Gas Processing 2

Gas processing (gas treating, gas refining) removes one or more components from the recovered (harvested) gas to prepare the gas for use. To include a description of all of the possible process for gas cleaning is beyond the scope of this book.

 

Gas processing is an instrumental piece of the natural gas value chain and is required to ensure that the natural gas intended for use is as clean and pure as possible, making it the clean burning and environmentally sound energy choice. In the processing sequence, common components removed to meet pipeline, safety, environmental, and quality specifications include hydrogen sulfide, carbon dioxide, nitrogen, hydrocarbons having a higher molecular weight than methane, and water. Once the natural gas has been fully processed and is ready to be consumed, it must be transported from those areas that produce natural gas to those areas that provide a market for natural gas.

 

Whatever the source (tight shale, tight sandstone, tight carbonate), natural gas needs to be processed before use because of the occurrence of the diluents and contaminants. The processes focus on sulfur removal and carbon dioxide removal. The processes that have been developed to accomplish gas purification vary from a simple once-through wash operation to complex multistep recycling systems. In many cases, process complexities arise because of the need for recovery of the materials used to remove the contaminants or even recovery of the contaminants in the original, or altered, form. However, process complexities in terms of the choice of the process also arise because of the varying composition of gas from tight formations. In fact, there are many variables in treating natural gas from tight formations, and the precise area of application of a given process may be difficult to define. In addition to hydrogen sulfide and carbon dioxide, gas may contain other contaminants, such as mercaptans (R-SH) and carbonyl sulfide (COS). The presence of these impurities may eliminate some of the sweetening processes since some processes remove large amounts of acid gas but not to a sufficiently low concentration. On the other hand, there are those processes that are not designed to remove (or are incapable of removing) large amounts of acid gases. However, these processes also capable of removing the acid gas impurities to very low levels when the acid gases are there in low to medium concentrations in the gas. Process selectivity indicates the preference with which the process removes one acid gas component relative to (or in preference to) another. For example, some processes remove both hydrogen sulfide and carbon dioxide; other processes are designed to remove hydrogen sulfide only. It is important to consider the process selectivity for, say, hydrogen sulfide removal compared to carbon dioxide removal that ensures minimal concentrations of these components in the product, thus the need for consideration of the carbon dioxide to hydrogen sulfide in the gas stream. In a general processing sense, many chemical processes and physical process are available for processing or refining natural gas.