JPS5935963B2 - Effective use of combustion exhaust gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for effectively utilizing the heat of combustion exhaust gas to regenerate moisture-absorbing lithium chloride when moisture contained in furnace air is removed using a lithium chloride moisture absorbent. In particular, it is characterized in that heat exchange between the high temperature exhaust gas and the hygroscopic lithium chloride liquid is carried out through an air circulation loop.

When blowing air to blast furnaces and other furnaces, the moisture contained in it varies widely depending on the temperature, and if there is a lot of moisture in the air, it increases fuel costs and changes the furnace condition, so after removing moisture with a dehumidifier, It is usually fed into the furnace.

Although there are several types of moisture absorbents used in dehumidifiers, lithium chloride (LiC1) liquid moisture absorbent is widely used because it provides very effective moisture absorption.

Contact is provided between the lithium chloride solution and the furnace blast in a dehumidifier, and the moisture in the furnace blast is absorbed by the lithium chloride solution.

This is called wet absorption method. The lithium chloride solution that has absorbed moisture is circulated between the dehumidifier and the regenerator for reuse after regeneration.

In order to efficiently regenerate such a moisture absorbent, Japanese Patent Publication No. 55 24q3 discloses a method of effectively utilizing the heat of combustion exhaust gas from a hot stove.

The method disclosed herein is one in which combustion exhaust gas from a plurality of hot blast furnaces is introduced into a dehumidifying function regeneration section of a moisture absorbent in a dehumidifying device for air supplied to a hot blast furnace for a blast furnace, and the water-containing dehumidifying agent is heated and dehumidified. It is.

FIG. 1 shows a schematic flowchart, and the air blown to the blast furnace 1 is dehumidified by the dehumidifier 5 before being heated to a predetermined temperature in the hot blast furnace 3.

In the dehumidification device 5, air entering from one end of the device is dehumidified by sufficient contact with the lithium chloride liquid spray sprayed from the lithium chloride liquid spray vibro and exits from the other end of the device.

The moisture-absorbing lithium chloride accumulated at the bottom of the device is returned to the dehumidifying device 5 after releasing the absorbed moisture in the regenerating device 7.

The hygroscopic lithium chloride is reheated in a heat exchanger H before entering the regenerator.

The heat exchanger HK receives combustion exhaust gas from the hot stove,
The temperature of the lithium chloride, which has absorbed moisture through the heat exchange wall and reached a temperature of around 30°C, is raised to around 80°C.

The hygroscopic lithium chloride heated in the heat exchanger H (
It is introduced into the regenerator 7 together with separately supplied heated air, and at its inlet, it is flushed through the spray pipe 8 to evaporate the contained moisture.

The heated air aids in water evaporation. The separated water vapor is released outside the apparatus, and the recycled lithium chloride from which moisture has been removed is stored at the bottom of the regenerator and circulated to the dehumidifier as described above.

The above dehumidification method provides very effective furnace air dehumidification,
Although it is beneficial in terms of saving thermal energy, one drawback was recognized when it was actually operated.

That is, corrosion holes are formed in the heat exchange tube in the heat exchanger H.

The heat exchange tube of heat exchanger H is placed in a severe corrosive environment where one side is exposed to combustion exhaust gas and the other side is exposed to lithium chloride liquid.

Heat exchange walls were made of monel metal etc. to withstand lithium chloride, but trace amounts of SOx contained in combustion exhaust gas
, NOx, etc. caused corrosion.

In particular, the influence of SOx seems to be strong.

We have investigated materials that can withstand both SOx and lithium chloride, but so far no suitable material has been found.

The present invention provides heat exchanger H in the above process.
The purpose of this is to avoid the occurrence of corrosion holes in the heat exchange walls in the heat exchanger and ensure stable operation over a long period of time.

The present invention solves the above problems by avoiding direct heat exchange between the flue gas and the lithium chloride liquid, and by providing heat exchange between the two through the mediation of an air circulation loop.

That is, the action of recovering heat from the combustion exhaust gas in the first heat exchanger and the action of transferring heat to the lithium chloride liquid in the second heat exchanger are performed by the air circulating between the exchangers. be.

Preferably, the circulating air enters the first heat exchanger at a temperature of 80° C. or higher to avoid condensation of SOx.

The present invention will be described with reference to FIG. 2, which is shown as being the same as FIG. 1 except for the heat exchanger H.

In FIG. 2, two heat exchangers H1 and N2 are used, with an air circulation loop L interposed between the heat exchangers.

Heat exchange takes place between the flue gas and air in the heat exchanger H0, while heat exchange takes place between the hygroscopic lithium chloride liquid and air in the heat exchanger H2.

Thus, in the heat exchanger H1, there is no need to consider special specifications for the heat exchange wall, and in the exchanger H2, it is only necessary to consider corrosion resistance to lithium chloride.

Advantageously, the circulating air enters the heat exchanger H1 at a temperature of about 80° C. or higher to prevent condensation of SOx in the flue gas.

The circulating air is heated to around 200°C in the heat exchanger H1, and in the heat exchanger H2, the lithium chloride liquid, which absorbs moisture and becomes around 30°C, is heated to around 80°C, while the air itself is cooled to around 80°C. and return to heat exchanger H1.

, the present invention uses a lithium chloride hygroscopic agent to dehumidify the air blown into a furnace in the fields of iron and steel smelting, nonferrous smelting typified by ferronickel smelting, ceramics, and other fields, and uses lithium chloride moisture absorbent to regenerate the air from nearby equipment. Both are applicable in situations where exhaust gas can be used.

Here, a brief explanation related to ferronickel smelting will be added.

For the purpose of supplying air at a rate of 60 ON/min to the ferronickel smelting blast furnace 1, equipment as shown in Fig. 2 was designed, and the blast air was heated to 900°C in the hot blast furnace 3.
On the other hand, from the hot air stove, 17% CO2, 74% N2, H2O4
0□ 5% Combustion exhaust gas containing trace amounts of NOx and SOx was generated.

In order to dehumidify the blown air, a lithium chloride solution is circulated between the dehumidifier 5 and the regenerator T at a flow rate of 900°C for 1 minute to remove 15 to 28 f/Ni moisture contained in the air. 8f
/Nty/K was dehumidified.

In the heat exchanger H1, the combustion exhaust gas at 250°C is
At a flow rate of Nm'/min, the incoming air at 60°C is heated to 200°C in loop L, and the heated air is indirectly heat exchanged with a hygroscopic lithium chloride liquid in heat exchanger H2 to cool the latter. The temperature was raised to 180°C.

The air circulation flow rate was 36 ON/min.

The heat transfer walls of heat exchanger H1 were made of Nisten 1 and the heat transfer walls of heat exchanger H2 were made of Monel metal.

During the long-term lithium chloride regeneration operation, no signs of heat exchanger corrosion were observed, and the regeneration cycle was carried out smoothly.

As described above, the present invention solves the conventional problem of corrosion of the heat exchanger when effectively utilizing the heat of the combustion exhaust gas in connection with the moisture absorption process of furnace air blowing, and provides a significant improvement in this field. be.

[Brief explanation of drawings]

FIG. 1 is a flow sheet outlining a conventional process in connection with blast furnace air dehumidification, and FIG. 2 is a similar flow sheet incorporating features in accordance with the present invention. 1: blast furnace, 3: hot blast furnace, 5: dehumidifier, 6: spray pipe, 7: regenerator, H: heat exchanger, Hl. N2: heat exchanger, L: air circulation loop.

Claims (1)

[Claims] 1 Heat of combustion exhaust gas is characterized by transferring the heat of the combustion exhaust gas to the moisture-absorbing lithium chloride liquid through an air circulation loop when the combustion exhaust gas is used in the regeneration process of lithium chloride liquid for dehumidifying furnace air. How to Use.