Producing gaseous fuels of high calorific value

Claim 2

A process of upgrading a methane gas stream contaminated with a minor but significant quantity of air by fractionation at sub-ambient temperatures and superatmospheric pressures, said process comprising the steps of compressing said air-contaminated methane gas stream to elevated pressure, cooling the compressed gas to condense said gas, expanding the condensate to fractionation pressure and thereafter fractionating said expanded condensate to yield a liquid first product stream having a methane content higher than that of the initial composition and a calorific value commensurate with that of natural gas, and a gaseous second product stream having a methane content below that of the initial composition but above the highest limit of the flammability range of methane-air mixtures under the conditions of temperature and pressure prevailing in said fractionation, said elevated pressure being sufficiently high for substantially the whole of the refrigeration requirements of said cooling step to be provided from said subsequent expansion to fractionation pressure, and said cooling of the compressed gas being effected by indirect countercurrent heat exchange with first product and with evaporating second product.

Claim 3

A process as claimed in claim 1 in which at least a part of the energy requirements of the process are provided by combustion of a fuel gas provided by the second product of the fractionation.

Claim 4

A process as claimed in claim 1 in which said air-contaminated methane gas stream is compressed in compressor means powered at least in part by prime mover means driven by combustion of a fuel gas provided by said second product stream.

Claim 5

A process as claimed in claim 1 in which at least one of said product streams after recovery from said fractionation is compressed to a pressure above said fractionation pressure, and the compression of the air-contaminated gas stream and of said at least one of said product streams is effected by compressor means powered at least in part by prime mover means driven by combustion of a fuel gas provided by said second product stream.

Claim 6

A process as claimed in claim 1 in which the air-contaminated methane gas stream contains at least one contaminant which would freeze under the fractionation conditions, and in which prior to condensation said contaminant is removed from said stream by adsorbing said contaminant on an adsorbent therefor, and said adsorbent is thereafter regenerated by the passage therethrough of a regeneration gas provided by one of said product streams.

Claim 7

A process as claimed in claim 5 in which before passing it through the adsorbent the regeneration has is directly or indirectly heated by combustion of a fuel gas provided by said second product stream.

Claim 8

A process as claimed in claim 5 in which said product stream is compressed after recovery from the fractionation and the regeneration gas is provided from the said compressed product stream.

Claim 9

A process as claimed in claim 5 in which said regeneration gas comprises a portion of said one product stream, and after passage through said adsorbent, said regeneration gas is recombined with the remainder of said one product stream for subsequent use as a fuel gas.

Claim 10

A process as claim 7 in which said regeneration gas comprises a portion of said compressed product stream and after passage through said adsorbent said regeneration gas is recombined with the remainder of said compressed product stream for subsequent use as a fuel gas.

Claim 11

Apparatus for upgrading an air-contaminated methane composition, said apparatus comprising in combination: a. first, second and third compression means each having a gas inlet and a gas outlet, b. gas-fuelled prime mover means for driving said first, second and third compression means, c. indirect countercurrent heat exchange means, d. expansion valve means, e. a fractionating column having an inlet, a liquid outlet below said inlet and a gas outlet above said inlet, f. a pump having an inlet and outlet, g. means for feeding said composition to the inlet of said first compression means, h. means for passing compressed composition from the outlet of said first compression means through said indirect countercurrent heat exchange means and then through said expansion valve means where it is expanded to a lower pressure and thence to the inlet of said fractionating column, i. means for separating a liquid product from the liquid outlet of said fractionating column into first and second portions, and means for recycling said first portion of said product through said heat exchange means in indirect countercurrent heat exchange with said compressed composition and back to the fractionating column, j. means for passing said second portion of the liquid product to the inlet of said pump, k. means for passing the liquid product from the outlet of said pump through said heat exchange means in indirect countercurrent heat exchange with said compressed composition and thence to the inlet of said second compression means, l. means for recovering a compressed fuel gas from the outlet of said second compression means, m) means for recoverng a gaseous product from the gas outlet of said fractionating column passing it through said m. exchange means in indirect countercurrent heat exchange with said compressed composition and thence to the inlet of said third compression means, and n. means for recovering a compressed lean fuel gas from the outlet of said third compression means and for feeding said gas as fuel to said prime mover means, said indirect countercurrent heat exchange means including first and second heat exchangers and in which said first heat exchanger contains first passage means for the passage therethrough of said compressed composition and second and third passage means for the passage therethrough respectively of said gaseous product and said second portion of said liquid product each in countercurrent to said compressed composition, and said second heat exchanger contains first passage means the inlet of which is connected to the outlet of said first passage means of said first heat exchanger for the passage therethrough of said compressed composition after it has traversed said first heat exchanger and second passage means for the passage therethrough of said first portion of said liquid product in countercurrent to said compressed composition.

Claim 12

Apparatus for upgrading an air-contaminated methane composition, said apparatus comprising in combination: a. first, second and third compression means each having a gas inlet and a gas outlet, b. gas-fuelled prime mover means for driving said first, second and third compression means, c. indirect countercurrent heat exchange means, d. expansion valve means, e. a fractionating column having an inlet, a liquid outlet below said inlet and a gas outlet above said inlet, f. a pump having an inlet and outlet, g. means for feeding said composition to the inlet of said first compression means, h. means for passing compressed composition from the outlet of said first compression means through said indirect countercurrent heat exchange means and then through said expansion valve means where it is expanded to a lower pressure and thence to the inlet of said fractionating column, i. means for separating a liquid product from the liquid outlet of said fractionating column into first and second portions, and means for recycling said first portion of said product through said heat exchange means in indirect countercurrent heat exchange with said compressed composition and back to the fractionating column, j. means for passing said second portion of the liquid product to the inlet of said pump, k. means for passing the liquid product from the outlet of said pump through said heat exchange means in indirect countercurrent heat exchange with said compressed composition and thence to the inlet of said second compression means, l. means for recovering a compressed fuel gas from the outlet of said second compression means, m) means for recoverng a gaseous product from the gas outlet of said fractionating column passing it through said m. exchange means in indirect countercurrent heat exchange with said compressed composition and thence to the inlet of said third compression means, and n. means for recovering a compressed lean fuel gas from the outlet of said third compression means and for feeding said gas as fuel to said prime mover means, said indirect countercurrent heat exchange means including first and second heat exchangers and in which said first heat exchanger contains first passage means for the passage therethrough of said compressed composition and second and third passage means for the passage therethrough respectively of said gaseous product and said second portion of said liquid product each in countercurrent to said compressed composition, and said second heat exchanger contains first passage means the inlet of which is connected to the outlet of said first passage means of said first heat exchanger for the passage therethrough of said compressed composition after it has traversed said first heat exchanger and second passage means for the passage therethrough of said first portion of said liquid product in countercurrent to said compressed composition.

Claim 13

Apparatus as claimed in claim 10 further including: adsorber means comprising at least two beds of adsorbent arranged for cyclic operation such that in each period of the cycle at least one of the beds receives for treatment compressed gas recovered from the outlet of said first compression means, the treated gas being thereafter passed to said heat exchange means, and at least another of the beds is being regenerated for re-use in a subsequent period of the cycle, said regeneration being effected by the passage of regeneration gas therethrough, and means for providing a portion of said gaseous product leaving said heat exchange means to said adsorber means as said regeneration gas.

Claim 14

Apparatus as claimed in claim 11 including means for passing the regeneration gas recovered from the adsorber means to the inlet of said third compression means.

Claim 15

Apparatus as claimed in claim 10 further including: adsorber means comprising at least two beds of adsorbent arranged for cyclic operation such that in each period of the cycle at least one of the beds receives for treatment compressed gas recovered from the outlet of said first compression means, the treated gas being thereafter passed to said heat exchange means, and at least another of the beds is being regenerated for re-use in a subsequent period of the cycle, said regeneration being effected by the passage of regeneration gas therethrough, and means for providing a part of said compressed lean fuel gas to said adsorber means as regeneration gas.

Claim 16

Apparatus as claimed in claim 13 including means for recombining the regeneration gas recovered from said adsorber means with the remainder of the compressed lean fuel gas.

Claim 17

Apparatus as claimed in claim 10 in which said first compression means comprises compression means operable with an inlet pressure below atmospheric pressure.

Claim 18

Apparatus as claimed in claim 11 further including means for heating the regenerating gas, prior to its passage through said adsorber means, by means of combustion of said compressed lean fuel gas.

Claim 19

Apparatus as claimed in claim 13 further including means for heating the regenerating gas, prior to its passage through said adsorber means, by means of combustion of said compressed lean fuel gas.