Boiler load adjusting device capable of rapidly adjusting peak

Abstract

The utility model discloses a boiler load adjusting device capable of rapidly adjusting peak. The boiler load adjusting device comprises a coal economizer water inlet header pipe, a coal economizer water return header pipe and a plurality of natural gas boilers. Each natural gas boiler comprises a boiler body, an economizer, a water inlet pump, a water inlet pipe, a water outlet pipe, a conveying pipe and a water return branch pipe. A gas inlet of the economizer communicates with a smoke outlet of the boiler body, a water inlet of the economizer communicates with an economizer water inlet header pipe, and a water outlet of the economizer communicates with an economizer water return header pipe. The water inlet pipe communicates with a water inlet of the boiler body. The water inlet pump is arranged on the water inlet pipe. The other end of the water outlet pipe is communicated with the water inlet end of the water inlet pump; one end of the conveying pipe is communicated with the water outlet end of the water inlet pump, and the other end is communicated with the economizer water inlet header pipe; and one end of the water return branch pipe is communicated with the water return port of the boiler body while the other end is communicated with the economizer water return header pipe. According to the device, rapid peak regulation can be achieved, the steam requirement of downstream heat users can be met, and energy waste can be reduced.

Description

TECHNICAL FIELD

[0001] The utility model relates to natural gas boiler technical field, concretely relates to a kind of boiler load regulating device of quick peak shaving. BACKGROUND

[0002] Natural gas boiler is composed of burner and two big components of boiler body. Boiler combustion system is configured with corresponding burner, fuel supply system according to fuel used, and generally, boiler uses air blower to carry out micro-positive pressure combustion, and under special circumstances, induced draft fan is needed to increase to carry out balanced ventilation. Boiler steam-water system should be configured with boiler body, tail energy-saving equipment (economizer, condenser etc.), water treatment device, feed water pump, steam cylinder etc.

[0003] Steam generated by natural gas boiler is mainly used for power generation in power plant, in order to realize central heating, part of steam of generator unit is pumped to heat user, realizes the step-by-step utilization of energy, avoids the waste of low-grade heat energy of power plant, reduces pollution emission of boiler in heating season simultaneously, is favorable to the development of environment-friendly society.

[0004] Due to the production plan of downstream heat user being different, steam consumption is also different, when steam demand of heat user is large, in order to meet the demand of heat user, natural gas boiler needs to be peak shaving. The existing power plant will additionally set up multiple standby natural gas boilers, when steam demand of heat user is large, start standby natural gas boiler to generate steam to carry out peak shaving and supply heat user, when natural gas boiler used for power generation can meet the demand of heat user, standby natural gas boiler will be stopped. Due to the steam demand of heat user being changed constantly, leading to standby natural gas boiler being frequently started, after natural gas boiler is stopped, water in natural gas boiler will be cooled, and when subsequent starting, water needs to be heated again, leading to slow peak shaving speed. UTILITY MODEL CONTENTS

[0005] The utility model aims at overcoming the above-mentioned problems, and provides a kind of boiler load regulating device of quick peak shaving, the device can realize quick peak shaving, meet the steam demand of downstream heat user, and also can reduce energy waste.

[0006] The utility model aims at overcoming the above-mentioned problems, and provides a kind of boiler load regulating device of quick peak shaving, the device can realize quick peak shaving, meet the steam demand of downstream heat user, and also can reduce energy waste.

[0007] A boiler load regulating device for rapid peak shaving includes an economizer inlet main pipe, an economizer return main pipe, and multiple natural gas boilers. Each natural gas boiler includes a boiler body, an economizer, an inlet pump, an inlet pipe, an outlet pipe, a delivery pipe, and a return branch pipe. The economizer's air inlet is connected to the boiler body's flue gas outlet; the economizer's water inlet is connected to the economizer inlet main pipe; and the economizer's outlet is connected to the economizer return main pipe. The inlet pipe is connected to the boiler body's inlet, and the inlet pump is mounted on the inlet pipe. One end of the outlet pipe is connected to the boiler body's outlet, and the other end is connected to the inlet end of the inlet pump and the inlet pipe. One end of the delivery pipe is connected to the inlet end of the inlet pump and the inlet pipe, and the other end is connected to the economizer inlet main pipe. One end of the return branch pipe is connected to the boiler body's return water inlet, and the other end is connected to the economizer return main pipe.

[0008] The working principle of the above-mentioned boiler load regulation device that can quickly adjust peak loads is as follows:

[0009] Water from multiple natural gas boilers can be interconnected through the economizer inlet and return water mains. When one or more natural gas boilers are in operation, the others are shut down and serve as standby boilers. The standby boiler's inlet pump operates, drawing water from the boiler body through the outlet pipe and inlet pipe. Under the pump's action, the water flows into the delivery pipe, converges through the economizer inlet main, and then enters the operating economizer. In the economizer, heat exchange occurs between the water and flue gas, lowering the flue gas temperature and raising the water temperature. The hot water exits the economizer and enters the economizer return water main. Finally, the hot water flows from the economizer return water main through return branch pipes into the standby boiler body, further raising the boiler body's water temperature and preventing cooling. When the heat user's steam demand is high, starting the standby natural gas boiler allows for rapid water heating and peak shaving.

[0010] In a preferred embodiment of this utility model, the inlet of the economizer is connected to the main inlet pipe of the economizer via an economizer inlet branch pipe; the outlet of the economizer is connected to the main return pipe of the economizer via an economizer outlet branch pipe. By providing economizer inlet branch pipes, the connection between each economizer and the main inlet pipe is facilitated; similarly, by providing economizer outlet branch pipes, the connection between each economizer and the main return pipe is facilitated, resulting in a more rational pipeline layout.

[0011] Preferably, the inlet pipe and the outlet pipe are connected via a first connector, and the inlet pipe and the delivery pipe are connected via a second connector. By providing the first and second connectors, water in the inlet pipe can sequentially pass through the first connector, the inlet pump, and the second connector before entering the boiler body from the inlet port to replenish the boiler body; simultaneously, water inside the boiler body can be transported through the outlet pipe, sequentially passing through the first connector, the inlet pump, and the second connector before entering the economizer inlet main pipe from the delivery pipe.

[0012] Preferably, the inlet pipe is equipped with a first valve and a second valve. The first valve is located between the inlet end of the inlet pipe and the first connector; the second valve is located between the second connector and the inlet of the boiler body; the outlet pipe is equipped with a third valve; the delivery pipe is equipped with a fourth valve; the economizer inlet branch pipe and / or economizer outlet branch pipe are equipped with a fifth valve; and the return branch pipe is equipped with a sixth valve. In the working state of the natural gas boiler, the first, second, and fifth valves are open, while the third, fourth, and sixth valves are closed. The opening of the first and second valves is for replenishing water to the working natural gas boiler. In the standby natural gas boiler, the first, second, and fifth valves are closed, while the third, fourth, and sixth valves are open. The water pump of the standby natural gas boiler operates, and water from the boiler body flows from the outlet pipe through the inlet pipe, and then, under the action of the water pump, flows from the inlet pipe into the delivery pipe. Because the first and second valves are closed, water from the boiler body only flows into the delivery pipe. In the delivery pipe, with the fifth valve closed, the water flows through the economizer inlet main pipe and into the economizer inlet branch pipe of the operating natural gas boiler. Through the economizer, the water exchanges heat with the flue gas, lowering the flue gas temperature and raising the water temperature. The high-temperature water exits from the economizer outlet branch pipe and enters the economizer return main pipe. Since the sixth valve of the operating natural gas boiler is closed, while the sixth valve of the standby natural gas boiler is open, the high-temperature water in the economizer return main pipe enters the boiler body of the standby natural gas boiler from its return branch pipe, raising the water temperature in the boiler body and preventing cooling. By setting valves, the water temperature of the standby natural gas boiler can be flexibly controlled, allowing for rapid water heating and peak shaving as needed.

[0013] Preferably, the first, second, third, fourth, fifth, and sixth valves are all solenoid valves. By using solenoid valves, electric control is easily achieved, thereby enabling rapid peak shaving.

[0014] Preferably, the boiler body includes a boiler drum, a furnace shell, a combustion chamber, a front smoke box, and a rear smoke box. The furnace shell and the combustion chamber are disposed inside the boiler drum. The front smoke box is disposed at the front end of the boiler drum, and the rear smoke box is disposed at the rear end of the boiler drum. The combustion chamber is disposed at the rear end of the furnace shell and communicates with the furnace shell. The front smoke box and the combustion chamber are connected by a first return smoke pipe, and the front smoke box and the rear smoke box are connected by a second return smoke pipe. A burner is provided at the front end of the front smoke box, and the burner is connected to the front end of the furnace shell. The flue gas outlet of the boiler body is disposed on the rear smoke box, and the water inlet, water outlet, and water return outlet of the boiler body are disposed on the boiler drum. The flame generated by the burner burns inside the furnace, which heats the water in the boiler drum to produce steam. The high-temperature flue gas generated in the furnace passes sequentially through the combustion chamber, the first pass flue, the front smoke box, the second pass flue, and the rear smoke box, and finally exits from the flue gas outlet of the rear smoke box and enters the economizer to exchange heat with the water in the economizer.

[0015] Preferably, the boiler load regulating device capable of rapid peak shaving includes a control module, which comprises a boiler control unit for controlling the burner and a standby control unit for controlling the solenoid valves and the water inlet pump. By setting the boiler control unit, the operation and shutdown of each natural gas boiler can be controlled. Specifically, the burner is controlled; when the burner is burning, the natural gas boiler produces steam; when the burner stops burning, the natural gas boiler stops producing steam. The standby control unit can control the opening and closing of each solenoid valve and the water inlet pump, improving the flexibility of the natural gas boiler operation and achieving rapid peak shaving.

[0016] Preferably, the number of natural gas boilers is three.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] This utility model discloses a boiler load regulation device capable of rapid peak shaving. Water from multiple natural gas boilers is interconnected via economizers. High-temperature flue gas from the operating natural gas boiler is exchanged with water from the standby natural gas boiler in the economizer of the operating boiler, resulting in a decrease in flue gas temperature and an increase in water temperature. The high-temperature water then flows back to the standby natural gas boiler after exiting the economizer, raising its water temperature and preventing cooling. When the steam demand of heat users is high, the standby natural gas boiler is activated, rapidly heating the water to achieve rapid peak shaving, meeting the steam demand of downstream heat users, improving energy utilization, reducing energy consumption, and thus improving economic efficiency. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of a boiler load regulating device capable of rapid peak shaving according to the present invention.

[0020] Figure 2 This is a schematic diagram of the structure of a natural gas boiler according to this utility model.

[0021] Figure 3 This is a schematic diagram of the boiler body in this utility model. Detailed Implementation

[0022] To enable those skilled in the art to fully understand the technical solution of this utility model, the present utility model will be further described below in conjunction with the embodiments and accompanying drawings, but the implementation of this utility model is not limited thereto.

[0023] See Figures 1-2 This embodiment discloses a boiler load regulating device capable of rapid peak shaving, including an economizer inlet main pipe 1, an economizer return main pipe 2, and multiple natural gas boilers 3; wherein, each natural gas boiler 3 includes a boiler body 4, an economizer 5, an inlet pump 6, an inlet pipe 7, an outlet pipe 8, a delivery pipe 9, and a return branch pipe 10; the air inlet of the economizer 5 is connected to the flue gas outlet of the boiler body 4, the water inlet of the economizer 5 is connected to the economizer inlet main pipe 1, and the water outlet of the economizer 5 is connected to the economizer return main pipe 2; the inlet pipe 7 is connected to the water inlet of the boiler body 4, and the inlet pump 6 is installed on the inlet pipe 7; One end of the outlet pipe 8 is connected to the outlet of the boiler body 4, and the other end of the outlet pipe 8 is connected to the inlet of the inlet pump 6 and the inlet pipe 7 (that is, the other end of the outlet pipe 8 is connected to the inlet pipe 7 located on the side of the inlet of the inlet pump 6); one end of the conveying pipe 9 is connected to the outlet of the inlet pump 6 and the inlet pipe 7 (that is, one end of the conveying pipe 9 is connected to the inlet pipe 7 located on the side of the outlet of the inlet pump 6), and the other end of the conveying pipe 9 is connected to the economizer inlet main pipe 1; one end of the return water branch pipe 10 is connected to the return water inlet of the boiler body 4, and the other end of the return water branch pipe 10 is connected to the economizer return water main pipe 2.

[0024] See Figures 1-2 In this embodiment, the water from multiple natural gas boilers 3 is interconnected through an economizer 5. The high-temperature flue gas generated by the operating natural gas boiler 3 and the water from the standby natural gas boiler (i.e., the natural gas boiler 3 in the shutdown state) exchange heat in the economizer 5 of the operating natural gas boiler 3. The flue gas temperature decreases and the water temperature increases. The high-temperature water flows back to the standby natural gas boiler after exiting the economizer 5, thereby increasing the water temperature in the standby natural gas boiler and preventing it from cooling down. When the steam demand of heat users is high, the standby natural gas boiler can be started to quickly heat the water, complete the rapid peak adjustment, meet the steam demand of downstream heat users, improve energy utilization, reduce energy consumption, and thus improve economic benefits.

[0025] See Figures 1-2The inlet of the economizer 5 is connected to the economizer inlet main pipe 1 via an economizer inlet branch pipe 11; the outlet of the economizer 5 is connected to the economizer return main pipe 2 via an economizer outlet branch pipe 12. By setting up the economizer inlet branch pipe 11, the connection between each economizer 5 and the economizer inlet main pipe 1 is facilitated; by setting up the economizer outlet branch pipe 12, the connection between each economizer 5 and the economizer return main pipe 2 is facilitated, resulting in a more rational pipeline layout.

[0026] See Figures 1-2 The inlet pipe 7 and the outlet pipe 8 are connected by a first connector 13, and the inlet pipe 7 and the delivery pipe 9 are connected by a second connector 14. By setting the first connector 13 and the second connector 14, water in the inlet pipe 7 can pass through the first connector 13, the inlet pump 6, and the second connector 14 in sequence, and then enter the boiler body 4 from the inlet of the boiler body 4 to replenish the boiler body 4 with water; at the same time, water in the boiler body 4 can be transported through the outlet pipe 8, passing through the first connector 13, the inlet pump 6, and the second connector 14 in sequence, and then enter the economizer inlet main pipe 1 from the delivery pipe 9.

[0027] See Figure 2 Both the first connector 13 and the second connector 14 are tee connectors.

[0028] See Figures 1-2The inlet pipe 7 is equipped with a first valve 15 and a second valve 16. The first valve 15 is located between the inlet end of the inlet pipe 7 and the first connector 13. The second valve 16 is located between the second connector 14 and the inlet of the boiler body 4. The outlet pipe 8 is equipped with a third valve 17. The conveying pipe 9 is equipped with a fourth valve 18. The economizer inlet branch pipe 11 and / or the economizer outlet branch pipe 12 are equipped with a fifth valve 19. The return branch pipe 10 is equipped with a sixth valve 20. In the working state, the first valve 15, the second valve 16, and the fifth valve 19 are open, while the third valve 17, the fourth valve 18, and the sixth valve 20 are closed. The opening of the first valve 15 and the second valve 16 is for replenishing water to the working natural gas boiler 3. In the standby natural gas boiler, the first valve 15, the second valve 16, and the fifth valve 19 are closed, while the third valve 17, the fourth valve 18, and the sixth valve 20 are open. The inlet pump 6 of the standby natural gas boiler is working, and water from the boiler body 4 flows from the outlet pipe 8 through the inlet pipe 7, and then, under the action of the inlet pump 6, flows from the inlet pipe 7 into the delivery pipe 9. Because the first valve 15 and the second valve 16 are closed, the boiler... Water in boiler body 4 flows only into delivery pipe 9. Since the fifth valve 19 is closed, the water in delivery pipe 9 passes through the economizer inlet main pipe 1 and enters the economizer inlet branch pipe 11 of the operating natural gas boiler 3. Through the economizer 5, the water exchanges heat with the flue gas, lowering the flue gas temperature and raising the water temperature. The high-temperature water exits from the economizer outlet branch pipe 12 and enters the economizer return main pipe 2. Since the sixth valve 20 of the operating natural gas boiler 3 is closed, and the sixth valve 20 of the standby natural gas boiler is open, the high-temperature water in the economizer return main pipe 2 enters the boiler body 4 of the standby natural gas boiler from the return branch pipe 10, raising the water temperature in boiler body 4 and preventing cooling. By setting valves, the water temperature of the standby natural gas boiler can be flexibly controlled, allowing for rapid water heating and peak shaving as needed.

[0029] During peak steam demand (when heat users have high steam requirements), only one standby natural gas boiler needs to be started. The first valve 15, the second valve 16, and the fifth valve 19 of the standby natural gas boiler to be started are closed, while the third valve 17, the fourth valve 18, and the sixth valve 20 are open. The first valve 15, the second valve 16, the third valve 17, the fourth valve 18, the fifth valve 19, and the sixth valve 20 of the other standby natural gas boilers that are not started can all be closed, thereby improving energy utilization and heating the water in the standby natural gas boiler.

[0030] See Figures 1-2The first valve 15, the second valve 16, the third valve 17, the fourth valve 18, the fifth valve 19, and the sixth valve 20 are all solenoid valves. By using solenoid valves, it is easy to achieve electric control, thereby realizing rapid peak shaving.

[0031] See Figures 2-3 The boiler body 4 includes a boiler drum 4-1, a furnace 4-2, a combustion chamber 4-3, a front smoke box 4-4, and a rear smoke box 4-5. The furnace 4-2 and the combustion chamber 4-3 are disposed inside the boiler drum 4-1. The front smoke box 4-4 is disposed at the front end of the boiler drum 4-1, and the rear smoke box 4-5 is disposed at the rear end of the boiler drum 4-1. The combustion chamber 4-3 is disposed at the rear end of the furnace 4-2 and communicates with the furnace 4-2. The front smoke box... The front smoke box 4-4 and the combustion chamber 4-3 are connected by a first return smoke pipe 4-6, and the front smoke box 4-4 and the rear smoke box 4-5 are connected by a second return smoke pipe 4-7. A burner 4-8 is located at the front end of the front smoke box 4-4, and the burner 4-8 is connected to the front end of the furnace 4-2. The flue gas outlet of the boiler body 4 is located on the rear smoke box 4-5, and the water inlet, outlet, and return outlet of the boiler body 4 are located on the boiler drum 4-1. The flame generated by the burner 4-8 burns inside the furnace 4-2, which heats the water in the boiler drum 4-1, thereby generating steam. The high-temperature flue gas generated by the furnace 4-2 passes sequentially through the combustion chamber 4-3, the first return smoke pipe 4-6, the front smoke box 4-4, the second return smoke pipe 4-7, and the rear smoke box 4-5, and finally exits from the flue gas outlet of the rear smoke box 4-5, entering the economizer 5 to exchange heat with the water in the economizer 5.

[0032] See Figures 1-3 The boiler load regulating device capable of rapid peak shaving includes a control module. This control module comprises a boiler control unit for controlling burners 4-8 and a standby control unit for controlling solenoid valves and the water inlet pump 6. By setting up the boiler control unit, the operation and shutdown of each natural gas boiler 3 can be controlled. Specifically, it controls burners 4-8; when burners 4-8 are burning, natural gas boiler 3 produces steam; when burners 4-8 stop burning, natural gas boiler 3 stops producing steam. The standby control unit can control the opening and closing of each solenoid valve and the water inlet pump 6, improving the operational flexibility of the natural gas boiler 3 and achieving rapid peak shaving.

[0033] See Figure 1 The number of natural gas boilers 3 is three, and the control module can be a PLC control module or a microcontroller control module.

[0034] See Figure 1The outlet of the economizer 5 is connected to the flue gas treatment device. After heat exchange, the flue gas is discharged from the economizer 5 and transported to the flue gas treatment device for treatment. After treatment, it is discharged into the atmosphere to prevent direct emission and environmental pollution.

[0035] See Figures 1-2 The working principle of the above-mentioned boiler load regulating device that can quickly adjust peak loads is as follows:

[0036] Water from multiple natural gas boilers 3 can be interconnected through the economizer inlet main 1 and the economizer return main 2. When one or more natural gas boilers 3 are in operation, the remaining natural gas boilers 3 are shut down and serve as standby natural gas boilers. The standby natural gas boiler's inlet pump 6 is activated, and water from the boiler body 4 flows from the outlet pipe 8 through the inlet pipe 7, and then, under the action of the inlet pump 6, flows from the inlet pipe 7 into the delivery pipe 9. After converging through the economizer inlet main 1, it enters the operating economizer 5. In the economizer 5, the water exchanges heat with the flue gas, lowering the flue gas temperature and raising the water temperature. The high-temperature water exits the economizer 5 and enters the economizer return main 2. Finally, the high-temperature water flows from the economizer return main 2 through the return branch pipe 10 into the boiler body 4 of the standby natural gas boiler, raising the water temperature of the boiler body 4 and preventing cooling. When the steam demand of heat users is high, starting the standby natural gas boiler can quickly heat the water and complete rapid peak shaving.

[0037] The above are preferred embodiments of the present utility model, but the embodiments of the present utility model are not limited to the above content. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present utility model shall be considered equivalent substitutions and shall be included within the protection scope of the present utility model.

Claims

1. A rapidly peakable boiler load regulating device, characterized by, The device comprises a coal economizer water inlet main pipe, a coal economizer water return main pipe and a plurality of natural gas boilers; wherein each natural gas boiler comprises a boiler body, a coal economizer, a water inlet pump, a water inlet pipe, a water outlet pipe, a conveying pipe and a water return branch pipe; the air inlet of the coal economizer is communicated with the flue gas outlet of the boiler body, the water inlet of the coal economizer is communicated with the coal economizer water inlet main pipe, and the water outlet of the coal economizer is communicated with the coal economizer water return main pipe; the water inlet pipe is communicated with the water inlet of the boiler body, and the water inlet pump is arranged on the water inlet pipe; one end of the water outlet pipe is communicated with the water outlet of the boiler body, and the other end of the water outlet pipe is communicated with the water inlet end of the water inlet pump and the water inlet pipe; one end of the conveying pipe is communicated with the water outlet end of the water inlet pump and the water inlet pipe, and the other end of the conveying pipe is communicated with the coal economizer water inlet main pipe; one end of the water return branch pipe is communicated with the water return port of the boiler body, and the other end of the water return branch pipe is communicated with the coal economizer water return main pipe.

2. A rapid peakable boiler load regulating device according to claim 1, characterized in that The water inlet of the coal economizer is communicated with the coal economizer water inlet main pipe through a coal economizer water inlet branch pipe; and the water outlet of the coal economizer is communicated with the coal economizer water return main pipe through a coal economizer water outlet branch pipe.

3. A rapid peakable boiler load regulating device according to claim 2, characterized in that The water inlet pipe is communicated with the water outlet pipe through a first joint, and the water inlet pipe is communicated with the conveying pipe through a second joint.

4. A rapid peakable boiler load regulating device according to claim 3, characterized in that The water inlet pipe is provided with a first valve and a second valve, the first valve is located between the water inlet end of the water inlet pipe and the first joint, and the second valve is located between the second joint and the water inlet of the boiler body; the water outlet pipe is provided with a third valve; the conveying pipe is provided with a fourth valve; the coal economizer water inlet branch pipe and / or the coal economizer water outlet branch pipe is provided with a fifth valve; and the water return branch pipe is provided with a sixth valve.

5. A rapid peakable boiler load regulating device according to claim 4, characterised in that The first valve, the second valve, the third valve, the fourth valve, the fifth valve and the sixth valve are all electromagnetic valves.

6. A rapid peakable boiler load regulating device according to claim 1, characterized in that The boiler body comprises a boiler drum, a furnace, a back pass box, a front smoke box and a rear smoke box, the furnace and the back pass box are arranged in the boiler drum, the front smoke box is arranged at the front end of the boiler drum, and the rear smoke box is arranged at the rear end of the boiler drum; the back pass box is arranged at the rear end of the furnace and communicated with the furnace, the front smoke box is communicated with the back pass box through a first back pass pipe, and the front smoke box is communicated with the rear smoke box through a second back pass pipe; the front end of the front smoke box is provided with a burner, the burner is communicated with the front end of the furnace; the flue gas outlet of the boiler body is arranged on the rear smoke box, and the water inlet, the water outlet and the water return port of the boiler body are arranged on the boiler drum.

7. A rapid peakable boiler load regulating device according to claim 5, characterized in that The quick peak-regulating boiler load regulating device comprises a control module, the control module comprises a boiler control unit for controlling the burner and a standby heating control unit for controlling the electromagnetic valves and the water inlet pump.

8. A rapid peakable boiler load regulating device as set forth in claim 1, wherein The number of the natural gas boilers is three.

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