GB2319585A - Adsorption gas dryer with cast manifold and integral valving - Google Patents

Abstract

A cast manifold for a an adsorption gas dryer comprises two conventional 2/2 inlet valves V1 and V2 and two 2/2 exhaust valves V3 and V4 modified to have a third port. The valves are arranged as pairs (i.e. one inlet and one exhaust). Each pair is associated in use with one of each of two drying towers. The inlet valve is connected between a source of gas to be dried and inlet port A of the exhaust valve. Gas to be dried is to be fed to the tower via the associated open inlet valve and exhaust valve which is arranged such that flow can occur from inlet A to port B and - flow to port C being prevented. During tower regeneration the inlet valve is closed and the exhaust valve is switched such that flow occurs from port B to port C - flow from port A being prevented by the closed inlet valve. The control and actuation system for the valves is incorporated into the manifold and the manifold is sealed to the towers by "O" rings (see figure 5).

Description

SUBJECT: ADSORPTION GAS DRYER WITH CAST MANIFOLDS AND INTEGRAL VALVING.

INVENTORS: Brian Walker Holly Hall Sandhoe Hexham Northumberland England Matthew D. Rowe ASSIGNEE: Walker Filtration Ltd.

BACKGROUND: Adsorption dryers for compressed air and gases have been marketed for many years and are widely used throughout the world. Although other types of dryer are available namely deliquescent and refrigeration they cannot give the low pressure dewpoint achieved by the adsorption dryer and which is essential for many applications. For instance a refrigeration dryer can offer a pressure dewpoint of +3 degrees C whereas an adsorption dryer can give a pressure dewpoint of less than -70 degrees C.

Normally adsorption dryers employ two containers (or towers) of desiccant material (commonly known as beds) one of which is 'on stream' drying the gas whilst the other is being regenerated, although a single tower system can be used. In the dual tower process the gas to be dried is passed through one desiccant bed continuously in one direction during the drying cycle and then after a predetermined time interval when the bed is considered to have adsorbed sufficient moisture the inlet gas is switched to the second desiccant bed and the first desiccant bed is regenerated by heating and/or by evacuation and/or by passing a purge gas there through, usually in reverse flow direction.

Adsorption dryers are available in two distinct types, heat regenerative and heatless. Heat regenerative, as the name implies uses heat in one form or another to reactivate the wet desiccant bed normally in conjunction with a purge gas flow. The heatless dryer uses a purge flow of dry gas which is usually a proportion of gas from the drying cycle tower which is passed through the regenerating bed at a lower pressure.

Unless sophisticated control systems are used both types of dryer are normally operated on a fixed time cycle for drying and regeneration and both cycles are usually of an equal duration.

The cycle times for heat regenerative dryers are usually measured in hours whereas for heatless dryers it is measured in minutes.

To control the flow of gas from one tower to the other, and to control the purge gas (either for the heatless or heat reactivated dryer), a series of usually actuated valves are employed. These valves consist of, but are not limited to, two inlet valves which switch the gas from one tower to the other, two exhaust valves which control the duration of the purge and repressurisation, and two outlet check valves which prevent the outlet air stream from pressurising the off stream bed.

In addition to these six valves, a number of other valves such as purge check valves, repressurisation valves, additional exhaust restrictor valves etc can be employed. The control of gas flow through an adsorption dryer is not limited by the type of valve used. For instance, the two inlet valves and the two outlet check valves can be replaced by two shuttle valves respectively. Indeed, just about any type of valve can be used whether it be a diaphragm, globe, gate, ball, plug, spool or any other 5/3, 5/2, 4/2, 3/2 or 2/2 commercially available valve.

Hitherto, manufacturers of adsorption dryers have usually sourced commercially available valves and piped them together using butt weld or threaded malleable iron fittings (others also attach commercially available valves to piping manifolds). A number of problems exist with this style of manufacture namely pressure drop through the individual fittings, leakage through threaded joints, limitations of commercially available designs, inflexibility with regard to method of actuation not to mention complex and expensive manufacturing procedures. Some manufacturers have attempted to develop manifold systems but these have been limited to using porting blocks made from bar stock attached to butt welded pipework and not the cast manifold with integral valves that this invention describes.

This invention describes a very simple desiccant dryer construction consisting of two pressure vessel towers connected together at the top & bottom by two substantially identical cast manifolds each with integral valving. One manifold will act as the wet gas inlet and the other manifold as the dry gas outlet. The invention includes a re-designed three ported bypass 2/2 valve which, in addition to the cast manifold concept, eliminates the problems of pressure drop, leakage & physical size while representing an economic solution to expensive and time consuming manufacturing methods.

DESCRIPTION OF THE INVENTION This invention is applicable to heatless or heat reactivated, upflow or downflow types of adsorption dryers. In addition, it's concept can be applied to any type of valve or actuator.

However, for the purposes of this description, a heatless downflow dryer utilising diaphragm valves is used as an example.

Figure 1 shows a typical adsorption dryer using commercially available valves with either butt welded or threaded malleable iron interconnecting pipework. Valves V1 & V2 represent the inlet valves which direct the incoming gas to either tower A or tower B. Valves V3 & V4 represent the exhaust valves which control the depressurisation and repressurisation of the offstream regenerating tower. All four of these valves are conventional 2/2 solenoid operated diaphragm valves.

Valves V5 & V6 represent the outlet check valves and are used to prevent the off-stream tower from being repressurised from the outlet gas stream. PO represents the purge orifice which controls the amount of regeneration gas used to desorb the off-sueam tower. S1 and S2 represent the exhaust silencers used to control the noise level when either tower is depressurised.

Suppose initially that tower A is being used to dry the incoming gas and tower B is being regenerated having been saturated on the previous drying cycle. Valve V1 would be open and valve V2 would be closed, thus directing the incoming gas stream through tower A. To prevent the incoming gas from escaping through silencer S1, valve V3 would remain closed.

Meanwhile, valve V4 has opened depressurising tower B through silencer S2 with check valve V6 shutting to prevent the outlet gas stream from escaping via tower B and through valve V4 and silencer S2. Check valve V5 stays open to allow the dried gas stream to exit via the outlet.

A small bleed of purge gas (typically 15% at 7 barg and 350C) then passes across orifice PO where it expands to essentially atmospheric pressure, passes through tower B stripping the adsorbed moisture from the bed, and passes through valve V4 and out via silencer S2.

When the purge gas has desorbed the moisture from tower B, valve V4 shuts to allow tower B to repressurise via the purge orifice PO. When tower B has reached line pressure, and tower A has become saturated, valve V2 opens and valve V1 shuts to then direct the incoming gas stream through tower B which has now become the on-stream tower. In order to regenerate tower A which has been saturated, valve V3 opens and the tower depressurises through silencer S1.

Check valve V5 shuts and check valve V6 opens to allow the dried gas stream to exit via the outlet. Once again a small bleed of purge gas passes across orifice PO where it expands to essentially atmospheric pressure, passes through tower A stripping the adsorbed moisture from the bed before passing through valve V3 and out via silencer S1.

When the purge gas has desorbed the moisture from tower A, valve V3 shuts and tower A repressurises via the purge orifice PO. When tower A reaches line pressure and tower B has become saturated, valves V1 and V2 switch once again and the cycle repeats on a continuous basis.

All compressed air or gas dryers need a control unit to sequentially operate the valve systems.

This may be by simple cam timer means or by electronic timer means or by more sophisticated process control such as energy management Various energy management systems are available such as that described in Patent Application 9602198.5 which, should the actual amount of moisture approaching the dryer be less than the design value, the amount of purge gas used to dex orb the saturated bed is restricted to just that required and hence excess purge gas is not wasted. Other systems are also on the market.

This invention utilises a valve and manifold arrangement which differs and improves upon conventional desiccant air or gas dryer systems. The two pressure vessel towers are connected together at the top & bottom by two substantially identical cast manifolds each with integral valve mechanisms (figure 2). One manifold will act as the wet gas inlet and the other manifold as the dry gas outlet.

The inlet manifold incorporates provision for at least four integral 2/2 valve mechanisms, representing the inlet valves (V1 & V2) and the exhaust valves (V3 & V4) (figure 3a). The outlet manifold incorporates provision for at least two check valve mechanisms (V5 & V6) and a means of directing a flow of dry purge gas to the tower under regeneration (PO) (figure 3b). It can be seen that each valve seat can be used as a controlled 2/2 valve or self actuating check valve and that the controlled 2/2 valves can be pneumatically actuated (as shown) or pilot solenoid actuated.

For larger dryers valves V1, V2, V5 & V6 can use a duplex configuration where two small valve mechanisms working in parallel can provide a means for a higher flowrate. This has several advantages, it increases the usage of all the small valve parts thereby cutting actual purchase costs, tooling costs and inventory costs. It also reduces the casting size and reduces the wear on the valve parts.

Another feature of the cast manifold is that it utilises integral three ported bypass 2/2 valves for the exhaust valves (V3 & V4). This is illustrated in figure 4 where ports A, B, and C represent the three ports. With the diaphragm seat sealing against the spigot leading to port C, and the 2/2 inlet valve open, the on stream gas is able to flow through port A, around each side of the spigot, before flowing through port B and on into the inlet of the tower. With the diaphragm in it's second operating mode and not sealing on the spigot, the off stream tower is able to depressurise via port B through port C. Because the inlet diaphragm valve (as shown on figure 4) is closed, the main inlet gas flow is prevented from escaping tllrough port A and consequently through port C. Finally the silencer, either S 1 or S2, can then be connected to port C to limit the noise on depressurisation. It is the combination of the three ported bypass 2/2 exhaust valves, working in conjunction the the standard 2/2 inlet valves, which is an essential feature of this invention.

By re-designing a conventional 2/2 valve to include a third port, it has been possible to create a 2/2 valve with integral bypass. This allows valves V3 & V4 on figure 1 to be re-positioned inside of the pressure vessel envelope which reduces the length of the flow passages (and hence pressure drop) and also considerably reduces the physical size of the unit (see section, figure4).

A further feature (and one which has not hitherto been available with existing equipment) is the inclusion of the control system (which sends the control signals to each of the valves) within the inlet manifold itself. Conventional manufacturers have tended to include seperate control enclosures which add cost, increase size and can lead to problems with electrical protection from ingress of moisture and dust. With this invention, each of these are elimiated by placing the control system within the manifold and utilising a manifold cover to form electrical protection.

Another feature of the cast manifolds is their method of attachment to the pressure vessel towers.

Conventional manufacturers use screwed unions or gaskets which are difficult to seal and are prone to subsequent leakage. The cast manifolds described in this invention use four simple sealing 'O'-rings which are located in the nozzles of the towers. These 'O'-rings serve two purposes in that they not only pro'vide compound sealing between the manifold and the vessel towers, but that they also captively hold the desiccant support screens in place (see figure 5).

This means that the manifolds can be removed from the vessel towers without fear that the desiccant beads will fall out of the vessel, thus making maintenance a much simpler task.

This invention, by incorporating standard and modified intgral valve mechanisms within a cast manifold system eliminates many of the problems associated with conventional dryer manifold systems which use commercially available valves and butt welded or threaded fittings.

The invention can be used with poppet or piston actuated valves as well as the diaphragm valves given in this example.

Various materials can be used for the casting ranging from Aluminium alloys to Spheroidal Graphite Iron to Polycarbonate composite plastics.

Claims (9)

1. A cast manifold with integral valving comprising a cast manifold arrangement incorporating two conventional 2/2 valves, two modified 3 ported 2/2 valves, provision for inclusion of control and actuation systems and unique attachment system.

2. A cast manifold with integral valving as claimed in Claim 1 wherein two conventional 2/2 valves are used to control the flow of compressed gas between the two towers of an adsorption dryer.

3. A cast manifold with integral valving as claimed in Claim 1 wherein two modified 3 ported 2/2 valves are used to discharge compressed gas from the two towers of an adsorption dryer.

4. A cast manifold with integral valving as claimed in Claim 1 or Claim 3 wherein the rnaln on stream gas bypasses a modified 3 ported 2/2 valve when the valve is closed.

5. A cast manifold with integral valving as claimed in Claim 1 or Claim 3 or Claim 4 wherein the main on stream gas is discharged through a modified 3 ported 2/2 valve when the valve is open.

6. A cast manifold with integral valving as claimed in Claim 1 wherein the control and actuation system for the valves in incorporated within the cast manifold of the adsorption dryer.

7. A cast manifold with integral valving as claimed in Claim 1 wherein the cast manifold with integral valving is attached to the two towers of the adsorption dryer using a unique attachment system comprising a captive 'o' ring system.

8. A cast manifold with integral valving as claimed in Claim 1 or Claim 7 wherein the manifold is attached and sealed to the adsorption dryer towers using a captive '0' ring seal.

9. A cast manifold with integral valving as claimed in Claim 1 or Claim 7 or Claim 8 wherein the captive '0' ring seal holds the desiccant support screens in place such that the desiccant beads are retained when the cast manifolds are removed from the adsorption dryer towers.