There are two district heating stations at the
plant employed for the heating of the towns of Velenje and Šoštanj, and
hot water supply to all the factories in the Šaleška valley. We transfer
the necessary thermal energy to the users and systematically deposit
the harmful by-products of burning, we filter the flue gasses for SO2
and the rest is exhausted into the higher strata of the atmosphere.
The main and only distributor of heat energy provided by the Šoštanj
thermal power plant is the Komunalno podjetje Velenje (Public utility
company Velenje) – Energetika (Energy) business unit. This unit which
has a 265MW capacity line, with a guaranteed supply of 219MW -
calculated for accounting purposes*, operates on four different pressure
and temperature regimes. With a distribution network of 141.5km, it
supplies 90 percent of the population of the Šaleška valley, including
remote settlements. The principal network that extends east and west of
the Šoštanj plant has a maximum flow of 2,115m3 of water per hour with a
temperature of 140 °C that is reduced to 80 °C on the return line.
The district heating system was built from 1959 on when the
three-pipe heat system, then supplied from the Velenje thermal power
plant, came into operation. Every three or four years the system was
extended and modernized and in 1995 it was completed with the connection
of the Topolšica resort locality.
The district heating stations can produce parallel output into the
principal line which is necessary in the winter, or one of them can be
shut down as we do in summer. The stations produce heat according to the
parameters set by the distributor. The maximum possible quantity of
heat produced is 500KWh. On average, we produce from 360 to 400 million
KWh. A power plant with a cogeneration facility is more profitable as
the energy efficiency is increased this way.
District heating station one, which is the older one, has a capacity
of 90MW. To produce heat it needs fresh steam directly from boilers 1-4.
This steam must be reduced in pressure and cooled to a suitable
temperature, so it can be used for water heating in the heat exchangers.
This way we waste a part of the superheat energy, which could be used
to drive the steam turbines and produce electric energy. The station can
also be supplied by the steam exhaust conduits of generating unit four.
This steam has already given away its superheat energy on the turbine
and could produce some more mechanical energy on lower pressure
turbines, but it is much more profitable to exploit the heat of this
steam for district heating. This way we avoid losses that would occur if
the steam continued its way into the condenser. If at all possible we
use the exhaust steam from the turbines of gen. unit four for the
operation of district heating station one, but because of the operating
regime of the power plant this is not always possible. The schematic
shows the cooling water from the principal line, pumped by the
circulation pumps, flowing through the condense cooler and then flowing
through the low-pressure heat exchangers. These heat exchangers give the
water the bulk of the heat and then the water goes on to the
high-pressure heat exchangers where it is further heated to a
temperature set by the distributor. The district heating steam cools
down to water during its flow in the heat exchangers and is pumped back
to the condenser of the turbine from which it was extracted after use.
The district heating water temperature is 140 °C in the winter and 120
°C in the summer and the pressure varies between 16 and 20 bars
according to the temperature. The return water has a temperature of 80
°C and a pressure of 8 bars.
District heating station two was built more recently and is more
efficient; therefore we operate mainly this heating station. It has
110MW of power installed in the heat exchangers. It is fed with the
steam from the high-pressure turbine that flows back to the boiler for
reheating. This steam has already released its superheat energy and is
cooled on the turbine from 540 to 340 °C. The secondary supply of steam
comes from the steam turbine exhaust conduit named A4; this steam has
also already released most of its energy on the turbines and has cooled
down to 240 °C, a temperature suited to heating hot water of the
principal district heating conduit. There is also a pipe from the
generating unit four steam line, which has a purpose built conduit for
district heating station two. This steam is from the A8 outlet and goes
to the reheater.
When building the desulphurisation facility we needed to find a way
to cool down the flue gasses so they could be processed in the scrubber.
This was achieved by installing a bank of heat exchanging tubes, where
the water from the primary water heating system flows. Here the water
receives its first cycle of heating and then continues on to the heat
exchangers in the district heating station. Thus, we recover a large
quantity of thermal energy that would otherwise be lost through the
chimneystack.