A METHOD AND A DEVICE IN GAS PURIFYING INSTALLATIONS FOR PREVENTING DISCHARGE OF UNPURIFIED GAS UPON CHANGES OF THE GAS-FLOW DIRECTION

Abstract: The invention relates primarily to gas purifying installations operating with reversal of the flow direction and having a double-purpose channel system, i.e. one which upon operation in one through-flow direction forms the inlet channel feeding polluted gas into the installation and upon operation in the opposite flow direction forms the purified gas discharging channel. In accordance with the invention polluted gas is prevented from being discharged into the atmosphere during and immediately after reversal of the flow direction by flushing the purifying installation with fresh air or other clean gas for a predetermined period of time.

Description: A METHOD AND A DEVICE IN GAS PURIFYING INSTALLATIONS FOR PREVENT DISCHARGE OF UNPURIFIED GAS UPON CHANGES OF THE GAS-FLOW DIRECTI The present invention relates to gas purifying instal¬ lations operating with reversal of the gas-through-flow direction, and more precisely it concerns a method and a device to prevent polluted gas which on account of the 5 reversal of the gas-flow direction remains untreated, from reaching the environment. The invention concerns e.g. the type of gas purificati installation which is described in SE 8403330-7 (Publicatio No. 441 623). In this type of purifying installation, the 10 gas to be treated travels through the installation alter¬ nately in opposite directions. The change of direction generally is effected with the aid of a reversing valve arranged in a manner ensuring that treated discharge gas and untreated supply gas alternately flow through the valve 15 chambers. However, one consequence of this arrangement is that when the gas flow direction is changed, untreated gas will be discharged into the surrounding atmosphere without having passed through the treatment zone of the purifying installation, unless special means are provided 20 to prevent this from happening. The main object of the present invention is to provide an efficient method and a device of simple construction by means of which untreated gases are positively prevented from reaching the atmosphere in connections with reversal 25 of the gas through-flow direction through the purifying installation. The object is achieved in accordance with the cha¬ racterizing features of the invention according to which prior to reversal of the direction of the gas, clean air 30 or other clean gas is made to flow to the operative part of the installation in order to temporarily fill the part of the installation which prior to the reversal of the direction of the gas serves as the inlet and after the reversal of the direction of the gas serves as the outlet. This method may be performed with the aid of a device in accordance with the invention which is adapted for use in gas purifying installations operating with reversal of the gas through-flow direction and comprising a double- purpose channel system, i.e. upon operation in one flow direction the system forms the inlet channel feeding pollute gas into the installation and upon operation in the opposite flow direction it forms the outlet channel discharging purified gas therefrom, the device being arranged to tem¬ porarily introduce clean gas into the double-purpose channel system prior to and during the reversals of the direction of the gas through-flow. One embodiment of the invention will be described in closer detail in the following with reference to the accompanying drawings, wherein FIG. 1 illustrates a purifying installation which is equipped with a device in accordance with the invention, immediately preceding the reversal of the flow direction of the gas through the pu:_ifying installation; FIG. 2 illustrates the installation immediately after completion of the reversal of the through-flow direction; FIG. 3 illustrates the same installation immediately prior to the next reversal of the through-flow direction, a FIG. 4 illustrates the installation immediately after the last-mentioned reversal of the through-flow direction. The purifying installation illustrated in the drawings and generally referred to by reference numeral 1 is of a type known per se and described e.g. in SE 8403330-7. The illustrated installation comprises a chamber having two perforated walls 2 defining between them a treatment zone 3, preferably consisting of sand, wherein heating elements 4 are positioned. At its top and its bottom the device comprises collection and through-flow chambers 5 and 6, respectively, to which are connected gas conduits 7 and 8, respectively. The gas conduits 7, 8 meet in a valve housing 9 into which opens a conduit 10 connecting the valve housing with the surrounding atmosphere. Both conduits 7 and 8 carry gas to and from the installation 1 , depending on the position in which a valve means 11 is set inside the valve housing 9. In the installation illustrated in the drawings, gas is heat-treated for combustion of the impurities contained in the gas. In case the inherent combustion of the gas is not sufficient to sustain a sufficiently high temperatur level inside the treatment zone 3, additional energy is supplied by the heating elements 4 to assist in elevating the temperature. To maintain a maximum temperature level inside the treatment zone 3, the gas is forced to pass alternately in opposite directions through the treatment zone, the reversals of direction being effected by means of the valve 9, 11. In the position of the valve illustrate in Fig. 1, untreated gas thus passes through an inlet chann 12 and via the valve housing 9 and the conduit 7 it enters the upper collection box 5 from which it passes through the treatment bed 3, whereupon the thus treated gas is discharged by way of the collection box 6, the conduit 8 and the valve housing 9 into the surrounding atmosphere through the outlet conduit 10. Fig. 3 illustrates the valve means in the alternative setting position in which untreated gas flows through the common channel 12, the valve housing 9, the conduit 8 and the collection chamber 6 to pass through the treatment bed 3. Gas treated therein passes further outwards through the collection chamber 5, the conduit 7, the valve housing 9 and it is discharged to the atmosphere through the out¬ let 10. Accordingly, if polluted gas to be treated is supplied continuously through the channel 12, any such gas that may remain in the regions closest to the valve housing at the time immediately following a reversal of the valve means, i.e. in the conduit temporarily serving as the inlet conduit from the valve housing and in the corresponding collection box in the treatment chamber, would reach the atmosphere in an untreated condition, since after a reversal these regions of the system will serve as outlet conduits and consequently gas present in these regions will not yet have reached the treatment zone 3 of the purifying installation. The purpose of the invention is to prevent such dis¬ charges of untreated gas and to this end it provides a device generally consisting of an auxiliary unit 13 which is mounted in the common inlet 12 leading to the valve housing 9. The auxiliary device 13 consists of a channel system including an inlet chamber 14, an outlet chamber 15 and a multi-channel system positioned intermediate the inlet and outlet chambers and comprising at least two channels 16 and 17. It goes without saying that the two channels could be in the form of two groups of channels 16 and 17, respectively. In the interior of the inlet chamber is located a flap valve 18 which, depending on its position, directs gas entering the common channel 12 to one or the other of the two channel systems 16 or 17. The outlet chamber 15 serves to direct gas discharged from the two channel systems 16, 17 to the common inlet channel 12 leading to the valve housing 9. Spaced from the outlet ends of the two channels 16, 17, preferably in the entrance region of said two channels, are fresh air intake channels 19 and 20, respectively, the flow area of which is relativel restricted in comparison with that of the rest of the channels 16, 17. Pressure-increasing devices, such as fans or similar means may be connected to the intake channels 19, 20. In operation, the device functions in the following manner. In the position of the valve flaps 11 and 18 illu¬ strated in Fig. 1 polluted gas flowing through the channel 12 will pass via the channel system 16, the outlet chamber 15, the valve housing 9, the conduit 7 and the collection chamber 5 up to the treatment zone 3 and from there further via the collection chamber 6, the conduit 8, the valve housing 9 to be discharged into the atmosphere in purified condition through the outlet 10. In the meantime, fresh air is supplied through the air intake 20 into the channel system 17, filling the latter, while polluted gas, pre¬ viously present in the channel system 17, will be forced into the channel 12 via the outlet chamber 15. Upon reversal of the valve 11 to change the flow direction of the gas through the installation 1 also the position of valve 18 is reversed, with the result that, as illustrated in Fig. 2, polluted gas instead will pass through the channel system 17 and into the valve housing via the outlet chamber 15 while the channel system 16 successively filled with fresh air entering through the intake 19 and polluted gas remaining inside the channel system 116 successively will flow into the installation 1 while the fresh air gradually fills the channel system 16. In Fig. 3 is illustrated the position when the entire channel system 16 is filled with fresh air entering at a comparatively slow rate. As a result thereof it may happen that some fresh air will be entrained by the pollute gases into the installation, also after filling of the associated channel system with fresh air, if some further time passes before a change of flow direction takes place. On account of the slow inflow of fresh air owing to the comparatively narrow intake passages 19 and 20, respectivel this does not constitute a significant disadvantage in the system. The volume of the channel systems 16, 17 should however, be sufficient to allow fresh air contained therein to flow through the entire purifying installation 1 before reversal of the valve flap 11 is effected. Owing to this arrangement no polluted untreated gas will remain inside that region of the system which after the reversal will act as an outlet channel. This also means that the reversal of the valve 18 should take place sufficiently ahead of the reversal of the valve 11 to allow the installation 1 to be filled with fresh air or other clean gas supplied through the intake passages 19, 20 before the valve 11 is reversed. In other words, flushing of the installation is allowed to take place before the flow direction is reversed. The volume of the channel systems 16, 17 should not either be too large since an unnecessarily slow through- flow of fresh air in the purifying installation 1 results in unnecessary cooling thereof. This is particularly delicate when the intervals between each reversal of the direction are brief. In the aforegoing one particular embodiment of the invention has been described but naturally the expert in the field may modify the construction in a variety of ways without departing from the inventive idea. For instance, other means than those described could be used to flush the installation 1 clean by means of fresh air or other clean gas prior to the reversal of the flow direction. In accordance with the embodiment illustrated in the drawing the auxiliary device 13 is in the shape of a channel system and in the aforegoing description reference is made to a channel system but obviously it is possible to arrange the chambers formed by the channels in some other way. Also other types of vessels may be filled alternately with fresh air and polluted gas and alternately be shunted into the regular supply inlet to the purifying installation.

Claims: AMENDED CLAIMS [received by the International Bureau on 22 November 1990 (22.11.90); original claims 1-7 replaced by amended claims 1-3 (2 pages)] 1. A device in gas purifying installations, preferably of combustion type, of the kind operating with reversal of the gas through-flow direction and having a double- purpose channel system, which system, upon operation in 5 one flow direction, forms the inlet channel feeding polluted gas into the installation and upon operation in the opposite flow direction, forms the outlet channel discharging purifie gas therefrom, c h a r a c t e r i z e d in that it is arranged to temporarily introduce clean gas into the double- 0 purpose channel system prior to and during the reversal of the direction of the gas through-flow, in that it com¬ prises a clean-gas vessel (16; 17) and valves (18) to shunt together said vessel and the regular gas inlet (12) to the purifying plant ( 1 ) , and means to synchronize the shunt 5 valves and the means of the installation provided to effect the reversal of the through-flow direction, in that the polluted-gas inlet channel (12) is formed ahead of the double-purpose channel system with at least two parallel channels (16, 17) merging at both ends with one single, 0 common channel (12), valve means (18) being provided to alternately make one or the other of said parallel channels form part of the polluted-gas supply channel (12). 2. A device as claimed in claim 1, c h a r a c ¬ t e r i z e d in that the valve means is a reversing valve 5 (18) located in the inlet end of the parallel channels and in that the part of the parallel channels positioned closest to the reversing valve has an intake channel (19, 20) which preferably is constantly open towards the sur¬ rounding atmosphere and which is at a higher pressure than 0 the pressure prevailing in the parallel channels, the cross sectional area of said intake channel being very small in comparison with the total through-flow area of the parallel channels. 3. A device as claimed in claim 2, c h a r a c ¬ t e r i z e d in that means are provided to equalize the pressures in the fresh air intake channels (19, 20) and the parallel channels (16, 17).

Inventors: KAELLSTRAND AAKE, KAELLSTRAND, AAKE
Applicants: ADTEC AB
Application year: 1990
Main classification: F23G7
IPC codes: F23G7