of condensate returned represents an average of 67.3 percent
with a generated bill credit of $34,654. Additionally, the
amount returned represents a savings of 7,868 MMBtu (78.7
ktherms) of fuel. (The energy savings rate is based on average
difference between heat energy received from condensate less
heat energy available from regular source water.)
Ever since the condensate return system has
been in place, the stadium and convention
center have seen both energy and cost savings.
The water, chemicals and energy savings made possible
by our new condensate return system make this statement
a correct one: “Sometimes the old way is the right choice,
Reinstallation of Back-Pressure Turbines
As Citizens saw with its ‘return to condensate return,’ the
basic processes of district energy dating back to its modest
beginnings are still relevant today. Many of our current
district energy systems were founded to utilize the byproduct
of providing electricity to customers. Generated steam was
often considered waste until it was captured for heating or
process load, which still holds true for many new engineering
In the past few years, we have been hearing more and
more about efficiency, sustainability (“meeting the needs of the
present without compromising the ability of future generations
to meet their own needs”) and cogeneration – the simultaneous
production of electricity and mechanical power from a single
heat source (using the steam twice). The term “cogeneration”
today is usually used to refer to combined heat and power.
The mechanical power portion of the cogeneration
Taking care of basics ties in here, as that may include
equation is sometimes forgotten. A large number of IDEA
members and industrial users have boilers that provide steam
for heating or processing. The steam also generates energy
through small turbines that are used to drive equipment.
This process happens prior to the steam moving into the
distribution system. This type of turbine is often referred to as
a “back-pressure turbine.” The back pressure goes to either a
deaerator tank for heating purposes and O removal or to the
steam distribution system as a salable or usable product. This
same type of cogeneration can be used to drive pumps, fans,
compressors or other pieces of equipment required to run
using a blowdown heat exchanger to recover the heat going
Courtesy Citizens Thermal Engineering Group.
Two 1.7 MW back-pressure turbines take 600 psig steam and reduce it to 250
psig, which provides cogeneration and sustainability, improving the efficiency
of the steam produced.
to waste from the boiler blowdown or other areas, for example.
Other basic improvement measures may involve managing
water treatment to remove both scale inside tubes, cleaning
soot and ash from the outside of tubes, reviewing oxygen
settings for efficient combustion, providing adequate
insulation of piping and equipment, or reviewing the heat
balance of your plant and total system in light of changes in
operation or equipment over the years.
This leads us to our second project – installing two back-pressure turbines to produce 1.7 MW (cogeneration) each,
instead of utilizing a PRV. It is another instance of looking
back to the system basics of the past to improve our
operations for the future.
In 2007 and 2008, as Citizens investigated system data
from the past, we noted that our system used to have a back-
pressure turbine rated at 11 MW. It had been installed in 1936
and removed during the 1980s. This back-pressure turbine was
used to take 600 psig steam and reduce the steam to 250 psig.
In its place is a full set of PRVs that was installed to
provide 250 psig steam to the distribution system. With our
cost of electricity increasing over the years and our escalating
electrical load, we needed to install approximately 3-4 MW
of additional generating capacity to meet our existing peak
electrical load. We have an existing 5 MW turbine that supplies
power on our side of the meter. But during outages or required
maintenance to this unit, we would set a new demand, which
involved a ratchet that required us to live with the additional
electric cost for the next 11 months.
With an understanding of our history, we began investi-
gating how we could lower our electrical cost and improve