Chevron Cogeneration (B-Train) Efficiency Upgrade
The Heat Recovery Steam Generator (HRSG) utilizes discarded heat from the combustion turbine generator’s (CTG) exhaust gas to produce steam for the 850 and 300 psig steam systems. It also provides gas emission controls for the CTG exhaust gasses.
The processed flue gas passes over the High Temperature Economizer (HTEC) tubes where feedwater receives final preheating before entering the HP boiler. The gas continues and passes over the new Low Temperature Economizer (LTEC) tubes where feedwater receives the first pre-heat before being directed to either the MP boiler tube section, or to the HT economizer tubes. This capture of waste heat by the HTEC and LTEC enables additional steam generation (with no additional duty/fuel) which increases Cogeneration efficiency (more steam is generated for the same fuel burned). The estimated duty reduction is ~13 MMBTU/hr or ~7,500 MT CO2 reduced for the same steam generation.
The original LTEC design had 10 rows of tubes in a serpentine design with upper and lower headers. The nature of this design led to large moments where the drains attach to the lower headers and forced the tube bend to accommodate the strain and to yield plastically. Buoyancy instability is present in several rows and was expected to cause plastic deformation in the upper tube bends, particularly during start up and transient conditions. These events led to low-cycle fatigue and tube failures that ultimately led to the decommissioning of the LTEC.
The new, upgraded LTEC design incorporates HRST’s ShockMaster technology and utilizes all up-flow circuits, eliminating the buoyancy instability and inlet-pass thermal shock during both steady-state and transient operating conditions. The HRST design includes no tube bends, acting further to eliminate moments and bending stress at the tube-header connections. The new single-pass panels result in a reduced overall pressure drop and increased reliability will sustain higher efficiency throughout the run of the Cogeneration unit.
Chevron partnered with SoCal Gas to participate in the Energy Efficiency Conditional Incentive Program (EECIP) and was one of the leading energy efficiency projects under this program. Furthermore, Chevron is working with the California Air Resources Board (CARB) to submit this project under the Low Carbon Fuel Standard (LCFS) Refinery Investment program.