Method for energy saving

Abstract

Method for coupling a first heat-requiring industrial process to a second cold-requiring industrial process, whereby a first circuit for energy recovery (1) from the first industrial process transfers heat to a second circuit for cold production (2) for the second industrial process, wherein the first circuit for energy recovery (1) the energy carrier is a binary mixture of water and ammonia that has two-phases and is compressed by a compressor (7) specifically suitable for compressing a two-phase fluid such as a compressor with a Lysholm rotor or equipped with vanes, whereby all or part of the liquid phase evaporates as a result of compression such that overheating does not occur and such that less working energy must be supplied.

Claims

1. Method for coupling a first heat-requiring industrial process to a second cold-requiring industrial process, whereby a first circuit for energy recovery (1) from the first industrial process transfers heat to a second circuit for cold production (2) for the second cold-requiring industrial process, wherein in the first circuit for energy recovery (1) the energy carrier is a binary mixture of water and ammonia that has two phases and is compressed by a compressor (7) specifically suitable for compressing a two-phase fluid, whereby all or part of the liquid phase evaporates as a result of compression such that overheating does not occur, whereby the circuit for energy recovery (1) of the first industrial process is coupled to the circuit for cold production (2) of the second industrial process, wherein the heat of the energy carrier in the first circuit for energy recovery, that remains after the expansion of the energy carrier in an expander (11) for electricity generation, is additionally utilised to heat the energy carrier of the second industrial process by means of a heat exchanger (13) between the first circuit (1) for energy recovery and the second circuit (2) for cold production that additionally heats the energy carrier of the second industrial process before it is expanded in the expander (20) for electricity and cold production of the second circuit (2) for cold production, wherein the second circuit (2) for cold production comprises a separator (22), between the expander (20) for expanding and a compressor (31) for compressing the energy carrier, for separating the liquid phase from the gas phase in the energy carrier, followed by one or more refrigerating installations (24,25,26,27,28) for one or more production stages in the second industrial process.

2. Method according to claim 1, wherein the energy carriers of the first (1) circuit for energy recovery and the second circuit (2) for cold production differ from one another.

3. Method according to claim 1, wherein the energy carrier of the second circuit (2) for cold production has a lower boiling point than the energy carrier of the first circuit (1) for energy recovery.

4. Method according to claim 1, wherein a proportion of the heat that is generated in the energy carrier of the first circuit (1) for energy recovery by a compressor (7), is utilised to heat a process fluid in the form of a liquid or a gas in the first industrial process (3) and this by means of a heat exchanger (9) between the first circuit (1) for energy recovery and a pipe for the supply of the process fluid to the process vessel of the first industrial process (3), where it is brought to the desired temperature for a production stage in the first industrial process.

5. Method according to claim 1, wherein the energy carrier of the second circuit (2) for cold production is ammonia.

6. Method according to claim 1, wherein t the second circuit (2) for cold production is equipped with an electric pump (17), by which the energy carrier of the second circuit (2) for cold production is brought to a higher pressure before being expanded in an expander (20) of the second circuit (2) for cold production.

7. Method according to claim 1, wherein the energy carrier of the second circuit (2) for cold production, after compression in a compressor (31) to a pressure whereby it becomes liquid again, is further guided to a heat exchanger (33), wherein surplus heat from the energy carrier can be optionally transferred to another process liquid that is used elsewhere in the coupled production processes.

8. Method according to claim 1, wherein the heat exchanger (33) for the surplus heat of the energy carrier is connected by means of a tap (36) to a separator (37) in which saturated steam and saturated demineralised water are separated from one another at a pressure of 400 kPa.

9. Method according to claim 8, wherein the non-condensed proportion in the separator (37) is utilised to heat hot water for industrial use.

10. Method according to claim 9, wherein the water originates from another separator (43), with which water vapour originating from the first production process (3) is recovered and is available for industrial use after filtration.

11. Method according to claim 1, wherein the energy carrier of the second circuit (2) for cold production is guided in gas form from the condenser (39), in which the energy carrier becomes liquid, to a pump (17) that further drives the energy carrier to a heat exchanger (13) between the first circuit (1) for energy recovery and the second circuit (2) for cold production, after which the energy carrier of the second circuit (2) for cold production is reused in a subsequent cycle.

12. Method according to claim 1, wherein the compressor is a screw compressor with a rotor or equipped with vanes.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 schematically shows a flow diagram of two industrial processes connected together according to the invention;

(2) FIGS. 2 to 5 show the heat flow as a function of the temperature through the heat exchangers 5, 9, 13 and 33 of FIG. 1;

(3) FIG. 6 shows the pressure-enthalpy diagram of ammonia.

(4) FIG. 1 shows the flow diagram of a circuit for heat recovery 1 of a first industrial production process that is coupled to a second circuit for cold production 2 of a second industrial production process. The first industrial production process 3 supplies hot gases or vapours that flow through pipe 4 to a heat exchanger 5 that forms part of the first circuit for heat recovery 1 and in which the energy carrier, i.e. a binary mixture of water and ammonia, of this first circuit is heated and guided via pipe 6 to a compressor 7, suitable for compressing a two-phase mixture from where the compressed energy carrier is guided via pipe 8 to a second heat exchanger 9 for steam production, and is further guided via pipe 10 to an expander 11 in which the energy carrier is expanded and further guided via pipe 12 to a third heat exchanger 13 for heat transfer to a circuit for cold production in the second industrial process 2, and is guided further via pipe 14 to a pump 15 that drives the energy carrier of the first circuit to the first heat exchanger 5 via pipe 16, in order to be heated again and to go through the first circuit 1 again for energy recovery.

DETAILED DESCRIPTION

(5) The pump 17 in the second circuit for cold production 2 drives the energy carrier of this second circuit for cold production, i.e. ammonia, via pipe 18 to the heat exchanger 13 in which the energy carrier absorbs heat from the first circuit for energy recovery 1, and is guided via pipe 19 to an expander in which the energy carrier is expanded, and is further guided via pipe 21 to a separator 22 for separating the gas phase and the liquid phase of the energy carrier from where the liquid phase of the energy carrier is guided via pipe 23 to industrial refrigerating devices, in this case a freezer tunnel 24, a frozen storage area 25 and a chilled area 26 for the collection of orders, and to other refrigerating installations 27,28 that all form part of the second industrial production process where cold is required.

(6) The evaporated energy carrier from the refrigerating devices is combined with the gas phase from the separator 22 via the pipes 29 and further guided via pipe 30 to a compressor 31 from where the compressed gas is guided via pipe 32 to the heat exchanger 33 where surplus heat can be emitted to a flow of demineralised water 34, that can flow to a steam generator 37 via pipe 35 when the tap 36 is open. The energy carrier of the second circuit for cold production is guided from the heat exchanger 33 via pipe 38 to a heat exchanger 39, in which the energy carrier is condensed by an air flow, after which the energy carrier is further guided via pipe 40 to the pump 17 from where the energy carrier is further guided by pipe 18 and reused in a subsequent cycle of the second circuit 2 for cold production. Additional supplements of energy carrier in the second circuit for cold production can be added via pipe 41 to the liquid phase in the separator 22. Via pipe 42 hot gases, that are supplied from the first production process 3, are used for heating water in the generator 43 for hot water.

(7) FIGS. 2 to 5 graphically show the relationship between the temperature in C. of the energy carrier and the heat flow in KJ/s through the subsequent heat exchangers: 5 (FIG. 2), 9 (FIG. 3), 13 (FIGS. 4) and 33 (FIG. 5). The temperature of the flow that is heated (OUT), and of the flow that is cooled (IN) in the heat exchanger, is indicated in each case.

(8) FIG. 6 shows a Mollier diagram of ammonia, the preferred energy carrier of the second circuit for cold production, whereby the enthalpy is presented along the abscissa in kJ/kg, and the pressure along the ordinate in MPa.

(9) The curve presents all pressure and enthalpy points where the liquid phase (below the curve) is in equilibrium with the gas phase (above the curve).

(10) The operation of the device 1 is very simple and as follows.

(11) A first production process that requires heat can be an industrial frying installation for French fried potatoes for example, in which they are pre-fried, or it can be an installation for frying potato crisps.

(12) The first production process 3 that requires heat is provided with a first circuit 1 for energy recovery in which the energy present in the hot vapours originating from the first production process 3 is partly recovered by transferring the heat of the hot gases in a heat exchanger 5 to an energy carrier, i.e. a mixture of water and ammonia, present in this first circuit 1 and then expanding the energy carrier in an expander 11 with which electrical energy is generated that can be used in the process again.

(13) Another fraction of the energy present in the hot vapours is utilised to generate hot water by guiding this fraction through pipe 42 to a hot water generator 43.

(14) Another fraction of the energy present in the hot gases is transferred via heat exchanger 13 from the energy carrier in the first circuit 1 for energy recovery to the energy carrier, i.e. ammonia, in a second circuit 2 for cold production, whereby the transferred heat is utilised to heat the energy carrier of the second circuit 2 for cold production before it is expanded in expander 20 with which electrical energy is generated that can be used in the process again.

(15) The cooled energy carrier of the second circuit 2 is guided to a separator 22 that separates the liquid phase of the energy carrier from the gas phase, after which the liquid phase (33 C.) is utilised in the second industrial process that requires cold, and from which the refrigerating installations are supplied with the liquid phase of the second energy carrier via the pipes 23 so that applications, such as a freezer tunnel 24, a frozen storage area 25, a collection zone 26 for frozen goods and other refrigerating installations 27,28 can be cooled. The second industrial process that requires cold can be the frozen and chilled storage of foodstuffs for example.

(16) For maximum energy recovery for the two coupled industrial processes it is advantageous to have a different energy carrier in the first circuit for energy recovery and in the second circuit for cold production. In the given example the energy carrier of the first circuit is water with a fraction of ammonia, while the energy carrier in the second circuit is ammonia.

(17) After expansion in the expander 11 the first energy carrier is a two-phase flow that has already been cooled, but from which more heat energy can be emitted to the second energy carrier, pure ammonia, that has a much lower boiling point (33 C.), and this absorbs heat in the heat exchanger 13. This additional heat is utilised in the expander 20 of the second circuit for cold production, where the energy carrier of the second circuit is expanded.

(18) The ammonia of the second circuit for cold production heated in the heat exchanger 13 is expanded in the expander 20 whereby the energy carrier becomes two phase (liquid and gas), whereby these phases are separated from one another in the separator 22. The liquid phase, liquid ammonia, has a temperature of 33 C. and can be used for the connected industrial refrigerating installations.

(19) The pressure-enthalpy diagram of FIG. 6 shows how much energy (work) can be recovered by lowering the pressure of ammonia in the liquid phase to a two-phase system, whereby this energy is extracted from the expander as electricity.

(20) In the following tables the energy coefficient of performance or COP is calculated for two examples of a heat-requiring process to a cold-requiring process.

(21) Table 1 gives the energy account for an installation for French fried potato production, coupled to a freezing installation. The energy recovered column gives the sum of all saved energy, while the energy supplied column gives the sum of the energy that had to be supplied to enable recovery. The ratio of the recovered energy to supplied energy or COP is 3.95 in this case and is higher than the COP for the total process in which the circuits for energy recovery and cold production are not coupled.

(22) TABLE-US-00001 TABLE I energy account for French fried potato production coupled to freezing installation. Energy account potato crisp production and refrigerating installation Energy saved Energy supplied gain kWh Loss kWh Hot water 323 Electricity 1206 Water/steam 815 Steam 1888 Refrigeration 1744 Water prod.

(23) Table II shows the energy account for an installation for potato crisp production, without coupling to a second industrial process. The energy recovered column gives the sum of all saved energy, while the energy supplied column gives the sum of the energy that had to be supplied to enable recovery. The ratio of the recovered energy to supplied energy or COP is 4.59 in this case.

(24) TABLE-US-00002 TABLE II energy account for potato crisp production. Energy account potato crisp production Energy saved Energy supplied gain kWh Loss kWh Hot water 595 Electricity 896 Oil heating 3513 Water Prod.

(25) It goes without saying that the invention can be applied to couple any industrial processes whereby one process requires heating and the other process requires cooling.

(26) The invention can also be applied at different temperature ranges and with different energy carriers than those stated in the examples, as long as they can be two-phase for the first circuit for heat recovery.

(27) The present invention is by no means limited to the embodiments described as an example and shown in the drawings, but a device for energy saving according to the invention can be realised in all kinds of forms and dimensions, without departing from the scope of the invention, as described in the following claims.