FI104052B - Method and arrangement for purifying the exhaust gases - Google Patents

Description

104052

METHOD AND ARRANGEMENT FOR EXHAUST GAS CLEANING -FÖRFARANDE OCH ARRANGEMANG FÖR RENING AV AVGASER

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The invention relates to a method for purifying the exhaust gases of an internal combustion engine, burner or other similar burner arrangement from environmentally harmful substances, in particular sulfur compounds, and to a scrubber arrangement for applying the method according to the preamble of claim 1.

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Various methods have been developed to reduce the harmful emissions caused by increasing energy production. In particular, many grades of fuel oil have a problem with the sulfur they contain, the combustion of which produces environmentally harmful sulfur dioxide (SO2). For example, a scrubber utilizing, for example, sodium hydroxide (NaOH) in a waste water stream containing water, sodium sulfates (Na2SO4, NaHSO4) and sodium sulfites (Na2SO3, NaHSO3) can be used to substantially eliminate or reduce sulfur dioxide emissions. Sodium umulphates are environmentally friendly salts, but instead. ·. ··. sodium sulphites are a burden on the environment, particularly because of their oxygen-consuming effect. To eliminate this disadvantage, after the scrubber wastewater-det directed to a oksidointireaktoriin, by adhering to the oxygen with sodium sulfite to form environmentally harmless natriumsulfaattisuoloja.

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• * ·· However, the solution is complex, bulky and expensive. From WO

97/24172 is a known arrangement in which air and alkaline wash solution are fed to 25 reactor units, without the need for a separate oxidation reactor tank.

It is an object of the present invention to provide an improved process for purifying the exhaust gases of an internal combustion engine, burner or similar burner arrangement from sulfur dioxide (SO 2) contained therein which is simpler and less expensive than known processes, It is a further object of the invention to provide a process which is particularly suitable for purifying the exhaust emissions of diesel engines from their sulfur emissions and provides a more compact solution for the application of the method.

The object of the invention is achieved as set forth in claim 1 and other claims. According to the invention, the washing solution recovered from the lower part of the reactor unit is pumped into the nozzles by utilizing a recirculation pump to which air or a mixture of air and water is added to the pressure side so that the washing solution reacts with harmful substances.

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Thus, the invention is based on the one hand that the exhaust gases of diesel engines in particular contain moderately oxygen, and on the other hand that when oxygen is added to the alkaline wash solution, the sulfur dioxide of the exhaust gases is absorbed and reacted still react with the available oxygen, whereby only environmentally harmless sulphate salts are formed without the use of a separate oxidation reactor. The solution according to the invention can improve the efficiency of the process. Except for the basic chemical reactions themselves, the sulphate and sulphite salts:. For the purpose of forming 20 herein, it is specifically meant the reactions whereby sulfate salts are further obtained from the sulfite salts.

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If the pH of the wash solution accumulating at the bottom of the reactor unit is determined, ι · ι v · * may be added to the wash solution as needed prior to the wash solution being introduced into the nozzles so that the pH of the wash solution in the reactor unit • V « , preferably between 6-8.

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• ·? A: As additional washing solution gradually builds up at the bottom of the reactor unit, it can sometimes be emptied as needed, since the neutral washing solution itself is not I I t 30 mil.

3 104052

The present invention relates to a butterfly arrangement utilizing the above-described method as defined in claims 4-7.

The invention will now be described, by way of example, with reference to the accompanying drawing, the sole figure of which shows in principle a practical application of the method according to the invention.

In the drawing, 1 denotes a tank reactor unit into which the exhaust gases of an unshown internal combustion engine or the like are introduced through conduit 2 and, after cleaning, are led from the top of the reactor assembly through conduit 3. The reactor unit 1 is provided with a plurality of nozzles 4 for supplying an alkaline wash solution to the exhaust gas stream flowing through the reactor unit 1.

Reference numeral 5 denotes a wash solution re-supply circuit through which the solution accumulating at the bottom of the reactor unit 1 is recovered and recirculated by pump 6 continuously through the nozzles 4. Circuit 5 includes an alkaline solution reservoir 7 from which pump 8 pumps the washing solution to circuit 5 as needed, and means 9 for supplying a mixture of air or air and water to the washing solution on the pressure side of the recirculation pump 6. The reactor unit 1 is provided with a pH measuring means 10 and a logic unit 11 which acts on the pump 8 to keep the alkaline solution from being supplied to the oh-20. The circuit 5 further comprises an outlet pipe 13 with an outlet valve 12.

Mil • · • »•« · • Il; In the initial stage of exhaust gas purification, the alkaline scrubbing solution is first introduced into the reactor unit 1 either through nozzle means 4 and by means of means 7 and 8.

It may be by means of a separate or separate feeding means (not shown) so that the scrubbing solution reacts with the sulfur compounds present in the exhaust gases, also utilizing the residual oxygen in the scrubbing gases. also compounds resulting from chemical reactions are continuously circulated through circuit 5 with the addition of air or air-water mixture to provide a continuous reaction process.

4, 104052

The alkaline solution to be fed may preferably be sodium hydroxide, which results in chemical reactions of at least the following formulas: (1) 2 NaOH + SO 2 + 1/202 -> Na 2 SO 4 + H 2 O 5 (2) 2 NaOH + SO 2 -> Na 2 SO 3 + H 2 O

The environmentally harmful sodium sulfite further reacts with oxygen by the process of the invention to form environmentally safe sodium sulfate as follows: 10 (3) Na2SO3 + 1/202 -> Na2SO4

Other suitable alkaline solutions such as calcium hydroxide (CaOH) can be used instead of sodium hydroxide (NaOH), whereby in the above formulas sodium (Na) is merely replaced by calcium (Ca).

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The pH of the washing solution accumulating at the bottom of the reaction unit is sought to be neutral using the means 7, 8, 10 and 11, whereby the value may vary, for example, between 6-8. This ensures that the reactor unit is surrounded by; a waste solution which is as harmless as possible to the system and can be discharged from the reactor unit by the outlet pipe 13 of the valves 12 and 20 once it has accumulated to the bottom of the reactor unit. The reactor unit can be emptied at the same time as the scrubbing of the exhaust gas, whereby the washing solution is also fed through the reflux circuit 5 to the nozzles 4.

The invention is not limited to the embodiment shown, but a number of variations are contemplated within the scope of the appended claims.

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Claims (7)

5 104052 1. A process for purifying the exhaust gases of an internal combustion engine, burner or similar burner arrangement from environmentally harmful substances, in particular sulfur compounds, by utilizing a tank reactor unit through which the exhaust gases are passed and providing an alkaline scrubbing solution which utilizes the exhaust gases wherein the washing solution accumulating at the bottom of the reactor unit is continuously collected and further injected through nozzles into the exhaust gas stream so that the substances continuously react with the washing solution, characterized in that the washing solution recovered from the bottom of the reactor and mixing the water so that the wash solution reacts with the harmful substances even before it is injected into the nozzles. 15 Process according to Claim 1, characterized in that the pH of the washing solution accumulating in the lower part of the reactor unit is determined and that, before introducing the washing solution into the nozzles, the alkaline solution is added to the washing solution as needed keeping the pH of the washing solution in the reactor unit. 8. Process according to Claim 1 or 2, characterized in that the reactor unit is emptied of any excess Ml. 4. A scrubber arrangement for purifying exhaust fumes from an internal combustion engine, burner or similar burner arrangement from substances harmful to the environment, in particular: sulfur compounds, the arrangement comprising a tank reactor unit (1) through which the exhaust gases are: arranged to be conducted and provided with nozzle means (4) for supplying an alkaline wash solution to the exhaust stream, the wash solution accumulating at the bottom of the reactor unit is arranged to be pumped (6) 6 through 104052 (4) utilizing a recirculation pump (6) to which air or a mixture of air and water is added to the discharge side so that the wash solution reacts with the harmful substances even before it is introduced into the nozzles (4). A scrubber arrangement according to claim 4, characterized in that the reactor unit (1) is provided with pH measuring means (10) for measuring the pH of the washing solution accumulating at the bottom of the reactor unit and comprising means (7, 8, 11) for adding the solution to the washing solution so that the pH of the washing solution accumulating at the bottom of the reactor unit (1) is within the desired range, preferably between 6-8. Washer arrangement according to claim 4 or 5, characterized in that the arrangement 15 comprises a separate transfer tube (5) for pumping the washing solution into said nozzles (4). A scrubber assembly according to any one of claims 4 to 6, characterized in that the arrangement comprises a valve (12) for emptying the reactor unit (1) as required from any excess washing solution accumulating at its bottom. • · «« • i «II · •« · * • t «• e • ff · • Ml • ·« «« • I I t I «<i« 7 104052