DE19752709C2 - exhaust converter - Google Patents

Description

The invention relates to a method for using the exhaust gas heat of a heat generator gers for hot water production in a heating system.

1. Problem

Many existing combustion plants have difficulties, but they are nonsensical legally stipulated by the Small Firing Plant Ordinance (1. BImSchV, / 3 /) meet the requirements for gross exhaust gas loss / 1 /. With "gross Exhaust gas loss "is the (sensible) heat content of the exhaust gas at the outlet of the boiler, which in the physically incorrect way of speaking of the 1st BImSchV is already treated as a relevant "waste gas loss" of the combustion system. (Only with the recent amendment 1996 of the 1st BImSchV was due to my criticism / 1 / the designation "Exhaust gas loss from the combustion system" for the gross exhaust gas loss in "Exhaust gas loss of the fireplace "is corrected). In / 4 / conventional methods for coping with the ses problem (secondary air devices, "chimney renovation" etc.) listed and crit Siert.

The combustion of fossil fuels for heating purposes is not fully exploitable the energy contained in the fuel (calorific value) can no longer be distributed It is the object of the invention to determine the net calorific value Exhaust gas loss (/ 1 /), i.e. the sensible and latent heat content of the exhaust gas at Leave the area of the house to be heated - by a suitable shape minimization and process control of the firing system and as far as possible dend from thermodynamically low-quality heat.

This task is accomplished through a method of utilizing the exhaust heat of a heater solved with the features of claim 1.

Advantageous refinements and applications of the method are in the dependent described claims.

The remaining inevitable net exhaust gas losses result from one  conventional fireplace that the discharge conditions for the fireplace (pressure and Temperature conditions according to DIN 4705, / 2 /) must be met:

Compliance with the temperature condition guarantees that the surface temperature in the Inside the chimney at the coldest point, usually above the water vapor dew point of the exhaust gas. In practice the tempera is used in many cases Door condition violated: precipitation of moisture and chimney sooting are the Episode. On the other hand, the flue gas conversion produces a dry flue gas, that inherently meets the temperature requirement of DIN 4705.

The remaining pressure condition of DIN 4705 guarantees that for the derivation of the Exhaust gases necessary negative pressure. It places demands on the overall buoyancy exhaust column and therefore only indirectly affects the temperature of the house exhaust gas from; however, this alone is decisive for the net Exhaust loss. The net exhaust gas losses can therefore be greatly reduced by converting the exhaust gas push down far; in addition, they largely consist of "low-value" Heat that was only extracted from the boiler flue gas at a low temperature and therefore not used for an alternative use in a hot water heating system can be set. - When using a roof fan, the pressure condition becomes me chanically enforced; the generation of the electrical current used for this purpose normally requires much less primary energy than the thermal supply of the Negative pressure in the fireplace.

Even with a pressure-resistant chimney, compliance with the pressure condition is not necessary DIN 4705. The exhaust gas transport may then only be carried out by one in the boiler area in installed exhaust fan can be effected. The net exhaust loss is then down only limited by the usage temperature of the heated house, i.e. the Room temperature below which the exhaust gas temperature will not be reduced in practice.

Since the exhaust gas converter (AGW) generates a dry exhaust gas, there are no requirements the moisture resistance of the fireplace. Conventional fireplaces can remain unchanged.

In recent years, heating technology has achieved a significant improvement in energy yield through the use of low and low temperature boilers and above all through the transition to condensing technology. The AGW process is an extension of the commercial process for using the condensing value. All existing boilers can be supplemented and improved by a downstream flue gas converter (AGW), which may only include a selection of the elements listed in Chapter 1. With new systems, the AGW can also be integrated directly into the boiler. Technological progress is that

• - The lowest usable condensation temperature does not depend on the temperature of the Heating return water is limited
• - There are no additional requirements for conventional fireplaces
• - An existing combustion system can be supplemented and thereby one cost-effective retrofitting to condensing technology becomes possible.

Even with advanced local heating technologies such as motor-driven gas heat pumps pe, heating with combined heat and power with motors ("power heating") or stationary The exhaust gas converter can be used for fuel cells in electricity and heat operation to free the moisture-containing exhaust gas from its moisture and the Condensation energy can be used for a low-temperature heating application tap.

The AGW process was presented for the first time in / 4 /. The techni specified there However, the realization still required too much space. In this scripture the Darstel further systematized and a compact implementation specified.

Embodiments of the invention are shown in the drawing and are in following described in more detail.

Show it:

Figure 1 A simplified block diagram of a combustion system with an exhaust gas converter.

Figure 2 The exhaust gas converter (AGW) according to Figure 1, but with minimal pressure drop in the exhaust gas path.

Figure 3 For comparison: conventional condensing boiler in the form of a block diagram analogous to Figures 1 and 2.

Figure 4 A specialized cross-flow heat exchanger as an air condensation cooler (LKK).

Figure 5 Interconnection of hot gas cooler (HGK), water condensation cooler (WKK) and air condensation cooler (LKK) to the exhaust gas converter (AGW)

2. The AGW process

In the exhaust gas converter (AGW) process, the original combustion exhaust gas ("boiler exhaust gas" 1) is further cooled down after the greatest possible transfer of its heat content to the heating water by heat exchange with ambient air or fresh air and then mixed with preheated external air to form "chimney exhaust gas" 8 . The chimney exhaust gas 8 is adjusted so that its water vapor dew point is below room temperature or so low that a water condensation inside the chimney can be excluded. In the case of a non-pressure-resistant chimney, the pressure condition of DIN 4705 can be met by using part of the air as external air which has been warmed up to cool the boiler exhaust gas; if necessary, the chimney exhaust gas 8 can be further heated by heat exchange with warmer parts of the boiler exhaust gas 1 .

In short: the flue gas converter converts hot and humid boiler flue gas 1 into lukewarm and dry chimney flue gas 8 with heat recovery.

Figure 1 shows a simplified block diagram of a combustion system with an exhaust gas converter. The original boiler exhaust gas 1 is first pre-cooled in the hot gas cooler 10 (HGK) without falling below the dew point and in the water condensation cooler 20 (WKK) the condensation heat is transferred as far as possible to the heating return. In the subsequent air condensation cooler 30 (LKK) there is an even more extensive cooling and dehumidification by heat transfer to ambient air (circulating air 4 and external air 5 ). The dew point of the cooled boiler exhaust gas is further reduced by the admixture of external air 5 and can be placed under the room temperature of the building without difficulty if the heat exchanger (rage) is designed accordingly. The boiler exhaust gas 1 mixed with external air 5 is referred to as chimney exhaust gas 8 . As external air 5 , the most used on the heated part of the LKK 30 for cooling the incoming boiler exhaust gas 1 is used air. After its maximum dehumidification in countercurrent, the boiler exhaust gas 1 is also reheated by the LKK 30 using low-temperature heat that is too cold to transfer heat to the heating return. If necessary, the flue gas 8 in the hot gas cooler 10 is warmed up even further and brought to the temperature necessary for maintaining the pressure condition of the fireplace 9 .

The mixing of the boiler exhaust gas 1 and external air 5 to the chimney exhaust gas 8 can, as shown in Figure 1 for the sake of simplicity, still take place in the LKK 30 after the maximum dehumidification of the boiler exhaust gas 1 . For technical reasons, however, efforts will be made to keep the pressure drop in the exhaust gas circuit as low as possible. It is therefore advisable to use the pressure force of the blower 60 , which drives the ambient air (circulating air 4 and external air 5 ) through the LKK 30 , as far as possible for the transport of the external air 5 and the external air 5 only after the heat transfer in the HGK 30 to mix the boiler exhaust gas 1 ( Fig. 2). While the circulating air 4 depends only on the cooling of the boiler exhaust gas 1 as far as possible, the precisely metered external air 5 should also receive the highest possible temperature increase in the LKK 30 . Therefore one will lead the external air 5 separately from the circulating air 4 on a longer path through the warmest part of the LKK 30 . The separately guided Kes selabgas 1 should lead because of the greatest possible utilization of the low temperature heat in countercurrent through the LKK 30 ; The transfer of high-quality heat in HGK 10 , on the other hand, can normally be restricted to outside air 5 (as shown in Figure 2). Only if there is very little external air supply must a direct re-heating of the boiler exhaust gas 1 in the HGK 10 be used.

energy value

An assessment of the heat transferred to the circulating air 4 in the LKK 30 was already made in section 2.2.3.2 of / 4 /. It can be attributed in part to the preheating of the combustion air and external air 5 from the outside temperature to the basement temperature. The further part serves the additional warming of the basement and thus partially benefits the ground floor thermally coupled to the basement / 7 /. The heat transferred to the circulating air 4 can of course also be used in the ventilation of utility rooms; due to the relatively low temperature, however, short distances should be observed.

The gross flue gas loss from the chimney flue gas 8 consists of a base of low temperature (NT) heat, which was recorded in the LKK 30 at a temperature which is below the return temperature of the hot water heating circuit, and a "high temperature" recorded in the HGK 10 ( HT) Percentage that was left in the heating circuit. This high-quality part and, in addition, a different part from the upper temperature range of the NT heat, depending on the local chimney conditions, is usually transferred as flue heat to the house to be heated during exhaust gas transport (/ 1 /). If the system is designed correctly, the net exhaust gas loss therefore consists exclusively of low-temperature "base heat", which ultimately comes entirely from the LKK 30 and could therefore not be used for transport via the hot water heating circuit. - It should be noted that in a conventional furnace the tangible net loss of exhaust gas comes almost entirely from high quality heat.

When fixing on the net exhaust gas loss, which is reasonable, the system is designed so that as little external air 5 is mixed in and takes a higher share of high-temperature heat from the HGK 10 in the gross exhaust gas loss. An undesirable transfer of high-temperature heat to the basement can be practically avoided if the warm flue gas 8 is introduced into the chimney at the upper edge of the basement through a well-insulated intermediate piece, as with a "stovepipe".

When fixing the gross exhaust gas loss, which is unreasonable but is suggested by the 1st BImSchV, one tries to minimize the amount of HGK heat and heats up a larger amount of external air 5 in the LKK 30 ; however, one must keep an eye on the higher resistance pressure due to the larger amount of chimney gas.

Classification of the conventional condensing boiler

Applying the Dastellungsweise of the image 1 or 2 to a conventional boiler, so one would have the boiler exhaust gas 1 to pass through the CHP 20 connect directly to the chimney 9 (Figure 3). The delivery pressure is usually generated by an exhaust gas fan, the chimney 9 must be pressure-resistant and moisture-resistant, that is, in old buildings, as a rule, "renovated". In addition, there is usually no defined structural separation between HGK 10 and WKK 20 , which makes the continuous use of stainless steel as a temperature-resistant and corrosion-resistant material necessary.

material selection

The constructive separation between HGK 10 and WKK 20 is not necessary for the functionality of the AGW, but results above all in technical and price advantages in the choice of materials. The hot gas cooler 10 (HGK) requires temperature-resistant materials, but these do not have to be particularly corrosion-resistant, because it is structurally prevented that the dew point in the HGK 10 is not exceeded. Copper for the heat exchanger and normal iron sheet for the other construction can be used. The water condensation cooler 20 (WKK) requires corrosion-resistant materials, but their temperature resistance can be limited, since the temperatures occurring in all operating states are limited by the upstream HGK 10 . In addition to stainless steel, copper plate protected by a plastic coating (see section 3.5 of / 10 /) can also be used as the heat exchanger surface. As other construction material, plastic, e.g. B. polypropylene (PP) can be used. If you also want to build the heat exchanger of the WKK 20 from plastic, you have to pay attention to the pressure resistance and oxygen tightness of the parts through which the heating water flows (/ 4 /). However, these restrictions no longer apply to the air condensation cooler 30 (LKK), which is a low-temperature gas-gas heat exchanger (heat exchanger = rage); standard plastics can therefore be used here, which provide the required corrosion resistance without difficulty.

scope of application

The exhaust gas conversion process can be applied to all modern combustion systems be applied. Old systems can be replaced without changing or modifying existing ones Plant parts can be supplemented, with new plants the exhaust gas conversion can be done from the start one can be integrated in the boiler. A detailed discussion of the different users The AGW procedure is carried out in Chapter 3; - in development The concept was initially inspired by the case of a natural gas boiler with a fan confessed.  

3. To implement the elements of the AGW process

In principle, conventional rage available on the market can be used for all elements of the AGW. However, the special conditions stimulate a new design that is tailored to the special requirements and possibilities. The considerations made in the laid-open documents / 8 / and / 9 / regarding the hot gas cooler 10 and water condensation cooler 20 have been transferred by division into the patent application / 10 /; reference is also made to the corresponding explanations in / 4 /. Therefore, the following application-related expressions on the air condensation cooler 30 and a comment on the chimney exhaust gas 8 can be limited.

3.1 Air condensation cooler (LKK)

In the air condensation cooler 30 (LKK), the pre-cooled exhaust gas 1 , which in the water condensation cooler 20 (WKK) has already lost its condensation heat, which is portable to the return water of the heating, is further cooled by ambient air (or, if available, fresh air) and thereby further dehumidified. Part of the ambient air preheated in countercurrent is then admixed as extraneous air 5 for further lowering the dew point and for generating lift to the boiler exhaust gas 1 . Section 3.11 specifies a simple version of the LKK 30 , which makes use of prefabricated plastic components from another area of application. Section 3.12 gives an indication of how the pressure conditions of the exhaust gas in the AGW can also be improved by using the fan 60 of the LKK 30 .

3.11 A simple air-exhaust gas heat exchanger

Upon entry into LKK 30, the boiler exhaust gas 1 is cooled down by the upstream Wärmeü bert rager the AGW that the LKK 30 can be fully manufactured from plastic gefer and should, as the condensate is corrosive, and wherein the air exhaust Wüt special requirements for pressure resistance and oxygen diffusion, as they occur with the WKK 20 , no longer exist. The basic concept can be assumed to be a cross-flow heat exchanger that is adapted to the special tasks of the LKK 30 .

The heat transfer on the flue gas side is significantly increased by the condensation, which greatly complies with the endeavor to deal with the pressure losses in the flue gas branch. On the air side, where an external blower 60 is unavoidable anyway, good heat transfer must and can be forced by appropriate pressure. Taking into account the special case that the condensation in the upstream WKK 20 fails due to an excessive return temperature, the air flow in the LKK 30 should be designed so large that, if necessary, a large part of the total heat of condensation can be absorbed. For natural gas, this corresponds to approximately ten times the stoichiometric exhaust gas flow.

The heated circulating air 4 should be free of exhaust gas components. This is guaranteed by the fact that the air in the LKK 30 has an overpressure to the boiler exhaust gas 1 , so that in the event of a leak, only additional external air enters the exhaust gas, which is harmless and takes place elsewhere anyway. Therefore, the air must not be sucked through the LKK 30 but must be pressed through it; the fan 60 must therefore be placed at the air inlet.

The upper part of the air flow facing the incoming boiler exhaust gas 1 is used as external air 5 . Therefore, its path through the external air heat exchanger 51 is doubled, which should cause the largest possible temperature rise. After passing through LKK 30, the boiler exhaust gas 1 is deflected by 180 degrees and returned upwards. In the upper part of the heat exchanger, the side part 57 of the LKK 30 , the cooling air heats up there, which is heated to a particularly large extent.

In the design example ( Fig. 4), the LKK 30 is built from commercially available multi-wall sheets (external air heat exchanger 51 , circulating air cooler 53 and side branch 57 ), which carry the air in their ducts (circulating air 4 and external fragrance 5 ) and the boiler exhaust gas 1 between their plates , The LKK 30 consists of a trunk in which the boiler exhaust gas 1 coming from the WKK 20 flows downwards through the external air heat exchanger 51 and the circulating air cooler 53 ; a right-hand exhaust side arm 55 and 58 is used for the conduction and reheating of the boiler exhaust gas 1 , a left-hand outside air side arm 59 for the removal of the outside air 5 .

Several multi-wall sheets are arranged in parallel. The distance between the plates is determined by strips attached to the side edge, which at the same time prevent the exhaust gas flow from escaping from the side. If necessary, additional spacers can be installed in the flow direction of the boiler exhaust gas 1 in the interior.

The incoming boiler exhaust gas 1 first flows from above into the external air heat exchanger 51 and then through the circulating air cooler 53 . After reversing the direction in the subspace 54 , it flows right through the exhaust side arm 55 upwards again and is warmed up somewhat in the side branch 57 of the LKK 30 . The boiler exhaust gas 1 then leaves the LKK 30 via the exhaust side arm 58 . Ambient air (circulating air 4 and external air 5 ) is drawn in from the left by the fan 60 and pressed into the distribution space 52 . The circulating air 4 is pressed through the lower, colder part of the LKK 30 , the circulating air cooler 53 , and is collected at the outlet thereof in the exhaust air duct 56 and led to the outside. From the exhaust air duct 56 , the only slightly warmed exhaust air can also be passed on in a duct or pipe to a place of use in the basement with particular heat requirements (eg "hobby room") or, for example, in the stairwell. Since the heat content of the exhaust air is relatively low, no expensive installation is worthwhile.

The outside air 5 is pressed out of the distribution space 52 into the lower part of the outside air heat exchanger 51 . This is flowed through in a loop, with at least some of the external air 5 still flowing back and forth through the side branch 57 of the LKK 30 , where the boiler exhaust gas 1 flowing upward is heated up again using low-temperature heat. In the upper part of the external air heat exchanger 51 of the LKK 30 , the external air 5 is then brought directly from the incoming boiler exhaust gas 1 to "low-temperature final temperature" and then flows out of the LKK 30 via the external air side arm 59 .

The commercially available multi-skin sheets are constructed as transparent components with special requirements for appearance, resistance to UV light, etc. Although they can be used well for the construction of an LKK 30 , their properties, which are not necessary for the LKK 30, lead to avoidable price increases. In mass production, therefore, 30 separate multi-wall sheets, e.g. B. made of polypropylene (PP). Their dimensions and material thicknesses can also be adapted and optimized for their use in the LKK 30 .

3.12 External air injector

The designer's ambition should be aimed at keeping the pressure losses in the AGW so low that a separate exhaust fan is not necessary for this area. An aid to this is the possibility of introducing the external air flow 5 , which is driven in a suitable design by the absolutely necessary fan 60 , into the boiler exhaust gas flow 1 at a high local speed. This injection effect creates a local vacuum which exerts a suction effect on the boiler exhaust gas 1 and thus helps to overcome the flow resistance of the AGW. The external air 5 can be injected at the outlet of the AGW (as shown in Figure 5) or even directly in the chimney 9 ; if necessary, the external air line can even be run a certain distance in the chimney 9 , so that the injecting effect also benefits the actual chimney draft.

It should be noted that it is an established method to increase the draft of a chimney by taking a part of the exhaust gas from the chimney with a separate fan and blowing it back into the chimney at high speed (see Recknagel-Sprenger / 5 /). The special conditions of the LKK 30 with its fan 60 , which is already available for another reason, make it possible to use this principle with only very little additional effort.

Especially when installing an AGW behind a boiler without a fan, e.g. B. an atmospheric gas boiler, the external air injection should be helpful.

3.2 Heat emission in the chimney

The temperature conditions of the chimney flue gas 8 in the chimney must meet the pressure conditions of DIN 4705 (Eq. (1) of / 2 /), i.e. guarantee the negative pressure required to discharge the flue gases. The buoyancy of the entire exhaust gas column can be described with sufficient approximation by the difference between the mean temperature of the exhaust gas in the chimney, T _m , and the outside temperature. If the design value of DIN 4705 is used for the outside temperature, this standard requires an exhaust gas temperature averaged over the length of the fireplace, which is determined by the geometry of the fireplace and the speed of the exhaust gas in the fireplace. However, the net to-gas losses are not determined by the average temperature of the flue gas, T _m , but by T _o , its final temperature when leaving the heated part of the building, i.e. at the upper cleaning flap.

A clever choice of the operating parameters of the chimney flue gas inlet temperature, T _e , and the proportion of external air as well as constructive measures in the design of the chimney can therefore reduce the net flue gas losses very far. However, these options cannot normally be used because the end temperature of the flue gas is held at a loss-making level by the temperature condition of DIN 4705 (Eq. (2) of / 2 /). Due to the extensive drying of the exhaust gas in the exhaust gas converter, this restriction no longer applies and the operating parameters of the chimney exhaust gas and the design of the fireplace can now be based entirely on the target value of low final temperature T _o and thus the lowest net exhaust gas losses.

The optimal selection of the operating parameters results from the equation for the average flue gas temperature in the chimney, T _m , (e .g. Eq. 7 of DIN 4705),

T _m = T _u + (T _e - T _u ) / K. (1 - exp (-K)), (9)

with the cooling number K

K = UkL / m / c _p (10)

Eq. (9) links the inlet temperature T _e with the mass flow m of the exhaust gas, where for a given boiler output the mass flow m can be taken as a measure of the outside air. In the Eq. (9) and (10) continue to denote (exact definitions see DIN 4705):
T _u = ambient temperature
U = inner chimney perimeter
L = length of the chimney
k = the heat transfer coefficient of the fireplace
c _p = specific heat capacity of the exhaust gas.

The optimization problem therefore consists in on the one hand obtaining the necessary buoyancy (pressure condition of DIN 4705) through T _m and on the other hand the exhaust gas temperature T _o which is decisive for the net exhaust gas loss (see Eq. (8) of / 2 /)

T _o = T _u + (T _e - T _u ) .exp (-K1) (11)

to keep it as small as possible. The cooling number K1 relates to the length L1 of the Chimney to the end of the heated area.

If one assumes full utilization of the chimney heat (cf. / 1 /), one becomes that Proportion of external air to that for the desired dew point temperature of the flue gas restrict the necessary size and choose its inlet temperature just high enough that the necessary boost comes about.

The ideal chimney, which allows very low net exhaust gas losses, is characterized by the following design features:

• - In the lower area a small cooling number K (according to Eq. (10), so good thermal insulation k, small U), which means that the exhaust gas temperature drops little at the beginning and produces thus buoyancy.
• - The best possible heat dissipation in the upper area of the building to be heated tion, i.e. a large cooling number K (large U and no insulation but rather one Increase the heat transfer to the chimney cheeks, as far as this is not too much Pressure consumed).

For example, a good chimney in terms of low net exhaust gas losses could be used by inserting a (possibly still insulated) plastic pipe into the lower one Realize part of a conventional chimney.  

In addition to these "passive" structural measures, the chimney gas can of course also be actively cooled in the upper area. The following are considered as heat-absorbing media:

• - circulating air from the heated house (see / 6 /)
• - Fresh air for ventilation of the house (see / 6 /)
• - Fresh air as combustion air
• - Heating water from a local low-temperature heating system (e.g. one for only one Limited floor heating).

4. Application of the AGW procedure 4.0 A compact exhaust gas converter

An example of a compact exhaust gas converter (AGW) is given in Figure 5 to illustrate the entire process. The AGW replaces, as it were, a piece of the connecting piece between the boiler and the chimney. The boiler exhaust gas 1 passes through the feed pipe 0 into the AGW, where it is diverted downward and flows through the hot gas cooler 10 (HGK), the water condensation cooler 20 (WKK) and the air condensing cooler 30 (LKK), and is then in the subspace 54 under the LKK 30 , where the condensate is also drained (not shown separately in Figure 5), diverted, passed in the exhaust side arm 55 past the LKK 30 without noticeable pressure loss, and then in the side branch 57 of the warmer part of the LKK 30 , the external air heat exchanger 51 to be warmed up again. In the exhaust side arm 58 , the boiler exhaust gas 1 is guided past the WKK 20 in order to then flow through the (“boiler exhaust gas”) side branch 101 of the HGK 10 into the mixing chamber 62 . There, or in the front part of the Ka min exhaust pipe 61 , the mixing of the boiler exhaust gas 1 with the external air 5 to the chimney exhaust 8 takes place.

The external air 5 , together with the circulating air 4 , is drawn in by the fan 60 , enters the distribution space 52 and finds its way there to the external air heat exchanger 51 of the LKK 30 . This external air heat exchanger 51 is flowed through in a loop, with at least some of the external air 5 still flowing through the side branch 57 of the LKK 30 and heating the backflowing boiler exhaust gas 1 again with low-temperature heat. In the upper part of the external air heat exchanger 51 of the LKK 30 , the external air 5 is then brought to the "low-temperature end temperature" by the boiler exhaust gas 1 coming directly from the WKK 20 and then flows over the external air side arm 59 past the WKK 20 and through the "Foreign air" side branch 105 of the HGK 10 through into the room 63 , where it can absorb the heat losses of the incoming boiler exhaust gas supply pipe 0. By means of the adjustable injector 64 , the outside air 5 finally flows at an increased speed with the target direction onto the chimney exhaust pipe 61 into the mixing chamber 62 . Due to the injection effect, part of the energy applied by the fan 60 is used to draw the boiler exhaust gas 1 through the AGW.

The circulating air 4 finds its way in the distribution space 52 through the circulating air cooler 53 of the LKK 30 , at the outlet of which it is collected in the exhaust air duct 56 and is conducted to the outside. (Of course, the heated exhaust air can also be routed from there to a specific location.)

The heating return that cools the WKK 20 was not shown in Figure 5. The HGK 10 is cooled either by a partial flow of the heating return or the heating flow.

The AGW can be designed in rough steps if, for practical reasons, some actuators are provided which enable the optimized adaptation to the given firing system (i.e. burner, boiler and exhaust system). These include (not shown in Figure 5):

• - An adjustable bypass in the HGK 10 both for the outside air 5 and for the boiler exhaust gas 1 , so that the transfer of high-quality HT heat to the chimney exhaust gas 8 can be limited to the extent necessary for compliance with the pressure condition. In the extreme case, both components of the flue gas flow must be able to pass the ribs of the side branches ( 101 and 105 ) of the HGK 10 . If the pressure in the boiler exhaust gas stream is scarce, the boiler exhaust gas stream 1 is passed past the boiler exhaust side branch 101 in any case.
• - Adjusting valves in the cooling circuit of the HGK 10 , which determine the temperature rise of the partial flow of the heating water flowing through the HGK 10 by specifying the flow quantity. In addition, the water flows through the two edge areas of the HGK 10 , to which heat flows from the boiler exhaust gas 1 and, where appropriate, heat flows out to the chimney exhaust gas 8 , must be regulated so that the temperature of their surface exposed to the boiler exhaust gas 1 is above the dew point ,
• - a throttle valve for measuring the external air flow. The throttle valve can simultaneously perform the function of the external air injector 64 (see section 3.12). Furthermore, the number of air ducts of the LKK 30 , which are used as external air ducts, should also be able to be changed in a few simple steps.

Depending on the type of upstream boiler, all ele elements or just a selection is required. The AGW can prepare for the most diverse given heating systems to be adapted. Some peculiarities are in fol listed below:

4.1 Subsequent connection of the AGW behind the standard boiler

The exhaust gas converter (AGW) can - with appropriate adaptation and design - in any existing furnace with a standard boiler or low temperature Switch on the sel afterwards.

Existing boilers are often under the pressure prescribed by the 1st BImSchV low gross exhaust gas loss and the technical requirement, the tempera To comply with the door condition of the fireplace (according to DIN 4705), on high combustion performance device and additional outside air. The AGW addresses these problems with ho hen security reserves solved in another way, so that the setting of the Kes sels fully on the actual energy saving and in particular on a minimie concentration of the net exhaust gas loss.

The boiler should be set to the highest possible CO2 content that Boiler power can be reduced to the optimal value. Because of who the slightly longer operating times with the same amount of heat supplied and a little generates higher dew point of the exhaust gas, which has a positive effect on the recovery of the high quality heat for the hot water heating circuit. An additional exhaust flap,  which are necessary to meet the nonsensical (cf. / 1 /) requirements of the 1st BImSchV in many systems had to be installed, should be ge to save energy be closed.

4.11 AGW behind gas boiler

Inserting an AGW behind a gas boiler with a forced draft burner should not be a problem special problems. The fan will normally still have enough reserve own the additional flow resistances of the AGW, which in its Ab gas branch can be designed for a particularly low pressure drop the.

Switching an AGW behind an atmospheric gas boiler requires some additional considerations. The flow protection is replaced by the controlled supply of outside air. The vacuum required to overcome the flow resistance in the boiler exhaust branch should be able to be provided by the injector effect when blowing in the external air 5 (see section 3.12), i.e. ultimately by the blower 60 of the LKK 30 . This external air injector 64 acts similarly to a downstream exhaust gas fan operating in suction mode. - In the case of particularly unfavorable local conditions, the pressure problem can be solved in any case by using an exhaust fan or a roof fan.

4.12 AGW behind oil-blowpipe

The exhaust gas from oil heaters differs from the exhaust gas from the combustion of natural gas in some points that are important for the application of the AGW. The petroleum exhaust gas:

• - contains less water vapor. With stoichiometric combustion, its dew lies point around 45 Celsius.
• - contains sulfur oxides; this makes it more aggressive and its condensate clearly clean more than is the case with natural gas exhaust.
• - May contain condensable hydrocarbons and soot components that lead to egg lead to pollution of the rage.

This has the following effects on the AGW:

• 1. The hot gas cooler 10 can and should be designed for a lower cooling temperature of the boiler exhaust gas 1 . The HGK preheater (see section 3.4 of / 10 /), which only has to guarantee a temperature of 45 Celsius in the HGK 10 , can be designed accordingly; the temperature spread of the HGK cooling water is much less critical than in the case of natural gas exhaust. In order to take the higher aggressiveness of the oil exhaust gas into account, the temperature spread will not be too small, however, so that the inevitable condensation area can be passed through particularly quickly when the heater is started up.
• 2. The water condensation cooler 20 (WKK) is of very little importance. It can therefore be omitted in the normal case, ie at the return temperatures of the usual hot water heating. The heat of condensation of the exhaust gas is then used exclusively in the LKK 30 , which is particularly corrosion-resistant due to the use of plastic.
• 3. The modular structure of the AGW makes the heat transfer easier to access for cleaning purposes. On easy expansion of the individual rage can and should be respected.
• 4. For safety reasons (theoretical risk of fire due to deposits), the automatic boiler shutdown at excessive temperatures behind the HGK 10 should be particularly safe and redundant.

Oil heaters are largely prevalent, even with smaller systems in the household rich -, operated with forced draft burners. This simplifies the application of the AGW.

4.13 Exhaust gas converter and 1st BImSchV

Since a boiler with AGW is a condensing boiler as defined in 1. BImSchV / 3 /, it is no longer subject to the annual according to §15 of the 1st BImSchV Supervision by the chimney sweep trade. Still, the requirements are the 1st BImSchV more than fulfilled. According to Appendix II of the 1st BImSchV the "exhaust gas ver lust ", that is, in physically correct terms, the gross exhaust gas loss is more noticeable Heat measured behind the last heat exchanger. By eliminating the one There are, however, restrictions due to the temperature conditions of DIN 4705 low values of the gross exhaust gas loss, because the pressure condition of the  DIN 4705 does not place high demands on the provision of fireplace heat. in the Normally, even by setting the boiler to high CO2 content and rather lower boiler output, the heat content of the boiler exhaust gas directly at Leaving the boiler comply with the limit value of the "exhaust gas loss" of the 1st BImSchV th.

The subsequent installation of an AGW thus represents an inexpensive and physically ver is a sensible means of sustainably adapting an existing firing system to adapt to increasingly stringent legal requirements. A badly isolated one The boiler can be subsequently insulated, a defective or "dirty" Burner can be repaired or replaced. So there is no need speed, to improve efficiency and in the transition to condensing technology replace the entire firing system immediately.

4.2 Condensing boiler with AGW 4.21 New system

With new systems, the integration of the AGW into the boiler brings customer-oriented advantages:

• - simple marketing
• - smaller footprint and compact appearance
• - Simple and unchanged installation compared to conventional condensing boilers
• - If the number of pieces is high, the overall price will also be cheaper.

A new firing system optimized according to the state of knowledge of the AGW process consists of a low-pollutant burner, a boiler with an integrated flue gas converter (i.e. a conventional condensing boiler with an additional built-in air condensation cooler 30 (LKK)) and a pressure-tight flue gas system. With a forced draft burner, the fan can be designed so strong that the pressure is sufficient for the entire boiler resistance (including AGW) and for the flue gas to pass through the flue pipe. The same applies to the use of an exhaust gas fan.

The heat transfer to the flue gas should be limited to the LKK 30 . The flue gas pipe should be installed inside the building without any special thermal insulation so that the heat content of the flue gas from the building can be largely used as chimney heat. The admixture of external air 5 should be set scarcely and should be limited to the amount required to lower the dew point below room temperature. In the case of a permanently moisture-proof and corrosion-resistant exhaust pipe, the external air 5 can then be dispensed with entirely if full utilization of the low-temperature heat of the LKK 30 is obtained; otherwise, the use of the low temperature heat by the chimney heat should be considered.

When replacing the boiler with burner in an existing firing system, a Boilers with integrated AGW can be purchased. A still functioning chimney stone can still be used.

If the boiler with AGW is used inside the apartment, - e.g. B. as "compact heating central" or the like -, so there is automatically a full use of the low temperature heat. When installing on the outside wall, direct fresh air cooling of the LKK 30 is obvious. An "AGW compact heating center" within a part of the building to be heated can use the calorific value of the fuel practically without loss. This is particularly attractive when using the condensation heat of an oil-heated system, where the use of a WKK 20 is hardly worthwhile and the entire condensation heat is therefore dissipated in the LKK 30 (see section 4.12). - However, attention must be paid to appropriate sound insulation.

4.22 Subsequent connection behind the existing condensing boiler

Even with a combustion system that is already equipped with a conventional condensing boiler, the connection of an AGW converter, which in this application is essentially reduced to an air condensation cooler 30 (LKK), can still be worthwhile. This applies in particular if

• - The flue gas fan usually installed in conventional condensing boilers is strong enough to overcome the additional flow resistance of the LKK 30
• - The heating system is not already at very low return temperatures, as with occur for example in underfloor heating.

4.3 Post-connection behind the fuel cell

The development of fuel cells for mobile, but also for stationary operation has Much progress has been made recently. For a stationary fuel cell that is in the "Electricity and heat operation" is used in the household or commercial area, read unusually high electrical and overall utilization rates are expected. (The The term "combined heat and power" instead of "electricity and heat operation" is used in Brenn fabric cells not appropriate, since the electricity is generated without mechanical "force" and electricity can also be used for purposes other than power generation). in the Contrary to a central "electricity and heat operation" can be decentralized Use of the fuel cell at the building level including low temperature heat and especially use the heat of condensation of the exhaust gas to a large extent. The common ones Fuel cells use natural gas, methanol or even hydrogen directly, so that this heat of condensation is not insignificant.

The exhaust gas from a fuel cell powered by natural gas does not differ basically that of a burner powered by natural gas. Because of the in ver process temperatures significantly lower than for the burner (this also applies to the "High temperature fuel cell") and the other properties of the fuel cell No nitrogen oxides can form, so that the exhaust gas must be very little corrosive te. For procedural reasons, fuel cell technology must be used for fuel cells Natural gas base, however, with a greatly increased air ratio lambda, e.g. B. lambda = 3 or more to be worked. For the application of the AGW, the exhaust gas can therefore be a Fuel cell with that of a very clean burner, with an excess of air of lambda = 3 and more, which equates to a dew point of approx. 40 ° Celsius and less speaks, be equated. Regarding the dew point, this corresponds approximately to the Ver Oil heating conditions, so that in Section 4.12 applies in this regard Let the considerations be transferred. The low corrosion effect of the fuel cell len exhaust gas also has a positive effect. (The dew point considerations of Exhaust gases require that no additional water for humidifying the fuel cell,  as is currently the case with PEM fuel cells must be set; otherwise the dew point is naturally higher.)

There is nothing against the heat and "waste heat" of fuel cells in the same ben way to use, like this with a burner with the around its flame built boiler and additional downstream exhaust gas use state of the art is. Then an overall efficiency can be achieved with stationary fuel cells, as you have so far only as a thermal efficiency only with boilers with know the condensing use. The decentralized use of fuel cells with one Extensive use of heat in the high temperature range for hot water and in the low temperature range as the first stage for the preparation of hot water and promised by the AGW for fresh air and ambient air heating most energetically sensible application of the use of natural gas for energy purposes become.  

literature

/ 1 / LUTHER, Gerhard: "A serious mistake in the ordinance on small combustion plants", GesundheitsIngenieur 117 (1996), pp. 113-126
/ 2 / DIN 4705 - Part 1: "Combustion calculations of chimney dimensions"; available among others in DIN Taschenbuch 146, Beuth-Verlag; Berlin; (1993)
/ 3 / First Ordinance for the Implementation of the Federal Immission Control Act (Ordinance on Small Combustion Plants - 1st BImSchV), Federal Law Gazette (1997), Part I No. 17, p. 491 ff., Issued on March 20, 1997
/ 4 / LUTHER, Gerhard: "Exhaust gas converter", laid-open specification DE 197 14 760 A1 from October 15, 1998 and associated patent specification DE 197 14 760 C2 from February 1, 2001
/ 5 / RECKNAGEL-SPRENGER: Paperback for heating and air conditioning technology, Olden bourg Verlag Munich, 59th edition 1977, page 526 (section 232-8)
/ 6 / LUTHER, Gerhard: "Usage-side heat recovery from exhaust gas", patent pending on July 21, 1994 at the German Patent Office in Munich under P 4425741.4
/ 7 / MRZIGLOD-HUND, Monika: "A new calculation method for the heat loss of components in contact with the ground", GesundheitsIngenieur 116 (1995), pp. 65-73 and 139-145
/ 8 / LUTHER, Gerhard: "Exhaust gas converter", published application DE 197 52 709 A1 from June 24, 1999
/ 9 / LUTHER, Gerhard: "Exhaust gas converter", published patent application EP 0 870 996 A2 from October 14, 1998
/ 10 / LUTHER, Gerhard: "Laminar, flat finned heat exchanger", publication DE 197 58 567 A1 of August 5, 1999
Author's address:
Dr. rer. nat. Gerhard Luther, Winterbergstr. 23, 66119 Saarbrucken
e-mail: luther.gerhard@vdi.de
Telephone: 0681-302-2737

Claims (9)

1. A method for using the exhaust gas heat of a heat generator for producing hot water in a heating system, the exhaust gases being successively precooled in a hot gas cooler ( 10 ) and cooled and partially condensed in a water condensation cooler ( 20 ), and wherein an additional heat exchanger (air condensation cooler 30 ) is used, characterized in that the air condensation cooler ( 30 ) is divided into two temperature sections in such a way that the lower temperature section is used for direct room air heating and the upper temperature section for heating outside air ( 5 ), and in that the heated outside air ( 5 ) is added to the exhaust gases to promote chimney draft and / or to reduce moisture. 2. Exhaust gas converter method according to claim 1, characterized in that the Heat generator coupled to power (engine heat pump, power heating) or directly electricity-operated (fuel cell) is operated. 3. Exhaust gas converter method according to claim 1 for further use and conversion of the exhaust gas of a conventional condensing boiler, an additional heat exchanger (air condensing cooler 30 ) being integrated into the condensing boiler or being connected as a separate unit at the lower temperature end, characterized in that the air condensing cooler ( 30 ) is in two temperature sections is divided so that the lower temperature section for direct room air heating and the upper temperature section for heating external air ( 5 ) is used, and that the heated external air ( 5 ) the boiler exhaust gas ( 1 ) to promote the chimney draft and / or to reduce the Moisture is added. 4. The exhaust gas converter method according to claim 1 for the further use and conversion of the exhaust gases of a heat generator, in particular an oil boiler, an additional heat exchanger (air condensation cooler 30 ) being integrated into the heat generator at the lower end of the temperature or being connected downstream as a separate unit, characterized in that the air condensation cooler ( 30 ) is divided into two temperature sections in such a way that the lower temperature section is used for direct room air heating and the upper temperature section for heating external air ( 5 ), and that the heated external air ( 5 ) is used for the boiler exhaust gas ( 1 ) to promote the chimney draft and / or is added to reduce the moisture. 5. Exhaust gas converter method according to claim 1 or one of claims 2 to 4, characterized in that the boiler exhaust gas ( 1 ) after its greatest dehumidification and cooling when passing through the air condensation cooler ( 30 ) as well as the external air ( 5 ) by the in the air condensation cooler ( 30 ) flowing boiler exhaust gas ( 1 ) is reheated. 6. Exhaust gas converter method according to at least one of claims 1 to 5, characterized in that the mixing of external air ( 5 ) and boiler exhaust gas ( 1 ) for chimney exhaust gas ( 8 ) takes place only in the chimney ( 9 ), the external air ( 5 ) in a dense Exhaust pipe can also be routed a suitable distance within the active chimney ( 9 ) or in a closed train of the chimney. 7. exhaust gas converter method according to at least one of claims 1 to 6, characterized in that the negative pressure in the exhaust gas path is not completely thermal, but mechanically by a roof fan or at least partially mechanically by the injection of external air ( 5 ) at the outlet of the air condensation cooler ( 30 ) or Suitable place in the chimney ( 9 ) is generated, and therefore in particular the heat transfer of high-quality heat that can still be absorbed by the heating water can be reduced or even avoided. 8. Exhaust gas converter method according to at least one of claims 1 to 7, characterized in that the preheated external air ( 5 ) in the air condensation cooler ( 30 ) is additionally heated in the hot gas cooler ( 10 ). 9. exhaust gas converter method according to at least one of claims 1 to 8 for minimizing the net exhaust gas losses from the chimney, characterized in that an optionally thermally insulated exhaust pipe is only inserted into the lower part of a conventional chimney ( 9 ).