Читать книгу Process Intensification and Integration for Sustainable Design - Группа авторов - Страница 27

Over the past decade, the shale gas boom has caused significant industrial development in the United States, with the promise of significant monetization opportunities for the manufacturing sector to produce various value‐added chemicals and fuels [1]. Shale gas is a form of natural gas where the gas is trapped within low permeability shale formations [2]. One major challenge with shale gas however is the wide variability in the composition and flow rate of the gas. The composition and flow rate, both between wells and within the same well over time, can differ significantly [3-5].

Dynamic and spatial variability in flow rate and composition pose major challenges when designing a gas processing plant of optimal size. In general, plants with larger process equipment are more flexible and are able to handle a wider range of inlet compositions. Nonetheless, these plants also have higher fixed and variable costs. A gas processing plant is needed to purify and separate natural gas and natural gas liquids (NGLs) and to isolate various possible containments including water, sulfur species, carbon dioxide, mercury, and oxygen [6]. Such separation operations may include acid gas removal, to remove sulfur species and carbon dioxide, dehydration, nitrogen rejection, mercury removal, NGL recovery, and NGL separation. One issue currently facing the gas production industry is a lack of capacity to handle greatly increased production [7]. Another issue is frequent unplanned shutdowns and a lack of efficiency in operations [8]. Regardless of the dynamic and spatial variability in shale gas flow rate and composition, gas processing facilities must have the ability to handle such variations and render a set of products with consistent qualities to satisfy pipeline constraints and downstream‐processing requirements [9-12]. In this chapter, the aim is to determine a method to find the optimal size of a plant and a strategy to process wellhead gas when feeds of various compositions are available to the facility. Process synthesis, simulation, and techno‐economic analysis were used to determine the optimal configuration and capacity of the gas treatment plant.

The approach will also incorporate safety into the early stages of process design, before changes in design become more costly and difficult to make [13-15]. The concept of inherent safety is that, by eliminating or reducing the sources of hazards in a chemical plant, the severity and likelihood of process safety incidents will be reduced [8]. One challenge of implementing inherent safety is the lack of information in early design stages. Most existing safety assessment tools are used retroactively, after the process design is completed or near completion [16]. In order to quantify the inherent safety of alternative process designs during the early design stages, a number of safety indices have been developed [14,15,17]. In this work the safety of different process designs will be compared using a modified version of the process route index (PRI) [18]. This safety index was chosen because the chemicals involved in natural gas processing are highly flammable and explosive [18,19].

Another important consideration is environmental impact. While natural gas is considered to be cleaner than coal and oil (from an emissions and energy consumption standpoint), there is potential for further reduction in environmental impact [20,21]. However to the author's knowledge fluctuating feedstock compositions have not been considered in literature for shale gas processing.