Boil–off Gas (BOG) for Siemens Import Terminals

 

Plant efficiency is the main focus for Siemens' market-leading solutions for Boil-off gas (BOG) compression. During storage some of the gas may vaporize, and our BOG technology increases efficiency by feeding this vaporized gas back into the cooling cycle or burning it as fuel to power the gas turbines. More than 90 individual machines using Siemens BOG recovery technology have been supplied to LNG production plants and receiving terminals worldwide. 

 

Siemens Oil & Gas in Duisburg has supplied a compressor that squeezes the carbon dioxide to around 200 bar in a separate cycle, allowing it to be sequestered. This will mean a reduction of around one million tons of the greenhouse gas emitted to the atmosphere every year once the plant has begun to operate at full capacity.

Another aspect of the LNG process is the recapture of so-called boil-off gases. The refrigerated LNG is stored in large insulated tanks until it is ready for shipment in tankers. As in a thermos bottle, there is a minimal temperature exchange between the liquefied natural gas and its surroundings. Heat gets into the tank and causes a small amount of the LNG to vaporize. This so-called boil-off gas is fed back into the cooling cycle or burned as fuel to power the gas turbines. Once again, the compressor for this part of the process is supplied by Siemens Oil & Gas, the market leader for boil-off compressors.

 

 

Siemens is enhancing the efficiency of a natural gas liquefaction plant operated by the Malaysian oil and gas company Petronas. Natural gas is liquefied at very low temperatures so that it can be transported in tankers. The market for liquefied natural gas (LNG) is growing worldwide, and experts forecast that the trading volume will rise in Europe from around €15 billion today to about €25 billion in 2020.

 

LNG has a temperature of minus 162 degrees Celsius and takes up 600 times less volume than when it is in its gaseous state. Although this is beneficial for transport purposes, it also has its drawbacks. For example, around one tenth of the liquefied natural gas in storage tanks evaporates. Instead of flaring this gas, as is usually the case, operators can reliquefy it for future use. This makes the overall process more efficient and reduces greenhouse gas emissions. Such a reliquefaction facility is now being built at one of the world's largest centers for liquid natural gas: the Bintulu complex on the island of Borneo. The reliquefaction facility will commence operations next year. Siemens is supplying the facility's main refrigeration compressor as well as the boil-off-gas compressor, each of which is driven by a Siemens SGT-700 industrial gas turbine. Because the gas turbines will run on the facility's natural gas, the system will make optimal use of the available resources. 

 

To enable the boil-off gas (BOG) from the storage tanks to be fed into the liquefaction process, it first has to be brought to a certain pressure by a separate compressor. Because the gas is not produced in a continuous stream, the Siemens BOG compressors are equipped with special control technology (variable inlet guide vanes) for handling variable flow rates. The unusual feature of the new facility is that Siemens is for the first time using a gas turbine to drive the boil-off-gas compressor. In this case, the same type of gas turbine is used for the BOG compressor as for the liquefaction plant's refrigeration compressor. This unique setup also enhances the efficiency of the entire liquefaction process. The natural gas produced at the site contains unusually large amounts of nitrogen. However, the Siemens SGT-700 turbine can run on natural gas that contains a high concentration of nitrogen without suffering any appreciable drop in efficiency