This invention relates to the injection of materials in atomised liquid form. It can be applied in a wide variety of industrial process plants.

BACKGROUND

Equipment providing heat for an industrial process, including but not limited to furnaces, process heaters, boilers and incinerators, are common yet critical units found in a variety of industries, such as petrochemical, refining, gas processing, shipping, steel, waste treatment, and waste-to-energy conversion plants. Designs of these units vary according to their function, heating duty, fuel type, and method of introducing combustion air. In furnaces and fired heaters, combustion heats up the fluid inside tubes to a desired temperature, whereas incinerators combust gaseous, fluid, or solid waste material. As a result of combustion, a variety of problematic fouling deposits build up that reduce heat transfer, block the flow of flue gas, and cause corrosion.

Hot gas expanders convert energy in a hot gas stream directly into mechanical energy, which is then used for another purpose, such as driving a compressor or generator. Sticky, corrosive substances in the flue gas can cause vibration, corrosion, and subsequent power degradation.

Industrial process units are periodically shut down for maintenance, such as cleaning, but it is desirable to minimise work during these outages so as keep them as short as possible. It is therefore preferable to reduce the build-up of deposits and/or to break down fouling deposits when the unit is in operation, thereby extending the run times between stops. There are established methods of injecting atomized liquid chemicals into such plant, some of which also neutralize corrosive and/or harmful substances.

Air-cooled heat exchangers (ACHEs) are one of the most efficient and widely used types of heat exchanger also found in a variety of industries, such as petrochemical, refining, gas processing, and power. However, a key problem is that ACHE performance decreases during high ambient air temperatures. Similarly, in gas-turbine power plants, higher ambient air temperatures lead to a decreased megawatt output and a higher heat rate. An established solution is to spray a water fog into the ACHE tube bundle or steam turbine air inlet, which allows an increased process flow through the ACHE or a decreased gas-turbine back pressure and a significant power increase.

ACHE fogging systems typically use high-pressure water pumps to pressurize demineralized water to between 70 bar to 200 bar. The water flows through a network of tubes to fog-nozzle manifolds that atomize the water into micro-fine droplets. Whilst effective, these systems suffer from a number of drawbacks: they are complex and expensive; they suffer from reliability issues; the nozzles have minuscule orifices that easily block and are expensive to replace; there are numerous installation requirements (such as cabling, power supply, concrete base for pump); high-pressure systems require annual certification in some countries.

Injecting a liquid fog/mist via an atomization nozzle results in much of the pump’s drive pressure being lost, and means the volume of liquid flowing from the nozzle is considerably less than the flow created by the pump; furthermore, the fog/mist exits the nozzle in a dense stream that travels a short distance from the orifice, and so the atomized liquid will spread minimally throughout the process equipment, without further assistance (such as blowers or fans).

PRIOR ART PATENT DISCLOSURES

UK Patent specification GB2395722 and European Patent specification EP0058086 describe a method for preventing and removing deposits from heating and ancillary surfaces of boilers and like equipment, by continuously or intermittently introducing into the combustion chamber of the equipment or into the flue gas stream a liquid additive in atomized form by means of at least one injection device. Published PCT specification WO1994/028091 describes a method of breaking up deposits laid down in a heating apparatus by combustion of bitumen-based emulsion fuels, comprises the introduction to said heating apparatus during an operational phase thereof a composition containing at least potassium nitrate, preferably with ammonium nitrate, and optionally a pH stabiliser, in an aqueous vehicle, by spraying said material or composition directly into the heating apparatus via atomising nozzles.

It should be noted that neither of the aforementioned Patent specifications provide any detail on the injection device, although WO1994/2028091 mentions employing an atomisation nozzle, and GB2395722 I EP0058086 would also typically employ an electric high-pressure pump to force the liquid through an atomisation nozzle. Such high-pressure pump and atomization nozzle systems are designed and built for a fixed drive pressure and liquid volume, and are not designed for these to be adjusted. Furthermore, these systems cannot inject small quantities of a liquid mist continuously, rather they inject the dose at intervals, where the pause duration increases as the injected quantity decreases.

GENERAL DESCRIPTION OF THE INVENTION

According to the present invention, a stream of liquid particles is generated by a fast-moving gaseous stream arranged to entrain a feed of liquid treatment agent and to break the liquid up so as to form a rapidly moving jet of liquid particles suspended in the gaseous stream and injecting the jet directly into industrial process equipment during its normal operation. The operation may be purely pneumatic.

Preferably, the apparatus used to put the present invention into practice, which also constitutes an aspect of the present invention, includes a venturi system where the reduced pressure in the gaseous stream immediately after passing through a narrowed section of a feed pipe or conduit is used to entrain liquid from an inlet port in the side of the pipe or conduit immediately downstream of the narrowed section. The method and apparatus according to the present invention provide an alternative to using high-pressure pumps and atomisation nozzles, and can be employed for either temporary or permanent use, depending on the purpose of application and type of liquid being injected.

The invention has a wide variety of applications, including but not limited to injecting atomised liquids into units providing heat (typically higher than 400 degrees Celsius) for an industrial process, into the air inlet of air-cooled heat exchangers, and into the air inlet on gas turbines.

The invention is particularly directed towards pneumatic injection devices for the purpose of precisely injecting atomized liquid additives into furnaces, process heaters, boilers and incinerators, as well as hot gas expanders, in order to break down fouling deposits and/or neutralise problematic contaminants in the flue gas.

In the present invention, the preferred embodiment is one relying purely on pneumatic injection, using a so-called vacuum injector device comprising a venturi gas flow tube with a constriction and, just downstream of the constriction, an adjoining outlet for a liquid feed tube, the inlet of which tube may simply be submerged in the liquid which is in a container of the liquid to be injected.

Such a system drive works with the liquid in the container subject to normal atmospheric pressure. The fast gas stream flowing through a constricted internal section of the gas flow tube, generates a local reduction in pressure in the gas stream, in accordance with Bernoulli's principle, to below atmospheric so the higher atmospheric pressure exerted on the surface of the liquid inside the container forces the liquid through the liquid feed tube and into the fast gas stream, where it is dispersed into extremely fine droplets, and is carried along the gas flow tube within the stream of gas. Conveniently the gas flow tube is generally horizontal and the liquid flow tube vertical with the container or reservoir located below the gas flow tube. Certain applications, such as injecting chemical additives into fired heaters, may require small liquid quantities and better results are achieved if the liquid is injected continuously. The present invention which uses a pneumatic injection device allows the drive pressure and liquid volume to be easily adjusted during operation, so one device is capable of injecting a wide range of liquid flows continuously.

Injecting the atomised liquid in a fast gas stream (typically between 3 bar and 10 bar) without the obstruction of a nozzle means the gas/liquid enters the process equipment in a more diffuse stream and spreads considerably further on its own volition.

Further advantages of the apparatus according to the present invention, compared with the known systems using a high-pressure pump and atomization nozzle, include: a considerably smaller, simpler, and more reliable system; lower drive pressure; a high degree of scalability; adjustable control over the mist droplet size and the distance it travels after exiting the downstream end of the gas flow tube; reduced energy usage; lower maintenance costs. The ability to adjust the droplet size without having to change an atomization nozzle (which might well involve a degree of dismantling and reinstallation) can be achieved by adjusting the gas flow using a suitable regulator. Additionally, if the fast gas stream is supplied by process plant utilities, there is reduction in any electrical or explosion hazard risks.

In cases where the injection is to be from the end of the gas flow tube into hot process equipment such as a furnace, it is desirable to provide, around the downstream end of the tube, means for keeping the tube cool, for example a water-cooled or air-cooled jacket surrounding those parts of the tube which are to be introduced into the heated area. This avoids the cost of providing the outlet end of the tube with a high temperature resistant, commonly high cost refractory endpiece.

The pneumatic injection device’s characteristics can differ depending on the required application: • It may be employed for either temporary or permanent use.

• Multiple devices may be used simultaneously, in one or more locations.

• Component (hose, tube, vessel) dimensions and capacities vary.

• The gas flow tube material could be stainless steel, plastic, or another material

• The gas flow tube outlet may be a single a tube with one outlet, a single tube with multiple outlets, or connect to a series of tubes, or a hose.

• The fast moving gas could be compressed air, oxygen, an inert or relatively inert gas or a mixture

• The gas and/or liquid inlets may have particle filters installed.

• The air and/or liquid flow regulators may be provided, integrated into the device’s drive or separate.

• Compressed gas may be provided by an air compressor, or plant utilities.

• If a lance cooling system is needed, this may be an open type where the air discharges into the combustion equipment, or the water discharges to a drain, or a closed-loop type where the water is cooled by a heat exchanger.

• The lance may be held by a technician and inserted through an external opening in the process equipment, such as a fired heater peephole, or it may be attached to or pass through a permanent fixture of the process equipment designed specifically for the purpose.

By way of illustration, the following is a detailed description of one embodiment of a pneumatic injection device according to the present invention, the embodiment being specifically designed for the permanent dosing of a chemical additive inside a fired heater to break down fouling deposits and/or improve emissions. The embodiment illustrated in the accompanying drawing.

Referring to the drawing, this shows diagrammatically a pneumatic injection device according to the invention connected to a fired heater, part of which is shown enlarged for ease of understanding.

The pneumatic injection device comprises a stainless steel injection lance 1 with a venturi 2 at one end. The venturi has two inlet tubes 4, 7 that extend much of the length of the lance, and one outlet 9: compressed air is supplied from the air inlet 3 to a pressure gauge 5, and an appropriate particulate filter (not shown); the chemical additive is supplied from a reservoir (not shown) at the liquid inlet 6 to a flow gauge 8 and an appropriate particulate filter (not shown).

The lance passes through a flange 10 installed on a wall 1 1 of a fired heater combustion chamber 12. The lance is enveloped inside a larger tube into which a supply of water flows in 13 and out 14 in order to cool the portion of the injection tube inside the fired heater and prevent it from overheating and distorting.

The air regulator 15 positioned before the lance precisely controls the volume and pressure of air flowing in to the venturi. Below a certain flow rate, the flow of air is laminar and the venturi will create a vacuum, thereby drawing the liquid into the venturi; however, at flow rates above this level, the air stream becomes turbulent and the venturi creates a pressure, which means the liquid is not drawn up the liquid inlet. These flow rates vary depending on the tube diameter, and can be established by using fluid dynamic flow calculations.

At a fixed liquid flow rate, there is an inverse relationship between the air pressure/volume and the size of the entrained liquid droplets and the spray dispersal range, which can be precisely set by adjusting the air regulator, where an increase in the compressed air pressure/volume results in smaller droplets, as well as a larger spray dispersal range, and vice-versa.

At a fixed compressed air pressure/volume, the quantity of liquid flowing up the liquid inlet has a direct relationship to the size of liquid droplets and dispersal range where a decrease in liquid flow results in smaller droplets and a larger dispersal range, which can be precisely adjusted using a liquid regulator 16.

The relationship between the diameter of the air inlet of the venturi and diameter of the narrowed section of the venturi is an important aspect, as the larger this ratio becomes, the more vacuum the venturi creates.

Once the system has been correctly installed, with the lance inserted into the fired heater during operation, a sufficient amount of fluid must be continuously circulated to ensure adequate cooling, even if no chemical injection treatment is in operation.

Prior to operation, the air pressure/volume is determined, depending on the spray range and liquid particle size required. The air regulator is then carefully opened until the pressure gauge confirms the correct pressure has been reached.

The quantity of liquid to be injected into the fired heater is also pre-determined, and the liquid regulator is carefully opened until the gauge reads the specified flow rate has been achieved.

As the flow rate is constant, the duration until the reservoir is empty can be calculated, at which point it will be refilled or replaced.

The reference numbers identify the following components shown in the drawing:

1 . Injection lance

2. Venturi

3. Air inlet

4. Venturi air tube

5. Pressure gauge

6. Liquid inlet

7. Venturi liquid tube

8. Flow gauge

9. Venturi outlet

10. Flange

1 1 . Fired heater wall

12. Fired heater combustion chamber

13. Cooling water inlet

14. Cooling water outlet

15. Air regulator

16. Liquid regulator