Fuels - Part V

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Petroleum gas : The component of petroleum gas is butane (C4H10). The other components are propane (C3H8) and ethane (C2H6). All these gases burn very easily and are highly flammable. These compounds are gases under ordinary temperatures and pressures. But they can be liquefied easily under pressure and then they are called liquefied petroleum gas or LPG. LPG is the domestic gas that we use in our kitchens. LPG is mostly butane but has small amounts of propane and ethane also. In domestic LPG cylinders, small quantities of foul smelling ethyl mercaptan (C2H5SH) are added so that any gas leak can be detected. LPG cylinder is filled under pressure and generally has 14 kg of liquid butane in it. This becomes very convenient to handle and transport. The LPG vapourises and is used as gas in the kitchens.  

Advantages of using LPG :  

  • LPG has high calorific value and is a good fuel. 1 gm of LPG burns to give 50 kJ of heat energy.

  • LPG burns with a smokeless fire.

  • LPG does not cause pollution as all its components burn and they do not produce any pollution causing gases.

  • LPG is convenient to transport and store in cylinders.  

Disadvantages of using LPG :  

  • It is a highly flammable gas and catches fire very easily.

  • If LPG gas leaks, it can cause an explosive mixture with air. There are numerous episodes of LPG explosions and severe accidents due to such explosions.

  • There are strict procedures for use and maintenance of LPG for use to avoid hazards associated with it.

  • If LPG is inhaled by accident, it is extremely harmful to health and may cause even death.  

Cracking : From the  fractional distillation of petroleum, there is a great demand for the gasoline or the petrol fraction. Higher boiling fractions such as heavy oil are converted to gasoline by the cracking process. In the cracking process fractions with number of carbon atoms from 12 to 18, are heated in the presence of a catalyst and they are converted into smaller hydrocarbons suitable for making petrol. Catalyst used is a correct proportion of silica, manganese oxide and alumina. The equation below shows one such cracking process.

 

 

Daily use of Liquefied Petroleum Gas

We routinely use liquefied petroleum gas (LPG) in our kitchens for cooking food. These LPG cylinders are used in cars as they emit less harmful pollution causing gases. But before the use of LPG there are a few precautions that have to be taken, as LPG is a highly flammable gas and may cause explosions if there is a leak. 

In LPG cylinders, small quantities of foul smelling ethyl mercaptan (C2H5SH) are added so that any gas leak can be detected. Before lighting the gas or starting the car ignition, we should check if there is any smell or leak. If there is a leak, we should ensure that the leak has been stopped and the gas leaked away is blown away. If there is a leak, the first thing to do is open windows, doors so that the gas is not confined in one place, which is dangerous. Even starting a switch for the exhaust fan may provide a spark for the gas to explode, this therefore has to be avoided.

Other cooking elements such as kerosene stove or electric heater should not be kept near the LPG cylinder. Precautions have to be taken so that the gas cylinder, its regulator and its tubing should not be damaged. The cylinder valve and the gas-stove knob have to be opened and closed in sequence. The lighter should be lighted before the gas is made to come out of the stove. It should not happen in the reverse order. This ensures that the gas is not spread in the room but burns first.

 

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