CH676435A5 - - Google Patents

Description

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The invention relates to a method with the features of the preamble of claim 1 and an apparatus for performing this method.

A similar but simpler method is already shown in the patent specification DE 3 511 669 C2. This uses substances as neutralizing agents, some of which cannot be used in practice for security or cost reasons. The calcium compounds that can be used do not allow a longer operating time over an entire heating period; instead, the substrate must be replaced several times. The problem lies on the one hand in the lack of solubility of the reaction compounds formed during the neutralization process, e.g. CaS03 / CaS04; on the other hand in the insufficient amount of condensed water from the cooled flue gas at insufficiently low temperatures of the cooling water used in the heat exchanger from the heating return. Under these conditions, both insoluble sulfate sludge and inert shells form on the surfaces of the granules in the substrate fixed bed, so that the proper functioning of this process technology can only be guaranteed by constant maintenance work on the system. In addition, the application of this method is limited to the combustion of low-dust fuels, for example heating oil EL.

A further development of the application DE 3 511 669 C2 is already described in the published patent application DE 3 611 655 A1, special emphasis being placed on the correct selection of the neutralizing substances and on the optimal flue gas flow. Long-term functionality is also a priority in this further development. For this purpose neutralizing substances are used, which are very soluble after chemical conversion to sulfate, nitrate or chloride, e.g. MgO / Mg (ÖH) ä. At the same time, the water phase on the granulate surfaces is improved by a moisture mist, so that the pollutants dissolve in large quantities on the one hand, and on the other hand the rinsing out of the neutralization products also improves. In addition, the heat recovery is increased by an optimized flue gas flow. However, practice has shown that sulfur oxides evaporate from the condensates during burner downtimes because the sulfation during the neutralization process, the chemical conversion of the dissolved sulfite and hydrogen sulfite ions to sulfates, takes too long periods. The good levels of desulfurization are subsequently worsened again. In addition, when used oil or solids are burned, large amounts of metallic constituents from the dust carried by the flue gas accumulate on the wet granulate surfaces, e.g. Lead, zinc, chromium, iron and cadmium, but also metal nitrates and metal sulfates, as well as carbon black and alkaline earth oxides. For example, iron hydroxide, iron oxide and iron oxide are formed on reaction to MgO from iron sulfates on the moist granulate surface

Magnesium sulfate. The iron hydroxides precipitate as flakes at a pH of approx. 6; The iron oxides permanently block the surfaces of the granulate spheres and create inert shells that can no longer react with the flue gas pollutants. The pH of the wet granulate surfaces drops into the acidic range, so that the solubility in the flue gas is also reduced entrained sulfur oxides is reduced. There are therefore further starting points for improving the functionality of this flue gas cleaning system.

A further development of this method is described in the present application. The aim of this invention is a method that more completely solves the tasks of the published patent application DE 3 611 655 A1 beyond the use in furnaces with heating oil EL / S, with particular emphasis being placed on largely preventing the desorption of sulfur oxides during downtimes of the furnace becomes. The aim of the invention also includes largely preventing the permanent accumulation of metals, metal compounds, soot, dust and other solids on the granule surfaces, so that the possibility of the formation of inert shells and a drop in the pH value is reduced, as a result of which the solubility of the pollutants is reduced as much as possible.

For this reason, an intensive spray system is used in the present invention, which, at regular intervals and for any length of time, neutralizes the products of neutralization that have formed on the surface of the granules during the chemical reaction process, e.g. Magnesium sulfite, quickly rinsed out, at the same time supplying oxygen, and then integrating it into a process water circuit which also oxidises through contact with air, so that the sulfation as a whole is accelerated and stabilized at the same time. In addition, the sulfate or pollutant-containing condensate, which accumulates as an excess amount of water, is collected in a collecting container, so that easy disposal is possible when the water has evaporated in the warm season. The process water cycle carries the pollutants transported in the water flow, e.g. dissolved MgS04, by means of a pump via another external filter system, where the pollutants are sometimes separated.

In addition, the soot and dust solids are flushed out with a powerful water flow with this spray system. As is well known in specialist circles, dust is understood to mean above all the very harmful heavy metal emissions. These particles are also fed into the external filter system via the water circuit, where they are fed to the flooded filter substrate with a large dwell time from bottom to top, so that they can accumulate there.

In a preferred embodiment of this process technology, this additional spray function is activated by means of a process water circuit in the respective burner downtimes when there is intermittent operation of the heating system. Thus, during burner 5

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Running in the primary filter from the flue gas stream, condensates that partially contain dissolved and solid pollutants are immediately integrated into the water stream and sulfated, which largely prevents the evaporation of sulfur oxides from the sulfite phase.

Firing systems operated with fossil fuels are known to contain large amounts of pollutants in their flue gases, which are significantly involved in environmental pollution with their known harmful consequences, e.g. Sulfur oxides, nitrogen oxides, carbon monoxides, soot, dust, heavy metals, hydrogen chloride, halogens etc.

When removing pollutants from flue gases, there is the problem that, on the one hand, the pollutants must be removed thoroughly, i.e. with a high degree of efficiency, since they should be usable in single-family houses, public buildings and commercial establishments as well as in large combustion plants, that the plants have a low manufacturing price must show that the plants may only have little moving and therefore serviceable parts, that the plants must have a low energy requirement and that the toxins occur in neutralized form and in small volumes.

The large combustion plants that are newly built today are generally provided with desulphurization plants; existing plants are partially retrofitted or shut down. The desulphurization plants in use today, which are used in large combustion plants, work largely with the lime water process - wet desulphurization - whereby the flue gas is sprayed with lime water after filtering off the dust it contains. The lime converts with the sulfur oxide to gypsum, which is then removed after drying. In a similar process, ammonia water is used instead of lime water, in which case the end product is ammonium sulfate, which can be used as an artificial fertilizer in agriculture.

This known principle is also used in a simplified form for smaller combustion plants, but minimum heat outputs of 200 kW are required for reasons of profitability. For cost reasons, small systems for single and smaller apartment buildings for combustion systems up to 50 kW are out of the question.

DE-OS 3 228 885 describes a flue gas scrubbing process in which the flue gases, after cooling, are passed in countercurrent through a conventional gas scrubber against sprayed-in water, and the acids which form during this process are then neutralized. Such flue gas scrubbers, which work with neutral liquid, are very expensive because of the large number of pumps required and high water consumption, and the process requires plants with a large construction volume.

DE-OS 3 210 236 describes the recovery of condensable substances from a gas stream. Condensable liquids are removed from a gas stream by

Cools liquid by supplying an identical, cooled liquid and then leads the partially cleaned gas stream in a second stage over an activated carbon bed in order to allow further condensable liquid to be absorbed by the activated carbon there. In the described method, the fixed bed serves solely as an absorbent, which does not cause any chemical change in the absorbed substance. It is therefore necessary that in a further step the absorbed substances have to be recovered again by regeneration or else have to be converted chemically.

Starting from the aforementioned prior art, it is an object of the present invention to provide a method for smaller, possibly already existing heating systems according to the preamble of the main claim, which allows inexpensive and yet effective removal of pollutants from the flue gases and their detoxification, and a device to provide for performing this procedure.

This object is achieved in a process according to the preamble of the main claim by allowing the cooled gases to react on regularly flushed granules, with the reaction products from the chemical neutralization process being quickly added with the aid of a separate process water circuit and spraying devices and pumps integrates the process water, which is permanently supplied with oxygen with the help of an oxidation device. These intensive rinses also prevent the accumulation of solids in the filter system. Rather, these solids and the neutralization products are fed into another, separate filter system, where they remain.

Practice has shown that the space available in the boiler rooms also requires a low-construction desulfurization system.

This object is achieved in that the heat exchanger and desulfurization system are arranged in parallel / next to one another (upright or hanging).

Practice has also shown that it is necessary to regularly rinse the granules in the filter system in order to remove foreign bodies (e.g. soot, dust, etc.). These rinses also increase the moisture level on the surfaces of the granules, so that the effectiveness of the desulfurization is increased.

New findings indicate that the SO2 molecules retained are very volatile in gas and in part escape again from the granules during downtimes, which means that the degree of desulfurization subsequently deteriorates.

This problem is solved by the fact that most S02 molecules that are integrated in the aqueous phase on the surfaces of the granules, e.g. as H2SO3 / H2SO4, or MgS03 / MgS04 are rinsed out as quickly as possible and integrated into a closed circuit water system. Within this system there is a second filter system, which is constantly under water. The granules contained therein, which

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partly contains CaCo3 and MgO-Mg (OH) 2, binds the sulfur-containing substances in the process water, so that a gaseous escape of sulfur-containing molecules is largely prevented. In some cases, sulfites, for example Ca-SQs, are formed, which precipitate downwards in the form of flakes. At the end of the heating period, they are disposed of and oxidized to sulfates if necessary, e.g. CaS04 / MgS04.

In the drawing, an apparatus for performing the method according to the invention is illustrated. Show it;

1 shows a device installed between the chimney and the furnace in a schematic representation;

Figure 2 shows the abdominal gas cleaning system in section.

Fig. 3 is a section along the line A-A of Fig. 2;

Fig. 4 is a section along the line B-B of Fig. 2 and

5 shows a detail according to FIG. 2, but enlarged compared to the latter.

According to FIG. 1, a flue gas cleaning system 2 is arranged between a combustion system, ie a boiler 3 and a chimney 1. The flue gas cleaning system 2 is installed in the flue gas line 4. The pipe 5 of the return water (see the arrows) is interrupted and is first led into the flue gas cleaning system 2; from there, the return water heated by a heat exchanger is passed on to the boiler 3. After complete heating in the boiler 3, the water is fed into the feed line 6, for which purpose the arrows must be used.

At 7, the flue gases emerging from the reaction container (see FIG. 2) are mixed with fresh air before entering the chimney 1. An electric motor (not shown) with a fan ensures that the flue gases are transported quickly. The neutralized condensates circulate with the process water (see arrows 8). The resulting sulfates and other pollutants are retained in the filter system 9.

It can be seen from FIG. 2 that the flue gases 10 are conducted from the firing system 3 into the reaction container. The still hot flue gases 11 are passed over the exchanger surfaces of a flue gas heat exchanger, the temperature decreasing to about 60 to 80 ° C. The inside diameter water of the heating return is warmed up. The cooled flue gases 12 and any condensates are directed downwards towards the sump or filter system. When flowing through the filter system, further cooling takes place, essentially the process water dissipates heat to the outside, which in turn heats the room air. This room air is used for combustion, so that overall these heat losses are negligible. For this purpose, reference is also made to FIG. 5.

Acidic condensates 13 are neutralized to pH 6.5 to 8.5. Excess water is drained off separately. The cooled flue gases 14

carry additional condensates with them as they flow up through the filter bed. The SOx content within the filter system is reduced by 60 to 98%. Further condensates drip down into the sump. Parts of the S02 molecules remain in the filter bed, other parts are rinsed out. Condensed water 15 and neutralized acid condensates in the process water are fed into the process cycle.

The process water carrying sulfates 16 enters a separate double tank which is designed for a certain level. There is a second filter system in the inner tank, which is completely flooded with process water. The process water flows through a downpipe into the lower area; from there it flows up to the overflow with sufficient dwell time, releasing the sulfates on contacting the granules. Some of the sulfur components from the condensates (e.g. H2SO3 or H2SO4 or MgS03 / MgS04) combine with the granules to form sulfite and precipitate downwards in flakes. In the second filter system 17 there is a granulate which contains a mixture of MgO / Mg (0H) 2 / Ca0 / CaC03 with the addition of iron oxides, aluminum oxides, silicon oxides and other neutralizing substances. The sulfates are transferred from the surrounding water into the granulate.

The process water freed from sulfates is conveyed back to the flue gas cleaning system 2 by means of a pump (cf. reference number 18), where it is used again for wetting and flushing out the first filter system. Wet granules increase the degree of SOx separation. The rinsing prevents clogging of the first filter system by soot, dust, sulfates and the like. The pump is preferably in operation during the burner downtimes (cf. also FIG. 5). Excesses 19 due to condensation of the flue gas water must be removed. If necessary, contact another substance that binds the sulfates. Excess water, which is largely free of sulfates, with a pH of approx. 7, can be fed into the sewage system 20. Excess water can optionally also be removed by care personnel using a collecting container 21.

The water of the heating return 22 (see also 5 in Fig. 1) is heated in the heat exchanger. This means that the burner in the boiler has to use less energy to bring the water to the supply temperature. The energy saving is between 5 and 15%, depending on the type, condition and mode of operation of the furnace. The water flows through the heat exchanger through horizontal holes from bottom to top, changing from one side to the other, always increasing one step higher. This function is ensured by covers on both sides of the heat exchanger. Optionally, process water is also used as the cooling medium, for which reference should also be made to FIG. 4.

The cleaned flue gases 23 (see FIG. 5) are 5

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which warmed up somewhat when entering the ventilation area (cf. FIG. 24 in FIGS. 3 and 5). The heat of neutralization also causes a slight warming. Any losses that occur are compensated for by a fan 24. The fan 24, which is designed as an induced draft fan, conveys the flue gases 25 with admixed fresh air in the direction of the chimney 1 (in this regard, reference is made particularly to FIG. 3). The fan 24 is preferably operated simultaneously with the burner.

The flue gases 26 flowing in the direction of the chimney 1 (see FIG. 5) are admixed with fresh air (approx. 3 to 6 times the amount of the flue gases). The water dew point can thus be reduced to up to 20 ° C. A closed tower 27 (see FIGS. 2 and 5) surrounds the first filter system. Like the heat exchanger, the tower 27 is constantly surrounded by fresh air from the bottom to the top, which is drawn in by the fan together with the flue gases. On the inside of the tower, the flue gases always hit relatively cold surfaces. A basket 28 of the first filter system hangs in the tower 27; this basket 28 is significantly smaller in the outer dimensions, so that a cross section remains for the rising smoke gases. From this cross-section, the flue gases initially flow radially / horizontally into the granulate. Then vertically upwards. The granules are e.g. made of MgO Mg (0H) 2, mixed with CaC03 and others Within the filter basket 28 there is a second, smaller basket 29 which ensures a cavity within the granulate fixed bed. The pressure losses are thus kept low. The pressure is monitored in the cavity 30 (FIG. 5) of the fixed bed. A pressure switch 31 is connected via a pipe connection. The pressure switch 31 puts the safety device into operation when a fixed value is exceeded or fallen short of. The flue gas flap 33 (FIG. 3) is brought into the respectively required position by means of a motor which is coupled to the blower, burner and pressure switch. The pump for the process water should also be considered part of this overall electrical switching coupling. The flue gas flap 33 is in any case to be regarded as a safety element. In normal operation it is closed so that the flue gases cannot flow directly to chimney 1, you then have to flow down the heat exchanger through a number of holes in the direction of the desulfurization system.

In the event of faults in the system, the flue gas flap 33 can open. The flap itself is not absolutely rigidly coupled to the motor shaft. In the case of strong external forces, e.g. in the event of a sudden deflagration from the combustion chamber, it can be pushed open. With the flap open. 33, the flue gases 34 flow directly to the chimney 1. At the same time, the fan 24 is switched off, so that they cannot escape downwards or outwards. With this flap position, the desulfurization system is out of operation.

The flue gases flow through vertical holes 35 in the heat exchanger when the heat exchanger is closed

Flap down. The water of the heating return flows through horizontal bores 36 in the heat exchanger, which are arranged between the vertical bores. The thermal insulation 37 (see FIGS. 2 and 4) prevents heat loss to the outside. Instead, this heat is absorbed by the air flowing in at 26 and fed to the cleaned flue gases. This ensures a better chimney draft. The basket 38 filled with granules according to FIG. 2 is immersed with the granules below the sump level. Moisture constantly rises from the swamp water and keeps the entire fixed bed or the surface of the granules constantly wet.

Claims (7)

Claims 1.Procedure for removing pollutants from the flue gases of combustion plants, whereby the flue gases are cooled down in the direction of the sump of the flue gas cleaning plant to the condensation area and the condensate is allowed to react with neutralizing substances and the flue gases are removed via a chimney, whereby the cooled gases together with the condensing gas components are passed upstream over solid substrates which at least partially contain the neutralizing substances magnesite and dolomite, and that they are flowed in beforehand from below and to the side of the substrate or granulate fixed bed , characterized in that the flue gases allow further heat to be given off to substrates and housing walls, that an additional process water circuit by means of a primary water filling and occasionally occurring condensates with the help of pump and spray elements over any period of time the surfaces of the substrate. b between the granulate fixed bed rinses and wets them so that, in addition to dust and soot, the flue gas pollutants on the wet surfaces in solution and then in the neutralization process are immediately integrated into the water * or condensate circuit and oxidized therein by high dwell time and air contact they pass through at least one additional separate filter system within the process water cycle, which both absorbs neutralization products, chemically through material conversions, and at least partially removes them from the cycle through flocculation, accumulation or settling, as well as the solids carried by the process water. 2. The method according to claim 1, characterized in that the heat removed from the process water is released into the room air, which in turn is used for combustion. 3. The method according to claims 1 and 2, characterized in that excesses are removed by condensation of the flue gas water from the second filter system and optionally contacted again with sulfate-binding substances. 4. The method according to claims 1 to 3, characterized in that the reaction vessel from the bottom up with fresh air from a 5 10th 15 20th 25th 30th 35 40 45 50 55 60 65 5 9 CH676435A5 Fan is sucked in together with the flue gases, flows around. 5. Device for carrying out the method according to claims 1 to 4, with a reaction vessel connected downstream of the firing system, characterized in that the reaction vessel is arranged parallel and vertically next to one another, a heat exchanger (11, 22, 36) and a 1. Has filter system (28) and on the bottom contains a sump into which the first cavity (29) having the first filter system (28) is immersed, which is provided with a downward-acting rinsing or spraying device (18) which is connected to the sump (38, 12-14), with a between the sump and rinsing or spraying device 2.Filter system is provided, which consists of an inner container (16) of a double container filled with granulate and under process water, the lower area of the inner container being connected to the process water line from the bottom of the reaction container via a downpipe and the inner one Container has an overflow and a pump is provided for transporting the process water to the rinsing or spraying device. 6. The device according to claim 5, characterized in that the outer container of the double container has an outlet (19) which serves to discharge excess process water, 7. The device according to claim 5 or 6, characterized in that there is a ventilation area above the 1st filter system, to which an induced draft fan (24, 25) for fresh air and the smoke gases emerging from the 1st filter system is connected, this ventilation area from the flue gas inlet chamber arranged above the heat exchanger is separated by a flue gas flap (33) as a safety element. 5 10th 15 20th 25th 30th 35 40 45 50 55 60 65 6