Energy & Power Generation Consulting,
Engineering & Management Services



Biomass 20'x20' Fluidized Bed Combustor rated at 38-40 MBH

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.


• 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.

• Performed a complete hardware evaluative assessment of the local area networked Allen-Bradley PLC system consisting of PC server/client based HMI's, ControlLogix redundant PLC's, redundant industrial switches, and ControlNet communication to remote I/O.

• Created functional logic drawings in MSVisio for the original EPI logic, the original BaileyCAD drawings, and the existing PLC logic in the ControlLogix processors. Used these three versions to determine the optimal logic for critical control loops.

• Found and corrected the preheat burner purge logic. It was clear that past logic changes had been implemented to bypass safety features of the standard purge as defined by NFPA. Implemented the correct changes and successfully commissioned the new logic.