WO2014183936A1

WO2014183936A1 - Venting dense phase carbon dioxide

Info

Publication number: WO2014183936A1
Application number: PCT/EP2014/057378
Authority: WO
Inventors: Gelein Mainza DE KOEIJER
Original assignee: Statoil Petroleum As
Priority date: 2013-05-15
Filing date: 2014-04-11
Publication date: 2014-11-20
Also published as: GB201308755D0; GB2514154A

Abstract

A system and method for venting dense phase carbon dioxide produced from a production plant. A conduit (1) is provided for carrying captured dense phase carbon dioxide, the conduit having an outlet (4). A body of liquid (5) is also provided through which vented carbon dioxide (6) can pass. The outlet is disposed in the body of liquid, such that dense phase carbon dioxide is vaporized in the body of liquid and vented. This eliminates a problem of dry ice forming around the outlet and reduces the problems of venting noise, and accumulation of carbon dioxide around the outlet.

Description

Venting Dense Phase Carbon Dioxide

TECHNICAL FIELD The invention relates to the field of venting dense phase carbon dioxide. BACKGROUND

Dense phase carbon dioxide is produced in large quantities for permanent geological storage and in smaller quantities for beverage, food preservation and other industries. The carbon dioxide source may be any of power plants, Liquid Natural Gas (LNG) plants, natural gas plants, hydrogen plants, cement plants, steel plants etc. Production demands compression, liquefaction, storage and purification systems. These systems need regular maintenance to reduce the risk of incidents when the dense or liquid carbon dioxide is to be released.

When carbon dioxide is captured from a carbon dioxide source, it is typically in liquid or dense phase form. The term dense phase carbon dioxide refers to carbon dioxide in either liquid form or supercritical form. When venting, the dense phase carbon dioxide is passed through a vent stack in order to gasify it and pass it into the atmosphere. This process may result in dry ice formation, which can be addressed by heating the portion of the vent stack in which dry ice collects.

A problem with existing venting of carbon dioxide is that the venting process can generate significant noise due to the rapid depressurization and expansion of carbon dioxide and air. Furthermore, on days without wind, cool gaseous carbon dioxide can accumulate at low spots since carbon dioxide is heavier than air. This is a known issue for which environmental regulations require that the concentration of carbon dioxide cannot exceed a threshold value. A further problem is that the formation of solid carbon dioxide (dry ice) as the carbon dioxide is vented can cause damage to equipment, or partially or completely block valves and other production equipment where the dry ice forms. Dry ice can also accumulate and its vaporization will form a longer term carbon dioxide source. SUMMARY

It is an object to improve the venting of dense phase carbon dioxide. According to a first aspect, there is provided a system for venting dense phase carbon dioxide produced from a production plant. A conduit is provided for carrying captured dense phase carbon dioxide, the conduit having an outlet. A body of liquid is also provided through which vented carbon dioxide can pass. The outlet is disposed in the body of liquid, such that dense phase carbon dioxide is vaporized in the body of liquid and vented. This eliminates the problem of dry ice forming around the outlet. Furthermore, it reduces the problem of accumulation of carbon dioxide around the outlet, and reduces venting noise.

Examples of the production plants are any of a power plant, a liquid natural gas plant, a natural gas plant, a refinery, a gasification plant, a hydrogen production plant, a cement plant and a steel plant. Dense phase carbon dioxide may be produced from, for example, purification of natural gas or liquefaction of hydrocarbon gas.

The location of the outlet in the body of liquid is optionally at a pressure above the triple point pressure of carbon dioxide. This ensures that the dense phase carbon dioxide becomes gaseous carbon dioxide suitable for venting. For similar reasons, the body of liquid may be at a temperature above the triple point temperature of carbon dioxide.

Exemplary bodies of liquid include a sea, a lake, a reservoir, an underground source of water or a tank of water. It will be appreciated that liquids other than water may be used.

Examples of dense phase carbon dioxide are liquid carbon dioxide and supercritical carbon dioxide.

Note that the dense phase carbon dioxide may contain impurities. The level and nature of the impurities may change, depending on the source of the dense phase carbon dioxide. However, the presence of impurities does not significantly affect the system's ability to reduce noise during venting, reduce the formation of dry ice, and reduce the system's ability to reduce accumulated carbon dioxide around the outlet. According to a second aspect of the invention, there is provided a method of venting dense phase carbon dioxide produced from a production plant. Dense phase carbon dioxide is passed through a conduit. The conduit has an outlet disposed in a body of liquid. The dense phase carbon dioxide is vaporized in the body of liquid, and can then be vented through the liquid to the atmosphere or carbon capture equipment.

The location of the outlet in the body of liquid is at a pressure above the triple point pressure of carbon dioxide. Furthermore, the body of liquid is optionally at a temperature above the triple point temperature of carbon dioxide.

Examples of suitable bodies of liquid are a sea, a lake, a reservoir, an underground source of water or a tank of water. It will be appreciated that liquids other than water may be used.

As an option, the method comprises, before passing the dense phase carbon dioxide through the conduit, forming the dense phase carbon dioxide as a product of purification of natural gas or liquefaction of hydrocarbon gas. BRIEF DESCRIPTION OF DRAWINGS

Figure 1 illustrates schematically an exemplary venting system for carbon dioxide; and

Figure 2 is a flow diagram illustrating exemplary steps.

DETAILED DESCRIPTION

Currently dense phase carbon dioxide vents directly into the atmosphere which, as described above, causes problems with noise, accumulation of carbon dioxide at low points, and the formation of dry ice blocking valves or other production equipment. The term "dense phase carbon dioxide" is used below to refer to liquid carbon dioxide or carbon dioxide in the supercritical form.

Turning now to Figure 1 , there is illustrates a pipe 1 carrying dense phase carbon dioxide produced from a source of carbon dioxide 2. A valve 3 is disposed at an outlet appreciated that the valve 3 may not be present at all, but it is advantageous to provide the valve 3 in order to control the flow of carbon dioxide. The outlet 4 of the pipe is placed below a surface of a liquid 5.

The liquid 5 is at a pressure and temperature above the triple point of carbon dioxide at the outlet 4. The triple point is the temperature and pressure at which gas, liquid and solid phases of carbon dioxide can coexist in thermodynamic equilibrium. For carbon dioxide, the triple point is around -56.6 °C and 517 kPa.

As carbon dioxide exits the pipe 1 , it is vaporized in the liquid 5 and vented as gaseous carbon dioxide 6 towards the atmosphere 7. The energy required for this vaporization is extracted from the liquid 5 through which the carbon dioxide 6 passes. Venting the carbon dioxide through a liquid rather than directly into the atmosphere has several advantages. The liquid 5 is a more efficient noise absorber than air, and so noise caused by venting carbon dioxide is reduced. Furthermore, venting carbon dioxide through a liquid 5 above the triple point pressure of carbon dioxide prevents the formation of dry ice. This therefore eliminates problems caused by dry ice forming solid blockages in the valve 3 or other equipment such as the pipeline 1 .

A further advantage of the venting of carbon dioxide through the liquid 5 is that it disperses the carbon dioxide over a larger area before the carbon dioxide arrives in the atmosphere than if it the carbon dioxide had been vented directly into the air. This reduces the probability of carbon dioxide levels at levels higher than acceptable thresholds.

The technique of venting carbon dioxide through a liquid 5 can be used at any point where carbon dioxide needs venting, such as power plants, LNG plants, natural gas plants, refinery, gasification plant, hydrogen plants, cement plants, steel plants with carbon dioxide capture.

In an embodiment, the liquid 5 is any large body of water such as a sea or a lake. Alternatively it can be a created volume like an artificial lake, tank or a cavern. An advantage of this is that the large volume of water can easily compensate for a local reduction in temperature caused by the venting of carbon dioxide. However, this may lead to the formation of hydrates or ice as the liquid 5 around the outlet 4 of the pipe 1 is cooled when the carbon dioxide is vented. Furthermore, venting carbon dioxide 6 through seawater or a lake may acidify the water by the formation of carbonic acid. A risk analysis can be used to suggest countermeasures to mitigate these problems.

Note that the pressure of the liquid 5 around the outlet 4 of the pipe should be above the triple point pressure of carbon dioxide (517kPa). If the liquid 5 is, for example, seawater, then disposing the outlet 4 of the pipe 1 at a depth greater than around 45m is sufficient to provide this pressure.

Turning to Figure 2, there is shown a flowing diagram illustrating exemplary steps. The following numbering corresponds to that of Figure 2: S1 . Dense phase carbon dioxide is produced, typically as a by-product to a purification process for natural gas or during the production of LNG, or from any other type of production plant that produces dense phase carbon dioxide as a by-product.

52. The dense phase carbon dioxide is passed through a pipe 1 having an outlet 4 disposed in a body of liquid 5 such as the sea or a lake, as described above.

53. As the dense phase carbon dioxide exits the outlet, the temperature and pressure of the liquid 5 causes the dense phase carbon dioxide to be vaporized in the body of liquid 5 to form gaseous carbon dioxide 6;

54. As the gaseous carbon dioxide 6 exits the body of liquid 5 it may be captured or vented to the atmosphere in a vent stack.

Note that, depending on the source, dense carbon dioxide can contain impurities. Different sources (e.g. purification of natural gas, power plants, LNG production or loading, hydrogen production plants, cement plants, steel plants etc.) of dense phase carbon dioxide can give rise to different impurity levels and different impurity species. Examples of impurites are oxygen, nitrogen, hydrogensulfide, hydrocarbons, hydrogen, carbon monoxide, argon, sulphur oxides, and nitrogen oxides. The system and techniques described above are still effective at reducing noise levels, reducing dry ice formation and reducing levels of carbon dioxide concentration in air even where the dense phase carbon dioxide contains impurities. The impurities typically vent along with the vented carbon dioide. It will be appreciated by a person of skill in the art that various modifications may be made to the embodiments described above without departing from the scope of the present disclosure. For example, the venting techniques described above can be used for venting dense phase carbon dioxide from any source, and not just dense phase carbon dioxide produced from purification of natural gas or the production of LNG. Furthermore, while seawater is described as a suitable liquid, the outlet may be disposed in a body of any suitable liquid. Finally, although the above description refers to venting the carbon dioxide into the atmosphere, it will be appreciated that the carbon dioxide may be captured for storage.

Claims

CLAIMS:

1 . A system for venting dense phase carbon dioxide produced from a production plant, the system comprising:

a conduit for carrying captured dense phase carbon dioxide, the conduit having an outlet;

a body of liquid through which carbon dioxide can pass;

wherein the outlet is disposed in the body of liquid, such that dense phase carbon dioxide is vaporized in the body of liquid and vented.

2. The system according to claim 1 , wherein the production plant is selected from any of a power plant, a liquid natural gas plant, a refinery, a gasification plant, a natural gas plant, a hydrogen production plant, a cement plant and a steel plant.

3. The system according to any one of claims 1 or 2, wherein the outlet is disposed in the body of liquid at a pressure above the triple point pressure of carbon dioxide.

4. The system according to any one of claims 1 to 3, wherein the body of liquid is at a temperature above the triple point temperature of carbon dioxide.

5. The system according to any one of claims 1 to 4, wherein the body of liquid is selected from any of a sea, a lake, a cavern and a tank.

6. The system according to any one of claims 1 to 5, further comprising equipment for purifying natural gas, wherein the dense phase carbon dioxide is a by-product of the purification.

7. The system according to any one of claims 1 to 6, wherein the dense phase carbon dioxide is selected from any of liquid carbon dioxide and supercritical carbon dioxide.

8. The system according to any one of claims 1 to 7, wherein the dense phase carbon dioxide contains impurities.

9. A method of venting dense phase carbon dioxide produced from a production plant, the method comprising:

passing dense phase captured carbon dioxide through a conduit, the conduit having an outlet disposed in a body of liquid;

allowing the dense phase carbon dioxide to be vaporized in the body of liquid and vent through the liquid.

10. The method according to claim 9, further comprising disposing the outlet in the body of liquid at a pressure above the triple point pressure of carbon dioxide.

1 1. The method according to claim 9 or 10, wherein the body of liquid is at a temperature above the triple point temperature of carbon dioxide.

12. The method according to any one of claims 9, 10 or 1 1 , wherein the body of liquid is selected from any of a sea, a lake, a cavern and a tank.

13. The method according to any one of claims 9 to 12, further comprising, prior to passing dense phase carbon dioxide through the conduit, purifying natural gas to form a by-product of dense phase carbon dioxide.

14. The system according to any one of claims 9 to 13, wherein the dense phase carbon dioxide is selected from any of liquid carbon dioxide and supercritical carbon dioxide