Process and apparatus for treating lean LNG
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Solution Overview
Problem
Lean LNG enriched in methane or ethane often generates a significant amount of boil-off gas (BOG) when transferred to tanks or trucks at atmospheric pressure, leading to increased energy consumption for compression and heating value adjustments.
Innovation Solution
A process and apparatus that branch and cool the lean LNG, using refrigerant LNG for pressure reduction and gas-liquid separation, followed by regasification and heat exchange to minimize BOG generation and optimize energy use.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If lean LNG is cooled in a distillation column to separate hydrocarbons, then heavy hydrocarbons are removed and methane-enriched lean LNG is obtained, but enthalpy increases and BOG generation occurs when sent to atmospheric pressure tanks
Solution Approach 1:
The process segments the lean LNG flow into two separate streams: one for product gas and another for product LNG. This allows independent treatment of each stream, enabling the product LNG to be cooled to minimize BOG while the product gas can be processed separately for heating value adjustment.
Solution Approach 2:
The product LNG stream is cooled in advance before being sent to atmospheric pressure tanks. By performing this cooling action preliminarily, the lean LNG maintains lower enthalpy and generates minimal BOG during storage and transportation.
2Quantity of substance
If lean LNG is heated to increase heating value for city gas or tank truck, then heating value requirement is met, but energy consumption increases
Solution Approach 1:
The process applies different quality treatments to different portions of the lean LNG based on destination requirements. Product LNG for atmospheric pressure storage is cooled to minimize BOG, while product gas for pipeline or tank truck is selectively heated only to the extent needed for its specific heating value requirement.
Solution Approach 2:
The process changes the temperature parameter differently for different product streams. The product LNG stream undergoes cooling (temperature decrease) to reduce enthalpy and BOG generation, while the product gas stream undergoes controlled heating (temperature increase) only to meet specific heating value specifications.
3Ease of operation
If lean LNG is sent to atmospheric pressure tanks without cooling, then storage is simplified, but large amount of BOG is generated requiring energy-intensive compression
Solution Approach 1:
The product LNG stream is cooled in advance before storage in atmospheric pressure tanks. This preliminary cooling action reduces the enthalpy of the stored LNG, thereby minimizing BOG generation during storage and eliminating the need for energy-intensive compression of BOG.
Solution Approach 2:
The process converts the potential harm of BOG generation into a benefit by selectively cooling only the product LNG stream that will be stored in atmospheric tanks. This targeted cooling transforms what would be a waste problem into an energy-saving opportunity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The process effectively reduces BOG generation and energy consumption by leveraging refrigerant LNG for cooling and pressure management, allowing for efficient treatment and transportation of lean LNG with adjusted heating values.
Implementation Method 1
cooling the lean LNG for product LNG in a cooler using a refrigerant
Implementation Method 2
subjecting the remaining LNG to pressure reduction
Implementation Method 3
gas-liquid separation to obtain a gas phase flow having the pressure P1 and a liquid phase flow having the pressure P1
Implementation Method 4
subjecting a flow resulting from the step f and the step g to pressure increase
Implementation Method 5
cooling through heat exchange with the lean LNG for product gas to liquefy the flow resulting from the step f and the step g
Implementation Method 6
regasifying the lean LNG for product gas after the step h and the step i to obtain the product gas
Data Source
AI summary
A process for obtaining a product gas and product LNG having pressure P1 close to the atmospheric pressure from lean LNG, includes: a) branching the lean LNG to obtain a first flow and a second flow; b) cooling the second flow by using a refrigerant; c) branching a liquid flow derived from the cooled second flow to obtain refrigerant LNG and remaining LNG; d) subjecting the remaining LNG to pressure reduction and gas-liquid separation to obtain a gas phase flow and a liquid phase flow (product LNG) having pressure P1; e) subjecting the refrigerant LNG to pressure reduction; f) using a flow from the step e as the refrigerant; g) joining, before or after the step f, the gas phase flow having pressure P1 to a flow from the step e; h) liquefying a flow resulting from the steps f and g by pressure increase and cooling (through heat exchange with the first flow); i) increasing the first flow in pressure before the step h; j) obtaining the product gas by regasifying the first flow after the steps h and i; and k) joining a flow liquefied in the step h to the second flow.