In liquefied natural gas (LNG) plants, the flare system provides a reliable and safe method for vapor and liquid hydrocarbon disposal. The flare system enables controlled handling of off-spec streams during plant upsets, emergencies, and short term operations such as start-up, shutdown, or equipment maintenance activities. Although the flare system is essential for the safe operation of the plant, proper design and optimization is necessary to control capital cost.
A typical LNG flare system includes Warm (or Wet), Cold (or Dry), and Low Pressure (or LP/Marine) flares. The disposal of streams with potentially freezable components originating from plant inlet and gas treating sections is achieved through the Warm flare. The Cold flare is utilized to dispose streams with non-freezable components and very low operating temperatures. Low pressure streams from the storage or loading area of the LNG plant are routed through the LP flare for safe disposal. Based on project design criteria, flare system can require elevated, ground, enclosed, or smokeless flare design.
Addressing flare optimization issues provides opportunities for controlling material loss during plant operation. In this paper, an overview of factors that influence flare type selection and determine flare size are discussed. Significance of flare type and size for overall plot space requirements is also addressed. Based on typical major relieving scenarios, flare load reduction strategies for each of the LNG plant flares are presented.
LNG plant design configurations for multiple trains, refrigerant compressors, and process recycle streams can significantly affect design flare loads. High design flare loads increase flare size and require large plot space due to flare radiation limits. Proper selection of design options for major LNG plant sections guided by flare reduction strategies can help in reducing flare design flow rate, flare size, and plot space requirements.