IT201800002643U1 - - Google Patents

Description

DESCRIPTION

Attached to application for PATENT FOR UTILITY MODEL entitled:

ENERGY RECOVERY SYSTEM FROM THE INTERCOOLER OF THE SECOND STAGE OF AN ENDOTHERMIC ENGINE

Technical field

The present invention belongs to the sector of cogeneration systems which use a supercharged internal combustion engine, especially gas, for the production of thermal and mechanical energy, the latter possibly destined for the production of electrical energy. In detail, the invention relates to the thermal recovery of the heat removed from the combustion mixture inside the intercooling unit, also known as the intercooler, of a supercharged engine, after compression and before entering the combustion chamber.

State of the art

In cogeneration plants that use endothermic engines, the heat produced by the engine is exploited as regards the cooling water of the thermal unit, the lubricating oil and the energy of the evacuated combustion gases. In the present patent text the term "water" will be used to indicate generically the thermal carrier fluid; it is therefore water which, as known in the sector, may contain other substances; for example it may have been added with ethylene or propylene glycol, as well as being subjected to chemical conditioning.

In the case of supercharged engines with intercooling stage, a further potentially recoverable amount of heat is that which is removed from the combustion air, whether or not mixed with the fuel, after it has been compressed.

In the intercooling unit of a supercharged engine, the thermal carrier fluid used to cool the mixture that feeds the engine undergoes heating, due to the subtraction of heat from the compressed mixture. The temperature of the compressed mixture must have decreased significantly and this implies that the subtracted heat is, at least in part, at a temperature so low as to make it difficult to use.

Ά by way of example we indicate that the temperature jump of the compressed mixture that is on average required in the intercooling stage of a gas engine is generally about 185 degrees Celsius, since the temperature of the compressed mixture at the inlet is about 235 ° C and the temperature of the compressed mixture leaving the intercooling unit is about 50 ° C.

To recover at least in part the heat that the intercooling unit takes away from the compressed mixture, plant engineering solutions have been developed in which the intercooling unit includes two cooling stages; in this way the thermal carrier fluid that cools the mixture in the first cooling stage has an outlet temperature, generally around 100 ° C, which allows it to be used directly or together with other thermal waste, such as for example those of evacuated flue gases from the engine.

The thermal carrier fluid leaving the second intercooling stage, on the other hand, is at a lower temperature, since it is necessary to ensure that the combustion mixture leaves the intercooling stage below a certain temperature; for this reason the thermal carrier fluid leaving the second intercooling stage is not exploited, but the heat it contains is dissipated in the air, to lower its temperature before reintroducing it into the heat exchanger of the second intercooling stage.

In addition to being a waste from an energy point of view, dissipation in the air is also a noisy operation that involves energy consumption.

In summary, a cogeneration unit with a supercharged internal combustion engine is divided into the combustion mixture part, in two stages:

first stage intercooler. This is heat recovered to date, at a temperature of 90-100 ° C. This heat is transferred to a civil or industrial process, with its own recovery circuit including, in series, heat recovery from the oil - heat recovery from the engine jackets;

second stage intercooler. This is currently non-recoverable heat, for any process, since the temperature of the fluid leaving the intercooler is 46-50 ° C. Currently this heat is continuously dissipated in the external environment with a water - air coil. The cooling of the water in the battery means that it is returned to the aircooler at a temperature of 38 - 43 ° C with a current consumption for the fans.

The Japanese patent application JP 2017116185 (A) proposes to place a heat pump in parallel to the dissipative circuit that cools the intercooling unit: the cogeneration plant described includes an internal combustion engine equipped with a single intercooling unit, this the latter is cooled by means of a gas-water exchanger; the cooling water leaves this exchanger at a temperature greater than 30 ° C and this temperature is further lowered by replacing the dissipation in the environment with a heat pump, in particular through an evaporative tower.

The recovery of thermal energy takes place through an insulation exchanger which has the purpose of transferring the heat to the heat pump only when there are the conditions to use a high temperature fluid; on the other hand, when said high temperature fluid is not required, the heat is not transferred to the insulation exchanger, and from there to the heat pump, but is dissipated. According to the teachings of the application JP 2017116185 (A) the heat pump works with a cold source temperature equal to or greater than 30 ° C while the evaporative tower has the function of disposing of the thermal energy that the heat pump is unable to exploit , so as to ensure that the temperature of the compressed mixture entering the engine is not higher than the desired one. The international patent application WO 2016051246 (A1) also describes the introduction of a heat pump to raise the temperature of the low temperature cooling fluids produced by cogeneration systems above 60 ° C; in this case the application is specially designed to use the recovered heat for heating the premises, preferably in district heating networks. The heat pump is placed in series with the heating network, on the return and the heat of the cold source of the heat pump comes from different sources, for example from the second intercooling stage and from the second exchanger with the evacuated flue gases.

The known solutions are complicated and are not easily applicable to all cogeneration units with gas engine already made, as they integrate the heat pump into the intercooling unit for the sole purpose of exploiting, at least in part, thermal energy that would otherwise be dissipated. in the environment.

Aims and summary of the invention

A first purpose of the present innovation is therefore to exploit a heat pump not only to recover thermal energy at low temperatures, but also to create systems with a smaller and less expensive dissipative cooling system than would be necessary in the absence of a heat pump. heat.

A further object is to exploit the thermal energy subtracted from the second intercooling stage to supply user circuits dedicated to district heating, the latter typically operating at temperatures between 60 ° C for the return and 90 ° C for the delivery.

Another object of the present invention is to supply the environmental heating systems of buildings and industrial complexes at temperatures between 60 ° C and 80 ° C.

Not least object of the present invention is that of supplying water at a low temperature to be used for cooking processes and other similar applications.

These and other purposes which will become clear to the skilled in the art are achieved by placing a heat pump directly on the outlet of the gas / water exchanger of the second intercooling stage inside a cogeneration plant with gas internal combustion engine.

The energy recovery system object of this patent application aims to ennoble the heat dissipated by the second intercooler stage, not currently used due to the very low temperature, in order to transfer it to a process that can use it at 80 - 82 ° C; for example: in the paper sector to make paper pulp; in rubber molding, to heat the molds; in the food industry for cooking food; in the civil sector for the production of hot water for heating; in district heating; in district cooling to produce freezing water.

In summary, the energy recovery system from the second stage intercooler of an internal combustion engine includes:

a heat pump (1) which: is fed on one side by the second stage intercooler circuit (source) at a temperature of 46 - 50 ° C, the same heat pump returns water to the same circuit, at a temperature of 38-43 ° C avoiding the use of the cooling aircooler, on the other hand the same heat pump transfers the heat to a condenser, at a temperature of 80-82 ° C for example a district heating with an inlet for example at 60 ° C;

a skid containing all the regulation and control elements of the source and user circuit, which supervises this transfer process;

piping and supports on the user side and source side with the necessary electro-instrumental works and with the control and power panels.

Preferably in the secondary circuit of the second intercooling stage the heat pump is placed upstream of the exchanger dedicated to the emergency cooling of the internal combustion engine, which is used when the cogeneration unit operates without thermal load.

In this way it is possible to undersize the air cooling coil of the dissipative cooling system.

The heat pump operates with very small temperature variations on the source side, for example between 4 ° C and 10 ° C, preferably between 5 ° C and 8 ° C; 6 ° C in the embodiment shown in the attached tables.

Brief description of the drawings

Fig. 1 shows a diagram of an embodiment of the cogeneration unit in which a gas / water heat exchanger (22) of a second intercooling stage of an internal combustion engine (2) is observed which also includes a heat pump (1 ) of the water / water type serving a thermal user (5), such as a district heating network. A circulation pump sends at least part of the water to the heat pump.

The coolers (3) and the emergency exchanger (4) are also visible.

In the embodiment shown in Figure 1, in an emergency condition, the thermal energy of the thermal carrier fluid C is disposed of by the second intercooling stage through the emergency exchanger (4). The figure shows how the heat pump (1) is placed on the outlet of the gas / water heat exchanger (22), before the emergency exchanger (4) and the coolers (3). In addition, the two and three-way valves are visible, which allow the operation of the second intercooling stage to be adapted to the working conditions.

Fig. 2 shows a plant diagram of an embodiment of the cogeneration unit that uses a GE Power® J620 F12 gas engine (2). The diagram shows the circuit (21) of the thermal vector fluid C for cooling the engine (2) which is heated first by the lubrication oil, then by the cooling liquid and finally by the combustion mixture. Under design conditions, the respective heat exchange devices bring the thermal carrier fluid C from 72 ° C to 76.4 ° C, then to 82.4 ° C and finally to 95 ° C, recovering approximately 1650 kW of power, in the hypothesis that the primary hot fluids escape from the respective heat exchange devices at temperatures of 80 ° C, 90 ° C and 101.3 ° C.

On the left of the figure is shown the gas / water heat exchanger (22) of the intercooling unit which disposes of a power of about 300 kW by heating the thermal carrier fluid A from 40 ° C to 46.5 ° C. In an advantageous embodiment, the design flow rate of the thermal vector fluid A which passes through the heat exchanger (22) is comparable to the flow rate of the same thermal vector fluid A which supplies the cold source of the heat pump (1) with a temperature difference from 46 ° C to 40 ° C, releasing about 300 kW of power. The heat pump (1) supplies heat to the thermal user (5) by heating a thermal carrier fluid B by about 20 ° C up to about 80 ° C.

At the bottom right you can see the return circuit from the thermal user (5) which delivers the thermal carrier fluid C to an emergency exchanger (4). Bottom left are the water / air coolers (3).

Fig. 3 shows an example of a different constructive solution.

Fig. 4 shows a diagram of an embodiment of the circuit of the thermal carrier fluid C, at the top, and of the circuit of the thermal carrier fluid A, at the bottom, this is a particularly suitable solution for a 3.3 MW cogeneration unit with a J 620 GS-F12 engine.

The inlet temperature of the fuel mixture in the first intercooling stage for a recovery of 771 kW is 236 ° C; the flow rate of the combustible mixture is about 5.5 kg / s;

The inlet temperature to the exchanger of the second intercooling stage is about 100 ° C while the outlet temperature is at most 50 ° C; the power to be disposed of by the second intercooling stage is about 305 kW since the water with the addition of 37% glycol achieves a jump of 6.5 ° C with a flow rate of about 12.5 dm <3> / s. The second intercooling stage is sized to ensure in any case an entry of water to the heat exchanger around or below 40 ° C to ensure cooling of the combustible mixture. The data shown in this figure has a tolerance of - 8% plus an additional 5% for cooling devices.

The diagram shows how the circuit of the thermal carrier fluid C can also recover the heat of the exhaust gases and / or the circuit of the thermal carrier fluid A can recover the heat of the engine oil after the latter has already been cooled in a first stage from the thermal carrier fluid C.

Detailed description of an embodiment of the invention

In a particularly simple and effective embodiment, the cogeneration unit object of the present patent application comprises a supercharged endothermic engine (2) which is cooled by a thermal vector fluid C which in turn transfers heat to a thermal user (5), this the latter is typically a district heating system, but also any system that requires thermal energy.

In the most common solutions the engine is a gas engine and the supercharging is carried out by compressing the mixture of fuel and combustion air, however the present invention can also be applied if the compression is carried out only on the combustion air. To cool the compressed fuel mixture that feeds the engine, the cogeneration system comprises an intercooling unit which, in the embodiment described here, consists of a first stage of high temperature intercooling, which heats a thermal carrier fluid C, placed in series, but not necessarily immediately downstream, with a second stage of low temperature intercooling which includes a gas / water heat exchanger (22) in which the compressed mixture transfers heat to a thermal carrier fluid A.

The second intercooling stage also comprises a water / water heat pump (1), fed by at least a part of the thermal carrier fluid A leaving the gas / water exchanger (22); the heat pump (1) in turn heats a thermal carrier fluid B which supplies a thermal user, the latter can be the same district heating system powered by the cooling of the motor or it can be a different thermal user.

In the embodiment described herein, the second intercooling stage also comprises coolers (3) of the water / air type, which cool the thermal carrier fluid A entering said gas / water heat exchanger (22), and an emergency exchanger ( 4) which lowers the temperature of the thermal vector fluid C by heating the thermal vector fluid A entering said water / air coolers (3); the emergency exchanger (4) guarantees the functioning of the motor for the production of electric energy even when the thermal user (5) does not absorb all the thermal energy produced by the motor (2). When the heat load is lower than the design heat output of the cogeneration unit, it is possible to intervene on the recovery of the burnt gases up to zero, thanks to a by-pass duct that introduces them directly to the chimney. Although other adjustments are known in the sector, when the thermal demand is zero or very low and only electric production is to be maintained, it is necessary to dispose of the excess heat coming from the motor (2). In this condition, which occurs especially if the cogeneration unit is conducted with electrical priority, the thermal carrier fluid C which cools the engine by subtracting the heat from the engine oil and / or from the coolant and / or from the first intercooling stage it must in turn be cooled to avoid damage to the motor.

Generally the water / air cooler (s) (3) transfer heat directly to the environment.

In a preferred embodiment, the heat pump (1) is sized to absorb all the heat of the second intercooling stage, so as to allow the water / air coolers (3) to be used only in an emergency, reducing the number necessary for operation with electric load only, i.e. when the thermal user is at zero. Preferably the thermal user (5) is constituted by a district heating network and, in a preferred embodiment, the thermal carrier fluid B increases the return temperature of the district heating water by operating in parallel with the thermal carrier fluid C and, possibly, to additional sources of thermal energy.

Claims (10)

CLAIMS 1. Cogeneration unit for powering at least one thermal user (5) and one mechanical user, comprising at least one supercharged endothermic engine (2) cooled by a thermal carrier fluid C which transfers heat to said thermal user (5), also comprising a group of intercooling of the compressed fuel mixture which feeds said engine (2), said intercooling unit comprising at least a first high temperature intercooling stage, which heats said thermal carrier fluid C, and a second low temperature intercooling stage which comprises at least one exchanger gas / water heat pump (22) in which said compressed fuel mixture heats a thermal carrier fluid A, characterized in that said second intercooling stage also comprises a water / water heat pump (1), fed by at least a part of said thermal carrier fluid A leaving said gas / water exchanger (22), called heat pump (1) ri heating a thermal carrier fluid B which supplies a thermal user. 2. Cogeneration unit as per claim 1 above, characterized in that said second intercooling stage comprises at least one water / air cooler (3) which cools the thermal carrier fluid A entering said gas / water heat exchanger (22). 3. Cogeneration unit as per claim 2 above, characterized in that it comprises an emergency water / water heat exchanger (4) which lowers the temperature of the thermal carrier fluid C by heating the thermal carrier fluid A entering said cooler (3) water / air. 4. Cogeneration unit according to any one of the preceding claims, characterized in that said thermal carrier fluid C also collects the heat of the lubricating oil of said engine (2). 5. Cogeneration unit according to any one of the preceding claims, characterized in that said thermal vector fluid C also collects the heat of the cooling liquid of said engine (2). 6. Cogeneration unit as per claim 2 above, characterized in that said water / air cooler (3) transfers heat to the environment. 7. Cogeneration unit according to any one of the preceding claims, characterized in that the temperature jump of said thermal vector fluid A as it passes through said heat pump (1) is comprised between 4 ° C and 10 ° C. 8. Cogeneration unit according to any one of the preceding claims, characterized in that the temperature jump of said thermal vector fluid A as it passes through said heat pump (1) is comprised between 6 ° C and 8 ° C. 9. Cogeneration unit according to any one of the preceding claims, characterized in that it comprises at least one recirculation pump for said thermal carrier fluid A. 10. Cogeneration unit as per claim 9 above, characterized in that said recirculation pump is placed immediately upstream of said heat pump (1).