POLYGENERATION: TECHNOLOGIES & POSSIBILITIES. Prof.Emeritus S.Srinivasa Murthy Refrigeration & Clean Energy Technologies

Transcription

1 POLYGENERATION: TECHNOLOGIES & POSSIBILITIES Prof.Emeritus S.Srinivasa Murthy Refrigeration & Clean Energy Technologies Department of Mechanical Engineering Indian Institute of Technology Madras Chennai

2 0 hat is Polygeneration? The term Polygeneration is most widely used to describe the generalisation or extension of the well known idea of cogeneration Cogeneration or Combined and Power (CHP) is defined as the simultaneous generation of thermal energy and electrical / or mechanical energy.

3 0 hat is Polygeneration? POLYGENERATION is the simultaneous generation of more than two energy forms in an integrated process. The term integrated process refers to multiple successive processes, where the output or by-product of one process is the input of another process. This succession of thermodynamic processes constitutes an energy supply system which can be understood in a broader sense. The idea of polygeneration can also be enlarged to include fuel and material generation. In some technologies like gasification processes based on biomass sources, some by-products may be used directly as fuel.

4 0 hat is Polygeneration? If only Power and is produced it is referred to as Cogeneration or Combined and Power (CHP) Trigeneration or Combined, Cold and Power (CHCP) if cooling is also one of the energy services delivered. In some cases to emphasize the decentralized nature of Polygeneration technologies with respect to central power stations these technologies are also named as Distributed Generation technologies or Distribued multi-generation technologies if the idea of multiple energy outputs is to be highlighted.

5 0 Polygeneration Systems

6 0 Polygeneration Systems: Trigeneration TRIGENERATION is basic and most popular form of Polygeneration. The term describes an energy conversion process with combined heat, cold and power generation (CHCP). Components: CHP module generating electricity and heat, and a heat-driven chiller generating cold. The chiller is driven with the heat delivered by the CHP. Depending on the demand, the generated heat is either used for heating or cooling purposes or both.

7 0 Polygeneration Systems: Trigeneration Trigeneration systems find application wherever the demand for heat, cold and power occurs. The application area is very vast ranging from small residential, towards big commercial, office or other (tertiary, sports, entertainment centres, hospitals, schools, airports, hotels, etc.) buildings. Trigeneration can be beneficial in the food industry where often simultaneous need for cooling, heating and power exists (heating and cooling is usually needed for freezing, pasteurization etc.) In buildings, the CHCP system produces heat for domestic hot water, space heating or dehumidification and cold for space cooling or airconditioning. The distribution of heat and cooling to end-users using District ing and Cooling networks (DHC) enhances high heat, cold and power generation efficiency

8 0 Polygeneration Systems : Biogas & CHP Biogas can be used to treat residues and also generate different forms of energy. Biogas results from an anaerobic break down of organic material by bacteria in wet medium. Organic waste is processed in the biogas plant which produces biogas and digestate. The solid digestate can be dried and further processed as fuel and the liquid digestate can be used by farmers as a biofertiliser.

9 0 Polygeneration Systems : Biogas & CHP The biogas is used by a CHP producing heat and power. In most of the plants, the biogas is stored in a tank and used on site in a CHP system. Alternatively, the biogas can be upgraded to the quality of natural gas and subsequently be fed into the gas distribution system. The generated heat is to a lesser extent used for the digestion process and the major part can be used for heat supply, generating cooling by using a thermally driven chiller or for drying products.

10 0 Polygeneration Systems : Gasification & CHP GASIFICATION is the thermal conversion of a solid fuel to a gaseous fuel. Large scale gasifiers are fuelled by coal, petroleum coke and petrochemicals. For medium and small scale gasifiers, biomass and municipal waste can be used. Low-value solid biofuels are especially significant in local utilization for energetic purposes. 0

11 0 Polygeneration Systems : Gasification & CHP GASIFICATION can yield higher conversion efficiencies of solid fuel to electrical power compared to conventional energy conversion systems. It is characterized by low emissions and the possibility to use the gas in many applications, eg. for combined heat and electricity production (CHP) or in the chemical industry.

12 0 Polygeneration Technologies Combustion Engines for Cogeneration Reciprocating Steam engines Engines External Combustión engines Rotary Steam turbines Otto Cycle Internal Combustión engines Reciprocating Diesel Cycle Rotary Gas turbines

13 0 Polygeneration Technologies Steam Turbines Steam turbines for power generation Steam turbines for power and heating Electrical power capacity: 00 k 00 M Electrical efficiency: 0 % Investment cost: /k

14 0 Polygeneration Technologies Reciprocating Internal Combustion Engines Least expensive and most commonly used CHP prime movers Type of engine: Spark ignition: natural gas Compression ignition: diesel Good part load operation available at two temp Levels: Exhaust gases and jacket cooling fluid Electrical power capacity: k 0 M Electrical efficiency: % Investment cost: /k JMS0 M

15 0 Polygeneration Technologies Gas turbines Electrical Capacity: 00 k 0 M Fuel: Natural gas, light petroleum distillates (gas oil,.. ) Electrical Efficiency: 0 % Investment Cost: /ke Advantages: Low initial cost High efficiency in larger size Fuel switching capabilities Fast manufacturing and installation Light weight and small volume High exhaust gas temperature Immediate response in load variations

16 0 Polygeneration Technologies Combined cycles Combined Cycles consist of the combination of basic power cycles in order to obtain better performance. The Brayton (Gas Turbine) /Rankine (Steam Turbine) Cycle is the most developed and wide-spread of all the conceived combined cycles. Main characteristics: high efficiency (close to %). Adequate for high power capacities (> 0 M).

17 Polygeneration Technologies TYPICAL HEAT-TO-POER RATIOS OF PRIME MOVERS TYPICAL HEAT-TO-POER RATIOS OF INDUSTRIES

18 0 Polygeneration Technologies Micro gas turbines Small Capacity turbines with regeneration Capacity range: k to 00 k Electrical Efficiency Range: % to 0% aste Thermal Energy: exhaust gases Advantages: Compact Size Low Emissions Fuel Flexibility Modular Lower Maintenance Disadvantages: Moderate Conversion Efficiencies Poor Part Load Operation

19 0 Polygeneration Technologies Organic Rankine Cycles (ORC) ORC is similar to that of a conventional steam turbine cycle, except for the working fluid, which is a high molecular mass organic fluid many of which are commonly used as refrigerants. Turbine Superheater Preheater aste Recovery Boiler Electric Generator 0 Regenerator Air-cooler Applications: - Low temperature heat sources - Small-medium size plants

20 Polygeneration Technologies Stirling Engines Crank-driven piston Free piston. A gas in a closed cycle is heated and cooled sequentially. Externally fired engine. orking fluid: air, hydrogen but helium is the most used. Stirling engines have not reached a mature phase of development (only very few manufaturers) and are only available at relatively low power levels (< 0 ke). Main applications: biomass and thermal solar energy (Solar Dish). Crank-driven piston Free piston

21 Polygeneration Technologies Fuel Cells Fuel Cells convert the chemical energy of the fuel directly into electricity, and are not restricted by the Carnot efficiency. In most cases, there is waste heat at different temperatures available at the exhaust.

22 Polygeneration Technologies Power Generating Systems Efficiency Comparison

23 Polygeneration Technologies Biomass and biofuel technologies

24 Polygeneration Technologies Biomass and biofuel technologies The gasification process takes place at high temperature and needs a supply of oxidant lower than required for a combustion process. Application of the produced gas: Fuel or Raw material for chemicals Higher electric plant efficiency than steam or ORC biomass combustion technologies specially for small-scale systems.

25 0 Polygeneration Technologies -Driven Refrigeration Technologies Absorption cooling technology Absorption and Adsorption - well known and commercially implemented - air-conditioning and refrigeration applications - wide range of power - use of low temperature heat driving sources

26 0 Polygeneration Technologies Absorption chillers Incorporate, in addition to an evaporator and a condenser, a solution (refrigerant /absorbent mixture) circuit including an absorber and a generator. Fluid mixtures used : - water/lithium bromide (Air-conditioning) - ammonia/water ( AC and Refrigeration) Single-effect chillers COP = ; Temp. heat source: 0-0 ºC; Chilled water at /ºC and wet cooling Double-effect chillers (water/libr) COP =.-. ; Temp heat source: 0-0 ºC Chilled water at /ºC and wet cooling

27 0 Polygeneration Technologies Market availability of absorption chillers Single effect: Many products for operation driving by hot water or steam in the capacity range > 00 k Only few machines for lower capacities Double effect : Often direct fired systems; very few products in the range <00 k

28 0 Polygeneration Technologies Adsorption Technology Adsorption chillers are driven by thermal energy like absorption chillers but a solid medium is used as sorbent instead of a liquid. An adsorption chiller is by nature a discontinuous cycle. To obtain continuous cooling a multiple bed system is used, typically two adsorbent beds out of phase.

29 0 Polygeneration Technologies Adsorption Technology AVAILABLE ADSORPTION CHILLERS - Only three manufacturers - Driving temperature starting at ºC - COP at design conditions 0. -Chillers driven by hot water with a capacity range 0-00 k - New developments of and k

30 0 Polygeneration Technologies 0

31 Polygeneration Technologies Desiccant cooling systems Chemical dehumidification removes the water vapour from the air by transferring it towards a desiccant material. Desiccants are materials with a high affinity for water vapour and may be solid or liquid. Regeneration heat must be supplied in order to remove the adsorbed water from the desiccant material.

32 Polygeneration Configurations A trigeneration system is very attractive to produce air conditioning in summer when the demand for heating is lower and there is a need to use the waste heat from the CHP.

33 Polygeneration Configurations Trigeneration System In A Sewage Treatment Plant

34 Polygeneration Configurations Solar heating, cooling & Desalination system Target capacities: Cooling capacity of k + potable water about 00 lit/day. Solar collector field: Evacuated tube collectors; 0 m exposure area; design temperatures up to 0 C on normal sunny days

35 Polygeneration Configurations Polycity project (Cerdanyola del Vallès, Spain) [] Figures in brackets show the expected demand in the first stage of the urban development. Thermal cooling facilities: - Single effect absorption chillers driven by hot water from the network generated with the engines waste heat. - Double effect absorption chiller directly driven by the hot exhaust gas from the engines. Renewable energy sources: - Biomass gasification plant using wood waste and byproducts integrated with a cogeneration engine (Me) - Thermal Solar plant with a total area up to 000 m

36 Polygeneration Configurations Polycity project (Cerdanyola del Vallès, Spain)

37 Polygeneration Configurations Polycity project (Stuttgart, Germany) Renewable energy supply: 0% Thermal power Biomass:. M Electrical power ORC-Module: M CO Reduction: t/a Fossil energy saving:, Mio m³ Gas/a 0 k of building integrated photovoltaics Low energy residential buildings:.000 m Commercial buildings:.000 m

38 Polygeneration Configurations Polycity project (Turin, Italy) Reduction in conventional energy consumption: % Photovoltaic system: 0 k integrated in the façade of ATC building 00 K on the roofs of the council buildings Natural gas cogeneration plant: 0. Mel,. Mth Innovative façade with PV, shading 0 residential buildings One high rise commercial building (ATC)

39 0 Importance and Suitability of Polygeneration for Sustainable Communities Sustainable Communities should choose Polygeneration for two main reasons: Optimisation of the use of primary energy sources: One unit of primary energy source can be used to provide more useful energy than a single plant without Polygeneration. Use of local resources to cover local energy needs: Polygeneration can be used to convert local available energy or material resources (i.e. waste) into other forms of energy or materials, which ideally should also be used at local level.

40 0 Importance and Suitability of Polygeneration for Sustainable Communities Suitability of type of Polygeneration depends on various factors such as: Type of community (rural, urban, ) Type and mix of buildings (residential, offices, ) Demand profiles (continuous, daytime, ) Available resources (biomass, waste heat, ) Climatic conditions 0

41 0 Importance and Suitability of Polygeneration for Sustainable Communities Suitability hich type of polygeneration for which community? There are a variety of polygeneration technologies and systems available. The appropriate system must be selected based on the type of community and the local resources. In the design phase of a district energy concept, the ambition of the energy experts is to design an efficient energy system which covers the overall energy needs whilst at the same time minimising the demand for primary resources. Following this approach, polygeneration technologies should be used to convert energy into energy carriers which are needed at local level and these needs in turn depend on the type of community.

42 CONCLUDING REMARKS Polygeneration looks always beneficial from a thermodynamic view point as the energy resources are brought down close to their reference levels. From environmental and ecological view points, polygeneration stands out in most cases. In practice one should find use for the various forms of energy recovered or generated. Load matching (in terms of quantity and time) is essential and is critical for the success of polygeneration. Suitable energy storage options can help in achieving this. Last, but not the least, economics is the deciding factor (cost and availability of energy sources; location; etc.).

43 0 CONCLUDING REMARKS Thanks ACKNOLEDGEMENTS Thanks are due to Prof.Alberto Coronas and Dr. Joan Carles Bruno, Universitat Rovira i Virgili, CREVER - Group of Applied Thermal Engineering, Tarragona (Spain) with whom the speaker has closely worked for a long time on various aspects of polygeneration and also for conducting the biennial International Conference on Polygeneration.