Energy & Power Generation Consulting,
Engineering & Management Services

1-888-705-0072

equipment

Allen-Bradley ControlLogix PLC


PROJECT: Simultaneous Restoration of Two Biomass Power Plants


Two mid 1980's vintage biomass power plants each rated at approximately 12.5 MW's had been shutdown and abandoned in mid year 2010 due to the loss of permanent financing. With the financial challenges prior to these plants being abandoned, the equipment had suffered from over use, lack of maintenance, and make shift repairs with limited site resources. The Allen-Bradley PLC based control systems were one of the casualties of the lack of maintenance and technical expertise to the point where the contract O&M service were unaware of the full extent of the problems.

The initial responsibilities started late in the "refurbishment" process (i.e., four weeks before the scheduled startup date) and included simply fixing some perceived "bugs" in the PLC system, PLC process & control tuning, and startup engineering support. The responsibilities grew to include a full upgrade of the Allen-Bradley system from their mid 1990's version to current hardware and software, rebuilding of many major process control loops, process & control tuning, and full unit engineering startup support which included engineering changes to various process methods.

The combustors for these sites are Energy Products of Idaho (EPI) bubbling fluidized bed combustors providing heat energy to a Zurn 122 kpph at 684 psig & 765F superheated steam boiler. Both sites burned agricultural waste which primarily amounted to chopped up almond orchards during the course of this startup.

The plants were built and placed in operation in 1988 and 1990 but were sold to the second owner in 1992. The facilities were shutdown in 1995 after the power purchase agreements (PPA's)were bought out. The third owners purchased the sites, refurbished the equipment and negotiated new PPA's. This major refurbishment was needed to correct damage for the 12 years of being abandoned the first time. Unfortunately, the control system upgrade was not managed well which resulted in many control loops being operated in manual. During the refurbishment, the sites were sold to the fourth owner which ended up having to fire the general contractor conducting the refurbishment and utilizing the contract O&M service to complete the work. After the startup of this first refurbishment beginning in 2008, the plant only ran to mid year 2010, again, being abandoned. The fifth owner purchased the plants and conducted these current refurbishments.

RESULTS


• Performed a complete control system evaluative assessment for the existing control logic in the PLC's, compared this to the OEM original design functional logic, and BaileyCAD logic. Provided a formal control system improvement program proposal document.

• Created and formally documented a proposed process and control logic upgrade for the boiler master, fuel flow, air flue, gas recirculation, and induced draft fan control logic. This new design included improved process monitoring and control philosophy.

• Completed a performance assessment of the required steam flow for full load capacity versus the historical performance and instrumentation calibration. Provided documented proof of a severe degradation in turbine performance.

• Completed a tuning program of the primary control loops necessary for stable automatic operation of the biomass combustor process, boiler controls, and turbine controls.

• Conducted final start up activities for both biomass generation units supporting all control system and process troubleshooting activities. Successfully placed in operation both full power generation facilities ahead of the expect schedule.