Making SNG: What You Need To Know?

Introduction

Synthetic Natural Gas (SNG) is a blend of Liquefied Petroleum Gas (LPG) and Air that has the same "Wobbe Index" as Natural Gas (Methane).

By matching the "Wobbe Index", SNG has the same combustion characteristics as, and can therefore be freely interchanged with, Natural Gas.

This has led to the use of LPG/Air mixture as both primary fuel sources and stand-by systems.

Business Description

• This precise and controlled mixing of LPG and air allows it to be used as an alternative to natural gas for “backup” use, ‘peak shaving’, and City Gas supply in regions where natural gas is not available.
• Combustion characteristics of LPG/Air are identical to Natural Gas.
• NO modifications of Natural Gas equipment: no burner modifications, no orifice changes, no regulator or line adjustments.
• LPG/Air mixture can directly replace the natural gas in combustion applications.
• You can switch to LPG/Air immediately - NO pre-purging or post purging of the line.
• When LPG is mixed with Air to the correct ratio, the resulting mixture will burn with the same characteristics as Natural Gas.

           "Wobbe Index" is a key measure of interchangeability        

                     LPG/AIR MIXED APPROXIMATELY RATIOS:
                           55% Propane / 45% air
                            47% Butane / 53% air        

SNG System Advantages

The mixing technology can be used as Back-up equipment or Gas costs Peak shaving. Technology is also economic alternative.

• Economic reasons (back-up system): uninterruptible gas service rates, better position to negotiate fuel cost with Natural Gas supplier.
• Alternative solution: pipelines maintenance and servicing, global cut-off of gas (emergency back-up), standby solution for accidents at pipelines.
• Supply a remote community with Natural Gas: permanent or temporary until extension of Natural Gas main.

SNG Facility

A basic SNG System includes:

• Storage tank: stores the liquid LPG.
• Tank loading facility: allows refilling the storage tank.
• Process Pump: transfers liquid LPG to the vaporizer.
• SNG Plant: Vaporizer and Blender – vaporize the LPG and blends in air.
• Piping and Tie-in: links everything together from the SNG System to the distribution network.

These five basic elements are installed adjacent to the facility on level ground.

A typical system with a single storage tank takes up approximately a 10m×25m area (250 sq. meters)        

Making SNG

For making SNG, there are 5 steps:

1. We need two ingredients: LPG and air.
2. Pump the liquid LPG from the storage tank to the vaporizer at an elevated pressure.
3. At the vaporizer, we heat the liquid LPG until it becomes LPG vapor.
4. Blend the LPG and air approximately 55:45 ratios. This mixture is SNG.
5. Discharge the SNG into the existing natural gas line and into the plant.

                              RULE OF THUMB

- Each 11 gallons of Propane (Storage Capacity) equals 1 MMBTU
- Each 1 gallon of liquid Propane will produce about 36 standard cubic feet (SCF) of vapor.
- Each 1 SCF of Propane vapor contains about 2,520 BTU of available energy when burned.
- A LPG/Air mixture containing 1,470 BTU/CF has burning characteristics similar to natural gas containing BTU/CF with a specific gravity of 0.6        

Operation:

No significant flame lift differences occur between natural gas and SNG mixtures.

In the basis of the system there are mixer and LPG vaporizer. Depending on its type the vaporizer uses electric or gas energy for transformation of LPG liquid to vapor. LPG vapor enters then the venturi mixer. As pressurized vapor passes through the mixer, the kinetic energy of the gas draws in air from the atmosphere through a check valve. The mixture is then re-pressurized through the diffuser before it enters the surge tank.

For bigger capacities and higher discharge pressures the air is supplied through compressor and mixing process is digitally controlled. Unlike diesel, fuel oil or propane, synthetic natural gas does not require additional gas trains, piping, regulators, or special fuel delivery systems inside the factory.

The LPG/Air mixture is simply connected to the natural gas piping just after the metering station (and pressure reducing station) but before entering the building.

Conclusion:

LPG vapor is not directly compatible with natural gas and must be mixed with air before it can be used in equipment and appliances that are set up for natural gas.

LPG/Air mixer systems mix vapor from a vapor source (such as a vaporizer) with air at a pre-set ratio, producing a gas, often called Synthetic Natural Gas (SNG) that is directly compatible with natural gas.

This allows users to switch back and forth between natural gas supplied by their utility company and their own, LPG based backup or peak shaving system, without having to change the setup of their burners, boilers, etc.