JP2007248017A - Temperature controller for fuel economizer of reheat boiler - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the corrosion of heat transfer tubes in a fuel economizer caused by the dew condensation of acidic moisture in exhaust gas, particularly to carry out energy saving and the reduction of facility cost, and to prevent a water hammer phenomenon in water supply piping. <P>SOLUTION: A recirculation passage 28 provided with the reheat boiler 2, an evaporator 10, the fuel economizer 12, and a water supply pump 24 is formed for recirculating supply water heated by the fuel economizer from the outlet side of the fuel economizer to the inlet side of the water supply pump. A heat exchanger 26 provided for carrying out heat exchange between supply water flowing in a water supply passage, and the supply water flowing in the recirculation passage and heated by the fuel economizer is interposed in each of the recirculation passage and the water supply passage between the water supply pump and the fuel economizer. A circulation water flow control means 30 provided for carrying out the flow control of the supply water flowing in the recirculation passage is interposed in the recirculation passage at the downstream side of the heat exchanger. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a temperature control device for a refueling boiler economizer that uses exhaust gas of an internal combustion engine such as a gas engine or a gas turbine as combustion air.

  An internal combustion engine such as a gas engine or a gas turbine has an exhaust gas temperature of 300 to 600 ° C., and the exhaust gas usually contains 10% or more of residual oxygen. By using the exhaust gas of the internal combustion engine as an oxygen supply source for burning the fuel of the boiler, the total amount of exhaust gas combined with the internal combustion engine and the boiler can be reduced, and environmental loads such as nitrogen oxides can be reduced. Factors can be reduced.

  Furthermore, by utilizing the temperature of 300 to 600 ° C. of the exhaust gas, the fuel consumption of the boiler can be reduced, thereby improving the overall energy efficiency. In recent years, the number of boilers employing such a combustion system is increasing. Here, a boiler equipped with such a combustion system is called an exhaust gas refired boiler.

  In a normal boiler, a gas-type air preheater is often used to perform heat exchange between the combustion air and the exhaust gas to lower the temperature of the exhaust gas and thereby increase the thermal efficiency. However, since the exhaust gas temperature of the internal combustion engine that originally enters the boiler is high in the exhaust gas reburning boiler, a gas-type air preheater cannot be used, and a economizer is used instead.

  Here, when this economizer is used, there is a problem that acidic moisture in the exhaust gas is condensed on the surface of the heat exchanger tube of the economizer and the heat exchanger tube is corroded, so that this corrosion is not caused. The feed water is supplied to the economizer after the feed water temperature at the economizer entrance is raised above the dew point temperature of the exhaust gas. However, in many plants, the feed water supplied to the boiler is often supplied at a temperature lower than the above-described exhaust gas dew point temperature. In this case, a device for raising the low temperature water supply to a temperature at which no condensation occurs around the heat transfer tube of the economizer is necessary.

  As shown in FIG. 3, as a temperature control device for a conventional economizer for a refired boiler, the feed water on the downstream side of the feed water pump 102 is heated using a high-temperature heat source such as superheated steam emitted from the superheater 100. As shown in FIG. 4, a part of the high-temperature and high-pressure water supply at the outlet side of the economizer 104 is recirculated to the inlet side of the economizer 104 by the economizer circulation pump 106 to save the economizer. A device for increasing the feed water temperature at the inlet of the water saver 104 or a device for increasing the feed water temperature at the inlet of the economizer (for example, by recirculating a part of the high-temperature high-pressure feed water at the outlet side of the economizer to the upstream side of the feed water pump) , See Patent Document 1).

  However, in the conventional apparatus shown in FIG. 3 for heating using a high-temperature heat source such as superheated steam emitted from the superheater 100, the steam efficiency is increased in order to increase the temperature of the feed water. There is a problem that it is not preferable from the viewpoint of energy saving. Further, the conventional apparatus shown in FIG. 4 for recirculating a part of the high-temperature water heated by the economizer 104 to the inlet side of the economizer 104 by the economizer circulation pump 106 is an economizer circulation pump. A high-temperature water pump is required as 106, and there is a problem that the cost is high in terms of equipment.

Furthermore, in the conventional apparatus described in Patent Document 1, a part of the high-temperature and high-pressure feed water on the outlet side of the economizer is recirculated to the upstream side of the feed water pump to increase the feed water temperature at the economizer inlet. In many cases, the feed water temperature at the economizer outlet is higher than the saturation temperature of the feed water pressure at the feed water pump inlet. For this reason, if flushing occurs at the outlet of the flow control valve for controlling the flow rate of the recirculated water, and this is joined as it is in the water supply pipe upstream of the water supply pump, a water hammer phenomenon occurs in the water supply pipe. There is.
JP 2000-154904 A (FIG. 1)

  The present invention has been made to solve such a problem, and is intended to prevent corrosion of the heat transfer tube of the economizer due to condensation of acidic moisture in the exhaust gas. It is an object of the present invention to provide a temperature control device for a economizer of a refired boiler that can be reduced and can prevent a water hammer phenomenon in a water supply pipe.

  In order to solve the above problems, the means employed by the present invention includes a recombustion boiler that uses the exhaust gas of the internal combustion engine as combustion air, and an evaporation that is disposed in the exhaust gas passage of the recombustion boiler and vaporizes the feed water. And a water-saving device that is disposed in the exhaust gas path downstream of the evaporator and heats the feed water supplied to the evaporator, and a feed water pump that pressurizes and supplies the feed water to the economizer through the water supply path A recirculation path for recirculating feed water heated by the economizer from the outlet side of the economizer to the inlet side of the feed water pump, and the recirculation path and the feed pump Heat exchanger that is inserted into a water supply channel between the water saving unit and the water saving unit, and exchanges heat between the water supplied through the water supply channel and the water supplied by the above economizer through the recirculation channel And inserted in the recirculation path on the downstream side of the heat exchanger. In that it comprises water in a circulating water flow rate adjusting means for a flow control that.

  According to the temperature control device for the economizer of the refired boiler of the present invention, the heat exchanger heats the feedwater flowing in the feedwater channel with the feedwater heated by the economizer flowing in the recirculation channel. The temperature of the feed water supplied to the charcoal increases, and corrosion of the heat transfer tubes of the economizer due to condensation of acidic moisture in the exhaust gas can be prevented.

  In addition, since the feed water supplied to the economizer is heated using a part of the feedwater from the economizer, the boiler efficiency is higher than that of a conventional device that uses a high-temperature heat source such as superheated steam. Energy saving can be achieved without lowering.

  Furthermore, the temperature of the feed water heated by the economizer is lowered by the heat exchanger while maintaining the high pressure state, and then recirculated into the low pressure feed channel on the inlet side of the feed water pump. The economizer circulation pump for high temperature water required in the conventional apparatus becomes unnecessary, and the cost in terms of equipment can be reduced.

  At the same time, the water supply heated by the economizer can be cooled by the heat exchanger without causing flushing upstream of the heat exchanger, so that the water hammer phenomenon in the water supply pipe generated in the conventional device Can be prevented. Moreover, since the feed water heated by the economizer is appropriately flow-regulated by the circulating water flow rate adjusting means and recirculated, the feed water supplied to the economizer can be optimally heated.

  Preferably, a feed water temperature detection sensor for detecting a feed water temperature at the inlet of the economizer and a controller for controlling the operation of the circulating water flow rate adjusting means based on the feed water temperature detected by the feed water temperature detection sensor. Thereby, the feed water temperature at the entrance of the economizer can be automatically adjusted.

More preferably, the controller controls the operation of the circulating water flow rate adjusting means so that the feed water temperature detected by the feed water temperature detection sensor is equal to or higher than a predetermined temperature. Thereby, the feed water temperature of the entrance of a economizer can always be maintained above a certain temperature.

  More preferably, the predetermined temperature is a lower limit temperature set in order to prevent dew condensation in the heat transfer tube of the economizer. Thereby, the dew condensation by the heat exchanger tube of a economizer and corrosion by it can be prevented reliably.

  A temperature control device for a refueling boiler economizer according to the present invention includes a reburning boiler that uses exhaust gas of an internal combustion engine as combustion air, an evaporator that is disposed in an exhaust gas passage of the reburning boiler and vaporizes feed water, and A reburning system comprising a economizer that heats feed water that is disposed in the exhaust gas path downstream of the evaporator and that supplies water to the evaporator, and a feed pump that pressurizes and supplies the feedwater to the economizer through the feed path In a temperature control device for a boiler economizer, a recirculation path for recirculating feed water heated by the economizer from the outlet side of the economizer to the inlet side of the feed water pump, and the recirculation path and the feed water pump and the economizer A heat exchanger that is inserted into a water supply channel between the charcoal unit and performs heat exchange between the water supply flowing through the water supply channel and the water supply heated by the economizer flowing through the recirculation channel; Water that is inserted into the recirculation path downstream of the heat exchanger and flows through this recirculation path Since it is equipped with circulating water flow rate adjusting means for adjusting the flow rate, it prevents corrosion of the heat transfer tubes of the economizer due to condensation of acidic moisture in the exhaust gas, and in particular, saves energy and reduces equipment costs. In addition, the water hammer phenomenon in the water supply pipe can be prevented.

  FIG. 1 shows a steam generation system using a recombustion boiler as an embodiment. A recombustion boiler 2 uses a combustion chamber 4 for combusting additional fuel using exhaust gas from an internal combustion engine as combustion air, and the combustion chamber. 4 and an exhaust gas passage 6 for exhausting the combustion gas (exhaust gas) burned in 4. In the exhaust gas passage 6, a superheater 8 for generating superheated steam, an evaporator 10 for generating saturated steam, and a economizer 12 for heating feed water supplied to the evaporator 10 are upstream. They are arranged in this order from the side to the downstream side.

  The feed water heated by the economizer 12 passes through the feed channel 14 and is led to the evaporator 10 via the flow rate control valve 16 to become saturated steam. The saturated steam generated in the evaporator 10 is led to the superheater 8 through the steam path 18 to become superheated steam, and then sent to the factory through the steam path 20.

  The water supply of the boiler 2 is guided to the water supply pump 24 through a water supply path 22 that leads to an external water supply source. The water supply pump 24 pressurizes and supplies water to the economizer 12 through the water supply path 22. A heat exchanger 26 is interposed in the water supply path 22 between the outlet of the water supply pump 24 and the inlet of the economizer 12. A recirculation path 28 branched from the outlet side of the economizer 12 and led to the inlet side of the water supply pump 24 is disposed. The recirculation path 28 includes the heat exchanger 26 and the circulating water flow rate. A control valve (circulating water flow rate adjusting means) 30 is inserted in this order from the outlet side of the economizer 12 to the inlet side of the feed water pump 24.

  That is, the recirculation path recirculates the feed water heated by the economizer 12 from the outlet side of the economizer 12 to the inlet side of the feed water pump, and the heat exchanger 26 supplies the feed water and the recirculation path flowing in the feed water path 22. While performing heat exchange with the feed water heated by the economizer 12 flowing in the interior 28, the circulating water flow rate adjustment valve 30 adjusts the flow rate of the feed water heated by the economizer 12 flowing in the recirculation path 28. To do.

  A water supply temperature detection sensor 32 for detecting the inlet water supply temperature Tw of the economizer 12 is disposed in the water supply path 22 between the outlet of the heat exchanger 26 and the inlet of the economizer 12. The feed water temperature detection sensor 32 is electrically connected to the controller 34, and the controller 34 controls the operation of the circulating water flow rate adjustment valve 30 based on the feed water temperature Tw detected by the feed water temperature detection sensor 32.

  Next, the operation of the steam generation system using the above-described refired boiler will be described with additional reference to FIG.

  The controller 34 reads the inlet water supply temperature Tw of the economizer 12 detected by the feedwater temperature detection sensor 32 (step S2), and determines whether the inlet water supply temperature Tw of the economizer 12 is equal to or higher than a predetermined temperature T1. (Step S4). Here, the predetermined temperature T1 is a lower limit temperature set in order to prevent condensation in the heat transfer tube of the economizer 12.

  When the determination result of step S4 is affirmative (Yes), that is, when the inlet water supply temperature Tw of the economizer 12 is equal to or higher than the predetermined temperature T1, and there is no possibility of occurrence of condensation in the heat transfer pipe of the economizer 12. Repeats steps S2 and S4 described above. On the other hand, when the determination result of step S4 is negative (No), that is, the inlet water supply temperature Tw of the economizer 12 is lower than the predetermined temperature T1, and there is a possibility that condensation occurs in the heat transfer tube of the economizer 12. In this case, the adjustment amount ΔV of the circulating water flow rate adjustment valve 30 is determined so that the inlet water supply temperature Tw of the economizer 12 becomes the predetermined temperature T1 (step S6).

  The controller 34 adjusts the circulating water flow rate adjustment valve 30 based on the adjustment amount ΔV. That is, the controller 34 automatically adjusts so that the feed water temperature Tw at the inlet of the economizer 12 is always equal to or higher than a predetermined temperature T1 for preventing condensation in the heat transfer tube of the economizer 12. And the above-mentioned step S2 and subsequent steps are repeated again.

  According to the temperature control device for the economizer of the refired boiler described above, the heat exchanger 26 heats the feed water flowing in the feed water path 22 by the feed water heated by the economizer 12 flowing in the recirculation path 28. The feed water temperature Tw supplied to the economizer 12 becomes high, that is, the temperature becomes equal to or higher than the lower limit temperature T1 set to prevent condensation in the heat transfer tube of the economizer 12. Therefore, corrosion of the heat transfer tube of the economizer 12 due to condensation of acidic moisture in the exhaust gas can be reliably prevented.

  Moreover, although the feed water supplied to the economizer 12 is heated using a part of the feedwater discharged from the economizer 12, the temperature rise of the feedwater due to this heating is an increase in the amount of recovered heat from the exhaust gas. Therefore, it is possible to save energy without lowering the boiler efficiency as compared with a conventional apparatus that uses a high-temperature heat source such as superheated steam. Further, the feed water heated by the economizer 12 flowing in the recirculation path 28 is cooled by the heat exchanger 26 and the temperature is lowered, and then recirculated into the low-pressure feed path 22 on the inlet side of the feed water pump 24. Therefore, the economizer circulation pump for high-temperature water required in the conventional device is no longer necessary, and the cost of the equipment can be reduced, and the water hammer phenomenon in the water supply pipe that occurs in the conventional device Can be reliably prevented.

  The present invention is not limited to the above-described embodiment. For example, the above-mentioned predetermined temperature does not necessarily need to be set as a temperature only for preventing condensation in the heat transfer tube of the economizer. It can be set about other elements, such as a feed water preheater, or including other elements.

  The effect at the time of implementing the temperature control apparatus of the economizer of the refired boiler of this invention on the following conditions was examined.

(Consideration conditions)
Boiler exhaust gas flow rate: 10,000 m ³ N / h
Gas saver inlet gas temperature: 200 ° C
Boiler feed water flow rate: 4.0t / h
Boiler feed water temperature: 20 ° C
Water saver inlet water supply temperature: 60 ° C
Water saving outlet water supply temperature: 120 ° C
Boiler feed pump inlet feed water pressure: 0.1 MPa (G)
Boiler feed pump outlet feed water pressure: 1.0 MPa (G)

(Study results)
For the economizer that satisfies the above consideration conditions, when the temperature control device of the economizer of the refired boiler of the present invention shown in FIG. 1 is implemented, the boiler feed pump inlet feed water pressure is 0.1 MPa (G). The saturation temperature is about 100 ° C. Moreover, since the boiler feed pump outlet feed water pressure is 1.0 MPa (G), the saturation temperature is 184 ° C.

  On the other hand, the economizer outlet feed water temperature is 120 ° C., and no steam is generated. However, if this feed water is returned to the boiler feed pump inlet side, water that is hotter than 100 ° C, which is the saturation temperature of the boiler feed pump inlet, will enter, so flushing will always occur downstream of the circulating water flow control valve. In a portion where the mixture of steam and saturated water is mixed with boiler feed water at 20 ° C., a severe water hammer phenomenon occurs when the generated steam condenses into water.

  As shown in FIG. 1, in order to avoid this, a heat exchanger 26 for cooling by low-temperature boiler feed water is provided before circulating water is mixed with the inlet water of the feed water pump 24, and is circulated by the heat exchanger 26. Cool the water under high pressure to a temperature below 100 ° C. Thus, no steam is generated even if the pressure is reduced from 1.0 MPa (G) to 0.1 MPa (G) by the circulating water flow rate adjustment valve 30 provided on the outlet side of the heat exchanger 26.

  Therefore, even if this cooled circulating water is mixed with the inlet water of the feed water pump 24, the water hammer phenomenon does not occur. Further, the temperature control device can raise the feed water temperature of the economizer to 60 ° C. Therefore, corrosion of the heat transfer tube of the economizer 12 due to condensation of acidic moisture in the exhaust gas can be reliably prevented.

  The circulating water flow rate of the economizer outlet water at 120 ° C is 2.4 t / h, and the exhaust gas temperature at the economizer outlet at this time is 87 ° C. On the other hand, when heating steam having a saturation temperature of 1.0 MPa (G) is used as an external heat source, the consumption amount of heating steam is about 270 kg / h, and this amount of heat cannot be recovered from the exhaust gas. The exhaust gas temperature is about 100 ° C.

  That is, the exhaust gas loss is increased by the temperature rise (13 ° C.) of the exhaust gas, and the thermal efficiency of the reburning boiler is reduced accordingly. Thus, the temperature control device for the economizer of the refired boiler of the present invention is extremely effective from the viewpoint of energy saving.

It is the schematic which showed the system of the recombustion boiler as one embodiment. It is a flowchart which shows the action | operation of the temperature control apparatus of the economizer of the recombustion boiler of FIG. It is the schematic which shows the temperature control apparatus of the conventional economizer of a refired boiler. It is the schematic which shows the temperature control apparatus of the economizer of another conventional refired boiler.

Explanation of symbols

2 Recombustion boiler 4 Combustion chamber 6 Exhaust gas path 8 Superheater 10 Evaporator 12 Carburizer 14 Water supply path 16 Flow control valve 18, 20 Steam path 22 Water supply path 24 Water supply pump 26 Heat exchanger 28 Recirculation path 30 Circulating water flow rate Control valve (circulating water flow rate adjusting means)
32 Feedwater temperature detection sensor 34 Controller 100 Superheater 102 Feedwater pump 104 Saver 106 Saver circulation pump Tw Feedwater temperature T1 Predetermined temperature ΔV Adjustment amount

Claims (4)

  A recombustion boiler (2) that uses exhaust gas of an internal combustion engine as combustion air, an evaporator (10) that is disposed in an exhaust gas passage (6) of the recombustion boiler and vaporizes feed water, and the exhaust gas passage (6) A economizer (12) which is disposed downstream of the evaporator and heats the feed water supplied to the evaporator, and pressurizes the feed water through the feed channel (22) to the economizer In a temperature control device for a economizer of a refired boiler having a feed water pump (24) to be fed, the feed water heated by the economizer is recirculated from an outlet side of the economizer to an inlet side of the feed pump. A recirculation path (28) to be circulated, and the water supply and the recirculation path that are inserted in the recirculation path and the water supply path between the water supply pump and the economizer, respectively, and flow in the water supply path. Heat exchanging heat with the feed water heated by the economizer And a circulation water flow rate adjusting means (30) for adjusting the flow rate of the feed water that is inserted in the recirculation channel on the downstream side of the heat exchanger and flows in the recirculation channel. A temperature control device for a economizer for a refired boiler.   A feed water temperature detection sensor (32) for detecting the feed water temperature (Tw) at the inlet of the economizer (12), and the circulating water flow rate adjusting means (30) based on the feed water temperature detected by the feed water temperature detection sensor The temperature control device for a refueling boiler economizer according to claim 1, further comprising a controller (34) for controlling the operation of the reburning boiler.   The controller (34) controls the operation of the circulating water flow rate adjusting means (30) so that the feed water temperature (Tw) detected by the feed water temperature detection sensor (32) is equal to or higher than a predetermined temperature (T1). The temperature control device of the economizer of the refired boiler according to claim 2 characterized by these. The said predetermined temperature (T1) is a minimum temperature set in order to prevent the dew condensation in the heat exchanger tube of the said economizer (12), The economizer of the refired boiler of Claim 3 characterized by the above-mentioned. Temperature control device.