COOLING ARRANGEMENT

FIELD OF THE INVENTION

This invention relates to a cooling arrangement and apparatus. More particularly, this invention relates to a cooling arrangement and apparatus for cooling the inlet air of gas turbines, particularly gas turbines for use in the generation of electricity within single site aluminium smelters utilizing the available waste heat produced by the smelting process or associated processes .

BACKGROUND TO THE INVENTION

Gas turbines are widely used in the generation of electricity where gas or liquid fuel is available. Steam turbines are used with gas turbines either in combined cycle or separately using the waste heat from the gas turbine to produce more power.

Generally, steam turbines, using nuclear, gas or coal fuel for producing heat for its boiler systems are used to generate electricity for towns, cities or the like.

On the other hand, gas turbines are often used where plants or factories require on-site electricity generating facilities. Such is the case in many aluminium smelting plants over the world because the high electricity requirements for this type of plant usually dictate these plants are located near an abundant source of energy such as natural gas, oil, coal, nuclear or hydroelectric.

Where a plant, such as an aluminium smelting plant, has its own on-site electricity generating plant, it is commonly referred to a "single site smelter".

Although gas turbines are well suited for the production of electricity at single site smelters, this type of turbine is not without its disadvantages. One of the main disadvantages of a gas turbine is that it is very sensitive to ambient temperature variations. A gas turbine will deliver more power in low ambient temperature conditions and deliver less power in high ambient temperature conditions.

This is mainly due to the reliance of a gas turbine on air density in its operation. It will therefore be appreciated that in hot climates, gas turbines are less efficient than in cold climates.

OBJECT OF THE INVENTION

It is accordingly an object of the invention to provide a means for cooling inlet air for a gas turbine for making the gas turbine more efficient in hot ambient temperature conditions utilizing available waste heat.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a cooling arrangement for cooling inlet air of a gas turbine including cooling means and a heat exchanger located in an air inlet path of the gas turbine.

In a preferred form of the invention, the cooling arrangement includes an absorptive refrigeration means. The refrigeration means is preferably a Lithium Bromide and water type absorptive refrigeration means.

It will be appreciated that any suitable type of absorptive refrigeration means may be used.

Because absorption refrigeration requires low grade heat as an energy source to function, it is well suited for cooling purposes in a plant such as an aluminium smelter where there is an abundance of hot waste gases.

The refrigeration means preferably includes a plurality of absorptive refrigeration units, each unit being supplied by hot water which has been heated by hot gases from a fume treatment plant in an aluminium smelting plant; a chilled water circuit wherein water is circulated through the refrigeration units during which time it is chilled, to a gas turbine air inlet and back to the refrigeration units.

The cooling arrangement may further include a cooling water supply and return circuit, via a cooling tower arrangement for purposes of condensing water used during the absorption process in the absorptive refrigeration units.

The cooling water is used to condense the working fluid such as Lithium Bromide during the absorption process in the absorptive refrigeration units.

The cooling means may include a plurality of absorptive refrigeration units, each unit being supplied by hot water which has been heated, in use, by hot gases from a fume treatment plant in an aluminium smelting plant; and a chilled water circuit wherein water is circulated through the refrigeration units during which time it is chilled, in use, to a heat exchanger located at a gas turbine air inlet and back to the refrigeration units.

The waste heat produced by the aluminium smelting process may be recovered for absorption cooling from the power production, casting process, the anode baking kilns or the electrolytic reduction cells.

According to a second aspect of the invention, there is provided a process for cooling gas turbine inlet air, including the steps of lowering the temperature of a

fluid by means of absorptive refrigeration and using the fluid to cool the gas turbine inlet air.

The chilled water from the absorption coolers may also provide air conditioning comfort cooling for the plant personnel.

According to a third aspect of the invention, there is provided a gas turbine including a cooling arrangement as described in the specification.

According to a fourth aspect of the invention, there is provided an aluminium smelting plant including at least one gas turbine as described herein.

The process may include the step of using waste hot gases to energize the absorptive refrigeration means.

BRIEF DESCRIPTION OF THE DRAWING

One embodiment of the invention will now be described in more detail with reference to the accompanying drawing which is a schematic representation of a cooling arrangement according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the drawing, a cooling arrangement 10 according to the invention is shown to include an absorption plant 12 including seven absorptive refrigeration units (not shown). In the preferred embodiment, the absorptive refrigeration units are of the Lithium Bromide and water type.

The absorptive refrigeration units are energized by via twenty four heat recovery points 14. In the present invention, the arrangement 10 is installed in an

aluminium smelting plant (not shown) and the heat recovery points 14 are located near fume treatment plants (not shown).

At the fume treatment plants hot gases from aluminium smelting cells (not shown) are treated - typically, by removing hydrogen fluoride by dry scrubbing with alumina.

Prior to scrubbing, the hot fumes 16 are ducted to the heat recovery points 14 as shown. At the heat recovery points 14, a water supply and return circuit 18 contains water which absorbs heat from the hot gases at the heat recovery points 14 and which is pumped at approximately 120 degrees Celsius via supply line 18.1 to the absorption plant 12 where the heated water energizes the absorptive refrigeration units (not shown). The water is then returned via return line 18.2 at approximately 90 degrees Celsius to the heat recovery points and the cycle is repeated.

The fumes exiting the heat recovery are cooled from 130 C to around 100 C. The adsorption efficiency of the alumina scrubbing media is consequently enhanced thus hydrogen fluoride recovery is improved in the order of 25%, reducing harmful emissions from the potroom fume treatment plants.

Hot exhaust fumes 17 exit the heat recovery points 14 and are scrubbed before being expelled to atmosphere.

At the absorption plant 12, a chilling water supply and return circuit 20 contains water which is cooled (or chilled) in the absorption plant 12 to about 15 degrees Celsius and which is then pumped via supply line 20.1 to four gas turbine heat exchangers 22. The water is then returned via return line 20.2 at about 25 degrees Celsius to the absorption plant 12 and the cycle is repeated.

Hot ambient air 24, which can have a temperature of 50 degrees Celsius or more in very hot climatic conditions, is ducted through the heat exchanges 22 and is cooled down to about 20 degrees Celsius when it exits. The cooled air 26 is then ducted to gas turbines (not shown) as inlet air where the lower inlet air temperature significantly increases efficiency of the turbines in the production of electricity.

A cooling tower arrangement 28 is provided for lowering the temperature of absorption plant cooling water. The cooling water is used to condense the working fluid of the absorption refrigeration units in the normal operation of these units. A cooling water supply and return circuit 30 contains cooling water which pumped via supply line 30.1 to the absorption plant 12 at about 34 degrees Celsius and returned via return line 30.2 at about 43 degrees Celsius and the cycle is repeated.

Applicant has found that in summer in very hot climatic conditions where the ambient temperature reaches 50 degrees Celsius, the efficiency of its gas turbines at its aluminium smelting plant can drop by up to 25%. The optimum temperature for gas turbine inlet air is about 15 degrees Celsius [ISO Standard] and by reducing the inlet air to about 20 degrees Celsius from 50 degrees Celsius ambient temperature, a significant increase in power output, efficiency and performance of the gas turbines is possible.

There are several advantages to the invention as defined when employed in a single site aluminium smelting plant, including the following:

Cooling the gases from the electrolytic reduction cells (not shown) improves the adsorption ability of alumina scrubbing media thus improving hydrogen fluoride recovery.

Cooling the gases entering the fume treatment plants from the electrolytic reduction cells allows operators to increase potline amperage without detrimental effect on the fume treatment plants.

Chilled water from the absorption refrigeration process may be used to provide comfort cooling [air conditioning] for plant personnel.

Waste heat for absorption cooling within an aluminium smelter may be recovered from power production, casting process, anode baking kilns, desalination or reduction cells.

Cooling the gases from the electrolytic reduction cells extends filter bag life.

It will be appreciated that many variations or modifications of this invention are possible without departing from the scope of the appended claims.