System and method for deriving storage tank operation plan

摘要

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.

主权项

1. A storage tank operation plan deriving system, comprising:
a storage device 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 an arithmetic processing device configured with a computer and computer programs executable on the computer, the computer programs, when executed, 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 computer programs including a first general-purpose solver for solving a mixed-integer linear programming problem, and a second general-purpose solver for solving a continuous non-linear programming problem, and a control program for controlling the first and second general-purpose solvers, the control program 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 by linearly approximating a non-linear expression in a non-linear constraint in the constraints on reception and storage and part of the constraints on discharge without considering non-linear constraints contained in the remaining part of the constraints on discharge, and solving the mixed-integer linear programming problem by using the first general-purpose solver 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 by fixing every reception pattern and discrete variable using the result obtained in the preceding first solving process and considering the non-linear constraints contained in the remaining part of the constraints on discharge being not considered in the preceding first solving process, and solving the continuous non-linear programming problem by using the second general-purpose solver 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, wherein one or more storage tanks among the plurality of storage tanks is controlled to receive the liquefied natural gas of the reception quantity designated by the reception plan information at each point of the reception time as prescribed by the reception pattern, and wherein one or more discharge pumps among a plurality of discharge pumps interposed between the storage tanks and the discharge line is controlled for discharge of the liquefied natural gas as prescribed by the discharge pattern.