Low temperature cogeneration using waste heat from research reactor as a source for heat pump

Transcription

1 National Centre for Nuclear Research in Poland Low temperature cogeneration using waste heat from research reactor as a source for heat pump Anna Przybyszewska International Atomic Energy Agency March 2016

2 Waste heat In steam-electric power plants the nuclear energy is converted into electric energy. The overall conversion efficiency of these stations is low: 33% to 40% for modern facilities. This means that significant part of the energy is lost in the form of "waste heat" discharged into rivers, lakes, oceans and the atmosphere. The management of waste heat from steam-electric power plants is important with regard to environmental impacts and to find economic and social benefits. 2

3 Waste heat Nowadays waste heat management is an integral aspect of almost all energy conversion facilities including steamelectric power stations, liquefied natural gas facilities and coal gasification but not in nuclear power plants. This is often a consequence of using waste heat as a source of preheating installation for water or air. 3

4 Challnage for NPP Schematic diagram of a cogeneration plant for electricity generation and district heating based on an extraction-condensing turbine Regarding to nuclear power plant, two ways to save energy are: to improve the system efficiency and to cogenerate energy. Conventional cogeneration use in NPP is: production of hot water for district heating. It is possible to take a certain amount of steam from the turbine (an extraction-condensing turbine). However the steam mass flow in the turbine is decreased, the overall electricity production will decrease, but the condensation heat that is possible to recover from steam is enough for district heating purposes. This solution also needs modification in the secondary circuit and has significant influence on design and operation of NPP. 4

5 Challnage for NPP Main goal should be to improve the efficiency of nuclear power plants by recovery low-temperature waste heat: C, temperature in condenser, cooling tower or C, temperature of water relese to river, lake or see 5

6 How works heat pump Operating principle A low temperature waste heat flow can be upgraded to useful high temperature heat with the use of a heat pump. Among the different types of heat pumps that have been developed, the mechanical heat pump is the most widely used. Its operating principle is based on compression and expansion of a working fluid, or so called 'refrigerant'. A heat pump has four main components: evaporator, compressor, condenser and expansion device. The refrigerant is the working fluid that passes through all these components. In the evaporator heat is extracted from a waste heat source. In the condenser this heat is delivered to the consumer at a higher temperature level. 6

7 How works heat pump Operating principle Source: 7

8 How works heat pump The thermodynamic cycle Source: 8

9 How works heat pump Mechanical heat pump Gas engine heat pump Absorption heat pump Adsorption heat pump Hybrid heat pump Different types of heat pumps Source: 9

10 How works heat pump Temperature Lift Heat-Source Type Heat-Sink Type Suggested Heat-Pump Type <35 ºC Sensible cooling of liquid Sensible heating of gas or liquid Closed-cycle mechanical HP or Absorption HP (with lithium bromide/ water as working fluid) Partial condensation of liquid from vapor stream liquid Sensible heating of gas or liquid Closed-cycle mechanical HP or Absorption HP (with lithium bromide/ water as working fluid) Condensing steam Evaporation of water Open-cycle mechanical HP (single stage compressor) or Thermocompression Condensing vapor (steam or other) >35 ºC All heat sources (except steam) LP steam Sensible heating of gas or liquid All heat sinks (except steam) Higher-pressure steam header Semi-open-cycle mechanical (single stage compressor) Absorption HP (with lithium bromide/ water as working fluid) or Multistage Mechanical Compression HP Open-cycle mechanical HP or Absorption HP (with high lift working fluid) or Multistage Mechanical Compression HP Source "Industrial Heat Pumps for Steam and Fuel Savings", U.S. Department of Energy, Energy Efficiency and Renewable Energy 10

11 Maria reactor 11

12 Maria reactor Maria is a pool type reactor with nominal power 30 MW, located at National Centre for Nuclear Research (NCBJ). The heat generated in the fuel channels as well as in the pools, is transferred to the secondary circuit by heat exchanger system and there is dissipated to atmosphere in a cooling tower. The coolant flow in the secondary circuit is provided by the pump. Inlet temperature of water is 50 C, both in the Fuel Channel Cooling System and in the Pool Reactor Cooling System. A secondary cooling circuit removes heat from both systems and gives it to the air by a fan cooling tower. It may be assumed that the inlet water temperature before cooling tower is about 40 C. 12

13 Heat pump for district heating 13

14 Heat pump for district heating According to this information, it can be concluded that the Maria reactor, and more specifically "waste heat" can be a source for heat pump. The use of heat pumps can support local district heating in the area of NCBJ. Partial deliveries of heat to the district heating can help to significantly reduce the costs associated with maintaining of current infrastructure based on small heat sources burning conventional fuel - oil. The reactor operates more than 4000 hours annually. Therefore, although the proposed concept would not replace existing boilers, it has a potential to decrease fuel oil costs by about 50%. 14

15 Target kw C C C C flow 50 m3/h flow 5-10 m3/h Running: 5000 h/year 15

16 Main goals of CRP project The idea of using heat from the Maria Reactor as a heat source for heat pump One of the main objectives is to prepare a case study using heat from the Maria Reactor as a heat source for heat pump. The results will predict the reasonableness of this project as well as assess feasibility of similar projects on a larger scale. Heat pumps for heating and cooling buildings can be involved as monovalent as well as bivalent. In case monovalent, the heat pump is the only one source of heat during heating season. In other case the heat can be supplied by heat pump and by additional heat source e.g. conventional - oil during cold days, when peak demand appears. The study will determine, which system - monoor hybrid heating is better. For the hybrid heating system, the study will also find optimal solution for the conventional part of the proposed system (i.e. propose optimal fuel) For analysis and optimization energy balance software for plants will be used (e.g. International Cycle Atomic Energy Tempo, Agency, Vienna or other available). 16

17 Advantages - Reduction of waste heat; - Solution without modification in the secondary circuit; - Based on experience: life of the HP system is about 25 years and 50 + years of internal elements of earth loop; - Public acceptance; - Huge potential market in Europe; - HP system can provide cooling during the summer; - In HP it is possible to increase of temperature and can be adapted for process temeprature. 17

18 Challenges - Economies of scale: the cost of installing HP system is returned to energy savings during the years 5-10 for small systems - Design hybrid system: geothermal heat pump and industrial recovery system - Some of the fluids used for heat transfer are of questionable sustainability and they raise environmental concerns, hence it is recommended to use biodegradable fluids - Electricity is required to run the heat pumps which means that they will never be entirely carbon neutral. 18

19 The main trends show that heat applications of low-temperature source e.g. heat pump technology for district heating is a promising approach. Water source heat pumps work on a similar principle to air source and ground source heat pumps. 19

20 National Centre for Nuclear Research