Becoming better acquainted with cogeneration, its technical, application principles and its potential, at least in general, means understanding the advantages it can offer in terms of energy efficiency and eco-sustainability.
The indications provided here do not intend being exhaustive or analytical from an engineering viewpoint. Rather they are a synthesis of the fundamental aspects of the topic.
Cogeneration is the combined production of electrical/mechanical and thermal energy [heat] obtained from dedicated plants using the same primary energy.
To produce electrical energy only, thermal power plants are generally used, which disperse part of the primary energy into the environment; this is thermal energy with a poor thermodynamic value as the temperature is low. On the other hand, to produce thermal energy only, boilers are traditionally used, which convert the primary energy - with high thermodynamic value - of the fuels into thermal energy with a reduced thermodynamic value.
Therefore, if requiring electrical energy and thermal energy, rather than installing a boiler and buying electrical energy from the power grid, one could think of a thermodynamic cycle to produce electrical energy exploiting the higher thermal levels and using the residual heat at lower temperature to meet the thermal requirements. From this point of view, cogeneration may help saving energy, however, this is not a foregone conclusion. It should therefore be assessed whether it is really advantageous and compared to which alternative. The fundamental objective to be pursued with cogeneration is to make best use of the energy contained in the fuel, resulting in lower fuel consumption and consequently reduced environmental impact.
Cogeneration allows an energy saving of up to 30% and assures objective and measurable benefits. Also trigeneration, i.e. simultaneous production of thermal, electrical and cooling energy from one energy source is based on this guiding principle. Cogeneration and trigeneration fall within the strategic choices of companies that see energy efficiency as a vital opportunity to reduce costs and be more competive.
Equally significant are the advantages on environmental impact level, as CO2 emissions are drastically reduced thanks to lower consumption of fossil fuels. That is why cogeneration falls fully into the sustainable energy policy in line with the European Union 20-20-20 target and with other EC provisions to safeguard the environment.
Compared to separate production of the same amount of electrical energy and heat, combined production, if effective, results in:
• an economic saving because of lower fuel consumption;
• reduced environmental impact because of reduced emissions as well as reduced release of residual heat into the environment (less atmospheric pollution and less thermal pollution);
• reduced transmission and distribution losses for the national power grid because of plant localisation in the proximity of user basins or self-consumption of the energy produced;
• replacement of less efficient and more polluting heat supply methods (boilers for both civil and industrial use characterised by lower efficiency levels, high environmental impact and little flexibility in the use of fuels).
The example shown in Figure 1 clarifies the significance of the energy saving that can be obtained with a cogeneration plant with respect to separate production of the same useful quantities of energy. Supposing that a cogeneration plant consumes 100 units of fuel to produce 35 units of electrical energy and 50 units of useful heat, the total thermodynamic conversion efficiency - understood as ratio between the useful energy produced (35 + 50) and the primary energy of the fuel used (100) - is 85%. On the other hand, considering separate production, supposing that a thermoelectric power plant produces 35 units of electrical energy with an electrical efficiency of approximately 40% and 50 units of useful heat with a boiler having a thermal efficiency of approximately 80%, the fuel consumption would be 140 units. In the case of separate production of the same quantities of electrical energy and heat, you would therefore have a consumption of 140 units of fuel rather than the 100 a cogeneration plant requires. The saving in primary energy achievable with cogeneration is hence 28%.
Bio-cogeneration represents both an extremely interesting business opportunity for agricultural concerns, as well as a far-sighted choice for public and private companies centred on the production and promotion of biogas in a perspective of high energy efficiency and eco-sustainability.
Bio-cogeneration involves the production of electricity and heat energy using agricultural and animal-farming wastes, or materials from dedicated crops, or even the organic parts of household wastes. Thanks to specific government incentive policies, agricultural concerns can profitably enter the electricity market, yielding the kWh produced by the plant to the power grid. Bio-cogeneration is a market of European dimensions with extraordinary growth prospects, in which the AB Group has to offer the expertise of over two hundred plants built using technologies and solutions that represent the "heart" of the entire system: the transformation of biogas in energy, ensuring the very highest performance standards in a context of total reliability.
Thanks to specific government incentive policies, agricultural enterprises can advantageously enter the electricity market y selling the kWh produced by the plant to the power grid. Apart from the Italian incentive policies, the European bio-cogeneration market has extraordinary growth prospects and the AB Group offers the potential to play a leading role, in particular, providing technologies and solutions that lie at the "heart" of the entire system: the transformation of biogas into energy, assuring the highest possible performance in a context of total reliability.
This is a biochemical conversion process that takes place in the absence of oxygen and consists of microorganisms destroying complex organic substances (lipids, protides, glucides) contained in vegetables and by-products of animal origin. The biogas produced is normally composed of 50-70% natural gas and the remainder of CO2 and other components.
The combined production of electrical energy and heat finds application both in the industrial sector, especially self-production, and in the civil sector.
The heat, which cannot be transported for long distances to avoid excessive costs and losses, is used in the form of steam or hot/superheated water in industrial or civil processes (e.g. urban heating by means of remote heating systems as well as cooling by means of absorption systems) or in the form of hot air for industrial drying processes, while the electrical energy that can rely on an extensive distribution network is self-consumed or injected into the power grid. The utilities that can gain most advantage from cogeneration are characterised by a quite constant demand for thermal and electrical energy over time, such as hospitals and nursing homes, swimming pools, sports centres, shopping centres as well as the food and paper industries tied to oil refining and chemical industries. In the case of civil use, among which interior heating or reote community heating, the heat is generally produced at a relatively low temperature and the vector fluid for the thermal energy is prevalently water. In the case of industrial use, the heat is generally produced at higher temperature and pressure. There are also mixed conditions where heat production is at various temperature and pressure levels. In these cases, there is normally only one place of use (for example, an industrial production unit) where the heat at high temperature is used for processing and that at lower temperature for heating the production areas. In some industrial sectors, the combined production of electrical energy and heat already is a widely consolidated production option and may become even more significant in terms of contribution to the national electricity demand and energy saving. Today, more and more people talk about trigeneration. A trigeneration system, as illustrated in Figure 2, is an energy system consisting of a cogeneration plant whose useful thermal energy is used, in whole or in part, to produce - by means of absorption chillers - refrigerated water for air-conditioning or for industrial processes. Exploiting the useful heat produced by the cogeneration plant for cooling as well, allows maximising the use of thermal energy, making it cost-effective to use the plant for an increased number of hours per year.