JP2017206726A - Waste heat recovery apparatus and waste heat recovery method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a waste heat recovery apparatus capable of managing temperature of preheated combustion air while suppressing a decrease in an energy efficiency.SOLUTION: An apparatus for recovering a waste heat from a heating furnace for heating a steel material is provided that comprises: a heat exchanger for preheating a combustion air supplied to the heating furnace; a waste heat recovery boiler for recovering a sensible heat of a waste gas discharged from the heating furnace; a first waste gas flow path that connects the heating furnace and heat exchanger together; a second waste gas flow path that connects the heat exchanger and the waste heat recovery boiler together; a bypass flow path that bypasses the heat exchanger and connects the heating furnace and the waste heat recovery boiler together; a thermometer for measuring a temperature of the combustion air after passing through the heat exchanger; and a mechanism for adjusting a flow rate of the waste gas that is flowed to the bypass path such that a temperature measured by the thermometer is equal to or lower than a predetermined temperature. It is preferred that the apparatus for recovering a waste heat from a heating furnace further comprises a mechanism for adjusting a flow rate of the waste gas which is flowed to the first waste gas flow path based on measurement result of the thermometer.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an exhaust heat recovery apparatus and an exhaust heat recovery method.

  In a hot rolling factory or the like, hot rolling is performed after heating a steel material such as a slab or billet in a continuous or batch heating furnace. In a thick plate factory or the like, a steel material such as a thick plate is heated in a continuous or batch heat treatment furnace, and then heat treatment is performed. For example, when manufacturing a thick plate in a thick plate factory, a slab cast by a continuous casting machine is transported by a carriage or the like and temporarily stored in a stock yard in front of a heating furnace. During this storage, the temperature of the slag decreases to a maximum of room temperature (about 25 ° C.). For this reason, this slab is sequentially charged from a stock yard into a heating furnace according to a heat treatment schedule, heated to a temperature of about 1200 ° C., and then sent to a rolling mill for rolling.

  As such a heating furnace, a walking beam type conveying device for conveying the slab from the charging side to the extracting side is disposed, and the fuel gas is burned by a plurality of burners disposed above and below the path of the conveying device. A heating furnace that heats the slab is known. Combustion air is supplied to the burner by a combustion air blower, and fuel gas is combusted. The exhaust gas after the combustion of the fuel gas is sent from the furnace bottom, which is the charging end of the heating furnace, to the chimney through the furnace bottom flue and exhausted to the outside. Part of the sensible heat of the exhaust gas exhausted from this heating furnace is recovered by a heat exchanger such as a regenerative burner or a recuperator and used for preheating combustion air, but most is exhausted from the chimney. . Therefore, for example, the energy efficiency of a heating furnace with a recuperator is only about 50%.

  In order to improve the energy efficiency, a heat recovery system is proposed in which an exhaust heat recovery boiler is installed and exhaust gas that has passed through a heat exchanger is sent to the exhaust heat recovery boiler (Japanese Patent Laid-Open No. 4). No.-311533 and JP2012-242029). This conventional heat recovery system improves energy efficiency by recovering sensible heat as steam from exhaust gas used for preheating combustion air in a heating furnace.

  By the way, when the temperature of the exhaust gas from the heating furnace is high, the temperature of the combustion air after preheating exceeds, for example, the heat resistance upper limit temperature of the combustion air flow rate adjustment valve that supplies this combustion air to the burner, May cause damage. For this reason, the management which makes the temperature of the combustion air after preheating below the said heat-resistant upper limit temperature is required. As such a management method, a method of cooling the exhaust gas flowing into the heat exchanger has been proposed (see Japanese Patent Application Laid-Open No. 2002-81641). In this method, by controlling the temperature of the exhaust gas supplied to the heat exchanger, the temperature of the combustion air after preheating is controlled to be equal to or lower than the heat resistant upper limit temperature.

  However, in the above conventional heat recovery system, sensible heat is recovered from the exhaust gas used for preheating the combustion air of the heating furnace. Therefore, when the above management is performed, the exhaust gas supplied to the exhaust heat recovery boiler The temperature of the also decreases. For this reason, when the temperature management of the conventional combustion air is performed using the conventional heat recovery system, the heat recovery rate of the exhaust heat recovery boiler is decreased, and the energy efficiency is decreased.

Japanese Patent Laid-Open No. 4-31533 JP 2012-242029 A JP 2002-81641 A

  The present invention has been made based on the above circumstances, and provides an exhaust heat recovery apparatus and an exhaust heat recovery method capable of managing the temperature of combustion air after preheating while suppressing a decrease in energy efficiency. Objective.

  The invention made to solve the above-mentioned problems is an apparatus for recovering exhaust heat from a heating furnace for heating a steel material, a heat exchanger for preheating combustion air supplied to the heating furnace, and the heating furnace An exhaust heat recovery boiler that recovers sensible heat of the exhaust gas discharged from the exhaust gas, a first exhaust gas passage that connects the heating furnace and the heat exchanger, and a second exhaust gas that connects the heat exchanger and the exhaust heat recovery boiler. An exhaust gas channel, a bypass channel that bypasses the heat exchanger and connects the heating furnace and the exhaust heat recovery boiler, and a thermometer that measures the temperature of the combustion air after passing through the heat exchanger; And a mechanism for adjusting the flow rate of the exhaust gas flowing through the bypass flow path so that the temperature measured by the thermometer is equal to or lower than a predetermined temperature.

  The exhaust heat recovery apparatus includes a bypass flow path that bypasses the heat exchanger. In addition, the exhaust heat recovery apparatus includes a mechanism that adjusts the flow rate of the exhaust gas flowing through the bypass flow path based on the measurement result of a thermometer that measures the temperature of the combustion air after passing through the heat exchanger. The exhaust heat recovery apparatus can manage the temperature of the combustion air after preheating by suppressing the flow rate of the exhaust gas supplied to the combustion air by this adjustment mechanism. As a method of managing the temperature of the combustion air after preheating, a method of managing by controlling the flow rate of the preheated air to be larger than the amount of air actually used for the combustion air is also conceivable. However, in this method, air that has not been used as combustion air is dissipated, so that the preheating energy of the dissipated air is wasted. On the other hand, the exhaust heat recovery apparatus supplies the exhaust gas and combustion air in an amount required for preheating to the heat exchanger, so that waste of preheating energy is small. Moreover, since the exhaust heat recovery apparatus supplies exhaust gas that is not used for preheating to the exhaust heat recovery boiler via the bypass channel, the temperature of the exhaust gas is unlikely to decrease. For this reason, the said exhaust heat recovery apparatus can suppress the fall of the heat recovery efficiency of an exhaust heat recovery boiler. Therefore, the exhaust heat recovery apparatus can manage the temperature of the combustion air after preheating while suppressing a decrease in energy efficiency.

  A mechanism for adjusting the flow rate of the exhaust gas flowing into the first exhaust gas flow path may be further provided based on the measurement result of the thermometer. Thus, by further providing a mechanism for adjusting the flow rate of the exhaust gas flowing through the first exhaust gas passage, the flow rate of the exhaust gas supplied to the heat exchanger can be accurately adjusted. Therefore, the energy efficiency of the heating furnace is further increased.

  A thermometer that measures the temperature of the combustion air before passing through the heat exchanger, a thermometer that measures the exhaust gas temperature before passing through the heat exchanger, and a flow rate of combustion air that is preheated by the heat exchanger And a flow meter for measuring the flow rate of the exhaust gas passing through the heat exchanger. By providing the measuring device as described above, the heat recovery rate of the heat exchanger can be predicted, and the adjustment accuracy of the flow rate of the exhaust gas flowing into the bypass channel is improved.

  A thermometer for measuring the exhaust gas temperature after passing through the heat exchanger may be further provided. By providing the thermometer in this way, the accuracy of predicting the heat recovery rate of the heat exchanger is further increased, and the accuracy of adjusting the flow rate flowing to the bypass channel is further improved.

  Another invention made to solve the above problems is a method for recovering exhaust heat from a heating furnace for heating a steel material, the heat exchanger preheating combustion air supplied to the heating furnace, and the above An exhaust heat recovery boiler that recovers sensible heat of the exhaust gas discharged from the heating furnace, a first exhaust gas passage that connects the heating furnace and the heat exchanger, and the heat exchanger and the exhaust heat recovery boiler are connected. The combustion after passing through the heat exchanger, using a waste heat recovery device comprising a second exhaust gas flow path and a bypass flow path that bypasses the heat exchanger and connects the heating furnace and the exhaust heat recovery boiler A step of measuring the temperature of the working air, and a step of adjusting the flow rate of the exhaust gas flowing through the bypass flow path so that the measured temperature becomes a predetermined temperature or less.

  In the exhaust heat recovery method, the temperature of the combustion air after preheating can be managed by adjusting the flow rate of the exhaust gas flowing to the bypass flow path using the exhaust heat recovery device. Further, in the exhaust heat recovery method, the temperature of the exhaust gas supplied to the exhaust heat recovery boiler via the bypass channel is unlikely to decrease. Therefore, the exhaust heat recovery method can manage the temperature of the combustion air after preheating while suppressing a decrease in energy efficiency.

  As described above, the exhaust heat recovery apparatus of the present invention and the exhaust heat recovery method of the present invention can manage the temperature of the combustion air after preheating while suppressing a decrease in energy efficiency.

It is a schematic diagram which shows the heating apparatus of one Embodiment of this invention. It is a flowchart which shows the waste heat recovery method of one Embodiment of this invention. It is a flowchart which shows the step of the waste gas flow rate adjustment process of FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.

  The heating apparatus shown in FIG. 1 mainly includes a heating furnace 100 and an exhaust heat recovery apparatus 1 according to an embodiment of the present invention.

<Heating furnace>
The heating furnace 100 heats the steel material charged into the charging port of the heating furnace main body 102 by the transfer device 101 to a predetermined temperature, and extracts the steel material from the extraction port of the heating furnace main body 102. Specifically, the heating furnace main body 102 mixes fuel gas supplied from a fuel gas flow path (not shown) with combustion air supplied from the combustion air flow path 103 and burns it with a burner. The steel is heated using gas.

  A known heating furnace can be used as the heating furnace 100. As a known heating furnace, for example, a walking beam type conveying device 101 is provided, and a heating furnace that heats a steel material while the steel material moves from the loading side end of the heating furnace main body 102 to the extraction side end is exemplified. be able to. In the heating furnace 100, the fuel gas is burned by a plurality of burners disposed above and below the steel material, and the temperature of the steel material is controlled in the pre-tropics, the heating zone, and the soaking zone in order from the charging side. Specifically, the heating furnace 100 is relatively high so as to reach a target temperature in the heating zone after heating the steel material at a relatively low temperature increase rate in the pretropical zone so that distortion is not caused by rapid heating. The steel material is heated at a rate of temperature rise, and the steel material is heated gently so as to eliminate temperature unevenness in the soaking zone.

  The combustion air flow path 103 is branched into three so that combustion air can be supplied independently to the pre-tropical zone, the heating zone, and the soaking zone. Further, combustion air flow rate adjustment valves 104 are disposed in the three flow paths downstream of the branch. With this combustion air flow rate adjustment valve 104, the heating furnace 100 can control the heating of the steel material by adjusting the flow rate of the combustion air supplied to the burner for each of the pretropical zone, the heating zone, and the soaking zone.

  Although it does not specifically limit as temperature after heating a steel material, For example, it can be set as 1100 degreeC or more and 1300 degrees C or less. The fuel gas is not particularly limited, and for example, coke oven gas (C gas), mixed gas of coke oven gas and blast furnace gas (M gas), or the like can be used.

The heating furnace 100 discharges the combustion gas after being used for heating the steel material, that is, the exhaust gas. The exhaust port for exhaust gas from the heating furnace 100 is preferably disposed on the loading side of the heating furnace body 102. By disposing the discharge port on the loading side, the direction in which the combustion gas flows and the conveying direction of the steel material are opposed to each other, so that the steel material can be efficiently heated. The temperature of the exhaust gas is determined by the combustion conditions of the fuel gas, and is, for example, 500 ° C. or higher and 900 ° C. or lower. Further, the flow rate of the exhaust gas is determined by the combustion condition of the fuel gas, but is, for example, 10000 Nm ³ / h or more and 50000 Nm ³ / h or less.

  The amount (flow rate) of the steel material heated in the heating furnace 100 is determined depending on the operation conditions and the like, but can be, for example, 100 t / h or more and 250 t / h or less.

<Exhaust heat recovery device>
The exhaust heat recovery apparatus 1 is attached to the heating furnace 100 and used. The exhaust heat recovery apparatus 1 mainly includes a heat exchanger 11, an exhaust heat recovery boiler 12, and a chimney 13. The exhaust heat recovery apparatus 1 includes a first exhaust gas flow path 14a that connects the heating furnace 100 and the heat exchanger 11, and a second exhaust gas flow that connects the heat exchanger 11 and the exhaust heat recovery boiler 12. A path 14b and a bypass channel 15 that bypasses the heat exchanger 11 and connects the heating furnace 100 and the exhaust heat recovery boiler 12 are provided.

  Further, the exhaust heat recovery apparatus 1 includes an exhaust gas flow rate adjustment valve 16 disposed in the second exhaust gas flow path 14b. In addition, the exhaust heat recovery apparatus 1 includes a bypass flow rate adjustment valve 17 disposed in the bypass flow path 15. The exhaust gas flow rate adjustment valve 16 and the bypass flow rate adjustment valve 17 constitute a mechanism for adjusting the flow rate of the exhaust gas.

  The exhaust heat recovery apparatus 1 includes a thermometer 18 a between the heat exchanger 11 and the heating furnace main body 102 of the combustion air flow path 103. The thermometer 18a measures the temperature T1 of the combustion air after passing through the heat exchanger 11. The arrangement position of the thermometer 18a is preferably on the upstream side of the combustion air flow rate adjustment valve 104 from the viewpoint of the accuracy of adjusting the exhaust gas flow rate.

  Further, the exhaust heat recovery apparatus 1 includes a thermometer 18 b on the upstream side of the heat exchanger 11 in the combustion air flow path 103. The thermometer 18b measures the temperature T2 of the combustion air before passing through the heat exchanger 11. The arrangement position of the thermometer 18b is not particularly limited, but may be close to the combustion air intake of the heat exchanger 11 from the viewpoint of the accuracy of adjusting the exhaust gas flow rate.

  Further, the exhaust heat recovery apparatus 1 includes a thermometer 18c in the first exhaust gas flow path 14a. The thermometer 18c measures the exhaust gas temperature T3 before passing through the heat exchanger 11. The arrangement position of the thermometer 18c is not particularly limited, but may be close to the exhaust gas intake port of the heat exchanger 11 from the viewpoint of the accuracy of adjusting the exhaust gas flow rate.

  Further, the exhaust heat recovery apparatus 1 includes a thermometer 18d in the second exhaust gas flow path 14b. This thermometer 18d measures the exhaust gas temperature T4 after passing through the heat exchanger 11. The disposition position of the thermometer 18d is upstream of the position where the bypass flow path 15 joins the second exhaust gas flow path 14b in order to avoid the influence of the exhaust gas flowing through the bypass flow path 15.

  In addition, the exhaust heat recovery apparatus 1 includes a flow meter 19a that measures the flow rate Q1 of the combustion air preheated by the heat exchanger 11. The arrangement position of the flow meter 19 a is in the middle of the combustion air flow path 103. The arrangement position of the flow meter 19a can be upstream of the heat exchanger 11 in the combustion air flow path 103, or can be downstream of the heat exchanger 11 in the combustion air flow path 103. . In FIG. 1, the flow meter 19 a is disposed upstream of the heat exchanger 11 in the combustion air flow path 103.

  The exhaust heat recovery apparatus 1 also includes a flow meter 19b that measures the flow rate Q2 of the exhaust gas that passes through the heat exchanger 11. The arrangement position of the flow meter 19b is in the middle of the first exhaust gas passage 14a or in the second exhaust gas passage 14b. The flow meter 19b is disposed at a position downstream of the position where the bypass flow path 15 branches from the first exhaust gas flow path 14a in order to avoid the influence of the exhaust gas flowing through the bypass flow path 15, and the bypass flow It is upstream from the position where the passage 15 joins the second exhaust gas passage 14b. In FIG. 1, the flow meter 19b is disposed in the middle of the second exhaust gas passage 14b.

  Further, the exhaust heat recovery apparatus 1 includes a control mechanism 20 that adjusts the open / close amounts of the exhaust gas flow rate adjustment valve 16 and the bypass flow rate adjustment valve 17 based on the measurement result of the measuring instrument.

(Heat exchanger)
The heat exchanger 11 is disposed in the middle of the combustion air flow path 103 and preheats the combustion air supplied to the burner of the heating furnace 100. Specifically, the heat exchanger 11 includes the exhaust gas supplied from the heating furnace 100 to the heat exchanger 11 via the first exhaust gas passage 14 a and the combustion air passage 103. The combustion air is preheated by exchanging heat with the combustion air supplied to the heat exchanger 11.

  The heat exchanger 11 is not particularly limited as long as the combustion air can be preheated. For example, a known recuperator or regenerative burner can be used.

  As a minimum of the temperature of the combustion air after preheating in heat exchanger 11, 150 ° C is preferred and 200 ° C is more preferred. On the other hand, the upper limit of the temperature of the combustion air after preheating in the heat exchanger 11 is preferably 700 ° C, more preferably 600 ° C. If the temperature of the combustion air after preheating in the heat exchanger 11 is less than the lower limit, the heat recovery rate in the heat exchanger 11 is low, and the energy efficiency may be reduced. Conversely, if the temperature of the combustion air after preheating in the heat exchanger 11 exceeds the upper limit, the combustion air flow rate adjusting valve 104 or the like through which the combustion air passes may be deteriorated or damaged by heat. is there.

(Exhaust heat recovery boiler)
The exhaust heat recovery boiler 12 is used for preheating in the heat exchanger 11 and supplies exhaust gas supplied via the second exhaust gas passage 14b and exhaust gas supplied from the heating furnace 100 via the bypass passage 15. Recover sensible heat.

  The exhaust heat recovery boiler 12 may be a known exhaust heat recovery boiler that produces saturated steam (steam) using the thermal energy of the supplied exhaust gas.

(chimney)
The chimney 13 is located downstream of the exhaust heat recovery boiler 12 and is connected to the exhaust heat recovery boiler 12 by a flue 21. The exhaust gas used in the exhaust heat recovery boiler 12 passes through the flue 21 and is discharged from the chimney 13 to the outside.

(Exhaust gas flow path)
The first exhaust gas channel 14a is a channel for supplying the exhaust gas discharged from the heating furnace 100 to the heat exchanger 11 as a preheating gas. The second exhaust gas flow path 14 b is a flow path for supplying the exhaust gas that has passed through the heat exchanger 11 to the exhaust heat recovery boiler 12.

(Bypass channel)
The bypass flow path 15 is branched from the upstream side of the heat exchanger 11 of the first exhaust gas flow path 14a. The bypass flow path 15 bypasses the heat exchanger 11 and joins the second exhaust gas flow path 14b on the downstream side of the heat exchanger 11 and the upstream side of the exhaust heat recovery boiler 12.
The exhaust heat recovery apparatus 1 can bypass the heat exchanger 11 and supply the exhaust gas discharged from the heating furnace 100 to the exhaust heat recovery boiler 12 by the bypass flow path 15.

(Flow control valve)
The exhaust gas flow rate adjustment valve 16 mainly adjusts the flow rate of exhaust gas supplied to the heat exchanger 11. Further, the bypass flow rate adjusting valve 17 adjusts the flow rate of exhaust gas flowing through the bypass flow path 15, that is, the flow rate of exhaust gas not supplied to the heat exchanger 11. By adjusting the opening / closing amounts of the exhaust gas flow rate adjustment valve 16 and the bypass flow rate adjustment valve 17, the exhaust heat recovery device 1 can control the exhaust gas flow rate supplied to the heat exchanger 11 and the exhaust gas flow rate flowing to the bypass flow path 15. Can be adjusted with high accuracy. The opening / closing amount is adjusted by a control mechanism 20 described later.

  The exhaust gas flow rate adjustment valve 16 and the bypass flow rate adjustment valve 17 are not particularly limited. For example, a known damper or the like can be used.

  The exhaust gas flow rate adjusting valve 16 is disposed on the upstream side of the position where the bypass flow channel 15 joins the second exhaust gas flow channel 14b.

  Further, the bypass flow rate adjustment valve 17 may be capable of blocking the exhaust gas supplied to the bypass flow path 15. The exhaust heat recovery apparatus 1 can supply the exhaust gas to the heat exchanger 11 by shutting off the exhaust gas supplied to the bypass flow path 15 by the bypass flow rate adjusting valve 17 in this way. For this reason, if there is no possibility of causing deterioration or breakage of the combustion air flow rate adjustment valve 104 even if the entire amount of exhaust gas is supplied to the heat exchanger 11, energy efficiency is obtained by supplying the entire amount of exhaust gas to the heat exchanger 11. Can be enhanced.

(Measuring instrument)
The exhaust heat recovery apparatus 1 uses the above-described thermometer and flow meter to measure the temperature T1 of the combustion air after passing through the heat exchanger 11, and the temperature T2 of the combustion air before passing through the heat exchanger 11. The exhaust gas temperature T3 before passing through the heat exchanger 11, the exhaust gas temperature T4 after passing through the heat exchanger 11, the flow rate Q1 of combustion air preheated in the heat exchanger 11, and the exhaust gas passing through the heat exchanger 11 Can be measured. The measurement result of the measuring device is sent to the control mechanism 20 described later.

  As said thermometer, a well-known radiation thermometer etc. can be used, for example. Moreover, as said flow meter, a well-known electromagnetic flow meter etc. can be used, for example.

<Control mechanism>
The control mechanism 20 uses the exhaust gas flow rate adjustment mechanism, that is, the exhaust gas flow rate adjustment valve 16 and the bypass flow rate adjustment valve 17, based on the measurement result of the measuring device, to control the combustion air after passing through the heat exchanger 11. The flow rate of the exhaust gas flowing to the bypass flow path 15 is adjusted so that the temperature is equal to or lower than a predetermined temperature. Specifically, when the temperature T1 of the combustion air after passing through the heat exchanger 11 exceeds a predetermined temperature, the control mechanism 20 controls the opening / closing amounts of the exhaust gas flow rate adjustment valve 16 and the bypass flow rate adjustment valve 17. adjust.

  The predetermined temperature is appropriately determined according to the heat-resistant upper limit temperature of the portion of the combustion air flow path 103 through which the preheated combustion air passes. The predetermined temperature can be, for example, the heat-resistant upper limit temperature of the combustion air flow rate adjustment valve 104, and can be 500 ° C. or more and 700 ° C. or less.

  In addition, the temperature of the combustion air after preheating is preferably lower than the predetermined temperature from the viewpoint of energy efficiency of the heating furnace 100 and higher. That is, it is preferable to adjust the flow rate of exhaust gas flowing through the bypass passage 15 so that the temperature of the combustion air after preheating becomes the predetermined temperature. Here, “becomes a predetermined temperature” is a concept including not only strictly a predetermined temperature but also the vicinity of the predetermined temperature, for example, a temperature within 10 ° C. of the difference from the predetermined temperature.

<Exhaust heat recovery method>
The exhaust heat recovery method recovers exhaust heat from the heating furnace 100 using the exhaust heat recovery apparatus 1 shown in FIG. As shown in FIG. 2, the exhaust heat recovery method includes a measurement step (S1) and an exhaust gas flow rate adjustment step (S2).

(Measurement process)
In the measurement step S1, the temperature of combustion air, the temperature of exhaust gas, and the flow rate of exhaust gas are measured by the above-described four thermometers and two flow meters. Specifically, in the measurement step S1, the following four temperatures and two flow rates are measured. In addition, the following six measurement results are sent to the control mechanism 20.
(1) Temperature T1 of the combustion air after passing through the heat exchanger 11
(2) Temperature T2 of the combustion air before passing through the heat exchanger 11
(3) Exhaust gas temperature T3 before passing through the heat exchanger 11
(4) Exhaust gas temperature T4 after passing through the heat exchanger 11
(5) Flow rate Q1 of combustion air preheated by the heat exchanger 11
(6) Flow rate Q2 of exhaust gas passing through the heat exchanger 11

(Exhaust gas flow rate adjustment process)
In the exhaust gas flow rate adjustment step S2, the control mechanism 20 adjusts the flow rate of the exhaust gas that flows to the bypass flow path 15 so that the temperature T1 of the combustion air after passing through the heat exchanger 11 is equal to or lower than a predetermined temperature. Hereinafter, the predetermined temperature will be described as T0.

  This exhaust gas flow rate adjusting step S2 can be performed using, for example, the flow shown in FIG. The exhaust gas flow rate adjustment step S2 includes a comparison step S21, a thermal efficiency calculation step S22, an exhaust gas flow rate determination step S23, a flow rate adjustment valve adjustment step S24, and a temperature and flow rate measurement step S25.

  First, in comparison step S21, the control mechanism 20 compares the predetermined temperature T0 with the temperature T1 of the combustion air after passing through the heat exchanger 11. If the temperature T1 is equal to or lower than the temperature T0, the process ends without adjusting the exhaust gas flow rate. On the other hand, when the temperature T1 exceeds the temperature T0, the process proceeds to the temperature efficiency calculation step S22.

ここで温度Ｔ１、Ｔ２、Ｔ３及びＴ４の単位は［Ｋ］である。 In the thermal efficiency calculation step S22, the control mechanism 20 calculates the temperature efficiency φ of the heat exchanger 11 according to the following equation (1).

Here, the units of the temperatures T1, T2, T3, and T4 are [K].

ここで、Ｃ_{ｐ−ａｉｒ}は空気の比熱［Ｊ／ｋｇ／Ｋ］を意味し、Ｃ_ｐ−ｅｘは排ガスの比熱［Ｊ／ｋｇ／Ｋ］を意味する。また、燃焼用空気の流量Ｑ１及び排ガスの流量Ｑ２_ｎｅｗの単位は、［Ｎｍ^３／ｈ］である。 Next, in the exhaust gas flow rate determination step S23, the control mechanism 20 calculates the flow rate Q2 _new of the exhaust gas that passes through the heat exchanger 11 such that T1 = T0 according to the following equation (2) using the temperature efficiency φ. . This equation (2) can be derived by solving an energy conservation equation with the heat exchanger 11 as a boundary.

Here, C _p-air means the specific heat of air [J / kg / K], and C _p-ex means the specific heat of exhaust gas [J / kg / K]. The unit of the flow rate Q1 of combustion air and the flow rate Q2 _new of exhaust gas is [Nm ³ / h].

Next, in the flow rate adjusting valve adjustment step S24, the control mechanism 20 adjusts the flow rate of the exhaust gas flowing through the bypass passage 15 so that the flow rate of the exhaust gas passing through the heat exchanger 11 becomes Q2 _new . Specifically, the control mechanism 20 adjusts the opening / closing amounts of the exhaust gas flow rate adjustment valve 16 and the bypass flow rate adjustment valve 17.

  Thereafter, in the temperature and flow rate measurement step S25, the control mechanism 20 detects the temperature T1 of the combustion air after passing through the heat exchanger 11, the temperature T2 of the combustion air before passing through the heat exchanger 11, and the heat. The exhaust gas temperature T3 before passing through the exchanger 11, the exhaust gas temperature T4 after passing through the heat exchanger 11, the flow rate Q1 of combustion air preheated in the heat exchanger 11, and the exhaust gas flow rate passing through the heat exchanger 11 Q2 is measured and the measurement result is updated.

  Based on the updated measurement result, the control mechanism 20 repeats the above five steps until the temperature T1 becomes equal to or lower than the temperature T0 in the comparison step S21.

  The measurement step (S1) and the exhaust gas flow rate adjustment step (S2) may be performed repeatedly at predetermined time intervals. By repeatedly performing in this way, even if the temperature T1 of the combustion air exceeds during the heating of the steel material, the exhaust gas that flows to the bypass passage 15 so that the temperature of the combustion air becomes a predetermined temperature or less The flow rate can be adjusted. Although it does not specifically limit as said time interval, For example, it can be 10 minutes or more and 30 minutes or less.

<Advantages>
The exhaust heat recovery apparatus 1 includes a bypass channel 15 that bypasses the heat exchanger 11. Further, the exhaust heat recovery apparatus 1 has a mechanism for adjusting the flow rate of the exhaust gas flowing through the bypass passage 15 based on the measurement result of the thermometer 18a that measures the temperature of the combustion air after passing through the heat exchanger 11. Prepare. The exhaust heat recovery apparatus 1 can manage the temperature of the combustion air after preheating by suppressing the flow rate of the exhaust gas supplied to the combustion air by this adjustment mechanism. Further, the exhaust heat recovery apparatus 1 supplies the exhaust gas and combustion air in amounts necessary for preheating to the heat exchanger 11, so that preheating energy is not wasted. In addition, since the exhaust heat recovery apparatus 1 supplies exhaust gas that is not used for preheating to the exhaust heat recovery boiler 12 via the bypass passage 15, the temperature of the exhaust gas is unlikely to decrease. For this reason, the exhaust heat recovery apparatus 1 can suppress a decrease in the heat recovery efficiency of the exhaust heat recovery boiler 12. Therefore, the exhaust heat recovery apparatus 1 can manage the temperature of the combustion air after preheating while suppressing a decrease in energy efficiency.

  The exhaust heat recovery apparatus 1 passes through the heat exchanger 11 after passing through the heat exchanger 11, the combustion air temperature T <b> 2 before passing through the heat exchanger 11, and the heat exchanger 11. The exhaust gas temperature T3 before passing, the exhaust gas temperature T4 after passing through the heat exchanger 11, the flow rate Q1 of combustion air preheated in the heat exchanger 11, and the exhaust gas flow rate Q2 passing through the heat exchanger 11 can be measured. Therefore, the exhaust heat recovery apparatus 1 has high adjustment accuracy of the flow rate of the exhaust gas flowing to the bypass flow path 15.

  Further, the exhaust heat recovery method of the present invention can manage the temperature of the combustion air after preheating while suppressing a decrease in energy efficiency.

[Other Embodiments]
The exhaust heat recovery apparatus of the present invention is not limited to the above embodiment.

  In the above embodiment, the case where the exhaust heat recovery apparatus includes four thermometers and two flow meters has been described. However, the thermometer for measuring the exhaust gas temperature T4 after passing through the heat exchanger may be omitted. it can.

When the thermometer is omitted, in the thermal efficiency calculation step of the exhaust gas flow rate adjustment step, the heat recovery rate η of the heat exchanger shown in the following formula (3) is used as the thermal efficiency.

Further, in the exhaust gas flow rate determination step of the exhaust gas flow rate adjustment step, the flow rate Q2 _new of the exhaust gas passing through the heat exchanger is calculated according to the following formula (4) using the heat recovery rate η.

  The exhaust heat recovery apparatus includes a thermometer for measuring the temperature T2 of the combustion air before passing through the heat exchanger, a thermometer for measuring the exhaust gas temperature T3 before passing through the heat exchanger, and a heat exchanger. The flow meter for measuring the flow rate Q1 of the combustion air to be preheated in the above and the flow meter for measuring the flow rate Q2 of the exhaust gas passing through the heat exchanger can be further omitted. That is, the exhaust heat recovery apparatus may include only a thermometer that measures the temperature T1 of the combustion air after passing through the heat exchanger as a measuring device.

  When only the thermometer that measures the temperature of the combustion air after passing through the heat exchanger is used as the measuring device, the exhaust gas flow rate adjusting step can be performed by the following steps, for example. First, the control mechanism compares the predetermined temperature T0 with the temperature T1 of the combustion air after passing through the heat exchanger. If the temperature T1 is equal to or lower than the temperature T0, the process ends without adjusting the exhaust gas flow rate. On the other hand, when the temperature T1 exceeds the temperature T0, the control mechanism opens and closes the exhaust gas flow rate adjustment valve and the bypass flow rate adjustment valve so that the flow rate of the exhaust gas passing through the heat exchanger is reduced by a predetermined amount. Adjust the amount. The predetermined amount can be, for example, an amount of 5% by volume to 10% by volume of the exhaust gas flow rate that passes through the heat exchanger before adjustment. Thereafter, the control mechanism measures the temperature T1 of the combustion air after passing through the heat exchanger, and updates the measurement result. Based on the updated measurement result, the control mechanism repeats the above steps until the temperature T1 becomes equal to or lower than the temperature T0.

  Further, in the above embodiment, in the comparison step of the exhaust gas flow rate adjustment process, if the temperature T1 of the combustion air after passing through the heat exchanger is equal to or lower than the predetermined temperature T0, the process may be terminated without adjusting the exhaust gas flow rate. As described above, the exhaust gas flow rate may be adjusted even if the temperature T1 of the combustion air is equal to or lower than the predetermined temperature T0. As described above, even when the temperature T1 of the combustion air is equal to or lower than the predetermined temperature T0, the heat recovery rate of the heat exchanger can be increased by adjusting the exhaust gas flow rate, so that the energy efficiency is further increased.

When the temperature T1 of the combustion air is equal to or lower than the predetermined temperature T0, the exhaust gas flow rate can be adjusted, for example, so that the temperature T1 of the combustion air approaches the predetermined temperature T0. Specifically, as in the case where the temperature T1 of the combustion air exceeds a predetermined temperature T0, the control mechanism performs a thermal efficiency calculation step, an exhaust gas flow rate determination step, a flow rate adjustment valve adjustment step, and a temperature and flow rate measurement step. Good. In the thermal efficiency calculation step and the exhaust gas flow rate determination step, the same equation as that when the temperature T1 of the combustion air exceeds the predetermined temperature T0 can be used. Further, the exhaust gas flow rate Q2 _new calculated in the exhaust gas flow rate determination step may exceed the exhaust gas flow rate discharged from the heating furnace. In this case, Q2 _new is the total flow rate of the exhaust gas discharged from the heating furnace. It is good to do.

  In consideration of the stability of the control mechanism, when the temperature is lower than the second predetermined temperature T10 lower than the predetermined temperature T0, the temperature T1 of the combustion air is equal to or higher than the second predetermined temperature T10. The control mechanism may adjust the flow rate of the exhaust gas flowing to the bypass flow path.

  In the above embodiment, the case where the exhaust gas flow rate adjustment valve is disposed in the second exhaust gas flow channel has been described. However, the exhaust gas flow rate adjustment valve may be disposed in the first exhaust gas flow channel.

  Further, the exhaust gas flow rate adjustment valve can be omitted. When the exhaust gas flow rate adjustment valve is omitted, the control mechanism adjusts the opening / closing amount of only the bypass flow rate adjustment valve so that the temperature of the combustion air after passing through the heat exchanger becomes a predetermined temperature or less. Adjust the flow rate of the exhaust gas flowing to the bypass channel.

  As described above, the exhaust heat recovery apparatus of the present invention and the exhaust heat recovery method of the present invention can manage the temperature of the combustion air after preheating while suppressing a decrease in energy efficiency.

DESCRIPTION OF SYMBOLS 1 Waste heat recovery apparatus 11 Heat exchanger 12 Waste heat recovery boiler 13 Chimney 14a 1st exhaust gas flow path 14b 2nd exhaust gas flow path 15 Bypass flow path 16 Exhaust gas flow rate adjustment valve 17 Bypass flow rate adjustment valve 18a, 18b, 18c, 18d Temperature Total 19a, 19b Flow meter 20 Control mechanism 21 Flue 100 Heating furnace 101 Transfer device 102 Heating furnace main body 103 Combustion air flow path 104 Combustion air flow rate adjustment valve

Claims (5)

An apparatus for recovering exhaust heat from a heating furnace that heats steel,
A heat exchanger for preheating combustion air supplied to the heating furnace;
An exhaust heat recovery boiler that recovers sensible heat of the exhaust gas discharged from the heating furnace;
A first exhaust gas flow path connecting the heating furnace and the heat exchanger;
A second exhaust gas flow path connecting the heat exchanger and the exhaust heat recovery boiler;
A bypass flow path that bypasses the heat exchanger and connects the heating furnace and the exhaust heat recovery boiler;
A thermometer for measuring the temperature of the combustion air after passing through the heat exchanger;
A mechanism for adjusting a flow rate of exhaust gas flowing through the bypass flow path so that a temperature measured by the thermometer is equal to or lower than a predetermined temperature.   The exhaust heat recovery apparatus according to claim 1, further comprising a mechanism for adjusting a flow rate of exhaust gas flowing through the first exhaust gas passage based on a measurement result of the thermometer. A thermometer for measuring the temperature of the combustion air before passing through the heat exchanger;
A thermometer for measuring the exhaust gas temperature before passing through the heat exchanger;
A flow meter for measuring the flow rate of combustion air preheated by the heat exchanger;
The exhaust heat recovery apparatus according to claim 1, further comprising: a flow meter that measures a flow rate of the exhaust gas that passes through the heat exchanger.   The exhaust heat recovery apparatus according to claim 3, further comprising a thermometer that measures an exhaust gas temperature after passing through the heat exchanger. A method for recovering waste heat from a heating furnace for heating steel,
A heat exchanger for preheating combustion air supplied to the heating furnace;
An exhaust heat recovery boiler that recovers sensible heat of the exhaust gas discharged from the heating furnace;
A first exhaust gas flow path connecting the heating furnace and the heat exchanger;
A second exhaust gas flow path connecting the heat exchanger and the exhaust heat recovery boiler;
Using a waste heat recovery device that bypasses the heat exchanger and includes a bypass passage that connects the heating furnace and the waste heat recovery boiler,
Measuring the temperature of the combustion air after passing through the heat exchanger;
Adjusting the flow rate of the exhaust gas flowing to the bypass flow path so that the measured temperature is equal to or lower than a predetermined temperature.

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