Saint Mary’s Hospital - 7.75 MW CHP System - Case Study
Quick Facts
LOCATION: Rochester, Minnesota
MARKET SECTOR: Healthcare
FACILITY SIZE:
3 Million Square Feet, 960 Licensed Beds
FACILITY PEAK LOADS:
Electric: 12.0 Megawatts
Heating: 130,000 lb/hr Steam
Cooling: 7,500 Tons
TOTAL CHP GENERATING CAPACITY: 7.75 Megawatts
HEAT RECOVERY RATE: 24,000 lb/hr of 250 psig Steam
HEAT RECOVERY UTILIZATION: Building heating or cooling, medical equipment sterilization, additional electricity generation
PRIME MOVERS:
(1) 3.0 MW Dresser-Rand Back Pressure Steam Turbine (installed 1971)
(1) 4.75 MW Solar Taurus 60 Gas Combustion Turbine (installed 1996)
FUEL TYPE: Natural Gas
TOTAL PROJECT COST: $5 Million*
EXPECTED PAYBACK: 5 Years*
ACTUAL PAYBACK: 3.5 Years*
BEGAN OPERATION: 1996*
*Data for 4.75 MW Combustion Turbine Installation Only
Project Overview
Saint Mary’s Hospital of Rochester, Minnesota, has long embraced combined heat and power (CHP). It first began operating a CHP system in 1912 with a 350 kW steam turbine system and today operates a CHP system that includes a 4.75 MW combustion turbine and 3.0 MW back pressure steam turbine. The facility upgraded the initial system based on expanding facility needs, while retiring aging equipment. For the most recent addition to the CHP system, the 4.75 MW combustion turbine installed in 1996, the hospital experienced a 3.5 year payback on their $5 million investment. The hospital can now meet approximately 75% of its peak electric demand.
The CHP system utilizes a 4.75 MW Solar Taurus 60 natural gas combustion turbine with a heat recovery boiler that recycles the exhaust gas from the turbine into approximately 24,000 lb/hr of 250 psig high pressure steam. To supplement the thermal energy provided by the Solar Taurus turbine Saint Mary’s utilizes three Nebraska 80,000 lb/hr high pressure boilers. The high pressure steam produced from the combined system is then either utilized in building heating or cooling, in medical equipment sterilization or sent to a 3.0 MW backpressure steam turbine that reduces the 250 psig steam to 8 psig. The 8 psig steam is then utilized for either heating or cooling throughout the hospital.
History of CHP at Saint Mary’s Hospital
The first two 350 kW steam turbines were installed in 1912 and 1919, respectively. In 1942 the hospital installed two 750 kW Westinghouse steam turbines to replace the original turbines, and in the 1950s added a 1,500 kW steam turbine to meet increased electrical needs. The current 3,000 kW Dresser-Rand steam turbine was added in 1967. Aging boilers and equipment were replaced in 1992 with a new plant and the retirement of the 3 oldest Westinghouse turbines. More recently in 1996, Saint Mary’s hospital installed a 4.75 MW Solar Taurus 60 natural gas combustion turbine that would supply high pressure steam to the 3.0 MW backpressure steam turbine or supplement building heating and cooling loads and medical equipment sterilization.
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