Natural Gas Alternative: Synthetic Natural Gas - SNG
With the looming potential for natural gas shortages and price escalations, large natural gas users need to examine the alternatives. One alternative is Simulated or Synthetic Natural Gas - SNG. SNG, made with LPG, is a direct substitute for natural gas. Most people have never even heard of synthetic natural gas let alone know that it can be made with LPG. Learn more about this flexible solution…
What is Simulated Natural Gas – SNG?
Simulated natural gas – SNG – is produced by mixing vaporised LPG with compressed air. SNG can be used in place of natural gas, as it has virtually identical combustion characteristics. It can be used alone or mixed with regular natural gas. No changes are required in burners, regulators or gas jets. Simulated natural gas has a number of names. In addition to SNG, it is also called propane-air and LPG-air.
What about Synthetic Natural Gas or Substitute Natural Gas?
You may have also heard of synthetic natural gas or substitute natural gas. Many use the terms interchangeably. These are not the same as simulated natural gas but they do cause a lot of confusion. Synthetic natural gas (substitute natural gas) is not made with LPG. They are made from other hydrocarbons like lignite coal, biomass, petroleum coke, or solid waste. However, there are some disadvantages. Synthetic or substitute natural gas is not as clean as simulated natural gas, as the gasification process itself generates CO2 emissions. There is also a substantial capital investment required for the gasification plants.
Why Use Simulated Natural Gas?
There are a number of reasons that SNG might be used:
Peak Shaving
To help meet peak demand when natural gas supplies are inadequate. The augmentation of natural gas pipeline supplies with SNG. Peak shaving systems are activated as needed to cope with times of peak demand and avoid any possible overrun penalty fees.
Base Load
SNG can provide gas to users in isolated areas where natural gas is currently not available due to a lack of infrastructure or natural gas resources. Bridging Fuel To operate while in preparation for the start-up of a natural gas supply. SNG can be used as a ‘bridge fuel’ in anticipation of natural gas availability.
Stand-By
As a stand-by in the event of a natural gas supply disruption, allowing customers to maintain gas related operations in the event of a natural gas limitation or temporary stoppage of supply.
Interruptible Service
In some areas, a user may be able to get substantial discounts for accepting interruptible service. Simulated natural gas systems allow for this option and the resultant savings without actually suffering the interruptions.
Benefits of SNG
With SNG, we can make sure that essential services, like hospitals and schools, are never without gas. The modular nature of the units make them easily transportable and quick to setup. In comparison to LNG, capital investment is lower for comparable output. There is no need to change the jets or burners of existing appliances, as SNG works exactly the same as natural gas. SNG allows for arbitrage based on the price differentials between the two fuels, taking advantage of market fluctuations. Most importantly, LPG is readily available.
How is Simulated Natural Gas Made?
Images courtesy of TransTech First, the LPG (propane) is vaporised from liquid LPG. Depending on the size of the storage vessels and the rate of consumption, this may require the use of a vaporiser. The vaporised LPG is then fed into an SNG processor, mixing the LPG with compressed air. The typical blend is 53% vaporised LPG (propane) and 47% air. From there, the gas proceeds directly to the users' applications.
Simulated Natural Gas Systems
SNG systems range in size from about 3,000MJ/hr all the way up to 500,000MJ/hr. The units can also be connected with manifold pipework to provide a virtually unlimited throughput. Smaller SNG units are usually modular, making them ‘plug and play’ for installation. The system controls are typically automated. Simulated natural gas systems usually consist of a vaporiser for converting liquid LPG to vapour and a propane air mixer, to blend the vaporised LPG with compressed air. LPG storage tanks, truck tanker unloading equipment and a pump for moving LPG to the vaporiser are also part of the fit out.
Why Add Air and what is a Wobbe Index?
Air is added because LPG – propane – has a higher energy content than natural gas – methane. Propane has about 91MJ/m3 compared to natural gas with 39MJ/m3, so more than 2x the energy content. The Wobbe Index is an indicator used to compare the energy output of different fuel gases. To be interchangeable gases, the Wobbe Index needs to be the same. By using air to reduce the LPG energy content, simulated natural gas and natural gas both have the same Wobbe Index. SNG and natural gas will both generate the same amount of heat from the same burner. SNG has essentially identical use characteristics, when compared to to natural gas, and can be used as a seamless substitute.
Environmental Advantages
LPG – propane – based simulated natural gas is environmentally friendly. Neither natural gas nor propane will contaminate the earth or ground water, if spilled. However, unlike natural gas, propane (LPG) is not considered a greenhouse gas. SNG has much less risk from fugitive gas, relating to the greenhouse gas effect. In contrast, natural gas – methane – is considered a potent greenhouse gas, much worse than CO2.
Final Thoughts
Simulated natural gas is the obvious alternative when natural gas is totally unavailable or in short supply. The establishment of an SNG system is clean, fast and affordable, with relatively low capital costs. If you have a natural gas supply problem, simulated natural gas might be your solution.