GB2050861A - Apparatus for cleaning gases - Google Patents

Abstract

Gas scrubbing apparatus for use in conjunction with a liquid storage tank for noxious liquids, comprises a drum 20 to be mounted on an opening in the top of the tank 12, the drum having upper and lower chambers 22, 23, a tangential liquid inlet 26 into the lower chamber, a bottom opening from this chamber into the main storage tank, a stand pipe 29 from the lower chamber with an opening 30 to atmosphere at its upper end and also containing a lateral duct 31 through which a water spray injector 33, positioned in a venturi throat 32, 35, draws gases from the strand pipe, scrubs the gases and conveys them into the upper chamber 22 from which they issue to atmosphere through a demister 41. <IMAGE>

Description

SPECIFICATION Apparatus for cleaning gases This invention relates to equipment for cleaning gases by scrubbing, that is to say by contacting the gas with a cleaning liquid. The invention is particularly though not exclusively applicable to removal of contaminating fumes or gases, especially acid fumes, (hereinafter referred to for convenience as fumes) from air or other gases.

A particular need exists for gas scrubbing equipment in connection with storage tanks for acids or other noxious liquids. When these are filled the air within the tanks must be allowed to escape but is normally mixed heavily with acid fumes. Moreover a further problem can arise from the pressurised air often used to impel the liquid from a mobile supply tanker into the static tank. The whole of the internal volume of the mobile tanker is pressurised and becomes filled with compressed air, and after the liquid contents have been discharged this air (known as "padair") is also heavily loaded with acid fumes.

The padair and fumes must be allowed to escape from the mobile tanker and one method of doing so is to discharge all these gases into the static acid storage tank, from which they then escape into the atmosphere. Obviously there is a serious risk of polluting the environment unless these fume-laden gases are cleaned. There is also a risk (particularly with synthetic plastics or g.r.p. tanks) that the tank may be damaged or ruptured by inplosion or explosion if there is any malfunction in the associated systems, and it is a further object of this invention to reduce or eliminate such problems.

Many systens already exist for cleaning fumeladen gases by scrubbing. Existing systems however tend to be complicated and elaborate, and they may require to be individually designed and installed to suit particular applications. They often require a number of individual pumps and motors with power supplies, in addition to cleaning liquid supply and discharge points, filtration systems, and discharge chimneys. To protect against malfunction of different parts of the system there may also be automatic escape or blow off valves. All these components and their installation are expensive and since they are only infrequently used whenever the tank is filled they require extra maintenance due to their irregular usage. It is an object of the invention accordingly to provide an improved gas scrubbing equipment which will at least reduce some of the existing problems and disadvantages.

Broadly stated the invention consists in apparatus for scrubbing gases comprising a transfer duct having a port to be connected to an opening in the top of a storage tank, the duct also having another port connected to an exhaust duct which opens to atmosphere and has a lateral connection to a liquid scrubbing device which includes a liquid injector for inducing a flow of the fumes from the exhaust duct, a liquid separating receptacle mechanically supported from the said transfer duct, and separate outlets for scrubbed gases and liquids from the receptacle.

In some cases the transfer duct may be provided with a third port through which the acid and/or fume-laden gases (e.g. padair) may be delivered, the acid entering the static tank while the fume-laden gases pass to the exhaust duct. In other cases the static tank may have an independent supply port for the acid, in which case the fume-laden air or gases may enter the transfer duct via the first mentioned port.

In some forms of the invention the apparatus includes a demister connected to the outlet from the liquid separating container to remove small liquid droplets from the gases issuing therefrom.

In a particular preferred construction the gas scrubbing device includes a venturi throat and the liquid injector directs a high velocity spray jet into the throat, so as to induce a flow of gas from the exhaust duct and also cause atomisation of the liquid spray droplets.

The invention may be performed in various ways and one specific embodiment with a number of possible modifications will now be discribed by way of example with reference to the accompanying drawings in which Figure 1 is a diagrammatic side elevation illustrating a mobile liquid tanker coupled to a static acid storage tank, Figure 2 is a side elevation, partly in section, illustrating the main components of the gas cleaning equipment, and Figure 3 is a diagram illustrating the interior components of the "demister".

Referring first to Figure 1 the transport tanker 10 is seen coupled by a hose 11 to a fill pipe 9 for the static storage tank 12. The tanker is provided with a valve 13, which may include automatic pressure or flow rate controls, designed to redue the flow rate to a predetermined low value when the liquid contents of the tanker have been discharged. The static tank 12 includes a normal manhole opening in its top cover and directly on and over this opening there is mounted the gas cleaning equipment 14 of the present invention, which will be described in more detail below.

Referring now to the construction illustrated in Figures 2 and 3 the equipment comprises a cylindrical drum 20 which is divided internally by a horizontal partition 21 to form upper and lower chambers 22, 23. The lower chamber 23 has a central opening in its bottom wall which acts as the first mentioned port and is directly mounted on the manhole opening 25 of the storage tank. The acid supply pipe 9 from the tanker is connected by a coupling 26 to the lower chamber 23 which includes an internal baffle 27 designed to encourage the liquid acid to circulate in a vortex before entering the opening 25, and this leaves a central passage clear for air or fume-laden gases to issue upwards from the static tank as the acid enters.

These fume-laden gases issuing from the tank (or the padair from the hose 11) pass through the lower chamber 23, and up a vertical stand pipe 29 which itself passes through and is separated from chamber 22, and has a direct opening 30 to the atmosphere at its upper end. This opening 30 is permanently open but is only effective as an exhaust in cases of malfunction or maloperation or non-operation and normally all the fume laden gases are drawn off through a lateral branch duct 31.

This branch duct 31 is connected to a vertical pipe 32 provided at its upper end with a high pressure water spray nozzle 33 connected to a hose 34 which can be coupled to an external mains supply. The spray nozzle 33 is directed downwards across the opening from the lateral duct 31 and the injector action of the high velocity water jet impels the gases downwards into a venturi throat 35. The normal pressure reducing action of the venturi causes the fine water particles to atomise and in doing so the acid fumes become absorbed in the water droplets and the air is very effectively cleaned. The combined air and acid mixture issues downwards from the venturi and impinges on the horizontal partition 21 where a quantity of the acid solution collects and overflows by a lateral passage 40 to a drain pipe.

Substantial quantities of water are used in the spray jet and the concentration of acid is low.

The air issuing from the lower end of the venturi may still contain a number of small droplets of the dilute acid and the air stream is then passed upwards into a "demister" 41 having an upper outlet 42, from which clean dry air finally emerges into the atmosphere. The liquid dilute acid collected in the demister 41 is returned to the pool of liquid above the partition 21. The construction of the demister may be of various different types but one form is illustrated in Figure 3 comprises a number of generally vertical corrugated plates 45 arranged in parallel and spaced apart by small gaps. The dropletladen air enters at the bottom between these corrugated plates and in moving upwards the droplets are caused by a momentum effect to impinge on and collect in small inverted troughs 46. The liquid collected in the troughs runs back to the pool of liquid above the partition 21.

The whole unit is constructed as one selfcontained item designed to be mounted on and above the manhole opening of the static acid tank.

This has many advantages. Firstly the system does not have to be entirely designed to suit any particular application since it is only necessary to provide one seal and connection to the opening 25 in the top of the tank, and to the fill line 9 and drain pipe, most of the remaining components and connections being part of the unit. Secondly it will be noted that the opening 30 at the top of the stand pipe 29 is permanently open and necessarily at a high level on top of the static tank. This is important since in cases of malfunction or maloperation or non-operation fumes and gases may issue from this port. For example if an operator should fail to turn on the water supply to the spray nozzle 33 there will be no suction action and all the fume-laden gases from the tank will issue through this opening 30.Likewise if at the end of the tank filling process the operator does not operate the valve 13 to reduce the flow rate from the mobile tanker then the compressed gases within the tanker 10 will escape at high rate through the hose 11, and most will issue through the opening 30 since the injector action of the spray nozzle will not be capable of accommodating such high volumetric flow rates.

Another advantage of the system is that there are no pumps, motors, or other moving parts. Even the automatic blow off valve effect provided by the opening 30 is without moving parts. There is no rotary suction pump or fan to draw off the gases and no gas or water pumps. Furthermore there is no electrical supply and the only energy input is from the water mains. Likewise the only by-product is a very dilute quantity of acid in the water discharge 41.

Substantially all the components illustrated are manufactured in glass fibre reinforced plastic material or corrosion-resistant polypropolene material which requires no maintenance or replacement. By placing the liquid acid solution bath above the partition 21 with the inlet chamber 23 immediately below the overall height is reduced and at the same time the component parts are arranged not only to provide the required fluid flow but also to give direct mechanical support one from the other.

Claims (7)

1. Apparatus for scrubbing gases comprising a transfer duct having a port to be connected to an opening in the top of a storage tank, the duct also having another port connected to an exhaust duct which opens to atmosphere and has a lateral connection to a liquid scrubbing device which includes a liquid injector for inducing a flow of the fumes from the exhaust duct, a liquid separating receptacle mechanically supported from the said transfer duct, and separate outlets for scrubbed gases and liquids from the receptacle.

2. Apparatus according to claim 1, in which the transfer duct is provided with a third port through which the fumes may be delivered, such that as the liquid enters the storage tank the fumes pass to the exhaust duct.

3. Apparatus according to claim 1, in which the storage tank has an independent supply port for liquid.

4. Apparatus according to claim 3, in which the transfer duct is arranged to receive fumes or gases via the said first port.

5. Apparatus according to any of the preceding claims, including a demister connected to the outlet from the liquid separating receptacle to remove small liquid droplets from the gases issuing therefrom.

6. Apparatus according to any of the preceding claims, in which the scrubbing device includes a venturi throat and the liquid injector directs a high velocity spray jet into the throat, so as to induce a flow of gas from the exhaust duct and also cause atomisation of the liquid spray droplets.

7. Apparatus for scrubbing gases in conjunction with a storage tank, substantially as in any of the forms herein described with reference to the accompanying drawings.