BE1026742A1 - Method for transferring condensing energy from steam from cogeneration fumes - Google Patents

Abstract

The invention provides a method of transferring condensation energy from the water vapor of cogeneration fumes (33), resulting from the combustion of fuel by a cogenerator (3), to the return water of a circuit. (4) heating or a sanitary circuit, the temperature of which is higher than the temperature of said condensation, which, which, unlike existing systems, does not include any intermediate heat transfer circuit, using a heat transfer fluid between the duct outlet and the evaporator. The method is implemented by means of a heat pump (2) in which the expanded refrigerant (21) is heated in an evaporator (25) traversed directly by the fumes (33) and at which the fumes are cooled below the water condensation temperature to transmit the intrinsic heat of the fumes to the refrigerant and the heat released by the condensation of the water they contain.

Description

Method for transferring condensation energy from the steam of cogeneration fumes

The present application relates to the field of increasing the efficiency of cogeneration systems.

Collective residential heating, in particular in apartment buildings, and possibly the distribution of collective hot water from a sanitary circuit (city water) are generally provided by gas or fuel oil boilers. Such boilers are generally turned off in summer, when there is no demand for heating.

The installation of the boilers can be completed by a cogenerator, that is to say an installation generally operating on fossil energy and supplying thermal energy and electrical energy, in a ratio generally 2 per 1 kW . Electrical energy is injected into the building's electrical circuit, thermal energy can be used to heat the water in the heating circuit. A cogenerator can nevertheless operate from other fuels or fuels such as bio-fuels such as vegetable oil, bioethanol, biodiesel, etc.

However, during operation of the cogenerator, part of the thermal energy is not recovered, which reduces the overall efficiency. For example, the energy included in the fumes, in sensitive form (intrinsic heat) or latent form (water vapor), is dissipated in the atmosphere.

The Applicant has therefore deemed it necessary to propose a method and a system making it possible to efficiently recover the lost energy or, in other words, to reduce fatal losses.

BE2018 / 5747

Solution of the invention

The present invention proposes, for this purpose, a method of transferring condensation energy from the water vapor of cogeneration fumes, resulting from the combustion of fuel by a cogenerator, to the return water of a heating or a sanitary circuit, the temperature of which is higher than the temperature of said condensation, by means of a heat pump comprising a closed circuit traversed by a refrigerant and on which are arranged a compressor, a condenser, a pressure reducer and an evaporator, process according to which:

(A) the refrigerant is compressed in the compressor, to heat it;

(B) heat is transmitted from the compressed refrigerant to the return water from the heating circuit or the domestic circuit in the condenser;

(C) the compressed refrigerant is expanded to lower the temperature below the condensation temperature in the pressure reducer (D) the expanded refrigerant is heated in the evaporator through which the flue gases pass directly and at which the fumes are cooled under the condensing temperature of

water for pass on at refrigerant the heat intrinsic fumes and the heat released over there condensation water that they contain.

We know the association of a cogenerator with a heat pump to recover the thermal energy of the fumes, in sensitive form (intrinsic heat) or latent form (water vapor). However, the known systems use heat pumps comprising an evaporator, not for smoke, but with heat transfer fluid, such as water and / or glycol, such as for example that of document FR 2 979 97 4, illustrated on the Figure 4. This document describes a thermocondenser 5 'cooling the fumes 34' of cogeneration from a cogenerator 3 'and connected to the evaporator 25' of a heat pump (PAC) 2 'by means of an intermediate circuit 5 ', 52' in ³ BE2018 / 5747 which circulates the heat transfer fluid. The energy initially recovered in the intermediate circuit 5 ′, 52 ′ passing through the thermocondenser 5 ′ and the heat pump 2 is retransmitted to the return water from the heating circuit 4 ′. The intermediate circuit 52 ′, here provided with an additional low potential heat source 51 ′, has a function of regulating the temperature of the heat source of the heat pump, which, otherwise, would not be favorable for the functioning of the heat pump , especially when it starts up.

The Applicant has nevertheless not only overcome this obstacle by proposing a heat pump operating with a new type of “smoke” evaporator, that is to say having a direct heat exchange interface between the smoke and the refrigerant of the PAC, but doc and also considerably simplified the combination of a cogenerator and a heat pump.

By "directly" or "direct", it should therefore be understood here that, unlike existing systems, no intermediate heat transfer circuit, using a heat transfer fluid, is provided between the flue outlet duct and the evaporator.

Preferably, there is also no intermediate circuit between the return of the heating circuit and the condenser of the heat pump, as is the case in the system of FR 2 979 974 where a liquid / liquid exchanger is also provided between the heat pump condenser and the domestic hot water return circuit. Heat is transferred from the compressed refrigerant directly to the return water from the heating circuit in the condenser.

The invention also provides a heat pump designed to transfer condensation energy from the flue gas vapor, resulting from the combustion of fuel, to water in a circuit, the temperature of which is higher than the temperature of said condensation, comprising a closed circuit traversed by a refrigerant and on which are arranged a compressor, a condenser, a pressure reducer and an evaporator, characterized by the fact * BE2018 / 5747 that the evaporator comprises a heat transfer interface between the refrigerant and combustion fumes.

The transfer interface is understood as a direct interface, that is to say that the fumes and the refrigerant pass respectively on the two sides of a wall separating them. No intermediate fluid is used.

There is obviously a technical relationship between the heat pump and the claimed method which is that the evaporator comprises an interface between the refrigerant of the heat pump and the cogeneration fumes. Both inventions therefore meet the requirement of unity of invention.

The invention finally proposes an assembly of a heat pump and a cogenerator, the assembly being arranged for transferring condensation energy from the steam water vapor, coming from the combustion of fuel in the cogenerator , to water in a circuit, the temperature of which is higher than the temperature of said condensation, the heat pump comprising a closed circuit traversed by a refrigerant and on which are arranged a compressor, a condenser, a pressure reducer and an evaporator, characterized in that the evaporator comprises a heat transfer interface between the refrigerant and the combustion fumes of the cogenerator.

Advantageously, the heat pump is electrically supplied by the cogenerator.

The invention allows a particularly compact arrangement of the assembly formed by the cogenerator and the heat pump, avoiding having to install intermediate circuits traversed by heat transfer fluids requiring additional maintenance. The method also makes it possible to avoid any loss of energy caused by such intermediate circuits and makes it possible to improve the efficiency of the assembly.

³ BE2018 / 5747

A refrigerant is a fluid that allows the implementation of a refrigeration cycle. It can be pure or a mixture of pure fluids present in the liquid, gaseous phase or both, depending on the temperature and the pressure thereof. Refrigerants are commonly used in heat generation systems by heat pumps and are well known to those skilled in the art. It is therefore not a question here of water or glycol. For example, freon, ammonia, propane or butane can be used as the refrigerant.

The invention will be better understood with the aid of the following description of several implementations of the invention, with reference to the attached drawing, in which:

FIG. 1 is a diagram of the whole of the invention;

FIG. 2 is a schematic illustration of the process of the invention;

FIG. 3 illustrates an energy balance of the assembly of the invention according to FIG. 1 and of the method according to FIG. 2 and FIG. 4 illustrates the prior art.

With reference to FIG. 1, an assembly 1 comprises a heat pump 2 and a cogenerator 3. The cogenerator 3 produces, via the combustion of fuel, electrical energy 31, thermal energy 32 and fumes 33. The fumes 33 are evacuated through an exhaust duct 34. The source of electrical energy 31 is connected to the heat pump 2 and to an electrical network 35. The source of thermal energy is near the water of a heating circuit 4 here supplying a radiator 41. The direction of water circulation in circuit 4 is illustrated by the arrows drawn on circuit 4.

The heat pump 2 includes a refrigerant circuit 21. The direction of circulation of the refrigerant in circuit 21 is illustrated by the arrows drawn on circuit 21.

Along the circuit 21 are arranged a compressor 22, a condenser 23, a regulator 24 and an evaporator 25. The condenser ° BE2018 / 5747 is traversed by the water of the heating circuit 4 and the evaporator 25 is traversed by the conduit 34 for evacuating fumes 33 from the combustion of the cogenerator 3.

Cogenerators are well known to those skilled in the art and can be used interchangeably for the implementation of the invention. The fuel can be natural gas, bio-gas, fuel oil, vegetable oil such as rapeseed oil for example, or bioethanol. The cogenerator can even be flexible and operate on several types of fuel.

Figure 2 shows a part of Figure 1, keeping the numbering, to illustrate the implementation of the method of the invention.

The cogenerator 3 burns a fuel and generates fumes which are evacuated by the exhaust duct 34 which passes through the evaporator 25 of the heat pump 2. The fumes 34 enter here in the evaporator at a temperature of 85 ° C. The return water from heating circuit 4 arrives at the condenser at 60 ° C, temperature is higher than the temperature that would be necessary for the condensation of flue gas water by direct exchange between the water in circuit 4 and the duct 34 smoke evacuation. The heat pump 2 is therefore inserted between these two elements. In a step A, the refrigerant 21 is compressed in the compressor 22, the pressure increases, the reaction is exothermic and the refrigerant heats up. The compressor 22 can be supplied with electricity by the cogenerator 3.

The compressor here is for example a conventional freon heat pump compressor.

In step B, at the outlet of the compressor 22, the refrigerant flows through the condenser 23. The condenser is arranged so that there is a large heat exchange surface between the refrigerant and the return water from circuit 4 The pressure of the refrigerant is constant in the condenser and this fluid will undergo 'BE2018 / 5747 several phases. At first, its temperature decreases while its sensible heat is transferred to the water in circuit 4.

In a second step, the refrigerant condenses, its temperature then remaining constant and its condensation energy being transferred to the water in circuit 4. Finally, the temperature decreases again, while its sensible heat is transferred to the water in circuit 4. During step B, heat of the compressed refrigerant is therefore transmitted to the return water of the heating circuit, which here passes from 60 ° C to 65 ° C, the refrigerant passes in the liquid state.

The condenser is a conventional heat pump condenser, which must however be able to withstand pressures of the order of several tens of bars, for example between 20 and 30 bars.

In step C, the refrigerant is expanded at the pressure reducer 24. The pressure drop causes the evaporation and lowering of the temperature of the refrigerant below the condensation temperature of water at atmospheric pressure, or temperature dew.

In step D, the refrigerant expands by passing through the evaporator 25 which is arranged so that there is a large surface area for heat / heat exchange between the refrigerant and the fumes 34 of combustion from the cogenerator 2. As the expansion is endothermic, the fumes are thus cooled there under the condensation temperature of the water by transmitting to the refrigerant the sensible / intrinsic heat of the fumes and the latent heat released by the condensation of the water contained in the fumes. The fumes come out of the evaporator at 35 ° C.

The temperatures of the heating water and flue gas circuits shown here are purely illustrative of an order of magnitude and are not absolute values.

^ö BE2018 / 5747

The heat pump 2 is therefore here an air / water heat pump, that is to say allowing the transfer of thermal energy from a gaseous medium to the water returning from the circuit 4. It nevertheless has the particularity to be arranged specifically so that the gaseous medium is hot smoke.

In particular, the evaporator is arranged to allow direct heat exchange between the fumes and the refrigerant. This implies in particular that the exchanger can withstand smoke on one side between 80 and 90 ° C and on the other side a very cold refrigerant. The evaporator must therefore withstand high temperature differences, much higher than in a heat pump conventionally used in aerothermal energy for example. The part of the evaporator through which the fumes pass must also be chemically resistant to the fumes, which can be acid, clogging the walls.

The exchange surface between the refrigerant and the fumes is calculated in a manner known to a person skilled in the art, in particular as a function of the smoke outlet temperatures, of the refrigerant as well as of the flow rates of the fumes and of the refrigerant.

As no evaporator specifically designed for hot smoke / refrigerant exchange is available on the market, the applicant has diverted water / freon exchangers by replacing the water with cogeneration fumes.

For example, the evaporator is a steel plate exchanger, like the Compact36 from Airec AB, allowing great mechanical resistance, although it induces high pressure losses on the flue side. One can also consider a tube evaporator, for example with two coaxial copper tubes wound in a spiral, which although less mechanically resistant, induces less pressure drop and back pressure on the smoke side.

With reference to FIG. 3, a cogenerator 3 is supplied with 97 kW of fuel, for example fuel oil. The combustion of fuel oil generates 33 kW of electrical energy (kWe), transmitted for ³ BE2018 / 5747 on the one hand, 3 kWe to the heat pump 2 and for the rest, 30 kWe to the electrical circuit 35, which corresponds to a yield of 34%. The combustion of fuel oil also produces 63 kW of thermal energy (kWt), which corresponds to a yield of 65%, transmitted to the hot water heating circuit 4, to reach a temperature of 75 ° C. The cogenerator therefore has a yield of 99%.

The combination with the cogenerator of the heat pump makes it possible here to transfer 13 kWt of the fumes to the heating water 4 by providing it with 3 kWe of the 33 kWe produced by the cogenerator. As a result, from 97 kW of fuel, the heat pump cogenerator assembly produces 30 kWe and 76 kwt (63 kWt of the cogenerator + 13 kWt recovered by the heat pump), i.e. a yield of 109%.

The balance of the direct combination of the cogenerator and the heat pump, specially arranged to directly recover the sensitive and latent energy of the fumes, is clearly superior to the balance of a cogenerator alone.

The figures given here are purely illustrative and obviously depend on the size of the installation and its particular configuration as well as the settings. For example, the heating circuit setpoint may not be set at 75 ° C but at another higher or lower temperature, depending on the particular configuration of the building installation. The parameters can also be different if the fuel is fuel oil, rapeseed oil or bioethanol.

A cogenerator also generally releases heat in the room where it is located. This room must be ventilated, ventilated to maintain a correct temperature. A heat pump can also be adapted to recover the thermal energy dissipated in the air surrounding the cogenerator. This heat pump can be the heat pump already used for the flue gases or another heat pump installed for example in series with the first on the heating water return circuit. For example, the ventilation circuit can be adapted to circulate the hot air from the room in the evaporator of the heat pump, to transfer the heat sensitive to the refrigerant.

BE2018 / 5747

It can be envisaged that the smoke evacuation duct from the cogenerator is diverted towards the heat pump which would be installed right next to it. The heat pump could also be installed directly on the flue gas exhaust duct without modifying the latter. Any suitable arrangement in the space of the cogenerator and the heat pump allowing the fumes from the cogenerator to pass through the evaporator of the heat pump is possible. It is nevertheless preferable to limit the distance between the two entities in the set.

The circuit 4 illustrated here is a heating water circuit. It could nevertheless be another type of circuit in which the return of water is at a higher temperature than the condensation of water in the fumes, for example in a particular industrial installation or simply a circuit of city water or sanitary circuit.

Claims (13)

Claims 1. Method for transferring condensation energy from the water vapor of cogeneration fumes (33), resulting from the combustion of fuel by a cogenerator (3), to the return water of a circuit (4) heating or sanitary circuit, the temperature of which is higher than the temperature of said condensation, by means of a heat pump (2) comprising a closed circuit traversed by a refrigerant (21) and on which are arranged a compressor (22), a condenser (23), an expansion valve (24) and an evaporator (25), method according to which: (A) the refrigerant (21) is compressed in the compressor (22) to heat it; (B) heat is transferred from the compressed refrigerant (21) to the return water from the heating circuit (4) or from the domestic circuit in the condenser (23); (C) the compressed refrigerant (21) is expanded to lower the temperature below the condensing temperature in the expansion valve (24), and (D) the expanded refrigerant (21) is heated in the evaporator (25) traversed directly by the fumes (33) and at which the fumes are cooled below the condensation temperature of the water to transmit to the refrigerant the intrinsic heat of the fumes and the heat released by the condensation of the water which they contain. 2. Method according to claim 1, in which heat is transmitted from the compressed refrigerant (21) directly to the return water from the heating circuit (4) in the condenser (23). 3. Method according to one of claims 1 and 2, wherein the cogenerator (3) electrically supplies the heat pump (2). ΒΕ2018 / 5747 4. Method according to one of claims 1 to 3, according to which the energy dissipated by the cogenerator (3) is recovered in the surrounding air. 5. Heat pump (2) arranged to transfer condensation energy from the flue gas vapor (33), resulting from the combustion of fuel, to water in a circuit (4), including the temperature is higher than the temperature of said condensation, comprising a closed circuit traversed by a refrigerant (21) and on which are arranged a compressor (22), a condenser (23), a pressure reducer (24) and an evaporator (25 ), characterized in that the evaporator (25) comprises a direct heat transfer interface between the refrigerant (21) and combustion fumes (33). 6. Heat pump according to claim 4, wherein the refrigerant (21) is freon. 7. Heat pump according to one of claims 5 and 6, wherein the evaporator (25) is a plate exchanger. 8. Heat pump according to one of claims 5 and 6, wherein the evaporator (25) is a tube exchanger. 9. Assembly (1) of a heat pump (2) and a cogenerator (3), the assembly being arranged for transferring condensation energy from the flue gas vapor (33), issuing from the combustion of fuel in the cogenerator (3), to water in a circuit (4), the temperature of which is higher than the temperature of said condensation, the heat pump (2) comprising a closed circuit traversed by a refrigerant (21) and on which are arranged a compressor (22), a condenser (23), a pressure reducer (24) and an evaporator (25), characterized in that the evaporator (25) comprises an interface for direct heat transfer between the refrigerant (21) and the fumes (33) from the combustion of the cogenerator (3). BE2018 / 5747 10. The assembly of claim 8, wherein the heat pump (2) is electrically supplied by the cogenerator (3). 11. Assembly according to one of claims 9 and 10, wherein the refrigerant (21) is freon. 12. Assembly according to one of claims 9 to 11, wherein the evaporator (25) is a plate or tube exchanger. 13. Assembly according to one of claims 9 to 12, in which a heat pump is arranged to recover the thermal energy dissipated by the cogenerator in the surrounding air.