JP2005055014A - Method of controlling number of boilers - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To combine boilers different in their amounts of evaporation and load following capability, and to stably supply the vapor. <P>SOLUTION: In this method of controlling the number of boilers 1, 2 for controlling the number of boilers 1, 2 to be ignited from the plurality of boilers 1, 2 to generate the vapor supplied to facilities 7 using the vapor, the boiler 2 having the amount of evaporation smaller than that of the other boilers is included, at least one of low load and load stable state is determined with respect to vapor load, and the combustion of the boiler of the smaller amount of evaporation is increased or decreased with priority. Further in this method of controlling the number of boilers 1, 2 generating the vapor supplied to the facilities 7 using the vapor among the plurality of boilers, the boiler having the load following capability higher than that of the other boilers is included, at least one of low load, load stable state and load variation zone is determined with respect to vapor load, and the combustion of the boiler of higher load following capability is increased or decreased with priority. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a boiler number control method for controlling the number of combustion of a plurality of steam boilers.
[0002]
[Prior art]
Various methods of controlling the number of boilers of this type have been proposed (for example, see Patent Document 1).
[0003]
However, these conventional number control methods are for controlling boilers having the same evaporation amount, and have the following problems. In situations where the steam load is low, for example, less than the minimum evaporation amount of the installed boiler, sufficiently stable steam supply is possible by stopping all cans, accompanying pressure drop and its change status, and generating an over-start instruction due to pressure drop There was a case that could not be done. And under the situation where the steam load is low, it may be difficult to maintain a stable pressure with a large pressure fluctuation due to combustion ON-OFF of one boiler.
[0004]
In addition, even when multiple boilers are burning, the steam load is relatively stable, but the boiler combustion state transition (starting / stopping according to the load, transition to low fuel consumption, high fuel combustion) ) As a result, there was a problem that the pressure fluctuated.
[0005]
By the way, the number control method which combined the boiler from which load followability differs is proposed (for example, refer patent document 2). However, in this conventional example, the priority is not the control in which the steam load is low load, the load is stable, or whether the load is fluctuating. For this reason, it may be difficult to maintain a stable steam supply depending on the load and its fluctuation state.
[0006]
[Patent Document 1]
No. 7-40803
[Patent Document 2]
Japanese Patent Laid-Open No. 2002-81604
[0007]
[Problems to be solved by the invention]
The problem to be solved by the present invention is to combine different boilers in terms of evaporation amount and load followability to enable stable steam supply.
[0008]
[Means for Solving the Problems]
This invention was made in order to solve the said subject, and the invention of Claim 1 is the number control method of the boiler which controls the number of combustion of the several boiler which produces | generates the supply steam to a steam utilization facility. Including a small evaporation amount boiler having a combustion state in which the evaporation amount is smaller than that of other boilers and / or a boiler having higher load followability than other boilers, and depending on the steam load and / or its fluctuation state, A small evaporation amount boiler or a boiler with high load followability is preferentially used as a target for increasing or decreasing the combustion amount.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment of the present invention will be described. This embodiment is applied to a boiler number control method for controlling the number of combustion of steam boilers.
[0010]
(Embodiment 1)
The first embodiment is a boiler number control method for controlling the number of combustion of a plurality of boilers that generate steam supplied to steam-using equipment, and includes a boiler having a smaller evaporation amount than other boilers. It is characterized by determining whether the load is low or not, and at the time of determining low load, the boiler number control method that preferentially increases or decreases the combustion amount of the boiler with a small evaporation amount. In the first embodiment, by determining whether or not the steam load is low, the priority order of the boiler with a small evaporation amount is changed according to the steam load. In this case, the priority order is increased by increasing the priority order of starting and stopping so that the combustion amount is subject to increase / decrease in a low load situation, and preferably the highest priority order.
[0011]
The first embodiment has an object to realize a stable steam supply when, for example, the steam load is low such that the steam load is lower than the low combustion state of one boiler.
[0012]
The boiler may be of any type and type as long as it generates steam and supplies it to the steam-using facility. The number of boilers to be controlled may be at least two.
[0013]
The steam supply line of each boiler is preferably provided with a steam collecting part for collecting steam generated in each boiler, and the steam is supplied to the steam using facility through this steam collecting part. Preferably, the steam collecting portion is provided with a pressure detecting means for detecting the internal pressure and controlling the number of units. Since the pressure of the steam collecting portion corresponds to the temperature of the steam on a one-to-one basis, in this embodiment, the pressure is indirectly detected by temperature detection.
[0014]
In the first embodiment, a boiler having a combustion state in which the amount of evaporation is smaller than that of other boilers is intentionally included in the plurality of boilers. The combustion state with a small amount of evaporation means a combustion state that outputs the smallest amount of evaporation in the case of a boiler whose combustion amount changes stepwise. The number of combustion stages is 1 for an ON (combustion) -OFF (stop) boiler, 2 for a 3-position boiler of ON-low combustion-high combustion, and N-1 for an N-position boiler.
[0015]
In the first embodiment, as an example, a plurality of three-position large evaporation amount boilers having a large evaporation amount and a single three-position small evaporation amount boiler having a small evaporation amount are included. These boilers are controlled by, for example, unit control called step value control. The plurality of large evaporation amount boilers may have different evaporation amounts.
[0016]
As described in Patent Document 1, the step value control is control for increasing or decreasing the number of boilers burned based on the absolute value (pressure value) of the pressure of the supply steam in a predetermined control pressure zone. For example, the control pressure band is set by a step value control pressure that is an upper limit value of the pressure band and a step value control width that is a width of the pressure band. This step value control is performed by controlling the number of burned units of the plurality of boilers based on the pressure value of the supplied steam in the control pressure zone and the priority of activation (hereinafter simply referred to as priority).
[0017]
In the number control of the first embodiment, it is determined whether or not the steam load is low. When it is determined that the load is not low, the plurality of boilers are subjected to combustion control (normal load control) according to a predetermined priority order. The priority order of the small evaporation amount boilers is arbitrarily set as appropriate, such as a priority order determined from boiler operating conditions such as the total combustion time and the number of start / stop times. Then, if it is determined that the load is low, the small evaporation amount boiler is preferentially set as the target boiler for increasing or decreasing the combustion amount, and preferably, the priority is set to the highest priority so that the combustion control based on the fluctuation of the steam load (low Load control). Thus, the small evaporation amount boiler is preferentially burned.
[0018]
As described above, when the low-evaporation amount boiler is preferentially burned at a low load, stable steam supply can be performed without stopping all the boilers. In addition, since the boiler is prevented from being stopped or started, an energy saving effect can be obtained.
[0019]
The switching between the normal load control and the low load control, that is, the determination as to whether or not the load is low is performed by one of the following methods, but is not limited thereto.
(1) Automatic determination based on evaporation
When the evaporation amount becomes equal to or less than a predetermined evaporation amount (for example, one high evaporation amount boiler high combustion), it is automatically determined that the load is low, and the control is switched to the low load control.
(2) Automatic determination based on steaming condition (boiler operating condition) and pressure fluctuation
If all the boilers are stopped by the number control or the pressure rises even in the low combustion state of one large evaporation amount boiler, it is determined that the load is low, and the control is switched to the low load control.
(3) Judgment by the registration program of the unit control device and external pointing device
When the variation pattern of the steam load is determined, the time is set in advance by the registration program of the unit control device or the external instruction device, and the control is switched to the low load control when the predetermined time comes.
(4) Determination by external signal
Switching to the low load control is performed based on a signal informing the low load from the steam using facility (steam load) side.
[0020]
As a method of preferentially burning the small evaporation amount boiler, the following method is used in addition to the method of increasing the priority by incorporating the small evaporation amount boiler into the control system of the large evaporation amount boiler as described above. it can. That is, by separating the small evaporation amount boiler from the number control system of the other large evaporation amount boilers, and setting the combustion control pressure of the small evaporation amount boiler higher than that of the other large evaporation amount boilers at the time of the low load It can also be realized. In this example, by setting the combustion control pressure of the small evaporation amount boiler higher than that of the other large evaporation amount boilers at the time of the low load, the small evaporation amount boiler is set as a target boiler for increasing or decreasing the combustion amount. Further, in this example, in a normal load state where the load is not low, the small evaporation amount boiler can be incorporated into the same number control system as other boilers so that the combustion time can be made uniform.
[0021]
Further, in the normal load control, when it can be determined that the large evaporation amount boiler is a load amount that can be stably started, the combustion time is made uniform by changing the priority order of the small evaporation amount boilers. Controls such as can be incorporated as needed. More specifically, the priority order of the small evaporation amount boiler is changed to a priority order determined from the operation state of the boiler such as the total combustion time and the number of start / stop times, and the boiler use such as the combustion time and the number of activations of the small evaporation amount boiler is performed. The situation can be similar to other boilers.
[0022]
Further, the normal load control may be target value control instead of step value control. The target value control is a method of controlling the combustion state of the boiler based on a determination condition for increasing or decreasing the number of boiler combustions so that a preset target pressure is obtained. The determination conditions include the following.
(1) Deviation from target pressure (displacement)
(2) Deviation from target pressure and duration of the state
(3) Pressure change situation (gradient of pressure change and whether the slope is increasing or decreasing)
(4) Pressure change status and duration of the state
(5) Displacement integrated value obtained from displacement from target pressure and time
[0023]
The determination condition is not limited to the above (1) to (5), and the determination condition is determined by combining a plurality of (1) to (5), and the number of combustion of the boiler is controlled. Can do.
[0024]
The control pressure band in the target value control is set by the target value control pressure indicating the stable target value of the supply steam pressure and the target value control width which is the width of the pressure band. As an example, the target value control pressure is set approximately at the center of the target value control width.
[0025]
The present invention is not limited to the above-described embodiment, but includes the following embodiment.
[0026]
(Embodiment 2)
The second embodiment is a boiler number control method for controlling the number of combustion of a plurality of boilers that generate steam supplied to steam-using equipment, and has a small evaporation amount having a combustion state with a smaller evaporation amount than other boilers. Boiler is included, it is determined whether or not the steam load is in a stable state, and when it is determined that the steam load is in a stable state, the small number of boilers is preferentially controlled for increasing or decreasing the combustion amount. Yes.
[0027]
In the second embodiment, whether or not the steam load is in a stable state is determined, thereby determining the fluctuation state of the steam load, and the priority order of the small evaporation amount boiler is changed accordingly. Also in this case, the priority order is changed so that the combustion amount is subject to increase / decrease under low load conditions. Changing the priority so as to become the combustion amount increase / decrease boiler here does not mean that the priority is made highest. Therefore, when the boiler in the combustion state that supports the stable state of the steam load is the small evaporation amount boiler and there is no other small evaporation amount boiler, the small evaporation amount boiler is used as a combustion increase / decrease boiler, instead. The other boiler is in a burning state.
[0028]
In this second embodiment, in the state where a plurality of boilers are burning, the steam load is relatively stable, but the increase and decrease of the combustion amount of the boiler (start / stop and low combustion according to the load, This is a method for solving the problem that the pressure fluctuates as a result of the shift to high combustion.
[0029]
Whether the steam load is stable can be determined as follows.
(1) Automatic judgment
When steam supply is performed at a preset number of units or combustion transition within the evaporation amount (evaporation amount increase / decrease adjustment), it is determined that the steam load is stable.
(2) Judgment by the registration program of the unit control device and external pointing device
When the variation pattern of the steam load is determined, the time is set in the registration program of the unit control device or the external instruction device, and it is determined that the steam load is stable when the predetermined time comes.
(3) Determination by external signal
It is determined that the steam load is stable based on a signal notifying the stability of the steam load from the steam using facility (steam load) side.
[0030]
Now, the maximum steam of the steam-using facility is 10 t / h, the large evaporation amount boiler is 3 positions, 5 t at 2 t / h, and the small evaporation amount boiler of 750 kg / h is combined to control the number of units. As an example, the second embodiment will be described.
[0031]
For example, even when the load is almost stable at a steam load of about 3 t / h, the load is not completely balanced. Repeat the transition of high combustion and start and stop. Therefore, the steam supply amount is alternately switched between 3 t / h and 4 t / h, for example, and since the amount of evaporation is large, the pressure varies greatly accordingly.
[0032]
In view of this, in the steam pressure stabilization control of the second embodiment, the small evaporation amount boiler is preferentially set as the combustion amount increase / decrease target. “Priority on combustion amount increase / decrease” means that “the priority order of the small evaporation amount boiler is arranged in the priority order zone for increasing / decreasing the combustion amount” or “preferentially controlling combustion as a boiler for increasing / decreasing the combustion amount” In other words. By doing this, increase / decrease in the number of boiler combustions due to load fluctuations can be handled by switching between low and high combustion of small evaporation boilers and high combustion, and pressure fluctuation due to increase / decrease in combustion amount can be suppressed. It becomes.
[0033]
(Embodiment 3)
Embodiment 3 is a method for controlling the number of boilers that controls the number of combustion of a plurality of boilers that generate steam supplied to steam-using equipment, and includes a boiler that has higher load followability than other boilers. It is characterized by determining whether or not the load is low and controlling the number of boilers that preferentially increase or decrease the combustion amount of the boiler having high load followability.
[0034]
In the third embodiment, as in the first embodiment, when the steam load is low such that the steam load is lower than the low combustion state of one boiler, it is an object to realize a stable steam supply. .
[0035]
In the third embodiment, boilers with high load following include all boilers with high start-up responsiveness, boilers with high steaming responsiveness, and boilers with high responsiveness to combustion amount increase / decrease (combustion transition). A boiler with high start-up responsiveness means a boiler that is in a pilot state (pilot burner is in a combustion state) or a purge state (a state in which purging is performed) and that can start combustion quickly, such as a boiler that starts quickly. Boilers with high steaming responsiveness are boilers that can supply steam at a predetermined pressure quickly, such as boilers that maintain pressure by continuous pilots (both pilot burners are continuously burned) and boilers that are capable of pressure holding control. means. Also, boilers with high combustion amount increase / decrease responsiveness do not require time to shift combustion from low to high combustion (short) boilers with high responsiveness to increase combustion amount, and shift combustion from high to low combustion It includes a boiler with a short combustion time reduction responsiveness and a boiler with a high stop responsiveness with a short transition time from the combustion state to the stoppage.
[0036]
Such load followability is used as follows as an example. As for the combustion transition responsiveness and start-up responsiveness, each boiler provides information to the unit controller that “how much time is required when startup or combustion transition is requested now”. Then, the boiler having a short time is transferred to combustion (or started). In addition, the steaming responsiveness is that each boiler compares the steam collecting section pressure with its own pressure, and if the pressure is high to some extent (there is no difference), the information indicating that the pressure is high is provided to the unit controller. The number controller starts with priority given to the boiler in which the flag is set. The information “high pressure” can also be expressed by time in the same manner as the “time until activation”.
[0037]
In the number control of the third embodiment, it is determined whether or not the steam load is low. When it is determined that the load is not low, normal load control is performed as in the first embodiment. When it is determined that the load is low, the boiler with high load followability is preferentially subject to combustion amount increase / decrease, and preferably, the highest priority is set to the combustion control based on the fluctuation of the steam load ( (Low load control). In this way, the boiler with high load followability is preferentially burned. Whether or not the steam load is low is determined in the same manner as in the first embodiment.
[0038]
According to the third embodiment, since the boiler with high load followability is preferentially subjected to combustion control, the pressure fluctuation can be reduced by improving the responsiveness, and stable steam supply can be performed.
[0039]
(Embodiment 4)
The fourth embodiment is a method for controlling the number of boilers that controls the number of combustion of a plurality of boilers that generate steam supplied to steam-using equipment, and includes a boiler that has higher load followability than other boilers. Is characterized in that it determines whether or not the engine is in a stable state and preferentially increases or decreases the combustion amount of the boiler with high load following ability.
[0040]
In the fourth embodiment, as in the second embodiment, it is an object to reduce pressure fluctuation due to increase / decrease in the amount of boiler evaporation in the load stable region.
[0041]
The fourth embodiment will be described based on a specific example. Although the steam usage on the steam-using facility (load) side is stable, the overall steam load is low, or the status of the steam-using facility, for example, in many steam supply pipes connected to the facility used In a situation where many of the valves are closed and the pipe volume is reduced, the pressure fluctuation may increase due to the combustion amount control by the pressure change. For example, in a multi-can installation facility of a 3-position boiler of 2000 kg / h, when there is a steam usage of 1500 kg / h, a low combustion state (1000 kg / h) and a high combustion state (2000 kg / h) of one 2000 kg / h boiler ) Are alternately transferred to adjust the steam supply. In this example, the steam supply amount fluctuation on the supply side with respect to the required evaporation amount is large, so that the pressure may fluctuate greatly depending on the combustion state of the boiler. Furthermore, this pressure fluctuation may cause excessive boiler start / stop.
[0042]
Therefore, one or a plurality of boilers with high load followability are preferentially subject to combustion increase / decrease. Thereby, the steam supply at a stable pressure can be performed. This specific example is an example in which the steam load is stable but low, but depending on the situation of the steam use facility, etc. Supply can be made.
[0043]
(Embodiment 5)
Embodiment 5 is a boiler number control method for controlling the number of combustion of a plurality of boilers that generate supply steam to a steam-using facility, and includes a boiler having higher load followability than other boilers. It is characterized by determining whether or not the load is fluctuating, and controlling the number of boilers that preferentially increase or decrease the combustion amount of the boiler having high load following characteristics corresponding to the load fluctuation range.
[0044]
In the fifth embodiment, “the boiler with high load following corresponding to the load fluctuation range is preferentially subject to increase / decrease in the combustion amount” means that priority is given to the combustion shift (stop or start) due to load fluctuation. This means that a boiler with high load followability is placed.
[0045]
The fifth embodiment has a problem of stable steam supply when the load fluctuates. The fifth embodiment will be described using a specific example. In the system of 10 three-position boilers of 2000 kg / h, if 5 are boilers with high start-up response and 4000 kg / h may be instantaneously generated as load fluctuation, stop at least 2 Priority change control is performed so as to ensure the boiler with high start-up response that can be preferentially burned when the load increases. For example, in the case where five units are burning at high combustion, and if all five units are boilers having a high startup response at the usual priority order, a boiler having a low startup response is used as a startup response. The control is performed in such a manner that the combustion state is prioritized over the high-boiling boiler and the boiler with high start-up response is stopped, that is, as many as the number of expected load fluctuations is secured as the target of combustion increase / decrease.
[0046]
In this specific example, instead of shifting at least two boilers with high startup responsiveness to a stopped state, boilers with low load responsiveness are burned. In this way, even when the load changes suddenly, the boiler with high start-up response is in a combustion state with good follow-up, so control with less pressure fluctuation can be performed with respect to load fluctuation.
[0047]
The present invention is not limited to the first to fifth embodiments, and is also applied to a boiler number control method performed by combining two or more of the first to fifth embodiments. Further, the controlled boiler of the present invention includes a system having both the small evaporation amount boiler and the high load following boiler as different types of boilers, and one boiler is the small evaporation amount boiler, and the load following Includes systems that are highly boilers. Further, the present invention determines the steam load as a determination condition for preferentially increasing or decreasing the combustion amount of the small evaporation amount boiler 2 and / or the high load followability boiler, and the fluctuation state of the steam load is also determined. Includes a system for judging.
[0048]
【Example】
Hereinafter, examples corresponding to the first embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram of an embodiment of a boiler system embodying the present invention, FIG. 2 is a flowchart for explaining a unit control method of the embodiment, and FIG. 3 is an example of a control pattern. FIG.
[0049]
As shown in FIG. 1, the boiler system according to the embodiment includes four (No. 1 to No. 4) first evaporation boilers 1, 1,. Two steam boilers 2 (hereinafter, the steam boiler is simply referred to as a boiler), the steam collecting portion 4 to which the steam supply pipes 3, 3,. A pressure detector 5 for detection and a number controller 6 are provided. The first boiler 1 is a three-position boiler with an evaporation amount of 2000 kg / h, and the second boiler 2 is a three-position boiler with an evaporation amount of 1000 kg / h. Both boilers 1 and 2 are different types of boilers in that the characteristic information of the combustion stage and the evaporation amount is different. The steam collecting unit 4 is connected to a steam use facility 7. The maximum evaporation load of the steam using facility 7 of this embodiment is set to about 9 t / h.
[0050]
The number controller 6 is connected to the pressure detector 5 and the boilers 1 and 2 via lines 8, 8,..., Based on an input signal from the pressure detector 5 and a predetermined priority order. The number control as shown in FIG. 2 is performed according to the stored control procedure. As shown in FIG. 3, the priorities are given priorities 1 to 4 to the first boilers 1 (No. 1 to No. 4), respectively, and priorities to the second boiler 2. 5 is given.
[0051]
The number control method by the number controller 6 will be described below with reference to FIGS. This number control method is performed by step value control.
[0052]
In FIG. 2, it is determined in step S1 (hereinafter, step SN is simply referred to as SN) whether or not the operation of the system is started. The operation start is determined by operating a system operation start switch (not shown). If YES is determined in S1, the process proceeds to S2 and it is determined whether or not the steam load is low. In this embodiment, the low load means that when the steam load is a load lower than the evaporation amount at the time of low combustion of the first boiler 1, that is, one unit is in a low combustion state, the pressure of the steam header portion is increased. It is time. The low load control is canceled when the steam load becomes equal to or greater than a predetermined (variable or fixed) evaporation amount (boiler combustion amount).
[0053]
The determination of the low load is not limited to this, and when the evaporation amount (boiler combustion amount) is equal to or less than a predetermined (variable or fixed) evaporation amount, it is determined that the load is reduced, and the predetermined (variable or fixed) ) It can be configured to determine that the low load control is to be released when the evaporation amount (boiler combustion amount) or more is reached.
[0054]
Now, at time t0 in FIG. 3, it is determined in S2 that the load is not low, and the process proceeds to S3, where the boilers 1, 1 are based on the pressure signal from the pressure detector 5 and the predetermined priority order. 2 is controlled (normal load control). The control pattern is as shown in FIG.
[0055]
When time elapses and the steam load decreases as shown in FIG. 3 and time t1 is reached, it is determined at S2 that the load is low. Then, it transfers to S5 and changes the priority which makes the priority of the said 2nd boiler 2 the highest. Based on the changed priority order and the pressure signal from the pressure detector 5, the number of burners of the boilers 1 and 2 is controlled (low load control). The control pattern is as shown in FIG.
[0056]
In this embodiment, at time t1, the timing of transition from low combustion to stop of the first boiler 1 of priority 1 (the former) and the timing of transition from stop of the second boiler 2 to low fuel (the latter) Are preferably the same, but preferably the former is after the latter. Thereby, the steam pressure fluctuation | variation in switching of a combustion boiler can be reduced.
[0057]
In this low load control, since the second boiler 2 having an evaporation amount of 1000 kg / h is controlled as stop-low fuel-high fuel, stable steam supply can be achieved without stopping all boilers even at low load. It becomes possible. Moreover, since the stop and starting of each said 1st boiler 1 are suppressed, the effect of energy saving is also acquired.
[0058]
During the low load control, when the steam load increases and becomes the set steam load, the low load control release is determined in S4, the process proceeds to S3 through S2, and the normal load is determined. Control is performed.
[0059]
When the operation stop switch (not shown) is operated, YES is determined in S6, and the process returns to S1.
[0060]
The present invention is not limited to the above-described embodiments, but includes the following embodiments. That is, in the embodiment, the number control is performed using the number controller 6, but the number control is performed without using the number controller 6 as disclosed in JP-A-2002-213702. Can be configured.
[0061]
【The invention's effect】
According to the present invention, the industrial value is great, such as a combination of boilers that differ in evaporation amount and load followability, and stable steam supply.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an embodiment of a boiler system embodying the present invention.
FIG. 2 is a flowchart showing a number control method of the embodiment.
FIG. 3 is a diagram showing a control pattern of the same embodiment.
[Explanation of symbols]
1 First boiler
2 Second boiler
7 Steam use facilities

Claims (1)

A method for controlling the number of boilers 1 and 2 that controls the number of combustion of a plurality of boilers 1 and 2 that generate steam to be supplied to the steam-using facility 7, and is a small evaporation having a combustion state with a smaller evaporation amount than other boilers. The boiler with higher load followability than the quantity boiler 2 and / or other boilers is included, and the small evaporation boiler and / or the boiler with high load followability are given priority in accordance with the steam load and / or the fluctuation state thereof. A method for controlling the number of boilers, characterized in that the amount of combustion is increased or decreased.

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