Acid Gas Injection

The hydrocarbon can be converted to hydrogen and carbon monoxide using the steam reforming reaction. 

Although the reaction given is for methane, other hydrocarbons can be substituted instead and the products remain hydrogen and carbon monoxide. The carbon monoxide can be further reacted with water via the water-shift reaction  

The reactions given above are not new technology. This is the most commonly used process for producing hydrogen and is used in most petroleum refineries that require hydrogen. 

The carbon dioxide from this process can then be injected. Since this is a high pressure stream, it requires only a fraction of the power to compress the low pressure stream that results from the post-combustion separation. 

A project like this was proposed by a company lead by BP in Peterhead, Scotland. The C02 was to be injected into the offshore Miller field, which had reached the end of its productive life. However, it was canceled largely due to delays by the government regarding incentives. 

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In the natural gas business, acid gas injection has quickly become the method of choice for the disposal of such gases. Larger producers are also considering injection because of the volatility of the sulfur markets. 

Some of the technologies for dealing with this C02 are the same as acid gas injection, and thus they will be discussed here as well. 

In addition, with the current depressed market for sulfur, some larger producers are considering acid gas injection as an alternative for dealing with unwanted sulfur. 

Figure 1.2 shows the basic block diagram for the acid-gas injection process, including a block for the natural gas sweetening unit. For CCS, the sweetening block is replaced by a carbon capture block, but the rest of the process is unchanged. The four main components of the injection scheme are 1. compression, 2. pipeline, 3. injection well, and 4. reservoir. Each of these will be discussed in some detail in this book. 

Figure 1.2 Block diagram of an acid gas injection scheme.

As was mentioned, acid-gas injection has become a viable option for the disposal of unwanted acid gas. 

Acid gas, a mixture of hydrogen sulfide and carbon dioxide, is a toxic by-product of the sweetening of natural gas. Acid-gas injection has become an environmentally friendly way to dispose of this by-product. In the remainder of this book, the detailed design considerations for acid-gas injection are presented. 

Maddocks, J. and D. Whiteside. 2004. Acid gas injection An operator s perspective. SOGAT, Abu Dhabi, United Arab Emirates. 

Root, C., H. Schadler, R. Bentley and Steve Tzap. 2007. Acid-gas injection in New Mexico relieves sulfur-recovery unit duty. Oil Gas J. Sept. 17, pp. 72-82. 

Whatley, L. 2000. Acid-gas injection proves economic for West Texas gas plant. Oil Gas. May 22, pp. 58-61. 

The foundation of a good process design is accurate physical property calculations. This is no less true for acid gas injection than for any design. The design of an acid gas injection scheme requires knowledge of the density, enthalpy, entropy, viscosity, thermal conductivity, and other properties of the acid gas mixtures. 

As was mentioned earlier, the properties of carbon dioxide have been studied thoroughly. Thus it is relatively easy to construct a diagram that shows the viscosity of pure C02 over a wide range of pressure and temperature. Figure 2.5 is such a diagram, which shows the range of temperature and pressure of interest to acid gas injection. The curve labeled 0 MPa is the same as the low pressure viscosity shown in figure 2.4. 

Furthermore, this correlation is applicable to the liquid, vapor, and dense-phase regions. However, it is limited to densities less than 1250 kg/m3, which is sufficient for most acid gas injection applications. 

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