JPH0626310A - Waste heat recovery method in wet sulfurization system - Google Patents

Abstract

PURPOSE:To provide a method of recovering low temperature level heat energy in exhaust gas or slurry from a wet exhaust gas desulfurization system as electricity while economizing make-up water. CONSTITUTION:The exhaust gas 21 of a generator boiler is desulfurized by a desulfurizer 2, and the exhaust gas or slurry is led into an indirect type heat exchanger 4 to vaporize a heat exchanger medium 28-1. The vaporized medium 23 is made into hot vapor 24 using extraction steam 26-1, -2, -3, -4 from the generator boiler and supplied into a binary generator tubine 10 to generate power.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering flue gas discharged from a desulfurization unit of a wet flue gas desulfurization system or a waste heat of a slurry generated in the unit and utilizing it for power generation. It also aims to save the makeup water of the system.

[0002]

2. Description of the Related Art Exhaust gas from a power generation boiler of a power plant is usually introduced into a wet desulfurization system after heat recovery by an economizer, denitration treatment, indirect exhaust gas cooling by an air heater, and removal of fly ash by a low-temperature electrostatic precipitator. , The gas-gas heater, indirect cooling with water, adiabatic humidification cooling with water, desulfurization with a wet desulfurization system, etc. are sequentially processed and cooled, and at the same time harmful compounds such as sulfur-containing compounds are removed and then discharged from the chimney. It That is, the boiler flue gas is about 100 ° C. after indirect cooling by the gas-gas heater of the desulfurization system, about 50 ° C. after adiabatic humidification, and the flue gas after desulfurization and the desulfurizer absorption liquid slurry are also 50%. It has a temperature around ℃.

[0003]

[Problems to be Solved by the Invention] By the way, along with the recent increase in the demand for electric power, the unit capacity of power generation is changed from the conventional 2000MW to 500MW.
MW, 7,000 MW, and 1000 MW are gradually becoming larger, and along with that, the amount of water used per unit, the amount of wastewater, the amount of solid waste, etc. are expanding quantitatively,
The measures are also qualitatively different from those in small scale.

For example, in terms of water, a boiler wet flue gas desulfurization device is a device that requires an extremely large amount of make-up water, and when the evaporative water make-up water is 4/4 ECR 200 MW power generation plant, it is about 1 hour / hour. What was 21 tons is about 105 tons per hour at 1000 MW. In addition, the amount of make-up water for drainage increases from about 5 tons per hour at 200 MW to about 25 tons per hour at 1000 MW, although it varies depending on the chlorine-containing or fluorine-containing amount of the fuel coal type.
Therefore, with only make-up water of the desulfurizer, it reaches about 130 tons per hour
In order to ensure the stable supply of this amount of water, even if the construction site of the power plant is often selected, it is no longer possible to rely solely on the supply from the local government. Inevitably, there is an urgent need to rationalize and reduce the amount of water used in power plants.

A further serious problem associated with the expansion of power generation scale is that the flue gas discharged after the boiler flue gas is introduced into the wet desulfurization system or the slurry produced at that time is at a low temperature level of about 50 ° C., but is relatively large. To have thermal energy. Despite the poor utilization efficiency of such low-temperature thermal energy, only the amount of smoke and slurry increases with the expansion of power generation scale.
The total amount of heat energy they have is becoming enormous when accumulated.

For example, the amount of heat energy of wet desulfurization water saturated flue gas at a power generation scale of 700 MW at 43 ° C. or higher is about 30 million kcal / hour, and at 1000 MW base is about hourly.
It is estimated to reach 42.6 million kcal. While there is a demand for efficient recovery of low-temperature level thermal energy, how to deal with an increase in make-up water to the wet desulfurization device has been an issue.

[0007]

The inventors of the present invention introduced flue gas discharged from a wet desulfurization system or an absorption liquid slurry of about 50 ° C. generated in the desulfurization system into an indirect heat exchanger, A huge low-temperature level of heat is recovered as vapor by evaporating the heat exchange medium (refrigerant) that circulates in the exchanger to form vapor, and this vapor is further heated to become superheated vapor, which is converted into a binary power generation turbine. At the same time as supplying and generating electricity, the condensed water generated by cooling the flue gas is recovered and reused as desulfurization equipment or other make-up water, or in the case of slurry, the slurry whose temperature has been lowered by heat exchange is returned to the desulfurization equipment. By recirculating, the temperature of the slurry in the desulfurizer is lowered to reduce the amount of water vaporized during desulfurization to reduce the make-up water,
It was found that the above problems can be solved at the same time.

That is, in the present invention, when recovering the waste heat from the wet flue gas desulfurization system, 1) the flue gas discharged from the desulfurization device of the wet flue gas desulfurization system or the slurry of about 50 ° C. generated in the device is used. It is introduced into an indirect heat exchanger, and 2) the heat exchange medium circulating in the heat exchanger is evaporated by heat exchange to form a vapor, and 3) the vapor is further heated by using bleed air from a power generation boiler. The present invention relates to a method for recovering waste heat from a wet flue gas desulfurization system, characterized in that it does not use superheated vapor, and 4) it is supplied to a turbine for binary power generation to generate power.

The wet desulfurization apparatus referred to in the present specification refers to an absorbent containing a calcium-based absorbent as a flue gas for the purpose of removing sulfur-containing compounds in boiler flue gas, especially sulfurous acid gas, from the flue gas. It is a device to contact. The flue gas after desulfurization in contact with the absorbing liquid contains heat generated as reaction heat when fixing the sulfurous acid gas and is accompanied by saturated steam of the temperature, and both of the generated slurries have a relatively low temperature level of about 50 ° C. Possesses thermal energy.

When these flue gas or slurry is introduced into an indirect heat exchanger, the heat exchange medium circulating in the heat exchanger is evaporated at around 40 ° C., and at the same time, the flue gas or slurry itself is cooled. Produces a relatively large amount of condensed water, which is recovered and reused. Further, in the case of slurry, the cooled slurry is circulated and used in the wet desulfurization apparatus, so that it is possible to reduce the amount of water vaporized during desulfurization, which also contributes to the saving of water.

The indirect heat exchanger used in the present invention is not required to have high heat resistance because the introduced smoke or slurry has a relatively low temperature. Therefore, there is no definite limiting factor other than the indirect type. For flue gas, a flue tube group built-in tube (bare tube or finned), economizer type, etc. can be used as appropriate. The pipe is a 2 to 3 ° oblique pipe in the cross-flow position with respect to the flow of smoke, the inner pipe is the evaporation of the medium, the outer pipe is a finned or bare pipe and is an economizer type that is built in the flue, or an absorbing liquid. In the case of a slurry, it is desirable to use a vertical sleeve type and a single-pass type sleeve type of the absorbing liquid slurry on the inner pipe side.

The heat exchange medium usable in the present invention includes alkanes, freons and freons (dunes) having 2 to 5 carbon atoms.
(Ponto's product), ammonia and other commonly used heat exchange media are used, but they are well used as a binary power generation heat exchange medium because they vaporize at 40 ° C and 5.2 kgf / cm ² and increase the enthalpy with temperature rise. Most preferred is isobutane.

The low-temperature level heat energy is recovered as evaporation latent heat by the heat exchange medium, but since the heat exchange medium vapor is very inefficient for driving the power generation turbine as it is, the boiler bleed air is mainly used to extract the bleed air. The most economical combination of acquisition location and quantity shall be used.
Preferably, the temperature is raised by utilizing the third to sixth bleed air, and after being made into a superheated vapor, it is introduced into a binary power generation turbine,
Generate electricity and collect it as electricity. The heat exchanger for heating the medium vapor is a box type with inner tube steam heating and outer tube fins.
(Elofin type) or fin type heat exchanger is used, and the most economical structure can be adopted. The heating of the vapor optimizes the boiler bleed air, and the steam condensate is recirculated to the boiler bleed air extraction section.

Further, in the present invention, the medium vaporized by heat exchange is preliminarily heated by using the high temperature exhaust gas in the duct upstream of the humidifying section, and then further heated by the boiler bleed air and introduced into the power generation turbine. You can also The medium vapor vaporized by heat exchange is introduced into a binary power generation turbine to generate power, then condensed in a condenser by seawater cooling, stored in a medium liquid tank, buffering the load, and corresponding the liquid heat exchange medium to the load. And recirculate to the indirect heat exchanger. In the method according to the present invention, the flue gas or the slurry, or both of them can be subjected to heat exchange.

[0015]

The waste heat recovery method of the present invention will be described with reference to the drawings. 1 is a flow diagram showing a method for recovering waste heat from flue gas, and FIG. 2 is a flow diagram showing a method for recovering waste heat from slurry. Example 1 A method for recovering waste heat from flue gas of a wet desulfurization system will be described with reference to FIG.

The flue gas 21 introduced into the humidifying / cooling unit 1 is cooled there by humidifying and is lowered in temperature to about 50 ° C., and then desulfurized by contacting with a calcium-based absorbent in the wet desulfurization device 2. Then, it is guided to the indirect heat exchanger 4 and cooled to about 43 ° C. The smoke discharged from the desulfurization device 2 has its mist removed by the mist eliminator 3 and the heat exchange medium 28-1 is circulated. Vertical vertical economizer type indirect heat exchanger 4 (heat transfer pipe part 15 m × 15 m × 15 m) Where the heat exchange medium isobutane is vaporized. At that time, the flue gas itself is cooled and the associated water vapor is condensed, and the condensed water 27 is collected in the condensed water tank 17 by the condensed water pump 16 and re-constituted as makeup water for the humidification cooling unit 1 and the desulfurization device 2. Used. On the other hand, the heat exchange treated flue gas 22 is heated by the gas-gas heater after the mist is removed, guided to the chimney, and released into the atmosphere.

The isobutane vapor 23 vaporized in the heat exchanger 4 is the third to sixth extraction airs 26-1, 26-2, 26-2 from the boiler.
Heaters 7-1, 7-2, 7-using 26-3, 26-4
It is sequentially heated by 3, 7-4 and becomes the superheated vapor 24 and is sent to the binary power generation turbine 10, where it is converted into power and converted into electricity by the generator 11. Isobutane vapor discharged from the binary power generation turbine 10 is cooled and condensed by the seawater 29 in the condenser 12, the condensate 25 is sent to the condensate receiving tank 13, and then as the heat exchange medium 28-1 by the heat exchange medium transfer pump 14. It is recirculated to the heat exchanger 4.

The steam condensate produced when superheated using the third to sixth bleed air from the boiler is collected in the steam condensate receiving tanks 8-1, 8-2, 8-3, 8-4, and then by the pump 9, respectively. Recirculated to the extraction section of the boiler. Medium 28 not evaporated in heat exchanger 4
-2 is transferred from the bottom by the heat exchange medium circulation pump 5, the condensed water cooler 6 cools the condensed water, and it is introduced into the vapor separator of the heat exchanger. The condensed water cooled by the cooler 6 is introduced to the top of the heat exchanger 4 and sprayed uniformly, and flows down to help increase the cooling efficiency of the heat exchanger 4.

Wet desulfurization equipment of a 700 MW base power plant Absorber treatment The temperature of the flue gas after indirect cooling of the flue gas is about 43.
In the case of ℃, the amount of heat energy recovered from flue gas in an indirect heat exchanger is estimated to be about 30 million kcal / hour, and when this heat energy is recovered by evaporative vaporization of isobutane, the isobutane vapor produced is about It is estimated to be 460 tons and the condensed water collected at that time is about 50 tons per hour.

This binary vapor is superheated up to 160 ° C. by the third to sixth extraction air which is a surplus heat source of the boiler, the binary turbine is driven to generate electricity, and the vapor after passing the turbine is condensed with seawater (condensing temperature maximum 28 ° C. ), When operating the binary power generation cycle, the efficiency of the binary turbine is 70%, the efficiency of the generator is 95%, and the in-house power cost of the related equipment including the binary power generation cycle (cooling water, circulation pump, etc.) Assuming about 30% 15 per hour
Power of 500kw can be obtained.

Boiler bleed steam for overheating is per ton
At 1100 yen, about 40 tons of steam is used every hour, so a steam cost of 1100 yen / ton x 40 tons / hour = 44000 yen / hour will be required. Assuming that the unit price of electricity is 12 yen per kilowatt hour, the electricity cost of 15500 kw per hour is 186,000 yen / hour, and it is estimated that 142,000 yen / hour will be surplus when steam costs are subtracted.

In this way, the low temperature heat energy of the flue gas of the wet desulfurizer was effectively recovered, and at the same time, a considerably large amount of makeup water could be recovered. Example 2 A method for recovering waste heat of slurry from a wet desulfurization system will be described with reference to FIG. The slurry 30 from the wet desulfurization device 2 is sent by a slurry circulation pump 18 to a vertical tube type indirect heat exchanger 4 (tube is tube, tube side single pass). Therefore, in order to prevent the occurrence of scaling on the inner pipe side, the slurry is made to flow down at a flow rate of 2.5 m / s, and the heat exchange medium isobutane 28-1 is introduced to the outer pipe side to use isobutane as a vaporization vapor. In this case, the temperature difference between the inside and outside of the heat transfer tube was 25 ° C.

The vaporized isobutane 23 was used as a superheated vapor in the same manner as in Example 1 to recover heat energy as electricity. Slurry cooled by heat exchange
No. 30 was recirculated to the desulfurization apparatus 2 again to lower the slurry temperature of the desulfurization apparatus, and to reduce the amount of water that accompanies flue gas, so that make-up water could be saved.

[0024]

According to the method of the present invention, the flue gas discharged from the desulfurization unit of the wet flue gas desulfurization system or the low-temperature level heat energy of the slurry generated in the unit can be effectively recovered and reused and condensed. Reuse of water or reduction of makeup water can also be achieved. Therefore, an industrially extremely valuable method is provided which can achieve effective use of thermal energy and reduction of water resources at the same time.

[Brief description of drawings]

FIG. 1 is a flow diagram showing waste heat recovery from flue gas from a wet desulfurization system.

FIG. 2 is a flow diagram showing waste heat recovery from slurry in a wet desulfurization system.

[Explanation of symbols]

1 Humidification cooling part 2 Desulfurization device 3 Mist eliminator 4 Indirect heat exchanger 5 Heat exchange medium circulation pump 6 Condensed water cooler 7-1, 7-2, 7-3, 7-4 Heat exchange medium vapor heater 8 1, 8-2, 8-3, 8-4 Steam condensate receiving tank 9 Steam condensate pump 10 Power generation turbine 11 Generator 12 Condenser 13 Heat exchange medium condensate receiving tank 14 Heat exchange medium transfer pump 15 Seawater pump 16 Condensation Water pump 17 Condensed water tank 18 Slurry circulation pump 21 Smoke exhaust 22 Heat exchange treatment flue gas 23 Heat exchange medium vapor 24 Overheat vapor 25 Heat exchange medium condensate 26-1, 26-2, 26-3, 26-4 Third ~ 6th extraction 27 Condensed water 28-1, 28-
2 Heat exchange medium 29 Seawater 30 Slurry

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[Procedure amendment]

[Submission date] July 24, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Correction content]

Further, in the present invention, the medium vaporized by heat exchange is preliminarily heated by using the high-temperature exhaust gas in the duct upstream of the humidification unit, and then further heated by the boiler bleed air to be introduced into the power generation turbine. You can also Also, if
Depending on the situation, the vaporized medium may be
After raising the pressure and temperature, heat it further by boiler extraction.
It can also be installed in a power generation turbine. The medium vapor vaporized by heat exchange is introduced into a binary power generation turbine to generate power, then condensed in a condenser by seawater cooling, stored in a medium liquid tank, buffering the load, and corresponding the liquid heat exchange medium to the load. In the method according to the present invention in which the heat is recirculated to the indirect heat exchanger, flue gas or slurry, or both of them can be subjected to heat exchange.

Claims (1)

[Claims] 1. A method for recovering waste heat from a wet flue gas desulfurization system, which comprises: 1) indirect heat of flue gas discharged from a desulfurization device of a wet flue gas desulfurization system or slurry produced in the device. 2) Introduced into the exchanger, 2) the heat exchange medium circulating in the heat exchanger is evaporated by heat exchange to form a vapor, 3) this vapor is further heated by using bleed air from the power generation boiler to become a superheated vapor And 4) A method for recovering waste heat from a wet flue gas desulfurization system, characterized in that it is supplied to a binary power generation turbine to generate electric power.