उद्योग संबंधी विषय
Consumers always seek purity in what they buy. They want fresh, whole foods; all-natural fabrics; the cleanest water and solidly-built furniture. Health, sustainability longevity are prime motivators when you buy what you buy. The same principle holds for fuel and its chemical composition. The cleanest-burning, most efficient combustible energy is to be desired above substances rife with impurities and contaminants. Why? Transport and sale of such energy requires stability and conformity to industry regulations. So it is with natural gas and landfill gas. Unless the gas meets certain quality standards, it needs refinement. This additional processing is called gas sweetening.
When testing the heating value of natural gas, for example, those responsible are measuring the amount of heat released upon combustion, the density of energy often expressed in joules per kilogram (MJ/kg). Natural gas should fall within a range of 42 to 55 MJ/kg. For perspective, gasoline falls between 44 and 46 MJ/kg while enriched uranium reaches about 3,900 GJ/kg. So, obviously, it takes much less uranium to generate more heat. That said, natural gas holds superior heating value over gasoline. Why, then, does some natural gas fail to meet heating value standards?
Natural gas sweetening is needed when gas is evaluated as sour. Just like with food, when high concentrations of acid make for a sour taste, natural gas is soured by acidic elements like hydrogen sulfide (H2S). In fact, when H2S levels exceed four parts per million (ppm) by volume, natural gas will be neither shipped nor sold until that number is reduced. Not only is H2S toxic, it emits a nauseatingly foul odor. In addition, it acts corrosively on pipes and valves and can damage gauges and meters throughout the gas management infrastructure. Once the H2S is removed — along with CO2 — in the sour gas sweetening procedure, the natural gas is consumer-ready in terms of health, safety and heating value.
The gas sweetening process is subject to what goes ahead of it in the processing sequence. Natural gas is made ready for use through the following stages. Conventional natural gas is found between layers of igneous and metamorphic rock. It is also located in the pores of sedimentary formations like shale and sandstone. Dissolved natural gas can be found within oil and coal deposits. The first order of business for this associated natural gas is to separate it from its crude oil host. Any water associated with the natural gas stream needs to be removed. Natural gas collected from wells often contains natural gas liquids (NGLs) which have economic value apart from the gas itself and are ordinarily separated. It is at this point that sulfur and carbon dioxide are dealt with by the gas sweetening process.
This procedure is very similar to the absorption techniques employed for dehydration and NGL separation. With H2S neutralization, however, an amine solution — amine being an ammonia derivative — is used in an overwhelming majority of natural gas sweetening process cases. At the sweetening plant, sour gas is moved through a gas sweetening unit, or tower, containing amine solution. The amine attracts and absorbs the sulfur molecules, liberating the gas from this poisonous, damaging compound, leaving you with sweet natural gas. Best of all, the amine solution can be recycled and used over again. Worth noting, at any rate, is that in some cases solid dessicants, such as iron sponges, are also effective in sulfur removal.
Natural gas must travel from where it is found to where it is consumed — mostly through pipelines. These pipelines are vulnerable to the damage of sour gas. Sweet gas is required to keep transmission infrastructure sustainable and intact over the long distances it must travel.
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Questions about gas sweetening for your facility?
