Liquefied Petroleum Gas

Application

Liquefied Petroleum Gas (LPG), or also known as LP Gas or auto gas, is a mixture of hydrocarbon gases used as a fuel in heating appliances and vehicles and increasing replacing chlorofluorocarbons as an aerosol propellant and a refrigerant to reduce damage to the ozone layer. These gases are called LPG because they liquefy under moderate pressure, and readily vaporize upon release of pressure. The pressure at which LPG becomes liquid is called its vapor pressure; likewise, each vapor pressure varies depending on composition and temperature. The ratio between the volumes of the vaporized gas and the LPG varies depending on composition, pressure, and temperature, but typically is around 250:1.
LPG is synthesized by refining petroleum or ‘wet’ natural gas. LPG has a higher calorific value (94MJ/m3) than natural gas, methane, (38 MJ/m3), which means it cannot simply be substituted for natural gas. LPG can be mixed with air to produce a synthetic natural gas (or also known as SNG) that can be easily substituted. LPG and air mixing ratios average 60:40 though this is widely variable based on the gases making up the LPG. The method for determining these mixing ratios can be determined by calculating the Wobbe index of the desired mix.

Process

The advantages of LPG are as follows:

• Because of its relatively fewer components, it is easy to achieve the correct fuel to air mix ratio that allows the complete combustion of the product. This gives LPG its clean-burning characteristics.
• Both Propane and Butane are easily liquefied and stored in pressure containers. These properties make the fuel highly portable, and hence, can be easily transported in cylinders or tanks to end-users.
• LPG is a good substitute for petrol in spark-ignition engines. Its clean-burning properties, in a properly tuned engine, give reduced exhaust emissions, extended lubricant, and spark plug life.
• As a replacement for aerosol propellants and refrigerants, LPG provides alternatives to fluorocarbons, which are known to cause deterioration of the earth's ozone layer.

The clean-burning properties and portability of LPG provide a substitute for traditional fuels such as wood, coal, and other organic matter. This provides a solution to deforestation and the reduction of particulate matter in the atmosphere (haze), caused by burning traditional fuels.

Challenges

LPG heating value control involves vaporizing LPG and mixing it with air to obtain a gas having the heat value of natural gas. The GD402 can be used to measure the heating value indirectly through its correlation with the density and specific gravity of the mixed gas. The relationship between specific gravity and the SNG mixture is well documented and can be used for process control. Since there will be some variation in the composition of the different SNGs from lot to lot, the SNG density and specific gravity is premeasured and the computational parameter data of the analyzer is set based on that so as to minimize the error due to the composition variation.

What are the Advantages of LPG

LPG heating value control involves vaporizing LPG and mixing it with air to obtain a gas having the heat value of natural gas. The GD402 can be used to measure the heating value indirectly through its correlation with the density and specific gravity of the mixed gas. The relationship between specific gravity and the SNG mixture is well documented and can be used for process control. Since there will be some variation in the composition of the different SNGs from lot to lot, the SNG density and specific gravity are premeasured and the computational parameter data of the analyzer is set based on that so as to minimize the error due to the composition variation.

Solution

Yokogawa’s GD402 gas density analyzer and GD40 gas density detector provide continuous measurement of gas density as well as other valuable parameters, including specific gravity and percent concentration. In applications where accurate, repeatable measurement of gas density is essential, Yokogawa’s family of gas density products deliver superior performance and reliability. From blending of fuel and product quality to hydrogen purity and replacement in utility turbines, our gas density analyzers provide accurate measurements with ease of maintenance and operability.

Key Advantages

• Improved operation efficiency and plant safety, continuous highly responsive and sensitive measurement of gas density and several other valuable parameters, including specific gravity and molecular weight
• Wiring between the detector and converter is based on a two-wire system, keeping installation cost to a minimum
• Only routine maintenance is required - for example, once per 3 months depending on application
• Configuration can be performed locally via the front panel or remotely by using the (optional) “Brain” terminal