SubscribeReduced maintenance and downtime for cleaning paid for the ELGA Process Water treatment system
Process Combustion has been designing and fabricating innovative combustion and heat transfer equipment since 1985 and has been particularly successful in supplying Liquified Natural Gas (LNG) vaporisers, more recently in partnership with Selas-Linde of Munich. LNG is stored at 85bar, and has to be heated to vaporise it prior to delivering into the national gas grid. The vaporisers are constructed using Process Combustion's proven submerged combustion technology, which has inherently high heat transfer efficiency. The hot gases from combustion are fed directly into a water bath containing about 150m3 of hot water which, in turn, is used to heat the stainless steel gas heat exchanger within the vaporiser. The quality of water in the bath has a major impact on the performance of the system, so Process Combustion turned to water treatment experts ELGA Process Water for help.
Acid gases - predominantly carbon dioxide - dissolve in the water lowering its pH and making it corrosive. This is corrected by the addition of caustic soda which reacts with carbon dioxide to produce sodium carbonate. This then reacts with any hardness (calcium or magnesium) in the water to precipitate calcium carbonate scale on the heat exchange surfaces. Descaling the heat exchangers is not only expensive but means extensive system downtime.
One of the environmental problems associated with combustion is the potential release of oxides of nitrogen (NOx) into the atmosphere. In order to suppress NOx emissions, water is sprayed directly into the burner to reduce the flame temperature. This water evaporates leaving behind any dissolved salts, particularly hardness salts, which deposit in the burner and need to be removed regularly.
The ELGA Process Water engineers recommended fitting a side stream reverse osmosis plant onto the water bath. The system continuously bleeds water from the bath, treats it by means of a membrane that removes most of the dissolved salts, and then recycles the purified water to the NOx suppression spray. Process Combustion's Alec Little explains: "The RO unit removes all the salts that accumulate in the water and virtually eliminates deposits in the burner. On vaporisers using mains water we have to clean the burner every two months - sometimes more frequently - but the installation of side stream RO should extend this period to around two years. Reduced maintenance and downtime for cleaning has more than paid for the RO unit."