Figure 3. Steam Load Before and After Cooling Load Added, University of Minnesota-Morris, Projected.
14,000
12,000
10,000
HGA Architecture Engineering Planning
Mlb/Month
8,000
6,000
4,000
2,000
0
Jan Feb Mar Apr May
Jun Jul Aug
Month
Sep Oct Nov Dec
Projected Steam Load
Projected Steam Load with Cooling
load was needed.
The evaluation determined the need
to ( 1) minimize on-site electricity production, given the high cost of generating equipment at this size and the low
purchase price of power from the utility
company, and ( 2) size the biomass system to match the steam baseload to
maximize the operating costs savings to
reduce the capital invested in the plant.
Figure 3 shows the impact of the
lb/hr year-round. The fall/winter/spring
minimum load was approximately
12,000 lb/hr. [Note that Figure 3
expresses cooling load in thousands of
pounds of steam per month, (Mlb/
month) not in lb/hr.]
Reducing the biomass boiler size to
15,000 lb/hr now provides a very nice
year-round load, ranging from roughly
60 percent to 100 percent, with most of
the time spent above 75 percent. Figure
ton absorption chiller. It would be less
expensive to produce chilled water using
biomass-fired steam than electricity.
Choosing an absorption chiller over
a steam-turbine generator reduced project capital cost by nearly 20 percent and
demand for electricity by about 400 k W.
Biomass steam proved to be an economical source power for the Morris campus.
Given that finding, HGA recommended keeping the existing plant
equipment. This included the three
high-pressure steam boilers and two
600-ton electric chillers. In addition,
new equipment to be installed should
include one 15,000-lb/hr biomass boiler
and one 600-ton two-stage absorption
chiller. The boilers were rated at 150
psig, but currently operate at 20 psig
Choosing an absorption chiller
over a steam-turbine generator
reduced project capital cost by
nearly 20 percent…
Figure 4. Biomass Boiler Load Before and After Cooling Added, University of Minnesota-Morris, Projected.
16,000
14,000
Monthly Average
Lbm/Hr
12,000
10,000
8,000
6,000
4,000
2,000
HGA Architecture Engineering Planning
0
Jan Mar
cooling load on the campus steam
loads, when served from a base-loaded
two-stage absorption chiller. A large
summertime dip still exists in the steam
load profile, but the situation is
improved. The summertime baseload
for steam now increases to nearly 9,000
May Jul
Month
Sep Nov
Projected Steam Load without Cooling
Projected Steam Load with Cooling
4, in which the monthly average steaming
rate is expressed in lb/hr, shows the
average monthly load of the biomass
boiler before and after adding the absorption cooling load. Steam from the biomass
boiler can be more fully utilized year-round by base-loading a two-stage, 600-
for heating steam. The University plans
to operate the boilers at 125 psig during
the summer to serve a two-stage absorber
and return the plant to a more efficient
20-psig operation during the winter.
To confirm this recommendation,
HGA examined selected power-generating options closely. The company
looked at turbine generators at a variety
of sizes less than 2. 5 MW and operating
at pressures from 60 psig to 750 psig.
It also considered extraction ports and
other schemes for normal- to large-scale
plants – to help match loads to the
equipment and provide operating flexibility in the event that market prices
and power sales rules change in the
future. (The University is in a regulated
electric market.) This design effort
showed that
( 1) the operating staff was more comfortable with an absorption chiller
than a portion of their plant operating at 750 psig;
( 2) the ability of the existing plant equipment to back up new equipment and
vice versa was better if the design
pressure (150 psig) of the existing
