TWI590862B - System for capturing carbon dioxide - Google Patents

Description

Carbon dioxide capture system

The invention is a gas purification system, especially an energy-saving carbon dioxide capture system.

Industrial development brings civilization, but also because of the large use of petrochemical energy, the global average temperature has risen significantly. This phenomenon is called the greenhouse effect.

In recent years, due to the rise of environmental awareness, governments have drawn up regulations to manage the emissions of various greenhouse gases. China also has a “Greenhouse Gas Reduction and Management Law”, especially for carbon dioxide, which accounts for the largest greenhouse gas emissions, and puts a lot of effort into promoting energy conservation and carbon reduction. Energy-intensive industries such as steel, petrochemicals and cement are also committed to To reduce the amount of carbon dioxide in the exhaust gas to meet the relevant government policies.

The use of chemical absorption method for carbon dioxide capture is one of the methods for treating carbon dioxide in exhaust gas. At present, industrial chemical absorbents mostly use Monoethanolamine (MEA) absorbent, but in the exothermic reaction of carbon dioxide absorption, alcohol amine heat Degradation of compounds to the atmosphere causes damage to the environment. Therefore, techniques for capturing carbon dioxide by a dilute ammonia process have been proposed, such as "M. Zhang and Y. Guo, "Process simulations of NH ₃ abatement system for large-scale CO ₂ capture using aqueous ammonia solution," International Journal of Greenhouse Gas Control, vol. 18, pp. 114-127, 2013" carbon dioxide capture system, which comprises a carbon dioxide absorption tower, an ammonia absorption tower, a carbon dioxide stripper and an ammonia stripper. Mainly through the chemical absorption method, ammonia is used as an absorbent to capture carbon dioxide in the exhaust gas, which has the advantage of high absorption load.

However, compared to the regeneration energy consumption of about 4.0 GJ/ton-CO ₂ during the operation of the carbon dioxide capture system using an alcohol amine absorbent, the above-mentioned carbon dioxide capture system using ammonia water can regenerate energy up to about 8.5 GJ/ton-CO. ₂ , making energy consumption a shortcoming that needs to be improved in this type of carbon dioxide capture system using ammonia.

The main object of the present invention is to solve the problem of high energy consumption of the conventional carbon dioxide capture system.

In order to achieve the above object, the present invention provides a carbon dioxide capture system comprising: a carbon dioxide absorbing portion that receives a flue gas stream, the carbon dioxide absorbing portion having a first bottom portion and a first top portion;

An ammonia absorbing portion communicating with the carbon dioxide absorbing portion, the ammonia absorbing portion having a second bottom portion and a second top portion;

a carbon dioxide stripping portion communicating with the carbon dioxide absorbing portion, the carbon dioxide stripping portion having a third bottom portion and a third top portion;

An ammonia stripping portion communicating with the ammonia absorbing portion and the carbon dioxide stripping portion, the ammonia stripping portion having a fourth bottom portion and a fourth top portion;

a main heat exchanger in communication with the carbon dioxide stripping section and the ammonia stripping section.

In the carbon dioxide capture system of the present invention, a first regenerated absorbent is output from the carbon dioxide stripping section, vaporized by the main heat exchanger to form a first absorbent, and the carbon dioxide is absorbed by the first top section. a portion, the flue gas stream input to the carbon dioxide absorbing portion is reacted with the first absorbent to form a carbon dioxide-lean gas stream output from the first top portion and a carbon dioxide-rich fluid output from the first bottom portion. a carbon dioxide-lean gas stream is input to the ammonia absorption portion to form a purified gas stream outputted by the second top portion and an ammonia-rich circulating water outputted from the second bottom portion; the carbon dioxide-rich fluid is input to the carbon dioxide vapor through the third top portion The handle forms a carbon dioxide gas stream output by the carbon dioxide stripping section.

The present invention is achieved by the above system, particularly the arrangement of the main heat exchanger in communication with the carbon dioxide stripping section and the ammonia stripping section, respectively. Vaporizing a fluid from the carbon dioxide stripping section and the ammonia stripping section through the main heat exchanger and recovering the latent heat released by the fluid, thereby improving the efficiency of the system of the present invention for heat energy and reducing the overall system energy consumption, In turn, the goal of energy saving and carbon reduction is achieved.

The detailed description and technical content of the present invention will now be described as follows:

1 is a schematic view showing the configuration of a carbon dioxide capture system according to an embodiment of the present invention, comprising a carbon dioxide absorbing portion 10, an ammonia absorbing portion 20, a carbon dioxide stripping portion 30, an ammonia stripping portion 40, and a main heat exchanger 50. .

The carbon dioxide absorbing portion 10 is configured to receive a flue gas stream 1 containing a carbon dioxide component, such as Blast Furnace Gas (BFG), and the carbon dioxide absorbing portion 10 has a first bottom portion 11 and a first top portion. 12. In order to promote the efficiency of the reaction, a plurality of first fillers may be selectively filled between the first bottom section 11 and the first top section 12.

The ammonia absorbing portion 20 is in communication with the carbon dioxide absorbing portion 10 and has a second bottom portion 21 and a second top portion 22. Similarly, in order to increase the reaction efficiency, the ammonia absorbing portion 20 may also selectively fill a plurality of second fillers between the second bottom portion 21 and the second top portion 22.

The first filler and the second filler may be identical to each other or different from each other, and may be, for example, a Raschig ring or a Pall ring. The present invention is not particularly limited.

The carbon dioxide stripping section 30 is in communication with the carbon dioxide absorbing section 10 and has a third bottom section 31 and a third top section 32, and the carbon dioxide stripping section 30 contains a first regenerative absorbent 4. In an embodiment of the invention, the carbon dioxide stripping unit 30 is further connected to a condensation portion 70, which may be, for example, a condenser.

The ammonia stripping section 40 is in communication with the ammonia absorbing section 20 and the carbon dioxide stripping section 30. The ammonia stripping section 40 has a fourth bottom section 41 and a fourth top section 42. In an embodiment of the invention, the ammonia stripping unit 40 is connected to a heating unit 60. The heating unit 60 can be, for example, a heater.

In order to make the heat transfer of a fluid between systems more efficient to achieve energy saving goals, the present invention provides the main heat exchanger 50 to communicate the carbon dioxide stripping section 30 and the ammonia stripping section 40. The fluid flowing through the main heat exchanger 50 can conduct a heat transfer there, thereby effectively increasing the efficiency of use of the system for thermal energy.

In addition to the main heat exchanger 50, in the present embodiment, the carbon dioxide capture system further includes a first heat exchanger 80 and a second heat exchanger 90, the first heat exchanger 80 being in communication with the carbon dioxide absorbing portion. 10 is between the carbon dioxide stripping section 30; and the second heat exchanger 90 is in communication with the ammonia absorbing section 20 and the ammonia stripping section 40.

In the following embodiments, the operation of the carbon dioxide capture system of the present invention will be specifically described by taking the flue gas stream 1 of a 500 MW coal-fired power plant unit as an example.

Please continue to refer to Figure 1. The flue gas stream 1 of 2125 metric tons per hour contains a flow rate of carbon dioxide of 400 metric tons, which is input from the first bottom section 11 of the carbon dioxide absorbing section 10 at an atmospheric pressure and a temperature of 50 °C.

At this time, a first absorbent 4b input from the first top section 12 to the carbon dioxide absorbing section 10 reacts with carbon dioxide in the flue gas stream 1, so that the flue gas stream 1 is formed by the first top section 12 The carbon dioxide-lean gas stream 2 and a carbon dioxide-rich fluid 3 output from the first bottom section 11. In an embodiment of the present invention, the composition of the first absorbent 4b comprises about 90.7 mol% of water, about 7.7 mol% of ammonia, and about 1.6 mol% of carbon dioxide, and the first absorbent 4b has a boiling point of about 82 °C. Further, the carbon dioxide absorbing portion 10 preferably contains a large amount of the first filler, thereby increasing the reaction area in which the flue gas stream 1 reacts with the first absorbent 4b.

Next, the flow of the carbon dioxide lean gas stream 2 and the carbon dioxide rich stream 3 will be discussed separately.

Flow of carbon dioxide-lean gas stream

The carbon dioxide-lean gas stream 2 is output from the first top section 12 and is input to the ammonia absorbing portion 20, and at this time, the carbon dioxide-lean gas stream 2 and a second absorbent 5 input from the second top portion 22 to the ammonia absorbing portion 20 The reaction forms a purified gas stream 6 outputted from the second top section 22 and an ammonia-rich circulating water 7 outputted from the second bottom section 21.

At this time, the ammonia concentration of the purified gas stream 6 is less than 50 ppmv, which complies with environmental regulations, and the flow rate of carbon dioxide in the purified gas stream 6 is not higher than 40 metric tons per hour, reaching a design specification of 90% carbon dioxide capture rate.

The ammonia-rich circulating water 7 flows through the second heat exchanger 90 and enters the ammonia stripping section 40 from the fourth top section 42. At this time, the heating portion 60 heats the ammonia-rich circulating water 7, and the ammonia gas of the ammonia-rich circulating water 7 is heated and vaporized to generate an ammonia-rich gas stream 8 that is firstly output to the fourth top portion 42 and output there; The ammonia-rich circulating water 7 of the gas forms the second absorbent 5.

The second absorbent 5 is output from the fourth bottom section 41 of the ammonia stripping section 40 and flows into the second heat exchanger 90. At this time, the ammonia-rich circulating water 7 and the ammonia stripping section 40 are The second absorbent 5 performs heat conduction to recover sensible heat, and then the ammonia-rich circulating water 7 enters the fourth top section 42; and the second absorbent 5 cools heat to the ammonia-rich circulating water 7 and then cools, by the second The top section 22 is input to the ammonia absorbing portion 20 to absorb the ammonia gas in the carbon dioxide-depleted vapor stream 2, and in this embodiment, is mainly input to the second absorbent 5 in the ammonia absorbing portion 20 for reacting with ammonia. The composition comprises about 99.9 mol% of water, about 0.05 mol% of ammonia, and about 0.05 mol% of carbon dioxide.

The composition of the ammonia-rich gas stream 8 comprises: water of about 61.5 mol%, ammonia of about 33.4 mol%, and carbon dioxide of about 5.1 mol%, and a temperature of 90 °C. The ammonia-rich gas stream 8 is introduced into the main heat exchanger 50 to be liquefied, and a first portion 8a of the ammonia-rich gas stream 8 is fed to the carbon dioxide stripping portion 30 as a heat source to heat the carbon dioxide stripping portion 30; one of the ammonia-rich gas streams 8 The second portion 8b, after flowing through the main heat exchanger 50, recovers its latent heat from the main heat exchanger 50 to form a condensed reflux, and the ammonia stripping portion 40 is input from the fourth top portion 42.

Flow of carbon-rich gas stream

Please refer to FIG. 1 to continue the flow of the carbon dioxide-rich fluid 3.

The carbon dioxide-rich fluid 3 is output from the first bottom section 11 and flows through the first heat exchanger 80 for heat exchange to recover the sensible heat of the first absorbent 4b, and the carbon dioxide gas is input from the third top section 32. Lift 30. Subsequently, the carbon dioxide-rich fluid 3 is vaporized and condensed by the condensation portion 70 to form a carbon dioxide gas stream 9 output by the third top section 32. The carbon dioxide gas stream 9 has a high concentration of carbon dioxide at this time, for example, 98%. Carbon dioxide, as well as low concentrations of ammonia, can be, for example, 1000 ppm ammonia.

The carbon dioxide stripping unit 30 includes the first regenerative absorbent 4, and after the first regenerative absorbent 4 is input from the third bottom section 31 to the main heat exchanger 50, the following occurs:

A third portion 4a of the first regenerative absorbent 4 is output from the third bottom section 31 to the main heat exchanger 50, and the latent heat released from the second portion 8b of the ammonia-rich gas stream 8 is obtained, and then returned. The carbon dioxide stripping section 30 serves as a heat source for the carbon dioxide stripping section 30.

After the third portion 4a of the first regenerative absorbent 4 is vaporized by the main heat exchanger 50, the remaining fluid is divided into a fourth portion 4b and a fifth portion 4c. In order to achieve the design goal of a carbon dioxide capture rate of 90%, the flow required by the fourth portion 4b is calculated in advance, and the flow required for the fourth portion 4b is split to the first heat exchanger 80, and the thermal energy of its own is supplied through the After the carbon dioxide-rich fluid 3 of the first heat exchanger 80, the temperature of the carbon dioxide-rich fluid 3 is lowered, and then the first top end 12 enters the carbon dioxide absorbing portion 10, and the first absorbent 4b is used to absorb carbon dioxide, thereby satisfying The first absorbent 4b is present in the operating conditions of the carbon dioxide absorbing section 10 at different concentrations depending on the situation. The fifth portion 4c is then returned to the fourth top section 42 to assist in cooling the ammonia-rich gas stream 8 as condensate reflux and to achieve mass balance of the system.

In the main heat exchanger 50 of a preferred embodiment of the present invention, a hot end temperature (i.e., a first temperature of the ammonia-rich gas stream 8) must be higher than a cold end temperature (i.e., the first regenerated absorbent). The second late temperature of 4) is at least 5 ° C to conduct the latent heat of liquefaction of the first portion 8a of the ammonia-rich gas stream 8 to the first regenerated absorbent of the third bottom section 31 in the main heat exchanger 50. 4, and through the main heat exchanger 50, the third portion 4a of the first regenerative absorbent 4 is vaporized into a heat source of the carbon dioxide stripping portion 30, and the second portion 8b of the ammonia-rich gas stream 8 is condensed into condensation Reflux and reflux to the fourth top section 42. The difference between the first temperature of the ammonia-rich gas stream 8 and the second temperature of the first regenerated absorbent 4 of the third bottom section 31 is preferably above 5 ° C, for example, the first of the ammonia-rich gas stream 8 The temperature is 90 ° C, and the second temperature of the first regenerated absorbent 4 of the third bottom section 31 is between 81 ° C and 85 ° C.

Further, in the present invention, an operating temperature of the main heat exchanger 50 is higher than a boiling point of the first regenerated absorbent 4. For example, in a preferred embodiment of the invention, the operating temperature of the main heat exchanger 50 is about 88 ° C, which is higher than the boiling point (about 82 ° C) of the first regenerated absorbent 4 . Therefore, the main heat exchanger 50 is sufficient to heat the third portion 4a of the first regenerated absorbent 4 to form one of the heat sources of the carbon dioxide stripping portion 30. The temperature difference between the operating temperature of the main heat exchanger 50 and the boiling point of the first regenerative absorbent 4 is preferably 5 ° C or higher, for example, the operating temperature of the main heat exchanger 50 is 88 ° C to 90 ° C. The boiling temperature of the first regenerated absorbent 4 is between 81 ° C and 85 ° C.

It has been tested that when the carbon dioxide load design value in this embodiment is at an optimum 0.21 mol-CO ₂ /mol-NH ₃ , the energy consumption of the heating portion 60 is 4.1 GJ/ton-CO ₂ , which is lower than that disclosed in the prior art. Energy consumption (8.5 GJ/ton-CO ₂ ), it is obvious that the energy-saving design of the carbon dioxide capture system proposed by the present invention can effectively reduce the overall system energy consumption and achieve the goal of energy reduction and carbon reduction.

In summary, the arrangement of the main heat exchanger of the present invention assists in providing a heat source to the carbon dioxide stripping section. In detail, the heat source of the carbon dioxide stripping portion of the present invention is derived from: (1) the main heat exchanger recovers the second portion of the ammonia-rich gas stream condensed into latent heat released by condensing reflux, and vaporizes the first portion by the latent heat. a third portion of the regenerated absorbent; and (2) latent heat of the first portion of the ammonia-rich gas stream. Therefore, for the carbon dioxide stripping portion, there is no need to provide an external heat source to maintain the operation of the carbon dioxide stripping portion, and the carbon dioxide capturing system of the present invention only needs to be provided to provide heating to the ammonia rich cycle. The heat source of the water can be used, thereby achieving the effect of reducing the overall system energy consumption.

The present invention has been described in detail above, but the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the scope of the invention. That is, the equivalent changes and modifications made by the scope of the present application should remain within the scope of the patent of the present invention.

1‧‧‧ flue gas flow
2‧‧‧Poor carbon dioxide gas flow
3‧‧‧Enriched carbon dioxide fluid
4‧‧‧First regenerative absorbent
4a‧‧‧Part III
4b‧‧‧Part 4 (first absorbent)
4c‧‧‧Part V
5‧‧‧Second absorbent
6‧‧‧purified airflow
7‧‧‧Ammonia-rich circulating water
8‧‧‧Ammonia-rich airflow
8a‧‧‧Part 1
8b‧‧‧Part II
9‧‧‧Carbon dioxide gas flow
10‧‧‧Carbon Dioxide Absorption Department
11‧‧‧ first bottom section
12‧‧‧First top section
20‧‧‧Ammonia absorption department
21‧‧‧second bottom section
22‧‧‧second top section
30‧‧‧ Carbon Dioxide Stripping Department
31‧‧‧ third stage
32‧‧‧ third top section
40‧‧‧Ammonia stripping department
41‧‧‧ fourth bottom
42‧‧‧fourth paragraph
50‧‧‧Main heat exchanger
60‧‧‧heating department
70‧‧‧ Condensation Department
80‧‧‧First heat exchanger
90‧‧‧second heat exchanger

FIG. 1 is a schematic diagram of a system configuration according to an embodiment of the present invention.

1‧‧‧ flue gas flow

2‧‧‧Poor carbon dioxide gas flow

3‧‧‧Enriched carbon dioxide fluid

4‧‧‧First regenerative absorbent

4a‧‧‧Part III

4b‧‧‧Part 4 (first absorbent)

4c‧‧‧Part V

5‧‧‧Second absorbent

6‧‧‧purified airflow

7‧‧‧Ammonia-rich circulating water

8‧‧‧Ammonia-rich airflow

8a‧‧‧Part 1

8b‧‧‧Part II

9‧‧‧Carbon dioxide gas flow

10‧‧‧Carbon Dioxide Absorption Department

11‧‧‧ first bottom section

12‧‧‧First top section

20‧‧‧Ammonia absorption department

21‧‧‧second bottom section

22‧‧‧second top section

30‧‧‧ Carbon Dioxide Stripping Department

31‧‧‧ third stage

32‧‧‧ third top section

40‧‧‧Ammonia stripping department

41‧‧‧ fourth bottom

42‧‧‧fourth paragraph

50‧‧‧Main heat exchanger

60‧‧‧heating department

70‧‧‧ Condensation Department

80‧‧‧First heat exchanger

90‧‧‧second heat exchanger

Claims (10)

A carbon dioxide capture system comprising: a carbon dioxide absorbing portion that receives a flue gas stream, the carbon dioxide absorbing portion having a first bottom portion and a first top portion; and an ammonia absorbing portion in communication with the carbon dioxide absorbing portion, the ammonia absorbing portion The portion has a second bottom portion and a second top portion; a carbon dioxide stripping portion in communication with the carbon dioxide absorbing portion, the carbon dioxide stripping portion has a third bottom portion and a third top portion; And an ammonia stripping portion connected to the carbon dioxide stripping portion, the ammonia stripping portion has a fourth bottom portion and a fourth top portion; and a main heat connected to the carbon dioxide stripping portion and the ammonia stripping portion An exchanger for outputting a first regenerated absorbent from the carbon dioxide stripping portion, vaporizing the main heat exchanger to form a first absorbent, and inputting the carbon dioxide absorbing portion from the first top portion, and inputting the The flue gas stream of the carbon dioxide absorbing portion reacts with the first absorbent to form a carbon dioxide-depleted gas stream output from the first top section and a rich dioxide dioxide output from the first bottom section a fluid, the carbon dioxide-lean gas stream is input to the ammonia absorbing portion to form a purified gas stream outputted by the second top section and an ammonia-rich circulating water outputted from the second bottom section; the carbon dioxide-rich fluid is input through the third top section The carbon dioxide stripping section forms a carbon dioxide gas stream output by the carbon dioxide stripping section. The carbon dioxide capture system of claim 1, wherein the carbon dioxide stripping portion further comprises a condensation portion connected to the third top portion. The carbon dioxide capture system of claim 1, wherein the ammonia stripping portion further comprises a heating portion coupled to the fourth bottom portion. The carbon dioxide capture system of claim 1, wherein the carbon dioxide absorbing portion communicates with the carbon dioxide stripping portion via a first heat exchanger. The carbon dioxide capture system of claim 1, wherein the ammonia absorbing portion and the ammonia stripping portion are in communication via a second heat exchanger. The carbon dioxide capture system of claim 4, wherein the carbon dioxide-rich fluid outputted from the first bottom section is thermally conducted through the first heat exchanger and then input to the carbon dioxide stripping section. The carbon dioxide capture system of claim 5, wherein the ammonia-rich circulating water outputted by the second bottom section is subjected to heat conduction through the second heat exchanger to be input to the ammonia stripping section to form a carbon dioxide capture system. An ammonia-rich gas stream output by the fourth top section and a second absorbent outputted by the fourth bottom section. The carbon dioxide capture system of claim 7, wherein the main heat exchanger vaporizes the ammonia-rich gas stream output by the fourth top section. The carbon dioxide capture system of claim 8, wherein a first temperature of the ammonia-rich gas stream is higher than a second temperature of the first regenerated absorbent. The carbon dioxide capture system of claim 1, wherein an operating temperature of the main heat exchanger is higher than a boiling point of the first regenerated absorbent.