JP2012207851A - Boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a boiler with a supplied water preheater at a low cost.SOLUTION: The boiler includes a water heating boiler 1, a supplied water tank 2 storing water for the boiler, an exhaust flue 5 exhausting flue gas generated in the boiler, and the supplied water preheater 6 installed in the exhaust flue, where a pipe 3 supplying water into the boiler 1 and circulation piping 7 supplying the water for the boiler into the supplied water preheater 6 and returning the preheated water for the boiler from the supplied water preheater to the supplied water tank are connected to the supplied water tank 2 to continuously circulate the water for the boiler between the supplied water tank 2 and the supplied water preheater 6 separated from water supplied to the boiler. The supplied water preheater 6 is of a type that a heat exchange coil 8 with tubes wound like a coil is installed in the exhaust flue 5. A lid is disposed at an outer peripheral part of the exhaust flue containing the heat exchange coil and a take-out port for taking out an end of the heat exchange coil from the exhaust flue is formed in a lid to take out the heat exchange coil 8 from the exhaust flue by opening the lid.

Description

  The present invention relates to a boiler having a feed water preheater.

  In boilers that generate steam, heat remains in the exhaust gas discharged after heat exchange in the boiler, so it is possible to improve boiler efficiency by preheating boiler feedwater with the heat of the exhaust gas. Widely done. A typical water supply preheater has a large number of water pipes installed in the exhaust pipe through which the combustion exhaust gas from the boiler passes, and each water pipe is connected to form a continuous flow path. It enters into the boiler after passing through the feed water preheater. If the feed water preheater can preheat the feed water at about 15 ° C. to about 100 ° C., the amount of combustion can be reduced even when the same amount of steam is generated in the boiler, so the fuel consumption can be reduced. .

  Water supply to the boiler is intermittent, and when the water supply stops, the water flow in the water supply preheater stops, but heating of the water supply with exhaust gas continues in the water supply preheater, so the water supply temperature rises in the water supply preheater. There is a risk of boiling. For this reason, the water supply preheater needs to have pressure resistance, and the cost is increased accordingly. In addition, if the feed water temperature is low, the flue gas becomes below the dew condensation temperature on the surface of the water pipe of the feed water preheater, and dew condensation water is generated. The combustion exhaust gas contains NOx and SOx, and when nitric acid or sulfuric acid is generated due to condensation, the water pipe is corroded. Therefore, the life of the feed water preheater is shorter than that of the boiler body. When the feed water preheater is installed, the efficiency of the boiler is improved, so that the fuel cost can be reduced. However, the initial cost and the replacement cost are increased.

  When the temperature of the feed water supplied to the feed water preheater is increased, condensation on the surface of the water pipe is less likely to occur. Therefore, in Japanese Patent Laid-Open No. 9-236207, a circulation flow path connecting the water supply outlet and the water supply inlet of the water supply preheater is provided, and a part of the preheated water heated by the water supply preheater is directed to the inlet side of the water supply preheater. There is a description of the boiler which is made to return and raises the temperature of the feed water entering the feed water preheater. Circulating a part of the feed water can raise the feed water temperature at the feed water preheater inlet, thereby preventing condensation and preventing low temperature corrosion. However, in this case, since a part of the water supply is not sent to the boiler, the water supply capacity is reduced. Further, even in this case, since there is a possibility of boiling in the feed water preheater, the fact that the feed water preheater must have a high pressure resistance remains the same.

JP-A-9-236207

  The problem to be solved by the present invention is to provide a boiler having a feed water preheater at a low cost.

  It is installed in a boiler that heats water by burning inside and generates steam, a water supply tank that stores boiler water to be supplied to the boiler, an exhaust pipe that discharges combustion exhaust gas generated in the boiler, and an exhaust pipe It has a feed water preheater that preheats boiler water using the heat of combustion exhaust gas. The feed water tank supplies the boiler water to the boiler, and supplies the boiler water to the feed water preheater and feeds the preheated boiler water. In the boiler that connects the circulation pipe returning from the preheater to the water supply tank, and separates the water supply to the boiler so that the boiler water can be continuously circulated between the water supply tank and the water supply preheater. The feed water preheater has a heat exchange coil in which a tube is wound in a coil shape installed in an exhaust pipe. A lid is provided on the outer periphery of the exhaust pipe that houses the heat exchange coil, and the lid portion is heated. May be provided a take-out port for taking out the end of the conversion coil from the exhaust cylinder, characterized in that as the heat exchange coils can be easily taken out from the exhaust cylinder by opening the lid.

  When the boiler water is circulated between the feed water tank and the feed water preheater, since the feed water tank is a release tank, the boiler water can be circulated without applying high pressure to the feed water to the feed water preheater. Since the circulation is continuously performed, the boiler water is not heated to the boiling temperature while the boiler water stays in the feed water preheater. Therefore, the boiler water does not boil in the feed water preheater, the pressure resistance of the feed water preheater need not be so high, and it becomes possible to use a pipe with low pressure resistance such as a flexible tube, It is possible to reduce the cost of the feed water preheater. Moreover, since the heat exchange coil is installed in the exhaust pipe, it can be added later to the existing boiler. By implementing this invention, the efficiency of a boiler can be improved without incurring big cost.

Flow diagram of boiler implementing the present invention Explanatory drawing which showed the water supply preheater assembly condition in one Example of this invention Sectional drawing of the feed water preheater which showed the combustion exhaust gas flow in one Example of this invention

  An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a flow chart of a boiler implementing the present invention, FIG. 2 is an explanatory diagram showing an assembly state of a feed water preheater in one embodiment of the present invention, and FIG. 3 is a combustion exhaust gas in one embodiment of the present invention. It is sectional drawing of the feed water preheater which showed the flow. The boiler 1 generates steam by heating boiler water by performing combustion inside. Boiler water is stored in a water supply tank 2 which is a release tank, and is supplied through a water supply pipe 3 connecting between the water supply tank 2 and the boiler 1. When the water level in the boiler falls to the water supply start water level, the water supply pump provided in the middle of the water supply pipe 3 is operated to supply water to the boiler, and when the boiler water level rises to the water supply stop water level, the water supply pump is operated. Stop and end water supply. Water is supplied to the water supply tank 2 through a softened water pipe 4 that supplies softened water that has been softened by a water softener (not shown). Even in the water supply tank 2, when the water level drops, water is supplied to raise the water level, and when the water level rises to a predetermined water level, the water supply is stopped.

  In the boiler 1, heat is generated by performing combustion, and steam is generated by heating the boiler water with radiant heat from the flame and high-temperature combustion gas. Then, the combustion exhaust gas after the heat exchange is taken out from the boiler, and is discharged outside through the exhaust pipe 5. Although the temperature of combustion exhaust gas decreases due to heat exchange in the boiler, it retains heat of about several hundred degrees Celsius when it is taken out of the boiler, so it can be used for applications that preheat feed water. it can. A feed water preheater 6 is installed in the middle of the exhaust pipe 5, and the combustion exhaust gas also exchanges heat with the feed water preheater 6. The feed water preheater 6 is connected to the feed water tank 2 by a circulation pipe 7 consisting of a forward path and a return path, and boiler water stored in the feed water tank 2 is sent to the feed water preheater 6 through the forward path of the circulation pipe 7. After heating with the feed water preheater 6, the water is returned to the feed water tank 2 through the return path of the circulation pipe 7.

  When the boiler 1 is operating, the boiler water stored in the feed water tank 2 is continuously sent to the feed water preheater 6 to preheat the boiler water. Since the combustion exhaust gas flows through the exhaust pipe 5 during the boiler operation, the circulation pump provided in the circulation pipe 7 is operated to send water to the feed water preheater 6 through the circulation pipe 7. When water flows, it is heated by the combustion exhaust gas flowing around the heat exchange coil 8. The circulation pipe 7 is returned from the feed water preheater 6 to the feed water tank 2, and the water whose temperature has risen by the heat exchange coil 8 returns to the feed water tank 2. Since the water supplied to the boiler 1 sends the water preheated by the feed water preheater 6, the efficiency of the boiler is improved.

  Since the circulation pipe 7 that circulates water between the water supply tank 2 and the water supply preheater 6 is a separate system from the water supply to the boiler, the circulation pipe is used even when the water supply to the boiler is stopped. The water flow at 7 can be carried out continuously. And the circulation piping 7 circulates water between the water supply tank 2 which is a release tank, and the water supply preheater 6, and the water pressure required for the circulation of water is not high. Therefore, a large amount of water can flow continuously in the circulation pipe 7 and the water does not boil in the heat exchange coil 8, so there is no problem even if a flexible tube with low pressure resistance is used. It is advantageous that it can be manufactured at low cost.

  The water supply preheater 6 includes a heat exchange coil 8 using a flexible tube, an outer cylinder 9 that surrounds the outside of the heat exchange coil 8, and an inner cylinder 10 that is inserted into the heat exchange coil 8. The heat exchange coil 8 supplies water from above in the figure on the downstream side of the combustion exhaust gas flow, and the preheated water is taken out from below. The diameter of the heat exchange coil 8 is larger than the exhaust cylinder diameter l and smaller than the outer cylinder diameter L, where L is the diameter of the outer cylinder 9 and l is the diameter of the exhaust cylinder 5 other than the feed water preheater. And installed in an annular space formed between the inner cylinder 10 and the outer cylinder 9.

  As can be seen from FIG. 3, the heat exchange coil 8 is composed of a plurality of flexible tubes. In the figure, the heat exchange coil 8 is composed of a total of four flexible tubes, two on the upper side and two on the lower side. ing. A circulation pipe branching portion 15 for dividing the boiler water sent from the feed water tank and supplying it to the feed water preheater is provided in the portion immediately before the feed water preheater of the circulation pipe 7, and divided into a plurality of tubes installed in parallel. Boiler water is supplied. In the circulation pipe 7 immediately after the feed water preheater, there is provided a circulation pipe joining portion 16 for joining the boiler water that has been divided and flowing in the heat exchange coil 8, and the preheated boiler water is fed through the common circulation pipe 7. Return to tank 2.

  Dividing the flexible tube and distributing the preheated water to reduce the pressure loss of the water flowing in the heat exchange coil 8 so that a large amount of water can flow with a small force Become. In addition, the division | segmentation number and length of a flexible tube will be suitably selected based on the amount of heat recovery, and the magnitude | size of flow-path resistance. If the target heat recovery amount is large, the total extension of the flexible tube becomes long. If the length of the flexible tube becomes long, the flow resistance becomes large, so that the number of divisions needs to be increased.

  The outer cylinder 9 is provided with a lid 11 so that half of the plate forming the outer periphery can be removed from the outer cylinder 9. The lid 11 is provided with a take-out port 12 for drawing out the end of the heat exchange coil 8. Since a plurality of take-out ports 12 are required for each flexible tube having an inlet and an outlet, a total of eight take-out ports 12 are provided in FIG.

  When the heat exchange coil 8 is installed in the exhaust cylinder 5, the cross-sectional area of the flow path through which the combustion exhaust gas flows is reduced by the heat exchange coil 8. Therefore, it is necessary to increase the diameter of the exhaust pipe at the portion where the feed water preheater 6 is installed. At this time, the expanded width of the exhaust cylinder diameter may be only the cross-sectional integral corresponding to the amount reduced by the heat exchange coil 8, but the diameter is intentionally increased beyond a necessary amount. The reason is to prevent an increase in the amount of heat absorption and intrusion of condensed water into the boiler.

  When the portion of the water supply preheater 6 is made larger than the diameter of the other exhaust cylinder 5, the outer cylinder 9 needs to have a portion connecting with the diameter of the exhaust cylinder 5. By providing the plate and the bottom plate, the outer periphery of the exhaust pipe 5 is connected. An annular bottom plate provided to connect the outer cylinder 9 and the exhaust cylinder 5 is provided with a drain hole 13 for discharging drain (condensed water), and the drain in the exhaust cylinder 5 below the water supply preheater 6. A drain inflow prevention wall 14 is provided to prevent entry. The drain inflow prevention wall 14 is a plate which stands upright with respect to the bottom plate, and is provided in an annular shape along the diameter of the exhaust pipe. The drain hole 13 is provided between the drain inflow prevention wall 14 and the outer cylinder 9, and the condensed water falling on the bottom plate portion does not flow to the exhaust cylinder 5 connected to the boiler, but is discharged to the outside through the drain hole 13. Will be. However, if the heat exchange coil 8 is installed in the vicinity of the central axis of the exhaust cylinder 5, the condensed water falls inside the drain inflow prevention wall 14, so the drain inflow prevention wall 14 and the drain hole 13 are provided. However, there is a problem that the condensed water cannot be prevented from flowing into the boiler.

  In addition, if the length of the chimney member is fixed and the length of the preheater 6 is the same as that of the chimney member, even if the feed water preheater 6 is added to the existing chimney later, the installation cost of the feed water preheater 6 Can be kept low. When the height of the feed water preheater is determined, the maximum value of the height of the heat exchange coil 8 is determined, and the length of the flexible tube in the heat exchange coil 8 is determined from the height and diameter of the heat exchange coil 8. As the length of the flexible tube increases, the amount of heat absorption increases. However, if the height of the heat exchange coil 8 is limited, it cannot be made longer than a certain length. Moreover, if the coil of a flexible tube is installed in the vicinity of the central axis, the condensed water is sent into the boiler as described above, which causes corrosion of the boiler. Therefore, it is not possible to increase the length of the flexible tube by installing the heat exchange coil 8 also in the vicinity of the central axis.

  Because of these problems, the diameter of the outer cylinder 9 is set to be significantly larger than the diameter of the exhaust cylinder 5. If the diameter of the outer cylinder 9 in the feed water preheater 6 is increased, the diameter of the heat exchange coil 8 can be increased, and the length of the flexible tube is increased even if the height of the heat exchange coil 8 is the same. , Heat absorption can be increased. However, if the increase in the flow path area due to the expansion of the exhaust cylinder diameter is larger than the decrease in the flow path area of the combustion exhaust gas by the heat exchange coil 8, the combustion exhaust gas flows widely and thinly in the portion of the feed water preheater 6; Decreasing the heat absorption efficiency at 8 is a new problem.

  Therefore, in the present invention, the inner cylinder 10 is installed near the central axis of the heat exchange coil 8. The inner cylinder 10 has a cylindrical structure with a lid on the upper side and an opening on the lower side so that an annular space is formed between the inner cylinder 10 and the outer cylinder 9. Since the upper side of the inner cylinder is covered with a lid, the combustion exhaust gas flows through an annular space formed between the inner cylinder 10 and the outer cylinder 9. If the heat exchange coil 8 is installed in an annular space formed between the inner cylinder 10 and the outer cylinder 9, the combustion exhaust gas will flow intensively in the heat exchange coil 8, and the heat exchange coil 8 is made efficient. Can be heated well.

  Moreover, since the feed water preheater 6 captures the heat of the combustion exhaust gas, the temperature of the combustion exhaust gas may decrease and condensation may occur. Since the boiler water entering the feed water preheater 6 is preheated and circulated, condensation in the feed water preheater 6 is less likely to occur, but the boiler water temperature is low at the first start-up. Therefore, the generation of condensed water cannot be completely eliminated.

  The condensed water generated in the heat exchange coil 8 falls directly below the heat exchange coil 8. However, if the diameter of the heat exchange coil 8 is increased and the inner cylinder 10 is provided near the central axis of the feed water preheater 6 so that the heat exchange coil 8 is not installed near the central axis, the heat exchange coil 8 The condensed water generated in the above step falls on the bottom plate provided at the bottom of the outer cylinder 9. Since the drain inflow prevention wall 14 is provided at the bottom of the feed water preheater 6 so that the condensed water does not flow into the boiler, the effect of preventing the main body of the boiler from being corroded by the condensed water. Obtainable.

  In addition, since the heat exchange coil 8 part contacts dew condensation water, corrosion of the heat exchange coil 8 itself cannot be prevented. However, the outer cylinder 9 is provided with a lid 11, and by removing the lid 11, the heat exchange coil 8 can be easily replaced while the water supply preheater 6 itself remains installed. The heat exchange coil 8 made of a flexible tube has a problem that its life is shortened because it is thin. However, if the heat exchange coil 8 can be easily replaced, the cost of the heat exchange coil 8 itself is low. It can be kept low.

  In addition, there are many boilers that are not preheated at the moment. When the connecting portion of the feed water preheater 6 to the exhaust pipe is the same as the diameter of a general exhaust pipe member, and the length of the feed water preheater 6 is also the same as the length of the general exhaust pipe member, the existing exhaust pipe Since it is easy to add the feed water preheater 6 of the present invention later, the efficiency of the existing boiler can be easily improved.

  The present invention is not limited to the above-described embodiments, and many modifications can be made by those having ordinary knowledge in the art within the technical 5099 concept of the present invention.

1 boiler
2 Water supply tank
DESCRIPTION OF SYMBOLS 3 Water supply pipe 4 Softened water piping 5 Exhaust pipe 6 Water supply preheater 7 Circulation pipe 8 Heat exchange coil 9 Outer cylinder 10 Inner cylinder 11 Cover 12 Drain outlet 13 Drain drain hole 14 Drain inflow prevention wall
15 Circulation piping branch 16 Circulation piping junction

Claims (1)

It is installed in a boiler that heats water by burning inside and generates steam, a water supply tank that stores boiler water to be supplied to the boiler, an exhaust pipe that discharges combustion exhaust gas generated in the boiler, and an exhaust pipe It has a feed water preheater that preheats boiler water using the heat of combustion exhaust gas. The feed water tank supplies the boiler water to the boiler, and supplies the boiler water to the feed water preheater and feeds the preheated boiler water. In the boiler that connects the circulation pipe returning from the preheater to the water supply tank, and separates the water supply to the boiler so that the boiler water can be continuously circulated between the water supply tank and the water supply preheater. The feed water preheater has a heat exchange coil in which a tube is wound in a coil shape installed in an exhaust pipe. A lid is provided on the outer periphery of the exhaust pipe that houses the heat exchange coil, and the lid portion is heated. A feed water preheater characterized in that an outlet for taking out the end portion of the exchange coil from the exhaust pipe is provided and the heat exchange coil can be easily taken out from the exhaust pipe by opening the lid. A boiler with it.

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