The invention in question is designed for a process for combined heat exchanging and gas cleaning, especially by heating of fossil fuel to achieve high efficiency in heating plants or similar air technical plants and device for the accomplishing of the process.

The significance of the treating of flue gases has increased, especially when solid fuel is used. Until now, this has mostly been accomplished through so called electrostatic filters or cyclones. A more efficient heat exchanging of the flue gases has not been possible, as these gases have contained too much dust even after the dust collectors. In addition, too heavy cooling of the flue gases has caused acid pre¬ cipitation and consequently corrosion problems. But -if the heat exchanging is economically effected, it allows large quantities of energy to be saved through higher efficiency in the boiler plant. Therefore, _. .it must be accomplished in combination with efficient dust separation as well as separation of the sulphur gases that caused the corrosion. An important aspect of above is, that if the problem can be satisfactory solved, technically and economically, the investment in such a system will be profitable in contrast to other investments in equipment for environmental management. These investments are often regarded as very costly from the point of view of business economics.

The process, described as follows, is based on cleaning of the flue gases through so called fabric filters and by adding basic substances to the flue gas. The heat exchanging is effected by so called regenerative heat exchanging. These components are already known, but the invention implies an expan¬ sion in this field.

The principal for a fabric filter is that dust particles in the gas, which flows through the filter, stick to the filter due to certain electrical and physical forces. Then the clogging of the filter has been in process for a certain time and the pressure drop accordingly has reached a certain rate, the filt- ration stops and clean gas passes in reversed direc¬ tion to dissolve the greater part of the jammed particles, and these settle down into a dustbin.

By adding basic substances and/or water to the flue gas, there is a chemical reaction between these and the greater part of the gaseous sulphur compounds, and the latter are transformed into solid sulphur compounds. These are thereafter separated together with remaining dust if dust filter is used.

Regenerative heat exchanging means that gases flow alternating through two heat exchanging masses. The colder gas then absorbs the heat, which has been emitted from hot gas to one of the heat exchanging masses in a previous cycle.

The purpose of the invention in question is to achieve a simple process with the appropriate equipment for combined heat exchanging and gas cleaning. It is characterized of what is made clear in the enclosed patent claims.

The invention will now be further described with reference to the enclosed drawing. Figure 1 shows the fundamental construction and figure 2 the gas exchanger 12 or 13 in figure 1.

In figure 1 , duct I is meant for hot uncleaned gas from a boiler plant, duct II pre-heated combustion air to the boiler plant, duct III cold combustion air from inlet hood and duct IV cold flue gas to the chimney. The gas ecchangers 12 and 13 are equal and the flows in the ducts I - IV are independent of the position of the gas exchangers. The other parts con¬ sist of two equal units a and b, where aO means a dustbin, a1 a gas reactor, a2 a filter cassette, a3 primary mass containing heat exchanger, a4 secondary mass containing heat exchanger, a5 duct for cold flue gas, a6 duct for cold combustion air, a7 pipe for con¬ densation water, a8 pipe for injection of water and/ or basic substances, a9 duct for hot uncleaned flue gas, a10 duct for preheated combustion air and all an instrument for the dosing of basic substances. The corresponding symbols are applicable for unit b. The gas exchangers 12 and 13 work as follows: gas flows simultaneously in the ducts a5, a9, b6 and blO when the unit a receives the flue gas. At this time no gas flows in ducts a6, a10, b5 and b9. Figure 1 shows this. The arrows in brackets show the flow when unit b is filtrating.

Suppose that unit a is filtrating. The hot flue gas from duct 1 then flows through the gas exchanger 12 and duct a9 into the gas reactor a1 of unit a, at which part of the dust has been deflected down to the dustbin aO. At the same time basic substances and/or water is injected through the pipe a8. A chemical

reaction is whit this possible between sulphur gases and the injected basic substance when the gas passes the gas reactor a1 , solid sulphur compounds are formed and these are filtrated on the filter cassette a2 to- gether with other dust particles. If just water is injected into the flue gas, an increased reaction between the alkalic components in the fly ash and the sulphur gases is achieved, especially on the filter cassette. After that, the gas is heating the masses in the primary a3 and the secondary heat exchanger a4, at which it is cooled itself and comes into duct IV via the gas exchanger 12 and duct a5. Condensated water from a4 is drained via pipe a7. During the same cycle, the cold combustion air comes from duct III via gas exchanger 13 and duct bβ to the masses in the secondary heat exchanger b4 and the primary heat exchanger b3. At this, the heat, which has been stored during the previous cycle in these heat exchanger masses is ab¬ sorbed, at which these are cooled.

The time of the cycle is so determined that the mass in the primary heat exchanger b3 does not get so cold that water is accumulated in this during the following cycle, when flue gas with a high percentage of water is passing and is cooled in. this heat exchanger mass. At this, water will only condensate in the mass in the secondary heat exchanger b4 and this will thereby work as a water separator. This water is led through pipe b7 to an accumulation tank to be injected in gas reactor b1 during the filtration cycle of unit b, possible together with basic substances via pipe b11. It is by this achieved that water, which has been used for the gas cleaning, can be recirculated.

The gas, which has been heated by the masses in the heat exchangers b3 and b4 will now clean the filter cassette b2 from dust, which settles down in the dust¬ bin bO. After that, the gas leaves b1 and flows via 5 duct b10 and gas exchanger 12 into duct II and then to the boiler to be used as pre-heated combustion air.

The gas exchanger 12 and 13 in figure 1 will now be further described in figure 2. The gas exchanger 13

10 consists of two triangular chambers, connected to each other along their respective base part, where one of the chambers receives gas through duct III. This gas is either led to duct a.6 or to duct bβ, depending on the position of a valve blade 1. The

15 other chamber emits gas through duct IV. This gas has been led to the same chamber, either from duct a5 or duct b5 depending on the position of a valve blade 2. The ducts a5, b5, a6 and bβ are led approp¬ riately far into respective chambers and so function

20 as valve seats for the valve blades 1 and 2. The valve blades 1 and 2 shift their positions simul¬ taneously by the link system 3, 4, 5 and F.

Of course, the invention does not restrict to this 25 model, but can be varied within the limits of the idea.

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-BUREAU