1. A process for liquefying natural gas or other methane-rich gases comprising:
cooling feed natural gas at a pressure of from 40 to 100 bar (4 to 10 MPa) to a temperature of \u221250\xb0 to \u221280\xb0 C. by means of a heat exchanger and a first gas expander, the heat exchanger receiving the feed natural gas and having an outlet temperature higher than the outlet temperature of the expander;
reheating the expander outlet stream in a first cold passage of said heat exchanger to just below the inlet temperature of the feed natural gas to said heat exchanger, compressing and recycling;
passing part or all of the cold outlet stream from said heat exchanger into a second expander in which it is partly liquefied;
separating the outlet stream of said second expander into vapour and liquid fractions;
collecting the liquid fraction for use as LNG product,
reheating the vapour fraction in a second cold side passage of said heat exchanger to just below the inlet temperature of the feed natural gas to said heat exchanger;
recycling the said reheated vapour fraction after compression in part to the said first expander and in part to the said heat exchanger;
wherein
the outlet stream of the second expander is at a pressure between 5 and 15 bar (0.5 and 1.5 MPa).
2. The process as claimed in claim 1 in which the heat exchanger receives all the feed natural gas.
3. The process as claimed in claim 1 in which the heat exchanger receives a large part, at least 30%, of the feed natural gas.
4. The process as claimed in claim 1 in which the feed natural gas is cooled to a temperature of \u221260\xb0 to \u221270\xb0 C.
5. The modification of the process claimed in claim 1 in which the said first and second gas expanders have essentially the same outlet pressure of between 5 bar and 15 bar (0.5 and 1.5 MPa), and the outlet streams from both expanders are combined prior to final reheating, compression and recycle.
6. The process as claimed in claim 1 in which any part or all of the feed andor compressor discharge andor recycle streams are cooled, typically by use of an absorption refrigeration cycles such as lithium bromide (LiBr).
7. The process as claimed in claim 1 in which the heat requirement for an absorption refrigeration system is supplied by gas engine or gas turbine exhaust heat, such gas engines or turbines which may be used for supplying power to the process compressors.
8. The process as claimed in claim 1 wherein such cooling of either feed andor recycle streams is combined with removal of carbon dioxide andor other impurities from the feed gas.
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 semiconductor light emitting device, comprising:
a substrate;
a first conductive semiconductor layer on the substrate;
an active layer on the first conductive semiconductor layer;
a second conductive semiconductor layer on the active layer, the second conductive semiconductor layer including a top surface and a bottom surface opposing to the top surface, the bottom surface being adjacent to the active layer;
a roughness layer disposed on the second conductive semiconductor layer and including Al material;
a conductive layer including Ti material on the roughness layer; and
at least one of a first AlGaN based semiconductor layer disposed on the active layer and a second AlGaN based semiconductor layer disposed under the active layer,
wherein the first conductive semiconductor layer includes a first GaN layer and the second conductive semiconductor layer includes a second GaN layer,
wherein the second conductive semiconductor layer includes a plurality of apexes on the top surface, the distance between at least two apexes of the plurality of apexes is about 0.3 \u03bcm to about 1.0 \u03bcm,
wherein the conductive layer includes a lower surface having a shape corresponding to the top surface of the second conductive semiconductor layer, and
wherein the roughness layer includes a lower surface having a shape corresponding to the top surface of the second conductive semiconductor layer.
2. The semiconductor light emitting device according to claim 1, further comprising an electrode on the second conductive semiconductor layer, wherein the electrode has a bottom surface with a shape corresponding to the top surface of the second conductive semiconductor layer.
3. The semiconductor light emitting device according to claim 1, wherein the conductive layer includes an upper surface having a shape corresponding to the top surface of the second conductive semiconductor layer.
4. The semiconductor light emitting device according to claim 1, wherein the roughness layer includes an upper surface having a shape corresponding to the top surface of the second conductive semiconductor layer.
5. The semiconductor light emitting device according to claim 1, wherein the roughness layer is a semiconductor layer.
6. The semiconductor light emitting device according to claim 1, wherein the roughness layer is formed of a same semiconductor material as that of the second conductive semiconductor layer.
7. The semiconductor light emitting device according to claim 1, wherein the roughness layer has a thickness of about 1000 \u212b to about 2000 \u212b.
8. A semiconductor light emitting device, comprising:
a first conductive semiconductor layer;
an active layer on the first conductive semiconductor layer;
a second conductive semiconductor layer on the active layer;
a roughness layer on the second conductive semiconductor layer and including Al material; and
a conductive layer on the roughness layer and including Ti material,
wherein a top surface of the second conductive semiconductor layer includes a roughness,
wherein the roughness layer includes a lower surface having a shape corresponding to the top surface of the second conductive semiconductor layer, and
wherein the conductive layer includes a lower surface having a shape corresponding to the top surface of the second conductive semiconductor layer.
9. The semiconductor light emitting device according to claim 8, wherein the first conductive semiconductor layer includes a first GaN layer and the second conductive semiconductor layer includes a second GaN layer.
10. The semiconductor light emitting device according to claim 8, wherein the second conductive semiconductor layer includes a plurality of apexes on the top surface, the distance between at least two apexes of the plurality of apexes is of about 0.3 \u03bcm to about 1.0 \u03bcm.
11. The semiconductor light emitting device according to claim 8, further comprising an electrode on the roughness layer, wherein the electrode has a bottom surface with a shape corresponding to the top surface of the second conductive semiconductor layer.
12. The semiconductor light emitting device according to claim 8, wherein the conductive layer includes an upper surface having a shape corresponding to the top surface of the second conductive semiconductor layer.
13. The semiconductor light emitting device according to claim 8, wherein the roughness layer includes an upper surface having a shape corresponding to the top surface of the second conductive semiconductor layer.
14. The semiconductor light emitting device according to claim 8, wherein the roughness layer has a thickness of about 1000 \u212b to about 2000 \u212b.
15. The semiconductor light emitting device according to claim 8, further comprising:
a first electrode electrically connected to the first conductive semiconductor layer; and
a second electrode electrically connected to the second conductive semiconductor layer.
16. The semiconductor light emitting device according to claim 8, further comprising an AlGaN based semiconductor layer disposed on the active layer.
17. A semiconductor light emitting device, comprising:
a first conductive semiconductor layer;
an active layer on the first conductive semiconductor layer;
a second conductive semiconductor layer on the active layer, the second conductive semiconductor layer including a top surface having a random structure in which protruding apex patterns and recessed valley patterns are arranged;
a roughness layer directly on the second conductive semiconductor layer, the roughness layer including top and bottom surfaces with a random structure corresponding to the random structure of the second conductive semiconductor layer; and
an electrode on the roughness layer, the electrode including a bottom surface with a random structure corresponding to the random structure of the second conductive semiconductor layer,
wherein a height of one of the protruding apex patterns of the random structure of the second conductive semiconductor layer is different from a height of another protruding apex pattern placed next thereto,
wherein a distance between two of the recessed valley patterns of the second conductive semiconductor layer placed next to each other is different from a distance between another two recessed valley patterns placed next thereto,
wherein a height difference between an uppermost protruding apex pattern of the random structure of the second conductive semiconductor layer and a lowermost recessed valley pattern of the random structure of the second conductive semiconductor layer is in a range of about 0.5 \u03bcm to about 1.2 \u03bcm, and
wherein a distance between two protruding apex patterns of the random structure of the second conductive semiconductor layer placed next to each other is in the range of about 0.3 \u03bcm to about 1.0 \u03bcm.
18. The semiconductor light emitting device according to claim 17, further comprising:
a conductive cladding layer on the active layer, the conductive cladding layer being an AlGaN based layer.
19. The semiconductor light emitting device according to claim 17, further comprising:
a conductive layer on the roughness layer including an upper surface having a shape corresponding to the top surface of the second conductive semiconductor layer.
20. The semiconductor light emitting device according to claim 17, wherein the first conductive semiconductor layer includes a first GaN layer and the second conductive semiconductor layer includes a second GaN layer.