JP2012233674A - Heat medium boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat medium boiler capable of keeping good combustion performance and stabilizing combustion by properly controlling a supply amount of combustion air in accordance with change of a combustion amount.SOLUTION: An air blower 28 supplies the combustion air to a burner 24. A heat exchanger 32 preheats the combustion air forced therein from the air blower 28 by an exhaust gas generated by the combustion of fuel by the burner 24. A second temperature sensor 36 detects a preheat temperature T of the combustion air preheated by the heat exchanger 32. A control device 44 controls a damper 42 to keep an opening according to the set combustion amount. The control device 44 adjusts a rotational frequency of the air blower 28 according to the set combustion amount on the basis of the preheat temperature T detected by the second temperature sensor 36, so that the air ratio reaches a predetermined target air ratio. The rotational frequency is adjusted so that an upper limit temperature Th of the predetermined preheat temperature T is not exceeded in every gas fuels different in heat generating amounts.

Description

  The present invention relates to a heat medium boiler.

2. Description of the Related Art Conventionally, there is known a heat medium boiler that heats a heat medium oil to a desired temperature and supplies it to a load in order to use high-temperature (250 ° C. to 300 ° C.) heat.
In general, heat medium boilers burn so that the temperature of the heat medium oil circulating between the load side and the heat medium boiler is maintained at a substantially predetermined temperature by exchanging heat with the combustion gas from the combustion of fossil fuel. It is controlled. However, the temperature of the heat transfer oil may be high, and the temperature of the heat transfer oil to be heated is around 300 ° C. Therefore, the exhaust gas temperature after heating with the heat transfer boiler is about 350 ° C. For example, a small once-through steam boiler has a boiler efficiency of about 92%, whereas a heat medium boiler has a low heat efficiency of about 80%.
In order to increase boiler efficiency, it is necessary to lower the exhaust gas temperature. However, in the case of heat medium boilers, feed water preheating is impossible, and oil preheating during steady operation cannot be expected to be effective. As shown in Patent Document 1, a recuperator (heat exchanger) is used for the exhaust gas exhaust part of the exhaust gas, and heat is exchanged with the combustion exhaust gas while pushing the combustion air into the recuperator with a blower to preheat the combustion air. To be done.

JP-A-08-312944

When combustion air is heated, there are the following problems.
If the combustion amount (fuel) is increased in proportion to the decrease in the temperature of the heat transfer oil that is circulated and returned to the heat transfer boiler, the combustion air must be increased as the combustion amount increases. Because the volume of the combustion air preheated by heat exchange with the air expands, if the rotation speed of the blower is constant, the speed of the air passing through the damper portion increases, the pressure loss at the damper portion increases, The amount of air pushed in decreases and the amount of combustion air decreases.
That is, the combustion air is insufficient (the oxygen concentration is lowered) and the combustibility is deteriorated.

  In addition, the amount of combustion changes with the fluctuation on the load side, but since the exhaust gas temperature changes, the amount of heat exchange with the exhaust gas changes, and the temperature of the combustion air changes, resulting in excessive air and air Insufficiency occurs, causing problems such as increased carbon monoxide, flame extinction, blowout, and other unstable combustion.

Therefore, when preheating the combustion air, it is necessary to accurately control the temperature change of the combustion air that accompanies the change in the combustion amount and to control the necessary amount of air to be supplied to the combustion site.
For this reason, in the technique of Patent Document 1, the air supplied to the burner is preheated by a recuperator in order to prevent the ignition from becoming unstable due to the increase in the flow velocity of the burner due to the expansion of the air due to the temperature rise. A flow adjustment valve is provided, and the air flow adjustment valve is held at a predetermined initial opening for a predetermined time after burner ignition, and the initial opening of the air flow adjustment valve is changed according to the detection result of the preheated air temperature. In the burner, combustion is performed within a predetermined air ratio range.
However, in the technique of Patent Document 1, it is expected that the load fluctuation is large and the temperature of the combustion air preheated until the combustion amount is stabilized after the burner is ignited is greatly changed. May become unstable.
The present invention has been made in view of the above points, and by appropriately controlling the amount of combustion air supplied in accordance with fluctuations in the amount of combustion, it maintains good combustibility and stabilizes combustion. It aims at providing the heat-medium boiler which can do.

  In order to solve the above-mentioned problems, the invention described in claim 1 is directed to a burner, fuel supply means for supplying gaseous fuel to the burner according to a set combustion amount, and a blower for supplying combustion air to the burner. And a heat exchanger that is provided between the blower and the burner and preheats the combustion air with exhaust gas generated by combustion of the gaseous fuel by the burner, and the combustion preheated by the heat exchanger A combustion air temperature detecting means for detecting a preheating temperature of the working air, a damper provided in an air supply path connecting the heat exchanger and the burner, the opening of which is controlled, and the set amount of combustion The opening of the damper is controlled, and the rotational speed of the blower is adjusted so that the air ratio becomes a predetermined target air ratio based on the preheating temperature detected by the combustion air temperature detecting means. And a controlling means for settling.

According to the first aspect of the invention, the opening degree of the damper is controlled according to the set amount of combustion, and the air ratio is determined from the preheating temperature of the combustion air detected by the combustion air temperature detecting means. The number of revolutions of the blower was adjusted so as to achieve a predetermined target air ratio.
Accordingly, the supply amount of combustion air can be accurately controlled in accordance with the change in the combustion amount, so that the air ratio can be controlled so as to become the target air ratio, and the combustion stability can be kept good and the combustion stability can be improved. Can be planned.

  According to a second aspect of the present invention, in the heat medium boiler according to the first aspect, the adjustment of the rotational speed of the blower by the control means maintains the air ratio at the target air ratio even if the preheating temperature changes. In order to supply a sufficient amount of combustion air to the burner, a relational expression indicating a correlation between the rotational speed of the blower and the preheating temperature is used.

  According to the second aspect of the present invention, since the processing required for adjusting the rotational speed of the blower is performed using the relational expression, the rotational speed of the blower can be precisely adjusted.

  According to a third aspect of the present invention, in the heat medium boiler according to the first or second aspect, an upper limit temperature of the preheating temperature is preset for each gaseous fuel having a different calorific value, and the control means The rotation speed of the blower is adjusted so that the preheating temperature detected by the combustion air temperature detecting means does not exceed the set upper limit temperature.

  According to the invention described in claim 3, since the upper limit temperature of the preheating temperature of the combustion air is set and the rotational speed of the blower is adjusted so as not to exceed the temperature, combustion with good combustion efficiency close to the target air ratio In addition, the increase in combustion gas temperature due to preheating can be suppressed, and NOx (nitrogen oxide) emission can be suppressed.

  According to a fourth aspect of the present invention, in the heat medium boiler according to the first or second aspect, an upper limit temperature of the preheating temperature is preset for each gaseous fuel having a different calorific value, and the heat exchanger Is a heat exchanger in which the heat transfer area is changed for each gaseous fuel so as to be equal to or lower than the upper limit temperature set for each gaseous fuel, and the upper limit temperature of the preheating temperature according to the type of the gaseous fuel The following heat exchanger is selected.

  According to the fourth aspect of the present invention, since the heat exchanger having the heat transfer area determined corresponding to the upper limit temperature is used, the efficiency of the heat medium boiler is improved and the combustion efficiency is improved and the combustion by the preheating is performed. An increase in gas temperature can be suppressed and NOx emission can be suppressed.

  According to a fifth aspect of the present invention, in the heat medium boiler according to the fourth aspect, the upper limit temperature corresponding to the heat exchanger selected according to the type of the gaseous fuel is a first upper limit temperature Th1, and the first When the temperature obtained by adding a predetermined temperature to the first upper limit temperature Th1 is defined as the second upper limit temperature Th2, the heat exchanger is configured to be able to preheat the combustion air to the second upper limit temperature Th2. The control means adjusts the rotational speed of the blower so that the preheating temperature is equal to or lower than the first upper limit temperature Th1.

  According to the fifth aspect of the present invention, the second upper limit temperature which is the upper limit value of the preheating temperature obtained by adding a predetermined temperature to the first upper limit temperature Th1 which is the upper limit value of the preheating temperature according to the fuel type of the gaseous fuel. The performance of the heat exchanger is Th2, and when the preheating temperature exceeds the first upper limit temperature Th1, the rotational speed of the blower is adjusted so that the preheating temperature is lowered to the first upper limit temperature Th1 or less. Therefore, the preheating temperature of the combustion air can be maintained at the upper limit temperature (first upper limit temperature T1) or a temperature close to the upper limit temperature, so that high efficiency can be maintained as a heat medium boiler and NOx emission can be suppressed.

  According to the present invention, by accurately controlling the amount of combustion air supplied in accordance with fluctuations in the amount of combustion, it is possible to maintain good combustibility, stabilize combustion, and suppress NOx emissions. can do.

It is a lineblock diagram showing the composition of heat carrier boiler 100 concerning a 1st embodiment. It is a perspective view which shows the structure of the can body 10, the wind box 22, the burner 24, and the damper 42 in the heat-medium boiler 100 which concerns on 1st Embodiment. (A), (B), (C) is operation | movement explanatory drawing of the damper 42 in the heat-medium boiler 100 which concerns on 1st Embodiment. It is a function diagram which shows the correlation with the preheating temperature T of the combustion air, and the rotation speed N of the air blower. It is a flowchart which shows operation | movement of the heat-medium boiler 100 which concerns on 1st Embodiment. It is explanatory drawing of the table which linked | related temperature difference (DELTA) T and the correction coefficient (alpha). It is a flowchart which shows operation | movement of the heat-medium boiler 100 which concerns on 2nd Embodiment.

(First embodiment)
Embodiments of the present invention will be described below.
FIG. 1 is a configuration diagram showing the configuration of the heat medium boiler 100.
The heat medium boiler 100 includes the can 10.
As shown in FIG. 2, the can 10 includes a heating tube 12 wound in a coil shape.
As shown in FIG. 1, the upstream end of the heating tube 12 is a heat medium return line 14, which is a line for releasing heat at the load side and returning the heat medium oil whose temperature has decreased to the heat medium boiler 100. The downstream end of the heating pipe 12 is a heat medium supply line 16 that supplies a heat medium to the load side.
The heat medium oil is circulated between the heating pipe 12 and the load via a heat medium return line 14 and a heat medium supply line 16 by a circulation pump (not shown).
A combustion chamber 18 is formed inside the heating tube 12 wound in a coil shape, and gas fuel (gaseous fuel) is burned in the combustion chamber 18 by a burner 24 described later, thereby circulating through the heating tube 12. The heat transfer oil is heated.

  As shown in FIG. 1, the heat medium boiler 100 includes a wind box 22, a burner 24, a fuel supply unit 26, a blower 28, an inverter 30, a heat exchanger 32, first, second, and third. The fourth temperature sensor 34, 36, 38, 40, the damper 42, and the control device 44 are configured.

In this example, as shown in FIG. 2, the wind box 22 is provided on the upper portion of the can body 10, and the burner 24 is accommodated and held therein.
The wind box 22 is a box for uniformly sending the combustion air supplied from the blower 28 to the burner 24. The combustion air supplied from the wind box 22 is mixed by the burner 24 with the fuel (gas fuel in the present embodiment) supplied from the fuel supply means 26 to the burner 24.

  As shown in FIG. 2, the burner 24 mixes and burns gas fuel supplied from the fuel supply means 26 and combustion air. The gas fuel mixed with the combustion air is burned by the burner 24 in the combustion chamber 18 inside the heating pipe 12 of the can body 10.

The fuel supply means 26 supplies fuel to the burner 24 in accordance with the set combustion amount.
As shown in FIG. 1, in the present embodiment, the fuel supply means 26 includes a gas fuel supply path 2602, a cutoff valve 2604, a governor 2606, a proportional valve 2608, and a control device 44 described later. Has been.
The gas fuel supply path 2602 has an upstream end connected to a gas supply source (not shown) and a downstream end connected to the burner 24.
The shut-off valve 2604 is provided in the gas fuel supply path 2602 and is opened and closed by a control signal supplied from the control device 44.
The governor 2606 is provided on the downstream side of the shutoff valve 2604 in the gas fuel supply path 2602 and adjusts the pressure of the gas fuel flowing through the gas fuel supply path 2602 to a constant pressure.
The proportional valve 2608 is provided on the downstream side of the governor 2606 in the gas fuel supply path 2602, and the opening degree is adjusted by the motor 27. The motor 27 is a stepping motor (pulse motor), and the opening degree of the proportional valve 2608 is adjusted by controlling the rotation amount (rotation stop position) of the motor 27 by the control device 44.
Therefore, the control device 44 controls the opening and closing of the shutoff valve 2604 to control the supply and stop of gas fuel to the burner 24, and the control device 44 adjusts the opening of the proportional valve 2608, so that the burner 24 The amount of gas fuel supplied to the fuel, that is, the amount of combustion is controlled.

The blower 28 supplies combustion air to the burner 24.
The blower 28 includes a motor 2802 and a fan (not shown) rotated by the motor 2802. By rotating the fan by the motor 2802, normal temperature air is sucked from the suction port and combustion air is discharged from the discharge port. .

The inverter 30 adjusts the rotation speed of the motor of the blower 28 by a control signal supplied from the control device 44.
As will be described later, the supply amount of the combustion air is adjusted according to the temperature of the combustion air by adjusting the rotation speed of the motor of the blower 28 through the inverter 30 by the control device 44.

The heat exchanger 32 (recuperator) includes a primary side 3202 and a secondary side 3204.
The primary side 3202 of the heat exchanger 32 is connected in the middle of the exhaust gas supply path 46 that guides the combustion exhaust gas to the outside.
The secondary side 3204 of the heat exchanger 32 is connected in the middle of the air supply path 33 that connects the discharge port of the blower 28 and the wind box 22.
That is, the heat exchanger 32 preheats the combustion air pushed from the blower 28 with the combustion exhaust gas after performing heat exchange between the combustion gas obtained by the combustion of the fuel by the burner 24 and the circulating heat transfer oil. Is.
Hereinafter, the temperature of the combustion air preheated by the heat exchanger 32 is referred to as a preheat temperature.

When heat exchange between combustion exhaust gas and combustion air is performed by the heat exchanger 32, the combustion temperature increases as the preheating temperature of the combustion air is increased. It is known that the NOx concentration contained in the combustion exhaust gas increases as the combustion temperature increases. The combustion temperature differs depending on the type of gas fuel.
According to the experiments by the inventors, the upper limit temperature of the preheating temperature necessary for suppressing the NOx concentration contained in the combustion exhaust gas to a predetermined concentration or less is, for example, about 300 ° C. in the case of city gas (13A), and liquefied petroleum gas. In the case of (LPG), it was revealed that the temperature was about 200 ° C. The reason for the difference in the upper limit temperature of the preheating temperature is that the calorific value varies depending on the type of gas fuel.
Therefore, in the present embodiment, in order to suppress NOx emission, the preheating temperature is prevented from exceeding the upper limit temperature as will be described later.

The first temperature sensor 34 is provided in the vicinity of the discharge port of the blower 28, detects the temperature of combustion air pushed into the air supply path 33 from the discharge port, and supplies the detection result to the control device 44. is there. The first temperature sensor 34 may be provided at the suction port of the blower 28.
The second temperature sensor 36 detects the temperature of the combustion air preheated by the heat exchanger 32, that is, the preheat temperature, and supplies the detection result to the control device 44. It is provided at a portion connecting the downstream end of the secondary side 3204 of the exchanger 32 and the wind box 22. The second temperature sensor 36 constitutes combustion air temperature detection means in the claims.
The third temperature sensor 38 is provided in a portion of the exhaust gas supply path 46 connected to the downstream end of the primary side 3202 of the heat exchanger 32, detects the temperature of the exhaust gas discharged to the outside, and the detection result Is supplied to the control device 44.
The fourth temperature sensor 40 is provided in the vicinity of the outlet of the can body 10 (heating pipe 12) in the heat medium supply line 16, detects the temperature of the heat transfer oil supplied from the can body 10 to the load, and detects the temperature. The result is supplied to the control device 44.

As shown in FIG. 1, the damper 42 includes a plate body 4202.
The plate body 4202 is configured to be rotatable at a portion of the air supply path 33 that connects the downstream end of the secondary side 3204 of the heat exchanger 32 and the wind box 22, and is proportional to the proportional valve 2608 by the motor 27. It is rotated in sync with.
Accordingly, when the motor 27 is rotated by the control signal supplied from the control device 44, the plate body 4202 is rotated, and the opening degree of the damper 42 is adjusted as shown in FIGS. 3 (A), (B), and (C). The opening degree of the damper 42 is adjusted in synchronization with the opening degree of the proportional valve 2608.
That is, when the motor 27 rotates, the opening degree of the damper 42 is controlled to control the supply amount of combustion air flowing through the air supply path 33, and the opening degree of the proportional valve 2608 is controlled to reduce the combustion amount. Be controlled.

The control device 44 receives a command for the amount of combustion required from the outside and detection signals from the first to fourth temperature sensors 40 and controls the fuel supply means 26, the blower 28 and the damper 42. .
The control device 44 can be configured by a microcomputer.
In other words, the microcomputer includes a CPU, a ROM, a RAM, an interface, and the like connected via a bus line. The ROM stores a control program for the heat medium boiler executed by the CPU, and the RAM provides a working area.
And the control means of a claim is implement | achieved when CPU runs the said control program.

Based on the temperature detected by the fourth temperature sensor 40, the control device 44 determines the combustion amount so as to maintain the temperature of the circulating heat transfer oil at a predetermined temperature, opens the shutoff valve 2604, and sets the opening to match the combustion amount. Then, the proportional valve 2608 is opened, and the opening degree of the damper 42 is controlled so that the air ratio is within a predetermined range. The combustion amount is set by the control device 44 in proportion to the temperature difference between the temperature detected by the fourth temperature sensor 40 and the predetermined temperature (by proportional control).
More specifically, assuming that the preheating temperature of the combustion air is maintained at a predetermined constant temperature (for example, 250 ° C.), the opening degree of the damper 42 having an air ratio within a predetermined range is set for each combustion amount. Seek experimentally.
Then, when the combustion amount (the opening degree of the proportional valve 2608) is set by the rotation of the motor 27, the opening degree of the damper 42 having an air ratio within a predetermined range is obtained. Accordingly, the proportional valve 2608 and the damper 42 are configured so that the opening degree of the proportional valve 2608 and the opening degree of the damper 42 are adjusted in synchronization.
Specifically, the rotation stop position of the motor 27 is determined for each combustion amount, and the combustion amount and the rotation stop position are stored in the ROM as a data table.
When determining the combustion amount, the control device 44 controls the motor 27 so that the rotation stop position is read from the data table based on the determined combustion amount. Thereby, the opening degree of the damper 42 which becomes the air ratio of the predetermined range corresponding to the combustion amount is adjusted.
Here, the air ratio will be described.
The air contains 20.9% oxygen (O ₂ ) at atmospheric pressure.
The air ratio is a value obtained by dividing the oxygen concentration (20.9%) of combustion air by the value obtained by subtracting the oxygen concentration of the exhaust gas from the oxygen concentration, and is defined by Equation (1).
Air ratio = 20.9 / (20.9−oxygen concentration in exhaust gas) (1)
Therefore, when air sufficient to perform theoretically complete combustion is supplied to the supplied fuel, the air ratio = 1 (theoretical air amount). From the viewpoint of thermal efficiency, the air ratio = 1 is ideal, but it is difficult to achieve such theoretical combustion in an industrial heat medium boiler. The air is supplied so that the air ratio is greater than 1, based on the amount of air larger than the amount of air, that is, based on the equation (1).
In this case, the air ratio in a predetermined range is a range of approximately 1.15 to 1.45 in which flammability that does not cause a sudden increase in carbon monoxide due to incomplete combustion or a flame extinction in the middle of the flame is obtained.

Then, the control device 44 sets the rotational speed of the blower 28 so as to obtain the target air ratio based on the detection value of the second temperature sensor 36 that detects the preheating temperature at the set damper opening, The blower 28 is adjusted via the inverter 30 based on the set rotation speed.
Here, the target air ratio will be described.
Although the air ratio in the predetermined range or the vicinity thereof can be adjusted by setting the opening degree of the damper 42, the preheating temperature varies depending on the atmospheric temperature, the combustion amount, the load variation, and the like.
As a result, only by adjusting the opening degree of the damper 42 by the combustion amount, the air amount fluctuates greatly and may deviate from an air ratio within a predetermined range, or the air ratio may be lowered to deteriorate the combustibility.
For this reason, it is necessary to adjust so that it may become target air ratio by adjusting the rotation speed of the air blower 28. FIG.
The amount of air to be supplied is ideally as close as possible to the theoretical air ratio = 1, but in the case of the heat medium boiler 100 of the present embodiment, this target air ratio is approximately 1.201 to 1.237. This excessive air amount also varies depending on the heat medium boiler.

The adjustment of the rotational speed of the blower 28 by the control device 44 (control means) is performed so that the amount of combustion air sufficient to maintain the air ratio of the burner 24 at the target air ratio even when the preheating temperature T of the combustion air changes. The relational expression showing the correlation between the rotational speed N of the blower and the preheating temperature T is used.
That is, the control device 44 sets and adjusts the rotational speed N of the blower 28 based on the relational expression described below from the preheating temperature T detected by the second temperature sensor 36.
FIG. 4 is a function diagram showing the correlation between the preheating temperature T and the rotational speed N. The horizontal axis represents the preheating temperature T, and the vertical axis represents the rotational speed N of the blower 28.
In the figure, the line indicated by N = f (T) indicates the correlation, and f (T) indicates the rotational speed N corresponding to the preheating temperature T for setting the air ratio to the target air ratio. This is a relational expression to be obtained (correlation formula).
That is, a curve indicating the correlation between the preheating temperature T at the outlet of the heat exchanger 32 and the rotation speed N of the blower 28 is obtained by calculation so that the air ratio becomes the target air ratio, and a correlation equation indicating this curve is obtained. It is created and incorporated in the control program of the control device 44.
For producing such a relational expression, various conventionally known methods can be used.

The gas fuel (gas type) used in the heat medium boiler 100 is determined by a user who uses the heat medium boiler 100.
Further, as described above, the calorific value changes for each of a plurality of types of gas fuel, so the upper limit temperature of the combustion air is set in advance for the gas fuel used in the heat medium boiler 100. In the following description, the upper limit temperature of the preheating temperature T preset for the gas fuel in the heat medium boiler 100 is assumed to be Th.
Therefore, the control device 44 adjusts the rotational speed N of the blower 28 adjusted based on the preheating temperature T by the control device 44 so that the preheating temperature T of the combustion air does not exceed the upper limit temperature Th. That is, the control device 44 adjusts the rotational speed N of the blower 28 so that the air ratio becomes the target air ratio in normal times, while the preheating temperature T of the combustion air is about to exceed the upper limit temperature Th. The preheating temperature T of the combustion air is prevented from exceeding the upper limit temperature Th by further increasing the rotational speed N of the blower 28 so that the air ratio becomes higher.

Next, the operation of the heat medium boiler 100 will be described with reference to the flowchart of FIG.
It is assumed that the heat medium boiler 100 is in a stopped state in advance.
When the heat medium boiler 100 is activated, the circulation pump starts to circulate the heat medium oil between the can 10 and the load. At the same time, the control device 44 is activated to execute the processing of FIG.

  The control device 44 sets a combustion amount (amount of fuel) based on a temperature difference between the temperature of the heat transfer oil detected by the fourth temperature sensor 40 and a preset target temperature of the heat transfer oil ( Steps S10 and S12).

  Next, the control device 44 controls the fuel supply means 26 based on the set combustion amount to supply gas fuel to the burner 24, sets the opening degree of the damper 42 according to the set combustion amount, The opening of the damper 42 is set by controlling the motor 4204 of the damper 42 (step S14).

Next, the control device 44 receives the detection result of the preheating temperature T detected by the second temperature sensor 36, and determines whether or not the preheating temperature T is equal to or lower than the upper limit temperature Th (steps S16 and S18).
If the preheating temperature T is equal to or lower than the upper limit temperature Th, the control device 44 calculates the rotational speed N of the blower 28 from the relational expression based on the preheating temperature T (step S20).
Next, the control device 44 controls the rotational speed of the blower 28 to be the rotational speed N via the inverter 30 (step S22), returns to step S10, and repeats the same processing.

On the other hand, if the preheating temperature T exceeds the upper limit temperature Th in step S18, the control means 44 calculates the rotational speed N of the blower 28 from the above relational expression based on the preheating temperature T (step S24). Based on a temperature difference (ΔT = Th−T) between the temperature T and the upper limit temperature Th, a correction coefficient α described later is calculated (step S26), and a rotation speed αN obtained by multiplying the rotation speed N by the correction coefficient α is calculated. (Step S28).
Here, the correction coefficient α will be described.
FIG. 6 is an explanatory diagram of a table in which the temperature difference ΔT and the correction coefficient α are associated with each other, and the control device 44 stores this table in advance.
As shown in FIG. 6, the correction coefficient α is determined such that the value increases as the value of the temperature difference ΔT increases.
For example, when the preheating temperature T detected by the second temperature sensor 36 at a certain combustion amount is lower than the upper limit temperature Th, the rotational speed N of the blower 28 is determined so as to achieve the target air ratio according to the preheating temperature T. Controlled (correction coefficient α = 1).
When the preheating temperature T detected by the second temperature sensor 36 is larger than the upper limit temperature Th, the correction coefficient α is determined according to the temperature difference ΔT in the rotational speed N of the fan 28 rotating as α = 1. The value to multiply.
Thus, the correction coefficient α may be determined experimentally according to the temperature difference ΔT.
Alternatively, while the preheating temperature T is detected by the second temperature sensor 36, the rotational speed αN may be obtained every predetermined time while increasing the correction coefficient α at a change rate of 0.01 / min, for example.
Next, the control device 44 controls the rotational speed of the blower 28 to be the rotational speed αN via the inverter 30 (step S30), returns to step S18, and repeats the same processing.
By performing such processing, the preheating temperature T of the combustion air is controlled to be equal to or lower than the upper limit temperature Th.

As described above, according to the present embodiment, the opening degree of the damper 42 is controlled according to the set combustion amount, and the preheat temperature T detected by the second temperature sensor 36 is used. The rotational speed N of the blower 28 is adjusted so that the air ratio becomes a predetermined target air ratio.
Therefore, by accurately controlling the supply amount of combustion air according to the fluctuation of the combustion amount, it is possible to increase boiler efficiency (combustion efficiency) by accurately preheating the combustion air and lowering the exhaust gas temperature, In addition, when the amount of combustion (fuel) is increased in accordance with the increase in load, the amount of combustion air supplied can be reduced while the combustion air is accurately increased while the thermal expansion of the preheated combustion air is reduced. Since the air blower 28 can be controlled such that the air ratio becomes the target air ratio by suppressing, the combustibility can be kept good and the combustion can be stabilized.
Accordingly, the supply amount of combustion air can be accurately controlled in accordance with the change in the combustion amount, so that the air ratio can be controlled so as to become the target air ratio, and the combustion stability can be kept good and the combustion stability can be improved. Can be planned.

  Further, according to the present embodiment, the adjustment of the rotational speed N of the blower 28 is such that the amount of combustion air sufficient to maintain the air ratio of the burner 24 at the target air ratio even if the preheating temperature T of the combustion air changes. Since the relational expression indicating the correlation between the rotational speed N of the blower 24 and the preheating temperature T for supplying the air to the burner 24 is performed, the rotational speed N of the blower 24 can be adjusted accurately. it can.

Further, according to the present embodiment, the upper limit temperature Th of the preheating temperature T of the combustion air is set in advance for each gas fuel having a different calorific value, and the detected upper limit temperature Th is set. The rotational speed N of the blower 24 is adjusted so as not to exceed.
Therefore, since the preheating temperature T is controlled so as not to exceed the upper limit temperature Th, the combustion efficiency with the combustion efficiency close to the target air ratio is maintained, the rise in the combustion gas temperature due to the preheating is suppressed, and the NOx emission is suppressed. can do.

(Second Embodiment)
Next, a second embodiment will be described.
In the following embodiments, description of the same parts as those of the first embodiment will be omitted, and only different parts will be described.
In the first embodiment, the case where the controller 44 adjusts the rotation speed N of the blower 24 so that the preheating temperature T does not exceed the upper limit temperature Th has been described. However, in the second embodiment, the preheating temperature is adjusted. In order to prevent T from exceeding the upper limit temperature Th, a heat exchanger 32 having a different heat transfer area is prepared for each gas fuel, and the upper limit temperature is adjusted according to the type of gas fuel used in the heating medium boiler 100. The heat exchanger 32 that is equal to or less than Th is selected.

  The operation of the heat medium boiler 100 in the second embodiment will be described with reference to the flowchart of FIG. The processing steps having the same contents as the processing steps in the flowchart of FIG. 1 will be described with the same reference numerals.

The control device 44 sets a combustion amount (amount of fuel) based on a temperature difference between the temperature of the heat transfer oil detected by the fourth temperature sensor 40 and a preset target temperature of the heat transfer oil ( Steps S10 and S12).
Next, the control device 44 controls the fuel supply means 26 based on the set combustion amount to supply gas fuel to the burner 24, sets the opening degree of the damper 42 according to the set combustion amount, The opening of the damper 42 is set by controlling the motor 4204 of the damper 42 (step S14).
Next, the control device 44 receives the detection result of the preheating temperature T detected by the second temperature sensor 36 (step S16).
The controller 44 calculates the rotational speed N of the blower 28 from the relational expression based on the detected preheating temperature T (step S20).
Next, the control device 44 controls the rotational speed of the blower 28 to be the rotational speed N via the inverter 30 (step S22), returns to step S10, and repeats the same processing.

  By performing such processing, the rotation speed N of the blower 28 is adjusted so that the air ratio becomes the ideal air ratio. As described above, since the heat exchanger 32 is selected to have the upper limit temperature Th or lower in accordance with the type of gas fuel used in the heat medium boiler 100, the preheating temperature T of the combustion air is lower than the upper limit temperature Th. It is controlled to become.

  In such a second embodiment, the supply amount of combustion air can be accurately controlled according to changes in the combustion amount so as not to exceed the upper limit temperature Th according to the fuel type. In addition, the air ratio can be controlled to be the target air ratio, the combustibility can be kept good, the combustion stability can be achieved, and the emission of NOx can be suppressed.

(Third embodiment)
Next, a third embodiment will be described.
In the description of the second embodiment, a heat exchanger 32 having a different heat transfer area is prepared for each gas fuel, and the upper limit temperature Th is reduced according to the type of gas fuel used in the heat medium boiler 100. The heat exchanger 32 was selected.
However, in reality, the temperature of the combustion gas increases or decreases due to changes in atmospheric temperature or humidity, and the preheating temperature T exceeds the upper limit temperature Th, or becomes lower than the upper limit temperature Th. There is a concern that the efficiency of the heat medium boiler will be lowered.
Therefore, in consideration of the influence of changes in atmospheric temperature and humidity, in the third embodiment, the preheating temperature in which the maximum value of the preheating temperature in the heat exchange in the heat exchanger 32 is set according to the fuel type. Is not designed to exceed the preheating temperature set in accordance with the fuel type, and a design with a margin is provided so that this can be selected in accordance with the fuel type, and the rotational speed of the blower 28 By appropriately adjusting N, the increase in the combustion gas temperature is suppressed.
That is, in the third embodiment, the upper limit temperature set for each gas fuel is a first upper limit temperature Th1, and a temperature obtained by adding a predetermined temperature to the first upper limit temperature Th1 is a second upper limit temperature Th2. The heat exchanger 32 is configured to be able to preheat the combustion air to the second upper limit temperature Th2.
And the control apparatus 44 performs adjustment of the rotation speed N of the air blower 28 so that the preheating temperature T may become below 1st upper limit temperature Th1.
The operation of the heat medium boiler 100 in the third embodiment is the same as that in the first embodiment shown in FIG. 5, and the upper limit temperature Th in FIG. 5 is replaced with the first upper limit temperature Th1.
That is, the control device 44 adjusts the rotational speed N of the blower 28 so that the air ratio becomes the target air ratio in the normal time, while the preheating temperature T of the combustion air tends to exceed the first upper limit temperature Th. In this case, the preheating temperature T is controlled to be equal to or lower than the first upper limit temperature Th1 by further increasing the rotational speed N of the blower 28 so that the air ratio is further increased.

In the third embodiment as well, similarly to the first embodiment, the supply amount of combustion air can be accurately controlled in accordance with the change in the combustion amount, so that the air ratio is set as the target. It is possible to control the air ratio so that the combustibility is kept good and the combustion stability can be improved.
That is, the heat exchanger 32 generates the second upper limit temperature Th2 that is the upper limit value of the preheating temperature T obtained by adding a predetermined temperature to the first upper limit temperature Th1 that is the upper limit value of the preheating temperature T according to the fuel type of the gas fuel. It was set as the performance to have. And when the preheating temperature T exceeded 1st upper limit temperature Th1, the rotation speed N of the air blower 28 was adjusted so that the preheating temperature T might be reduced below 1st upper limit temperature Th1. Therefore, since the preheating temperature T of the combustion air can be maintained at the upper limit temperature (first upper limit temperature T1) or a temperature close to the upper limit temperature, high efficiency can be maintained as a heat medium boiler, and NOx emission can be suppressed. .

DESCRIPTION OF SYMBOLS 100 ... Heat-medium boiler 10 ... Can body 12 ... Heating pipe 15 ... Combustion chamber 14 ... Heat-medium return line 16 ... Heat-medium supply line 18 ... Combustion chamber 22 ... Wind box 24 ... Burner 26 ... Fuel supply means 28 ... Blower 30 ... Inverter 32 ... Heat exchanger 34 ... First temperature sensor 36 ... Second temperature sensor (combustion air temperature detection means)
38 …… Third temperature sensor 40 …… Fourth temperature sensor 42 …… Damper 44 …… Control means (control means)
100 …… Heat medium boiler

Claims (5)

With a burner,
Fuel supply means for supplying gaseous fuel to the burner according to a set combustion amount;
A blower for supplying combustion air to the burner;
A heat exchanger that is provided between the blower and the burner and preheats the combustion air with exhaust gas generated by combustion of the gaseous fuel by the burner;
Combustion air temperature detection means for detecting a preheating temperature of the combustion air preheated by the heat exchanger;
A damper provided in an air supply path connecting the heat exchanger and the burner, the opening degree of which is controlled;
The opening degree of the damper is controlled according to the set combustion amount, and the air ratio is set to a predetermined target air ratio by the preheating temperature detected by the combustion air temperature detecting means. Control means for adjusting the rotational speed of the blower,
A heating medium boiler characterized by that. Adjustment of the rotation speed of the blower by the control means is as follows:
In order to supply the burner with an amount of combustion air sufficient to maintain the air ratio at the target air ratio even if the preheating temperature changes, a relational expression showing the correlation between the rotational speed of the blower and the preheating temperature It is made using
The heat-medium boiler according to claim 1. For each gaseous fuel having a different calorific value, an upper limit temperature of the preheating temperature is preset,
The control means adjusts the rotation speed of the blower so that the preheating temperature detected by the combustion air temperature detection means does not exceed the set upper limit temperature.
The heat-medium boiler of Claim 1 or Claim 2. For each gaseous fuel having a different calorific value, an upper limit temperature of the preheating temperature is preset,
The heat exchanger is a heat exchanger in which a heat transfer area is changed for each gaseous fuel so as to be equal to or lower than the upper limit temperature set for each gaseous fuel, and the preheating is performed according to the type of the gaseous fuel. A heat exchanger that is lower than the upper limit temperature is selected,
The heat-medium boiler of Claim 1 or Claim 2. The upper limit temperature corresponding to the heat exchanger selected according to the type of the gaseous fuel is a first upper limit temperature Th1, and a temperature obtained by adding a predetermined temperature to the first upper limit temperature Th1 is a second upper limit temperature Th2. The heat exchanger is configured to be able to preheat the combustion air to the second upper limit temperature Th2,
The control means adjusts the rotation speed of the blower so that the preheating temperature is equal to or lower than the first upper limit temperature Th1,
The heat-medium boiler according to claim 4.

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