Understanding Natural Gas and Its Safety

Natural gas formed millions of years ago from the decomposition and decay of the remains of plants and animals whose bodies were driven to the lower parts of ancient lakes and oceans. The greater part of these remains decomposed in the air and entered the atmosphere, but a portion of them that were buried before decomposing, or entered stagnant, oxygen-free waters, were prevented from oxidizing, and over centuries and ages sand, mud, and other sediments gradually accumulated on top of them and compressed them. Eventually the weight of the accumulated layers created such pressure and heat that the organic materials were converted into oil and gas and stored in underground reservoirs at depths of three to four thousand meters under a pressure of around several hundred atmospheres. Types of natural gases and their derivatives Natural gases come in very many types, four examples of which are referred to in this article. To access supplementary material, you can obtain and study the book "Comprehensive Natural Gas Safety in Stations and Gas-Distribution Networks, with a Review of Accident Analysis" from the Hak Publications website. 1- Synthesis Gas: A colorless, odorless, and toxic gas that burns without a flame in the presence of air at a temperature of 647 degrees Celsius. The weight of this gas depends on the percentages of hydrogen and carbon monoxide. This gas can be used as a source for producing ammonia and methanol, for hydrogenation in refining operations, and even as a fuel. 2- Substitute Natural Gas: Substitute natural gas, like synthesis gas, can be obtained from the gasification of coal or the gasification of organic materials. The heating value of this gas is much higher compared to synthesis gas, because, like natural gas, the major part of it is composed of methane. 3- Town Gas: This term refers to a gas that is delivered through a pipeline from a gas-production complex to consumers. The composition of town gas includes: hydrogen 50%, methane 20% to 30%, carbon monoxide 7% to 17%, carbon dioxide 3%, nitrogen 8%, hydrocarbons 8%, and other impurities such as water vapor, sulfur, and hydrocyanic acid. It should be noted that the composition of town gas in Iran is not similar to the composition mentioned. 4- Compressed Natural Gas (CNG): This gas is used as a fuel in internal-combustion vehicles. For this purpose, the compressed gas must be stored in a heavy, large tank at a pressure equal to 220 atmospheres. Safety in gas-distribution networks: Gas-distribution installations consist of three parts: 1- Feeding and gas-distribution networks 2- Pressure-reduction stations 3- Cathodic protection stations The safety of the valves in gas-distribution networks is of great importance, because they play a key role in stopping the continuation of a possible leak in the main network. Therefore, to increase the network's safety, valves are installed at specified intervals and locations so that, in the event of physical impact or a leak, the gas can be cut off in time, before a fire accident occurs, through the installed valves. In the design of pressure-reduction stations, systems such as safety valves and automatic shutoff valves are provided so that, in abnormal situations, they can serve as line relief for the station. As a result of the inefficiency of the mentioned system and an increase in internal pressure, irreparable damage to the station is likely, so these valves must be analyzed and tested periodically and carefully. Cathodic-protection systems, in order to control the corrosion process in metals and reduce its corrosion rate, use electrochemical methods that give it a dynamic nature; in other words, the main and fundamental component in these electrochemical methods, as the name suggests, is the electrolyte component. The anode, cathode, and electrolyte are the main components in the corrosion process, and therefore systems such as the cathodic-protection system used to protect metals from corrosion must cover these three elements properly from the standpoint of electrochemistry. The cathode and anode are two components with opposing functions; that is, at the anode, oxidation reactions take place and electrons pass from the metal into the surrounding medium, namely the electrolyte, while at the cathode the opposite function occurs, which is in fact called a reduction reaction.