PROCESS AND APPARATUS FOR COOLING A GAS CONTAINING SO2 AND/OR SO3 AND TRACES OF WATER

Abstract

The above mentioned invention describes a process for cooling a gas mixture of SO.sub.2 and/or SO.sub.3 and water, wherein the gas mixture is cooled by means of a first heat exchanger carrying a coolant. The temperature of the coolant lies above the dew point of the gas or gas mixture.

Claims

1.-12. (canceled)

13. A process for cooling a gas mixture of SO.sub.2 and/or SO.sub.3 and water comprising cooling the gas mixture with a first heat exchanger carrying a coolant, wherein the temperature of the coolant lies above the dew point of the gas or gas mixture, the coolant is water, and the dew point given in C. is calculated according to the following equation: $\begin{array}{c}=e^{\left(6.0006-\left(\frac{3.158.Math.{10}^{-7}}{p.Math.1.244.Math.{10}^{-9}.Math.c}\right)\right)+\left(0.1387.Math.\ln \left(p.Math.1.244.Math.{10}^{-9}.Math.c\right)\right)}\\ \mathrm{with}\\ p=\mathrm{gas}.Math..Math.\mathrm{pressure}.Math..Math.\mathrm{in}.Math..Math.\mathrm{mbar}.Math..Math.a.Math..Math.\mathrm{and}\\ c=\mathrm{water}.Math..Math.\mathrm{content}.Math..Math.\mathrm{in}.Math..Math.\mathrm{mg}/{\mathrm{Nm}}^3.\end{array}$

14. The process according to claim 13, wherein the water content is determined by a method based on a laser diode system.

15. The process according to claim 13, wherein the gas mixture is cooled from a temperature between 400 and 500 C. to a temperature between 130 and 180 C.

16. The process according to claim 13, wherein the coolant is heated so that the coolant at least partly evaporates.

17. The process according to claim 13, wherein the gas mixture is guided through the first heat exchanger counterflow to the coolant.

18. The process according to claim 13, wherein a second heat exchanger is provided before the first heat exchanger and that the coolant is guided first through the second heat exchanger and then through the first heat exchanger.

19. An apparatus for cooling a gas mixture of SO.sub.2 and/or SO.sub.3 and water comprising a first coolant-carrying heat exchanger with an inlet and an outlet for the coolant, a control or regulating device which adjusts the temperature of the coolant at the inlet to a temperature above the dew point of the gas or gas mixture, and a measuring device for determining the water content of the gas mixture, which is coupled with the control or regulating device such that the dew point given in C. is calculated according to the following equation: $\begin{array}{c}=e^{\left(6.0006-\left(\frac{3.158.Math.{10}^{-7}}{p.Math.1.244.Math.{10}^{-9}.Math.c}\right)\right)+\left(0.1387.Math.\ln \left(p.Math.1.244.Math.{10}^{-9}.Math.c\right)\right)}\\ \mathrm{with}\\ p=\mathrm{gas}.Math..Math.\mathrm{pressure}.Math..Math.\mathrm{in}.Math..Math.\mathrm{mbar}.Math..Math.a.Math..Math.\mathrm{and}\\ c=\mathrm{water}.Math..Math.\mathrm{content}.Math..Math.\mathrm{in}.Math..Math.\mathrm{mg}/{\mathrm{Nm}}^3.\end{array}$

20. The apparatus according to claim 19, further comprising a second coolant-carrying heat exchanger with an inlet and an outlet, wherein a conduit connects the outlet of the second heat exchanger with the inlet of the first heat exchanger.

21. The apparatus according to claim 20, wherein the first and/or the second heat exchanger includes cast ribs in its interior, by which the coolant is guided from the inlet to the outlet.

22. The apparatus according to claim 20, wherein the first and the second heat exchanger are mounted in the same housing.

23. The apparatus according to claim 21, wherein the first and the second heat exchanger are mounted in the same housing.

24. The apparatus according to claim 20, wherein a three-way valve is provided, from which a feed conduit extends into the inlet of the first heat exchanger and into which extends a conduit from the outlet of the second heat exchanger and a conduit for supplying additional coolant, wherein the three-way valve is designed such that it adjusts the mixture of coolant from the second heat exchanger and additional coolant such that via the conduit coolant enters into the inlet of the first heat exchanger with a temperature above the gas or gas mixture.

25. The apparatus according to claim 21, wherein a three-way valve is provided, from which a feed conduit extends into the inlet of the first heat exchanger and into which extends a conduit from the outlet of the second heat exchanger and a conduit for supplying additional coolant, wherein the three-way valve is designed such that it adjusts the mixture of coolant from the second heat exchanger and additional coolant such that via the conduit coolant enters into the inlet of the first heat exchanger with a temperature above the gas or gas mixture.

26. The apparatus according to claim 22, wherein a three-way valve is provided, from which a feed conduit extends into the inlet of the first heat exchanger and into which extends a conduit from the outlet of the second heat exchanger and a conduit for supplying additional coolant, wherein the three-way valve is designed such that it adjusts the mixture of coolant from the second heat exchanger and additional coolant such that via the conduit coolant enters into the inlet of the first heat exchanger with a temperature above the gas or gas mixture.

27. The apparatus according to claim 23, wherein a three-way valve is provided, from which a feed conduit extends into the inlet of the first heat exchanger and into which extends a conduit from the outlet of the second heat exchanger and a conduit for supplying additional coolant, wherein the three-way valve is designed such that it adjusts the mixture of coolant from the second heat exchanger and additional coolant such that via the conduit coolant enters into the inlet of the first heat exchanger with a temperature above the gas or gas mixture.

Description

[0038] Further developments, advantages and possible applications of the invention can also be taken from the following description of the drawings and the exemplary embodiment. All features described and/or illustrated form the subject-matter of the invention per se or in any combination, independent of their inclusion in the claims or their back-reference.

[0039] In the drawings:

[0040] FIG. 1 shows a cooling according to the prior art

[0041] FIG. 2 shows a cooling according to the prior art

[0042] FIG. 3 schematically shows a cooling of a gas mixture containing SO.sub.2 and/or SO.sub.3 by means of a first and a second heat exchanger designed according to the invention

[0043] FIG. 4 schematically shows a cooling of SO.sub.2 and/or SO.sub.3 and water with a first heat exchanger designed according to the invention and with two further heat exchangers.

[0044] FIG. 1 schematically illustrates the typical solution of the problem underlying the invention. Via conduit 31 the temperature of the entering water is measured in a measuring device 32 before the feed water then gets into a steam drum 30. There, it is preheated to a temperature slightly above the dew point to be expected, which typically is 120 to 130 C.

[0045] Via a conduit 34, the water preheated in this way then is introduced as cooling water via an inlet 11 into a heat exchanger 10 which it then leaves again via an outlet 12. Via a conduit 35, the cooling water gets back from the outlet 12 into the steam drum 30, where the energy gained by absorption of heat is recovered and can be used at some other point of the process.

[0046] Via a conduit 13, the gas to be cooled is fed into the heat exchanger 10, before it then is withdrawn again via a conduit 14.

[0047] This system has the disadvantage that it cannot react to a shift in the dew point and therefore fails to safely avoid corrosion and the related risks.

[0048] FIG. 2 shows a further formation of the prior art, in which the heat exchanger either, as shown, is split up into two individual separate modules or only the heat-exchange surface is divided. Via a conduit 41, cooling water gets into an inlet 21 of a heat exchanger 20. After the cooling water has traversed the heat exchanger 20, it exits again via an outlet 22.

[0049] Conduit 42 connects the outlet of the heat exchanger 20 with the inlet 11 of the first heat exchanger 10. The heat exchanger 10 also is traversed by the cooling water, which subsequently exits again via an outlet 12 and via a conduit 35 gets into the steam drum 30. Via conduit 13, the gas to be cooled again is fed into the heat exchanger(s) and withdrawn again via conduit 14. A conduit 15 connects the first heat exchanger 10 with the second heat exchanger 20.

[0050] FIG. 3 shows the inventive design of an apparatus for cooling a gas containing SO.sub.2 and/or SO.sub.3 as well as water. Via a conduit 60 and a conduit 61 the cooling water gets to the inlet 21 of a second heat exchanger 20. Via the outlet 22 the cooling water gets from the heat exchanger 20 into a conduit 71 and there into a three-way valve 70. Into this three-way valve a conduit 62 opens, which branches from the cooling water supply 60. Thus, it is possible to mix two different streams of cooling water with each other in the three-way valve, namely the cooling water originating from the first heat exchanger 10 and the cooling water originating from the second heat exchanger 20.

[0051] Control variable is the temperature of the resulting mixed stream, which is determined via the measuring device 82. The water content of the gas serves as control variable, which is determined via the measuring device 83 in the gas outlet conduit 14. In the same way, the measurement can also be effected in the inlet conduit 13. Due to the water content, the dew point of the gas can be inferred by the following equation, so that via a control device 80 the three-way valve 70 can be actuated correctly.

[0052] The gas with the temperature adjusted in this way is passed via a conduit 72 into the gas inlet 11 and thus passes the heat exchanger 10, before via the outlet 12 it gets into conduit 35 and from there into the steam boiler 30.

[0053] FIG. 4 shows two heat exchangers connected in parallel. Via conduit 60, 61 and an inlet 21, the coolant gets into a heat exchanger 20. After passing the heat exchanger 20 and exiting via the outlet 20, it gets into a three-way valve 70 via a conduit 71. In the three-way valve 70, parts of the fresh cooling water from conduit 60 also are supplied by means of conduit 62. Via conduit 72, the stream dosed in the three-way valve is supplied to a second three-way valve 90. The same splits the cooling water stream into two partial streams.

[0054] Via conduit 91 and the inlet 11 the first fraction gets into the heat exchanger 10 and again leaves the same via the outlet 12. Via conduit 35 and a separator 36 provided therein the cooling water then gets into the steam boiler 30.

[0055] Via conduit 92 and an inlet 94, the second partial stream gets into a heat exchanger 93. After passing the heat exchanger 93, the gas likewise is supplied to the steam boiler 30 via an outlet 95 as well as conduit 98 and the separator 99 provided therein.

[0056] The heat exchanger 20 and the heat exchanger 10 are charged with the gas to be cooled via the conduits 13, and 15, which subsequently is discharged via conduit 14. Via conduit 96, the heat exchanger 93 is charged with gas to be cooled, which then is withdrawn via a conduit 97.

[0057] Control variable for the first three-way valve 70 is the temperature of the stream 72, which is checked via a temperature meter 82. The temperature is dependent on the water content of the gas to be cooled, which in general is determined by a device 83. In the control unit 80 of the dew point system, the temperature of the cooling water in conduit 72 hence can be determined from this control variable as temperature above the dew point temperature.

[0058] The division in the second control valve 90 is effected such that the outlet temperatures of the cooling water both in conduit 35 and in conduit 98 still are above the dew point, wherein the control valve 90 actuated by the control device 100 still is important, as the acid dew point in the flowing gas also is determined in the heat exchanger 93.

[0059] Preferably, the division in the control valve 90 is made such that the outlet temperatures measured in the measuring devices 102 and 103 are equal. It hence is ensured that both heat exchangers in the heat offerings correspondingly are supplied with cooling water.

[0060] In some cases, the combined heat offerings go beyond what is required for heating the cooling water up to the boiling temperature. In the heat exchanger, a pre-evaporation takes place up to a certain extent. This can be up to 5 to 10% of the introduced water. Thus, steam mixtures exit from the heat exchangers, which have identical temperatures and therefore no longer are suitable for the aforementioned distribution of the preheated water to the two heat exchangers on the basis of these temperatures. If this is the case, the distribution of the preheated cooling water can be controlled by means of the two gas outlet temperatures, which are determined via the measuring device 101 and 14.

[0061] In principle, the concept also can be applied to more than two heat exchangers operated in parallel on the water side.

LIST OF REFERENCE NUMERALS

[0062] 10 first heat exchanger [0063] 11 inlet [0064] 12 outlet [0065] 13 gas inlet [0066] 14 gas outlet [0067] 15 gas conduit [0068] 20 second heat exchanger [0069] 21 inlet [0070] 22 outlet [0071] 30 steam boiler [0072] 31 measuring device [0073] 33-35 conduit [0074] 36 separating device [0075] 41, 42 conduit [0076] 60-62 conduit [0077] 70 three-way valve [0078] 71, 72 conduit [0079] 80 control device [0080] 81 signal generator [0081] 82 temperature measuring device [0082] 83 temperature measuring device [0083] 90 three-way valve [0084] 91, 92 conduit [0085] 93 heat exchanger [0086] 94 inlet [0087] 95 outlet [0088] 96 gas inlet [0089] 97 gas outlet [0090] 98 conduit [0091] 99 separator [0092] 100 control device [0093] 101-103 temperature measuring device