JP2011226712A - Waste heat recovery facility for arc furnace for steel making, and arc furnace facility for steel making - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a waste heat recovery facility for an arc furnace for steel making capable of efficiently recovering waste heat by suppressing temperature fluctuation of exhaust gas.SOLUTION: A waste heat recovery facility for an arc furnace for steel making is provided with: first exhaust gas passages for discharging exhaust gas from each of a plurality of arc furnaces for steel making; waste heat boilers 6 that are installed in the first exhaust gas passages, and that recover the waste heat from the exhaust gas as saturated steam; a steam accumulator 62 that accumulates steam by merging the saturated steam generated by each of the waste heat boilers 6; a steam superheater 43 that produces superheated steam by heating the steam accumulated in the steam accumulator 62; second exhaust gas passages that discharge exhaust gas, which has been obtained from the waste heat recovered by the waste heat boilers 6, guided to the steam superheater 43, and provided for superheating of the saturated steam; third exhaust gas passages that discharge exhaust gas, which has been obtained from the waste heat recovered by the waste heat boilers 6, but which bypasses the steam superheater 43; switching means that switch the exhaust gas passage, after waste heat has been recovered, between the second exhaust gas passages and the third exhaust passages.

Description

  The present invention has a waste heat recovery facility for a steel arc furnace for recovering waste heat of exhaust gas from a steel arc furnace as saturated steam and further heating it to superheated steam, and such a waste heat recovery facility. The present invention relates to an arc furnace facility for steel making.

  Steelmaking arc furnaces (also referred to as “electric furnaces”) are raw steel scrap, reduced iron (DRI), hot briquette iron (HBI), hot metal, cold iron (model iron), etc. Is inserted into the furnace, the electrode is inserted into the arc furnace and energized to melt the raw material, the energization is stopped, and the intermittent operation is performed with the process of discharging the melted steel as one cycle.

  Since iron scrap, which is a raw material, often has paint and machine oil attached to it, and synthetic resin may be mixed in, it produces white smoke and bad odor. Also, carbon contained in iron scrap and DRI is generated as carbon monoxide. For this reason, exhaust gas is completely burned by positively taking in air between the furnace and the furnace lid or in the secondary combustion tower.

  Since this combustion gas has a high temperature exceeding 1200 ° C. and has a great deal of energy, it has been attempted to recover its waste heat. For example, Patent Document 1 discloses a technique of installing a waste heat boiler in an electric furnace exhaust gas pipe and recovering sensible heat and combustion heat of exhaust gas from a steelmaking arc furnace.

  The recovered steam is used for power generation by a steam turbine, and the steam supplied as a driving source of the steam turbine is preferably superheated steam from the viewpoint of increasing the enthalpy on the turbine inlet side. Discloses that the waste heat of the steelmaking arc furnace is recovered as saturated steam and then converted to superheated steam.

JP-A-8-277212 JP 2002-286209 A

  However, in an arc furnace for steelmaking, when one cycle of operation is 70 minutes, hot gas and cold air alternate, such that hot gas flows for about 55 minutes and cold air flows for about 15 minutes. Since it will flow, exhaust gas temperature will change a lot. When the exhaust gas temperature fluctuates greatly in this way, the amount of steam generated varies and the amount of recovered steam also varies. When the amount of recovered steam varies, when the recovered steam is supplied to the steam turbine, the amount of power generation decreases, or steady operation of the steam turbine becomes difficult.

  Further, since the steam recovered by the waste heat boiler is saturated steam, it has little utility value as it is, and it is desirable to use superheated steam when generating power by using a steam turbine or the like, as described above. Discloses that the waste heat of the steelmaking arc furnace is recovered as saturated steam and then converted to superheated steam. However, in the method of Patent Document 2, in order to use saturated steam as superheated steam, it is necessary to use another heat source such as fossil fuel, resulting in low energy economy.

  The present invention has been made in view of such a situation, and the waste heat of exhaust gas discharged from a steelmaking arc furnace is recovered as saturated steam, and when this is further heated to superheated steam, the temperature of the exhaust gas is recovered. To provide a waste heat recovery facility for a steelmaking arc furnace, which can efficiently recover waste heat while suppressing fluctuations, and has high energy economy, and a steelmaking arc furnace facility having such a waste heat recovery facility. Let it be an issue.

In order to solve the above-mentioned problems, in the first aspect of the present invention, the waste heat of exhaust gas discharged from a plurality of steelmaking arc furnaces is recovered as saturated steam, and further, the saturated steam is heated to form superheated steam. A waste heat recovery facility for an arc furnace, which saturates exhaust gas waste heat installed in the first exhaust gas flow path for discharging exhaust gas from each steelmaking arc furnace and the first exhaust gas flow path. A waste heat boiler to be recovered as steam, a steam accumulator for storing saturated steam generated in each of the waste heat boilers, a steam superheater for heating the steam stored in the steam accumulator to form superheated steam, The exhaust gas after the waste heat is recovered by the waste heat boiler is guided to the steam superheater and used for heating the saturated steam, and the exhaust gas is discharged by the waste heat boiler. After A third exhaust gas flow path for discharging the exhaust gas without passing through the steam superheater, and a flow path for the exhaust gas after the waste heat is recovered, the second exhaust gas flow path and the third exhaust gas flow path. A waste heat recovery facility for an arc furnace for steel making, characterized in that it comprises a switching means for switching in step (b).

  In the waste heat recovery facility, the waste heat of the exhaust gas is typically sensible heat of the exhaust gas, or sensible heat and combustion heat of the exhaust gas.

  In the waste heat recovery facility, the first exhaust gas flow path includes an exhaust gas duct and a combustion tower for burning the exhaust gas, and the waste heat boiler constitutes the exhaust gas duct and / or the combustion tower. Can be provided. The waste heat boiler is preferably provided in a range where the temperature of the exhaust gas at the outlet is 600 ° C. or higher.

  The apparatus further comprises a gas thermometer provided at an outlet of the waste heat boiler and / or an inlet of the steam superheater, and an exhaust gas temperature at the outlet of the waste heat boiler and / or an exhaust gas temperature at the inlet of the steam superheater. Is equal to or higher than a predetermined temperature, the exhaust gas is caused to flow through the second exhaust gas flow path, and the exhaust gas temperature at the outlet of the waste heat boiler and / or the exhaust gas temperature at the inlet of the steam superheater is predetermined. When the temperature is lower than the temperature, the switching means is preferably operated so that the exhaust gas flows through the third exhaust gas flow path.

  The third exhaust gas flow path includes a ventilation duct for ventilating the surroundings of each steelmaking arc furnace and / or a steelmaking factory where the plurality of steelmaking arc furnaces are installed, and the second flow path. It can be set as the structure which has the connection piping which connects the said ventilation duct, and the ventilation assembly duct which the said ventilation duct gathered. In this case, it can be set as the structure further equipped with the dust collector which collects the waste gas from the said 2nd exhaust gas flow path, and the cooler which cools the waste gas before reaching the said dust collector. And a dust collector for collecting the exhaust gas from the second exhaust gas flow path, wherein the exhaust gas from the second exhaust gas flow path is mixed with the cold air of the ventilation collective duct in the mixed state. It can also be set as the structure led to a duster. Specifically, the second exhaust gas flow path extends from an exhaust gas duct downstream of each waste heat boiler, an exhaust gas assembly duct in which these exhaust gas ducts are aggregated, the exhaust gas assembly duct, and the steam superheater A downstream exhaust gas duct connected thereto, the downstream exhaust gas duct connected to the ventilation collective duct, the exhaust gas collective duct connected to the dust collector connected to the ventilation collective duct, and the downstream The exhaust gas from the side exhaust gas duct may be guided to the dust collector via the exhaust gas dust collection duct in a state where the cold air of the ventilation assembly duct is mixed with the exhaust gas. Further, the exhaust gas from the second exhaust gas passage is configured to be guided to the dust collector in a state where the cold air of the ventilation collective duct is mixed, and further includes a cooler. You can also

  In order to suppress fluctuations in the temperature of the exhaust gas flowing into the superheater, it is preferable to further include a heat storage body provided on the upstream side of the steam superheater in the second exhaust gas flow path.

  Depending on the temperature of the superheated steam, a saturated steam flow control valve that controls the flow rate of saturated steam that flows into the steam superheater, a superheated steam thermometer that detects the temperature of superheated steam discharged from the steam superheater, and the temperature of the superheated steam And a controller for controlling the amount of superheated steam by controlling the saturated steam flow control valve.

  An exhaust gas flow meter for detecting the flow rate of exhaust gas flowing into the steam superheater, an exhaust gas thermometer for detecting the temperature of exhaust gas flowing into the steam superheater, and a flow rate of saturated steam flowing into the steam superheater And a controller for controlling the flow rate of the exhaust gas by controlling the flow rate adjusting means according to the temperature of the exhaust gas and the flow rate of the saturated steam. It is preferable to further comprise

  In the second aspect of the present invention, the waste heat of exhaust gas discharged from a plurality of steelmaking arc furnaces and the plurality of steelmaking arc furnaces is recovered as saturated steam, and the saturated steam is further heated to superheated steam. A steelmaking arc furnace facility comprising a waste heat recovery facility, wherein the waste heat recovery facility comprises the waste heat recovery facility according to the first aspect. .

  According to the present invention, since saturated steam generated by a waste heat boiler provided in each of a plurality of steelmaking arc furnaces is joined, even if there is a variation in the amount of steam generated in the operation of one steelmaking arc furnace, After that, the amount of steam is leveled. In addition, when heating saturated steam to superheated steam, heating energy is supplied using exhaust gas after waste heat recovery, so there is no need for a separate fuel for generating superheated steam, and energy economy Is expensive. Furthermore, when the superheated steam is generated, the period during which the low temperature exhaust gas is discharged in the steel arc furnace is switched so that the exhaust gas flows through the exhaust gas passage not via the steam superheater. The temperature drop of exhaust gas can be suppressed, and superheated steam with a predetermined superheat degree can be generated stably.

It is a schematic block diagram which shows the arc furnace equipment for steelmaking provided with the waste heat recovery equipment of the arc furnace for steelmaking which concerns on one Embodiment of this invention. It is sectional drawing which shows the structure of the steam superheater used for the waste heat recovery equipment of the arc furnace for steel manufacture which concerns on one Embodiment of this invention. It is a figure for demonstrating the switching aspect of the exhaust gas flow path by a damper. It is a figure which shows the example of a temperature change of the combustion tower entrance in the arc furnace for steel manufacture when 1 heat is 70 minutes. The figure for demonstrating time until the output recovers when the output of a steam turbine falls. The figure for demonstrating the preferable structure for switching by the exhaust gas flow path which supplies an exhaust gas flow path to a steam superheater, and the exhaust gas flow path which does not go through via a steam superheater. The figure for demonstrating the other example of the preferable structure for switching by the exhaust gas flow path which supplies an exhaust gas flow path to a steam superheater, and the exhaust gas flow path which does not go through via a steam superheater. The figure for demonstrating the further another example of the preferable structure for switching by the exhaust gas flow path which supplies an exhaust gas flow path to a steam superheater, and the exhaust gas flow path which does not go through via a steam superheater. It is a figure which shows the principal part of the waste heat recovery equipment of the arc furnace for steel manufacture which concerns on other embodiment of this invention. It is a figure which shows the principal part of the waste heat recovery equipment of the arc furnace for steel manufacture which concerns on other embodiment of this invention. It is a figure which shows the principal part of the waste heat recovery equipment of the arc furnace for steel manufacture which concerns on another embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic configuration diagram showing a steelmaking arc furnace facility provided with a waste heat recovery facility for a steelmaking arc furnace according to an embodiment of the present invention. The steelmaking arc furnace facility 100 includes four arc furnace units 10a, 10b, 10c, and 10d. These arc furnace units 10a to 10d are arranged in a steelmaking factory (not shown), and all have a steelmaking arc furnace 1, and an exhaust duct 2 is connected to each steelmaking arc furnace 1. High temperature exhaust gas discharged from the steelmaking arc furnace 1 flows into the exhaust duct 2. A water-cooling duct 4 on the front stage side is connected to the exhaust duct 2, a combustion tower 3 for combusting exhaust gas is connected to the water-cooling duct 4 on the front stage side, and a water-cooling duct 4 on the rear stage side is connected to the combustion tower 3. A duct 5 is connected to the water cooling duct 4 on the side. The exhaust duct 2, the water cooling duct 4, and the duct 5 function as exhaust gas ducts. The water cooling duct 4 and the combustion tower 3 on the front stage side and the rear stage side constitute a waste heat boiler 6. Note that the waste heat boiler 6 may be composed of only the water cooling duct 4 or only the combustion tower 3. A ventilation hood 11 is provided around the arc furnace 1 for steel making of each arc furnace unit, and a ventilation duct 12 is connected to the ventilation hood 11.

  In this embodiment, the steelmaking arc furnace 1 includes a furnace body 21, a furnace lid 22 that can be opened and closed, and three arc electrodes 23 that are inserted into the furnace body 21 from above the furnace lid 22. It constitutes a three-phase AC type arc furnace. The steelmaking arc furnace 1 is not limited to a three-phase AC type arc furnace in which the number of arc electrodes 23 is three, and the arc electrode may be another number of arc furnaces. Then, raw materials such as iron scrap, DRI, HBI, hot metal, cold iron (type iron) are charged into the furnace body 21, and the raw material is melted by an arc formed by energizing the arc electrode 23 to obtain molten steel. It is designed to be melted. Although not shown, the steelmaking arc furnace 1 may be provided with an oxygen gas blowing lance for refining and / or a carbonaceous material blowing lance for adding a charcoal.

  The combustion tower 3 of each arc furnace unit is harmless by completely burning carbon monoxide, white smoke substance, malodorous substance, etc. in the high-temperature exhaust gas discharged from the furnace body 21 with air introduced from the air inlet 8. The temperature of the exhaust gas further rises due to the heat of combustion at this time.

  The waste heat boiler 6 of each arc furnace unit recovers waste heat of exhaust gas (here, sensible heat and combustion heat of exhaust gas) as saturated steam, and flows into the exhaust gas flow path flowing out from the steelmaking arc furnace 1. Provided. At this time, the waste heat boiler 6 is preferably provided in a range in which the exhaust gas temperature is equal to or higher than a predetermined temperature. The water cooling duct 4 and the combustion tower 3 on the front side and the rear side constituting the waste heat boiler 6 have heat transfer tubes 7.

  Each arc furnace unit has a steam drum 13. The steam drum 13 is supplied with cooling water (pure water) to the heat transfer tube 7 and the cooling water (pure water) from the heat transfer tube 7 to the steam drum 13 ( A return pipe 15 for returning steam) is connected. The supply pipe 14 is provided with a circulating water pump 16. Thereby, the cooling water is circulated and supplied to the heat transfer tube 7. The cooling water accommodated in the steam drum 13 is sent to the heat transfer pipe 7 through the supply pipe 14 by the circulating water pump 16. The cooling water sent to the heat transfer tube 7 is heated by the sensible heat of the exhaust gas generated from the steelmaking arc furnace 1 and the combustion heat generated by the combustion of the exhaust gas in the combustion tower 3, converted into saturated steam, and returned. The steam is returned to the steam drum 13 through the pipe 15 and is separated into steam and water in the steam drum 13. A saturated steam transport pipe 17 is connected to the steam drum 13, and the saturated steam in the steam drum 13 is transported to the accumulator 62 through the saturated steam transport pipe 17.

  Note that a pure water tank (not shown) is connected to the steam drum 13, and cooling water (pure water) is appropriately supplied from the pure water tank so that a predetermined amount of water is stored in the steam drum 13. Is done. Further, in the drawing, the supply pipe 14 and the return pipe 15 are shown one by one for convenience, but in actuality, the number of heat transfer pipes 7 (the number of boiler parts divided as necessary) is provided. Yes.

  Each of the arc furnace unit ducts 5 is connected to the exhaust gas collecting duct 41, and the exhaust gas collecting duct 41 is connected to one downstream exhaust gas duct 42. The exhaust gas is collected by the exhaust gas collecting duct 41 and reaches the downstream exhaust gas duct 42. The downstream exhaust gas duct 42 is connected to a steam superheater 43 that further heats the saturated steam to form superheated steam. Therefore, the exhaust gas after the waste heat is recovered is used for heating the saturated steam in the steam superheater 43 through the duct 5, the exhaust gas collecting duct 41, and the downstream exhaust gas duct 42. The steam superheater 43 will be described in detail later. An exhaust gas flow meter 47 is provided in a portion of the downstream side exhaust duct 42 upstream of the steam superheater 43. On the other hand, each of the ventilation ducts 12 of each arc furnace unit is connected to a ventilation collective duct 51. The downstream exhaust gas duct 42 after passing through the steam superheater 43 is connected to the ventilation collective duct 51, and the exhaust gas dust collecting duct 52 is connected to the ventilating collective duct 51. For example, a dust collector 54 having a bag filter and an exhaust fan 55 are connected to the exhaust gas dust collection duct 52, and the exhaust gas removed by the dust collector 54 is discharged to the atmosphere at the end of the exhaust gas dust collection duct 52. A chimney 56 is connected. The exhaust gas dust collecting duct 52 upstream of the dust collector 54 is provided with an exhaust gas cooler 53 for setting the temperature of the exhaust gas below the heat resistant temperature of the dust collector 54 as necessary.

  The saturated steam transport pipe 17 of each arc furnace unit is connected to the steam collecting pipe 61, and the saturated steam transported through each saturated steam transport pipe 17 is collected by the steam collecting pipe 61. A steam accumulator 62 is connected to the steam collecting pipe 61, and saturated steam generated in the steam drum 13 of each arc furnace unit is stored in the steam accumulator 42. A steam superheater 43 is connected to the steam collecting pipe 61 after passing through the steam accumulator 62. In addition, the steam accumulator 62 may be one as shown in the figure, or may be plural.

  As shown in FIG. 2, the steam superheater 43 includes a housing 44 and a heat transfer tube 45 that is bent and provided inside the housing 44. The casing 44 is connected to the downstream side exhaust gas duct 42, and high-temperature exhaust gas flows through the casing 44. On the other hand, the saturated steam from the steam accumulator 62 is supplied to the heat transfer tube 45, and the saturated steam flowing through the heat transfer tube 45 is heated by the exhaust gas and converted into superheated steam. In the present embodiment, the converted superheated steam is supplied to the power generation steam turbine 63.

  Each arc furnace unit is provided with a connecting pipe 18 that connects the duct 5 on the downstream side of the waste heat boiler 6 and the ventilation duct 12. The connection pipe 18 is for flowing the exhaust gas after the waste heat is recovered to the ventilation duct 12. A damper 31 is provided on the downstream side of the connecting pipe 18 connecting portion of the duct 5, and a damper 32 is provided in the vicinity of the duct 5 connecting portion of the connecting pipe 18. By operating these dampers 31 and 32, the exhaust gas from the steelmaking arc furnace 1 is switched between the exhaust gas flow path on the steam superheater 43 side and the exhaust gas flow path on the ventilation duct 12 side that does not pass through the steam superheater 43. It is possible. That is, the dampers 31 and 32 function as a switching unit that switches between an exhaust gas passage that supplies exhaust gas after waste heat recovery to the steam superheater 43 and an exhaust gas passage that does not pass through the steam superheater 43. Specifically, during the period when the exhaust gas temperature during operation of the steelmaking arc furnace 1 is high, the damper 31 is opened and the damper 32 is closed and the steelmaking arc furnace 1 is opened as shown in FIG. The exhaust gas is guided to the steam superheater 43 through the duct 5, the exhaust gas collecting duct 41, and the downstream exhaust gas duct 42. On the other hand, during the period when the exhaust gas temperature is low, such as when the operation of the steelmaking arc furnace 1 is stopped, the damper 31 is closed and the damper 32 is opened as shown in FIG. Low-temperature exhaust gas from the furnace 1 is guided to the ventilation duct 12 through the connection pipe 18. Thus, in this embodiment, the low temperature exhaust gas from the steelmaking arc furnace 1 is not supplied to the steam superheater 43 so that the temperature of the exhaust gas for heating the saturated steam is prevented from decreasing. ing.

  A first exhaust gas flow path for recovering waste heat of the exhaust gas is formed from each steelmaking arc furnace 1 through the exhaust duct 2 to the portion constituting the boiler 6 of the combustion tower 3 and the water cooling duct 4. . The duct 5, the exhaust gas collecting duct 41, and the downstream exhaust gas duct 42 function as a second exhaust gas flow path for discharging the exhaust gas after the waste heat has been recovered after being led to the steam superheater 43. Further, the connection pipe 18, the ventilation duct 12, and the ventilation collective duct 51 function as a third exhaust gas flow path for discharging the exhaust gas after the waste heat is recovered without passing through the steam superheater.

  Such a steelmaking arc furnace facility 100 has a monitoring / operation / control unit 70 for monitoring operation and operating / controlling each unit. The monitoring / operation / control unit 70 is a monitoring unit for grasping the operation status of the steelmaking arc furnace facility 100, and for the operator to perform various operations for operations such as starting and stopping energization of the arc electrode 23. It has an operation panel and a control unit that performs necessary control during operation.

Next, the processing operation of the steelmaking arc furnace facility 100 configured as described above will be described.
First, the raw material is charged into the furnace body 21 of the steelmaking arc furnace 1, and the arc electrode 23 is energized to start melting of the raw material by arc discharge. Refining including decarburization refining and adjustment of ingredients by charcoal. When the refining is completed, energization to the arc electrode 23 is stopped, and molten steel is discharged from the furnace body 21. As a result, the operation for one heat is completed, and such operation is repeated.

  On the other hand, in the present embodiment, four arc furnace units are installed, and the same operation as described above is performed in each steelmaking arc furnace 1, but the operation start timing of the four steelmaking arc furnaces 1 is usually shifted. It becomes.

  During such operations, high-temperature exhaust gas is discharged from each steelmaking arc furnace 1, and an exhaust duct 2, a front-side water-cooled duct 4, a combustion tower 3, and a rear-stage water-cooling constituting the first exhaust gas flow path. While passing through the duct 4, waste heat (sensible heat and combustion heat) is recovered by the waste heat boiler 6. Specifically, the waste heat of the exhaust gas is converted into saturated steam in a heat transfer pipe 7 that constitutes the waste heat boiler 6, and this saturated steam passes through the steam drum 13, the saturated steam transfer pipe 17, and the steam collecting pipe 61, and then is a steam accumulator 62. It is stored in. The saturated steam stored in the steam accumulator is supplied to the steam superheater 43, where it is heated by the high-temperature exhaust gas and converted into superheated steam. The converted superheated steam is supplied to the power generation steam turbine 63 for power generation.

  On the other hand, the exhaust gas after the waste heat is recovered reaches the steam superheater 43 through the duct 5, the exhaust gas collecting duct 41, and the downstream exhaust gas duct 42 constituting the second exhaust gas flow path, and is saturated in the steam superheater 43. It is used for steam heating.

  The surroundings of the steelmaking arc furnace 1 and / or the inside of the steelmaking factory (not shown) are ventilated through the ventilation hood 11 and the ventilation duct 12, and the cold air from the ventilation duct 12 reaches the ventilation collective duct 51. Further, the exhaust gas after being used for heating the saturated steam reaches the ventilation collective duct 51 through the downstream exhaust gas duct 42 and is supplied to the dust collecting duct 52 while being mixed with the cold air supplied from the ventilation duct 12. The dust is collected by the dust collector 54 and discharged from the chimney 56. In this way, the exhaust gas dust collecting duct 52 is supplied with the exhaust gas having a lowered temperature by combining the hot exhaust gas in the downstream exhaust gas duct 42 and the cold air for ventilation in the ventilation collective duct 51, and is supplied from the bag filter. It becomes possible to make the temperature of the exhaust gas flowing through the dust collector 54 to be equal to or lower than the heat resistant temperature of the dust collector 54. Further, by providing the cooler 53 in the exhaust gas dust collection duct 52 upstream of the dust collector 54 as described above, it becomes easier to set the exhaust gas temperature below the heat resistance temperature of the dust collector 54.

  Here, in one steelmaking arc furnace 1, as described above, a series of processes of raw material charging-melting (-raw material additional charging-melting-refining) -tapping steel is performed as one heat. The exhaust gas temperature fluctuates greatly during this 1-heat period. FIG. 4 shows the temperature change at the entrance of the combustion tower in a steelmaking arc furnace in which one heat is 70 minutes. As shown in this figure, the temperature of the exhaust gas rises and reaches around 1400 ° C. after the start of energization, and once decreases to about 400 ° C. due to the additional charging of the raw material, but again to about 1200 ° C. as the melting of the raw material proceeds. It rises, and after the raw material has completely melted (dissolved), the period during which the exhaust gas temperature is high (high temperature period) continues until the subsequent refining period. On the other hand, the exhaust gas temperature decreases with the steel output after the end of the refining period, and becomes 200 ° C. or less after the steel output is completed. And it becomes a period (low temperature period) when the exhaust gas temperature is low at 200 ° C. or less from the completion of the steel output to the start of energization of the next heat through the charging of the next heat. As the temperature of the exhaust gas changes, the amount of saturated steam recovered using the sensible heat and combustion heat of the exhaust gas changes.

  However, in the present embodiment, the steelmaking arc furnace facility 100 has four steelmaking arc furnaces 1, which are in a state in which the normal operation start timing is shifted by a predetermined time. As a result, the high temperature period and the low temperature period of the four steelmaking arc furnaces 1 are shifted from each other, and the saturated steam collected in the four steelmaking arc furnaces 1 is merged by the steam accumulator 62. The amount of saturated steam will be leveled. At this time, by controlling the operation timing of each arc furnace 1 for steelmaking, the distribution of the saturated steam amount after joining can be made desired.

  Further, in this embodiment, when the saturated steam is changed to superheated steam, heating energy can be supplied to the steam superheater 43 using the exhaust gas after waste heat recovery. Fuel is unnecessary and energy economy is high.

  By the way, when the exhaust gas after the waste heat is recovered is used as a heat source for generating superheated steam, it is necessary to secure a heat quantity for generating superheated steam having a predetermined superheat degree. It is necessary to prevent the temperature of the exhaust gas supplied to the superheater 43 from decreasing as much as possible. However, low temperature exhaust gas may be discharged in the steelmaking arc furnace 1. For example, in the arc furnace 1 for steelmaking, low temperature exhaust gas is discharged immediately after energization, immediately after raw material addition, and after steel output. If this low temperature exhaust gas is mixed with the high temperature exhaust gas of another steelmaking arc furnace in operation, the gas temperature after mixing will decrease. When the exhaust gas temperature is lowered, there is a disadvantage that the amount of heat for generating superheated steam having a predetermined superheat degree is insufficient. As a result, the superheated steam flow rate and / or the degree of steam superheat decreases, the output of the quantity steam turbine decreases, and even after the superheated steam flow rate and / or steam superheat degree recovers, it takes a long time to recover to the steady output. Power generation will be reduced. For example, as shown in FIG. 5, when the output is 23 MW, it takes about 15 minutes to recover the steady state even if the superheated steam flow rate and / or the steam superheat degree is reduced by about 6 MW, and it is reduced by about 20 MW. In some cases it takes nearly 40 minutes.

  Therefore, in the present embodiment, the connection pipe 18 connected to the ventilation duct 12 is provided in the duct 5 on the downstream side of the waste heat boiler 6, and the exhaust gas flow path for supplying exhaust gas after waste heat recovery to the steam superheater 43 side is provided. Dampers 31 and 32 are provided as switching means for switching between the exhaust gas passage not passing through the steam superheater 43. And in the period (high temperature period) in which high temperature exhaust gas is discharged from the steelmaking arc furnace 1, the damper 31 is opened and the damper 32 is closed as shown in FIG. To be supplied to the vessel 43. On the other hand, during a period when low temperature exhaust gas is discharged (low temperature period) such as when the operation of the steelmaking arc furnace 1 is stopped, the damper 31 is closed as shown in FIG. The exhaust gas from the steelmaking arc furnace 1 is led to the ventilation damper 12 so that the exhaust gas from the steelmaking arc furnace 1 is not supplied to the steam superheater 43. Thereby, it can prevent that the temperature of the exhaust gas for superheated steam generation falls, and can generate the superheated steam of the predetermined superheat degree stably.

  In this case, an exhaust gas temperature profile for one heat is obtained in advance, and when the exhaust gas temperature is lower than a predetermined temperature, the exhaust gas is not supplied to the steam superheater 43.

  From the viewpoint of more stably generating superheated steam, as shown in FIG. 6, a thermometer 81 is installed at the outlet of the waste heat boiler 6 of each arc furnace unit, and the temperature of the thermometer 81 is higher than a predetermined temperature. When the temperature becomes low, the dampers 31 and 32 of the corresponding steelmaking arc furnace 1 may be operated so that the exhaust gas is not supplied to the steam superheater 43. In this case, a controller 82 is provided as shown in FIG. 6, and the signal of the thermometer 81 is output to the controller 82, and the controller 82 automatically operates the dampers 31 and 32 based on the signal. It is preferable to do. In addition to the thermometer 81, a thermometer 83 may be provided at the inlet of the steam superheater 43 as shown in FIG. In this case, when the thermometer 83 becomes lower than the predetermined temperature, the exhaust gas does not flow into the steam superheater 43 for each of the arc furnace units whose temperature is lower than the predetermined temperature. The dampers 31 and 32 are operated as described above. At this time, it is preferable to perform such an operation under the control of the controller 82. Furthermore, as shown in FIG. 8, only the thermometer 83 is provided, and when the temperature becomes lower than a predetermined temperature, the operating state of the four steelmaking arc furnaces 1 is grasped, and is in a low temperature period. For the arc furnace unit corresponding to the steelmaking arc furnace 1, the dampers 31 and 32 may be operated so that the exhaust gas does not flow to the steam superheater 43. At this time, the controller 82 gives a command to operate the dampers 31 and 32 to the arc furnace unit corresponding to the steelmaking arc furnace 1 in the low temperature period based on information from the monitoring / operation / control unit 70. Is preferred.

Next, the range of the waste heat boiler 6 will be described.
When the exhaust gas after the recovery of sensible heat and combustion heat is used as a heat source for the generation of superheated steam, the amount of heat generated is the amount of generated saturated steam and the degree of superheat, and the pipe line from the waste heat boiler 6 to the steam superheater 43. Determined by heat dissipation. Now, when trying to obtain 350 ° C superheated steam from 215 ° C saturated steam, assuming that the heat quantity at the inlet of the waste heat boiler 6 is 100%, the endothermic amount in the waste heat boiler 6 is 50 to 55%. The amount of heat necessary to superheat the generated steam is 5 to 10%. Further, when heat dissipation from the pipe line is taken into account, the range of the waste heat boiler 6 is such that the exhaust gas temperature at the outlet of the waste heat boiler 6 is 500 ° C. or higher.

On the other hand, the waste heat boiler 6 of the arc furnace for steel making is mainly subjected to heat exchange by radiant heat transfer, and the heat exchange amount by radiant heat transfer can be determined by the following (1).
Q = CA [(Tg / 100) ⁴ − (Tw / 100) ⁴ ] (1)
Q: Radiation heat transfer amount Tg: Gas temperature Tw: Water-cooled wall tube surface temperature A: Effective radiation heat transfer area C: Effective radiation coefficient

  Actual radiant heat transfer is a complicated phenomenon, but assuming that there is no change in the effective radiant coefficient, when trying to obtain the same amount of heat absorbed when the gas temperature is 1000 ° C., the exhaust gas temperature However, an effective radiant heat transfer area of approximately 2.5 times is required at 800 ° C and approximately 8 times greater at an exhaust gas temperature of 600 ° C. The amount of recovered steam is small compared to the rate of increase in the heat area, which is not economical. From this and the above-described heat balance, the range in which the waste heat boiler 6 is installed is preferably an exhaust gas temperature of 600 ° C. or higher, more preferably 700 ° C. or higher.

Next, another embodiment of the present invention will be described.
Here, as shown in FIG. 9, in addition to the equipment of FIG. 1, a heat storage body 75 is further provided in the upstream side portion of the steam superheater 43 of the downstream exhaust gas duct 42, and the exhaust gas flows through the heat storage body 75. I am doing so. As the heat storage body 75, a block body having a large heat capacity such as a checker brick can be used. Furthermore, it is more preferable to use a checker with a special shape that can store more heat in a heat storage chamber having a large heat transfer area and the same capacity. As described above, by operating the dampers 31 and 32 so that the low temperature exhaust gas is not supplied to the steam superheater 43, it is possible to prevent the temperature of the exhaust gas supplied to the steam superheater 43 from being lowered as much as possible. Some exhaust gas temperature fluctuations still occur. However, the heat storage body 75 can store a large amount of heat with the high-temperature exhaust gas, and even when there is a temperature fluctuation of the exhaust gas, when the exhaust gas passes through the heat storage body 75, heat is supplied from the heat storage body 75 to the exhaust gas. Variations in the temperature of the exhaust gas supplied to the steam superheater 43 can be mitigated. Thereby, the temperature fluctuation | variation of waste gas can be made still smaller, and the temperature of the steam of the steam superheater 43 can be made more uniform.

Next, still another embodiment of the present invention will be described.
Here, as shown in FIG. 10, a saturated steam flow rate control valve 91 is provided at the inlet of the steam superheater 43, a superheated steam thermometer 92 and a superheated steam flow meter 93 are provided at the outlet of the steam superheater 43, and the superheated steam temperature is increased. A controller 94 is provided for controlling the saturated steam flow to be supplied by controlling the saturated steam flow control valve 91 in accordance with the signal from the meter 92. Accordingly, the saturated steam flow rate control valve 91 can be controlled so as to control the saturated steam flow rate so that the amount of superheated steam according to the superheated steam temperature can be obtained, so that the superheat degree of the superheated steam can be made constant. . Instead of providing the superheated steam flow meter 93, the controller 93 sets the relationship between the opening degree of the saturated steam flow control valve 91 and the saturated steam amount obtained in advance, and the saturated steam flow according to the superheated steam temperature. The opening degree of the saturated steam flow control valve 91 may be controlled so that

Next, another embodiment of the present invention will be described.
Here, as shown in FIG. 11, an exhaust gas thermometer 83 is provided at the inlet of the steam superheater 43, a saturated steam flow meter 97 is provided at the inlet of the steam superheater 43, and a controller 98 for controlling the exhaust gas flow rate is provided. Then, a signal from the exhaust gas thermometer 83 and the saturated steam flow meter 97 and a signal from the exhaust gas flow meter 47 provided in the downstream exhaust gas duct are input to the controller 98. The opening degree of the dampers 31 and 32 is controlled in accordance with a signal from the saturated steam flow meter 97. Thereby, the exhaust gas flow rate flowing into the steam superheater 43 can be controlled according to the saturated steam flow rate.

  Exhaust gas from steelmaking arc furnaces is mainly composed of nitrogen, oxygen, and carbon dioxide, and there are few fluctuations due to operation, and there is little fluctuation in specific heat due to fluctuations in gas components, so if the relationship between gas temperature and specific heat is measured in advance The amount of thermal energy possessed by the exhaust gas can be ascertained only by measuring the flow rate and the exhaust gas temperature. Therefore, by measuring the exhaust gas flow rate and the exhaust gas temperature, the heat energy required for generating the superheated steam flows into the steam superheater 43 from the saturated steam amount vented to the steam superheater 43 and the required superheat degree. The amount of exhaust gas to be controlled can be controlled. For this reason, it is possible to generate superheated steam having a substantially constant superheat degree, and it is possible to drive the steam turbine power generation turbine 63 with extremely high efficiency. At this time, by providing a thermometer at the outlet of the waste heat boiler 6 of each arc furnace unit, the temperature of the exhaust gas whose flow rate is controlled can be accurately grasped, so that the accuracy can be further improved. In addition, by controlling the thermal energy of the exhaust gas for superheating the saturated steam in this way, excessive heating of the superheated steam or burning of the dust collector after the exhaust gas becomes too hot and passes through the steam superheater 43 Inconvenience such as doing can be prevented.

  In addition, this invention is not limited to the said embodiment, A various deformation | transformation is possible. For example, in the above example, an example using four steelmaking arc furnaces is shown, but the number of steelmaking arc furnaces may be any number as long as it is two or more. Moreover, although shown about the case where saturated steam is utilized for electric power generation, it does not restrict to this. Furthermore, in the above-described embodiment, the case where the exhaust gas is burned in the combustion tower and the sensible heat and combustion heat of the exhaust gas are recovered as waste heat is shown. However, the combustion tower is not necessarily required, and the waste heat without the combustion tower is used. It is also possible to burn in the boiler. In addition, if only steel scrap generated in the steel works is dissolved, there is no generation of white smoke or offensive odor, and the amount of carbon monoxide generated is small, so there is no need to actively suck in combustion air. Heat recovery from higher temperature exhaust gas becomes possible. In this case, the waste heat recovered from the exhaust gas is substantially only sensible heat.

DESCRIPTION OF SYMBOLS 1; Steelmaking arc furnace 2; Exhaust duct 3; Combustion tower 4; Water cooling duct 5; Duct 6; Waste heat boiler 7; Heat transfer pipe 8; Air inlet 10a, 10b, 10c, 10d; Hood 12; Ventilation duct 13; Steam drum 17; Saturated steam transfer pipe 18; Connection pipe 21; Furnace body 23; Arc electrode 31, 32; Damper 41; Exhaust gas collecting duct 42; Downstream exhaust duct 43; Steam superheater 51; Ventilation collecting duct 52; exhaust gas dust collecting duct 54; dust collector 61; steam collecting pipe 62; steam accumulator 63; power generation turbine 70; monitoring / operation / control unit 75; heat storage body 81, 83; thermometer 82; 91; saturated steam flow control valve 92; heating steam thermometer 93; heating steam flow meter 94; controller 95; exhaust gas flow meter 96; exhaust gas thermometer 7; saturated vapor flow meter 98; controller 100; steel-making arc furnace facilities

Claims (14)

A waste heat recovery facility for a steelmaking arc furnace that recovers waste heat of exhaust gas discharged from a plurality of steelmaking arc furnaces as saturated steam and further heats the saturated steam to superheated steam,
A first exhaust gas flow path for discharging exhaust gas from each steelmaking arc furnace;
A waste heat boiler installed in the first exhaust gas flow path for recovering waste heat of exhaust gas as saturated steam;
A steam accumulator that combines and stores saturated steam generated in each waste heat boiler;
A steam superheater that heats the steam stored in the steam accumulator to form superheated steam;
A second exhaust gas flow path for discharging the exhaust gas after the waste heat has been recovered by the waste heat boiler to the steam superheater and heating the saturated steam;
A third exhaust gas flow path for discharging the exhaust gas after the waste heat is recovered by the waste heat boiler without passing through the steam superheater;
Waste heat recovery for a steelmaking arc furnace, comprising switching means for switching the exhaust gas flow path after the waste heat has been recovered between the second exhaust gas flow path and the third exhaust gas flow path Facility.   The waste heat recovery equipment for a steelmaking arc furnace according to claim 1, wherein the waste heat of the exhaust gas is sensible heat of the exhaust gas, or sensible heat and combustion heat of the exhaust gas.   The first exhaust gas flow path has an exhaust gas duct and a combustion tower for combusting exhaust gas, and the waste heat boiler is provided to constitute the exhaust gas duct and / or the combustion tower. The waste heat recovery equipment for an arc furnace for steel making according to claim 1 or 2.   The waste heat recovery of the arc furnace for steel making according to any one of claims 1 to 3, wherein the waste heat boiler is provided in a range where the temperature of the exhaust gas at the outlet thereof is 600 ° C or higher. Facility.   A gas thermometer provided at the outlet of the waste heat boiler and / or the inlet of the steam superheater is further provided, and the exhaust gas temperature at the outlet of the waste heat boiler and / or the exhaust gas temperature at the inlet of the steam superheater is previously set. If the temperature is equal to or higher than a predetermined temperature, the exhaust gas is allowed to flow through the second exhaust gas flow path, and the exhaust gas temperature at the outlet of the waste heat boiler and / or the exhaust gas temperature at the inlet of the steam superheater is more than a predetermined temperature. The arc furnace for steelmaking according to any one of claims 1 to 4, wherein the switching means is operated so that the exhaust gas flows into the third exhaust gas flow path when the exhaust gas is low. Waste heat recovery equipment.   The third exhaust gas flow path includes a ventilation duct for ventilating the surroundings of each steelmaking arc furnace and / or a steelmaking factory where the plurality of steelmaking arc furnaces are installed, and the second flow path. The waste heat of the arc furnace for steel making according to any one of claims 1 to 5, further comprising a connection pipe connecting the ventilation duct and a ventilation collecting duct in which the ventilation ducts are gathered. Recovery equipment.   The steelmaking according to claim 6, further comprising a dust collector that collects the exhaust gas from the second exhaust gas flow path, and a cooler that cools the exhaust gas before reaching the dust collector. Waste heat recovery equipment for electric arc furnaces.   A dust collector for collecting the exhaust gas from the second exhaust gas flow path; and the exhaust gas from the second exhaust gas flow path is mixed with the cold air of the ventilation collective duct, The waste heat recovery equipment for a steelmaking arc furnace according to claim 6, wherein   The second exhaust gas flow path includes an exhaust gas duct on the downstream side of each waste heat boiler, an exhaust gas assembly duct in which these exhaust gas ducts are aggregated, and a downstream side to which the steam superheater is connected. An exhaust gas duct, the downstream exhaust gas duct is connected to the ventilation collective duct, the exhaust gas collect duct connected to the dust collector is connected to the ventilation collective duct, and the exhaust gas duct from the downstream exhaust duct The waste heat recovery equipment for an arc furnace for steel making according to claim 8, wherein the exhaust gas is guided to the dust collector through the exhaust gas dust collection duct in a state where the cold air of the ventilation collective duct is mixed with the exhaust gas. .   The waste heat recovery facility for an arc furnace for steel making according to claim 8 or 9, further comprising a cooler for cooling the exhaust gas before reaching the dust collector.   The arc furnace for steel making according to any one of claims 1 to 10, further comprising a heat storage body provided on the upstream side of the steam superheater in the second exhaust gas flow path. Waste heat recovery equipment.   Depending on the temperature of the superheated steam, a saturated steam flow control valve that controls the flow rate of saturated steam that flows into the steam superheater, a superheated steam thermometer that detects the temperature of superheated steam discharged from the steam superheater, and the temperature of the superheated steam And a controller for controlling the amount of superheated steam by controlling the saturated steam flow control valve, and disposing of the arc furnace for steelmaking according to any one of claims 1 to 11. Heat recovery equipment.   An exhaust gas flow meter for detecting the flow rate of exhaust gas flowing into the steam superheater, an exhaust gas thermometer for detecting the temperature of exhaust gas flowing into the steam superheater, and a flow rate of saturated steam flowing into the steam superheater And a controller for controlling the flow rate of the exhaust gas by controlling the flow rate adjusting means according to the temperature of the exhaust gas and the flow rate of the saturated steam. The waste heat recovery facility for an arc furnace for steel making according to any one of claims 1 to 12, further comprising: Steel making comprising a plurality of steelmaking arc furnaces, and a waste heat recovery facility for recovering waste heat of exhaust gas discharged from the plurality of steelmaking arc furnaces as saturated steam, and further heating the saturated steam into superheated steam Arc furnace equipment for
An arc furnace facility for steel making comprising the waste heat recovery facility according to any one of claims 1 to 13 as the waste heat recovery facility.

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