Trigeneration

Trigeneration is a procedure that extends the cogeneration system by adding cold production. In the cogeneration system, electricity and heat are produced from the same fuel or the same source of primary energy; Cold production is added to this system.

The appearance of trigeneration systems has its origin in the so-called distributed or decentralized generation, which consists of locating the generation system in the same place where the end users are, or very close to them.

The traditional way of obtaining these energies is separately: electricity is consumed from the grid, heat is produced by fossil fuel boilers and cold from compression refrigeration cycles, which consume electrical energy. Trigeneration and cogeneration systems have certain economic and environmental advantages compared to the conventional form of generation, among them a higher overall energy yield, which allows savings in primary energy and a reduction in emissions.

Operation

The primary energy source used in trigeneration systems can be a fossil fuel such as natural gas or also renewable energy sources or even waste heat from industrial processes, which adds even more environmental benefits. In addition, it allows the production of electricity, heat and cold independently of the electricity grid and, if the energy source is renewable, from the consumption of fossil fuels. This reduces dependence on the outside, providing security of supply and energy independence to users. There are trigeneration facilities that use biomass, solar thermal energy, geothermal energy, and even combinations of several of them as primary energy.

In general, a trigeneration facility is made up of three main systems:

Primary energy transformation system

The existence and characteristics of this system depend on the type of primary energy used. In the case of using biomass, a boiler would be necessary to obtain energy from the fuel or, in the case of solar thermal energy, a system of solar collectors.

Primary Motor System

Or cogeneration equipment, which produces electricity and usable residual heat.

There are different types of technologies applicable as prime mover: steam cycle (Rankine cycle and Rankine organic cycle), gas turbine, internal combustion engine, Stirling engine and fuel cell. The choice of one technology or another depends mainly on the electrical power to be installed and the primary energy source available and its characteristics. Since the motors that produce electricity generate heat, this residual energy is used for heating.

The cold generation system

The combination of cogeneration with a cold production system by absorption gives rise to trigeneration. Absorption cycles are processes in which cold can be obtained from a heat source and are the most used in trigeneration facilities, although conventional compression refrigeration cycles can also be used. This heat can be the residual heat of the primary motive or come directly from the transformation of the primary energy.

In the summer, the demand for heat drops considerably, so the heat produced in the cogeneration equipment can be used to generate cold for the cooling necessary at this time. Cold production means an increase in operating hours and in the utilization factor of the facilities compared to cogeneration, allowing the system to operate with a more stable load throughout the year, favoring its economic viability. In this way, three types of energy are obtained from primary energy, together with significant economic savings and a good alternative for the environment.

Advantages

The first advantage of the system (whether cogeneration or trigeneration) over traditional procedures is that, although the production of electrical energy by fuels on a large scale has a higher yield, the subsequent transport, including the necessary voltage transformations, supposes a great loss of energy, which does not happen in this case, in which the energy is consumed in the same place of production. With large-scale production, and contemplating the production of a country as a whole, the losses for this concept are close to 50% percent of the total electrical energy produced.

Another advantage is the use of thermal energy, which is an obligatory residue in the generation of electricity from fuels, which in the best of cases is 50% of the energy used and is normally higher.

Applications

The potential market for trigeneration facilities is very broad. Includes applications with a high demand for heat and cold, for example in the residential sector (homes, district heating networks: district heating and cooling), in the service or tertiary sector (tourist and sports complexes, shopping centers, supermarkets, stations railway, airports, etc.) and also in the industry (pharmaceutical, food, etc.)

Examples of trigeneration plants

• "Trigeneration with biomass and photovoltaic in cosmetics industry". Archived from the original on 21 June 2012. Consultation on 5 September 2013.
• "Trigeneration in food products factory". (breakable link available on the Internet Archive; see history, first version and last).
• "Trigeneration in shopping centers". Archived from the original on March 4, 2016. Consultation on 5 September 2013.
• «Trigeneration at airport». Archived from the original on August 3, 2012. Consultation on 5 September 2013.