CN1186575C - Deep utilization of heat energy in exhaust gas and method of using its aqueous vapour as natural resources - Google Patents

Abstract

The invention discloses a method for deep utilization of heat energy of flue gas and resource utilization of water vapor. The flue gas with high moisture content coming out of the boiler is divided into two parts: a part of flue gas is passed through a heat exchanger to reduce the temperature of the flue gas to Below the water vapor dew point temperature, the low-quality heat released by the flue gas is absorbed by the refrigerant medium, realizing the deep utilization of the heat energy of the flue gas, and at the same time, the water vapor in the flue gas is condensed and recovered by the liquid collection tank and treated by the water treatment tank to make the condensed water It becomes resource-based water that can be used in industrial and agricultural production and life; the other part of the flue gas is not used for the recovery of flue gas heat energy, but passes through the bypass flue where the flow valve is located, mixes and heats the former part after heat exchange Flue gas with a lower temperature to facilitate the flow of flue gas in the chimney. The method has clean smoke exhaust, prevents chimney corrosion, has large heat energy utilization depth, and realizes resource utilization of water vapor in flue gas.

Description

A method for the deep utilization of heat energy of flue gas and the resource utilization of water vapor in it

1. Technical field

The invention belongs to the field of thermal energy utilization, and relates to a thermal energy utilization method, in particular to a method capable of realizing deep utilization of flue gas thermal energy and resource utilization of water vapor therein.

2. Background technology

At present, the commonly used boilers, whose fuels (including coal, oil and natural gas) are burned, produce flue gas and flue gas with relatively high exhaust temperature, and have a considerable part of heat energy (especially when the flue gas contains water vapor with high enthalpy and high proportion). ) is discharged into the atmosphere through the chimney, resulting in a great waste of heat energy, and the smoke exhaust is not clean. In ordinary conventional boilers, water vapor is not utilized as a resource, but flows down the chimney when it encounters cold in the chimney, causing corrosion and scaling of the chimney.

According to the data retrieval carried out by the applicant, the relevant or similar materials of the present invention are as follows:

1) In the utility model patent "Boiler waste heat recovery device" with the patent application number of 99222731.3, although the waste heat of the flue gas has been utilized, when the high-moisture flue gas flows through the waste heat recovery device, the temperature of the flue gas decreases. Lots of condensation. If the condensed water is not discharged from the flue in time, a large amount of water will accumulate in the chimney and the corrosion will be serious. Moreover, after 100% of the flue gas passes through the waste heat recovery device, the temperature of the flue gas is very low, which is not conducive to the flow of flue gas in the chimney. .

2) In the patent "Condensing type boilers" with US Patent No. 4998508, although the thermal energy utilization of the flue gas is high, there is also the problem of recovering the condensed water in the flue gas, and this type of boiler is an integral boiler with a relatively complicated structure , not suitable for use in boilers with large capacity and high pressure parameters, and the scope of use is limited.

3. Contents of the invention

In order to overcome the deficiencies of the above-mentioned conventional boilers in the deep utilization of heat energy and the resource utilization of water vapor in the flue gas, according to Professor Che Defu of Xi'an Jiaotong University in the second edition of "Condensing Boilers and Their Systems" (Mechanical Industry Press, 2002) In chapters, chapters 3, 4 and 7, the optimization of boiler outlet flue temperature, the deep utilization of flue gas heat energy, the treatment of condensed water and its resource utilization are analyzed in detail. Starting from the three aspects of utilization and water resource utilization, a method of deep utilization of flue gas heat energy and water vapor resource utilization is proposed. Using this method, the smoke exhaust can be clean, the depth of heat energy utilization can be large, and the water vapor in the flue gas can be reduced. Recycling makes the proportion of water vapor in the flue gas entering the chimney low, preventing corrosion and scaling of the chimney.

In order to achieve the above object, the technical solution adopted in the present invention is: the method of deep utilization of the heat energy of the flue gas and the resource utilization of water vapor in it is carried out according to the following steps:

1) Divide the high-moisture flue gas from the boiler into two parts;

The ratio of the two parts of flue gas can be distributed according to the depth utilization of flue gas heat energy and the flow characteristics of flue gas in the chimney after heat energy utilization, namely:

β＝ΔQ/Q (1)

In the formula (1), β-the proportion of the flue gas condensed and exchanged by the heat exchanger in the total flue gas 2;

    ΔQ-condensation heat transfer in the heat exchanger, kW;

       Q-The heat released when all the flue gas 2 at the boiler outlet is reduced to the flue gas temperature at the outlet of the heat exchanger

Quantity, kW;

In order to make the flue gas entering the chimney have good fluidity, the temperature t after mixing the two parts of flue gas calculated according to the following formula should meet the following conditions:

t=(G ₁ J ₁ +G ₂ J ₂ )/(G ₁ +G ₂ )=φt _s (2)

Among them, G ₁ =(1-β)G;

G ₂ =β(GG′);

In the formula (2), t-the temperature after the two parts of flue gas are mixed, °C;

G- The mass flow rate of all flue gas 2 at the boiler outlet, kg/s;

     G′-The condensed water condensed when all the flue gas 2 at the boiler outlet is lowered to the flue gas temperature at the outlet of the heat exchanger

Quantity, kg/s;

J ₁ - flue gas temperature of flue gas 2 at the boiler outlet, °C;

J ₂ - flue gas temperature at the outlet of the heat exchanger, °C;

t _s - the saturation temperature under the partial pressure of water vapor in the flue gas after the two parts of flue gas are mixed, °C;

2 ²

      φ - Correction coefficient related to flue gas flow characteristics;

Among them, the selection range of φ is between 1.1 and 2.5, and the selection range of β is between 0.65 and 0.95;

2) Part of the flue gas passes through the heat exchanger to reduce the temperature of the flue gas to below the water vapor dew point temperature, and the low-quality heat released by the flue gas is absorbed by the cold medium to realize the deep utilization of the heat energy of the flue gas, and at the same time condense the water vapor in the flue gas Recovered from the liquid collection tank and treated by the water treatment tank, the condensed water can be turned into resource-based water that can be used in industrial and agricultural production and life;

3) The other part of the flue gas is not used for the recovery of flue gas heat energy, but is sent to the bypass flue where the flow valve is located, to mix and heat the flue gas with a lower temperature after heat exchange in the former part, so as to facilitate the flue gas Gas flows in the chimney.

Some other features of the present invention are that the heat exchanger adopts a partition heat exchanger made of corrosion-resistant materials or a direct contact heat exchanger.

The method of the invention can bring beneficial social and economic benefits, mainly in that boiler exhaust is clean, chimney corrosion is prevented, heat energy is deeply utilized, and water vapor in flue gas is utilized as a resource.

4. Description of drawings

Figure 1 is a schematic diagram of the method of the present invention.

Fig. 2 is another schematic diagram of the method of the present invention.

5. Specific implementation

In order to understand the present invention more clearly, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments given by the inventor.

In Figure 1, 1 represents the boiler, 2 represents the outlet flue gas with optimized flue temperature, 3 represents the flow valve, 4 represents the flow distribution plate, 5' represents the partition wall heat exchanger, 6 represents the liquid collection tank, and 7 represents the water treatment tank . The flow valve 3 and the flow distribution plate 4 are fixed on the flue wall, the partition heat exchanger 5' is arranged horizontally in the flue, the flue gas and the refrigerant are arranged in countercurrent, and the liquid collection pool 6 and the water treatment pool 7 are connected in sequence below it. A water treatment system that neutralizes and softens the condensed water is installed in the water treatment tank 7 .

The outlet flue gas 2 of the boiler 1 is divided into two parts: one part passes through the partition wall heat exchanger 5' made of corrosion-resistant materials to reduce the temperature of the flue gas to below the dew point temperature of the water vapor in the flue gas, and at the same time, the condensed water passes through the liquid collection tank 6 is recovered and treated by the water treatment tank 7, so that the condensed water becomes resource-based water that can be used in industrial and agricultural production and daily life; the other part of the flue gas is mixed and heated by the bypass pipe where the flow valve 3 is located into the chimney.

In Fig. 2, 5" indicates a direct contact heat exchanger, 8 indicates a partition heat exchanger placed in the liquid sump 6, 9 indicates a water pipe, and 10 indicates a water pump. The flow valve 3 and the flow distribution plate 4 are fixed on the flue gas On the channel wall, the direct contact heat exchanger 5" is arranged in the flue, and the cooling water and the flue gas are arranged in countercurrent. The flue gas is sent in from the bottom of the direct contact heat exchanger 5", and is sent into the chimney from the top of the direct contact heat exchanger 5" after direct contact with the cooling water; The contact heat exchanger 5″ exchanges heat with the flue gas, and discharges it into the liquid collection pool 6 after the heat exchange. The partition wall heat exchanger 8 placed in the liquid collection pool 6 exchanges the heat energy of the flue gas obtained by recycling the cooling water, Realize the deep utilization of flue gas heat energy. The condensation of water vapor in the flue gas will make more and more water in the liquid collection pool 6, which can enter the water treatment pool 7 through the overflow port above the liquid collection pool 6, and become Water that can be used as a resource for industrial and agricultural production and life.

The lower the flue gas temperature at the boiler outlet, the lower the exhaust heat loss, which is beneficial to improve the efficiency of the boiler. However, if the exhaust gas temperature is too low, part of the water vapor in the flue gas will condense in the boiler body, causing serious corrosion of the boiler and making the replacement The heat transfer temperature and pressure between the flue gas and the working fluid in the heater are reduced, and the heat transfer area is increased. Therefore, the temperature of the flue gas 2 at the outlet of the boiler 1 is an optimally designed temperature on the basis of fully considering the design requirements of the heat exchanger.

If all the flue gas is condensed and exchanged through the heat exchanger, although the heat energy of the flue gas is well utilized, the water vapor in the flue gas from the heat exchanger is in a saturated state, which is not conducive to flow in the chimney. In order to make the flue gas The gas has good flow characteristics in the chimney, and the water vapor in the flue gas must be in a superheated state in the chimney. Therefore, the flue gas can be divided into two parts, and the uncondensed part of the flue gas is used to heat the other part of the condensed flue gas. Gas, so that the water vapor in the flue gas is superheated when it enters the chimney. The ratio of the two parts of the flue gas can be allocated according to the depth of heat energy utilization of the flue gas and the flow characteristics of the flue gas in the chimney after heat energy utilization, namely:

β＝ΔQ/Q (1)

In the formula (1), β-the proportion of the flue gas condensed and exchanged by the heat exchanger in the total flue gas 2;

    ΔQ-condensation heat transfer in heat exchanger 5″, kW;

      Q-The heat released when all the flue gas 2 at the boiler outlet is reduced to the flue gas temperature at the outlet of the heat exchanger,

kW;

In order to make the flue gas entering the chimney have good fluidity, the temperature t after mixing the two parts of flue gas calculated according to the following formula should meet the following conditions:

t=(G ₁ J ₁ +G ₂ J ₂ )/(G ₁ +G ₂ )=φt _s (2)

Among them, G ₁ =(1-β)G;

G ₂ =β(GG′);

In the formula (2), t-the temperature after the two parts of flue gas are mixed, °C;

G-The mass flow rate of all flue gas 2 at the boiler outlet, kg/s;

     G′-The condensed water condensed when all the flue gas 2 at the boiler outlet is lowered to the flue gas temperature at the outlet of the heat exchanger

Quantity, kg/s;

J ₁ - flue gas temperature of flue gas 2 at the boiler outlet, °C;

J ₂ - flue gas temperature at the outlet of the heat exchanger, °C;

t _s - the saturation temperature under the partial pressure of water vapor in the flue gas after the two parts of flue gas are mixed, °C;

      φ - Correction coefficient related to flue gas flow characteristics;

Among them, the selection range of φ is between 1.1 and 2.5, and the selection range of β is between 0.65 and 0.95.

Most of the water vapor in the flue gas is condensed in the heat exchanger, preventing corrosion and fouling of the chimney. The heat exchanger is a partition heat exchanger made of corrosion-resistant materials or a direct contact heat exchanger. When the heat exchanger is maintained, all the flue gas can pass through the bypass channel where the flow valve 3 is located, without affecting the normal operation of the boiler. run. After being neutralized and softened by the water treatment tank 7, the condensed water can be used as water for industrial and agricultural production and domestic use, and can also be used for irrigation or water for humans and animals in arid areas with little rain, so as to realize the resource utilization of water vapor in the flue gas.

Claims (2)

1. the utilization of the heat energy degree of depth of a flue gas and the wherein method of steam resource is characterized in that, carry out according to the following steps:

1) will be divided into two parts from the flue gas that contains high-moisture (2) that come out boiler (1);

The ratio of described two-part flue gas can be distributed according to the flow behavior of flue gas in chimney behind degree of depth utilization of flue gas heat energy and the heat energy utilization, that is:

β＝ΔQ/Q (1)

In the formula (1), β-the account for share ratio of whole flue gases (2) through the flue gas of heat exchanger condensing heat-exchange;

Condensing heat-exchange amount in the Δ Q-heat exchanger, kW;

Q-drops to heat exchanger exit cigarette temperature time institute liberated heat, kW with whole flue gases (2) of boiler export;

In order to make the flue gas that enters chimney that good flowability be arranged, the mixed temperature t of two parts flue gas that is calculated as follows is met the following conditions:

t＝(G ₁J ₁+G ₂J ₂)/(G ₁+G ₂)＝φt _s (2)

Wherein, G ₁=(1-β) G;

G ₂＝β(G-G′)；

In the formula (2), the mixed temperature of t-two parts flue gas, ℃;

The mass flow of whole flue gases (2) of G-boiler export, kg/s;

G '-whole flue gases (2) of boiler export are dropped to the condensing capacity of heat exchanger exit cigarette temperature time institute condensation, kg/s;

J ₁The flue-gas temperature of-boiler export place flue gas (2), ℃;

J ₂The exit flue-gas temperature of-heat exchanger, ℃;

t _s-two parts flue gas mixes its saturation temperature under the shared partial pressure of steam in the flue gas of back, ℃;

φ-the correction factor relevant with the flow of flue gas characteristic;

Wherein, the scope of choosing of φ is between 1.1～2.5, and the scope of choosing of β is between 0.65～0.95;

2) part of smoke drops to below the steam dew-point temperature flue-gas temperature through heat exchanger, and the low-quality heat that flue gas is emitted is absorbed by the refrigerant medium, and the steam in the flue gas is condensed through collecting tank (6) recovery also

Handle through water treating pond (7), make condensate water become the water of the resource that can utilize for industrial and agricultural production and life;

3) another part flue gas is not used in the recovery of flue gas heat energy, but this partial fume is sent into the bypass flue at flow valve (3) place, mix and heating before the lower flue gas of temperature after a part of heat exchange, be beneficial to flue gas and in chimney, flow.

2. the utilization of the heat energy degree of depth of flue gas according to claim 1 and the wherein method of steam resource is characterized in that described heat exchanger adopts the dividing wall type heat exchanger or the direct-contact heat exchanger of resistant material.

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