“Let’s cogenerate”! What is a "CHP", Cogeneration plant and how it works?

The world's first power plant (built in New York by Thomas Edison in 1882) was essentially a cogeneration plant because it provided electrical heat and power to Manhattan's buildings.

From a performance point of view, the generator is a machine that "sucks".

Indeed, all the generators have a poor performance because, to produce electricity, they waste enormous amounts of heat energy dispersed through the exhaust gas, the radiator and the natural irradiation of the hot parts of the engine.

cogeneratore orefice generators.jpeg

The cogeneration plant, also called CHP, allows the simultaneous production of electrical energy and thermal energy in the form of hot water or steam.

For years, cogeneration has been an exclusive technology of companies and large plants that consume huge amounts of heat, but today it’s a technology increasingly closer to small and medium-sized companies and even the private sector, due to the evolution of energy costs which has made cogeneration systems more competitive than ever before, and a technology that makes small plants more and more reliable and economically sustainable.

Most of the cogenerations operating in Europe are powered by low-cost fuels:

·        CHP plants using natural gas

·        Biogas CHP plants

·        Vegetable oil-fuelled CHP (palm oil, rapeseed oil..)

·        Syngas CHP (gas produced by pyrolysis processes)

·        Diesel CHP plants

In Europe the installations’ trend follows that of incentives, so the choice of which fuel to use is based on economic factors.

Companies that choose to produce energy with a CHP plant are those that consume large amounts of thermal and / or electrical energy, better if both.  Think of a hotel, shopping centres, sports facilities, dairies, these are just some of the major energy consumers who choose a CHP cogeneration.

The advantage of a CHP plant is not only in the cost of self-producing energy, but also in the energy independence that is achieved. The most virtuous and careful structures that we follow have chosen a triple power source: CHP plant + Emergency Generator + Electricity Grid. In this way, not only do they have a low energy cost, but they do not risk staying in the dark in the event of a CHP plant malfunction or during maintenance stops.

When is a CHP plant worthwhile?

The entrepreneur who chooses to install a CHP plant, wants to make profits by reducing costs, and has made one or all of the following evaluations.

He assessed the energy demand of his structure by doing an energy audit. In the event that electrical consumption prevails over the thermal consumption, assess whether there is a physical proximity between the CHP plant and any thermal user, bearing in mind that this must go in unison with the electrical one, while maintaining a certain flexibility, as the demand heat and electricity can be disproportionate to each other in some periods.

The actual convenience is finally assessed on the basis of the cost of energy by the supplier and the sale of the same with the introduction into the network. The advantage is certainly that of putting all the electricity that is not consumed into the grid, earning a profit.

Finally, the assessment is objectively influenced by the cost of the fuel and its purchase conditions, on which the market price fluctuates (the fuel, whatever it is, is subject to price variations) and to the possibility of deducting costs and excise taxes. .


Business Plan is not a "Fable".

When designing a cogeneration plant, the conditions that allow a return on investment within the terms set in the financial plan are to be considered.

Unfortunately,  the conditions resulting from the experimental calculations are not reflected in the real operating conditions and in general during the whole life of the CHP plant.

Even the best CHP plants stay off many hours a year for small or big problems. From direct experience in the operation of cogeneration plants we can say that a small component, even a simple temperature probe, or a sleeve is enough to force a generator to stop.

The business plan is not a fable, it is a tool to validate the financing of the bank, but it is above all the project that every entrepreneur should check and use to make further assessments on the investment time and duration of exposure that this involves. . With this we must not imply that a CHP plant is a nut to track, but only that the best of conditions is not said to be the most realistic. All this because the income statement is based on the incentives provided for the plant, therefore only costs are accumulated when the plant is stationary.

How does a CHP plant work?

Simplifying to the extreme, we can state that the CHP plant consists of two main elements, the Generator, in turn composed of engine and alternator, and one or more heat exchangers.

At a theoretical level, the exhaust gases emitted by the generator and the coolant used to cool the engine and keep the temperature constant during operation, are already potentially usable because they are available at high temperatures. In reality, obviously, it is not possible to use these fluids directly, as being contaminated they are harmful.

The exchanger is installed in such a way as to intercept the exhaust fumes, these give heat to another fluid (be it air or water or other fluids in the liquid state).

The most common exchangers are plate and tube bundle exchangers. In the first, the fluids at different temperatures exchange their thermal content through the appropriately arranged surfaces of the exchanger, the plates in fact.