JPS6073204A - Coal-water slurry combustion apparatus - Google Patents

Abstract

PURPOSE:To decrease the quantity of supplying water to a system, and the power consumption for an induced fan, by decreasing the wet rate and the volume of exhaust gas, as well as to recover circulating liquid by a cooling pipe while it is circulating through the absorption tower of a desulfurizer, in a boiler system for combustion of coal-water slurry, combined with an exhaust gas desulfurizer of wet type. CONSTITUTION:Exhaust gas generated in a boiler 1 is led into the cooling tower 3 of a wet type exhaust gas desulfurizer, after the temperature in the gas is lowered down to about 80 deg.C by a gas . gas heat exchanger 9. The gas is cooled by cooling water which is circulating through the cooling tower 3 by a circulating pump 4, and then the gas is led into an absorption tower 5, where sulfurous acid in the gas is absorbed by lime- water slurry fed into the absorption tower 5. The purified exhaust gas is heated again in the gas . gas heat exchanger 9 in order to prevent white smoke, and is exhausted outside from a stack 10. In this case, the quantity of cooling water circulated by the pump 4 can be saved by the method of cooling slurry by dipping a cooling pipe 7 in the slurry in the absorption tower 5. Besides, the consumption of power for an induced fan can be saved as much as the volume corresponding to the decreased exhaust gas, by installing an induced fan 2 on the downstream side of an exhaust gas desulfurizer.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a coal-water slurry combustion apparatus, and more particularly to a coal-water slurry combustion apparatus for reducing the amount of make-up water and the power consumption of a blower.

Recently, the use of coal as a fuel instead of oil has become active, mainly in thermal power plants. However, coal itself is a solid fuel and is difficult to handle, so transportation costs are high, and this has a large impact on the price of coal. Therefore, the development of technology for handling coal by turning it into a fluid is actively underway. One method is to use COM (Coal
and Oi 1 'M i x t u r e
) However, in the case of COM, the weight ratio of coal to heavy oil is approximately 1:1, so it cannot be said to be a perfect membrane oil fuel, and the cost is low in terms of price. Furthermore, methacol, which is a mixture of methanol and coal, is expensive and has not yet reached the practical stage.

In contrast, CWM (Coa
and Water MixturC) is quite practical in terms of price and has recently been gaining attention. C.W.M.
It is preferable that the water content in the CWM be lower than 1, from the point of view of make-up water supply cost and wheeler efficiency. There is also the problem that pressure loss increases. Recently, C.
'Development of technology to reduce the water content in WM is progressing, and the water content has now reached approximately 30%.

To produce CWM with a moisture content of 30% using 1 kg of coal, 0.33 kg of water is required, but when generating 1 million KWH of thermal power per hour, the amount of coal used is 1.01 million KWH. A large amount of make-up water of 33,001 tons is required to convert 9 tons into CWM.

When CWM is combusted, a flue gas desulfurization device is usually installed in order to generate sulfur dioxide gas, similar to coal combustion.

Although various types of flue gas desulfurization equipment are used, wet type flue gas desulfurization equipment is currently the mainstream. In the so-called limestone-gypsum flue gas desulfurization equipment that absorbs sulfite scum using a limestone-water slurry, 0.32 kg of make-up water is required to treat the flue gas generated from 1 kg of coal. is 1 million KW as mentioned above
If applied to thermal power generation, 3,200 tons of make-up water would be required per day.

Therefore, considering both CWM production and flue gas desulfurization, a large amount of make-up water of 6,500 tons per day is required, but from the perspective of securing water resources, which is becoming increasingly difficult every year.
Reducing the amount of make-up water is an important technological development issue.

Another problem when burning CWM with a moisture content of 30% is that as the moisture in the CWM evaporates, the amount of flue gas increases by approximately 6% compared to the case of pulverized coal combustion. The capacity and power consumption of the blower increases.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the drawbacks of the prior art described above and to provide a coal-water slurry combustion apparatus that requires less make-up water and less power consumption of an induced blower.

As a result of intensive research into a method for recovering water from a coal-water slurry combustion equipment equipped with a flue gas desulfurization device, the present inventors have found that the total amount of make-up water for CWM production and flue gas desulfurization can be reduced by approximately 50% compared to conventional methods. We have developed a technology that can reduce this by 30%.

In short, the present invention provides a coal-water slurry combustion boiler and a wet υ
1 In a system that combines smoke desulfurization equipment, water is recovered by cooling the liquid circulating in the absorption tower of the desulfurization equipment, and at the same time, the flue gas is dehumidified and its volume is reduced, thereby increasing the amount of water supplied to the system and the attraction This reduces the power consumption of the blower.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be explained in detail with reference to the drawings in comparison with the prior art.

FIG. 1 shows an example of a coal-water slurry combustion boiler system constructed using the conventional technology. The flue gas generated in the boiler 1 passes through the induced fan 2 and is sent to the gas-gas heat exchanger 9 at approximately 80%
After cooling down to °C, it is supplied to the cooling tower 3 of the wet flue gas desulfurization equipment. Here, the flue gas is further cooled to 40 to 60°C by the cooling liquid circulating through the cooling tower circulation pump 4, and then the sulfur dioxide gas in the flue gas is absorbed by the limestone-water slurry introduced into the absorption tower 5. The purified flue gas is reheated in a gas-to-gas heat exchanger 9 to prevent white smoke, and then is discharged from a chimney 10. As described above, this method has the disadvantage that the amount of make-up water to the cooling tower 3 and the absorption tower 5 is large, and the power consumption of the induced blower 2 is large.

FIG. 2 shows a similar boiler system illustrating an embodiment of the present invention, except that the limestone-water slurry in the absorption tower 5 is different from the prior art system of FIG. The absorbent cooling pipe 7 is immersed in the slurry to cool the slurry, and the induced blower 2 is installed between the gas-gas heat exchanger 9 and the chimney 10 on the downstream side of the flue gas desulfurization device 5.

In the present invention, the limestone-water slurry in the absorption tower is cooled for the following reasons. In other words, if you try to cool the circulating fluid in the cooling tower 3 instead of the absorption tower,
This circulating fluid becomes acidic with an I)H value of 0.5 to 7.0 due to contact with the acidic gas sent from the boiler, which corrodes the metal heat transfer surface of the cooling heat exchanger and reduces the lifespan of the equipment. This causes the problem that the length becomes shorter. In addition, even if you try to prevent corrosion by lining the heat transfer surface with synthetic resin, etc.
Not only does the cost increase, but the heat transfer coefficient as a heat exchanger decreases, making it impossible to exhibit sufficient cooling performance. Another problem with cooling the cooling tower circulating fluid is that even if the cooling tower circulating fluid is cooled to a temperature lower than that of the limestone-water slurry, the moisture in the limestone-water slurry in the absorption tower is As a result, the exhaust gas becomes humid, which is contrary to the purpose of the present invention. On the other hand, the limestone-water slurry on the absorption tower side has a pH value of 5.5 to 5.5 due to the limestone.
9.0, which is close to neutral, so there is no risk of corrosion on the heat transfer surface of the heat exchanger for cooling this liquid. Furthermore, since the absorption liquid in the absorption tower 5, which is the most downstream part of the system that makes contact with gas and liquid, is cooled, the amount of moisture carried out of the system by the flue gas is reliably reduced. From the above, it can be seen that the cooling of flue gas for water recovery and reduction of flue gas volume is preferably carried out by the limestone-water slurry of the circulating fluid in the absorption tower, rather than by the circulating fluid of the cooling tower. The cooling method is preferably indirect cooling using a cooling fluid such as seawater or river water, but is not limited thereto.

In the example of FIG. 2, the limestone-water slurry is sprayed from the top of the absorption tower 5, and simultaneous transfer of heat and water vapor occurs on the droplet surface and on the surface of the liquid film formed on the device wall. Droplet size, velocity, density,
As a result of experiments conducted by changing the temperature of the gas and the droplet, and the gas flow rate, the amount of heat transferred around the droplet was determined by the enthalpy difference between the gas and the droplet,
It was proved that hg-hd (k c a 1 /cJ) is expressed by the following equation as the driving force.

Here, qd: heat transferred from the gas to the droplet it (k c
a l /5) Red: Reynolds number (-) Sc: Schmidt number (-) γg: Specific weight of gas (cn+/%) I): Diffusion coefficient (rrr/S) d: Droplet diameter (m) Ad: Droplet surface area Transfer heat between gas and vertical plane 1iqfs (kcal/
s) is expressed by the following formula.

Here, Res: Raynozzle number of membrane (-) ds: Iq length (m) As: membrane area (bo).

hfs: membrane enthalpy (k c a 1 /cJ) The amount of heat transferred between the gas and the horizontal plane qfb (kcal/S) is expressed by the following formula.

Here, ■g: gas velocity (m/S) Ab: membrane area (
rrr) hfb: IIQ enthalpy (k a l /ci)
Using equations (1) to (3), the change in gas enthalpy and the amount of heat transferred can be calculated, and the temperature of the gas that is in equilibrium with this can be determined.

The above are the results of basic experiments, but in an experiment using a pilot plant conducted separately from this, it was proven that stage loads based on formulas (1) to (3) are possible.

The greater the amount of cooling for the limestone-water slurry, the greater the amount of water recovered. As an example, when the slurry is cooled by 10°C, the amount of recovered water is 0.32 kg per 1 kg of coal, and C
Total supplement for WM production and flue gas desulfurization.

The amount of water supplied will be 51% of that of the conventional method. Moreover, this makes it possible to secure water equivalent to make-up water for the desulfurization equipment. This amount is equivalent to saving 73,200 tons of water per day for 1 million KW of thermal power generation.

If the limestone-water slurry is cooled by 10°C as described above, and if it is combusted so that the oxygen concentration in the flue gas becomes 3%, the volume of flue gas will be reduced by 8% compared to the conventional method. . Therefore, by installing the induced blower 2 on the downstream side of the υ1 smoke desulfurization device, it is possible to reduce the power consumption of the induced blower commensurate with this reduction in the exhaust gas volume. In addition, when a gas-gas heat exchanger 9 is installed as shown in Fig. 2, it is better to install an induced blower LJ on the downstream side of this heat exchanger.
Less chance of dew point corrosion.

The method of cooling the limestone-water slurry is not limited to immersing the cooling pipe 7 in the slurry in the cooling tower, but may be cooled with an external cooler, for example.

FIG. 3 shows another embodiment of the present invention, in which the limestone-water slurry is absorbed into the absorption liquid installed between the absorption tower circulation pump 6 outlet and the absorption tower 5 in the absorption key circulation system. In the cooler 8, it is indirectly cooled by a cooling body such as seawater. According to this embodiment, in addition to the above effects,
Since the absorption tower cooler 8 is a dedicated heat exchanger, it is possible to optimize the flow of the cooling body and slurry, and an economical design can be achieved.

As described above, according to the present invention, the following effects are achieved.

(1) By cooling the slurry circulating in the absorption tower of the wet flue gas desulfurization equipment in the system that burns limestone-water slurry,
As well as recovering water from the flue gas, the flue gas can be dehumidified and reduced in weight, thereby reducing the amount of make-up water to the system by, for example, about 50%.

(2) By installing the induced blower in the system through which the reduced exhaust gas passes, the power consumption thereof can be reduced by about 8%, for example.

(3) By dehumidifying the flue gas, corrosion of the duct and equipment on the downstream side of the flue gas desulfurization device can be reduced.

[Brief explanation of the drawing]

Fig. 1 is a system diagram of a coal-water slurry combustion boiler system according to the prior art, and Fig. 2 shows an embodiment of the present invention, in which limestone-water slurry in an absorption tower is cooled. , Coal with an induced blower installed downstream of the flue gas desulfurization equipment.
FIG. 3, a system diagram of a water slurry combustion boiler system, shows another embodiment of the present invention, and shows a similar system in which a limestone-water slurry is cooled between an absorption tower circulation pump and an absorption tower. It is a system diagram. 1... Boiler, 2... Induced blower, 3... Cooling tower, 4... Cooling tower circulation pump, 5... Absorption tower, 6...
・Absorption tower circulation pump, 7... Absorption liquid cooling pipe, 8...
Absorption liquid cooler, 9... Gas-gas heat exchanger, 1o...
·chimney. Agent Patent Attorney Takenaga Kawakita

Claims (1)

[Claims] (1) A furnace for burning a coal-water slurry, a wet flue gas desulfurization device equipped with a cooling tower and an absorption tower, installed in the exhaust gas flow path of the furnace, and means for cooling the circulating liquid of the absorption tower. A coal-water slurry combustion device comprising: (2. A coal-water slurry combustion device according to claim 1, characterized in that a flue gas induced blower is installed downstream of the wet flue gas desulfurization device.