FI94597C - Method for separating fine dust from hot pressurized process gas - Google Patents

Description

- 94597

METHOD FOR THE SEPARATION OF FINE DUST FROM HOT PROCESS GAS

The invention relates to the purification of fuel gas produced by pressurized fluidized bed combustion or other gasification techniques before gas turbines and in particular to a hot purification method before a gas turbine.

In a fluidized bed boiler, the combustible gas is further gassed from solid fuel or combustible broth. Only a small amount or no heat is recovered from the fluidized bed boiler in the partial combustion. The released energy remains in the gas leaving the boiler as heat and pressure energy to be recovered, mainly by a gas turbine connected downstream of the boiler, at the same time as the final chemical energy of the gas is released by combustion. After the turbines, thermal energy can still be recovered from the flue gases in waste heat boilers. The process thus formed achieves a high efficiency of electricity and heat production. In order to achieve a high efficiency, the purification of the gas coming from the boiler and intended for the turbine fuel should take place with the lowest possible heat loss.

The turbine blades are made of an iron, nickel or cobalt based alloy to which chromium and / or aluminum have been added to prevent oxidation. Due to the additives, a dense oxide layer is formed on the surface of the turbine blades to prevent the progress of oxidation. Such a layer may crack due to dust particles colliding with it, or its surface may melt under the influence of alkali metals entrained in the dust, causing corrosion in the turbine impeller. To minimize these problems, limit values must be set for gas purity and dust particle size. The level of gas purity required depends on the materials used to make the gas turbines, but in general the dust content of hot gas turbines should be less than 10 mg / m3 and the particle size less than 5. Chemical contaminants in the gases cause corrosion in the impeller of turbine 94597 2.

Cleaning pressurized gases to a sufficiently high temperature at high temperatures has proven difficult.

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For the purification of hot, high-pressure gases, dust separation cyclones have been used as the first purification stage, i.e. as primary separators. In fluidized bed combustion, the air dust separated from the gas is returned to the fluidized bed. Collision filters, particulate filters, electrostatic precipitators or others, such as melt bath filters, are used as secondary separators. Due to the operating conditions of the secondary separators, pressure and heat losses occur.

The method and apparatus according to the invention are characterized by what is set forth in the characterizing parts of the claims.

A significant advantage of the invention can be considered that the new invention is better able to separate small particles from the gas, and the separation can be carried out with the lowest possible pressure and heat losses. At the same time, emissions from combustion can be reduced. Clogging of the filters can be slowed down or their use can be completely eliminated. Their service interval is extended, etc.

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The invention will now be described in detail with reference to the accompanying drawing.

The only figure shows the gas cleaning method in a kaa-30 fault pattern.

The solid fuel is gasified by fluidized bed technology. The temperature of the fluidized bed may be, for example, 850 ° C. the temperature of the gas can still be raised by more than one thousand 35 degrees if necessary. When it is then desired to purify such a gas at high temperature and high pressure (e.g. 10-16 bar), the purification is carried out according to the invention as follows. Prior to gas turbines, particles 3 to 94597 contained in the gas are bound to larger solid or molten particles which are injected directly into the pressurized gas flow. Larger injected particles of about 20-50 μιη and smaller particles adhering to them are separated from the gas using a classification technique. The particles in the gas to be cleaned are usually of the order of less than 10 μιη.

The figure shows the equipment for the cleaning method. The high-temperature and pressurized gas is injected 10 before the gas turbines 1 with particles a few tens of micrometers in size or droplets of molten material through a jet-dispersing nozzle 2 placed in the gas-conducting tube 3. The injection pressure is set higher than the gas pressure so that the gas and the particles to be fed collide with each other. The mouthpiece 2 is located, for example, at the end of the pipe 4 introduced into the center of the gas pipe. The nozzle 2 provides a continuous "particle mist" distributed over substantially the entire cross-sectional area of the gas pipe, which penetrates the gas stream. The injectable particles are mixed with the injectable carrier gas in a separate tank 8. The gas thus obtained is passed through a differential pressure-maintaining feeder 9, e.g. a shut-off feeder, to the injection pipe 4.

In order to enable the separation, the gas pipe 3 is contracted after the nozzle 25 before the gas turbines 1 ns. venturi tube 5 • shape. In the venturi, the gas flow rate increases and due to the turbulence, the injected particles and the gas impurities collide and adhere to each other. Adhesion is based on the agglomeration of small particles contained in the gas at high temperature to the surfaces of larger injected particles. Electrical charges can also expose particles to attach to each other.

After the venturi 5, the velocity of all particles is the same as the velocity of the gas flow. A classifier 6 or several classifiers 6 and 7 are connected directly to the venturi. When the classification takes place immediately after the venturi, the velocity of the gas and particles entering the classifiers 6 and 7 is at its maximum, which allows the classifiers to operate efficiently from 4 to 94597.

Cyclones are used as a classifier in the purification of hot gases. Cyclones can be utilized if the particles contained in the gas are made to fully bind to the larger particles injected. One possible classifier type is cyclones. Today, there are several types of classifiers that are more efficient.

10 Melt can be used instead of solid particles, eg fly ash particles. In melt injection, the material to be melted is melted and pressurized in a separate tank from where it is injected directly into the gas stream. The melt is injected into the gas stream, for example by means of ceramic nozzles.

15 Pressurized gas contaminants adhere and adhere to melt droplets, eg through surface forces, dissolution, chemical reactions. As the molten material, for example, inorganic salts can be used.

20 The injectable substance can also be used to remove chemical substances such as sulfur and nitrogen compounds from a pressurized and hot gas stream. The injectable reacts with the chemical compounds, whereby the resulting new compound is either removed in solid form or the new compound is not harmful, allowing it to be passed on in the process.

· * The injectable substance can also act as a catalyst for the reaction of chemical compounds. For example, CaO, i.e. quicklime or BaO or alkali metal salts, can be injected to remove or reduce sulfur compounds. For nitrogen compounds 30, e.g., alumina acts as a catalyst in the decomposition of nitrogen oxides.

The materials of the classifiers can be, for example, ceramic materials resistant to the prevailing hot corrosion and erosion conditions, such as, for example, dense alumina.

The amount of larger particles to be injected in the pressurized gas depends on e.g. the quality of the gas to be cleaned, e.g.

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5 - 94597 of the number of purities, etc. Several nozzles can be used. They can also be placed on the circumference of the compressed gas pipe at a distance from each other.

In particular, it should be noted that the invention has been described above with reference to only one preferred embodiment thereof.

However, this is in no way intended to limit the invention to this example only, but many modifications are possible within the scope of the inventive idea defined by the following claims.

Claims (9)

A method for cleaning a gas turbine gas under pressure and high temperature, in which process is partially injected into the pressurized gas stream, the gas. . and the injected particles are passed into a tapered pipe portion - (5), whereupon the mixture is passed into a classifier (6,7), by means of which the gas pollution particles are separated, characterized in that particles are injected into the gas stream under pressure. the pressure of the carrier gas is greater than the pressure of the combustion gas to be cleaned, to allow collision and adhesion of the gas's contaminant particles and the injected particles, to purify a high pressure gas which is typically obtained at temperatures corresponding to the flow-bed processes, the particles -and agglomerated particles are separated from the gas before being passed to the gas turbines (1). 5 Process according to claim 1, characterized in that the particles introduced into the gas under pressure have a particle size which exceeds the particle size of the gas present in the gas. 10 Method according to claim 1, characterized in that the tapered pipe part (5) is a venturi tube. Method according to claim 1, characterized in that the gas is passed directly from the venturi tube (5) to the gas and particle separating devices (6,7) and that the separation of the gas and particles is carried out at substantially the same pressure and temperature as that under pressure. being the gas exhibits. • «i (0 Process according to claim 1, characterized in that the injected particles are composed of substances used for cleaning gases, such as e.g. burnt lime for removing sulfur compounds and e.g. alumina as catalytic in the decomposition of nitrogen compounds. 25 « Method according to claim 1, characterized in that the injected particles are composed of fluidizable solid particles, e.g. flue gas particles or melt droplets, e.g. inorganic salts. 30 Process according to claim 1, characterized in that the gas contaminants are of the order of about 10 μηι or less. Apparatus for use in a process according to any of the preceding claims for cleaning the gas to a gas turbine coming under pressure and high temperature prior to the gas turbines (1), characterized in that there are included in it (9) injection of particles for high pressure gas purification, a tapered pipe part (5) for mixing the gas and the injected particles, a classifier (6,7) in which the gas pollution particles are separated from the gas turbine coming under pressure. gas. Apparatus according to claim 8, characterized in that the classifier (6,7) consists of at least one separator unit, preferably a vortex cleaner. <> · S ·