Micro-trigeneration for energy sustainability: Technologies, tools and trends

doi:10.1016/j.applthermaleng.2013.11.037

Applied Thermal Engineering

Volume 71, Issue 2, 22 October 2014, Pages 790-796

https://doi.org/10.1016/j.applthermaleng.2013.11.037 Get rights and content

Highlights

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Review of micro-trigeneration systems and technologies is presented.
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Attractive option to use waste heat for cooling and heating.
•
Very efficient on total energy performance, fuel savings and CO₂ reduction.
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Alternative fuels, like bio-fuels, hydrogen, and wooden-gas can also be used.
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Potential sustainable energy systems for residential and small applications.

Abstract

The path towards energy sustainability is the incremental adoption of available technologies, practices and policies that help to decrease environmental impact of energy sector, with adequate standards of energy services.

Trigeneration systems use waste heat from prime movers to generate heating and cooling along with power. They are more efficient, less polluting & more economic than conventional systems. Small scale trigeneration power plants, typically, below 15 kW_e, are called micro-trigeneration plants. In such systems, over 80% of fuel energy is converted to useable energy.

Over-exploitation of fossil resources has led to increase in pollutants and CO₂ levels in atmosphere, causing severe health hazards. Low carbon society is less dependent on fuels with high carbon content. Also, Kyoto protocol set reduction targets for the nations. Alternative fuels promise sustainable development, energy conservation, efficiency and environmental preservation. Various alternate fuels & micro-trigeneration technologies can be combined, leading to sharp decrease in almost all the emissions.

This paper presents a brief review of micro-trigeneration systems. They are projected as strategic means to achieve energy security and efficiency, with positive impact on economy, simultaneously reducing environmental threats, leading to sustainable development.

Introduction

Sustainable development meets the needs of the present without compromising the ability of future generations to meet their own needs. It integrates economic, social and environmental aspects [1].

Energy is the fundamental driver of sustainable development.

Sustainable access to energy with modern fuels is strongly related to the millennium development goals of UNO [2], [3].

Integrated Energy Systems (IES), as comprehensive integrated approach, combine on-site power or distributed generation technologies with thermally activated technologies to provide cooling, heating, humidity control, energy storage and/or other process functions. IES produce electricity and use by product thermal energy onsite, with the potential of converting 80 percent or more of the fuel into use-able energy. Integrated Energy Systems (IES), offer key solution to global warming and energy security through high overall energy efficiency and better fuel use [4], [5].

Cogeneration or Combined Heating and Power (CHP) is simultaneous production of power and heat. Tri-generation or Combined Cooling Heating and Power (CCHP) is simultaneous production of power, heating and cooling. CHP or CCHP uses only one source of primary energy, represented by fossil fuels or by some appropriate renewable energy sources (biomass, biogas, solar energy, etc) [6].

Thus, CHP and CCHP systems are units of IES that use recovered waste thermal energy from the prime mover to produce heating and cooling. Integrated CCHP system solutions can address all of the following requirements at once: increase in overall thermal efficiency, conservation of scarce energy resources, moderation of pollutant release into our environment, and assured comfort for home-owners [6], [7], [8].

Also, in the Energy Performance of Buildings Directive of the European Union, CCHP is seen as a technology to fulfil the energy requirements of buildings [9], [10].

Small scale poly-generation power plants, typically below 15 kW_e, are called micro-CHP (m-CHP) or micro-CCHP (m-CCHP) plants. Micro-CCHPs are especially interesting due to their technical and performance features like, high overall energy conversion efficiency and low emissions [9], [11]. They are emerging in various applications like, residential buildings, hotels, hospitals, university campuses, automobiles, etc [11], [12].

A typical m-CCHP system consists of five basic elements: prime mover; electricity generator; waste heat recovery exchanger/boiler; thermally activated equipment and the management and control system [6], [12].

The line diagram of a typical micro-trigeneration system using internal combustion diesel engine as prime mover coupled to an absorption chiller and a heat exchanger is shown in Fig. 1 [11].

Performance and emission experiments were conducted in a laboratory on a small internal combustion diesel engine (3.7 kW) based micro-trigeneration system. Useful energy output was found to be much higher than in single generation. The thermal efficiency of trigeneration was 155.49% higher than that of single generation at full load, as shown in Fig. 2 [11].

Energy management and optimization was found to be better in small scale CCHP systems based on natural gas and liquefied petroleum gas (LPG) driven engine. Primary Energy Saving (PES) was found to be more for m-CCHP system than m-CHP system [13].

Two different m-trigeneration configurations using micro-turbine (m-turbine) and Internal Combustion Engine (ICE) were configured, tested and found viable [14]. Also, two typical residential m-CHP alternatives, namely gas engines and fuel cell were found to be good alternatives from environmental and economical points of view [15]. District heating/cooling networks have also been developed with trigeneration plant sizing for business building application [16]. Even a truck cabin air-conditioning system, driven by low grade waste heat (80–90 °C) from engine coolant loop has been tested successfully [17].

Section snippets

Prime movers

A prime mover in a m-CCHP system generates electricity and the waste heat is recovered downstream. Main prime movers include reciprocating engines, micro steam and gas turbines, stirling engines and fuel cell systems.

Need, types and benefits

The search for alternative fuels, which promise sustainable development, energy conservation, efficiency and environmental preservation, has become highly pronounced.

Bioethanol is formed through fermentation of biomass like corn, wheat, sugar beet, etc. It can be used in 5% to 85% blends with petrol. Methanol (or bio-methanol), hydrogen and syngas can be produced from biomass via partial oxidation/gasification. Biodiesel (BD), alternative diesel fuel, made from biological sources, like

Environmental and economic benefits

Currently, more than 85% of our energy is supplied from fossil resources. The break-up of the World primary energy consumption in 2004 is given in Fig. 3 [54]. Combustion of fossil fuels has led to increase of both regulated pollutants (NO_x, CO, HC, PM etc) and unregulated pollutants (formaldehyde, benzene, toluene, xylene i.e, BTX, aldehydes, SO₂, CO₂, methane etc) in atmosphere contributing to severe health hazards [3], [43], [54], [60].

Findings indicated that m-CHP systems have the potential

Tools and trends

Optimization of energy systems should be based on a systems approach, leading to better understanding about the suitability of technologies. There are possible objective functions such as minimizing carbon emissions, minimizing total costs, and maximizing energy output. The point is to integrate them into one volume considering the pertinent regional priorities in the process of integrated analysis.

Simulation and optimization tools have played a major role in better understanding and control of

Discussion

Keystone of full energy utilization of micro-CCHP system lies in efficient recovery of waste heat from the prime movers. Small scale trigeneration test facility supplies better test-rig platform for cooling, heating and power generation.

1.
Micro-trigeneration has more choices for useful energy outputs. It has high energy conversion efficiency, net fuel costs reduction, hence a positive impact on economy.
2.
Low grade heat can be utilized effectively.
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There is a vast reduction in CO₂ emissions.
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It is

Conclusion

Rising concerns about impact of climate change has led to a vision of long term sustainability, looking to reduction of greenhouse gases. The environmental benefits offered by micro tri-generation systems can meet CO₂ emission reduction targets, such as Kyoto protocol and Agenda 21. There is a very large market potential for micro tri-generation systems. But, the market introduction has to be supported actively by research institutes, producers and installation and service networks.

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View full text

Micro-trigeneration for energy sustainability: Technologies, tools and trends

Highlights

Abstract

Introduction

Section snippets

Prime movers

Need, types and benefits

Environmental and economic benefits

Tools and trends

Discussion

Conclusion

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