WO2018002309A1

WO2018002309A1 - High-temperature furnace with heat recovery

Info

Publication number: WO2018002309A1
Application number: PCT/EP2017/066288
Authority: WO
Inventors: Hans Krämer; Udo Neumann; Thomas Kirchhöfer
Original assignee: Hans Krämer; Udo Neumann; Thomas Kirchhöfer
Priority date: 2016-07-01
Filing date: 2017-06-30
Publication date: 2018-01-04
Also published as: DE102016112103B4; DE102016112103A1

Abstract

The invention relates to a high-temperature furnace with heat recovery, comprising: - a flame (26) in a flame tube (44); - a waste gas outlet (24); - a fuel gas inlet (21); - and a fresh-air inlet (52). The invention is characterised in that: - a rotating heat exchanger (50) with a rotating, rotationally symmetrical axial flow body is provided for transferring heat from the waste gas (46), which flows out through the waste gas outlet (24), to the fresh air in order to produce heated fresh air (34); - downstream of the rotating heat exchanger (50) and upstream of the flame tube-jet compressor (44) there is a jet compressor mixing nozzle (28) provided, which has a hot air inlet (60), for introducing the heated fresh air (34), and an inlet for compressed air (36), which leads to the flame tube-jet compressor (44) and which has a fuel gas inlet (21) leading to an end region of the jet compressor mixing nozzle (28) in the direction of flow in order to introduce the fuel gas (40); - the flame tube jet compressor (44) comprises a waste gas inlet (68) at its entrance for waste gas (46); - and the cross section of the flame tube jet compressor (44) widens in the direction of flow.

Description

High temperature furnace with heat recovery

The present invention relates to a high-temperature furnace with heat recovery, comprising a flame in a flame tube,

an exhaust outlet,

a fuel gas inlet,

a fresh air intake,

In high-temperature furnaces, hereinafter furnaces, which gain the energy by burning a fuel, exhaust gases are produced. The temperature of these exhaust gases is usually above the useful temperature of the furnace, because only thereby the energy from the fuel gas can flow to the furnace. The effective amount of energy that can be used to heat the furnace is mitigated by the energy trapped in the exhaust. Efficiency values of less than 50% are the rule for ovens which operate at a working temperature of 1000 ° C.

For this reason, the efficiency has been increased for some time by the fact that the energy or heat bound to the exhaust gas is withdrawn and used for preheating the fuel gas. This eliminates the proportion of primary energy, which is required for heating the fuel gas to the discharge temperature in the oven. The aim of such heat recovery is the highest possible heating of the combustion air from the exhaust gas. In favorable cases, the efficiency value of the furnace can be raised to 90% or more. This can lead to energy savings of up to 50%.

Various methods or devices are known in the art. For example, compact burners are used in which the exhaust gas is passed out of the furnace at the outer walls of the burner and thereby emits a portion of its heat to the combustion air. These burners are, as the name implies, very compact and easy to install. However, the exhaust gas is taken from the furnace at the same point where the burner releases its hot air into the furnace. Due to the compactness of the transition of heat from the exhaust gas into the combustion air is very limited and recovery rates of well below 50% are common. This reduces the total recovery potential to 15 to 25%.

DE 10 2006 000 174 B4 describes an oil premix burner and an operating method in which exhaust gas is mixed into the fuel gas mixture. This is intended to improve the efficiency. From DE 197 29 047 Cl a mixing device for generating a mixture of gas and combustion ^¬ air is known, which improves the efficiency of combustion. By using a Venturi nozzle, the modulation range for the supply of the gas-air mixture is broadened depending on the heat demand, because the Venturi nozzle in the flow generated by the fan increases the pressure difference across Venturi nozzle and throttle body. As a result, flow resistance should be positively influenced. Both documents describe advantageous devices and methods, but they are not suitable for all applications, especially not in connection with all types of heat exchanger. Alternatively, a heat recovery with a plate heat exchanger in conjunction with a special burner is possible, which can work with the preheated air. This is currently the most common solution and is described for example in DE 10 2008 058 500 AI. The combustion air required for the burner is brought to the required 20 to 50 mbar overpressure with the aid of a commercially available cold air compressor, passed through the heat exchanger and then into the burner before the heat exchanger. Since plate heat exchangers are usually almost completely gas-tight, there are no problems with the required pressure differences between exhaust gas and combustion air. In this case, transfer rates of up to 80% can be achieved with appropriate plate heat exchangers. However, such high transfer rates require air-to-air countercurrent exchanger with very large surfaces, since the heat must be transferred from one side of the heat exchanger through the material of the heat exchanger to the other ^¬ re side of the heat exchanger. If the surfaces foul, the transfer efficiency drops very sharply. In addition, the production of the air-to-air countercurrent exchanger is complex and therefore expensive.

Easier tube bundle exchangers are easier to manufacture and also to clean. However, these only achieve transmission efficiencies of max. 50% and thus also reduces the total recovery potential 15 to 25%. In both heat exchangers, a compromise between compactness and pressure loss during flow is closed.

The document DE 10 2010063839 A1 describes, for example, a method for operating a furnace, in which heat from the exhaust gas is used via a heat exchanger. Spi ^¬ ralwärmeübertrager, tube heat exchangers, jacket tube heat exchangers or countercurrent layer heat exchangers are proposed in particular as a suitable heat exchanger.

Finally, a heat recovery with a flow-through rotationally symmetric rotary body is known. This type of heat recovery works with an axially flow-through rotary body. The exhaust gas flows through a segment of about 40% of the cross-sectional area of the rotating body, emits its energy and emerges from the rotating body cooled down at the end. On the opposite side, the fresh gas flows through a similar segment of the rotary body in the opposite direction, heats up on the rotary body and cools down accordingly. In this case, the rotating body rotates slowly about its axis, so that the flow-through segments are successively heated alternately ^¬ and then cooled again. The rotational speed is to be adjusted so that the material in the flow-through time only slightly cools (30-50 ° C) but only so slowly that a Abgasverschleppung makes up only a small part of the total amount of air.

Advantageously, the heat transfer in such rotary bodies always takes place on the same surface both during heating and during cooling. This eliminates the reduction in the efficiency of surface contamination. By eg a honeycomb structure can be realized in a very compact space, a very large surface. Due to a large number of channels, the flow resistance is reduced while still very small dimensions. Such a structure can be completely resistant plants ^¬ gen materials, such as ceramics manufacture. The cost of the material are relatively low. The disadvantage of this design is that this type of heat exchanger are inherently not tight. The rotary body has no seals at its inlet and outlet openings. The seal is only rudimentary over small gaps between the rotating body and housing. These can meander be guided and thus make it difficult to overflow between the two gases and the environment, completely sealed or even pressure-resistant, such a construction can not produce.

The overpressure required for the burner must therefore be generated after the heat exchanger. This can be done either with a high-temperature blower or with a nozzle compressor. State of the art are high temperature compressor. These are extremely expensive and vulnerable, which is why this type of heat recovery is rarely used.

The object of the invention is to provide a high-temperature furnace, which has a high efficiency, the production of which is still simple and inexpensive. The high-temperature furnace should also be robust and work reliably, in particular, the maintenance and repair should be associated with low cost and little effort. A further object of the invention is to propose a method for operating a high-temperature furnace, which enables the best possible utilization of the energy used.

The object is achieved by a high-temperature furnace having the features of patent claim 1. Furthermore, a method according to the independent method claim for solving the problem is proposed. The high-temperature furnace according to the invention accordingly comprises the following components or elements: a flame in a flame tube jet compressor,

an exhaust outlet,

a fuel gas inlet,

- a fresh air inlet,

a rotary heat exchanger for transferring heat of the exhaust gas flowing out through the exhaust gas outlet to fresh air, which is supplied to the flame tube jet compressor via at least one hot air air inlet,

a jet compressor mixing nozzle arranged in the flow direction behind the rotary heat exchanger for mixing compressed air, fuel gas and heated fresh air and for generating negative pressure at the inlet passage of the flame tube and necessary overpressure at the outlet of the flame tube and to generate a pressure difference to the movement of gases.

Hereinafter, the term compressed air for pre-compressed air, the term fresh air for untreated air, for example, ambient air, preheated fresh air for fresh air, which has been heated in the rotary heat exchanger and the term exhaust gas used for combustion gas. Furthermore, the term air mixture designates the mixture of compressed air and preheated fresh air, the term fuel gas mixture, the mixture of compressed air, preheated fresh air and fuel gas.

The component referred to here as a jet compressor is technically known under the name jet pump and is z. B. core component in a flow heat pump. The mixed term jet compressor mixing nozzle describes an extension of the simple jet compressor function with the task of intensive turbulence of additional fuel gas.

In a particularly advantageous embodiment, the jet compressor mixing nozzle is constructed in two stages. Ultimately, this construction according to the invention then involves three nested jet compressors. The flame tube jet compressor is a jet compressor whose Materialen- shafts are suitable for a flame tube.

The jet compressor mixing nozzle generates the necessary pressures in the flame tube and allows the use of the highly effective, cost-effective and compact rotary heat exchanger. It generates negative pressure at the inlet and necessary overpressure at the outlet of the flame tube, which is part of the combustion chamber. In addition, fuel gas is mixed with the air mixture to maintain an optimal flame. The heated fresh air and the compressed air are passed through the jet compressor mixing nozzle and then fed to the fuel gas. The resulting turbulence leads to a very good mixing of fuel gas and air mixture, which allows a low-emission and complete combustion. The jet mixer nozzle generates a high turbulence at its output due to the principle whereby the otherwise necessary form for turbulence generation is reduced and thus the principle low efficiency of a jet compressor compared to other types of compressor is compensated.

In a particularly advantageous embodiment variant, the gas velocity after the mixing zone is additionally reduced by suitable means in order to allow a controlled and clean combustion.

Feed exhaust gas can be sucked in a kind Mantelstrahlansaugung just before the flame zone and be admixed in the flame zone, whereby the temperature of the flame is reduced. This admixture prevents the flame temperature from rising to areas where the materials used reach their strength limit and where more nitrogen oxides are generated. The basic mixing ratios are dictated by the geometry of the burner components and can be adapted accordingly to a desired performance and the individual structure of the high-temperature furnace. A reduction or regulation of the gas volumes can be achieved in a particularly simple and advantageous embodiment variant by slide. These can be changed dynamically in the course of the combustion process, for example, can be dispensed with an admixture of exhaust gas in a heating phase, at full load, however, exhaust gas can be admixed. Advantageously, there is a continuous monitoring of the exhaust gas and a continuous control of the mixture, since the volume requirement of the preheated fresh air exceeds that of the cold air volume by a multiple.

The use of a particular ceramic Wehenrehkörpers as a heat exchanger has the significant advantage that a high efficiency is maintained even when dirty. The production costs are significantly cheaper, especially at high temperatures, than with plate heat exchangers or tube bundle exchangers made of metal. Also, the durability in aggressive environments when using ceramics for the heat transferring components of the rotary heat exchanger is much higher than for metal. The rotary heat body preferably has a modular pipe guide made of ceramic. The otherwise significant and above-described disadvantages of the rotary heat exchanger are compensated by the use of the combination of flame tube jet compressor and jet compressor mixing nozzle.

It has been shown that an embodiment of the rotary heat exchanger as a rotary rotary heat exchanger provides particularly good results.

An essential aspect of the invention is that already preheated fresh air is compressed without contact. This has the advantage that a heat exchanger can be connected upstream, which can be operated without or only with a small pressure difference and thus does not have to be designed pressure-tight in two ways.

In the literature and in patents such. For example, DE 42 41 984 A1 also describes such a rotary body as a "regenerative heat exchanger for gaseous media." The exhaust gas produced can be used in two ways according to the invention: On the one hand, the heat energy contained therein is transferred to the fresh air The necessary negative pressure at the inlet of the flame tube is generated by the use according to the invention of the jet compressor mixing nozzle The jet compressor mixing nozzle can preferably be designed as a two-stage or multi-stage nozzle The first compressed air is preferably pre-compressed to about 1.5 bar, and the first nozzle opens into another nozzle, into which fresh air, which has also been preheated, is fed in. The third inflow Fuel gas, such as propane gas is fed into a turbulent mixing zone. The resulting fuel gas mixture is ignited, wherein in the flow direction in the further course of a slowing down of the gas flow, for example, by a cross-sectional widening takes place in the flame tube. The resulting exhaust gas is discharged through a discharge pipe from a boiler and fed partly to the rotary heat exchanger and partly to the flame tube. From the rotary heat exchanger, the exhaust gas then passes to a chimney or a partial flow is diverted and fed to the flame tube. Ultimately, the jet compressor mixing nozzle generates the necessary pressure difference in the system for moving the gases. Another drive is not necessary. In principle, a negative pressure is created which reaches to the outlet of the rotary heat exchanger. The compressed air can in principle also be pre-compressed to 1 to 5 bar. It causes a negative pressure in the system, whereby the other incoming gases are sucked.

The exhaust gas supplied to the jet compressor mixing nozzle causes an encapsulation of the flame and an advantageous cooling of the walls of the jet compressor mixing nozzle.

The method according to the invention includes the method steps:

Transfer of heat energy from exhaust gas by means of a rotary heat exchanger with an axially flow-through rotationally symmetrical rotary body to fresh air,

Introducing the preheated fresh air together with compressed air into a jet compressor mixing nozzle, for producing an air mixture and for generating negative pressure at the inlet of the flame tube jet compressor and necessary overpressure at the outlet of the flame jet jet compressor and for generating a pressure difference for the movement of gases,

Introducing fuel gas into the jet compressor mixing nozzle and thus into the air mixture to produce a fuel gas mixture,

Introducing exhaust gas into the flame tube,

Ignition of the fuel gas mixture in a jet compressor flame tube, reduction of the flow velocity of exhaust gas formed in the flame tube,

- Supplying the resulting exhaust gas to the rotary heat exchanger.

The high-temperature furnace according to the invention and the inventive method cause a significant reduction of the primary energy in the form of fuel gas. Due to the use of compressed air and the jet compressor mixing nozzle, very few moving and thus wear-prone parts are required. The jet compressor mixing nozzle acts as a drive for the already preheated air and if necessary, for the partial flow of the exhaust gas, which is also fed to the jet compressor mixing nozzle. Another advantage is that the flame is isolated as it were via the supplied partial flow of the exhaust gas. It is also advantageous that, in contrast to the prior art, the air is compressed when hot.

Preferably, a regulator may be used to maintain the desired mixing ratios. A flame monitoring is advantageous, which interrupts the fuel gas flow when no flame is present.

The ignition of the fuel gas via conventional ignition mechanisms, if necessary. Also by auto-ignition.

The invention is explained in more detail below with reference to the greatly simplified schematic diagram. This shows a schematic diagram of the high temperature furnace according to the invention.

Shown is a boiler 20 with an exhaust gas outlet 24 and an upstream jet compressor mixing nozzle 28. The jet compressor mixing nozzle 28 is designed in the embodiment shown as a two-stage nozzle. A first nozzle 30 opens into a second nozzle 32.

A fuel gas inlet 21 opens in an end portion of the second nozzle 32. The supply can selectively, that through a single opening or a single fuel gas inlet 21 take place, but advantageously 21 may be provided also several Publ ^¬ voltages or Brenngaseinlässe that the over the outer periphery End region of the second nozzle 32 are arranged in a ring. In a flame tube jet compressor 44, the flame 26 is formed.

In the first nozzle 30 preheated fresh air 34 and compressed air 36 from a compressed air reservoir 37 are introduced into a hot air inlet 60, in the second nozzle 32 also preheated fresh air 34 is passed into a hot air inlet 60. The resulting air mixture 38 is then mixed with fuel gas 40 from a fuel gas supply 41 to a fuel gas mixture 42. This creates a turbulent flow, which is ignited, so that the flame 26 is formed. In the exemplary embodiment shown, the second nozzle 32 opens into the flame tube jet compressor 44 and encounters branched-off hot exhaust gas 46, which is introduced through an exhaust gas inlet 66. The exhaust gas 46 encapsulates the one hand, produced in the flame ^¬ pipe 44 flame 26, on the other hand, it cools the walls of the flame-tube jet compressor 44. The exhaust gas 46 is pressure at the entrance of the flame-tube jet compressor 44 is sucked by the resulting lower ^¬. It can also be seen that the cross section of the flame tube jet compressor 44 widens in the flow direction of the exhaust gas 46, thereby lowering the flow velocity again. The exhaust gas 46 flowing out of the exhaust gas outlet 24 is, as already explained above, partly conducted into the flame tube jet compressor 44 and partly into a rotary heat exchanger 50. In the rotary heat exchanger 50 fresh air 52 is further introduced, which is heated therein and transferred into preheated fresh air 34. The preheated fresh air 34 is supplied in each case via one of the hot air inlets 60 of the first nozzle 30 and the second nozzle 32. The cooled exhaust gas 46 flowing out of the rotary heat exchanger 50 is discharged into the environment, for example via a chimney.

Pipe guides for the passage of the hot gases (preheated fresh air 34 and exhaust gas 46) are preferably insulated from high temperature and in particular made of ceramic.

Claims

claims

1. High temperature furnace with heat recovery, comprising

a flame (26) in a flame tube jet compressor (44),

an exhaust gas outlet (24),

a fuel gas inlet (21),

- Fresh air inlet (52), characterized in that

a rotary heat exchanger (50) is provided with an axially flowed rotationally symmetrical rotary body for transmitting heat of the exhaust gas (46) flowing through the exhaust gas outlet (24) to fresh air for producing heated fresh air (34),

a jet mixing nozzle (28) arranged in the flow direction behind the rotary heat exchanger (50) and in front of the flame tube jet compressor (44) is provided

a hot air inlet (60) for introducing the heated fresh air (34) and an inlet for compressed air (36),

- in the flame tube jet compressor (44) opens and a flowing in the flow direction in an end region of the jet compressor mixing nozzle (28) opening fuel gas inlet (21) for introducing fuel gas (40),

- The flame tube jet compressor (44) at the entrance an exhaust gas inlet (68) for exhaust gas (46),

- The flame tube jet compressor (44) widens in the flow direction in cross section.

2. High temperature furnace according to claim 1, characterized in that the jet compressor mixing nozzle (28) is designed as at least two-stage nozzle, wherein in a first nozzle (30) preheated fresh air (34) and compressed air (36) for generating an air mixture (38) and in a second nozzle (32), the air mixture (38) and fuel gas (40) for generating a fuel gas mixture (42) are initiated.

3. High temperature furnace according to claim 1 or claim 2, characterized in that means are provided for regulating the gas volumes.

4. High-temperature furnace according to one of claims 1 to 3, characterized in that the heat-transmitting components of the rotary heat exchanger (50) are made of ceramic.

5. High-temperature furnace according to claim 7, characterized in that pipe guides for the passage of gases (34, 46) insulated high temperature resistant and are preferably made of ceramic.

6. A method for operating a high-temperature furnace, characterized by the method steps

Transfer of heat energy from exhaust gas (46) to an axially flow-through rotationally symmetrical rotary body on fresh air (34),

- Introducing the preheated fresh air (34) together with compressed air (36) in a jet compressor mixing nozzle (28) for generating an air mixture (38) and for generating negative pressure at the inlet of a flame tube jet compressor (44) and necessary overpressure at the outlet of the flame tube jet compressor (44) and for generating a pressure difference for the movement of gases,

Introducing fuel gas (40) into the air mixture (38) to produce a fuel gas mixture (42),

Introducing exhaust gas (34) into the flame tube jet compressor (44),

Igniting the fuel gas mixture (42),

Reducing the flow velocity of exhaust gas (34) formed in the flame tube jet compressor (44), - Supplying the resulting exhaust gas (46) to the rotary heat exchanger (50).

7. The method of claim 9, further comprising the step - supply of exhaust gas (46) in the fuel gas mixture (42).