PROJECT: 45 MW Biomass Boiler Stability

Completed the design, installation, commissioning, and tuning of improved boiler fuel and air control logic for a 45 MW biomass shaker grate boiler power generator. Previously and since early 2014, it was not uncommon for the 1400 psig boiler to experience pressure swings as great as +-100 psi. Many thought that this was a direct result of the diverse BTU content in their fuel mix. After the completion of the commissioning and tuning portion of the project, the improved control logic design now achieves boiler pressure stability within +-10 psi; even while holding the MW output within +-0.5 MW and not using the turbine for pressure control.

The primary components for this improvement was the implementation of correct control theory and traditional boiler fuel/air process and control logic designs. Prior to the installation of the improved logic/tuning, it was not uncommon for the operators to respond to approximately 100 pressure control associated annunciation alarms. In the first four days of operation with the new logic, not a single pressure control alarm came in!

The boiler fuel and air controls always remain in fully automatic mode with very little need for operator attention.

PROJECT: Hydrogen Sulfide Incinerator Replacement for Geothermal Generation

A large number of generating units were installed in the Geysers area around Clear Lake, CA, while PG&E owned these facilities. A by-product of using the steam out of the ground is the off gassing of hydrogen sulfide (H2S) gas which has a strong odor of rotten eggs. While PG&E owned these units, the local air pollution control district implement regulations to control release of H2S gas. PG&E had their Department of Engineering Research build a pilot incinerator at one of the generating site's location. In the year 2000, this pilot incinerator was at least 5 years old and was failing. An independent power producer (IPP) purchased the majority of PG&E's geysers units and also bought a used incinerator of much larger capacity to replace the pilot incinerator. The used incinerator system consisted of a simple antiquated hardwired analog control system using basic control theory to maintain combustion and quenching water flow rates.

The IPP requested that the control system be upgraded to an Allen-Bradley ControlLogix PLC including building the burner management system in a stand-alone ControlLogix PLC. The IPP specified that process safety and stability were a premium due to past challenges from the original prototype incinerator. Therefore, process and control engineering design, testing, construction, and startup services were provided for a completely new and upgraded control system. Included in these services was the development and finalization of the functional process organization for H2S abatement.

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.