Vaporizer is used to convert LNG to gas. There are several type of vaporizer that popularly used:
- Ambient Air Vaporizer (AAV)
- Intermediate Fluid Vaporizer (IFV)
- Open Rack Vaporizer using Seawater (ORV)
- Submerged Combustion Vaporizer (SCV)
Ambient Air Vaporizer is the most simple type of LNG vaporizer. It utilizes ambient air to vaporize LNG. LNG is flowing through tubes and it is vaporized by air. It can be done naturally or by force. If it is done naturally, then it requires no power, and vice versa.
Intermediate Fluid Vaporizer utilized fluid as heating medium. The fluid can be glycol/water or propane. The fluid is heated by seawater, air, or fire heater. The hot fluid is then used to vaporize LNG. As I know, it is popularly used in Floating Storage Regasification Unit.
Open Rack Vaporizer uses seawater directly to vaporize LNG. Seawater is pumped from seawater intake. Before it is used to vaporize LNG, seawater is treated by seawater treatment (such as chlorination).
Submerged Combustion Vaporizer utilized hot exhaust gas from gas turbine in power plant to increase temperature of hot water. Hot water is circulated and injected to water bath to heat LNG.
More about Ambient Air Vaporizer
As mentioned previously, Ambient Air Vaporizer is the most simple type of vaporizer.
When is the best application of ambient air vaporizer?
It is best used in warm climate application. As it utilized air, the warmer air temperature, the better vaporization will be.
Is it difficult to operate ambient air vaporizer?
Operation of the vaporizer is very simple. However, because the vaporizer will cause frosting due to water in air, thus it requires periodic defrosting every 4-8 hours, depend on ambient air temperature and outlet temperature of natural gas. If we wish to get higher temperature of natural gas, then we need to switch vaporizer more often. As a consequence, if we choose ambient air vaporizer, we need to provide two groups of vaporizers: one for operation, and the other one is standby. During defrosting, we switch to other group of vaporizer.
To ease operation we can provide control valve at upstream to each group of vaporizer although manual switching is enough.
Is there any environmental constraints regarding application of AAV?
The biggest constraint of using ambient air vaporizer is fog formation. When we use several unit of ambient air vaporizers, fog formation is a true problem. As I know, to minimize this problem, we can provide fog reduction unit or to manage spacing between vaporizers.
NFPA 59A (Standard for the Production, Storage, and Handling of Liquiefied Natural Gas) stated a clearance at least 5 ft (1.5 m) shall be maintained between vaporizers.
Is it possible to use many AAV’s? Some vendors will not recommend this as too much fog will be generated. The area filled with fog will become a cold temperature trap and the whole area will make its own weather condition as its temperature is lower than the surrounding area.
I want to purchase ambient air vaporizer. What data I should provide and vendor should declare?
BS EN 1473 stated values to be specified for LNG vaporizer. As for ambient air vaporizer, they are:
- Minimum and maximum through put
- Minimum outlet temperature vaporized gas
- LNG/NG pressure drop
- Minimum air temperature, wind speed, and humidity
- Battery limit condition for utility
- For LNG –> heating curves, thermal duty, inlet and outlet temperature, inlet and outlet pressure, composition, and mass flow rate
That’s all I want to share. Hopefully you get better understanding about ambient air vaporizer.