Plant Modernization Project: Centrifugal Compressor for Hydrogen-rich Gas Recycling in LG-35 Unit

Project Overview

Catalytic reforming with R-56 bimetallic catalyst (platforming) is one of the most important processes used in petroleum refining industry. This process plays a central part in the production of high-octane components for automotive and aviation fuels.

Process unit LG-35-11/300-95 with a feedstock capacity of 300.000 tons per year. The unit is operated in a gasoline mode producing high-octane component with research octane number up to 95.

The catalytic reformer consists of the following sections:

• Straight-run gasoline (naphtha) preliminary hydrotreatment
• Hydrotreated gasoline (hydrogenate) platforming
• Platformate stabilization.

There are two process streams:

• Feedstock stream
• Hydrogen-rich gas stream.

Raw hydrogen-rich gas with hydrogen content of not less than 75% vol. flows from the discharge of CK-1 recycling compressor of the reformer unit into the intake line of hydrotreating recycling compressors. Reformer feedstock at a pressure up to 50 kg/cm² is fed through filters into the tee for blending with hydrogen-rich recycle gas from CK-1 centrifugal compressor.

Within the scope of LG-35 Unit modernization and upgrading package CK-1 compressor will be changed over to standby duty mode and a new CK-2 compressor will be made the main one and connected in parallel to the existing unit.

Both units are centrifugal compressors, but the former one has a “drum” design, and the latter is a multi-shaft-unit with a built-in speed increaser multiplier and three compression stages.

To accommodate the second compressor a knockdown shelter will be constructed on the plant premises.

Detail documentation was developed by the refinery's engineering department based on the basic design stage (detail design specifications).

A 3-D model of the proposed compressor station was developed according to the version proposed at the basic design stage; design assignments were prepared for the construction of the compressor foundation, shelter, process piping, power supply and instrument connections, along with detail drawings and diagrams. Necessary corrections and additional provisions were incorporated in the detailed documentation in accordance with the plant’s existing LG-35 operating procedure and applicable safety standards.

Specific features of this project include the following:

1. New equipment is to be connected to existing process unit.
2. Variable gas composition (hydrogen-rich gas) – compressor is to be adjusted to the variations of gas molecular weight.
3. A part of the process gas will be diverted to other plant cycles (besides the main process in LG-35), for this reason the new compressor will have a 1.5 greater capacity than the existing one, while the turndown limit of the new compressor (using inlet guide vanes) will correspond to the rated capacity of the existing compressor.