POWER October 2013 - 42

Top planTs
heating season that ended on Apr. 15, 2012.
After the power plant modifications and
addition of the absorption chillers and other
auxiliary equipment were completed, the
new heat recovery systems on Units 1 and
2 were immediately placed into operation to
help meet the heating season thermal load.
Operation of the absorption chillers and central
heating season is reported as having gone
smoothly and met the required performance
standards. Phase two was recognized as a key
urban construction project in 2012 by the municipal
government of Shuozhou and cost an
additional 400 million yuan (~$65.3 million)
to heat another six million square meters.
The central heating project will eventually
serve about 20 million square meters of
central heating area in Shuozhou City when
completed in 2020. Total investment cost of
the project is estimated at 1.41 billion yuan
(~$230 million).
Unit Upgrades
The new central heating system is based on
absorption heat pump technology to recycle
the low-grade waste heat normally rejected
by power plants to produce hot water for central
heating. Each of Shentou Second Power
Plant's four units was originally equipped
with a Czechoslovakia-made 500-MW condensing
steam turbine that was modified to
supply extraction steam, up to 550 metric
tons per hour (tph) at 0.5 MPaG (~72 psig),
to the heat recovery system as part of the
project. The main steam flow rate for each
of the four units is 1,650 tph. The extraction
steam is the heat source that drives the
operation of the lithium-bromide absorption
heat pump system. The condensed extraction
steam from the absorber's generator
section is returned to the unit's condensate
steam (Figure 1).
The waste heat originates with the cooling
(condensing) water system, from which
it is recovered before it leaves the plant
for the evaporative cooling towers. The
amount of water that goes to the cooling
tower remains constant, but the temperature
entering the tower is reduced, which
reduces the tower's heat duty, the evaporation
rate, and thereby the makeup water
required. Cooling water at 30C enters and
leaves the evaporator section of the absorption
heat pump at 26C.
The return water from the central heating
system enters the absorption system at
55C, where it is heated by energy removed
from the cooling water before it then enters a
separate final heater, where the heating water
temperature is further increased to 130C before
entering the central heating system. Extraction
steam is the energy source to power
the absorption heat pump and the final heater.
42
1. Key component. The absorption heat pump extracts heat from cooling water by using
steam turbine extraction steam as its energy source. Extraction steam also heats the water
used in the central heating loop to its 130C operating temperature. One absorption heat pump
was installed on each of the Shentou Second Power Plant's four 500-MW units. Courtesy:
Shanxi Shuangliang Renewable Energy Industry Group Co.
New circulating pumps and controls ensure
the entire heated water system operates at
constant pressure. The design supply water
pressure is 1.49 MPa and the return water
pressure is 0.49 MPa.
The central heating network is a closed
system. Sub-networks are isolated from the
central heating network by means of a plate
heat exchanger located at the many secondary
heat exchange stations. Individual users
connect their homes and businesses to
these secondary networks. This approach
allows the central heating network to operate
at maximum pumping efficiency even as
older existing networks and new customers
are added. (A flow diagram of the complete
absorption chiller/central heating system is
available via a link in the online version of
this article at powermag.com.)
Another qualitative efficiency measure is
to examine the energy produced in relation
to the energy added. If the extraction steam
from the plant is 1 MW thermal, then the
absorption system recovers ~0.7 MW to 0.8
MW thermal from the cooling water and the
central heating system receives ~1.7 MW to
1.8 MW thermal. Balancing the improved
central heating efficiency is reduced plant
power output because less steam travels completely
through the steam turbine. During
non-heating periods, the extraction steam is
secured so the full 500 MW from each steam
turbine is available.
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Major Implications
There are 15 provinces in northern China that
require winter heating, representing 40% of
China's population and 70% of its land area.
In general, a 300-MW coal-fired unit can use
absorption heat pump technology to produce
central heating for about 2.5 million square
meters of urban area. There are approximately
6.5 billion square meters of urban
construction area requiring winter heating
now in north China, so the potential for improved
energy conservation while reducing
air emissions could have a significant impact
on China's overall energy efficiency.
According to SSREIGC, the equipment
and technology supplier for this project,
China's market for absorption heat pump
technology when combined with the readily
available steam and condensing water supply
found in the typical coal-fired power plant
for urban area central heating is huge. Also,
the central system approach allows municipal
authorities to close smaller facilities and
homes that burn coal for space heating to reduce
regional emissions.
Using a holistic approach to reach energy
efficiency goals on the supply side that complement
conservation on the demand side-
while reducing regional emissions-well
qualifies the Shentou Second Power Plant as
a 2013 POWER Top Plant. ■
-Dr. Robert Peltier, PE is POWER's
consulting editor.
POWER | October 2013

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POWER October 2013

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