SYSTEM AND METHOD FOR DERIVING STORAGE TANK OPERATION PLAN

• US 20140303792A1
• Filed: 10/19/2012
• Published: 10/09/2014
• Est. Priority Date: 10/24/2011
• Status: Active Grant

• Current Assignee: Osaka Gas Company Limited
• Original Assignee: Osaka Gas Company Limited
• Inventors: Kawamoto, Kaoru, Tsuzaki, Kenji, Okamura, Tomohito, Tani, Hiromasa, Ueda, Tomokazu, Hashimoto, Nobuaki, Kawata, Keisuke, Tanabe, Takahito, Harada, Kouhei, Nitanda, Atsushi, Nitta, Toshihiro
• Granted Patent: US 9,513,639 B2
• Time in Patent Office: Days
• US Class Current: 700/281
• CPC Class Codes: G05D 9/12 characterised by the use of electric means
• CPC Class Codes: G06Q 10/04 Forecasting or optimisation specially adapted for administrative or management purposes, e.g. linear programming or "cutting stock problem" market predictions or forecasting for commercial activities G06Q30/0202
• CPC Class Codes: G06Q 10/06 Resources, workflows, human or project management; Enterprise or organisation planning; Enterprise or organisation modelling
• CPC Class Codes: G06Q 50/06 Energy or water supply

Abstract

To derive a feasible solution for an operation plan problem for storage tanks for storing liquefied natural gas, which is a complicated mixed-integer non-linear problem, given tank initial state information, reception plan information, and feed plan information, two solving processes are executed alternately two or more times, respectively: a first solving process that replaces a mixed-integer non-linear programming problem with a mixed-integer linear programming problem by linear approximation of a non-linear expression in non-linear constraints containing the non-linear expression, and solves the problem to derive provisional solutions or final solutions for a reception pattern that prescribes a storage tank that is to receive liquefied natural gas, and a discharge pattern that prescribes a storage tank that is to discharge liquefied natural gas, and a second solving process that replaces a mixed-integer non-linear programming problem with a continuous non-linear programming problem by provisionally fixing a discrete variable in discrete form constraints containing the discrete variable, and solves the problem to derive provisional solutions or final solutions for transitions of storage quantity and storage heat quantity of liquefied natural gas in each storage tank.

Claims

1. A storage tank operation plan deriving system, comprising:

storage means configured to accept respective inputs of tank initial state information containing initial storage quantity and initial storage heat quantity of liquefied natural gas of each of a plurality of storage tanks for storing the liquefied natural gas, reception plan information containing reception time, reception quantity and reception heat quantity of the liquefied natural gas in each of plural reception plans for the liquefied natural gas, and feed plan information containing feed plan quantity on a predetermined unit period basis in a feed plan for feeding the liquefied natural gas directly or after being vaporized from one or more discharge lines to feeding destinations assigned to each of the discharge lines, in a predetermined planning period, to save each information as input information, and to store a plurality of constraints on reception and storage of the liquefied natural gas into the storage tanks, and a plurality of constraints on discharge of the liquefied natural gas from the storage tanks to the discharge lines; and

arithmetic processing means for finding a feasible solution for the storage tank operation plan problem at least on operations of reception and discharge of the liquefied natural gas configured as a mixed-integer non-linear programming problem by the input information and the constraints through computerized arithmetic processes,

the arithmetic processing means including first processing means for solving a mixed-integer linear programming problem, and second processing means for solving a continuous non-linear programming problem, and being configured to execute, given the input information;

a first solving process including conducting a first relaxing process on each of plural non-linear constraints containing a non-linear expression of the constraints, to replace the mixed-integer non-linear programming problem with a mixed-integer linear programming problem, and solving the mixed-integer linear programming problem by using the first processing means to derive at least provisional solutions or final solutions for a reception pattern that prescribes one or more of the storage tanks that are to be objectives of reception of the liquefied natural gas in each of the reception plans in the planning period, and a discharge pattern that prescribes the storage tank that is to discharge the liquefied natural gas corresponding to the feed plan quantity on the unit period basis, and

a second solving process including conducting a second relaxing process on a plurality of discrete form constraints containing discrete variables of the constraints, to replace the mixed-integer non-linear programming problem with a continuous non-linear programming problem, and solving the continuous non-linear programming problem by using the second processing means to derive at least provisional solutions or final solutions for transitions of storage quantity and storage heat quantity of the liquefied natural gas for each of the storage tanks, two or more times, respectively, and

in the first solving process of the second or later time, configured to execute the first relaxing process on at least part of the non-linear constraints by using provisional solutions for transitions of storage quantity and storage heat quantity of the liquefied natural gas derived in the preceding second solving process, and

in the second solving process of the first or later time, configured to execute the second relaxing process on at least part of the discrete form constraints, by using the discrete variables derived in the preceding first solving process.

2. The storage tank operation plan deriving system according to claim 1, wherein, given the input information, the arithmetic processing means is configured to execute in sequence:

a first arithmetic process that executes the first solving process to derive a final solution for the reception pattern, a provisional solution for the discharge pattern, and provisional solutions for transitions of storage quantity and storage heat quantity of the liquefied natural gas in each of the storage tanks,

a second arithmetic process that executes the second solving process based on the final solution and each of the provisional solutions derived through the first arithmetic process, to derive at least new provisional solutions for transitions of storage quantity and storage heat quantity of the liquefied natural gas in each of the storage tanks,

a third arithmetic process that executes the first solving process based on the final solution and each of most recent ones of the provisional solutions derived through the first and the second arithmetic processes, to derive at least a new provisional solution or a final solution for the discharge pattern, and

a fourth arithmetic process that executes the second solving process based on the final solution and each of most recent ones of the provisional solutions derived through the first to the third arithmetic processes, to derive at least new provisional solutions or final solutions for transitions of storage quantity and storage heat quantity of the liquefied natural gas in each of the storage tanks.

3. The storage tank operation plan deriving system according to claim 2, wherein, in the case where specific storage tanks of the plurality of storage tanks are connected by a transfer line, and the liquefied natural gas is transferable therebetween,

the storage means is configured to further store as constraints of the mixed-integer non-linear programming problem, a plurality of constraints on transfer of the liquefied natural gas between the storage tanks, and

the arithmetic processing means, given the input information, is configured to sequentially execute the first to the fourth arithmetic processes while not considering at least part of the constraints on transfer, to further derive a provisional solution for a transfer pattern that prescribes the specific storage tanks between which transfer of the liquefied natural gas is to be conducted in the planning period in the first arithmetic process, and a new provisional solution for the transfer pattern in the third arithmetic process, and to further execute:

a fifth arithmetic process that executes the first solving process based on the final solution and each of most recent ones of the provisional solutions derived through the first to the fourth arithmetic processes while considering the constraints on transfer, to derive a new provisional solution of the transfer pattern, and

a sixth arithmetic process that executes the second solving process based on the final solution and each of most recent ones of the provisional solutions derived through the first to the fifth arithmetic processes while considering the constraints on transfer, to derive final solutions for transitions of storage quantity and storage heat quantity of the liquefied natural gas in each of the storage tanks and a final solution of the transfer pattern.

4. The storage tank operation plan deriving system according to claim 1, wherein the arithmetic processing means is configured to execute the first and the second solving processes by using density of the liquefied natural gas that can be approximately converted into the heat quantity in place of heat quantity of the liquefied natural gas contained in the input information and the constraints, and to derive a provisional solution for transition of density of the liquefied natural gas in each of the storage tanks in place of the provisional solution for transition of storage heat quantity of the liquefied natural gas in each of the storage tanks.

5. The storage tank operation plan deriving system according to claim 4, wherein in the first relaxing process, mass of the liquefied natural gas represented by a non-linear expression of product of density and volume of the liquefied natural gas contained in the constraints is linearly approximated to a linear polynomial composed of a volume term including standard density as a coefficient, a density term including standard volume as a coefficient, and a constant term.

6. The storage tank operation plan deriving system according to claim 1, wherein, in the first and the second solving processes, the arithmetic processing means is configured to derive the final solution and the provisional solutions as feasible solutions that minimize an objective function established by weighted summing one or more penalty, the penalty being deviation from a predetermined standard value of an item to be monitored defined by at least one variable of the continuous variables and the discrete variables.

7. The storage tank operation plan deriving system according to claim 6, wherein in at least one of the first and the second solving processes, deviation between average heat quantity of the liquefied natural gas fed in a predetermined period for each discharge line, and a predetermined standard heat quantity is contained as one of the penalty.

8. The storage tank operation plan deriving system according to claim 1, wherein

the storage means is configured to further accept input of detailed feed plan information containing feed plan quantity per unit subdivided period that is subdivision of the predetermined unit period, and to save the information as the input information, and

the arithmetic processing means is configured to derive final solutions of the reception pattern and the discharge pattern by executing the first and the second solving processes at least twice, respectively, and to derive subsequently, given the input information containing the detailed feed plan information, discharge quantity per unit subdivided period for each of the storage tanks based on the derived final solutions and each of the preceding provisional solutions.

9. The storage tank operation plan deriving system according to claim 1, wherein the discharge pattern prescribes one or more of discharging pumps to be used for discharge of the liquefied natural gas among the discharging pumps interposed between the storage tanks and the discharge line for each discharge line.

10. The storage tank operation plan deriving system according to claim 1, wherein the arithmetic processing means uses a processing result at the last point of time of an elapsed part of first planning period that has started but not ended yet, as an initial condition in the first and the second solving processes for a second planning period that starts from the beginning of an unelapsed part of the first planning period.

11. The storage tank operation plan deriving system according to claim 1, wherein the constraints contain a constraint for preventing layering that occurs when the liquefied natural gases having different compositions are stored in the storage tank.

12. A storage tank operation plan deriving method comprising:

an input information storage step of accepting respective inputs of tank initial state information containing initial storage quantity and initial storage heat quantity of liquefied natural gas of each of a plurality of storage tanks for storing the liquefied natural gas, reception plan information containing reception time, reception quantity and reception heat quantity of the liquefied natural gas in each of plural reception plans for the liquefied natural gas, and feed plan information containing feed plan quantity on a predetermined unit period basis in a feed plan for feeding the liquefied natural gas directly or after being vaporized from one or more discharge lines to feeding destinations assigned to each of the discharge lines, in a predetermined planning period, and saving each information as input information in predetermined storage means; and

an arithmetic processing step of finding a feasible solution for the storage tank operation plan problem at least on operations of reception and discharge of the liquefied natural gas configured as a mixed-integer non-linear programming problem by the input information, a plurality of constraints on reception and storage of the liquefied natural gas into the storage tanks, and a plurality of constraints on discharge of the liquefied natural gas from the storage tanks to the discharge lines through computerized arithmetic processes,

wherein, in the arithmetic processing step, given the input information,

a first solving process including conducting a first relaxing process on each of plural non-linear constraints containing a non-linear expression of the constraints, to replace the mixed-integer non-linear programming problem with a mixed-integer linear programming problem, and solving the mixed-integer linear programming problem by using first processing means to derive at least provisional solutions or final solutions for a reception pattern that prescribes one or more of the storage tanks that are to be objectives of reception of the liquefied natural gas in each of the reception plans in the planning period, and a discharge pattern that prescribes the storage tank that is to discharge the liquefied natural gas corresponding to the feed plan quantity on the unit period basis, and

a second solving process including conducting a second relaxing process on a plurality of discrete form constraints containing discrete variables of the constraints, to replace the mixed-integer non-linear programming problem with a continuous non-linear programming problem, and solving the continuous non-linear programming problem by using second processing means to derive at least provisional solutions or final solutions for transitions of storage quantity and storage heat quantity of the liquefied natural gas for each of the storage tanks are executed two or more times, respectively, and

in the first solving process of the second or later time, the first relaxing process is executed on at least part of the non-linear constraints by using provisional solutions for transitions of storage quantity and storage heat quantity of the liquefied natural gas derived in the preceding second solving process, and

in the second solving process of the first or later time, the second relaxing process is executed on at least part of the discrete form constraints, by using the discrete variables derived in the preceding first solving process.

13. The storage tank operation plan deriving method according to claim 12, wherein, in the arithmetic processing step, given the input information,

a first arithmetic process that executes the first solving process to derive a final solution for the reception pattern, a provisional solution for the discharge pattern, and provisional solutions for transitions of storage quantity and storage heat quantity of the liquefied natural gas in each of the storage tanks,

a second arithmetic process that executes the second solving process based on the final solution and each of the provisional solutions derived through the first arithmetic process, to derive at least new provisional solutions for transitions of storage quantity and storage heat quantity of the liquefied natural gas in each of the storage tanks,

a third arithmetic process that executes the first solving process based on the final solution and each of most recent ones of the provisional solutions derived through the first and the second arithmetic processes, to derive at least a new provisional solution or a final solution for the discharge pattern, and

a fourth arithmetic process that executes the second solving process based on the final solution and each of most recent ones of the provisional solutions derived through the first to the third arithmetic processes, to derive at least new provisional solutions or final solutions for transitions of storage quantity and storage heat quantity of the liquefied natural gas in each of the storage tanks are executed in sequence.

14. The storage tank operation plan deriving method according to claim 13, wherein, in the case where specific storage tanks of the plurality of storage tanks are connected by a transfer line, and the liquefied natural gas is transferable therebetween,

as constraints of the mixed-integer non-linear programming problem, a plurality of constraints on transfer of the liquefied natural gas between the storage tanks are further included,

in the arithmetic processing step, given the input information,

the first to the fourth arithmetic processes are sequentially executed while at least part of the constraints on transfer are not considered to further derive a provisional solution for a transfer pattern that prescribes the specific storage tanks between which transfer of the liquefied natural gas is to be conducted in the planning period in the first arithmetic process, and a new provisional solution for the transfer pattern in the third arithmetic process, and

a fifth arithmetic process that executes the first solving process based on the final solution and each of most recent ones of the provisional solutions derived through the first to the fourth arithmetic processes while considering the constraints on transfer, to derive a new provisional solution of the transfer pattern, and

a sixth arithmetic process that executes the second solving process based on the final solution and each of most recent ones of the provisional solutions derived through the first to the fifth arithmetic processes while considering the constraints on transfer, to derive final solutions for transitions of storage quantity and storage heat quantity of the liquefied natural gas in each of the storage tanks and a final solution of the transfer pattern are executed.

15. The storage tank operation plan deriving method according to claim 12, wherein, in the arithmetic processing step, the first and the second solving processes are executed by using density of the liquefied natural gas that can be approximately converted into the heat quantity in place of heat quantity of the liquefied natural gas contained in the input information and the constraints, to derive a provisional solution for transition of density of the liquefied natural gas in each of the storage tanks in place of the provisional solution for transition of storage heat quantity of the liquefied natural gas in each of the storage tanks.

16. The storage tank operation plan deriving method according to claim 15, wherein in the first relaxing process, mass of the liquefied natural gas represented by a non-linear expression of product of density and volume of the liquefied natural gas contained in the constraints is linearly approximated to a linear polynomial composed of a volume term including standard density as a coefficient, a density term including standard volume as a coefficient, and a constant term.

17. The storage tank operation plan deriving method according to claim 12, wherein, in the first and the second solving processes of the arithmetic processing step, the final solution and the provisional solutions are derived as feasible solutions that minimize an objective function established by weighted summing one or more penalty, the penalty being deviation from a predetermined standard value of an item to be monitored defined by at least one variable of the continuous variables and the discrete variables.

18. The storage tank operation plan deriving method according to claim 17, wherein in at least one of the first and the second solving processes of the arithmetic processing step, deviation between average heat quantity of the liquefied natural gas fed in a predetermined period for each discharge line, and a predetermined standard heat quantity is contained as one of the penalty.

19. The storage tank operation plan deriving method according to claim 12, wherein in the input information storage step, input of detailed feed plan information containing feed plan quantity per unit subdivided period that is subdivision of the predetermined unit period is further accepted, and the information is saved as the input information, and

in the arithmetic processing step, the first and the second solving processes are executed at least twice, respectively, to derive final solutions of the reception pattern and the discharge pattern, and then given the input information containing the detailed feed plan information, discharge quantity per unit subdivided period for each of the storage tanks is derived based on the derived final solutions and each of the preceding provisional solutions.

20. The storage tank operation plan deriving method according to claim 12, wherein the discharge pattern prescribes one or more of discharging pumps to be used for discharge of the liquefied natural gas among the discharging pumps interposed between the storage tanks and the discharge line for each discharge line.

21. The storage tank operation plan deriving method according to claim 12, wherein in the arithmetic processing step, a processing result at the last point of time of an lapsed part of first planning period that has started but not ended yet is used, as an initial condition in the first and the second solving processes for a second planning period that starts from the beginning of an unelapsed part of the first planning period.

22. The storage tank operation plan deriving method according to claim 12, wherein the constraints contain a constraint for preventing layering that occurs when the liquefied natural gases having different compositions are stored in the storage tank.