Diazo developer absorption apparatus

Abstract

 Apparatus for removing ammonia or other alkaline diazo developer from copier exhaust gas, uses a packed column (5) through which the air passes, while acid solution as absorbing liquid is continuously circulated in countercurrent until the acid solution in the reservoir (21, 24) becomes exhausted, and is replaced. A multistage fan (1) is employed to drive the air against the back pressure produced by the packed column (5). The apparatus can treat the exhaust air from a high throughput copier and is surprisingly free from clogging by salts evaporated from the absorber solution.

Description

[0001] This invention relates to an absorption apparatus for diazo copiers which use an alkaline gas, especially ammonia, as the developing medium. The invention is particularly concerned with absorbing substantial amounts of developer for disposal.

[0002] Diazo copiers which use ammonia as a developing medium generally require some provision to be made for the removal of excess ammonia vapour not utilised in development which would otherwise be vented to the immediate surroundings and discomfort users of the copier. Traditionally excess ammonia is drawn off and vented through ducting to the outside atmosphere. The provision of such ducting may be inconvenient, and the venting of ammonia to the outside atmosphere may be unacceptable.

[0003] There have been proposals for the absorption of excess ammonia by bubbling it into citric acid solution e.g. UK-A-1456912 and US-A-3900862 or by blowing it through dry filter canisters containing solid material, such as activated charcoal granules, impregnated with acid. These proposals have often been in connection with low speed copiers for occasional use. However, our own U.K. Patent Application No.80.34960, published under UK-A-2063512 did propose that ammonia-laden exhaust air from a high throughput copier should be blown into a large vessel of citric acid solution. This apparatus was not marketed commercially.

[0004] We have found that the above techniques are not suitable in large high throughput copiers which require much higher air flows. We have found that in bubbler systems high air flows cause a high amount of noise with unacceptable splashing. The apparatus shown in our above- mentioned U.K. application tended to suffer from constriction of the air path over a period of time and even blockage, arising from evaporation of absorber solution, especially overnight evaporation of solution deposited on the splash barrier. We have also found that high air flow could not be handled successfully with dry solid absorbers, which apparently led to over-high back pressure. In each case absorption is inefficient.

[0005] An object of the present invention is to provide an absorber system having higher air flow handling capabilities, as are required for high throughput diazo copier machines in order to be able to cope with the high_.air flows containing high levels of ammonia produced with higher operation speeds, larger print volumes and continuous processing. Such machines could well be in operation for the majority of a working day, copying onto large sheets of paper with concomitant release of ammonia.

[0006] Broadly, in the present invention absorption is effected by subjecting ammonia-laden exhaust air to a scrubbing flow of absorption solution . Preferably the air and solution flows are in countercurrent.

[0007] Consequently, the present invention provides absorption apparatus for a diazo copier comprising a vessel for the throughflow of liquid absorption medium and exhaust air, the vessel having inlets and outlets for air and absorption medium and the apparatus also including means for circulating liquid absorption medium from a reservoir, through the column and back to the reservoir.

[0008] There is preferably means to enhance the surface area over which the liquid and gas phases are in contact. Preferably this consists of bodies over which the scrubbing liquid flows and more preferably these take the form of a column packing.

[0009] Surprisingly we have found that blockage through evaporation of scrubbing liquid is not a problem, even when the apparatus stands unused overnight or over a weekend.

[0010] Preferably the air inlet opens into a lower part of the vessel, the inlet for said absorption medium'opens into a higher part of the vessel, the outlet for said absorption medium is at a lower part of the vessel, and the outlet for said air is at a higher part of said vessel so that flows are countercurrent..

[0011] The apparatus may also include means for blowing exhaust air from a diazo copier through said vessel, or the apparatus may be employed in combination with a diazo copier which itself incorporates means for exhausting air from the copier and blowing it through the said vessel, preferably in countercurrent to the absorption medium. In either case, such means preferably comprises a multi-stage fan, because this has been found to be successful in driving high air flow against the back pressure created in the absorber.

[0012] The apparatus may include connections for two reservoir vessels and valve means operable to enable circulation of absorption medium from and back to one vessel while the second vessel is detached from its connection for exchange or refilling.

[0013] The apparatus of this invention may be contained within a diazo copier, as an integral part of that machine. Alternatively it may be contained within a separate modular unit to be connected to a diazo copier. In the latter case the multistage fan could be incorporated within this separate unit, or could be contained within the diazo copier, as mentioned above.

[0014] In a second aspect this invention provides a method of purifying exhaust air from a diazo copier which comprises contacting the air with a flowing liquid absorption medium, preferably flowing in countercurrent, which medium is circulated from a reservoir, into contact with the air and back to the said reservoir.

[0015] It has been found that the ammonia can be removed efficiently from the exhaust air from a copier by counter- current absorption into solution, the absorption medium being recirculated to maintain flow. Any suitable liquid which absorbs ammonia may be used as the absorption medium. Water may be used but though initially it is satisfactory it soon becomes inefficient as its ammonia content increases. Since the invention is particularly concerned with absorbing substantial amounts of ammonia, for disposal, it is therefore preferred to use a non-volatile acid, for example citric or phosphoric acid dissolved in the water to increase the absorption capacity for ammonia.

[0016] The absorption system preferably employs a multi- stage fan to extract surplus ammonia from the copier's developer section. This type of fan has a capability of maintaining sufficient air-flow against substantial back-pressure. The multistage fan removes the ammonia laden air from the developer section of the copier and blows it through the absorber vessel, preferatjy in counter- current against the flow of absorbing liquid.

[0017] In order to obtain a large surface area for efficient absorption it is preferred to use a packed absorption column as the absorber vessel. The packing is preferably a random packing made up of pieces of hollow cylindrical tube which are made from non-corrodable material and which offer a large surface area of contact for a given volume. Suitably the absorbing liquid is pumped from a supply bottle and evenly distributed at an optimum rate on top of the packing. As it finds its way down the random packing it comes in intimate contact with air travelling up the packing and absorbs the ammonia contained in the air with extremely high efficiency, leaving the outgoing air almost totally free of ammonia. The scrubbing liquid is then returned to the supply bottle and kept recirculating, until its absorption capability drops to a level at which it cannot neutralise the ammonia efficiently. When the traces of ammonia in the emission become perceptible, the absorber medium is replaced by fresh solution. Conveniently this may be done by use of solenoid operated valves to switch the flow to a second container of absorber solution. The bottle of exhausted absorber can then be replaced when convenient to the operator. Such a changeover system offers an uninterrupted copier operation.

[0018] The use of packing material in the absorption column helps minimise noise and splashing. The provision of a mesh at the top of the column serves to reduce splashing further, and can eliminate splashing altogether.

[0019] We have found that preferred forms of the present invention can achieve the additional advantage of providing a compact apparatus for ammonia absorption.

[0020] An embodiment of the present invention will now be described in detail with reference to the accompanying drawing which is a somewhat diagrammatic illustration of an absorption apparatus.

[0021] Referring to the drawing, air laden with ammonia is drawn from the developer section D of a diazo copier by a multistage fan 1 and passed along a pipe 3 to the counter-current flow absorption column 5 which is shown in cross section. The supply pipe 3 connects with an inlet tube 7 which opens at a lower part of the column 9. Air laden with ammonia then travels up the column through a mesh 11 on which rests a column packing 13 which consists of short lengths of glass tube. The air passes through the packing 13 at the same time as a liquid absorption medium is fed down the column and the ammonia is therefore absorbed leaving only traces of ammonia in the air which leaves the column through a mesh or filter 15 which prevents splashing.

[0022] The absorption medium is fed to the column bed 13 by a sprayhead 17 which distributes the medium evenly over the bed. The sprayhead 17 is fed by a pump 19 from a detachable reservoir bottle 21 through pipes 23, 25. Absorption medium which has passed through the column is returned to the reservoir bottle 21 for recirculation via a pipe 27. A standby absorption medium reservoir 24 is,also provided which is also connected to the pipes 25, 27 connecting the reservoir to the pump 19 and column outlet. Only one reservoir bottle is in use at any one time and solenoid operated valves 29, 31 are provided which enable the detachable reservoir bottles to be changed over whilst the apparatus remains in use. When the absorption medium in one reservoir becomes incapable of absorbing further developer, the changeover solenoid valves 29, 31 (which may be linked) are operated to switch flows to the other vessel. The saturated absorption medium bottle 21 may then be replaced when convenient.

[0023] The absorption medium preferably is water containing citric or phosphoric acid. Ammonia is much the commonest developer used but methylamine has also been used and this or other alkaline vapour could be absorbed using the apparatus shown. The apparatus described gives very efficient absorption with low pressure loss, reduced splash and negligible noise. The recirculating system allows easy replacement of spent solution even during operation.

[0024] An example of absorption column as shown in the drawing had a diameter of 150 mm, with an air inlet pipe 7 which was 38 mm in diameter. The column packing was supported on a mesh 11 placed 60 mm above the base of the column. The packing itself extended over a height of 160 mm; there was an air space between it and the splash barrier 15. The packing consisted of glass tube of about 8 to 10 mm o.d., chopped into lengths of about 10 mm.

[0025] In this example the splash barrier 15 consisted of a small quantity of the same packing material held between meshes 16. However, various other splash barriers could be employed.

[0026] It was found that the liquid flow rate could be set low enough that there was little or no gross splashing onto the splash barrier 15. This barrier 15, however, served to remove entrained droplets of moisture from the air stream.

[0027] Surprisingly, the evaporation of absorber liquid, either on the splash barrier or on the column packing, was not found to be a problem even though the circulation of absorber liquid was stopped overnight and over weekends, and the liquid drained from the column when circulation stopped.

[0028] Examples of various experiments using scrubbing liquids in such a column are given below in Table I.

Claims

1. A method of removing alkaline developer from exhaust air from a diazo copier which comprises contacting the air with a flowing liquid absorption medium, which medium is circulated from a reservoir, into contact with the air and back to the said reservoir.

2. A method according to claim 1 wherein the liquid medium is a solution of an acid, and is discarded and replaced when it is spent.

3. A method according to claim lor claim 2 wherein contact between said liquid medium and exhaust air is effected by distributing said liquid medium from the reservoir over a column packing, and blowing said exhaust air through the column packing in countercurrent to said liquid by means of a multistage fan.

4. Diazo-developer removal apparatus for removing alkaline developer from exhaust air from a diazo copier, comprising a vessel for the throughflow of liquid absorption medium and exhaust air, the vessel having inlets and outlets for air and absorption medium and the apparatus also including means for circulating liquid absorption medium from a reservoir, through said vessel and back to the said reservoir.

5. Apparatus according to claim 4 wherein the air inlet opens into a lower part of the vessel, the inlet for said absorption medium opens into a higher part of the vessel, the outlet for said absorption medium is at a lower part of the vessel, and the outlet for said air is at a higher part of said vessel so that flows are countercurrent.

6. Apparatus according to claim 1 including a multi- stage fan for blowing said exhaust air through said vessel.

7. Apparatus according to any one of claims 4 to 6 wherein the said vessel contains a packing over which the liquid medium flows, and the inlet for liquid to the vessel is connected to means for distributing the liquid medium over the packing.

8. Apparatus according to claim 7 with a splash barrier above said means for distributing the liquid medium, the said barrier permitting the escape of exhaust gas but being positioned to intercept splashes of liquid medium.

9. Apparatus according to any one of claims 4 to 8 having at least two reservoirs, and further having changeover valve means operable so that liquid medium is circulated from either one of said reservoirs and returned thereto, permitting spent liquid medium in the other reservoir to be replaced, each said reservoir being detachable and/or provided with means for emptying and refilling it.

10. A diazo copier provided with apparatus according to any one of claims 4 to 9.

Drawing