Project Measures

To improve thermal efficiency, the steam system was upgraded to operate at a much higher initial pressure and temperature. Two of the three original boilers were targeted for decommissioning and two new dual-fuel 115,000 lbm/h (52,000 kg/h) Babcock and Wilcox watertube boilers with low-NOx burners and flue gas recirculation were installed. The new units generate steam at 1,100 psig/850°F (77 bar/454°C) that is used to power a new Dresser-Rand 5 MW back-pressure steam turbine generator. The new turbine generator produces electricity at a voltage of 13.8 kV to match the plant's existing normal and emergency electrical distribution systems, thereby avoiding the additional expense of a new step-down transformer. The plant has black-start capability and can operate isolated from the grid if necessary. As an additional redundancy measure, a new Caterpillar 1,250 kW reciprocating Diesel engine generator was installed.

Also installed was a boiler plant master control (BPMC) system to oversee operation of the new boilers, turbine generator set, chiller, water treatment, condensate, etc. Header pressure controllers and other "off skid" items are controlled directly through the BPMC, as well as the supervisory and data sharing with the other controllers. The system serves to reduce operating and repair costs related to pressure problems and the amount of employee time required to monitor the systems. The BPMC system works in conjunction with the individual control system on the existing boilers, turbines, and chillers.

A newly installed medium-pressure steam header, which cross-connects to the existing header, delivers 250 psig/500°F (18 bar/260°C) steam, exhausted from the new turbine, to the two existing extraction/condensing turbine generators, three steam turbine-driven chillers, and turbine-driven boiler feed pumps and draft fans. Extraction steam at 50 psig (4.4 bar) is then used to power a new 5,000 ton

(17,580 kWr) turbine-driven York centrifugal chiller designed for reasonably efficient operation at this relatively low operating pressure. Instead of replacing the entire system with a larger turbine generator operating with one larger pressure drop, the retrofit design optimized capital costs by keeping the existing steam turbine generators in operation. The new unit captures the enthalpy drop (extra ability to do work) at the now higher work availability level resulting from the generation of higher temperature/pressure steam by the new boilers.

In addition to the major combined heat, power, and cooling project, the other six implemented measures provided a combination of infrastructure improvements and operating cost savings. Five of the six measures, described as follows, offered simple paybacks of less than five years.

• Lighting System Upgrade: The lighting system upgrade involved the installation of about 27,000 new fixtures. Significant savings were achieved as a result of the new fixtures, as well as the reduction in the total number of lamps and ballasts needed to provide proper light levels. The reduced electric demand and cooling requirement and the added heating requirement resulting from this measure were interactively considered in the savings analysis, heat balance, and capacity selection of the boilers, turbine-driven generator, and chillers.

• EMCS Upgrade: This measure involved the replacement of the old imprecise controls with state-of-the-art technology. This was achieved by overlaying the existing pneumatic system with direct digital controls (DDC) and expanding the number of control points at the facility by 65%. The reduced electric, heating, and cooling loads and altered load profiles were considered interactively with the other measures.

• Electric Motor Upgrade: This upgrade included the replacement of 134 motors with high-efficiency models. Due to the relatively large average capacity of the motors that were replaced, the total of which was 5,000 hp (3,728 kWm), the simple payback for this measure was extremely low at 1.6 years.

• Small Chilled Water System Upgrade: This measure produced a good payback while providing for some air handling system improvements.

• Domestic and Process Water Improvements: This measure provided for new bathroom fixtures, a new reverse osmosis demineralized water system, and the redesign of cooling water flow for the refrigeration system.

The sixth measure involved the conversion to a variable air volume (VAV) system with the use of VFD technology for variable speed HVAC fan operation. The measure improved the indoor air quality and comfort conditions at the facility, but provided a modest economic return with a simple payback of 11 years.

Implementation of the overall project required careful planning to minimize and, in many cases, eliminate interruptions to facility operations. Boilers, turbines, and chillers were brought into the plant, staged, and installed while the existing plant was fully operational. Equipment cut-overs were carefully scheduled during off-peak periods to minimize the impact on the facility's critical care and emergency operations.

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