|Total system capacity is 224,000 pounds/hour.
|Steam is generated at up to 225 PSIg at saturated conditions or 397F.
|Approximately 5.5 miles of underground piping distributes steam to 72 campus buildings—providing heat to 3.9 million square feet (or roughly 58% of entire campus square footage)
|The primary fuel source is natural gas purchased through an interruptible supply contract. Secondary backup fuel is Ultra Low Sulfur No. 2 Heating oil, and a few days’ supply is securely stored in underground tanks for times when natural gas is temporarily interrupted.
|Several older “satellite” boilers in other campus locations are used for emergency back-up heating only.
Five (5) industrial sized water-tube boilers are housed within the Main Campus plant to produce steam.
Boilers #1 through #4 are each capable of generating ~40,000 lbs of steam per hour. Boiler #5 has a generating capacity of 64,500 lbs per hour. In total this makes a plant generating capacity of 224,500 lbs. of steam per hour. By design, the university campus has never needed this much steam at any one time. Having excess capacity built into the system is both intentional and essential since the university is only permitted to run four boilers at any given time. This also provides flexibility in the event that a boiler is taken off-line for maintenance, we can still provide heat to campus.
Inside each boiler, water is circulated through steel tubes which are heated by the combustion of fuel. Natural gas is used as the primary fuel source. The water is boiled with enough intensity to convert it into high-pressure (225 PSI) steam with a temperature of about 400°F. Steam rises into a drum and moves to the pipe that will carry it out to campus buildings through a steam distribution loop.
Recycling Steam Condensate Back through the System
Steel pipes return condensed steam (a.k.a. hot water) back to the Plant and into a condensate collection tank. The UVM system has a highly efficient return rate of about 90% -- meaning that almost all of the steam pushed out to campus makes its way back to the Plant in the form of condensate. The 10% of “make-up” water needed for the system comes from the City of Burlington municipal water supply. This municipal water must first be chemically treated with softeners to reduce water hardness (which can corrode pipes) before it is added to the condensate collection tank. Condensate (hot water) enters the tank at about 130F while the municipal water is about 40F.
From the collection tank, the hot water mixture (i.e, the condensate and the make-up water) is pumped through a set of tanks known as chemical polishers which are designed to remove any heavy metals or non-water molecules that were picked up from the steam distribution or building piping along the way (because the water re-entering the boilers must be impeccably pure to prevent corrosion).
The water is next pumped a short distance to a 5,600 gallon de-aerator tank. The purpose of the de-aerator is to remove dissolved oxygen from the water to prevent any further oxidation, pitting or rusting inside the steel pipes of the campus distribution system. Removing this oxygen also serves to increase the fuel efficiency of the boilers.
After being polished and de-aerated, the hot water is recycled back into one of the industrial boilers and the process starts all over again.
This continually flowing closed-loop process occurs 24 hours per day, 360 days per year, to ensure stream is available for heating during the winter and for steam-driven cooling in the summer.
Distribution and Piping
We will explain more about underground piping, insulation of pipes and improvements made over the years to reduce steam loss and thermal loss.
a tank for heating water or turning it into steam for use in heating, cooling or industrial processes.
the removal of dissolved oxygen in water using pressure and temperature above boiling point. Inside the de-aerator, water interfaces with low-pressure steam that transfers heat and pressure to the water and forces oxygen to bubble out.
a box type heat exchanger that is mounted on the exhaust outlet of a boiler and that contains a series of fin tubes. Water enters the top of the economizer and flows through the tubes to the bottom, which is near the boiler’s outlet, picking up some heat from the boiler as it goes. This process reduces the amount of fuel required to generate 225 psi steam.