GB2087258A - Spray scrubbing and filtering air - Google Patents

Abstract

A filter system, particularly for use in conjunction with a gas turbine engine power plant located on an oil rig at sea, comprises a solid particulate entraining spray device (20) and a liquid separator (22). The spray device (20) has a number of spaced apart nozzle a (28) arranged to spray warm sea water from the crude oil cooling plant of the rig into the intake air. The sea water droplets amalgamate with the air borne contaminants, such as cement dust and salt, and the droplets are removed from the air by a separator comprising two louvre type separators (22), (38) and a coalescer (36). <IMAGE>

Description

SPECIFICATION Improvements in or relating to filters This invention relates to filters, more particularly to a filter which can remove solid and liquid contaminants from a gaseous stream, in conjunction with a gas turbine engine.

In a particular instance, gas turbine engines which operate on off-shore oil rigs require filters to remove both salt water and solid particulates from the engine intake air. Currently available filters are designed primarily for removing either solid or liquid particulate from gas streams. Problems arise if a gas stream contains both solid and liquid particulate. The filter systems designed, for liquid removal either allow a majority of the solid particulate to pass through or they rapidly become clogged requiring frequent maintenance. Filters designed for solid particulate from a gas stream either allow liquid through the system or distintegrate when wet.

The present invention seeks to provide a filter system which is capable of removing both solid and liquid particulate from a gas and which is substantially self-cleaning thereby reducing maintenance.

The filter system of the present invention is aimed primarily at filtering intake air for a gas turbine engine which is sensitive to both solid particulate which causes erosion of the rotating blades and fouling, and any salt in the air stream which may be in solid or liquid form, which causes hot corrosion.

However, the present invention can be used to remove both solid and liquid particulate from a gas stream in other circumstances, e.g. filtering the intake of any gas breathing engine, in a process system, or in a ventilating system.

Accordingly the present invention provides a filter system comprising in flow series a means for entraining solid and liquid particulate in a liquid carrier from a gas stream and a filter means for extracting the liquid carrier containing the solid and liquid particulate from the gas stream.

The entraining means may comprise liquid spray means including spray nozzles arranged to spray the liquid carrier into the gas stream. The liquid carrier may comprise water, salt water or any liquid which does not adversely affect the performance or structure of the downstream filter means.

The filter means may comprise a louvre type separator and if necessary a downstream coaleser and a further louvre type separator can be provided.

The present invention will now be more particularly described with reference to the accompanying drawings in which, Figure 1 shows diagrammatically an air intake of a gas turbine engine with a filter system according to the present invention, Figure 2 shows in more detail the filter system illustrated in Figure 1, Figure 3 is a part-section on line 3-3 in Figure 2, Figure 4 shows a modified form of filter system to that shown in Figures 1 and 2, Figure 5 is a part-section on line 5-5 in Figure 4 and Figure 6 is a part section on line 6-6 in Figure 4.

Referring to Figures 1,2 and 3 a gas turbine engine 10 only a part of which is shown and which provides power on an off-shore oil rig, is mounted in a duct 12 which also contains an intake flare 14, silencer splitters 16 and a filter system 18.

As shown more clearly in Figures 2 and 3 the filter system 18 comprises a liquid and solid particulate entraining spray device 20 and a liquid separator 22.

The spray device includes a manifold 24 arranged to receive a supply of liquid carrier, in this case warm sea-water from the crude oil cooling plant of the oil rig, to which are connected a number of horizontal nozzle bars 26, each having a number of a spaced apart nozzles 20. The number spacing and design of the nozzles are all arranged to substantially fill the duct 12 with a spray of liquid carrier, the purpose of which is to entrain, encapsulate or merge with the solid and liquid particulate in the gas stream, which in this case is air. The nozzle spray is preferably counter-current i.e. the spray is against the gas flow, but it is possible that the general direction of the spray and gas flow may make an angle with each other without affecting the ability of the spray to entrain the solid and liquid particulate to too great an extent.

The nozzle spray parameters of pressure, flow rate, droplet size and distribution and shape of the spray pattern are defined depending on the type of contaminant to be removed from the gas stream and the velocity of the gas stream. The nozzle parameters are chosen such that the droplets of liquid carrier are of a size and velocity to entrain, encapsulate or merge with the solid and liquid particulate contaminant in the gas flow.

The effect is to enlarge the size of the contaminant droplets or the captured solid contaminant such that are removed from the gas stream by the liquid separator 22. The liquid carrier containing the solid and liquid particulate passes into a drain 30 which contains an agitator (not shown) provided to prevent silting of the drain. Excess liquid carrier is removed by a drain 32 which can also have an agitator if necessary. The liquid separator 22 is of the louvre type having louvres 34 (Figure 3) and is of a readily available design.

In some cases it may be necessary to provide further filters downstream of the separator 22 as shown in Figure 4. The further filters comprise a coalescer 36 to remove any remaining droplets and another louvre type separator 38 having louvres 40 (Figure 6) to remove re-entrained droplets which can be formed in high humidity on the coalescer 36.

Thus, one or more filters can be provided downstream of the spray device 20 to remove the liquid which includes the solid and liquid contaminants from the gas stream, the essence of the invention is to use a liquid spray to convert the contaminants into-a form which a conventional liquid separator can treat as all liquid.

Tests have been performed on a reduced scale three stage separator of the type shown in Figure 4 having a scrubbing spray pre-filterto entrain solid and liquid particulate in a liquid carrier. The tests were designed to simulate engine intake conditions on a North Sea oil rig in which the principal contaminants are cement dust, which fouls and blocks the filters, and salt which has a corrosive effect on engine components.

The scrubbing spray pre-filterwas similar to the spray device 20 and a range of spray nozzles, spray angles and and spray droplet sizes at different humidities were tested to establish the most effective arrangement for removing cement dust and salt.

All the scrubbing sprays removed between 75% and 90% of cement dust. The highest dust removal efficiency of 90% was obtained using salt water at a pressure of 60 psig. at a flow rate of 0.9 gallons/ minute, with a mass mean droplet size diameter of 348calm. The droplet sizes tested varied betwen 2261lm and 348cm, but it is estimated that droplet sizes in the range 20-500Fm would be useful in removing cement dust and salt.

The cement dust reaching the coalescer of the separator was reduced by a factor of 8, and that penetrating the separator as a whole by a factor of 10. The salt water scrubbing spray does not penetrate the separator.

The scrubbing spray improved the salt removal at low humidity by a factor of 2 and at high humidity by a factor of 10.

The scrubbing spray acts as a self-cleaning prefilter and as such will be maintenance free, and does not add to the pressure loss of the separator.

Whilst the invention has been described particularly with respect to an oil rig mounted gas turbine engine, it can be applied to gas breathing engines operating in other environments, to process and ventillation systems.

In addition, the temperature of the liquid spray may be adjusted to provide a heating effect to prevent icing of the spray of the filter.

Claims (10)

1. A filter system comprising in flow series a means for entraining solid and liquid particulate in a liquid carrier from a gas stream and a filter means for extracting the liquid carrier containing the solid and liquid particulate from the gas stream.

2. A filter system as claimed in claim 1 in which the entraining means comprises liquid spray means including an array of spray nozzles arranged to spray the liquid carrier into the gas stream.

3. A filter system as claimed in claim 1 or claim 2 in which the liquid carrier comprises water or salt water.

4. A filter system as claimed in any one of the preceding claims in which heating means are provided to heat the liquid carrier.

5. A filter system as claimed in any one of the preceding claims in which the filter means includes a louvre type separator.

6. A filter system as claimed in claim 5 in which the filter means includes a coalescer downstream of the louvre type separator and a further louvre type separator downstream of the coalescer.

7. A filter system as claimed in any one of the preceding claims in which the droplet size of the liquid carrier is arranged to be in the range 20 500cm.

8. An air intake filter system for use in conjunction with a gas turbine engine power plant located on an oil rig at sea, the filter system comprising an upstream liquid spray means and downstream filter means the liquid spray means being arranged to spray sea water through a plurality of nozzles into the intake air for the power plant, the sea water being supplied by the crude oil cooling plant of the oil rig, and the size of the sea water droplets produced by the liquid spray means being the range 20-5001lm, the downstream filter means including at least one louvre type separator.

9. A filter system as claimed in claim 8 in which the filter means comprises in flow series a louvre type separator, a coalescer and a further louvre type separator.

10. A filter system constructed and arranged for use and operation substantially as herein described and with reference to the accompanying drawings.