Lignite drying in a lignite fired power plant with a heat pump
The invention relates to a lignite fired steam power plant comprising a water/steam power cycle and a lignite dryer system having a heat pump circuit configured and arranged to provide heat energy to a lignite dryer of the dryer system. The heat pump includes a dryer heat exchanger, an expansion device and an evaporator heat exchanger connected to the first outlet line so as to enable heat energy transfer from the vapour of the first outlet line to the first working fluid. A compressor is also included in the heat pump circuit. In addition the heat pump circuit is connected to the water/steam power cycle by a steam makeup line from the pressure series of steam turbines and a condensate return line.
1. A lignite fired steam power plant comprising:
a water/steam power cycle having:
a pressure series of steam turbines;
a condenser, at a low pressure end of pressure series of steam turbines, configured and arrange to condense a steam exhausted from the low pressure end of the pressure series of steam turbines; and
a low pressure condensate system, arrangement downstream of the condenser, adapted to preheat a condensate from the condenser;
a dryer system for drying lignite coal, the dryer system having:
a dryer;
a first outlet line for removing a vapour from the dryer; and
a heat pump circuit, configured and arranged to provide heat energy to the dryer, comprising:
a first working fluid;
a dryer heat exchanger in the dryer;
an expansion device fluidly connected and downstream of the dryer heat exchanger;
an evaporator heat exchanger fluidly connected to and downstream of the expansion device and further connected to the first outlet line so as to enable heat energy transfer from the vapour of the first outlet line to the first working fluid;
a compressor, fluidly connected to and downstream of the evaporator heat exchanger and upstream of the dryer heat exchanger, for compressing the first working fluid;
a steam makeup line, extending from the pressure series of steam turbine to a first point fluidly between the dryer heat exchanger and the compressor; and
a condensate return line extending from a second point fluidly between the dryer heat exchanger and the expansion device to the low pressure condensate system so as to return a condensate from the heat pump circuit into the water steam power cycle.
2. The lignite fired steam power plant of claim 1 wherein the dryer is a fluidised bed dryer.
3. The lignite fired steam power plant of claim 1 wherein the dryer is a steam heated rotary tube dryer.
4. The lignite fired steam power plant of claim 1 wherein the expansion device is a valve.
5. The lignite fired steam power plant of claim 1 wherein the expansion device is a turbine.
6. The lignite fired steam power plant of claim 1 , further comprising a first condensate preheater, in parallel or in series with at least a portion of the low pressure condensate system, wherein the first outlet line, downstream of the evaporator heat exchanger, extends through the first condensate preheater so as to enable transfer of heat energy from the vapour of the dryer to a condensate of the water steam cycle.
7. The lignite fired steam power plant of claim 1 , further comprising a first condensate preheater, in parallel or in series with at least a portion of the low pressure condensate system, wherein the first outlet line, upstream of the evaporator heat exchanger, extends through the first condensate preheater so as to enable transfer of heat energy from the vapour of the dryer to a condensate of the water steam cycle.
8. The lignite fired steam power plant of claim 6 , wherein the first condensate preheater and the evaporator heat exchanger are combined as a single unit.
9. The lignite fired steam power plant of claim 1 , further comprising a first condensate preheater, in parallel or in series with at least a portion of the low pressure condensate system, wherein a branch in the first outlet line, upstream of the evaporator heat exchanger extends through the first condensate preheater so as to enable transfer of heat energy from the vapour of the dryer to a condensate of the water steam cycle.
10. The lignite fired steam power plant of claim 1 , further comprising a combustion air heat exchanger, thermally connected to the first outlet line for heating a combustion air for use in the lignite fired steam power plant.
11. The lignite fired steam power plant of claim 10 further comprising an intermediate water loop comprising:
a second working fluid;
an intermediate heat exchanger thermally connected to the first outlet line; and
the combustion air heat exchanger,
wherein the intermediate water loop is adapted to receive a thermal energy from the vapour of the first outlet line in the intermediate heat exchanger and transfer the received thermal energy to the second working fluid where it is transfer to the combustion air by means of the combustion air heat exchanger.
12. The lignite fired steam power plant of claim 10 wherein the combustion air heat exchanger is fluidly connected to the first outlet line in parallel of the evaporator heat exchanger.
13. The lignite fired steam power plant of claim 11 wherein the intermediate heat exchanger is fluidly connected to the first outlet line in parallel of the evaporator heat exchanger.
14. The lignite fired steam power plant of claim 11 wherein the intermediate heat exchanger is combined with the evaporator heat exchanger and fluidly connected to the first outlet line.