Method and system for flexible heating plant by integration of biomass heating system and electrical heat pump system

Abstract

The invention relates to a flexible method and a system for production of hot water (district heating) by integration of a biomass heating system and an electrical heat pump system, so that district heating can be produced in an optimal way – with high efficiency via the heat pump system and / or the biomass heating system. Such high efficient and fuel flexible system is especially attractive when fuel- and electricity prices are varying.

Description

[0001] 85335PC01

[0002] 1

[0003] Method and system for flexible heating plant by integration of biomass heating system and electrical heat pump system

[0004] The invention relates to a flexible method and a system for production of hot water (district heating) by integration of a biomass heating system and an electrical heat pump system, so that district heating can be produced in an optimal way - with high efficiency via the heat pump system and / or the biomass heating system. Such high efficient and fuel flexible system is especially attractive when fuel- and electricity prices are varying.

[0005] District heating systems - where warm water is distributed to houses, apartment houses, offices, industries and cooled (where it releases energy) and hereafter returned to the heating plant - are well known.

[0006] Present invention is an optimized and flexible way of producing district heating from biomass and electricity.

[0007] Reference is made to WO27036236A1, which describes a biomass heating system where heat can be recovered from hot gas produced in a thermal reactor (1), by injecting water into the gas at one or more injection zones (4) in such an amount and in such a way that the gas temperature due to water evaporation is reduced to below 400°C, preferably below 300°C, possibly below 150 - 200°C, and the gas dew point becomes at least 60°C, preferably at least 70°C, possibly 80 or 85°C. The gas can then be led through a condensing heat exchanger unit (8), where at least some of the gas contents of water vapour are condensed, and the condensing heat can be utilized for heating of a stream of fluid, mainly water.

[0008] Reference is further made to US11821637, which describes an energy-saving system using electric heat pump to recover flue gas waste heat for district heating using a flue gas waste heat recovery tower to absorb the sensible and latent heat in the high-temperature flue gas by direct contact heat and mass transfer. The circulating water is sprayed from the top and the flue gas flows upwards in the tower. The electric heat pump is indirectly connected with circulating water through the anti-corrosion and high-efficiency water-water plate heat exchanger. The return water of the heat-supply network enters the electric heat pump through the anti-corrosion and high-efficiency water-water plate heat exchanger 85335PC01

[0009] 2 and exchanges heat indirectly with the high-temperature circulating water. The electric heat pump uses the electric energy of the power plant as the driving power.

[0010] Reference is further made to EP3064841A1, which describes a gas-steam combined cycle centralized heat supply device and a heat supply method. The gas-steam combined cycle centralized heat supply device comprises a gas-steam combined cycle system, a heating network return water heating system and a thermal station, and the gas-steam combined cycle system is connected with the thermal station through the heating network return water heating system; the gas-steam combined cycle system comprises a gas turbine, a waste heat boiler, a direct contact type flue gas condensation heat exchanger and a steam turbine; the gas turbine is connected with the waste heat boiler, and the waste heat boiler is connected with the direct contact type flue gas condensation heat exchanger and the steam turbine; the thermal station comprises a hot water type absorption heat pump and a water-water heat exchanger; the heating network return water heating system comprises a steam type absorption heat pump for recovering flue gas waste heat and a steam-water heat exchanger; and the steam type absorption heat pump for recovering flue gas waste heat is respectively connected with the steam-water heat exchanger, the direct contact type flue gas condensation heat exchanger, the waste heat boiler, the steam turbine and the thermal station, and the steam-water heat exchanger is respectively connected with the waste heat boiler, the steam turbine and the thermal station. The present invention can be widely applied to the industry of power plant waste heat recovery.

[0011] SUMMARY OF THE INVENTION

[0012] In a first aspect, the invention relates to an energy plant for producing warm forward water to a district heating system, the energy plant comprising a biomass heating system and an electrical heat pump system, wherein:

[0013] • the energy plant is configured to receive from the district heating system, return water and to deliver forward water having a supply temperature being a higher temperature than a temperature of the return water to the district heating system; 85335PC01

[0014] 3

[0015] • the biomass heating system comprises: o a furnace for production of hot flue gas by conversion of carbonaceous fuel, preferably the hot flue gas has a temperature larger 600°C and preferably lower than 1200°C, o a boiler system configured to cool the hot flue gas to a cooled flue gas having a temperature, preferably, in the range of 100-300°C by transferring heat of the hot flue gas to a hot water circuit,

[0016] • the electrical heat pump system comprises: o an evaporator, a compressor, a condenser and an expansion valve, the condensor is configured to selectively heat the return water to provide heated return water,

[0017] • the biomass heating system comprising o a first heat exchanger system configured to selectively further heat the heated return water or selectively heating the return water by transferring heat from the hot water circuit, preferably in amount to keep a temperature in the hot water circuit above 90°C.

[0018] "Supply water" as used herein may also be referred to as forward water.

[0019] "System" as used herein e.g. in connection with heat exchanger system, refers to that such a system may comprise a single unit, e.g. a single heat exchanger, or a number of heat exchangers which is combined into a system for heat exchange.

[0020] "Heat exchanger" as used herein preferably refers to a non-mixing heat exchanger in which a warmer and colder fluid are separated by one or more walls so that the warmer and colder fluids do not physically come into contact or mix, and in which heat from the warmer fluid is transferred to the colder fluid is through the one or more walls.

[0021] Media" as used herein is used to reference a fluid.

[0022] Preferred embodiments of the invention relates to district heating systems, dedicated to provide district heating. 85335PC01

[0023] 4

[0024] Due to increased production of electricity from wind and solar, it has become political acceptable and feasible to use electricity for district heating, and electrical heat pumps for district heating is now being introduced in the district heating market.

[0025] As production of electricity from wind and solar is unstable the price of electricity become unstable: Huge variations of electricity prices have been seen the latest years and this tendency is expected to continue.

[0026] District heating companies therefore seek energy efficient and flexible solutions which can operate with high efficiency on electricity and / or biomass and / or other fuels.

[0027] Preferred embodiments of the present invention relate to such a flexible and high efficient heating plant herein also referred to as an energy plant, which typically has been optimized for high efficiency of both the biomass heating system and the electrical heat pump system by integrating an electrical heat pump system with a biomass heating system.

[0028] Efficiency of biomass heating plants can be increased by adding a flue gas condenser system after the boiler. The efficiency of the flue gas condenser become higher the more the flue gas can be cooled, whereby more of the latent energy of the flue gas is recovered.

[0029] As realized by the inventors, in order to cool the flue gas preferably as much as possible a heat pump system can be be added to the system, preferably an absorption heat pump system or an electrical heat pump system.

[0030] As realized by the inventors, the efficiency of an electrical heat pump becomes higher when the temperature difference between the warm side (condenser side) and the cold side (evaporator side) becomes as small as possible. The maximum theoretical efficiency of the coefficient of performance (COP) is:

[0031] COPmax=Tcondensor / (Tcondensor-Tevaporator). 85335PC01

[0032] 5

[0033] Electrical heat pumps can in preferred embodiments use various media to move energy from condenser to evaporator such as ammonia, CO2 or other.

[0034] In preferred embodiments, an energy plant is provided in which a biomass heating system is integrated with an electrical heat pump system in ways to make the overall energy plant efficient and flexible.

[0035] When both the heat pump system and the biomass heating system are in operation:

[0036] • The flue gas condenser of the biomass heating system can be cooled both by district heating water and by the evaporator side of the heat pump system, thus ensuring coldest possible water to the flue gas condenser, thus ensuring high efficiency of the biomass heating system.

[0037] • When the heat pump system can receive warm water from the flue gas condenser the efficiency of the heat pump system (the COP) will increase.

[0038] • Two stage hot water production increase efficiency: When the heat pump system produces an intermediate district heating temperature (also referred to herein as heated return water) which is further heated by hot water from the biomass boiler the COP of the heat pump system will increase even further.

[0039] When the biomass heating system is in operation and heat pump system is not in operation:

[0040] • The biomass heating system operates as a stand-alone biomass heating system with flue gas condenser: The flue gas condensation produces a flue gas condensate which is cooled by indirect heat exchange of the cold return water of the district heating system. The district heating water is further heated by the hot water from the boiler.

[0041] When the heat pump system is in operation and the biomass heating system is not in operation:

[0042] By having air-coolers (or other heat source) for the evaporator side of the heat pump system, the heat pump system can produce district heating without the biomass heating system is in operation.

[0043] BRIEF DESCRIPTION OF THE FIGURES 85335PC01

[0044] 6

[0045] The present invention and in particular preferred embodiments thereof will now be described in more detail regarding the accompanying figures. The figures show ways of implementing the present invention and are not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

[0046] Figure 1 schematically illustrates components of a preferred embodiment of a energy plant with integration of a biomass heating system with an electrical heat pump system. In Figure 1, material flows and components are numbered by numerals.

[0047] Figure 2 illustrates a maximum output from a preferred embodiment of an energy plant;

[0048] Figure 3 illustrates maximum COP by utilizing a scrubber condensate;

[0049] Figure 4 illustrates efficiencies of a preferred embodiments of the present invention compared to stand-alone heat pump

[0050] Figure 5 illustrates a energy plant output of a preferred embodiment with 10°C evaporator temperature.

[0051] DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0052] Reference is made to Figure 1. As seen in Figure 1, various processes and flow of media, such as water flue gas and refrigerant are identified by a reference numeral. The processes and flow are described in the following with reference to the numerals used in Figure 1. Herein, "hot" "warm" and "cold" are used to indicated temperatures relatively to each other where "hot" has a higher temperature than "warm" which has a higher temperature than "cold". Dotted lines in Figure 1 indicates alternative streams and an alternative stream may be a bypass or additional flows.

[0053] As illustrated in Figure 1, a number of options are available for heating the return water 31. In embodiments of an energy plant for producing warm forward water to a district heating system, the energy plant comprises a sub-set of the what is 85335PC01

[0054] 7 disclosed in Figure 1. A number of such sub-sets are detailed below as preferred embodiments.

[0055] A preferred embodiment of an energy plant has a biomass heating system and an electrical heat pump system which are indicated in Figure 1 by dotted lines forming boxes. The energy plant is configured to receive from a district heating system, return water 31 and to deliver forward water 38 having a supply temperature being a higher temperature than a temperature of the return water 31. The forward water is supplied to the district heating system.

[0056] In the illustrated embodiment, the biomass heating system comprises a furnace 2 for production of hot flue gas 3 by conversion of carbonaceous fuel. The temperature of the hot flue gas 3 is preferably larger 600°C and preferably lower than 1200°C.

[0057] In the biomass heating system a boiler system 4 is provided. The boiler system is configured to cool the hot flue 3 gas to a cooled flue gas 5. The temperature of the cooled flue gas 5 is preferably within the range of 100-300°C. The hot flue gas 3 is cooled by transferring heat of the hot flue gas 3 to a hot water circuit 18, 20. In Figure 1, reference sign 18 refers to a pipe feeding water to the first heat exchanger system 19, and 20 refers to a pipe feeding water from the first heat exhanger system 19 back to the boiler 4. The function of the first heat exchanger 19 system will be detailed below.

[0058] The temperature at the inlet of the hot water circuit 18, 20, which is at the inlet of pipe 18 is preferably between 100-200°C and the temperature at the outlet of pipe 20 is preferably larger than 90°C, although being lower than the temperature at the inlet of the hot water circuit.

[0059] The electrical heat pump system comprises an evaporator 21, a compressor 22, a condenser 23 and an expansion valve 24. The heat pump system operates in a way where heat from a low temperature reservoir, such as ambient air, is transported to a reservoir having a higher temperature. In an embodiment, the higher temperature reservoir is return water 31, which may have a temperature between 40-60°C. This is provided by the condensor 23 is configured to selectively 85335PC01

[0060] 8 heat the return water 31 to provide a heated return water 34. As illustrated in Figure 1, the return water 31 may be split into return water 32 to the heat pump system and return water 33 for the biomass heating system. In the heat pump condensor 23 the returnwater 32 is heated and exit the condensor 23 warmer at 34 as heated return water. "Selectively heat" the return water 31 refers to that preheating of the return water 31 can be selected, and if not selected, the return water is not fed into the condensor 23 or the electrical heat pump system is not in operation so that no heat is transferred to the return water during passage of the condensor 23. Such a selection can be provided by a valve regulating the flow into the condensor 23, and having a setting in which no return water is fed into the condensor 23 and / or by controlling the heat pump system to be not in operation.

[0061] The heated return water 34 is in an embodiment futher heated by first heat exchanger system 19 being configured to selectively further heat the heated return water 34 (heated by the condensor 23). Hence, when the return water is heated by the heat pump system and further heated by the biomass heating system, the return water heated by the heat pump system may be referred to as preheated, such as preheated return water. As illustrated in Figure 1, heat is transferred from the hot water circuit 18, 20 to the heated return water by the first heat exchanger system 19. The amount of heat transported to the heated return water is typically in an amount keeping a temperature in the hot water circuit 18, 20 above 90°C. This may be controlled by controlling the flow rate and / or temperature of the water flowing in the hot water circuit 18, 20.

[0062] In an embodiment, where the return water 31 is not heated by the heat pump system, the return water is heated by the first heat exchanger system 19. Not heated by the heat pump system can be accomplished by not feeding return water into the condensor 23 or by the heat pump system not being in operation as detailed above. Hence, the first heat exchanger system 19 is configured to selectively further heating the heated return water after the condensor 23 or selectively heating the return water without the return water being heated by the heat pump system. Such a selection may be provided a valve regulating the flow of return water to the condensor 23 and / or the first heat exchanger system 19. 85335PC01

[0063] 9

[0064] In other embodiments, the return water 31 is divided into two fractions, where a first fraction 32 flows into the heat pump system for preheating providing a first fraction of heated return water. A second fraction 33 flows into second heat exchanger system 13 for heating. Heat for heating of the second fraction by the second heat exchanger system 13 comes from flue gas condensation 6 providing a flue gas condensate 11 which flows into the second heat exchanger system 13 and delivers heat to the second fraction of return water to provide a second fraction of heated return water 36. The first and the second fractions of heated return water are mixed and heated in the first heat exchanger system 19. Alternatively to mixing the first and second fractions of heated return water, the first fraction of heated return water may be mixed into forward water 38 as illustrated by dotted arrow with reference numeral 37.

[0065] In addition, a fraction 35 of the heated return water after the condensor 23 of the heat pump system may be mixed with the second fraction of return water as illustrated in Figure 1 by dotted line labelled 35.

[0066] The biomass heating system may in an embodiment further comprise a third heat exchanger system 13 as illustrated in Figure 1. In an embodiment comprising such a third heat exchanger system 13, the flue gas condensate 11 after being cooled by the second heat exchanger system 13, leaves the second heat exchanger system 13 as a cooled condensate 14. The cooled condensate 14 is further cooled in the third heat exchanger system 16, and the further cooled condesate 17 is returned to the flue gas condensation system 6.

[0067] As shown in Figure 1 with dotted lines, a fraction or all of the flue gas condensate 11 from the flue gas condensation system 6, may bypass the second heat exchanger system 13 as a bypass stream 12. Further, a fraction or all of the cooled condensate 14 may bypass the third heat exchanger system as a bypass stream 15.

[0068] The third heat exchanger system 16 is in an embodiment fluidicly connected with the evaporator 21 of the heat pump system - see Figure 1 for such a fluidic connections. Hence, in such an embodiment, the cooled condensate is a low temperature reservoir for the heat pump system. The cooled condensate 14 heats up a cold heat transfer media 25 flowing from the evaporator to the third heat 85335PC01

[0069] 10 exchanger system 16 and the heated transfer media 30 flows into the evaporator 21 of the heat pump system as illustrated.

[0070] Alternatively or in combination with the cooled condensate 14 being a low temperature reservoir for the heat pump system, a fourth heat exchanger system 28 can be implemented. This fourth heat exchanger system 28 may operate either as a heat source in addition to the cooled condensate 14 and / or used as the only heat heat source for the evaporator 21.

[0071] In the embodiment of Figure 1, the heat exchanger system 28 is used for preheating the cold transfer media 25, by directing a fraction or all of the cold transfer media 25 through the fourth heat exchanger system 28 as stream 26. After heating of the stream 26, the heated stream 29 is mixed into the cold transfer media 25. If all the cold transfer media is directed through the fourth heat exchanger system 28, all of the heated cold transfer media is fed into the third heat exchanger system 16. Heat for heating the cold transfer media by the fourth heat exchanger system 28 may come from e.g. outside air, sea water and / or excess industrial heat.

[0072] In an embodiment, the biomass heating system comprising a sixth heat exchanger system 9. Such a sixth heat exchanger system is used to heat the flue gas after the flue gas condensation, and aims at raising the temperature of the flue gas before exit to the surroundings by a chimney as otherwise disclosed herein.

[0073] In the various embodiments of the invention, the heat pump system and the biomass heating system can be operated in different manners. For instance, the heat pump system can be in operation while the biomass heating system is not in operation or vice versa. This provide a high degree of flexibility as use of energy for production of heated return water can be optimized. For instance, if electricity comes at a high cost and biomass comes at a low cost, production of forward water can be based on biomass with the heat pump turned off. On the other hand, if electricity comes at a low cost and biomass comes at high cost, production of forward water can be based on electrical power with the biomass heat system turned off. These two examples represent "end points" in an 85335PC01

[0074] 11 optimization, and optimization of the use of the heat pump system and the biomass heating system is preferably carried out setting the heat pump system and the biomass heating system in operation being less than maximum productions offered by the heat pump system and the biomass heating system. Such optimization can advantageously be carried out in combination with the different options of heating the return water as detailed herein.

[0075] In embodiments, where the heat pump system is in operation and the biomass heating system is not in operation, the return water 31 is heated by by the condensor 23 and bypasses the first heat exchanger system 19 as indicated by reference sign 37 in Figure 1. Alternatively, the return water 31 heated by the condensor 23 flows through the first heat exchanger system 19 without significant heat transport. Hence, the return water 31 heated by the condensor 23 is used as forward water 38. The heat for heating the return water may be provided by the fourth heat exchanger system 28, by extracting heat from e.g. outside air, sea water and / or excess industrial heat, as disclosed above.

[0076] In embodiments, where the heat pump system is not in operation and the biomass heating system is in operation, the return water 31 is not heated by the heat pump system and flows towards the second heat exchanger system 13. The return water heated by the second heat exchanger system 13 flows into the first heat exchanger system 1 for further heating and leaves the first heat exchanger system 1 as forward water 38. The second heat exchanger system 13 may be bypassed, so that the return water flows directly to the first heat exchanger system 19.

[0077] In embodiments, where both the heat pump system and the biomass heating system are in operation, heating of the return water may be said to be a serial heating of the return water, wherein the return water is first heated by the heat pump system and subsequently heated by the biomass heating system. As detailed above, a fraction or all of the return water may be heated by the heat pump system, and also in such embodiments, the heating may be referred to as a serial heating. Such a serial heating has shown to improve the COP of the heat pump system. 85335PC01

[0078] 12

[0079] In embodiments, where both the heat pump system and the biomass heating system are in operation, return water 31 may be split into a fraction heated by condensor 23 of the heat pump system to provided heated return water 34, and a fraction flowing into and heated by the second heat exchanger system 13 where the fraction is heated by the flue gas condensate as disclosed herein. The return water heated by the second heat exchanger system 13 is mixed with the heated return water from the condensor 23 and flows into the first heat exchanger system 1 for further heating by the hot water circuit 18, 20 (as disclosed hereing) and leaves the first heat exchanger system 1 as forward water 38.

[0080] Kindly observe that Figure 1 and the following description refer to preferred embodiments and are not be considered limiting to the scope of the invention. In the following, the labelling used in Figure 1 is detailed.

[0081] 1 : Biomass input. Biomass is added to the biomass heating system. The biomass may be virtually all types of carbonaceous materials originating from plant, animals and / or waste products.

[0082] 2: Furnace. In the Furnace is the biomass converted into hot flue gas in a thermal process, such as gasification or combustion by adding reaction agents, such as oxygen, air and / or water.

[0083] 3: Flue gas - hot. The fully reacted flue gas, preferably, consists of more than 90% CO2, H2O, N2 and 02. The temperature is, preferably, between 600 - 1200°C.

[0084] 4: Boiler. Major part of the heat (such as 50-90%) from the hot flue gas is, typically, transferred to a liquid media, such as water, in a boiler or heater type component. In some embodiments, the furnace 2 and the boiler 4 are integrated into one component.

[0085] 5: Flue gas - warm. The cooled flue gas leaves the boiler, preferably at a temperature of 100-600°C. 85335PC01

[0086] 13

[0087] 6: Flue gas condensation. The flue gas is further cooled, preferably to 0-80°C in a flue gas condensation system also referred to herein as a flue gas condenser. The heat is transferred from the flue gas to a liquid media, such as condensate from the flue gas. The flue gas condenser can be of one or several stages. The flue gas condensate will typically contain acids from the flue gas and pH can be low such as between 2-6. It can be an advantage to neutralize the condensate by adding an alkaline substance to the condensate, for example sodium hydroxide (NaOH). This will increase the lifetime of components in contact with the condensate or lower the cost.

[0088] 7: Flue gas outlet. The cold flue gas exits the system and can be led to the atmosphere via a stack.

[0089] 8: Flue gas bypass (optionally). All or part of the cold flue gas can be reheated before emitted to the atmosphere. Advantages can be to avoid flue gas falling to the ground and / or that flue gas plume becomes less visible. The flue gas temperature may be increased with 5 - 30°C in the reheat system.

[0090] 9: Fifth heat exchanger system for flue gas reheat. A heat exchanger transfers heat from the reheat media to the flue gas.

[0091] 10: Heat input for reheat system (fifth heat exchanger system 9). A hot media supplies heat for the reheat system. The hot media should preferably be more than 10°C warmer than the cold flue gas. The media can be liquid, gas or air.

[0092] 11: Flue gas condensate - hot. The hot media (30-80°C) is pumped from flue gas condensation system to one or several heat exchangers.

[0093] 12: Flue gas condensate bypass (optionally). Part of or all the hot media may bypass second heat exchanger system 13 to boost the temperature and power of third heat exchanger system and give more power to the heat pump system.

[0094] 13: Second heat exchanger system for flue gas condensate. A heat exchanger transfers heat from the flue gas condensate to the district heating system (return 85335PC01

[0095] 14 water 31). The amount of heat transferred from the flue gas condensate can be 0- 100%, where rest of the heat is transferred by third heat exchanger system 16.

[0096] 14: Flue gas condensate - warm. The warm media (typically between 30-80°C) is discharged from the second heat exchanger system 13.

[0097] 15: Flue gas condensate - bypass. Part of the warm flue gas condensate (typically between 0-90%) can be returned to the flue gas condensation system. It can be an advantage to build the flue gas condensation system in two stages:

[0098] • a warm stage which receive warm flue gas condensate from the second heat exchanger system 13 (from 14), a cold stage which receive cold flue gas condensate from the third heat exchanger system 16 (from 17).

[0099] These two stages can be separate condenser reactors or integrated into a two- stage condenser.

[0100] 16: Third heat exchanger system 16 for exchanging heat between the flue gas condensation 6 and evaporator 21 of the heat pump system.

[0101] In preferred embodiments, the second heat exchanger system 13 is configured to transfer heat from the flue gas condensate 11 to the district heating system (return water 31). In the second heat exchanger system 13 is the flue gas condensate 14 cooled to a lower temperature than then inlet temperature 11.

[0102] At least part of the cooled condensate from second heat exchanger system 13 may be supplied to heat exchanger system 16.

[0103] 17: Flue gas condensate - cold. The cooled flue gas condensate is returned to the flue gas condensation system.

[0104] 18: Boiler media - hot. The hot media preferably having a temperature between 80-400°C. The hot media, such as oil, pressurized water or steam, is pumped to first heat exchanger system 19. 85335PC01

[0105] 15

[0106] 19: First heat exchanger system - boiler. A heat exchanger transfers heat from the hot boiler media to the district heating system (return water 31). In some cases the heat exchanger can be omitted and the district heating media can flow directly through the boiler. The systems can however have different types of media, such as water and oil, or be designed for different pressure levels and must be isolated from each other.

[0107] 20: Boiler media - cold. The cooled boiler media preferably having a temperature between 60-300°C. The cold boiler media, such as oil, pressurized water or steam, is pumped back to boiler. In preferred embodiments, the boiler media labelled hot or cold is the same media, preferably flowing in a recirculating manner.

[0108] 21: Heat pump system - evaporator. Heat is transferred from the heat source to the coolant media, such as ammonia, whereby the coolant evaporates. The temperature of fluid leaving the evaporator and entering the heat exchanger 27 and / or third heat exchanger system 16 may be, as a non-limiting example, 0°C.

[0109] 22: Heat pump system - compressor. The pressure of the gaseous coolant media is increased by the means of a compressor which uses electricity. The compressor can consist of several stages. It can be an advantage to have one stage at a low pressure level and another stage at a higher pressure level to decrease plant cost and operational cost. For example, first stage can be a 25 bar system delivering appoximately 55°C water which is boosted with a 40 bar system delivering approximately 72°C.

[0110] 23: Heat pump system - condenser. Heat is transferred from the coolant media to the district heating media (return water), whereby the coolant condenses.

[0111] 24: Heat pump system - expansion valve. The pressure of the coolant media is reduced through an expansion valve.

[0112] 25: Heat transfer media - cold. The cold heat transfer media, such as water - or a media which preferably has lower freezing point than 0°C, is pumped from the 85335PC01

[0113] 16 heat pump system to the biomass heating system. The temperature is preferably -20°C to +30°C.

[0114] 26: Heat transfer media - cold - bypass forward (optionally). Part of or all the cold heat transfer media can be pumped to a secondary heat source.

[0115] 27: Heat exchanger - secondary heat source (optionally). Part or all of the cold heat transfer media can be preheated by a secondary heat source.

[0116] 28: Fourth heat exchanger system for a supplementary heat source (optionally). Supplementary heat can be added in cases where the biomass heating system cannot supply enough heat for the heat pump system or where it is economically beneficial to add a secondary heat source. The heat source could for instance be outside air, sea water, excess industrial heat. The temperature of the heat source, e.g. outside air, may be, as a non-limiting example, 3°C.

[0117] 29: Heat transfer media - preheated - bypass return (optionally). The preheated media is pumped to the biomass heating system.

[0118] 30: Heat transfer media - warm. The warm heat transfer media is pumped from the biomass heating system to the heat pump system. The temperature is preferably 10-60°C.

[0119] 31: District heating - cold return - source. The biomass heating system and heat pump system is connected to a district heating system. A cold media, such as water (return water), is pumped from the district heating system and heated in the biomass / heat pump system before it is pumped back to the district heating system. The cold media may be between 0-70°C.

[0120] 32: District heating system - cold return. Part of or all the cold district heating media (return water) is optionally pumped to the heat pump system condenser.

[0121] 33: District heating system- cold return. Part of the cold district heating media (return water) may bypass the heat pump system and pumped to the "Heat exchanger flue gas condensate" - second heat exchanger system 13. 85335PC01

[0122] 34: District heating system - preheated. When the district heating media is preheated by the heat pump system it is pumped to the biomass heating system. The temperature is, preferably, 40-90°C. 34 is also referred to as heated return water.

[0123] 35: District heating system - preheated - bypass (optionally). Part of or all of the

[0124] Cdonenser preheated district he ttemperaureating media (heated return waster) may be pumped to "Heat exchanger flue gas con °Cdensate" - second heat exchanger system 13 to be heated further.

[0125] 36: District heating system - warm. After the district heating media has been warmed by the flue gas condensation system it is pumped to "Heat exchanger - boiler" - first heat exchanger system 19 for further heating.

[0126] 37: District heating system - preheated - bypass (optionally). If the district heating media has been sufficiently heated by the heat pump system it can (partly or wholly) be pumped directly to the district heating system end-consumers.

[0127] 38: District heating system - hot. The hot district heating media (forward water) is pumped to the end-consumers. Temperature is preferably between 40-120°C.

[0128] Scenarios: 10 MW Biomass heating system and 15 MW heat pump system

[0129] A major benefit of preferred embodiments is to increase the efficiency of the heat pump system (CP). It was previously described that the maximum theoretical efficiency of the coefficient of performance (COP) is:

[0130] COPmax=Tcondensor / (Tcondensor-Tevaporator).

[0131] Table 1: Illustration of COPmax dependend on Tcondensor & Tevaporator

[0132] Maximum Evaporator temperature °C theoretical COP 0 5 10 15

[0133] 7.1 8,0 9,1 10,6

[0134] 6.5 7,2 8,1 9,2

[0135] 6,0 6,6 7,3 8,2

[0136] 5.6 6,1 6,7 7,4

[0137] 5.2 5,6 6,1 6,8 85335PC01

[0138] 18

[0139] Three scenarios are considered as non-limiting examples of the benefits of preferred embodiments of the invention. A system as described in Figure 1 is considered, with these key data:

[0140] • Biomass heating system capacity: Total 10.000 kW heat, delivered on heat exchanger systems 13, 16 and 19. Capacity from boiler is constant 7.700 kW delivered to first heat exchanger system 19. The remaining 2.300 kW is split between second and the third heat exchanger systems 13 and 16, depending on the scenario and heat pump system load.

[0141] • Heat pump system capacity: 15.000 kW heat, delivered on condenser 23

[0142] • District heating system return temperature 31 : 40°C

[0143] • District heating system forward temperature 38: 80°C

[0144] • Secondary heat source 28: Outside air temperature app: 3 °C

[0145] Figure 2 illustrates a scenario, wherein the biomass heating system delivers 10 MW to the district heating system network. The water returning from the district heating system network - return water 31 - will be divided between the heat pump system condenser 23 and the heat exchanger flue gas condensation - second heat exchanger system 13. The two streams will be heated and both added to heat exchanger system 19 which will boost the temperature to the desired supply temperature for the district heating system network.

[0146] In this scenario, the heat pump system evaporator 21 will primarily utilize heat from the outdoor air, which the evaporator temperature of the heat pump system shall correspond to. In this scenario the heat pump system will have an evaporator temperature of 0°C at 25 in Figure 1. In Figure 2, the scenario is simulated with varying heat pump system load. The COP of the heat pump system is decreasing in respond to the higher load, this is mainly due to the higher temperature that the heat pump system shall supply to the district heating system network, which requires an increase of the condenser temperature, which leads to a lower COP. 85335PC01

[0147] Table 2: Key data behind figure 2:

[0148] Biomass heating system kW 10.000 10.000 10.000 10.000 10.000 10.000 10.000

[0149] Heat pump system kW 0 2.500 5.000 7.500 10.000 12.500 15.000

[0150] TOTAL kW 10.000 12.500 15.000 17.500 20.000 22.500 25.000

[0151] T Evaporator °C 0 0 0 0 0 0 0

[0152] T Condenser °C 45,0 51 ,8 58,2 62,3 65,1 67,1 68,6

[0153] COP 4,5 4,1 3,7 3,5 3,4 3,3 3,2

[0154] Figure 3: Use of scrubber condensate for heat pump system evaporator.

[0155] In Figure 3 another scenario is illustrated wherein the COP is increased further by utilizing heat exchanger flue gas condensate in the third heat exchanger 16 as heat source for the heat pump system.

[0156] In this scenario, the biomass heating system will operate similar to the scenario illustrated in Figure 2, but in Figure 3 the heat pump system evaporator will utilize the energy from the flue gas condensation, when possible. When all of the energy to the heat pump system can be delivered from heat exchanger flue gas condensate by the third heat exchanger 16, then no energy is needed from heat exchanger - secondary source 27, thereby the evaporator temperature of the heat pump system can be increased - for instance from 0°C to 10°C at 25 in Figure 1. This will improve COP of the heat pump system, because less compressor work is needed. The biomass heating system will deliver less heat directly to the district heating system network, and the heat pump system will deliver more.

[0157] In Figure 3 and 4, a scenario is illustrated with a varying heat pump system load. From 1.000 kW to 5.000 kW, the heat pump system can fully utilize the heat from the flue gas condensation, increasing the COP, due to higher evaporator temperature. From 5.000 kW and above, the heat pump system needs more energy than the flue gas condensation can supply and the heat exchanger - secondary source 27 is included and the evaporation temperature is lowered from 10°C to 0°C, which decreases the COP. The third heat exchanger system 16 is still utilized by the heat pump system, which will result in less use of secondary source - outdoor air 28. 85335PC01

[0158] 20

[0159] Table 3: Key data behind Figure 3:

[0160] Biomass heating system kW 10.000 8.712 7.876 7.876 7.876 7.876 7.876

[0161] Heat pump system kW 0 2.500 5.000 7.500 10.000 12.500 15.000

[0162] TOTAL kW 10.000 11.212 12.876 15.376 17.876 20.376 22.876

[0163] T Evaporator °C 10 10 0 0 0 0 0

[0164] T Condenser °C 45,7 50,1 55,8 59,8 62,7 64,8 66,5

[0165] COP 4,9 4,6 3,8 3,6 3,5 3,4 3,3

[0166] In Figure 4, the COP from scenario 1 and 2 is displayed, with a reference COP for a stand-alone heat pump system supplying district heating system in similar conditions as scenario 1 and 2.

[0167] The increased COP when the heat pump system is cogenerating with a biomass heating system is because the evaporation temperature can be increased, and the condensation temperature can be decreased. A standalone heat pump system need to supply final district heating system temperature (in this example 80°C) to the district heating system network. When cogenerating, the heat pump system will only need to supply a lower temperature (in this example between 45-65 °C), depending on the heat pump system load, as the biomass heating system will boost the temperature to the supply temperature typically 80°C. When utilizing the flue gas condensation heat, scenario 2, the evaporator temperature can be increased in some cases, increasing the COP even more.

[0168] Table 4: Key data behind Figure 4:

[0169] Heat pump system

[0170] Load kW 0 2.500 5.000 7.500 10.000 12.500 15.000

[0171] Reference COP 2,7 2,7 2,7 2,7 2,7 2,7 2,7

[0172] COP with boost 4,5 4,1 3,7 3,5 3,4 3,3 3,2

[0173] COP Utilizing Scrubber 4,9 4,6 3,7 3,5 3,4 3,3 3,2

[0174] Figure 5: Maximum COP, Heat pump system evaporator temperature 10 °C

[0175] In Figure 5 is a third scenario illustrated wherein the outdoor temperature is higher than 10°C, and the evaporator temperature does not need to be lowered to 0°C. In these scenarios, it is not important for the heat pump system if the heat is received from the flue gas condensation or outdoor air, since the evaporator will be at the same temperature (10°C). The heat pump system will still benefit from the lower condenser temperature, as the biomass heating system is used to boost 85335PC01 the temperature of the district heating water allowing the heat pump system condenser to operate at a lower temperature compared to the reference heat pump system.

[0176] Figure 5 shows that the heat pump system will have a higher COP compared to Figure 2 due to the higher evaporator temperature.

[0177] Table 5: Key data behind Figure 5:

[0178] Biomass heating system kW 10.000 10.000 10.000 10.000 10.000 10.000 10.000

[0179] Heat pump system kW 0 2.500 5.000 7.500 10.000 12.500 15.000

[0180] TOTAL kW 10.000 12.500 15.000 17.500 20.000 22.500 25.000

[0181] T Evaporator °C 10 10 10 10 10 10 10

[0182] T Condenser °C 45,75 50,48 56,61 60,63 63,47 65,58 67,22

[0183] COP 4,94 4,60 4,18 3,91 3,73 3,60 3,50

[0184] Preferred embodiments of the energy plant comprises a Thermal Energy Storage (TES). TES is a pivotal technology in advancing sustainable district heating systems. By storing excess thermal energy generated from various sources, TES helps balance energy supply and demand, enhances system efficiency.

[0185] Benefits of TES may be:

[0186] 1. Operational Efficiency and Cost Savings. TES enables district heating systems to operate more efficiently by reducing peak load production. This not only leads to cost savings but also extends the operational lifespan of production facilities.

[0187] 2. Grid Balancing and Renewable Integration. TES systems play a crucial role in balancing the electrical grid, especially with the increasing integration of renewable energy sources like wind and solar. By storing excess heat during periods of low electricity prices and discharging it when prices are high, TES helps stabilize the grid and optimize the use of renewable energy. This is akin to functioning as a "virtual battery" for the energy system.

[0188] For the present invention it can be an advantage to produce more heat than currently needed with the heat pump when electricity price is low. 85335PC01

[0189] 22

[0190] In preferred embodiment, the TES comprises a water reservoir fluidicly connected to or integrated with energy plant so that water in the reservoir is heated by the heat pump system or the biomass heating system or both. The heated water is stored in the reservoir for later use, and when used, the stored and heated water is used for heating preferably the return water 31. However, the invention is not limited to water based TES, as other types of energy storage and / or storage medium can be used.

[0191] ITEMIZED LIST OF PREFERRED EMBODIMENTS

[0192] Item 1. An energy plant for producing warm supply water to a district heating system, said energy plant comprising a biomass heating system and an electrical heat pump system, wherein:

[0193] • said energy plant is configured to receive from said district heating system return water (31) and to deliver forward water (38) having a supply temperature being a higher temperature than a temperature of said return water (31) to said district heating system;

[0194] • said biomass heating system comprises: o a furnace (2) for production of hot flue gas (3) by conversion of carbonaceous fuel, preferably said hot flue gas (3) has a temperature larger 600°C and preferably lower than 1200°C, o a boiler system (4) configured to cool said hot flue (3) gas to a cooled flue gas (5) having a temperature, preferably, in the range of 100-300°C (5) by transferring heat of said hot flue gas (3) to a hot water circuit (18, 20) by use of a first heat exchanger system (19), preferably in an amount to increase a temperature in the hot water circuit to above 90°C, o a flue gas condensation system (6) configured to cool said cooled flue gas to a temperature below a water dew point (7), preferably being below 80°C thereby producing a warm flue gas condensate (11) of more than preferably 50°C,

[0195] • said electrical heat pump system comprises: o an evaporator (21), a compressor (22), a condenser (23) and an expansion valve (24)

[0196] • said energy plant comprises 85335PC01

[0197] 23 o a second heat exchanger system (13) configured for cooling said flue gas condensate by said return water (33). o

[0198] Item 2. An energy plant according to item 1, comprising a third heat exchanger system (16) configured for cooling said flue gas condensate by said evaporator of the electrical heat pump system (21).

[0199] Item 3. An energy plant according to item 1 or 2, wherein said transfer of heat of said hot flue gas (3) is a transfer of heat to a flow of water flow exiting said condenser (23).

[0200] Item 4. An energy plant according to any one of the preceding items, comprising a valve and a pump for controlling a flow of said flue gas condensate through said second heat exchanger system (13) and / or through said third heat exchanger system (16).

[0201] Item 5. An energy plant according to any one of the preceding items, comprising

[0202] • a fourth heat exchanger system (28) configured for heating a flow of fluid, preferably water, exiting said evaporator (21),

[0203] • a heat source, such as air coolers to cool said evaporator (21) of said heat pump system (25), wherein said fourth heat exchanger system (28) is configured to provide said heating of said flow of fluid is provided.

[0204] Item 6. An energy plant according to any one of the preceding items, comprising a fifth heat exchanger system (9) arranged to receive flue gas from the flue gas condensation system (6) and configured to reheat said received flue gas.

[0205] Item 7. An energy plant according to any one of the preceding items, wherein said heat pump system comprising a plurality of heat pumps, such as two, three, four or five heat pumps.

[0206] Item 8. An energy plant according to item 7, wherein said heat pumps each are individually controllable, such as controllable to operating point and / or start and stop. 85335PC01

[0207] 24

[0208] Item 9. An energy plant according to item 7, wherein said plurality of heat pumps are arranged in series, so that an upstream condenser is fluidicly connected with an downstream evaporator in a fluid circuit, whereby temperature increases provided by the plurality of heat pumps is an increasing temperature in upstream direction.

[0209] Item 10. An energy plant according to any one of the preceding items, wherein the flue gas condensation system (6) comprises a two stage flue gas scrubber.

[0210] Item 11. An energy plant according to any one of the preceding items, comprising a source of NaOH and an injection arranged to introduce an amount of NaOH into said flue gas condensate in an amount sufficient to neutralize said flue gas condensate.

[0211] Item 12. An energy plant according to any one of the preceding items, wherein said first heat exchanger system (19), said second heat exchanger system (13) and / or said third heat exchanger system (16) each comprises one or more heat exchanges arranged in series and / or parallel.

[0212] Item 13. An energy plant according to any one of the preceding items, when dependant on item 5, said fourth heat exchanger system (16) comprises one or more heat exchanges arranged in series and / or parallel.

[0213] Item 14. An energy plant according to any one of the preceding items, when dependant on item 6, said fifth heat exchanger system (16) comprises one or more heat exchanges arranged in series and / or parallel.

[0214] Item 15. An energy plant according to any one of the preceding items, comprising a thermal energy storage, wherein said energy plant is configured to store in and extract heat from said thermal energy storage.

[0215] Item 16. An energy plant according to item 15, wherein said energy plant is configured to heat said return water (31) by heat stored in said thermal energy storage. 85335PC01

[0216] 25

[0217] Item 17. An energy plant according to item 15 or 16, wherein said thermal energy storage comprises a water reservoir configured to contain water storing said stored heat.

[0218] Item 18. A method of operating an energy plant according to any one of the preceding items, said method comprises

[0219] • operate said biomass heating system to produce hot flue gas (3), and

[0220] • operate said heat pump system to provide a stream of heated water exiting said evaporator (21).

[0221] Item 19. A method according to item 18, wherein said biomass heating system is operated to produce hot flue (3) while said heat pump system is operated not to provide said stream.

[0222] Item 20. A method according to item 17 or 18, wherein said biomass heating system is operated not to produce hot flue (3) while said heat pump system is operated to provide said stream.

[0223] Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is set out by the accompanying claim set. In the context of the claims, the terms "comprising" or "comprises" do not exclude other possible elements or steps. Also, the mentioning of references such as "a" or "an" etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.

Claims

85335PC0126CLAIMS1. An energy plant for producing warm forward water to a district heating system, said energy plant comprising a biomass heating system and an electrical heat pump system, wherein:• said energy plant is configured to receive from said district heating system, return water (31) and to deliver forward water (38) having a supply temperature being a higher temperature than a temperature of said return water (31) to said district heating system;• said biomass heating system comprises: o a furnace (2) for production of hot flue gas (3) by conversion of carbonaceous fuel, preferably said hot flue gas (3) has a temperature larger 600°C and preferably lower than 1200°C, o a boiler system (4) configured to cool said hot flue (3) gas to a cooled flue gas (5) having a temperature, preferably, in the range of 100-300°C by transferring heat of said hot flue gas (3) to a hot water circuit (18, 20),• said electrical heat pump system comprises: o an evaporator (21), a compressor (22), a condenser (23) and an expansion valve (24), said condensor (23) is configured to selectively heat said return water (31) to provide heated return water (34),• said biomass heating system comprises: o a first heat exchanger system (19) configured to selectively further heat said heated return water (34) and / or selectively heating said return water (34) by transferring heat from said hot water circuit (18, 20), preferably in amount to keep a temperature in the hot water circuit above 90°C.

2. An energy plant according to clam 1, comprising a flue gas condensation system (6) configured to cool said cooled flue gas to a temperature below a water dew point (7), preferably being below 80°C thereby producing a warm flue gas condensate (11) of more than preferably 50°C.85335PC01273. An energy plant according to claim 2, comprising a second heat exchanger system (13) configured for cooling said flue gas condensate by said return water (33).

4. An energy plant according to any one of the preceding claims 2 or 3, comprising a third heat exchanger system (16) configured for cooling said flue gas condensate by said evaporator of the electrical heat pump system (21).

5. An energy plant according to any one of the preceding claims, wherein said transfer of heat of said hot flue gas (3) is a transfer of heat to a flow of water exiting said condenser (23).

6. An energy plant according to any one of the preceding claims, comprising a valve and a pump for controlling a flow of said flue gas condensate through said second heat exchanger system (13) and / or , when dependant on claim 4, through said third heat exchanger system (16).

7. An energy plant according to any one of the preceding claims, comprising• a fourth heat exchanger system (28) configured for heating a flow of fluid, preferably water, exiting said evaporator (21),• a heat source, such as air coolers, wherein said fourth heat exchanger system (28) is configured to provide said heating of said flow of fluid exiting said evaporator (21) from said heat source.

8. An energy plant according to any one of the preceding claims, comprising a fifth heat exchanger system (9) arranged to receive a flue gas from the flue gas condensation system (6) and configured to heat said received flue gas.

9. An energy plant according to any one of the preceding claims, wherein said heat pump system comprising a plurality of heat pumps, such as two, three, four or five heat pumps.

10. An energy plant according to claim 9, wherein said heat pumps each are individually controllable, such as controllable as to operating point and / or start and stop.85335PC012811. An energy plant according to claim 9 or 10, wherein said plurality of heat pumps are arranged in series, so that an upstream condenser is fluidicly connected with an downstream evaporator in a fluid circuit, whereby temperature increases provided by the plurality of heat pumps is an increasing temperature in upstream direction.

12. An energy plant according to any one of the preceding claims, wherein the flue gas condensation system (6) comprises a single stage and / or two stage flue gas scrubber.

13. An energy plant according to any one of the preceding claims, comprising a source of NaOH and an injection arranged to introduce an amount of NaOH into said flue gas condensate in an amount sufficient to neutralize said flue gas condensate.

14. An energy plant according to any one of the preceding claims, wherein said first heat exchanger system (19), said second heat exchanger system (13) and / or said third heat exchanger system (16) each comprises one or more heat exchanges arranged in series and / or parallel.

15. An energy plant according to any one of the preceding claims, when dependant on claim 7, said fourth heat exchanger system (16) comprises one or more heat exchanges arranged in series and / or parallel.

16. An energy plant according to any one of the preceding claims, when dependant on claim 8, said fifth heat exchanger system (16) comprises one or more heat exchanges arranged in series and / or parallel.

17. An energy plant according to any one of the preceding claims, comprising a thermal energy storage, wherein said energy plant is configured to store in and extract heat from said thermal energy storage.

18. An energy plant according to claim 17, wherein said energy plant is configured to heat said return water (31) by heat stored in said thermal energy storage.85335PC012919. An energy plant according to claim 17 or 18, wherein said thermal energy storage comprises a water reservoir configured to contain water storing said stored heat.

20. An energy plant according to any one of the preceding claims, wherein heat exchanger(s) of said first heat exchanger system (19) is(are) non-mixing heat exchanger(s), such as shell and tube heat exchanger(s), and / or plate heat exchanger(s).

21. An energy plant according to any one of the preceding claims 3-20, wherein heat exchanger(s) of said second heat exchanger system (13) is(are) non-mixing heat exchanger(s), such as shell and tube heat exchanger(s), and / or plate heat exchanger(s).

22. An energy plant according to any one of the preceding claims 4-21, wherein heat exchanger(s) of said third heat exchanger system (16) is(are) non-mixing heat exchanger(s), such as shell and tube heat exchanger(s), and / or plate heat exchanger(s).

23. An energy plant according to any one of the preceding claims 7-2, wherein heat exchanger(s) of said fourth heat exchanger system (16) is(are) non-mixing heat exchanger(s), such as shell and tube heat exchanger(s), and / or plate heat exchanger(s).

24. An energy plant according to any one of the preceding claims, wherein said evaporater (21) comprising at least one non-mixing heat exchanger for transferring heat to a coolant media.

25. An energy plant according to any one of the preceding claims, wherien said condenser (23) comprising at least one non-mixing heat exchanger for transferring heat from a coolant media.

26. An energy plant according to any one of the preceding claims, comprising a thermal energy storage, and wherein said energy plant is configured for85335PC0130 selectively store heat produced by the energy plant in said thermal energy storage.

27. A method of operating an energy plant according to any one of the preceding claims, said method comprises• operate said biomass heating system to produce hot flue gas (3), and• operate said heat pump system to provide a stream of heated water exiting said evaporator (21).

28. A method according to claim 27, wherein said biomass heating system is operated to produce hot flue (3) while said heat pump system is operated not to provide said stream.

29. A method according to claim 27 or 28, wherein said biomass heating system is operated not to produce hot flue (3) while said heat pump system is operated to provide said stream.

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