JP5686285B2 - Boiler blow water heat recovery system - Google Patents

Description

  The present invention relates to a heat recovery system for boiler blow water that recovers heat of blow water discharged from a boiler and heats (preheats) supply air (combustion air) of the boiler.

  In the boiler, soft water such as ion-exchanged water obtained by exchanging calcium ions or magnesium ions with sodium ions is used to prevent corrosion, and an alkaline agent is added to the boiler water as an additive, so that the pH of the boiler water is 11 The operation is adjusted to the front and back (alkaline).

  Thus, in the boiler, the generation of steam concentrates impurities such as minerals in the boiler water and the alkaline agent. However, when the concentration of the impurity and alkaline agent in the boiler water becomes high, scale and the like are generated, and the steam is dried. The problem that the maintenance of the degree becomes difficult occurs. For this reason, in boilers, a part of boiler water having a high concentration of impurities and alkaline agent is discharged (blow down) as blow water, and the remaining boiler water is diluted with makeup water. In this case, since the pH of the blown water discharged is strong at around 11, it is neutralized with an acid in the neutralizer so that the pH of the blown water becomes a value in the neutral region of about 5-9. It is made to discharge (for example, refer patent document 1).

In the neutralizer, carbon dioxide is mixed with blow water to form carbonates on cations such as Na ⁺ and K ⁺ derived from strong alkali components contained in the blow water, and the pH of the blow water is moderated. The one that leads to the value of the neutral region is known. In this case, since carbon dioxide gas is difficult to be absorbed by the high-temperature blow water, the blow water is diluted with a large amount of cooling water in the neutralizer and the temperature is lowered to 40 ° C. or lower, and then carbon dioxide gas is blown into the blow water. I try to absorb it.

  By the way, since the blow water discharged | emitted from a boiler has considerable thermal energy, it is desired to collect | recover and reuse this thermal energy. For example, in Patent Document 2, blow water discharged from a boiler is introduced into a flash tank and decompressed to separate low-pressure steam and hot water, and the separated low-pressure steam is compressed by a compressor to generate high-pressure steam. Thus, an energy recovery system that discharges the water has been proposed.

  In Patent Document 3, steam supplied to a boiler is heated (preheated) with a heat pump, or supply air (combustion air) supplied to the boiler is heated (preheated) with exhaust gas from the boiler. A supply system has been proposed.

JP 2005-000755 A JP 2009-250582 A JP 2006-308164 A

  However, in order to reduce the temperature to 40 ° C. or less by diluting the blow water discharged from the boiler with a large amount of cooling water in the neutralizer as in the prior art, and to make the pH near neutral, a large amount of cooling water is used. There is a problem of need. Further, discharging blow water having a considerable amount of thermal energy as it is has a problem that the efficiency of energy use is poor and the operating cost of the boiler cannot be reduced.

  In addition to requiring a flash tank and a compressor, the energy recovery system proposed in Patent Document 2 has a problem that the hot water separated in the flash tank is discharged as it is, so that the thermal energy of the hot water cannot be recovered. . Further, the steam supply system proposed in Patent Document 3 does not employ a method for recovering the thermal energy of blow water.

  The present invention has been made in view of the above problems, and the object of the present invention is that it is not necessary to cool the blow water with a large amount of cooling water, and the heat energy of the blow water is recovered to supply air to the boiler. It is providing the heat recovery system of the boiler blow water which can reduce the operating cost of a boiler by heating.

In order to achieve the above object, the invention according to claim 1 is a heat recovery system for boiler blow water that pumps up heat of blow water discharged from the boiler by a heat pump and heats supply air to the boiler by the heat. The blow water discharged from the boiler is introduced and stored in the blow tank without going through the cooling heat exchanger, and the blow water stored in the blow tank is circulated to the evaporator of the heat pump, so that the heat pump The blow water in the blow tank is cooled by heat exchange with the refrigerant in the evaporator, the supply air to the boiler is heated by the heat of condensation of the refrigerant in the condenser of the heat pump, and is cooled by the heat exchange with the refrigerant in the evaporator of the heat pump. Is fed to the neutralizer via a drain pump and mixed with carbon dioxide from a carbon dioxide cylinder. Characterized in that it to neutralize.

  According to the present invention, since the blow water discharged from the boiler is cooled by heat exchange with the refrigerant in the evaporator of the heat pump, it is not necessary to cool the blow water with a large amount of cooling water, and cooling equipment is unnecessary. Equipment costs can be reduced. Also, since the supply air (combustion air) to the boiler is heated (preheated) by the heat of condensation of the refrigerant in the heat pump condenser, less fuel is required to generate a predetermined temperature and a predetermined amount of steam. Therefore, the fuel cost can be reduced by that amount, and the operating cost of the boiler can be reduced.

  Further, in the neutralization device, for example, carbon dioxide gas is blown into blow water cooled by heat exchange with the refrigerant in the evaporator of the heat pump, so that carbon dioxide gas is mixed with the blow water and the blow water is efficiently neutralized. The

It is a lineblock diagram of the heat recovery system of boiler blow water concerning the present invention. It is a Mollier diagram which shows the state change of the refrigerant | coolant in the heat pump used for the heat recovery system of the boiler blow water which concerns on this invention.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a configuration diagram of a heat recovery system for boiler blow water according to the present invention, and FIG. 2 is a Mollier diagram showing changes in refrigerant state in a heat pump used in the heat recovery system.

  The heat recovery system shown in FIG. 1 pumps up the heat of blow water discharged from the boiler 1 by a heat pump 2, and heats (preheats) the supply air (combustion air) to the boiler 1 by the heat. A blow water introduction pipe 3 extends from the boiler 1, and the blow water introduction pipe 3 is opened at an upper portion of a blow tank 4 for storing blow water. In the boiler 1 according to the present embodiment, supply air (combustion air) is supplied by the fan 5, and fuel (oil or gas) is injected into the supply air to mix a predetermined air-fuel ratio (A / F). Gas is formed, and this air-fuel mixture burns in the combustion section of the boiler 1, thereby generating a predetermined temperature and a predetermined amount of steam in the boiler 1.

  A blow water discharge pipe 6 extends from the blow tank 4, and a drain pump 7, a carbon dioxide suction part 8, and a reaction cylinder 9 are provided in the blow water discharge pipe 6. A gas blowing pipe 11 extending from the carbon dioxide gas cylinder 10 is connected between the drain pump 7 of the blow water discharge pipe 6 and the carbon dioxide suction section 8. Here, the carbon dioxide suction part 8, the reaction cylinder 9, and the carbon dioxide cylinder 10 constitute a neutralizer 12.

  The heat pump 2 is basically configured by connecting a compressor 13, a condenser 14, an expansion valve 15 as a decompression means, and an evaporator 16 by refrigerant pipes L1, L2, L3, and L4. The evaporator 16 and the blow tank 4 are connected by blow water pipes 17 and 18, and a circulation pump 19 is provided in one blow water pipe 17. The condenser 14 is installed in an air supply passage through which air is supplied to the combustion section of the boiler 1. In the present embodiment, a chlorofluorocarbon-based HCFC (R-22) is used as the refrigerant circulating in the heat pump 2.

  Thus, when the boiler 1 is operated and steam is generated, impurities such as minerals and alkaline agent in the boiler water are concentrated, so that a part of the concentrated high boiler water is introduced as blow water. It is introduced from the tube 3 into the blow tank 4 and stored. The boiler water remaining in the boiler 1 is diluted with makeup water to maintain a predetermined water quality.

  The high-temperature blow water stored in the blow tank 4 is introduced from the blow water pipe 17 to the evaporator 16 of the heat pump 2 by the circulation pump 19 and cooled by heat exchange with the refrigerant here. That is, as will be described later, since the heat held in the blow water is taken away as latent heat of evaporation of the refrigerant in the evaporator 16, the blow water is cooled, and the cooled blow water returns to the blow tank 4 through the blow water pipe 18. Thereafter, the same operation is repeated, and the blow water in the blow tank 4 is sequentially cooled.

  The blow water in the blow tank 4 cooled as described above is pumped up by the drain pump 7 and flows through the blow water discharge pipe 6. In the process, carbon dioxide supplied from the carbon dioxide gas cylinder 10 through the gas blow pipe 11 is supplied. The gas is sucked into the carbon dioxide suction section 8, and the sucked carbon dioxide gas is brought into contact with the blow water in the reaction tube 9 and mixed with the blow water, and the alkaline alkaline blow water having a pH of about 11 is neutralized to have a pH of 5 Neutralized to about ~ 9. In this case, since the blow water is cooled and the temperature thereof is lowered, the carbon dioxide gas is efficiently absorbed into the blow water. In the present embodiment, blow water having a temperature of 80 ° C. is cooled to a temperature of 40 ° C.

  Then, the blow water neutralized with carbon dioxide gas in the neutralizer 12 is discharged from the reaction tube 9 through the blow water discharge pipe 6.

  On the other hand, in the condenser 14 of the heat pump 2, the supply air that passes through the condenser 14 is heated (preheated) by the heat of condensation of the refrigerant, and this heated supply air is supplied to the boiler 1 to be used for forming an air-fuel mixture. . In the present embodiment, the supply air at a temperature of 20 ° C. is heated to a temperature of 36.5 ° C.

  Here, the state change of the refrigerant in the heat pump 2 will be described based on the Mollier diagram (Pi diagram) shown in FIG.

When the compressor 13 is driven by an electric motor (not shown), the gas refrigerant (temperature 20 ° C.) in the state (pressure P ₁ , enthalpy i ₁ ) shown in FIG. It becomes a high-temperature (70 ° C.) and high-pressure gas refrigerant in the state indicated by b (pressure P ₂ , enthalpy i ₂ ) (compression stroke), and this gas refrigerant is introduced into the condenser 14 through the refrigerant pipe L1. Note that the compression power W (calorie conversion) of the compressor 13 at this time is represented by (i ₂ −i ₁ ), and in this embodiment, W = 30 kJ / kg.

In the condenser 14, the high-temperature (70 ° C.) and high-pressure gas refrigerant releases the condensation latent heat Q ₂ to the supply air to heat (preheat) the supply air, and the state changes from b to c in FIG. 2 (phase change). Then, it is liquefied (condensation process) and becomes a high-pressure liquid refrigerant (temperature 20 ° C.) in a supercooled state (pressure P ₂ , enthalpy i ₃ ) shown in FIG. Incidentally, the condensation latent heat _{Q 2} of the refrigerant at this time is represented by _(i 2 -i _3), in this embodiment a _Q 2 = _190kJ / kg, the supply air temperature 20 ° C. This condensation latent heat _{Q 2} Is heated (preheated) to a temperature of 36.5 ° C.

The high-pressure liquid refrigerant liquefied and supercooled in the condenser 14 as described above passes from the condenser 14 through the refrigerant pipe L2 to the expansion valve 15 and is reduced in pressure by passing through the expansion valve 15 to be adiabatic expansion (isoenthalpy). 2) (expansion stroke), the state changes to the state of c → d (pressure P ₁ , enthalpy i ₃ ) in FIG. 2, and a part thereof is gasified. The partially gasified refrigerant (temperature 20 ° C.) is introduced into the evaporator 16 through the refrigerant pipe L3, evaporated and superheated by blowing water while passing through the evaporator 16 deprives vaporization latent heat Q ₁ ( (Evaporation process), the gas refrigerant in the state of d → a (pressure P ₁ , enthalpy i ₁ ) in FIG. At this time, the latent heat of vaporization Q ₁ of the refrigerant is expressed by (i ₁ −i ₃ ). In this embodiment, Q ₁ = 160 kJ / kg, and the latent heat of vapor Q ₁ cools the blow water having a temperature of 80 ° C. The temperature drops to 40 ° C.

Thus, the gas refrigerant (temperature 20 ° C.) evaporated in the evaporator 16 is guided to the compressor 13 through the refrigerant line L4, and is compressed again by the compressor 13 as described above. Thereafter, the same operation as described above is performed. The blow water is repeatedly cooled and the supply air is heated (preheated). The coefficient of performance (COP) of the heat pump 2 according to the present embodiment is Q _{2 /} W = 190 (kJ / h) / 30 (kJ / h) = 6.3.

As described above, in the present embodiment, blow water having a temperature of 80 ° C. discharged from the boiler 1 is cooled to a temperature of 40 ° C. by heat exchange with the refrigerant in the evaporator 16 of the heat pump 2 (the latent heat of vaporization Q _{1 of the} refrigerant). As a result, it is not necessary to cool the blow water with a large amount of cooling water as in the prior art, so that no cooling equipment is required and equipment costs can be reduced. The heat recovery amount Q from the blow water at this time is expressed by the following equation using the flow rate G (= 250 kg / h) of the blow water, the specific heat c (= 1 kJ / kg ° C.), and the temperature difference ΔT (= 40 ° C.). expressed.

Q = G × c × ΔT = 250 (kg / h) × 1 (kJ / kg ° C.) × 40 (° C.)
= 10000 kJ / h = 11.6 kW (1)
Furthermore, because of the by condensation heat Q ₂ of the refrigerant in the condenser 14 of the heat pump 2 to heat the supply air (combustion air) to the boiler 1 (preheat) required for generating a predetermined temperature and a predetermined amount of steam The combustion energy is reduced, the fuel cost is reduced accordingly, and the operating cost of the boiler 1 is reduced.

  Here, the amount of heat Q recovered from the blow water (= 10000 kJ / h), the temperature rise ΔT of the supply air at a temperature of 20 ° C., the flow rate G of the supply air (= 2515 kg / h), the specific heat c of the air (= 0.241 kJ / h) kg kg)), the following equation holds:

Q = G × c × ΔT (2)
Therefore, the temperature increase ΔT of the supply air can be obtained by the following equation from the equation (2).

ΔT = Q / (G × c)
= 10000 (kJ / h) / (2515 (kg / h) × 0.241 kJ / kg ° C.))
= 16.5 ° C (3)
Accordingly, the supply air at a temperature of 20 ° C. is heated (preheated) to a temperature of 36.5 ° C. by heat exchange with the refrigerant in the condenser 14.

  Next, when the increase / decrease in the operating cost of the boiler 1 when using the boiler blow water heat recovery system according to the present invention is calculated, it is as follows.

Since the calorific value of the fuel is 9700 kcal / m ³ N, the amount of heat recovered from the blow water is 10000 kJ / h (see formula (1)), and the fuel is saved by the amount obtained by the following formula.

10,000 (kcal / h) / 9700 lcal (kcal / m ³ N) = 1.03 m ³ N / h
If the unit price of fuel is 60 yen / m ³ N, the fuel efficiency is
60 yen ^{/ m 3 N × 1.03m 3 N} / h = 61.8 yen / h ... (4)
Only saved.

  On the other hand, the electric power necessary for driving the compressor 13 of the heat pump 2 is expressed as the following equation from the heat recovery amount Q (= 11.6 kW (electric power conversion)) from the blow water and the coefficient of performance (COP) = 6.3. Is required.

11.6kW / 6.3 = 1.84kW
If the unit price of electricity charges is 15 yen / kWh,
15 yen / kWh × 1.84 kW = 27.6 yen / h (5)
Only increase.

Therefore, from the equations (4) and (5), the operating cost of the boiler 1 is
61.8 yen / h-27.6 yen / h = 34.2 yen / h (6)
Will only go down.

  In the present embodiment, since carbon dioxide gas is blown into blow water whose temperature has been lowered to 40 ° C. by heat exchange with the refrigerant in the evaporator 16 of the heat pump 2 in the neutralization device 12, the carbon dioxide gas is blown water. It is also possible to obtain an effect that the blow water is neutralized efficiently.

  In this embodiment, the carbon dioxide gas filled in the carbon dioxide gas cylinder 10 is used for neutralizing the blow water. However, the exhaust gas discharged from the boiler 1 is blown into the blow water, and the carbon dioxide contained in the exhaust gas. You may make it neutralize blow water with gas.

DESCRIPTION OF SYMBOLS 1 Boiler 2 Heat pump 3 Blow water discharge pipe 4 Blow tank 5 Fan 6 Blow water discharge pipe 7 Drain pump 8 Carbon dioxide suction part 9 Reactor 10 Carbon dioxide cylinder 11 Gas blow pipe 12 Neutralizer 13 Compressor 14 Capacitor 15 Expansion valve 16 Evaporator 17, 18 Blow water pipe 19 Circulation pump L1-L4 Refrigerant piping

Claims (1)

A heat recovery system for boiler blow water that pumps the heat of blow water discharged from the boiler by a heat pump and heats the supply air to the boiler by the heat,
The blow water discharged from the boiler is introduced and stored in the blow tank without going through the cooling heat exchanger,
The blow water stored in the blow tank is circulated to the evaporator of the heat pump and cooled by heat exchange with the refrigerant in the evaporator of the heat pump, and the supply air to the boiler is heated by the heat of condensation of the refrigerant in the condenser of the heat pump And
The blow water in the blow tank cooled by heat exchange with the refrigerant in the evaporator of the heat pump is sent to a neutralizer through a drainage pump, and mixed with carbon dioxide from a carbon dioxide cylinder to neutralize. Boiler blow water heat recovery system.

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