and performing speed limit processing on the automatic command of coal supply in the original logic; multi-channel rate summation module SUM4. Among them, the speed limit bias value setting module, the two-way rate summation module, and the speed limit module include a total of 6 channels.

In Fig. 2, V1<～V6< is a speed limiting module, whose function is to limit the change rate of the input signal at the longitudinal input terminal within the range of the rate set at the horizontal control terminal.

Implementation steps

(1) Confirmation of the original control logic.

Before implementing this scheme, it is necessary to analyze the control logic of the unit’s coal supply to confirm that its basic logic structure is the same as that of the equal-proportion following control system shown in Figure 1. This control scheme can be applied as long as it conforms to the basic feature of distributing the total coal feed command to the coal feed command of each coal mill in equal proportion. In addition, in different control logics, the command unit of the unitized coal feed amount is different, some are kg/s, some are t/h, and some are the percentage of the rated coal feed amount of the unit, etc., when calculating the speed limit value, it is necessary to Scale conversion.

(2) Control logic configuration.

Comparing with Figure 2, in the on-site control devices such as DCS (distributed control system) and PLC (programmable logic controller) of the unit, the control logic is realized by configuration, and the new logic is added in the dashed box. Figure 2 shows the control logic of a 600MW unit with 6 coal mills. The configuration scheme for units with different numbers of coal mills and different capacities is similar to it. The difference is that the number of coal mill command channels is different.

In field configuration, the speed limiting module can be replaced by other modules such as inertial and low-pass filtering, which can also achieve the same functions as the present invention, and the design method remains unchanged and is within the scope of this patent claim.

(3) Operation screen design.

On the operation screen of the corresponding equipment in the DCS and PLC operator station of the unit, add the analog quantity input operation panel for the offset value of the coal feed rate limit of each coal mill and the speed limit set value of the total coal feed rate. Realize the function of setting the speed limit value of the coal feeding amount of each coal mill and the speed limiting value of the total coal feeding amount by the operating personnel.

The control logic described in the present invention can be used directly without debugging.

Advantages of the invention

(1) The control effect is good. For thermal power units with coal distribution in bins, the present invention can individually control the change rate and range of coal feed to each coal mill according to the coal quality, and solve the problem of fluctuations in coal feed to coal pulverizers and burners due to low-quality coal in the process of unit load change. If the amplitude is large, problems such as blockage of the coal mill, vibration of the coal mill, and unstable combustion of the burner will occur.

(2) Simple configuration, no debugging, easy to use. The control scheme of the present invention is easy to be implemented in a configuration mode in control devices such as DCS and PLC, and can be directly used without debugging parameters. The parameters involved in the present invention need to be set by operating personnel with clear physical meaning, simple setting operation and convenient use.

Claims (3)

1. A method for optimally distributing coal supply of coal-fired power units in bins, characterized in that the method adopts an equal-proportion follow-up control system to control the coal supply of each coal mill of the thermal power unit and each pulverizes coal in the control logic. A speed limit module is added at the position of the machine coal supply command, and a speed limit bias value setting module is set at the control end of each speed limit module. By setting the output values of each speed limit bias value setting module respectively, the total supply When the coal quantity changes, the rate of change of the command of the quantity of inferior coal is lower than the rate of change of the command of the quantity of high-quality coal. 2. A method for optimally distributing coal supply to thermal power units according to claim 1, characterized in that, the method is also provided with a rate balance logic, and the rate balance logic includes a total coal supply limit Speed value setting module (C), rate balance PID control module (PID-2), multi-channel rate summation module (SUM4) and multiple dual-channel rate summation modules corresponding to each coal mill, the The set value input terminal of the rate balance PID control module (PID-2) is connected to the total coal supply rate limit value setting module (C), and the feedback value input terminal is connected to the output terminal of the multi-channel rate summation module (SUM4); One input terminal of a two-way rate summation module is connected to the speed limit bias value setting module of the corresponding coal mill speed limit module, and the other input terminal is connected to the output terminal of the rate balance PID control module (PID-2). The output terminal of the rate summation module is connected to the input terminal of the speed limiting module of the corresponding coal mill and connected to an input terminal of the multi-channel rate summation module (SUM4). 3. According to claim 1 or 2, a control method for optimizing the distribution of coal supply of thermal power units in bin distribution, characterized in that, the equal-proportion follow-up control system includes a multi-channel coal supply summation module (SUM3) , coal supply PID control module (PID-1) and multiple two-way coal supply summation modules and multiple coal supply offset value setting modules corresponding to each coal mill. The multiple input ends of the coal quantity summation module (SUM3) are respectively connected to the actual coal supply signal of each coal mill, and the output terminals of the multi-channel coal supply quantity summation module (SUM3) are connected to the coal supply quantity PID control module (PID- 1) Feedback value input terminal; the set value input terminal of the coal supply PID control module (PID-1) is connected to the boiler total coal supply command signal; one input terminal of each two-way coal supply summation module Connect to the output terminal of the coal supply PID control module (PID-1), the other input terminal is connected to the coal supply offset value setting module of the corresponding coal mill, and the output terminal of the two-way coal supply summation module is the corresponding mill The coal machine provides the coal quantity instruction.