Dairy cattle are in practice milked with a milking machine or milking robot, after which the fresh milk is stored in a milk tank. This milk tank is periodically emptied and the milk taken to a dairy using a truck. There is an energy demand in this process for transport and processing, particularly cooling, of the fresh milk flow.

The present invention has for its object to perform the above stated process in more efficient manner.

The present invention provides for this purpose a method for generating energy from a fresh milk flow, comprising the steps of :

- realizing a fresh cooled milk flow;

generating an energy flow from the fresh milk flow using an energy transfer system comprising a heat pump, wherein the fresh milk flow is cooled to substantially the storage temperature in a storage tank; and

- supplying the generated energy flow to one or more external and/or internal users.

As part of the invention the inventors have discovered that the energy content of a dairy farm can to a substantial extent supply the energy requirement of this farm and a possibly attached dwelling.

The produced milk has a temperature of about 3 °C and in conventional practice this is usually reduced to about 19°C using a pre-cooler. The use of this pre-cooler is optional. The milk tank is provided with a refrigeration unit to further reduce the temperature of the incoming milk to the desired storage temperature .

It has been found for instance in the case of a farm with dairy cattle where about one million kilograms of milk is produced per year that the heat content, or energy content, of this produced milk flow could supply at least a substantial part of the energy requirement of this farm and the attached dwelling. For this purpose an energy flow is generated with the realized milk flow using an energy transfer system comprising a heat pump. According to the invention the fresh milk flow is cooled from the production temperature of about 3 °C to substantially the storage temperature in a storage tank or milk tank. This storage temperature is in practice usually about 4°C. The amount of energy generated with the energy transfer system is subsequently transported to the one or more external users. External users are here understood to mean consumers of energy outside the milking plant. This achieves that the milking plant becomes an energy-producing plant.

Thus is achieved that energy generated with the method according to the invention is transported to external users outside the milking plant such that the energy content of the fresh milk flow supplies a substantial part of the energy requirement of a farm and a possibly attached dwelling.

An efficient and highly effective use of the energy content of the produced milk flow can in this way be realized. The energy consumption for the various required processes on the farm and the possibly attached dwelling is hereby covered, and energy consumption from more conventional sources, such as oil and gas, is reduced. Additionally or alternatively, it is also possible to use the obtained energy for internal processes in the milking plant, such as for the purpose of flushing.

A further advantage of the method according to the invention is the possibility of so-called maintenance cooling such that a separate refrigeration unit on the milk tank is unnecessary. This increases the energy efficiency and reduces maintenance and installation costs for the user.

An additional advantage of generating energy from the produced milk flow is that no substantial investment is necessary in process equipment, as is the case with biomass power plants. In addition, no complicated procedures, for instance in order to obtain permits, are required.

The energy transfer system can be placed in existing systems between a possibly already present pre-cooler and the milk tank. The pre-cooler for instance makes use of the energy from cooling of the fresh milk flow from 34 °C to 19°C in order to heat drinking water, for instance for cows. In this way the method according to the present invention can be applied in both new and already existing systems without requiring great modifications to the system. With new systems the additional advantage is achieved that conventional cooling systems for the milk tank can be given significantly smaller dimensions since the supplied milk is introduced into the milk tank when already at the storage temperature. The refrigeration unit for the milk tank need only keep the milk cool and does not therefore have to cool it. This has the additional effect that the energy consumption of this cooling system is further reduced. It has been found surprisingly that the energy which can be recovered from keeping the milk cool, i.e. without actually cooling the incoming flow, is sufficient to heat water for the purpose of flushing the plant itself. The energy required for the first and third flushing steps usually performed in practice is hereby relatively simple to recover or save. The first flushing step is usually performed when the flushing water used is at 40°C and the third flushing step when it is at 20 °C. This achieves that the energy which can be saved from keeping the milk cool in the milk tank can be used in effective manner and that no energy is needlessly lost. This contributes toward a generally more efficient use of energy by a farm with a milking system. A second flushing step is usually performed in practice at a flushing water temperature of 80°C, so that an additional gas boiler is usually used for this purpose. Similar advantages can be gained in the case of alternative flushing procedures.

A further additional advantage of generating energy from a fresh milk flow is that, by introducing the incoming milk flow into the milk tank or storage tank at substantially storage temperature, fluctuations in the milk temperature in this tank remain limited, and are even substantially absent . Surprisingly, it has been found that, with an even lower consumption of energy due to a reduction in the fluctuations in the temperature, a slightly lower mean temperature of the milk in the milk tank is a possibility, wherein the quality, including the germ count, of the stored fresh milk is (better) maintained. This results in a higher return on this milk.

By providing the energy transfer system with a heat pump heat is absorbed at a relatively low temperature of the milk, which is thereby cooled, after which this heat is preferably relinquished at a higher temperature. Achieved in this manner is that energy can be extracted from a fresh milk flow, which is here further cooled, preferably to the storage temperature in the milk tank, and energy is transferred to a heat flow preferably having a higher temperature.

The system and the method according to the invention can be applied with milking robots as well as with more conventional milking systems.

In an advantageous preferred embodiment according to the present invention the generated energy flow is provided as a hot water flow with a temperature of at least 60°C and preferably at least 65°C.

Providing the generated energy flow as a hot water flow achieves that the generated energy can be transported in effective manner to external users and/or internal users such as the flushing system. The generated energy is here of a higher value because it has been brought to a higher temperature. The {temporarily surplus) hot water flow is preferably stored in a supply vessel. It has been found here that in the above-mentioned example of a farm where one million kilograms of milk is produced per year, a supply vessel of about 1000 litres provides the energy reguirement.

The one or more external users preferably come from the group of central heating systems, boilers, tap ^' water, calf drinking apparatus and cold and heat storage. These users may be on the farm as well as the associated dwelling. Alternatively or in combination, it is further possible to also supply energy to energy users located further away, such as dwellings in the vicinity of the farm.

In a further advantageous preferred embodiment according to the present invention the heat pump is used to convert energy with a buffer vessel placed between a heat exchanger and the heat pump as energy source for the heat pump.

By providing a buffer vessel between a heat exchanger where fresh milk is cooled and the heat pump, energy is stored in the vessel. A substantially constant heat flow can hereby be delivered to the heat pump such that this heat pump can operate at an efficient working point. In the above-mentioned example of a dairy farm with an annual production of one million kilograms of milk, corresponding to more than about 3000 litres per hour, with a flow of 18 m ³ between the heat exchanger in the fresh milk flow and a ΔΤ of 5°C for the buffer vessel of 500 litres, the milk can be cooled from for instance 19°C to 4°C. The heat pump then converts the ΔΤ of 5°C, in the stated example the difference between 2°C and 7°C, of the buffer vessel into a rise in temperature in for instance an intermediate water flow with a higher temperature. This intermediate water flow is for instance at a temperature of 60°C, preferably about 65°C. A substantially continuous flow of heat can be carried to the pump through use of the buffer vessel. The heat pump is hereby used in effective manner and maximum efficiency is achieved. In the discussed example the efficiency can be increased still further by making the ΔΤ between heat exchanger and buffer vessel larger, for instance 23°C. With this temperature difference a lower flow is necessary, for instance about 4 mVhour, whereby the pump energy required can remain limited. Dimensions of the heat exchanger and optionally the buffer vessel are adapted to the operating conditions .

In a further advantageous preferred embodiment according to the present invention the method comprises the step of switching between an energy-generating and an inactive mode using a switching system.

By switching between an energy-generating mode, wherein use is made of an energy transfer system, and an inactive mode wherein use is for instance made of more conventional pre-coolers and tank refrigeration units without activated energy system according to the invention, this subject to outside temperatures and energy requirements, a choice can be made in effective manner between processes to be operated. Switching preferably comprises of detecting an energy demand from the one or more users and subsequently deciding on the desired mode of the switching system. The switching system is preferably provided with one or more mixing valves, for instance between heat exchanger in the milk supply conduit and the buffer vessel, between the buffer vessel and the heat pump and between the heat pump and the supply vessel. These mixing valves are advantageous during startup of the plant, among other purposes for heating conduits and not allowing any unnecessary energy loss during startup.

In a further advantageous preferred embodiment according to the present invention the fresh milk flow is preferably carried as a substantially constant flow to the energy transfer system.

Realizing a preferably substantially continuous fresh milk flow achieves that in fixed conditions this energy transfer system can be operated in efficient manner. A continuous fresh milk flow can be realized in effective manner by providing a small buffer in the fresh milk conduit. By providing this buffer and the thereby realized, preferably substantially constant milk flow it is even possible to dispense with the buffer vessel, since the heat pump can already be operated at an efficient working point due to the constant flow. A smaller buffer vessel can optionally be provided.

In a further advantageous preferred embodiment according to the present invention energy is generated with solar collectors combined with the energy generated from a fresh milk flow.

Combining generation of energy from a fresh milk flow with the use of solar energy makes it possible to realize a relatively sustainable farm operation. An additional advantage of such a combination is that dependencies on weather conditions and other factors is greatly reduced.

The dependence on external conditions can be further reduced by storing a part of the generated energy flow, which at the moment of generation is surplus to requirement, in a cold and heat storage. Energy generated during the summer months can hereby be used in the winter months when the energy requirement is usually greater, for instance for central heating systems. Such a storage thereby has a long-term function, while a preferably provided supply vessel has a shorter-term function.

In a currently preferred embodiment there is also provided, in addition to a flushing tank, an extra-high-temperature flushing tank for use for the purpose of flushing the tank. A practical and energy-effective flushing is hereby realized.

The present invention further relates to an energy system, comprising :

a supply conduit for a fresh milk flow connected to a milking plant;

an energy transfer system connected to the supply conduit and comprising a heat pump for cooling the fresh milk flow and generating an energy flow; and

an energy transport system connected to the energy transfer system for storing and/or transporting energy to one or more external and/or internal users. Such a system makes it possible to perform a method as described above and thereby provides the same effects and advantages as described in respect of the method.

The energy system preferably comprises a switching system for switching between an energy-generating active mode and an inactive mode as described above. The energy system is preferably kept almost continuously in the active mode. In an advantageous embodiment the energy system according to the invention further comprises a coupling for coupling the system to an external energy-generating and/or energy storage system. An example hereof is the use of solar collectors and/or PV panels as generating system, and/or cold and heat storage as storage system. Solar collectors can be used to heat water further in the supply vessel and PV panels can for instance be used to supply energy for the pumps in the system.

The energy system preferably comprises a milk buffer placed in a fresh milk flow conduit. Such a relatively small milk buffer makes it possible to convert the milk produced with the milking machine or milking robot into a substantially continuous flow, whereby it becomes possible to adapt the energy system in effective manner thereto. This further increases the efficiency of this system.

Further advantages, features and details of the invention are elucidated on the basis of preferred embodiments thereof, wherein reference is made to the accompanying drawings, in which: figure 1 shows a process diagram of a conventional system; figure 2 shows a process diagram of the system according to the invention;

figure 3 shows the diagram of the system of figure 2 with additional systems.

A conventional system 2 (figure 1) realizes a fresh milk flow 4 from dairy cattle 6. Fresh milk flow 4 is optionally reduced in temperature using pre-cooler 8 to a slightly cooled milk flow 10 which is carried to milk tank 12. In order to cool milk flow 10 in tank 12 use is made of a cooling system 14 with a first heat exchanger 16 and optionally a second heat exchanger 18 for the purpose of heating water in a flushing tank 20 and optionally providing a supply point 19 for cold water. Flushing tank 20 is used as buffer for transport of heated water for the purpose of flushing the whole milking plant 2, or components thereof, via conduit 21. In a usual second flushing step use is also made of an extra-high-temperature flushing tank 22 which makes use of gas heating in the form of a gas boiler to heat flushing water to about 80°C using conduit 23. An alternative to the gas boiler is to provide a gas water heater suitable for the stated temperature ranges. When the flushing water is at temperature, residual heat is in practice usually discharged via heat exchanger 16 to the environment using fans.

System 24 (figure 2), with which energy usable by external users can be generated, begins at fresh milk flow 4 from cows 6, wherein flow 4 is optionally carried via pre-cooler 8. In system 24 pre-cooler 8 is optionally used to cool the fresh milk flow 4 from 3 °C to 19°C, and the energy generated hereby is used to heat groundwater flow 26 to form drinking water flow 28 for cows 6. In the case of an annual production of one million kilograms of milk per year, this corresponds to a slightly cooled fresh milk flow 10 of about 3063 litres/hour. Flow 10 is carried to the energy-generating system 30. Flow 10 is here cooled in heat exchanger 32 from 19°C to 4°C, and carried as cooled milk flow 34 to milk tank 12 at a temperature of about 4°C. Provided on the other side of heat exchanger 32 is a 500-litre, or alternatively an 800-litre buffer vessel 36, wherein about 18 m ³ water per hour is pumped between heat exchanger 32 and vessel 36 and, at least in the shown embodiment, heated from 2°C to 7°C in heat exchanger 32. A supply conduit 38 and return conduit 40 are provided for this purpose between heat exchanger 32 and buffer vessel 36. As stated above, the required water flow can be reduced to for instance 4 m ³ per hour between heat exchanger 32 and vessel 36 by employing a greater temperature difference of for instance 21°C. For the above stated reasons mixing valves 148,150 are also provided between respectively heat exchanger 32 and buffer 36, and buffer 36 and heat pump 40. Information/control signals 152 and 154 connect respective valves 148,150 to control system 96.

Buffer vessel 36 is used as energy source for heat pump 40 which is connected to buffer vessel 36 with a supply conduit 42 and a return conduit 44. On this side of heat pump 40 use is likewise made in the shown embodiment of a difference in temperature of 5°C, i.e. the difference between 2°C in conduit 42 and 7°C in conduit 44.

Heat pump 40 is connected to diverse sensors for optimum control of heat pump 40, including sensors and information flows 122 to buffer vessel 36, information flow 124 to conduit 44, information flow 126 to flushing tank 20, control signal 128 to valve 46 in conduit 48 and the conditions in conduit 48 via signal 130.

In a flush energy mode heat pump 40 is connected via valve 46 and conduits 48,50 to heat exchanger 52. Conduit 54 forms the connection in opposite flow direction in this mode. Heat pump 40 produces a difference in temperature of 5°C, i.e. about 45°C in conduits 48,50 and 50°C in conduit 54. On the other side of heat exchanger 52 cold water is supplied with conduit 56 at about 10°C and heated to about 45°C in heat exchanger 52, and subsequently carried via conduit 58 to flushing buffer 20.

In another mode of energy system 30 external energy is generated, wherein conduit 48 is connected via valve 46 and conduit 60 to open distributor 62 and in return flow to return conduit 55. In the shown embodiment a difference in temperature of about 5°C is also realized between conduits 48 and 55 in this mode. The temperature difference is converted in open distributor 62 into a temperature difference of 20°C between discharge conduit 64 and return conduit 66, which in the shown embodiment are connected to a supply vessel 68 of about 1000 litres. In the shown embodiment it is possible, in addition to heating from the fresh milk flow, to optionally heat water in vessel 68 additionally using kettle 70 via conduit is 72,74. Vessel 68 is connected via conduit 76 to the external users, including a boiler 78, tap water of the farm 80, tap water for the attached dwelling 82, central heating for the office of farm 84, central heating 86 for the attached dwelling and calving accommodation 88.

In an inactive mode of the system a short-circuit flow is optionally possible between slightly cooled milk flow 10 and cooled milk flow 34 via valves 90,92 and conduit 94. Switching of the different valves between the different modes is realized with control system 96 which is connected to the relevant components by means of various operating, control and measuring signals. Alternatively, conduits 10 and 34 can be connected via heat exchanger 32, wherein heat exchanger 32 is inactive. Valves 90, 92 and conduit 94 are hereby not necessary.

In the shown embodiment control system 96 is for instance connected to a valve 98 via signal 100 for discharging a flow out of vessel 68 via open distributor 62. The conditions in vessel 68 are fed as information flow to control system 96 using sensors 102,104 and respective measuring signals 106, 108. Provided in the shown embodiment in conduit 66 is an additional valve 110 which can be controlled using control signal 112. Valve 110 is particularly relevant during startup of the system for preventing heat being lost from supply vessel 68 through the still cold conduits. Through circulation over valve 110 the heat is retained in vessel 68 and conduits can be heated. The conditions in conduit 64 are fed to control system 96 using sensor 114 and information signal 116. The conditions in conduit 55 are also measured by sensor 118 and fed to control system 36 using information signal 120.

It will be apparent that it is possible to combine the various control signals, measuring signals or other signals in one control system or to integrate them in a coordinated system for the whole farm.

A more comprehensive system 132 (figure 3) is based substantially on system 24 (shown in figure 2) with some additional systems. Surplus hot water from vessel 68 can here be stored via conduit 136 in a cold and heat storage 138 in times of energy surplus, and be fed back via conduit 140 to for instance vessel 68 in times of energy shortage. An alternatively embodied option or one embodied in combination therewith heats water in buffer vessel 68 using solar collectors and/or PV panels 142 via conduits 144,146 via sun 134. Efficiency can hereby be further increased, for instance through use of generated electricity to operate the pumps (not shown) in the system.

Produced milk 4 is cooled using energy system 30, optionally via a pre-cooler 8, to a cooled fresh milk flow 34 and carried at the substantially desired storage temperature to milk tank 12. The generated energy is preferably carried using a hot water flow via a number of subsystems to buffer vessel 68. From vessel 68 energy is carried via conduit 76 to further users

78,80,82,84,86,88. It will be apparent that other optional external users are also possible. This optional addition makes it possible to switch between external supply of energy and internal use of energy from the fresh milk flow for flushing of for instance the milking plant.

The present invention is by no means limited to the above described preferred embodiments thereof. The rights sought are defined by the following claims, within the scope of which many modifications can be envisaged. It will be apparent that the stated dimensions and utilized temperatures and flows depend on the specific situation in which the system and the method according to the invention are applied. Relevant parameters here are for instance the required conduit lengths and the use of a milking robot or conventional milking system. In addition to use with dairy cows, it is of course also possible to apply this system to milk goats or other milk flows. It is also possible to apply the invention in equivalent manner on flows other than milk flows. Combinations with other systems, such as wind turbines, are also possible.