Courtesy: Cheniere
United Kingdom will be receiving US LNG cargo to its South Hook LNG Terminal.
Sabine Pass LNG currently has five operational trains and Train 6 pending FID.
LNG Process Chain
Natural Gas consists entirely of methane, typically LNG is 85 to 95 plus percent methane along with a few percent ethane, and even less propane and butane with traces of Nitrogen. This exact composition varies according to the source of feed gas and the processing technology applied. To obtain LNG and delivering it to the end user consists of a series of steps as listed below.
Exploration & Production
Typically, when oil is produced you also produce some gas. Depending on the type of reservoirs the amount of gas produced can vary drastically. Also, the use of smart engineering techniques such as hydraulic fracturing and horizontal drilling can be crucial especially when it comes to producing from complex shale plays such as in the US.
Liquefaction
Once this Natural Gas is produced through Exploration it becomes the feed gas to the Liquefaction or LNG Plant. In this facility, the feed gas is treated and processed to form Liquefied Natural Gas. The facility can almost be thought of as a big refrigeration unit where the entering feed gas is processed and condensed to its liquid form. This enables storage and transportation of the chilled fuel more viable.
Shipping
Once LNG is produced and stored at the facility. LNG carriers or vessels are loaded with LNG to carry it to its destination.
Storage and Regasification
At the destination, the LNG carrier would transfer LNG at the receiving terminal where it would be transformed to its gaseous state and delivered to users.
LNG Chain – The Optimized Cascade Process
Courtesy: ConocoPhillips Website
Making LNG involves liquefying natural gas for storage. To achieve this, first the feed gas must be treated to remove impurities such as CO2 and Water. The goal of the process is to increase methane concentration and to remove all impurities before liquefaction.
Let’s study the main equipment utilized in this process.
1. Auxiliary Oil Heater – This is an important component for the LNG process which provides the initial heat to the gas exchangers.
2. Acid Gas Removal Unit (AGRU): It removes sour gas from the feed gas before it enters the cooling phase.
3. Dehydration: From the AGRU the gas now moves to the dehydration unit where any remaining water is removed so it does not form ice when liquefied.
4. Mercury removal units: It is crucial to remove mercury primarily because of its corrosive nature on aluminum before it enters the cooling stage.
5. Compression: Gas is progressively compressed through the ConocoPhillips Optimized Cascade process. The gas is forced through by one of two independent compressors.
6. Cold Boxes: Propane, Ethylene, Methane are used as the three refrigerants to liquefy the natural gas to liquid. The cooling process takes place in the Cold Box’s within each train. It contains a cryogenic brazed aluminum heat exchanger.
7. Inlet Air Chilling: All the three Curtis Island projects have inlet air chilling on each gas turbine to boost compressor driver power in order to maximize LNG production.
The main highlights of the Optimized Cascade Process can be summarized as follows
- Two trains in one configuration yields higher plant efficiency
- Can handle a broad range of plant ambient temperatures and feed compositions
- Flexible operations which enable easy start up, shutdown and maintenance
- Use of Brazed Aluminum Heat Exchangers, Aeroderivative Gas Turbines with Waste Heat Integration leading to higher thermal efficiency.