JP5131448B2 - Steam generator - Google Patents

Description

  The present invention relates to a steam generator provided in parallel with a plurality of once-through boilers capable of controlling the combustion amount in stages, and each of the once-through boilers is made to follow fluctuations in a load supplied with steam from the once-through boiler. The present invention relates to a steam generator capable of optimally controlling the amount of combustion of the gas.

  Sterilizers used for sterilization of beverages, liquid foods, etc. (liquid products) are configured to heat the liquid products using steam. Incidentally, the sterilization temperature of the liquid product in the sterilizer varies depending on the supply amount of the liquid product to be passed through the sterilizer and the steam supply amount to the sterilizer. Therefore, generally, the pressure (steam pressure) of steam output from the steam generator is controlled to be constant according to the operating conditions of the sterilizer (load), thereby stabilizing the sterilization temperature for the liquid product. I am doing so.

Incidentally, in a steam generator using a large-capacity ordinary boiler, stabilized high-pressure steam is obtained by reducing the pressure of high-pressure steam generated by the boiler via a pressure reducing valve. However, it is necessary to increase the pressure of the steam generated by the boiler as much as the steam pressure is reduced by using the pressure reducing valve, and it is undeniable that energy is wasted. Therefore, a plurality of once-through boilers having a small capacity are used, and the plurality of once-through boilers are selectively operated according to the required amount of steam (see, for example, Patent Documents 1 and 2). This control is referred to as boiler operation number control. The once-through boiler is generally capable of switching the burner combustion amount between two stages or three stages, so that the amount of combustion in each of the once-through boilers is step by step according to the required amount of steam. It is also being controlled.
JP 2004-317105 A JP 2006-317104 A

  By the way, when controlling the amount of combustion of each once-through boiler while controlling the number of operation of a plurality of once-through boilers, the amount of combustion can be controlled almost continuously as a whole. However, since each of these once-through boilers is independent, for example, when the combustion amount is increased by one stage, there may occur a state where the stopped once-through boiler must be reignited. Moreover, if the once-through boiler to be re-ignited is in the cold can state, it cannot be denied that it takes time until the steam is obtained from the ignition. The combustion characteristics of such a once-through boiler are control characteristics including a dead time delay from the viewpoint of feedback control, and in general, the combustion control is very difficult.

  Each once-through boiler can control the amount of combustion only in a stepwise manner as described above. Therefore, when feedback control is performed for the combustion amount of the once-through boiler following the load fluctuation, generally, the pressure of the steam (load steam pressure) generated under the stepwise combustion control and the target steam pressure There is no denying that there is a gap between them. Accordingly, the once-through boiler is alternately controlled between a combustion amount capable of generating steam exceeding the target steam pressure and a combustion amount capable of generating steam lower than the target steam pressure one stage lower than the combustion amount. . As a result, the load vapor pressure is alternately changed in a short cycle with the target vapor pressure interposed therebetween, and when the load vapor pressure is averaged over time, the load vapor pressure is controlled to become the target vapor pressure.

  However, as described above, since the once-through boiler includes a dead time delay element, if the amount of combustion of the once-through boiler is feedback-controlled as described above, overshoot is likely to occur, resulting in a problem that the fluctuation of the steam pressure increases. . Furthermore, if the control gain is increased, that is, if the pressure control width is narrowed, the possibility of step-out (oscillation) starting from slight pressure fluctuation increases.

  The present invention has been made in view of such circumstances, and its purpose is to provide the pressure of steam to supply the combustion amount of a plurality of once-through boilers whose combustion amount can be controlled in stages to the load from the once-through boiler. Steam generating apparatus that performs feedback control according to the control, and has a control system capable of stably following and controlling the load steam pressure against load fluctuations without causing control out-of-step (oscillation) To provide an apparatus.

In order to achieve the above-mentioned object, a steam generator according to the present invention includes a plurality of once-through boilers provided in parallel, a steam header that outputs steam generated by these once-through boilers, and the steam. A controller for controlling the amount of steam generated by each once-through boiler according to the steam pressure supplied from the header to the load,
The control device divides the plurality of once-through boilers into two boiler groups, and controls the combustion amount of one of the boiler groups in accordance with the change in the steam pressure accompanying the change in the amount of steam generated in the once-through boiler. A first control system and a second control system for controlling the combustion amount of the other boiler group according to the change in the vapor pressure accompanying the change in the load are provided.

  Incidentally, the first control system uses P control (proportional control) or PD control (proportional / differential control) for the combustion amount of the one boiler group in accordance with the deviation between the steam pressure supplied to the load and the target steam pressure. The second control system is realized by using a first PID controller, and a combustion amount of the other boiler group according to a deviation between a steam pressure supplied to the load and the target steam pressure. Is realized using a second PID controller that performs PI control (proportional / integral control).

Each of the once-through boilers is provided with a burner capable of controlling the combustion amount in multiple stages, and the first and second control systems have the plurality of units according to the vapor pressure to be supplied to the load. The number of operating once-through boilers is controlled, and the combustion amount of each once-through boiler is controlled stepwise.
The boiler group whose combustion amount is controlled by the first control system is composed of at least one once-through boiler that is constantly ignited, and the boiler group whose combustion amount is controlled by the second control system is: The remaining once-through boilers in the plurality of once-through boilers are selectively fired and stopped and used for controlling the number of operating units.

  The load comprises a sterilizer that heats and sterilizes the liquid product through a conduit through which the liquid product flows, for example, via a flow rate adjusting valve.

  According to the present invention, one of the two groups of boilers is controlled according to the change in the steam pressure accompanying the change in the amount of steam generated in the once-through boiler, whereby the steam accompanying the stepwise combustion control of the once-through boiler. Since the pressure fluctuation is kept small, it is possible to suppress the influence on the control system that controls the combustion of the other boiler group in accordance with the change in the steam pressure accompanying the load fluctuation. As a result, the one boiler group can be controlled with high responsiveness under a high control gain, and the other boiler group can be stably controlled with a control time delay.

  More specifically, P control (proportional control) with a narrow pressure control width is performed using at least one once-through boiler (one boiler group) that is always in a combustion state, and unintentional pressure is used as necessary. Since D control (differential control) is executed to suppress the fluctuation, when the steam pressure fluctuates due to the excess or deficiency of the steam amount with respect to the load, the combustion amount of the once-through boiler is quickly controlled, and the load steam pressure is reduced. Can be constant. In addition, when the load fluctuates, the combustion state of the other boiler group in accordance with the fluctuation of the load steam pressure accompanying this, that is, the number of operation of a plurality of once-through boilers included in the other boiler group and each Since the stepwise combustion amount of the once-through boiler is controlled, it is possible to smoothly control the load steam pressure by following the fluctuation of the load. In this case, the control of the combustion amount is controlled without abruptly changing the control amount by executing the feedback control mainly based on the I control (integral control) in anticipation of the delay in the control response, and the generated steam amount is fluctuated in the load. It becomes possible to follow.

  Therefore, when using multiple once-through boilers that can only perform stepwise combustion control, and when controlling the number of operating these once-through boilers, it is possible to control changes in the load state through extremely fine combustion control according to the load state. It becomes possible to stably obtain the following vapor pressure. Accordingly, the operating state of the load can be kept stable.

Hereinafter, with reference to drawings, the steam generator concerning one embodiment of the present invention is explained.
FIG. 1 is a schematic configuration diagram of a sterilization system for sterilizing a liquid product using steam, in which 10 is a steam generator for generating steam, and 20 is a sterilizer serving as a load for the steam generator 10. The sterilizer 20 is provided along a conduit 22 through which the liquid product supplied with the flow rate adjusted via a flow rate adjusting valve 21 is supplied, and the flow rate adjusted via the flow rate adjusting valve 23. And a steam pipe 24 for heating the liquid product flowing through the pipe 22 through the supplied steam.

  The steam generator 10 according to the present invention drives the sterilizer 20 by supplying steam to the sterilizer 20 described above, and basically a plurality of once-through boilers 11a to 11n provided in parallel. The steam generated by each of the once-through boilers 11a to 11n using the steam header 12 is integrated (collectively) and output. Note that the pressure of the steam (load steam pressure) supplied from the steam header 12 to the sterilizer (load) 10 described above is detected by a pressure gauge 13, and the controller 14 controls the combustion of each of the once-through boilers 11a to 11n. Provided.

  Incidentally, each of the once-through boilers 11a to 11n is a so-called small capacity type capable of generating a steam pressure of about 1.0 MPa at maximum by generating, for example, steam of up to about 2.5 t per hour. The once-through boilers 11a to 11n can generally control the amount of combustion in two stages, for example, 100% combustion and 50% combustion, or in three stages of 100% combustion, 66% combustion, and 33% combustion. Configured. It can be said that the combustion amount can be controlled in three stages and four stages including stop (fire extinguishing).

  Now, the steam generator 10 according to the embodiment of the present invention includes a first boiler group A including at least one once-through boiler in which the above-described plurality of once-through boilers 11a to 11n are always kept in an ignition state, and the rest. Divided into a second boiler group B which is stopped and ignited according to the load state and used for operation number control, and the combustion amount of each of these boiler groups A and B is transferred to the pressure gauge 13 Control is performed according to the load vapor pressure detected in this manner. In particular, a first control system 14a that performs P control (proportional control) or PD control (proportional derivative control) on the first boiler group A according to a deviation between the target steam pressure and the load steam pressure, and a second control system 14a The boiler group B includes a second control system 14b that performs PI control (proportional integral control) in accordance with a deviation between the target steam pressure and the load steam pressure.

  That is, as shown in the block diagram of the boiler pressure control in FIG. 2, the steam generated in the plurality of once-through boilers 11 a to 11 n (first and second boiler groups A and B) passes through the steam header 13. It is sent out through integration. The pressure of the steam sent to the load in this way changes due to disturbance caused by the capacity of the piping system and ignition / combustion delay of a burner (not shown) in each boiler, and the load (sterilizer 20 ) Also varies depending on the driving condition. The load steam pressure including such a variable element is detected by the pressure gauge 13 and fed back to control the combustion amount of each of the once-through boilers 11a to 11n (first and second boiler groups A and B). Is done.

  Incidentally, the combustion amount control of the boiler is performed by using the PID controllers that respectively construct the first and second control systems 14a and 14b based on the deviation between the target steam pressure and the load steam pressure as described above. In particular, the first control system 14a that executes the combustion control for the once-through boiler of the first boiler group A that is always in the ignition state has a control condition in which the control gain is increased, that is, the pressure control width is reduced. Based on the above deviation, the combustion amount is controlled by P control, preferably PD control. In other words, for the once-through boiler that is always kept in the ignition state, the time delay element that accompanies the operation stop and the resumption of combustion does not enter its control characteristics. And the amount of combustion is controlled by multiplying by D control which works to suppress pressure fluctuation. As a result, even if the steam pressure fluctuates due to the excess or deficiency of the steam amount with respect to the load (sterilizer 20), the combustion amount can be changed with good responsiveness to the fluctuation.

  On the other hand, for the once-through boiler of the second boiler group B, the amount of combustion is PI-controlled including the operation stop of each once-through boiler based on the deviation by the second control system 14b described above. Is done by. Specifically, among the once-through boilers of the second boiler group B, P control with a wide pressure control range is applied to at least the once-through boiler that continues the low combustion state. Then, I control for canceling the pressure control deviation is applied to the second boiler group B, and the amount of combustion is variably controlled stepwise according to the load fluctuation. The control of the combustion amount of the second boiler group B by the second control system 14b not only changes the combustion amount of each once-through boiler stepwise but also the operation of selectively operating and stopping the once-through boiler. This includes control of the number of units, and is control for adjusting the amount of generated steam to the state of the load. At this time, the second control system 14b executes the combustion amount control mainly on the I control to moderate the change in the operation amount with respect to the load fluctuation, and performs the combustion control in consideration of the time delay element accompanying the recombustion of the boiler. Run.

  Ideally, the above-described first boiler group A may be P-controlled or PD-controlled, and the second boiler group B may be I-controlled. However, since it is generally difficult for a PID controller used for this type of control to execute only the I control, the control parameters may be set so that the I control is performed while loosely applying the P control. For sudden load fluctuations, combustion control (D control) that immediately changes the amount of steam generated for the once-through boilers in the low combustion state in the first and second boiler groups A and B is performed. First, it is preferable to press down so that a sudden pressure fluctuation does not occur.

  Thus, according to the steam generator constructed with the control system as described above, in the once-through boiler that can only change the combustion amount in stages, the steam pressure and the generated steam amount are always imbalanced. The fluctuation can be effectively suppressed by the P control for the first boiler group A that is always kept in the combustion state. In particular, the pressure fluctuation having a short fluctuation cycle can be suppressed by P control and D control for the first boiler group A. As a result, it becomes possible to prevent the influence of the pressure fluctuation resulting from the stepwise combustion characteristics of the once-through boiler from reaching the pressure fluctuation accompanying the load fluctuation.

  In addition, since the combustion control for the second boiler group B is performed mainly based on the I control (integral control) according to the pressure fluctuation caused by the fluctuation of the load state, the once-through boiler in the stopped state is reignited. Even in such a case, the amount of generated steam can be adjusted based on the delay in the control response, and the combustion amount of the once-through boiler can be controlled without causing problems such as overshoot and hunting. . Therefore, by using multiple once-through boilers whose combustion amount can only be changed in stages, it is possible to control the steam pressure stably, and to control the steam pressure by following the load fluctuation. In practice, a great effect can be obtained.

  FIG. 3 shows a case where two once-through boilers are prepared as the first boiler group A, and the combustion control is performed as described above in a steam generator using two once-through boilers as the second boiler group B for operating number control. It shows the change characteristics of vapor pressure when the product flow rate is changed. As shown by the broken line in FIG. 3, the liquid product is supplied to the sterilizer 20 at a flow rate of 100 liters per minute for 4 hours, and then the flow rate is changed to 140 liters per minute for 4 hours. The change of the vapor pressure when it is supplied over the line is shown by a solid line. In particular, the change in the vapor pressure only exhibits a pressure fluctuation of about ± 0.01 MPa centering on about 0.82 MPa as shown in an enlarged view in FIG. 4, and the stability is very good. It could be confirmed.

  By the way, when all of the four once-through boilers are only P-controlled, a large pressure fluctuation of about 0.07 MPa occurs with the stepwise combustion amount control of the once-through boiler, and all the four once-through boilers. Even when PI was controlled by PI, a large pressure fluctuation of about 0.1 MPa occurred. Therefore, compared to such pressure fluctuations, the above-described control system of the present invention can control the load steam pressure with high accuracy even though a plurality (four) of once-through boilers are used. Moreover, it was confirmed that the controllability was very good.

  When the steam pressure fluctuates abruptly with the load fluctuation, the control system for the second boiler group B reacts with the imbalance between the target steam pressure and the load steam pressure, and the combustion amount becomes the load fluctuation. When the steam pressure changes slowly, the controllability to the first boiler group A reacts, and the combustion amount is controlled in small increments to suppress the fluctuation of the steam pressure. It was confirmed that

  The present invention is not limited to the embodiment described above. For example, the number of once-through boilers to be used may be determined according to the specifications of the load, and it is sufficient to determine the number of once-through boilers used as the first boiler group A that is always kept in an ignition state according to the specifications. It is. Needless to say, the control parameters such as the pressure control width for the once-through boiler may be determined according to the specifications of the steam generator required according to the load specifications and the like. In addition, the present invention can be variously modified and implemented without departing from the scope of the invention.

The schematic block diagram of the sterilization system constructed | assembled using the steam generator which concerns on this invention, and sterilizes a fluid product using steam. The figure which shows the block diagram of the pressure control with respect to the several once-through boiler in the steam generator which concerns on this invention. The figure which shows the fluctuation | variation characteristic of the steam pressure with respect to load fluctuation | variation in the steam generator which concerns on this invention. The figure which expands and shows the fluctuation | variation characteristic of the vapor pressure shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Steam generator 11 Cross-flow boiler 12 Steam header 13 Pressure gauge 14 Controller (PID controller)
14a First control system (P control or PD control)
14b Second control system (PI control)
20 Sterilizer

Claims (5)

A plurality of once-through boilers provided in parallel, a steam header that integrates and outputs steam generated by these once-through boilers, and each of the once-through boilers according to the steam pressure supplied from the steam header to a load. And a control device for controlling the amount of generated steam,
The control device divides the plurality of once-through boilers into two boiler groups, and controls the combustion amount of one of the boiler groups in accordance with the change in the steam pressure accompanying the change in the amount of steam generated in the once-through boiler. A steam generator comprising: a first control system; and a second control system that controls a combustion amount of the other boiler group in accordance with a change in the steam pressure accompanying a change in the load. The first control system includes a first PID controller that performs P control or PD control on a combustion amount of the one boiler group according to a deviation between a steam pressure supplied to the load and a target steam pressure,
2. The second control system includes a second PID controller that performs PI control of a combustion amount of the other boiler group in accordance with a deviation between a steam pressure supplied to the load and the target steam pressure. The steam generator described in 1. Each once-through boiler is provided with a burner capable of controlling the combustion amount in multiple stages,
The first and second control systems control the operation number of the plurality of once-through boilers in accordance with the vapor pressure to be supplied to the load, and stepwise control the combustion amount of each once-through boiler. The steam generator according to claim 1. The boiler group whose combustion amount is controlled by the first control system is composed of at least one once-through boiler that is always in an ignition state,
The boiler group whose combustion amount is controlled by the second control system is the remaining once-through boiler in the plurality of once-through boilers, and is selectively ignited and stopped to be used for controlling the number of operating units. The steam generator according to claim 1, wherein   The steam generator according to claim 1, wherein the load is a sterilizer that is supplied with steam through a flow rate adjusting valve and heat sterilizes the liquid product through a conduit through which the liquid product flows.

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