These engineering challenges are best summarized by their interdependencies, as illustrated in Figure 2. As may be observed from Figure 2, high impeller tip speeds will enable high pressure ratios to be attained with fewer stages. Thus, a major challenge for the project has been to identify the material that can enable the highest tip speeds to be attained, while also sustaining the stresses that are imposed by these tip speeds. CN has met all of these engineering challenges in order to provide a pipeline compressor system that meets DOE’s specifications.

A summary of the results and accomplishments of this project to date are given in Figure 3 for each of the engineering specifications and objectives as set by DOE for the project.

In order to achieve these accomplishments, CN developed several computer design models that would optimize the design choice. These models include:

  • Compressor Package Performance Model that provides a single point summary of each of the components within the package.
  • Cost Model using algorithms to determine the relative component cost and operational risks associated with compressor design specifications.
  • Engineering Reliability and Maintenance Cost Model that uses a consistent methodology and algorithms to determine the relative reliability and maintenance cost for a piston and centrifugal compressor pipeline package.

The Cost and Performance Model enabled the analysis of over 30 combinations of centrifugal compressor impeller speeds, the number of stages, with a single or dual impeller-shaft design using a one or two-step gearbox, with a high- or low-speed prime mover drive arrangement. The best choice, with respect to conformity to commercially available system specifications along with high efficiency and low operational risk, is highlighted. This choice is a single, overhung (cantilevered) impeller attached to a drive shaft that includes a shaft seal, bearing, and drive pinion. The impeller rotor is designed without a bored-hub in order to reduce the hub “hoop” stresses. This requires the impeller to be mechanically attached to the high strength steel alloy drive shaft with a patented design attachment system that enables the rotor to be removed from the gearbox without removing the drive shaft and thus without disturbing the shaft seal and bearings.

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