GB2136311A

GB2136311A - Air intake equipment

Info

Publication number: GB2136311A
Application number: GB08307354A
Authority: GB
Inventors: John Shackell
Original assignee: PREMABERG
Current assignee: PREMABERG
Priority date: 1983-03-17
Filing date: 1983-03-17
Publication date: 1984-09-19
Also published as: GB8307354D0

Abstract

Air intake equipment for an I.C. engine or heating and ventilating plant comprises an air intake duct and a moisture separation unit hingedly mounted in the duct, so as to be movable out of the air stream to open passage through the duct in the event of the unit becoming blocked. By this means the provision of a separate by-pass door is avoided. The moisture separation unit may comprise a coalescing pad and one or more sets of vanes and may be latched in place across the duct, with the latch being automatically released in response to increased downstream suction which then moves the unit. Alternatively a pressure switch controls a motor which positively moves the unit.

Description

SPECIFICATION Air intake equipment This invention relates to air intake equipment, more particularly but not solely for gas turbine engines, diesel engines, air heating and ventilating systems used in a marine or other adverse environment, to remove moisture, and particularly salt water, from the air stream entering the intake.

Vane type moisture separation systems have been widely used over many years in the natural gas, petro-chemical, nuclear, steam generation and marine industries wherever high efficiency removal of liquids from a gas stream has been required. In more recent times, with the advent of gas turbines as major power sources on ships and offshore oil and gas platforms, it has been a natural development to use these systems to remove salt water entrained in the air streams entering such engines.

Gas turbines used in marine or coastal installations are subjected to salt ingestion via their combustion air intakes and even under the calmest weather conditions the salt content in the surrounding air is likely to exceed the extremely low level necessary for a satisfactory engine life. It is also to be remembered that gas turbine air intakes situated in close proximity to the sea will not only be subjected to air-borne salt in spray or aerosol droplet form, but they will also experience massive water loadings often of green sea intensity when weather conditions are bad.

Specialised intake protection systems therefore became necessary to reduce the salt-inair content to the acceptable level of 0.01 ppm by weight demanded by gas turbine manufacturers under any environmental condition and, furthermore, it was vital that this duty should be performed by equipment with a low pressure drop, compact dimensions, low weight, high strength and prolonged resistance to atmospheric attack.

In order to meet these exacting requirements, resort is normally had to a three-stage air intake equipment. This type of equipment has been in regular use for a number of years, and consists of three distinct separate elements placed in series.

The first and third stages rae each a developed form of vane type separator which consists of a number of parallel vanes mounted vertically, with vapour flow at right angles to the face of the vane unit. The vapour flows through a tortuous path between the separator vanes resulting in impingement of moisture droplets on the vane bodies. Each vane has multiple changes of direction and multiple catchment pockets to trap the moisture droplets separated by impingement.

These droplets drain vertically downward to a catchment trough underneath the vane section.

Many different vane profiles are now available.

Boxing or framing is built around the outsides of the vane bank to hold the vanes in place as well as to provide "cover-up" to prevent by-passing of air around the vane edges or tops. Water is removed from the bottom drain trough by way of auxiliary drains.

In the three-stage system, a filter/coalescer pad is situated between the first and third stage vane elements and this serves the purpose of coalescing any fine aerosol droplets which may have passed through the first stage into larger sizes which are then easily removed by the vane type separation elements of the third stage.

The purpose of the first stage is to remove all large water loads from 'green sea' intensity down through the sprays and mists to aerosol droplets of approximately 13 microns in diameter. It is necessary for the first stage to be extremely efficient in the removal of these entrainments in order to prevent excessive loading of the second stage coalescer.

The second stage acts as a filter/coalescer serving to catch and coalesce the smaller aerosol droplets which may have passed through the first stage. These enlarged coalesced droplets will then either drain off the second stage itself, or be reentrained into the air stream and carried on to the third, separator, stage.

The third stage of the system is the final separation stage and removes from the airstream those relatively large coalesced droplets which are re-entrained off the second stage. It also serves to protect the air stream against the re-entrainment of highly concentrated droplets of brine solution which are generated on the second stage medium after the system has been operated, at relative humidities below approximately 70%. In this environment condition the second stage acts as a filter and captures dry or partly dry salt particles.

These collect in solid form in the coalescer medium, but when the relative humidity of the environment rises above 70% the hygroscopic nature of the salt will cause condensation to occur along with some re-entrainment of brine droplets, which contain high concentrations of salts. The third stage serves to prevent the passage of these droplets into the air stream entering the gas turbine.

In addition to the use of gas turbine engines or marine diesel engines, such vane type air intake equipment may also be used with heating and ventilating equipment. In heating and ventilating applications, use is often made of a two stage equipment comprising a coalescer and one stage of vane separation.

In most applications, it is necessary to provide an emergency by-pass door so that in the event that the air intake equipment becomes blocked e.g. by icing or a build up of foreign matter, the downstream equipment and ducting is protected against the effect of possibly massive vacuum resulting from blockage. The effect may include collapse of ducting or serious damage to equipment or the gas turbine itself, which would be more damaging than exposure to salt water for a limited period until the blockage is removed. The by-pass door is normally one or more fairly large doors which may be automatically or manually operated in the very rare event of blockage. In many cases they are unlikely to be used in earnest throughout the life of the equipment being protected. However they do represent a considerable capital amount and also need to be subject to regular maintenance.Further, the need for provision of a bulky by-pass door may be a significant design constraint in building a plant in the most economical manner. For instance in a heating and ventilating plant for a deep sea platform there may be no room for a by-pass door, so the equipment may go unprotected.

In accordance with one apsectofthe invention, there is provided an air intake duct and a moisture separation unit sealingly mounted in the duct for removal of moisture from an air stream entering the duct, in which the moisture separation unit is mounted so as to be readily movable, wholly or partially, out of the air stream to open passage thrrough the duct and allow itself to be by-passed.

A particular piece of equipment may have more than one inlet duct, or more than one separate unit to a single duct, and in such a case there may not be a necessity for all the moisture separation units to be readily released.

In accordance with a second aspect of the invention, air intake equipment comprising a plurality of air intake ducts each having a moisture separation unit sealingly mounted therein for removal of moisture from the air stream entering via the respective duct, in which at least one moisture separation unit is mounted so as to be readily movable, wholly or partially, out of the air stream to open passage through the duct and allow itself to be by-passed.

In an alternative form a single duct, particularly that to a gas turbine, might well contain a multiplicity of separators, only one or perhaps two of which need to be arranged as in-built by-pass doors.

In one form of the invention, the movable moisture separation unit may be hingedly mounted in the duct and retained in a normal position sealed in the duct by a readily releasable catch mechanism.

The movable moisture separation unit may be manually movable upon a suitable warning signal being given, but it is preferred that the opening be automatic. The opening may be initiated by sensing a pressure fall downstream of the moisture separation unit and thereby releasing the catch mechanism, directly or indirectly, or alternatively actuating a suitable opening mechanism.

The moisture separation unit may be a three stage unit as described above, or alternatively a two stage unit, incorporating a coalescer and a downstream vane type separator may be used, e.g. in a heating and ventilating plant intake which is normally shielded from spray.

A separator arranged as a by-pass unit, could in fact be motivated in several different ways.

On one form, it would normally be retained in the closed position by a catch which on receipt of a signal from a depression switch downstream of the separators would be released by means of a solenoid, or by a hydraulic or pneumatic jack, according to preference. The door would then actually be sucked open by the forece of the depression on its downstream face. To resist the kinetic energy build up in the abrupt opening of the door, either a buffer mechanism or more probably a torsion bar, would be incorporated.

Another type of by-pass door would be retained in its closed position by some form of screw jack mechanism. On a recept of a signal from the pressure switch referred to above an electric motor would be activated which in turn would open the door by positive means through the screw face mechanism.

In the latter case the opening force actually comes from the electric motor, whereas in the former case the opening force is derived from the depression in the ducting acting on the downstream face of the door.

There is also the possibility that the movable separator could merely be wound open manually as some users prefer this type of actuation.

The seal in these devices will normally be trace heated by the self-limiting type of electric heating element.

Various modifications may be made within the scope of the invention.

Claims

1. Air intake equipment comprising an air intake duct and a moisture separation unit sealingly mounted in the duct for removal of moisture from an air stream entering the duct, in which the moisture separation unit is mounted so as to be readily movable, wholly or partially, out of the air stream to open passage through the duct and allow itself to be by-passed.

2. Air intake equipment comprising a plurality of air intake ducts each having a moisture separation unit sealingly mounted therein for removal of moisture from the air stream entering in the respective duct, in which at least one moisture separation unit is mounted so as to be readily movable, wholly or partially, out of the air stream to open passage through the duct and allow itself to be by-passed.

3. Air intake equipment as claimed in claim 1 or 2, in which the movable moisture separation unit is hingedly mounted in the duct and retained in a normal position sealed in the duct by a readily releasable catch mechanism.

4. Air intake equipment as claimed in claim 1, 2 or 3, in which the movable moisture separation unit is automatically releasable on the occurence of a given pressure reduction on the downstream side thereof.