1. A process for removing contaminants from a natural gas stream, the process comprising the steps of:
(a) contacting part of the natural gas stream as a first gas stream at an elevated temperature with a first adsorbent bed in regeneration mode, to remove contaminants present on the first adsorbent bed, and to obtain a second gas stream that is enriched in contaminants compared to the first gas stream;
(b) submitting the second gas stream to a gasliquid separation step comprising cooling the second gas stream to a temperature such that at least some contaminants begin to condense into a first liquid phase that is rich in contaminants, and separating the first liquid phase from the second gas stream to create a third gas stream;
wherein the gasliquid separation step forms a first gasliquid separation step, and wherein the process further comprises
(c) submitting the third gas stream to a second gasliquid separation step to obtain a second liquid phase that is rich in contaminants, and a lean gas stream having a cricondentherm lower than that of the natural gas stream.
2. The process according to claim 1, further comprising contacting another part of the natural gas stream with a second adsorbent bed in adsorption mode, to obtain a purified gas stream.
3. The process according to claim 2, wherein the lean gas stream is contacted with the second adsorbent bed together with the other part of the natural gas stream.
4. The process according to claim 2, wherein the lean gas stream is added to the purified gas stream.
5. The process according to claim 4, wherein step (c) is performed in such a way that the lean gas stream has a cricondentherm at least 10\xb0 C. lower.
6. The process according to claim 5, wherein step (c) is performed in such a way that the lean gas stream has a cricondentherm below 10\xb0 C.
7. The process according to claim 6, wherein the lean gas stream is added to the purified gas stream in such a way that the resulting gas stream has a cricondentherm below 10\xb0 C.
8. The process according to claim 7, wherein the cooling in step (b) is done against a temperature above water freezing temperature, in particular using a water cooler.
9. The process according to claim 8, wherein the temperature of the second adsorbent bed is between 5 and 45\xb0 C.
10. The process according to claim 9, wherein the temperature of the first adsorbent bed is between 200 and 350\xb0 C.
11. The process according to claim 10 wherein step (c) comprises cooling the third gas stream to a temperature that is below a temperature at which contaminants in the third gas stream will begin to condense into a second liquid phase, and separating the second liquid phase from the third gas stream.
12. The process according to claim 11, wherein the third gas stream is cooled to a temperature below the cooling temperature in step (b).
13. The process according to claim 12, wherein the second gasliquid separation in step (c) is effected by means of an accelerated velocity inertia separator.
14. The process according to claim 13, wherein the accelerated velocity inertia separator is a supersonic inertia separator and the fluid stream flows at supersonic velocity.
15. The process according to claim 14, wherein a swirling motion is induced to the fluid stream flowing at supersonic velocity, thereby causing the contaminants, in particular water and hydrocarbons, to flow to a radially outer section of a collecting zone in the stream.
16. The process according to claim 11, wherein the cooling of the third gas stream is effected by refrigeration
17. The process according to claim 16 wherein a hydrate inhibitor, is injected into the third gas stream prior to refrigeration.
18. The process according to claim 17, wherein step (a) comprises
(a1) heating the first gas stream in a heating zone to obtain a heated first gas stream;
(a2) contacting the heated first gas stream with the first adsorbent bed in regeneration mode.
19. The process according to claim 18, wherein the first gas stream is passed through a third adsorbent bed in cooling mode, prior to being contacted with the first adsorbent bed.
20. A system for removing contaminants from a natural gas stream, the system comprising:
a first adsorption bed arranged to receive part of the natural gas stream as a first gas stream, and provided with a means for heating the first adsorbent bed, which first adsorption bed has an outlet for a second gas stream.
a cooler for cooling the second gas stream;
a first gasliquid separator for separating the cooled second gas stream into a first liquid phase and a third gas stream; and
a second gasliquid separator for separating the third gas stream into a second liquid phase and a lean gas stream.
21. The system according to claim 20, further comprising a second adsorbent bed arranged to receive another part of the natural gas stream at a temperature at which contaminants are adsorbed, and having an outlet for a purified gas stream.
22. The system according to claim 21, wherein the second adsorbent bed is arranged to receive the lean gas stream together with the other part of the natural gas stream.
23. The system according to claim 22, wherein the first gasliquid separator comprises a cooler arranged to condense liquid at a temperature above the freezing point of water, and wherein the second gasliquid separator is arranged to separate contaminants that condense at a temperature lower than 0\xb0 C.
24. The system according to claim 23, wherein the second gasliquid separator an accelerated velocity inertia separator.
25. The system according to claim 24, wherein the accelerated velocity inertia separator comprises means for inducing a swirling motion the fluid stream entering this separator, thereby causing the contaminants, in particular water and hydrocarbons, to flow to a radially outer section of a collecting zone in the stream.
26. The system according to claim 23, wherein the second gasliquid separator comprises a refrigerator.
27. The system according to claim 26, wherein the means for heating the first adsorbent bed comprises a heater for the first gas stream.
28. The system according to claim 27, further comprising a third adsorbent bed arranged to receive the first gas stream prior to the first adsorbent bed.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A zoom lens comprising:
a first lens group having negative refracting power;
a second lens group having positive refracting power; and
a third lens group having positive refracting power, disposed in the order from an object side to an image side,
wherein, during zooming from a wide angle end to a telephoto end, the first lens group is moved and the second lens group is moved together with a stop toward the object such that an air space between the first lens group and the second lens group decreases and such that an air space between the second lens group and the third lens group increases,
the second lens group includes a positive lens aspherically shaped on at least a side thereof facing the object and having a convex surface facing the object and a negative lens positioned on the image side of the positive lens, aspherically shaped on at least a side thereof facing the image and having a concave surface facing the image, and
the zoom lens is configured to satisfy the following Conditional Expressions (1) and (2)
0.7<R2fR2r<2.0\u2003\u2003(1)
1.0<|SgaSgs|<1.5\u2003\u2003(2)
wherein R2f represents a paraxial radius of curvature of the object-facing surface of the positive lens; R2r represents a paraxial radius of curvature of the image-facing surface of the negative lens; Sgs represents the sag of the paraxial radius of curvature of the image-facing surface in the effective aperture of the image-facing surface of the negative lens; and Sga represents the sag of the aspherical shape of the image-facing surface in the effective aperture of the image-facing surface of the negative lens.
2. The zoom lens according to claim 1,
wherein the second lens group includes the positive lens, a positive lens which has a convex surface facing the object and the negative lens, which are disposed in the order from the object side to the image side.
3. The zoom lens according to claim 1,
wherein the second lens group includes the positive lens and a cemented lens formed by bonding a positive lens having a convex surface facing the object and the negative lens, which are disposed in the order from the object side to the image side.
4. The zoom lens according to claim 1,
wherein the first lens group includes a negative lens aspherically shaped on both sides thereof and having a concave surface facing the image and a positive meniscus lens aspherically shaped on at least a side thereof facing the object and having a convex surface facing the object, which are disposed in the order from the object side to the image side.
5. The zoom lens according to claim 1, the zoom lens satisfying the following Conditional Expressions (3), (4) and (5)
1.5<|f2fw|<2.5\u2003\u2003(3)
2.0<|f1fw|<3.2\u2003\u2003(4)
0.5<D2fw<1.5\u2003\u2003(5)
wherein f2 represents the focal length of the second lens group; fw represents the focal length of the entire lens system at the state of the wide angle end; f1 represents the focal length of the first lens group; and D2 represents the thickness of the second lens group measured on the optical axis thereof.
6. The zoom lens according to claim 1,
wherein the third lens group is configured by a single lens having a focusing function.
7. The zoom lens according to claim 4, the zoom lens satisfying the following Conditional Expressions (6), (7) and (8)
n11>1.8\u2003\u2003(6)
n12>1.9\u2003\u2003(7)
\u03bd12<25\u2003\u2003(8)
wherein n11 represents the refractive index of the negative lens in the first lens group measured using a d-ray, n12 represents the refractive index of the positive meniscus lens in the first lens group measured using a d-ray; and \u03bd12 represents the Abbe number of the positive meniscus lens in the first lens group.
8. The zoom lens according to claim 1, not changing an aperture diameter of the stop during zooming.
9. The zoom lens according to claim 3,
wherein alignment is performed between a positive lens of the second lens group positioned on the object side and a cemented lens of the second lens group.
10. An imaging apparatus comprising:
a zoom lens; and
an imaging device converting an optical image formed by the zoom lens into an electrical signal,
wherein the zoom lens includes a first lens group having negative refracting power, a second lens group having positive refracting power, and a third lens group having positive refracting power, disposed in the order from an object side to an image side,
during zooming from a wide angle end to a telephoto end, the first lens group is moved and the second lens group is moved together with a stop toward the object such that an air space between the first lens group and the second lens group decreases and such that an air space between the second lens group and the third lens group increases, and
the second lens group includes a positive lens aspherically shaped on at least a side thereof facing the object and having a convex surface facing the object and a negative lens positioned on the image side of the positive lens, aspherically shaped on at least a side thereof facing the image and having a concave surface facing the image, and
the imaging apparatus is configured to satisfy the following Conditional Expressions (1) and (2)
0.7<R2fR2r<2.0\u2003\u2003(1)
1.0<|SgaSgs|<1.5\u2003\u2003(2)
wherein R2f represents a paraxial radius of curvature of the object-facing surface of the positive lens; R2r represents a paraxial radius of curvature of the image-facing surface of the negative lens; Sgs represents the sag of the paraxial radius of curvature of the image-facing surface in the effective aperture of the image-facing surface of the negative lens; and Sga represents the sag of the aspherical shape of the image-facing surface in the effective aperture of the image-facing surface of the negative lens.