Paper: Non-Process Design Considerations for CO2 Processing Facilities

The processing of streams containing high concentrations of carbon dioxide (CO21 is becoming more commonplace as enhanced oil recovery (EOR) projects come to reality. The process begins with production from naturally occurring CO2 reservoirs in New Mexico, Colorado, Wyoming, Texas, and Mississippi shown in Figure 1, or with the recovery of CO2 from vent or flue gases in chemical plants and power plants. These streams must be processed to produce a relatively pure stream of about 95% CO2 to meet purchaser specifications. Once the CO2 has been purified, it will typically be transported long distances to oil fields in West Texas, Oklahoma, New Mexico, North Dakota, or Mississippi where it will be injected into the oil bearing formations. The CO2 mixes with the reservoir fluid to expand it and produce a less viscous mixture that flows through the formation more easily, resulting in increased crude oil recovery. The components of the produced fluid, water, crude oil, and gas (hydrocarbon and CO2), are separated into three phases. The produced gas, which contains varying amounts of CO2 must be processed before it is suitable for further use. Figure 2 shows a simplified Block Diagram for some process options. The water content of the gas makes it too corrosive to simply compress and reinject into the formation, and the high CO2 content makes it unsuitable for sale to a natural gas pipeline. Several process schemes are available to separate and purify the components of the gas stream, but the simplest approach is to dehydrate the stream, to make it less corrosive, and then reinject it. As more complicated processes such as membranes, chemical solvents, physical solvents, and fractionation are used, the design problems become more complex. The purpose of this presentation is to highlight a few of the areas of non-process concern and offer possible design approaches. Some of the subjects discussed are specific to CO2 processing units, and others, such as sparing and compression selection, apply to other types of facilities as well.