Configurations and methods for small scale LNG production
A small scale natural gas liquefaction plant is integrated with an LNG loading facility in which natural gas is liquefied using a multi-stage gas expansion cycle. LNG is then loaded onto an LNG truck or other LNG transport vehicle at the loading facility using a differential pressure control system that uses compressed boil off gas as a motive force to move the LNG from the LNG storage tank to the LNG truck so as to avoid the use of an LNG pump and associated equipment as well as to avoid venting of boil off vapors into the environment.
1. A small scale LNG plant with integrated loading terminal, comprising:
a refrigeration unit comprising a closed refrigeration cycle, wherein the refrigeration unit is configured to provide refrigeration content to a natural gas feed in an amount sufficient to produce LNG from the natural gas feed in a cold box;
a LNG storage tank fluidly coupled to the cold box, wherein the LNG storage tank is configured to receive and store the LNG;
a first boil off vapor conduit configured to provide a first boil off vapor from an LNG transporter to the cold box, and to transfer the first boil off vapor from the cold box to the LNG storage tank to thereby allow use of the first boil off vapor as a motive force to move the LNG out of the LNG storage tank to the LNG transporter;
a second boil off vapor conduit configured to provide a second boil off vapor from the LNG storage tank to the cold box, and from the cold box to the natural gas feed; and
a compressor that is configured to allow compression of at least one of the first boil off vapor or the second boil off vapor.
2. The plant of claim 1 , further comprising a differential pressure controller configured to maintain a predetermined pressure differential between the LNG storage tank and the LNG transporter.
3. The plant claim 2 , wherein the differential pressure controller is configured to allow liquefaction operation concurrent with filling operation of the LNG transporter.
4. The plant of claim 2 , wherein the predetermined pressure differential is between 10-50 psi.
5. The plant of claim 1 , wherein the refrigeration unit further comprises at least 3 exchanger passes configured to provide the natural as liquefaction refrigeration duty with a two stage nitrogen compression expander cycle.
6. The plant of claim 1 , wherein the closed refrigeration cycle comprises a two stage turboexpander that is fluidly coupled with a two stage compression system, wherein the two stage turboexpander is configured to generate low level cooling, wherein the two stage compression system is configured to generate chilled gas feeding the turbo expanders while the power produced from the turbo expanders are used to reduce the gas compression energy requirement, and wherein the refrigeration cycle is configured to operate with a non-hydrocarbon refrigerant.
7. The plant of claim 1 , wherein the refrigeration unit and storage tank are configured to provide an LNG production capacity of 10 to 200 tons per day.
8. The plant of claim 1 , wherein the plant does not comprise a LNG pump configured to pass the LNG from the LNG storage tank to the LNG transport.
9. The plant of claim 5 , wherein the refrigeration unit further comprises an exchange pass that is configured to recover refrigeration content from at least one of the first and second boil off vapors.