Underwater gas pressurization units and liquefaction systems, as well as pressurization and liquefaction methods are provided. Gas is compressed hydraulically by a rising pressurization liquid that is separated from the gas by a water immiscible liquid layer on top of an aqueous salt solution. Tall vessels are used to reach a high compression ratio that lowers the liquefaction temperature. The pressurizing liquid is delivered gravitationally, after gasification, transport to smaller water depths and condensation. Cooling units are used to liquefy the compressed gas. A cascade of compression and cooling units may be used with sequentially higher liquefaction temperatures, which allow eventual cooling by sea water. The pressurizing liquid, dimensions of the vessels, the delivery unit, the coolants and the implementation of the cooling units are selected according to the sea location, to enable natural gas liquefaction in proximity to the gas source.

Underwater gas pressurization units and liquefaction systems, as well as pressurization and liquefaction methods and gas field development methods are provided. Gas is compressed hydraulically by seawater introduced into vessels and separated from the gas by a water immiscible liquid layer. Tall, possibly vertical helical vessels are used to reach a high compression ratio that lowers the liquefaction temperature. Cooling units are used to liquefy the compressed gas, possibly by a coolant which is itself pressurized by a similar mechanism. The coolant may be selected to be liquefied under surrounding seawater temperatures. The seawater which is used to pressurize the gas may be used after evacuation from the vessels to pressurize intrastratal gas in the production stages and broaden the gas field development.

A semi-closed loop system for producing liquefied natural gas (LNG) that combines certain advantages of closed-loop systems with certain advantages of open-loop systems to provide a more efficient and effective hybrid system. In the semi-closed loop system, the final methane refrigeration cycle provides significant cooling of the natural gas stream via indirect heat transfer, as opposed to expansion-type cooling. A minor portion of the LNG product from the methane refrigeration cycle is used as make-up refrigerant in the methane refrigeration cycle. A pressurized portion of the refrigerant from the methane refrigeration cycle is employed as fuel gas. Excess refrigerant from the methane refrigeration cycle can be recombined with the processed natural gas stream, rather than flared.

A liquefied natural gas (LNG) facility that employs a system to remove incondensable material from one or more refrigeration cycles within the facility. One or more embodiments of the present invention can be advantageously employed in an open-loop refrigeration cycle to remove at least a portion of one or more high vapor pressure components that have accumulated in the refrigerant cycle over time. In addition, several embodiments can be advantageously employed to stabilize facility operation in the event of drastic changes to the concentration of the natural gas feed stream introduced into the facility.

A process and apparatus for liquefying a gas stream comprising hydrocarbons and sour species is provided in which the sour species are removed in liquefied form as the sweetened gas stream is progressively cooled to liquefaction temperatures. The process involves cooling the gas stream in a manner to produce a cooled gas stream comprising gaseous hydrocarbons and residual sour species. The cooled gas stream is then treated with a cold solvent to deplete the cooled gas stream of residual sour species. The resulting cooled sweetened gas stream is then further cooled to produce liquid hydrocarbons.

A method of processing natural gas to produce liquefied natural gas using a consolidated refrigeration and liquefaction module. The natural gas is cooled in a first array of one or more heat exchangers using a first refrigerant from a first refrigerant circuit, wherein the first refrigerant is compressed in a first compressor. A second refrigerant from a second refrigerant circuit is compressed in a second compressor. The second refrigerant is cooled and partially condensed using the first refrigerant in a second array of one or more heat exchangers located in the consolidated refrigeration and liquefaction module. The partially condensed second refrigerant is separated into liquid and vapor phases using a refrigerant separator located in the consolidated refrigeration and liquefaction module. The natural gas is liquefied to produce LNG in a third array of one or more heat exchangers using the vapor and liquid phases of the partially condensed second refrigerant.

A hydrocarbon processing plant, such an LNG plant, is disclosed. A piperack structure has a major axis parallel to the major axis of the train with which it is associated. A first multipurpose module, substantially pre-assembled prior to being transported to an operating location, has a major axis that is either parallel or perpendicular to the major axis of the piperack. The first multipurpose module contains: process components that perform a function related to hydrocarbon processing or handling; piping systems that connect the process components directly to a second module that is adjacent the first multipurpose module, and wherein at least part of the piping systems are aligned with the major axis of the piperack structure; and at least one heat exchanger located in the first multipurpose module and operationally connected to process components in the hydrocarbon processing plant.

By using the power generated by an expander by an expansion of material gas, the outlet pressure of a compressor is increased, and a requirement on the cooling capacity of a cooler is reduced. The liquefaction system (1) for natural gas comprises a first expander (3) for generating power by expanding natural gas under pressure as material gas; a first cooling unit (11, 12) for cooling the material gas depressurized by expansion in the first expander; a distillation unit (15) for reducing or eliminating a heavy component in the material gas by distilling the material gas cooled by the first cooling unit; a first compressor (4) for compressing the material gas from which the heavy component was reduced or eliminated by the distillation unit by using the power generated in the first expander; a second heat exchanger for exchanging heat between the material gas introduced into the first compressor and the material gas compressed by the first compressor; and a liquefaction unit (21) for liquefying the material gas compressed by the first compressor by exchanging heat with a refrigerant.

The disclosure provides a method and system for optimizing production of a natural gas liquefaction process, the method comprising the steps of: selecting at least one manipulated variable (MV) for controlling the liquefaction process; selecting at least one control variable (CV), the at least one control variable at least comprising liquefied natural gas (LNG) throughput; providing at least one model, each model providing a dependency of the at least one control variable (CV) on the at least one manipulated variable (MV); using the at least one model to estimate LNG throughput for at least one of the manipulated variables (MV); obtaining process data from the liquefaction process, the process data at least including observed values of LNG throughput; creating a gain matrix based on said interdependencies; and using the gain matrix to optimize a process control system of the liquefaction process.

Implementations described and claimed herein provide systems and methods for removing nitrogen during liquefaction of natural gas. In one implementation, a nitrogen rejection unit is used in an LNG facility to remove nitrogen from natural gas during an LNG liquefaction process. The nitrogen rejection unit contains at least two columns and at least one 3-stream condenser, 2-stream condenser or a two 2-stream condenser.