SK500912011U1 - Method and system for processing of flue gas heat source - Google Patents

Abstract

Combustion products resulting from the combustion of gaseous fuels (19) containing hydrogen as an exit from the heat source (2) in thermo capacitor (1) cooled to a temperature that is below the dew point of flue gas and is lower than the temperature of the return branch (4) heating medium, the cooling occurs condensation of water vapor and dry gas. Combustion products may cool to below the liquefaction temperature of CO2 from the flue gas CO2 into the atmosphere. Heat from the thermo capacitor (1) can divert the heat pump (9), its output heats the heating medium, preferably in the return line (4). At least part of the heat source (2) may take the form of a cogeneration unit (8), generating electricity, at least a portion of electricity generated is then used to drive the heat pump (9). Flue gas after leaving the thermo capacitor (1) can be heated in the second heat exchanger (11). The flue is connected the thermo capacitor (1) as heat source for heat pump (9) and / or separator (6) CO2.

Description

Method and system of flue gas treatment of heat source

Technical field

The utility model relates to a method and system for treating flue gases arising from combustion processes in heating plants, cogeneration units, power plants and the like, where a gaseous fuel, in particular natural gas or methane, biogas, geothermal gas or other gas mixtures containing hydrogen is combusted. The utility model describes a more efficient and unconventional use of gaseous fuel for heating, the flue gas being treated to obtain additional usable heat and possibly also to remove CO ₂ from it.

BACKGROUND OF THE INVENTION

Gas boilers are known which use condensation heat. When burning natural gas CH ₄ or propane C ₃ H ₈ or other gaseous fuel, the hydrogen H ₂ contained in these gases burns. Combustion of hydrogen H ₂ together with CO ₂ also generates water vapor. Cooling the flue gas below the dew point condenses the water vapor H ₂ O contained in the flue gas and releases condensation heat. The gas with a volume of 1 m ³ contains approximately 0.17 kg of hydrogen H ₂ , and its combustion produces 1.54 kg of water H ₂ O in the form of approximately 2 m ^{3 of} water vapor. At a water heat sink of 2,499 kJ / kg, the condensation of this steam is 3,848.5 kJ of latent heat. The known condensing boiler solutions operate in such a way that the heating medium in the return branch has a temperature sufficiently lower than the dew point, which is less than 57 ° C under normal combustion conditions. The temperature of the heating medium in the return line of the condensing boiler should be between 35 and 40 ° C. Such a solution is useless in central heating, where the heating plant operates with a much warmer heating medium in the return line.

The known connection of thermocapacitors to the flue gas outlet of central heating boilers has the disadvantage that the flue gas cannot be cooled below the return flow temperature. Partial condensation starts already at the flue gas temperature below 70 ° C, but effectively i

the utilization of specific latent heat occurs only at a temperature below the dew point. The more it is possible to cool the flue gas and the more intense the condensation of water vapor from the flue gas, the more residual heat we can use. The currently used thermocapacitors connected in the flue gas duct of central heating boilers essentially only increase the heat exchange surface of the boilers. Similarly, the solutions described in published patent applications FR2921717A1, CN1865815A do not solve the formation of a sufficient temperature gradient on the thermocapacitor.

A solution is required that allows the flue gas to be cooled and used for heating at various, even higher, return temperatures, while a higher degree of cooling of the flue gas could help the subsequent removal of CO ₂ in liquid form.

SUMMARY OF THE INVENTION

The deficiencies of the prior art are substantially eliminated by the method of treating flue gases resulting from the combustion of a gaseous fuel in a heat source, in particular flue gases from a gaseous fuel such as natural gas, methane, biogas, geothermal gas or other hydrogen-containing gas. branch and heating medium return to the heat source according to this technical solution, which is based on the fact that the flue gases after leaving the heat source are cooled in the condenser to a temperature that is lower than the flue gas dew point and lower than the return temperature condensation of water vapor and drying of flue gases. The thermal condenser is a specific type of heat exchanger that is adapted to the aggressive action of condensate precipitated from the flue gas.

This cooling of the flue gas below the return temperature cannot be done by a heat exchanger operating with the heating medium in the return branch, on the contrary, a sufficient thermal gradient is required, which at first sight causes technical complications. The central heat sources operate at a relatively high return temperature, and at such a temperature, it is not possible to achieve flue gas condensation even with large heat exchange surfaces with direct use of the return flow. In principle, even when the outlet temperature and consequently the return temperature in conventional condensing boilers is increased, for example at increased heat losses of the heated object, there is a real decrease in efficiency of condensing boilers, which are designed mainly for low-temperature heating.

In the case of central heating according to this invention, the flue gases from the heat source will be cooled in a thermocapacitor whose cooling circuit will not be directly connected to the return branch of the heating medium. The described cooling has two main, combinable advantages. Cooling in the thermocapacitor releases heat, and at the same time CO ₂ , which is considered a greenhouse gas and whose release to the air is sanctioned at different levels, can be removed from the dried flue gas by further cooling. The heating medium usually takes the form of treated water.

The heat released in the thermocapacitor is low in relation to the heating medium and cannot be directly transferred to the return line, therefore, in a preferred solution, the flue gas-cooling thermocapacitor will be connected to the heat pump so that heat from the thermocapacitor is supplied to the heat pump via by which the heat is transferred to the return branch of the heating medium. In this way, the heating medium is preheated before it enters the main heat source. In a preferred embodiment, the heat pump will operate such that the low temperature circuit at the heat pump inlet is closed in loop with the thermal condenser, but at the same time an adjustable three-way valve and circulation pump will be wired in the circuit to deliver the heat transfer medium from another source of low potential heat.

The flue gas cooled in the thermocapacitor may be partially heated at its outlet in a second heat exchanger, which may be connected to the first heat exchanger upstream of the thermocapacitor. Even if the flue gas would be heated to its original temperature prior to entering the thermocapacitor, the heat balance is positive as there is essentially no water in the dry flue gas, so there is no need to heat it back. It will be advantageous to heat the flue gases only partially, just above the dew point, so that even any residual water does not tend to condense in the chimney. A flue gas fan can be installed downstream of the second heat exchanger.

An essential advantage of the folded solution is the possibility to remove CO ₂ from the dried flue gas, for example by liquefaction. The CO ₂ separator can be connected downstream of the thermal condenser or after the second heat exchanger.

It will be particularly preferred that the heat source or at least a portion of the heat source is formed by a cogeneration unit that generates both electricity and heat. The electricity generated can be used to drive the heat pump as well as to power the other control elements and circulation pumps.

The shifting of the individual stages of the preheater branch can be of various configurations, for example by first heating the heating medium with a heat pump, then with the waste heat from the cogeneration unit and then directly with the flue gas in the first gas / liquid heat exchanger. Such an order is advantageous in view of the necessary temperature gradients, but in principle other ordering or omission of any type of preheating is possible, while maintaining the essence of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The technical solution is explained in more detail in the examples according to Figures 1 to 4.

Figure 1 is a schematic view of the inclusion of a thermocapacitor in the flue gas outlet of the boiler along with two heat exchangers and a flue gas fan, where the thermocapacitor transfers heat to the heat pump.

Figure 2 is a schematic view of the arrangement of the separator in the flue gas outlet of the boiler together with two heat exchangers and a flue gas fan.

Figure 3 shows an overall wiring diagram of a conventional heating boiler with a cogeneration unit and a heat pump, which is powered by electricity from the cogeneration unit.

In FIG. 4 shows the connection of a cogeneration unit with a thermal condenser without a boiler.

Examples of technical solution

Example 1

In this example according to FIGS. 1 and 3, the connection in a central heating plant, which forms the flue gas treatment system of the heat source 2, is described. The heat source 2 comprises a gas boiler 7 or cascaded multiple gas boilers 7 and a cogeneration unit 8. it also burns natural gas.

The flue gases from the cogeneration unit 8 and from the gas boilers 7 are led to a common flue gas line 5, in which a first plate heat exchanger 10 of the gas / liquid type is arranged. In this first heat exchanger 10 heat is transferred to the heating medium at temperatures above the return temperature 4. Behind it is a thermocapacitor X which is able to cool the flue gas below the return temperature of the heating medium as it is not connected to a relatively hot return branch. 4, but connected to the heat pump 9. Heat is dissipated from the thermal condenser X by a separate heat transfer circuit 20 to the heat pump 9, where this low-potential heat is pumped to a higher temperature now usable in the heating system. In a preferred setting, the outlet of the heat pump 9 will heat the return medium 4 of the heating medium, since in this way a better temperature gradient is achieved on the respective fluid / liquid exchanger 12. In this example, treated water is used as heating medium and heat transfer medium 20.

Since the initial temperature conditions at the outlet of the thermal condenser X will not usually be suitable for starting the heat pump 9, the otherwise closed circuit with the heat transfer medium 20 and the circulation pump 13 is supplemented by a three-way valve 14 and connected to another low-potential heat source 16, e.g. , wells, rivers and the like. After the system is started, the inlet temperature of the heat transfer medium 20 is controlled by the three-way valve 14 and connected to the treated water source so that the heat pump 9 operates in the effective zone of its characteristic. After the temperature conditions have been consolidated, the inlet heat pump 9 operates exclusively with the heat transfer medium 20 in a closed circuit with a thermocapacitor L ·

In the flue gas branch in this example, a CO2 separator 6 is arranged downstream of the thermocapacitor. It could also be included in another part of the exhaust flue gas drying, but at this point the exhaust gas is basically the coldest and therefore the separator 6 working on the principle of CO ₂ liquefaction will work most effectively here. The use of a CO ₂ separator is not necessary, but only improves the overall performance of the circuit.

Downstream of the CO ₂ separator 6 is a second gas / liquid heat exchanger 11. The task of the second heat exchanger is to heat the dried flue gas to a temperature above the dew point. The first heat exchanger 10 is connected in series with the second heat exchanger 11 and the outlets of this connection are connected to the return branch 4 of the heating medium, preferably only after the connection of the heat exchangers 12 from the heat pump 9 and the cogeneration unit 8. Thus, the flue gases first transfer part of their heat in the first heat exchanger 10 and this heat is used to heat the return branch 4 and the heat exchanger 4, respectively. for later heating of the flue gas cooled and dried in the thermocapacitor L The low-potential heat we obtain from the flue gas in the thermocapacitor, including the condensation heat of the water vapor, is the heat source at the heat pump inlet 9.

Downstream of the second heat exchanger 11 in the flue gas line 5 is a flue gas fan 15 which improves the draft in the chimney. The chimney draft also improves the heating of the dried flue gas in the second heat exchanger 11.

In this example, the cogeneration unit 8 consists of a conventional internal combustion engine adapted to be powered by a gaseous fuel 19, which is natural gas, the flue gases being connected to a common flue gas line 5. The cogeneration unit 8 generates heat that is discharged to the return line 4. it may be a direct circuit or, in the preferred embodiment according to this example, a separate circuit which is connected to the return line 4 of the heating medium via a liquid / liquid heat exchanger 12. Circulation in the heat exchanger - cogeneration unit 8 will be ensured by the circulation pump 13. The circulation pump 13 can also be used on the side of the heat exchanger 12 to the return branch 4. Due to the hydraulic conditions in the piping and the heat exchanger 12 this circulation pump will also provide The conventional valves 17 may be positioned as a bypass at the first heat exchanger 10, as a bypass at the heat exchanger 12 of the heat pump 9, to connect another low-potential heat source 16 and elsewhere.

The cogeneration unit 8 is connected with its electrical output to the public electricity supply 18, for which known connections of the control, synchronization elements and possibly a transformer serve. To meet the needs of the heating plant, the electrical output of the cogeneration unit 8 is used to power all systems including the heat pump 9, the circulation pumps 13 and the control elements.

The courses of temperatures, temperature gradients in the individual wiring parts can be described in this example as follows. The central heating plant supplies its housing heat in the city, while the return medium 4 at the inlet to the heating plant has a heating medium temperature of 50 ° C. In the conventional circuit, the gaseous fuel boiler 7 would have to heat the 50 ° C heating medium to the 75 ° C required in the outlet branch 3 only as a direct heating in the boiler. The first branch in the return line 4 represents the connection of the heat exchanger 12 in the heat pump branch 9. The controlled bypass of this connection is provided by the valve 17. In the heat exchanger 12 the heating medium is heated to 52 ° C due to a temperature gradient of 55 ° C / 50 ° C. The heat pump 9 is thus able to preheat the return line by 2 ° C. A circulation pump 13 is provided in the circuit between the heat pump 9 and the heat exchanger 12.

Furthermore, a heat exchanger 12 is connected to the cogeneration unit 8 via the circulation pump 13 via the recirculation branch 4. From the cogeneration unit 8, flue gases with a temperature of 60 [deg.] C. are produced. From the cogeneration unit 8, a heat transfer medium of 78 ° C also emerges, which, after the heat is transferred, exits from the heat exchanger 12 with a temperature of 56 ° C. This temperature gradient ensures that the heating medium is heated from 52 ° C to 55 ° C. Subsequently, the inlet and outlet of the first and second heat exchangers 10, 11 are connected to the return branch 4, which are connected in series with each other. The heating medium having a temperature of 55 ° C initially by means of a circulation pump 13 enters the second heat exchanger 11 where it heats the flue gas, the outlet of the second heat exchanger H. is connected to the inlet to the first heat exchanger 10 where the heating water is still heated with hot flue gas by entering them into the thermocapacitor L Here, the heating medium is heated to 57 ° C and returned to the return branch 4 at 56 ° C (the difference between 56 ° C and 57 ° C is the heat loss).

Boiler 7 enters the heating medium preheated to 56 ° C, which represents a significant thermal savings of the system, when the boiler 7 heats the heating medium in the outlet branch with substantially less directly released heat. To put it simply, in this example, we saved energy that corresponds to heating the heating medium from 50 ° C to 56 ° C. A heat transfer medium circulates in a separate circuit of the heat pump 9, having a temperature gradient of 10 ° C / 18 ° C directly at the inlet. At the outlet of the thermocapacitor there is a temperature gradient of 10 ° C / 31 ° C. Suitable temperature control is ensured by the three-way valve 14. In the example of these temperatures we see the advantage of the proposed arrangement, where the cooling branch of the thermocapacitor i is fed by a heat transfer medium of only 10 ° C, which guarantees a sufficient temperature gradient. Deň: 32 ° C.

All temperatures given in this example are to be considered as an example which may differ from the other examples beyond the range of + - 10 ° C, the relative level of temperature levels being more important than the specific value. It is therefore necessary to take the indicated temperature values as an example, which does not limit the scope of protection to the given values.

Example 2

In this example of FIGS. 2 and 4, a circuit is described with a cogeneration unit 8 which is powered by a gaseous fuel, in this example a biogas and also forms a heat source 2. In contrast to the previous example, this is not a heat pump 9 but flue gas after passing the first heat exchanger 10 is fed to a CO ₂ separator 6 where it is cooled below the temperature of the return medium 4 of the heating medium to the CO ₂ liquefaction level. Subsequently, the dried flue gas is heated in the second exchanger 11 and discharged through the flue gas fan 15 into the atmosphere. In principle, such an arrangement can also be combined with the connection of the gas-fired boiler, in particular the connection will be influenced by the ratio of the required electrical and thermal output.

Industrial usability

Industrial applicability is obvious. According to this technical solution, it is possible to industrially and reuse heat from the flue gas of a heat source and preferably also to remove CO ₂ from the flue gas. The associated method increases the thermal efficiency of the system and increases the technical usability of the gaseous fuel.

Claims (22)

PROTECTION REQUIREMENTS Method for treating flue gases resulting from combustion of gaseous fuel (19) in a heat source (2), in particular flue gases from a gaseous fuel (19) containing hydrogen, wherein the heat source (2) transfers heat to the heating medium at the outlet branch (3) and the heating medium returns to the heat source (2) by the return branch (4), characterized in that the flue gas, after leaving the heat source (2), is cooled in the thermocapacitor (1) to a temperature lower than the dew point of the flue gas at least partially condensing water vapor, releasing heat from the flue gas and at least partially drying the flue gas. Method for treating flue gases of a heat source (2) according to claim 1, characterized in that the flue gases are cooled to a temperature in the range of 10 ° C to 50 ° C, preferably 25 ° C to 40 ° C. 3. A process for treating exhaust gases of the heat source (2) according to claim 1, characterized in that the flue gases are cooled to a temperature at or below the liquefaction of CO ₂ from the flue gas and discharged into the air into the atmosphere of _CO2. Method for treating the flue gas of a heat source (2) according to any one of claims 1 to 3, characterized in that the heat from the flue gas, preferably by means of a thermocapacitor (1), is discharged to a heat pump (9) which heats the heating medium. in the return line (4) of the heating medium. Method for treating flue gases of a heat source (2) according to claim 4, characterized in that the flue gases are passed upstream of the thermocapacitor (1) via a first heat exchanger (10) which heats the heating medium in the return branch (4). n Method for treating flue gases of a heat source (2) according to any one of claims 1 to 5, characterized in that at least a part of the heat source (2) is formed by a cogeneration unit (8) that generates electricity. Method for treating flue gases of a heat source (2) according to claim 6, characterized in that at least a part of the generated electrical energy is used to drive the heat pump (9) and / or the control elements and / or circulation pumps (13). Method for treating flue gases of a heat source (2) according to any one of claims 1 to 7, characterized in that the cogeneration unit (8) heats the heating medium with its waste heat, preferably in the return branch (4) and preferably via a heat exchanger (12). a circulation pump (13). Method for treating the flue gas of a heat source (2) according to any one of claims 1 to 8, characterized in that the flue gas, after leaving the thermocapacitor (1), is heated in a second heat exchanger (11), preferably above the dew point of the flue gas or flue gas point. Method for treating flue gas of a heat source (2) according to claim 9, characterized in that the heat used to heat the flue gas after leaving the thermocapacitor (1) is obtained from a first heat exchanger (10) upstream of the thermocapacitor (1) or from heating medium in the return branch (4). Method for treating flue gases of a heat source (2) according to any one of claims 4 to 10, characterized in that the heat transfer medium between the thermocapacitor (1) and the heat pump (9) is mixed with one another via a three-way valve (14) or mixed with the heat transfer medium. from another low-potential heat source (16). System for treating flue gases resulting from the combustion of gaseous fuel (19) in a heat source (2), in particular flue gases from a gaseous fuel (19) containing hydrogen, wherein the heat source (2) is connected to the outlet and return branches (3, 4) characterized in that a thermal element with a heat exchange surface cooled to a temperature lower than the return temperature of the heating medium (4) is connected in the flue gas line (5), preferably the thermal element is part of a thermocapacitor (1). Flue gas treatment system of a heat source (2) according to claim 12, characterized in that a CO ₂ separator (6) operating on the cooling principle is provided in the flue gas duct (5), preferably in the part of the exhaust at least partially dried flue gas. Flue gas treatment system of a heat source (2) according to claim 12 or 13, characterized in that the thermocapacitor (1) is connected to the inlet of the heat pump (9) and the outlet of the heat pump (9) is connected to heating the return branch (4) of the heating. the media. Flue gas treatment system of a heat source (2) according to claim 14, characterized in that the output of the heat pump (9) is connected to the return branch (4) of the heating medium by means of a heat exchanger (12). Flue gas treating system of a heat source (2) according to any one of claims 12 to 15, characterized in that the heat source (2) is formed by a gas fuel boiler (7) and / or a cogeneration unit (8), connected to the heat pump (9) as a power source. Flue gas treatment system of a heat source (2) according to claim 17, characterized in that the cooling of the cogeneration unit is connected to heat the heating medium, preferably in the return branch (4) via the heat exchanger (12). Flue gas treatment system of a heat source (2) according to any one of claims 14 to 17, characterized in that a foreign low-potential heat source (16) is connected to the heat transfer medium circuit (20) between the heat pump (9) and the thermal condenser (1). . Flue gas treatment system of a heat source (2) according to claim 18, characterized in that a three-way valve (14) is provided in the circuit with the heat transfer medium (20). The flue gas treatment system of a heat source (2) according to any one of the claims 5 to 12, characterized in that a first heat exchanger (10) is arranged in the flue gas line (5) upstream of the thermocapacitor (1) and / or the CO ₂ separator (6), downstream of the thermocapacitor (1) and / or a second heat exchanger (11) is arranged by a CO ₂ separator (6), both heat exchangers (10, 11) are connected to the return branch (4) of the heating medium, preferably they are mutually 10 connected in series. Flue gas treatment system of a heat source (2) according to any one of claims 12 to 20, characterized in that a flue gas fan (15) is provided in the flue gas line (5). The flue gas treatment system of a heat source (2) according to any one of the claims 15 to 21, characterized in that it has at least one circulation pump (13) and at least one valve (17).