JP5242225B2 - Boiler blowdown energy recovery system - Google Patents

Description

  The present invention relates to a system for recovering energy from boiler blowdown.

  In the boiler, impurities such as minerals in the boiler water are concentrated by generating steam. When the concentration of impurities in boiler water becomes high, problems such as difficulty in maintaining the dryness of the generated steam occur. For this reason, in the boiler, as described in Patent Documents 1 and 2, a part of the concentrated boiler water is discharged (blow down) to the outside, and the remaining boiler water is diluted with make-up water. It is necessary to keep the water quality below a certain standard.

  As a technique related to such blowdown control, for example, Patent Document 1 describes a technique for adjusting the blow amount based on the hardness of boiler water, and Patent Document 2 describes the electrical conductivity of boiler water. A technique for adjusting the blow rate based on this is described.

  Further, the blown-down boiler water has a considerable amount of heat energy, and it is desired to recover and reuse the energy. In Patent Document 3, blown boiler water is introduced into a flash tank, low-pressure steam is separated from blown boiler water, and this low-pressure steam is introduced into make-up water of a deaerator, so that blow-down is performed. A known technique for recovering a part of the energy of the boiler water is described.

  Furthermore, in the system of Patent Document 3, a turbine is rotated using hot water separated from low-pressure steam in a flash tank, and a pump driven by the turbine is used as a steam-type air preheater drain as a low-pressure feed water heater. Further energy efficiency is improved by using it for further transport.

  However, in a small boiler, since a small amount of boiler water is blown down, there is no flow rate sufficient to turn the turbine, and it is difficult to recover energy.

For example, in a small-scale plant such as a fiber dyeing plant, there are laws and regulations related to boiler installation, and a large boiler is not adopted and a plurality of small once-through boilers are often provided side by side. In such a plant, the energy of the blown-down boiler water is not recovered at all and is actually discarded. Actually, as a result of investigating the blowdown amount in a plant having 22 small once-through boilers, it was found that 300 to 2000 kg / hr of steam was discarded.
JP 2008-2739 A JP 2001-165403 A JP 11-344203 A

  In view of the above problems, an object of the present invention is to provide a boiler blowdown energy recovery system that can be applied to a small boiler.

In order to solve the above problems, a boiler blowdown energy recovery system according to the present invention introduces boiler water blown down from a boiler, depressurizes it and separates it into steam and hot water, and separates it in the flash tank. A compressor that sucks and compresses and discharges the steam; a confluence channel that merges the vapor discharged from the compressor with the steam generated by the boiler; and a branch from the confluence channel, and discharge of the compressor Open the pressure reducing valve so that the pressure of the preheating flow path for introducing the steam to the make-up water of the boiler through the pressure reducing valve and the joining flow path after the preheating flow path becomes constant. And a confluence pressure control device for adjusting the degree .

  According to this configuration, it is possible to recover the thermal energy by depressurizing the blown-down boiler water in the flash tank and evaporating a part thereof, and pressurizing the obtained low-pressure steam to a pressure usable by the compressor. can do.

Moreover, according to this structure, since the recovered energy can be reused as the output or input of the boiler, there is no loss and the efficiency is high.

  The boiler blowdown energy recovery system of the present invention may further include a flash pressure control device that controls the output of the compressor so as to keep the pressure of the flash tank constant.

  According to this configuration, the vapor temperature separated in the flash tank becomes constant, and stable energy recovery can be performed.

  According to the present invention, the steam obtained by depressurizing the boiler water blown down from the boiler is reused by pressurizing the steam to a pressure that can be used by the compressor. Thermal energy can be recovered stably.

Reference examples and embodiments of the present invention will now be described with reference to the drawings.
FIG. 1 shows a steam generator equipped with a blowdown energy recovery system 1 of a first reference example of the present invention. The blow-down energy recovery system 1 introduces boiler water blown down from a boiler 2 that generates steam of about 0.5 MPaG and supplies it to a demand facility, and depressurizes the introduced boiler water, And a screw compressor 4 that sucks and compresses the low-pressure steam separated in the flash tank 3 and discharges it as high-pressure steam.

  The boiler 2 supplements boiler water that has been reduced due to generation of steam and blow-down with makeup water supplied from a water supply tank 5. The water supply tank 5 is automatically supplied with soft water from a water softener (not shown) so that the amount of water is constant.

  The blowdown energy recovery system 1 also includes an output of a flash pressure gauge 6 that detects the pressure Ps in the flash tank 3 and an inverter (variable frequency power source) 8 that supplies a drive current to a motor 7 that drives the screw compressor 4. A flash pressure control device 9 that performs PID control on the frequency based on the detected value of the flash pressure gauge 6 is provided.

  In the blowdown energy recovery system 1, the flash pressure control device 9 is configured so that the rotation speed of the screw compressor 4, in other words, the output of the screw compressor 4, is maintained so that the pressure Ps of the flash tank 3 is maintained at substantially atmospheric pressure (0 MPaG). To control. The screw compressor 4 compresses the low-pressure steam separated in the flash tank 3, pressurizes it to about 0.5 MPaG, which is substantially the same as the steam generated by the boiler 2, and discharges it. The steam discharged by the screw compressor 4 joins the steam generated by the boiler 2 via the joining flow path 10 and is supplied to the demand facility.

In this reference example , in the flash tank 3, the blown-down boiler water is decompressed to lower the saturation temperature and generate low-pressure steam. In other words, in the flash tank 3, the boiler water introduced is deprived of heat energy by the low-pressure steam and the low-pressure steam that retains the decrease in the overall temperature (sensible heat) as evaporation heat (latent heat), and the low-pressure steam is desorbed. Separation separates into warm water in which impurities are further concentrated. In the blowdown energy recovery system 1, only this concentrated warm water is discharged to the outside.

  The steam separated in the flash tank 3 cannot be effectively used as it is because the pressure is low. However, a part of the high-pressure steam to be supplied by the boiler 2 is compressed by the screw compressor 4 into high-pressure steam. Can be replaced with That is, by compressing with the compressor 4, it becomes possible to collect | recover the thermal energy of the low pressure steam isolate | separated with the flash tank 3 in a steam generator.

In this reference example , the flash pressure control device 9 adjusts the output of the screw compressor 4 and keeps the internal pressure of the flash tank 3 low at substantially atmospheric pressure (0 MPaG), so the amount of evaporation from the blow-down boiler water Can be maintained, the energy recovery rate can be increased, and the discharge pressure of the screw compressor 4 can be stabilized.

  In addition, each time the boiler 2 is blown down, the screw compressor 4 may be operated with a predetermined output for a predetermined time.

Next, FIG. 2 shows a steam generator provided with the blowdown energy recovery system 1a of the second reference example of the present invention. Note that in this reference example , the same components as those in the first reference example are denoted by the same reference numerals, and description thereof is omitted.

In the blowdown energy recovery system 1 a of this reference example , the low-pressure steam separated in the flash tank 3 is compressed by the screw compressor 4 and introduced into the water supply tank 5 through the preheating channel 11. That is, in this reference example , the heat energy recovered from the blown-down boiler water and the energy applied by the screw compressor 4 are used to raise the temperature of the makeup water of the boiler 2.

In this reference example , the low pressure steam separated in the flash tank 3 can be introduced into the pressurized water supply tank 5 by being pressurized by the screw compressor 4. By introducing steam recovered from the blown-down boiler water, the temperature of the makeup water rises, which requires less energy for the boiler 2 to generate steam, so the fuel consumption of the boiler 2 The amount can be reduced.

Further, in FIG. 3, showing a steam generating device comprising a blowdown energy recovery system 1b of implementation of the invention. In the present embodiment, the same components as those in the first reference example or the second reference example are denoted by the same reference numerals and description thereof is omitted.

  The blow-down energy recovery system 1b of the present embodiment includes, for example, 22 cans of small through-flow boilers 2a of about 2 t / h installed in parallel, and each boiler 2a is supplied with makeup water from a water supply tank 5 via a water supply header 12. The steam that is supplied and generated by each boiler 2a is collected in the steam header 13 at one end and then supplied to the demand facility.

Moreover, in this embodiment, the boiler water blown down from each boiler 2a is introduce | transduced into the one flash tank 3, and the low pressure steam isolate | separated with the flash tank 3 is pressurized with the screw compressor 4, and a high pressure steam is produced | generated. In the present embodiment, as in the first reference example , the high-pressure steam discharged by the screw compressor 4 is joined to the steam supplied from the steam header 13 to the demand facility via the joining flow path 10. A preheating channel 11 is provided that branches from the merging channel 10, and a part of the high-pressure steam discharged by the screw compressor 4 is introduced into the water supply tank 5 through the preheating channel 11. Yes.

  Further, a pressure reducing valve 14 whose opening degree can be adjusted is provided in the preheating channel 11. The confluence channel 10 after the preheating channel 11 is branched is provided with a pressure gauge 15 for measuring the pressure of the steam. Based on the measured value of the pressure gauge 15, the merging pressure control device 16 controls the opening of the pressure reducing valve 14 so that the measured value of the pressure gauge 15 becomes equal to the set pressure of the steam supplied from the steam header 13. To maintain.

  In the present embodiment, since the pressure of the high-pressure steam discharged from the screw compressor 4 is adjusted by the merging pressure control device 16, the steam pressure supplied to the demand facility does not fluctuate. Moreover, in order to perform this pressure regulation stably, it is preferable that the discharge pressure of the screw compressor 4 is set slightly higher than the set pressure of the steam supplied to the demand facility. And all the excess steam taken out from the merging flow path 10 to reduce the steam pressure by this pressure regulation is introduced into the water supply tank 5 and consumed for the temperature rise of the makeup water, so there is no waste of energy. .

  In the blowdown energy recovery system 1b of the present embodiment, when the amount of steam separated by the flash tank 3 and compressed by the screw compressor 4 and recirculated to the blowdown energy recovery system 1b is converted into the fuel consumption of the boiler 2a, The amount of steam corresponds to 0.3 to 2% of the energy consumption of the entire boiler 2a.

  The energy recovered by the steam generator includes the energy applied by the screw compressor 4. In the present embodiment, about 4 yen is required to generate 0.5 MPaG steam in the boiler 2a. / Kg fuel cost is required, whereas the electricity cost required to compress the low-pressure steam separated in the flash tank 3 to 0.5 MPaG with the screw compressor 4 is only about 0.7 yen / kg. . Therefore, the economic effect of this embodiment is not small.

1 is a schematic diagram of a steam generator including a first reference example of the present invention. The schematic of the steam generator containing the 2nd reference example of the present invention. 1 is a schematic view of a steam generator including one embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 1a, 1b ... Blowdown energy recovery system 2, 2a ... Boiler 3 ... Flash tank 4 ... Screw compressor 5 ... Water supply tank 6 ... Flash pressure gauge 9 ... Flash pressure control apparatus 10 ... Merge flow path 11 ... Preheating flow path 14 ... Pressure reducing valve 15 ... Confluence pressure gauge 16 ... Confluence pressure control device

Claims (2)

A flash tank that introduces boiler water blown down from the boiler, depressurizes and separates it into steam and hot water,
A compressor that sucks and compresses and discharges the vapor separated in the flash tank ;
A merging flow path for merging the steam discharged from the compressor with the steam generated by the boiler;
A preheating flow path that branches from the merge flow path and that introduces steam discharged from the compressor into the boiler make-up water via a pressure reducing valve;
A boiler blowdown energy recovery system comprising: a confluence pressure control device that adjusts an opening of the pressure reducing valve so that a pressure of the confluence passage after the preheating passage is branched becomes constant . The boiler blowdown energy recovery system according to claim 1 , further comprising a flash pressure control device that controls an output of the compressor so as to keep the pressure of the flash tank constant.

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