Dual-GT set-up maximizes efficiency, reliability
Rowan Cogeneration Plant
Combined Cycle Journal
2007 fourth quarter
A site assessment and engineering study completed by Concord Engineering Group of Voorhees, N.J., in 2001 indicated that Rowan University’s energy infrastructure was ready for a major overhaul. Its 1.5-megawatt Kawasaki gas turbine, only 10 years old at the time, was a maintenance headache, parts were increasingly difficult to come by, and the campus steam system’s condensate return line was leaking like a sieve.
In addition, the utility-owned electric distribution line serving the university was nearly maxed out, enrollment was growing, the campus underground electrical infrastructure was rated only 4.16 kV (inefficient for a university that had grown to 250 acres and 35 buildings with two million square feet of conditioned floor space), and absorption chillers located in many buildings were near the end of life.
The first work started in 2002. Electrical was high on the priority list, and upgrading of the 4.16-kV infrastructure to 12.47 kV began. The existing utility service at 15 kV was inadequate so the utility supported construction of a new 69-kV substation. It would have two full-size 69/12.4-kV transformers owned by Rowan. Power from this substation would flow to the university’s existing south substation for distribution to the campus.
A new north substation was built to receive power from the two Solar Turbines, Inc., (San Diego) gas turbines (GTs) installed as part of the project and to distribute that energy to a portion of the campus. The onsite generating units operate in parallel with the utility, but are not capable of providing electricity to the grid. However, Rowan can disconnect from the grid and operate in the “island” mode.
When Concord Engineering began its study in 2000, the university’s utilities department operated out of the right side (low rise) of the building shown in Fig. 1. Infrastructure consisted of the 1.5-MW GT mentioned earlier and several boilers. One of those units, a 26,000-lb/hr boiler installed in 1960, is still in service. Two 40,000-lb/hr packaged boilers were installed in 2005.
Kevin Muldoon, a senior project manager in Rowan’s facilities planning and construction group, said the university asked Concord to investigate the feasibility of cogeneration and a central chiller plant to satisfy growing energy needs, reduce the cost of electricity, steam and chilled water, and minimize pollutant emissions.
Infrastructure rehabilitation and expansion projects advance very deliberately in the institutional sector. It was 2005 before Rowan moved forward on the design of its cogeneration plant (combined heat and power, CHP) with the hiring of PS&S of Warren, N.J., and it took nearly another three years to complete design, build and commission the nominal 5-MW facility.
While the campus electric distribution system was being upgraded and condensate lines were being replaced, a demand-side load-reduction program was implemented to optimize operation of the heating/cooling system and upgrade lighting. After this was completed, PS&S could design the cogen plant based on current needs and also develop operational guidelines that assured energy send-out would match the actual load profile.
New central chiller
A new central chiller plant was erected adjacent to the existing steam plant (tall building in Fig. 1). Its two 1,000-ton electric chillers (Fig. 2) and one 2,550-ton steam-turbine-driven chiller (Fig. 3) replaced ageing absorption units in most buildings. The university also has an auxiliary chiller plant (two 400-ton electrics) to serve a cluster of four buildings located a short distance from the main chilled-water loop. They were scheduled to be integrated into the main loop later.
Each of the main electric units is capable of chilling about 2,000 gpm to between 42F and 54F; energy requirement is 0.63 kW/ton. The turbine-driven unit, which can operate at loads as low as 200 tons, chills about 4,700 gpm to between 42F and 54F at full load; it consumes 10.5 lb/hr of steam per ton.
Two separate chilled-water loops serve the campus and operate year-round–one 1,400-ft, 16-in. main and one 2,000-ft, 20-in. main. Nominal 45F water (Fig. 4) is delivered to the plant-and-frame heat exchangers installed in most buildings. Hot water is used to regulate air temperature and humidity at the VAV (variable air volume) boxes–one per thermostat.
The 150-psig steam loop also is in service 24/7. It serves the HVAC system, steam-turbine-driven chiller, and the domestic hot-water system.
Cogen plant design
Design of the cogen plant is matched to thermal requirements because power can’t be exported. The optimum arrangement for Rowan was to install one Solar Turbines, Inc., Centaur® 40, rated 3.5 MW at ISO conditions, and one Solar Saturn® 20, rated 1.2 MW.
Having two GTs avoids the inefficiency associated with operating one large machine at part load most of the time. It also contributes to higher reliability, which was particularly important at Rowan, Muldoon said, because the university has been designated a “place of refuge” in the unlikely event of an area emergency.
The new generating assets had to be installed while the existing plant was in service – another challenging aspect of the project. The plan, in sequence: install the Centaur 40 in the new chiller building along with its heat-recovery steam generator (HRSG); remove the old Kawasaki and its HRSG from the original building; install the Saturn 20 and its HRSG in the space formerly occupied by the Kawasaki.
HRSG from RENTECH
RENTECH Boiler Systems, Inc., of Abilene, Texas, provided the unfired HRSGs for both Solar machines. The boiler serving the Saturn is rated 8,300 lb/hr at 150 psig saturated (Fig. 5); the Centaur’s HRSG can produce 19,550 lb/hr (Fig. 6). Both units are equipped with SCRs using catalyst supplied by Cormetech, Inc., of Durham, N.C. The reducing agent is 19 percent aqueous ammonia. CO catalyst from EmeraChem LLC of Knoxville only was installed in the Saturn. The Centaur is equipped with Solar’s SoLoNOx™ dry, low-emissions combustion system, which is not available on the Saturn.
Both GTs are capable of burning both natural gas and distillate; however, oil firing is limited by the state to about 200 hours annually. A 6-inch-diameter gas line was installed to serve the GTs. This is uninterruptible gas; gas for the fired packaged boilers is interruptible and priced at a higher rate. Gas compressors were installed to boost line pressure to that required for the engines (Fig. 7). A 750-kW diesel/generator assures black-start capability (Fig. 8).
To assist the operators, PS&S developed a custom program that suggests what equipment to run based on fuel cost and outside temperature. It also is able to compare predicted to actual values to identify equipment deficiencies. Note that this is not a means for automated operation; it is designed to keep operators involved by using prompts. For example, on a warm summer day, the program would suggest that both the Centaur and Saturn be operating and supplying steam to the turbine-driven chiller. Any shortfall in chilling capacity would be made up with the electric chillers.