SE502283C2 - Methods and supply means for regulating mixing conditions in a combustion or gasification plant - Google Patents

Abstract

In a combustion or gasification plant having a chamber (4) the mixing conditions or ratio are controlled via a fluid supplied by perforated tubes (13) to maintain a combustion or gasification process. To have an effect on the mixing of the fluid in the combustion gases the tubes (13) are displaced axially in mutual cooperation at longer or shorter time intervals in the chamber. Then the flue gas or gas parameters of the process can be optimized. Further, the tubes are rotatable around their axis and may for replacement purpose be completely withdrawable from the chamber. The tubes are cleaned in connection with their withdrawal. Object of protection are also a feeding means for use in a combustion or gasification plant of the mentioned type.

Description

502 283 2 Examples of ash- and / or slag-rich fuels are wood fuels, straw, waste, such as industrial, household, environmentally hazardous and hazardous waste, as well as coal, lignite, peat, mesa and black liquor. Crematorium and cement kilns also belong to this category of combustion / gasification systems.

Ash is a term for inorganic and non-combustible substance, which is originally present in the fuel.

Slag is a term for "additives" of inorganic and / or non-combustible substance, e.g. metals, ceramics, glass, stone, etc. "ash" is often included in the term "slag". Examples of non-ash and / or slag-rich fuels are oil, natural gas, LPG and certain biofuels.

The fuel price is another important parameter when optimizing flue gas or gas parameters. The content of sulfur and to some extent also the content of nitrogen in the fuel is in direct proportion to the emission level before a flue gas purification system. This of course has the consequence that the fuel price will be higher, when e.g. the nitrogen content of the fuel is lower. Of course, the economic outcome is also affected by the market price, which sometimes changes rapidly.

Trading in emission rights according to the so-called bubble models are systems that are expected to have a major impact in the future.

The above-mentioned parameters shed light on an expected future need for flexible combustion / gasification systems that can be quickly adjusted to allow the economically optimal operating point to be achieved at any given time.

In an optimization method of the type in question here, a fluid consisting of gas or liquid or possibly solid particles is supplied to the perforated pipes in the combustion or gasification chamber. Examples of gas are air, oxygen, oxygen-enriched air, flue gas, inert gas (C02, NZ, etc), fuel for reburning (LPG, natural gas, etc.), N0; 1-reducing substances (N fl y urea, etc.) and a 502 285 water vapor of optimal flows, pressure and temperature. Examples of liquids are water, NH 4, urea, etc.

Examples of solid particles are powders from biofuels including peat as well as coal and waste (plastic, etc). These can be used as reburning fuel.

Existing oxidizing agents, e.g. air, shall oxidize unburned gases, e.g. CO, while the reducing agents, e.g. NH¿ or e.g. LPG, should reduce e.g. NO to the optimal extent desired for individual occasions.

The pipes are applied in the combustion / gasification plant in a suitable place to achieve optimal conditions.

In e.g. a grate-fired boiler with over-combustion, whereby air under the fuel gives flue gas directed upwards, the pipes are placed over the grate, for example in connection with the transition to the first draft of the boiler. The opposite applies to a boiler with so-called underburning.

In e.g. a fluidized bed with varying pressure, the pipes can be placed in the combustion chamber, e.g. over the bed in a bubbling bed.

State of the art Today, combustion / gasification of fuels takes place in a number of different types of appliances and plants in the form of furnaces, fireplaces, etc. with burners, grills, fluidizing and / or bubbling beds, etc.

Characteristic of such furnaces and fireplaces is that the flue gas emissions of CO, Cgg (hydrocarbons), NOX, SOU IQO, dioxin, PAH etc. are often high due to poorly combustion-optimized plants. Some plants are also equipped with different types of flue gas cleaning systems, e.g. electric or textile filters, SCR, scrubbers etc. after the actual combustion / gasification apparatus, 502 283 4 which reduces the emission level in the subsequent chimney / gas duct.

As an example of known devices for minimizing emission levels, EP-0 286 077 A2 (Müllverbrennungsanlage Wuppertal) describes a method of incinerating waste in which the flue gases are drawn out of the combustion chamber and made to perform a vortex movement by adding secondary air. The secondary air is supplied via nozzles in such a way that the flue gases are braked in a uniform temperature zone in the combustion chamber and caused to remain in it for a period of about 8 seconds.

SE, C, 139,072 (Larsson) describes a fireplace, especially in boilers or for connection to the fireplace room of such boilers, at which inlets for primary air are located on the side of the fireplace, which inlets lead to a resp. several fixed tubes arranged along the fireplace, which in turn contain a rotatable tube, which allows adjustment of the outlet area of the air by rotating the tube about its axis and / or axial displacement of the tube.

DE, C, 107.755 (Lindemann) describes a device for supplying air over a fuel layer, which device has a pipe grid with mesh-like arranged pipes one above the other and with lateral openings, so that a plurality of intersecting air jets arises.

SE, C, l15.046 (Sinding) describes an apparatus for preheating and controllable supply of secondary air to fireplaces, which apparatus is provided with concentrically, tightly around each other arranged pipes, which extend into a preheating chamber for air supply to this and are mutually rotatable so that in the same occupied openings can be angled relative to each other for control of the passage area and thereby of the air supply.

Supply devices in the form of perforated pipes which insert into a combustion chamber are known e.g. by WO-A1-91 / 00134 (Fuel Tech p. 502 283 Europe), US-A-4,883,003 (Hoskinson) and SE-C-139,563 (Svenska Maskinverken).

Further examples of the state of the art can be found in SE, C, 45,212 (Reck) and SE, B, 458,147 (Lantmännen ODAL).

FI-B-87014 (Tampella) describes a device for feeding powdered lime with the aid of gas flow to a fireplace. To feed the lime, a nozzle mounted at the end of a tubular arm is used, to which displacement devices for displacing the nozzle are connected to a temperature-suitable place of the fireplace in the flue gas stream. The preamble of the present claim 1 relates to a method of this kind which can be considered to be the closest prior art.

None of these known methods and plants allows a precise optimization of the combustion process in such a way that a reliable adaptation to its variations in the combustion or gasification chamber is achieved.

Neither of the known systems allows an influence on the mixing ratio between the combustion gases and / or between them and the different fluid or fluids supplied to the combustion chamber.

Object of the invention In accordance with this, an object of the present invention is to minimize existing disturbances in known combustion and gasification methods as well as associated plants with the achievement of increased efficiency and lower emission level of combustion resp. the gasification process.

Another purpose is to increase the method's resp. the flexibility of the plant to enable, where desired, a quick and easy conversion from one desired emission level (eg high CO-, low 502 283 is NO content) to another (eg low CO-, high NO content) depending on the economic outcome.

A further purpose is to provide a method resp. a supply device that can be quickly adapted to process changes that take place in the combustion or gasification chamber.

A further purpose is to provide a method resp. a supply device which enables a continuous or substantially continuous combustion process, ie without this having to be interrupted for sooting resp. cleaning of in combustion resp. pipes introduced into the gasification chamber, e.g. for the supply of secondary air.

Brief description of the invention These and other objects are fulfilled by a method according to the present invention which is of the type indicated above and which is essentially characterized by measures specified in the characterizing part of claim 1.

The stated displacement of the pipes means that the mixing of the supplied fluid with the combustion gases is made more efficient, which enables a more efficient combustion and an optimization of current flue gas or gas parameters. By means of the invention it is thus possible to choose the best possible mixing ratio in each combustion situation.

The same or different fluids, e.g. of the kind indicated above, can be supplied via the pipes cooperating with each other in the manner indicated.

In practice, it is preferred that the pipes be displaced by means of outside the chamber, preferably holding and driving means engaging at their ends, so that the pipes are completely extendable out of the chamber.

This makes it possible to combine the extraction movement with a cleaning operation, preferably so that mechanical brushes or other corresponding means engage against the outside of the pipes so that they are cleaned of soot and other adhesive particles in connection with the extraction movement.

According to one embodiment, the tubes are pulled to an inactive position outside the chamber on impulse from one or more different sensors which activate the pull-out mechanism at e.g. power outage or breakdown of the refrigerant supply to the plant.

In order to improve the mixing, it is also preferred that the tubes for changing the velocity, flow pattern and direction of the delivered fluid are also rotated about their respective longitudinal axes.

In this case, it is preferred that the pipes are displaced and / or rotated on impulse from sensors arranged inside or outside the chamber which sense the combustion condition.

Different types of sensors can be used for the purpose, e.g. sensors for temperature, pressure, flow, flue gas components present, etc. Optical sensors can also be used for this purpose.

Signals generated by the sensors can also be used to regulate the supply of fluid resp. solid particles to the respective pipes, which supply may take place intermittently or intermittently. The specified rotation of the perforated pipes can ensure that the supply, if desired, takes place at predetermined, varying angles in the combustion chamber.

The tubes are furthermore suitably arranged replaceable on the holding and drive means located outside the chamber. This enables further simple adaptation to different operating conditions for the plant, which can thus take place by a simple replacement of one or more of the supply pipes. It will be appreciated that the arrangement 502 285 s additionally facilitates and inexpenses repair and maintenance of the plant.

In general, the method according to the invention can be applied to both existing and new combustion / gasification plants.

New pans resp. Furnaces can be manufactured with a smaller fireplace volume due to the more efficient mixing of the gases, which reduces costs. The best possible operating case with optimal emission level at each individual occasion can be more easily achieved than with hitherto known systems.

In addition, a cooling fluid can be supplied to reduce the jacket temperature of the pipes, so that slag and other dust coating on it becomes of such a nature that the cleaning of the pipes is facilitated or the number of cleaning operations is minimized.

Such a cooling fluid may optionally be supplied separately, possibly abruptly and preferably in connection with the pipes being pulled out. It is preferably supplied in a ring gap around the respective pipe. Cooling makes slag and other dust deposits on the pipes less glassy or "sticky", thus facilitating and speeding up the cleaning operation.

The invention also relates to a supply device for regulating mixing conditions in an incineration or gasification plant by means of supplied fluid for optimizing flue gas or gas parameters, which essential characteristics of the supply device are stated in claim 8.

Advantageous embodiments of the supply device are specified in the following claims.

Additional characteristics for resp. advantages of a way resp. a supply device according to the invention will appear from the following description of some preferred embodiments thereof. The description is made in connection with the attached drawing. 9 502 283 Description of the drawing figures Fig. 1 is a partially cut-away perspective view of a combustion plant for solid fuels which plant has supply devices according to the invention.

Fig. 2 is a side view showing a supply device according to the invention in the form of a perforated pipe together with its means located outside the combustion chamber for its displacement, rotation, control and cleaning. The figure shows the supply device in the inserted position in the combustion chamber.

Fig. 3 is a side view corresponding to Fig. 2 with the supply device in a position completely extended from the combustion chamber.

Fig. 4 is a sectional view taken along line 4-4 of Fig. 3.

Fig. 5 is a horizontal section through the combustion chamber and shows three pieces on one level in this cooperating supply device for increased action of the fluid mixing in the combustion gases.

Fig. 6 is a vertical section through a schematically indicated alternative embodiment in which a number of different fluid supply means are accommodated in an "revolver socket" located outside the combustion chamber for selectable, alternative insertion into the combustion chamber. Description of preferred embodiments In Fig. 1, the numeral 1 denotes an incineration plant consisting of a furnace 2 for burning solid fuels with a grate 3 and an overhead combustion chamber 4.

The fuel can be supplied intermittently or continuously, and combustion air is blown in the form of primary air from below and up through the grate 3.

Secondary air is supplied via a number of supply devices according to the present invention which are included in the combustion chamber 4 502 283 10 through special ports in the wall 5 of the boiler and which will be described in more detail below. Via these supply devices, secondary air is supplied in order to completely burn formed reaction products in the form of gas and solid particles.

Particles in the flue gas above the grate 3 consist of ash, slag and / or unburned fuel. These can be merged into larger particles, so-called agglomerate, or reduced to smaller, more or less pure ash particles. Slag-richer fuels often give a higher proportion of dust and slag in the flue gas.

Some of the particles deposit on the inside of the combustion chamber, which is lined with water tubes 6 with an external insulation. Dust particles are also deposited on the supply pipes 13, whereby the holes 13a for the supply of the secondary air can be completely or partially closed, which thereby affects the secondary air supply, alternatively baking takes place directly on the mantle surface of the pipe.

This means that the combustion becomes incomplete and not optimal with further problems of the stated type as a result.

Poor mixing conditions in the gas chamber of this kind give the incineration plant a poorer combustion efficiency.

This becomes particularly clear with N0; reducing measures, as the proportion of unburned gases / particles is higher than before the measure.

Throttled air supply and / or flue gas recirculation creates reducing conditions which lead to lower Nqphalter and higher levels of unburned gases and particles. The requirement for efficient mixing of secondary air then becomes even more important, which in turn leads to requirements for frequent cleaning or sooting of the secondary air pipes.

In the plant shown in Fig. 1, the supply pipes for fluid, e.g. secondary air, arranged to form a curtain system comprising a number of parallel pipes 13 at one or more levels in the combustion chamber 4. The pipes 13 are provided with perforations 13a along the entire circumferential surface of the pipes. The holes can have an equal pitch and a row of holes can be located on each side of the respective pipe.

The flow area of the holes 13a determines the flow of the fluid at a given pressure. As the velocity profile over the current cross-section in a gasification or combustion plant, where the device is to be installed, often varies, this must be compensated for by the supply of fluids.

A fluid, e.g. secondary air of high pressure, is supplied via a fan 10 connected to a collection box 11, from which flexible hoses 12 emanate which are connected by means of quick couplings to the end flanges 13b of the pipes 13. The opposite ends of the pipes may be plugged or provided with outflow holes (not shown).

Depending on the actual combustion process, the pipes 13 are inserted in and pulled out in the axial direction from the chamber 4 at longer or shorter time intervals. In this way, the emission level of the combustion process can be kept optimal.

Figs. 2 and 3 illustrate the used mechanisms for the displacement of the tubes 13 into resp. out of the combustion chamber 4 and for their rotation, control and cleaning. The tubes 13 are accommodated in a housing 14 which carries some of the indicated mechanisms. For displacement of each tube, an electric motor 16 is used, the output shaft of which drives a disc 17, over which an endless belt or chain 20 is passed which is also passed over rollers 18, 19. With the belt 20 is connected a holder in the form of a carriage 25. which engages against the end of the tube 13 during the formation of a bed 25b, so that the tube is simultaneously rotatable about its longitudinal axis. The holder 25 is slidably controlled via a guide 26.

Fig. 2 shows the tube 13 in the inserted position in the combustion chamber, while Fig. 3 illustrates the tube when it is completely pulled out of the chamber. The holder 25 is then arranged so that easy replacement of the tube 13 can take place in the extended position.

An electric motor 27 drives a belt 28 which is passed over a number of rollers 29, which engage against the periphery of the tube 13 to rotate it.

As can be seen from Fig. 4, the holder 25 is formed with fork-shaped legs 25a which support the bed 25b, in which the tube 13 rests. The holder or carriage 25 is slidably guided on the guide 26.

At its front end, the housing 14 is connected to a housing 30 which receives the opposite guide rollers 15 for the pipe and also to an arrangement of steel brushes 21, between which the pipes pass during the extraction and the subsequent insertion movement. These brushes 21 provide an efficient cleaning of the pipes, so that they are free from dust and slag coatings.

It will be appreciated that the arrangement shown substantially simplifies the cleaning of the pipes and that the pipes can be pulled out one by one or a few at a time, whereby the combustion process can continue, since e.g. secondary air is supplied via pipes remaining in the combustion chamber.

Alternatively or additionally, automatic shaking (percussion or the like, not shown) or sound sooting (infrared or ultrasonic) can be connected for continuous or intermittent slag removal.

Fig. 5 illustrates how the flow pattern of fluid supplied via adjacent pipes 13 can be changed, partly by displacing one or more pipes to different positions in the combustion chamber 4 and partly by turning one or more of the pipes. Furthermore, such an effect can be achieved by changing the pressure, velocity and / or flow of the supplied fluid. As can be seen from Fig. 5, different mixing ratios can be achieved in that the fluid flow from adjacent pipes can reinforce each other, more or less quench each other resp. offer an effect in between.

Pig. 6 illustrates a "turret arrangement" in which the housing 14 is replaced by a housing 14 'which is rotatable on a shaft 40 and which receives a number of fluid supply tubes with different distances and positions for perforations 13a arranged thereon.

To respond to different combustion conditions in the chamber 4, the housing 14 'is rotated so that the fluid supply pipe 13 which is most suitable in the current situation is inserted into the combustion chamber 4. Bellows-shaped hoses 12' for fluid supply to the respective pipes are connected to the ends of the pipes 13.

In a plant used in practice, the pipes 13 can have a length s of between 1 to 2 and 5 m and a diameter of 120-200 mm. The diameter of the perforations 13a can vary from 1 to 2 mm up to 2 to 4 cm and the distance between the perforations can be between 10 and 40 cm.

The regulation of fluid to the respective pipe 13 can furthermore take place via signals from sensors for different gas parameters, gas contents, temperatures, pressure, flow, etc. (not shown). These sensors can also be used to, e.g. via a computer, determine the times when the cleaning or sooting operation is to be initiated. As mentioned above, the combustion process does not have to be interrupted. In Fig. 1, the numeral 42 denotes a sensor of this kind. 43, 44 indicate the presence of an optical sensor where 44 marks a lens. In the event of, for example, a power failure or breakdown of the coolant supply to the system, there is one or more sensors that sense this and provide an impulse for pulling out the pipes to an inactive position outside the chamber. This is a very important safety measure which is within the scope of the basic idea of the invention. With a device according to the invention in a combustion chamber an improved combustion result is achieved with lower levels of NOX, CO, D50, hydrocarbons and unburned particles as well as dioxin.

A device with supply devices according to the invention is simple to assemble and is thereby particularly suitable for converting existing, operating furnaces, gasification and combustion plants on the market.

The pipes do not have to be horizontally oriented in the combustion chamber. One or more of these can thus be inclined or run vertically.

Claims (10)

502 285 15 Claims 1. l. Method of controlling mixing conditions in a combustion or gasification plant by means of fluid supplied via supply for optimizing flue gas or gas parameters, with a combustion or gasification chamber (4) accommodating an axially displaceable tube through which the fluid is supplied to the chamber to maintain a combustion or gasification process therein, characterized in that two or more perforated tubes (13) with longer or shorter time intervals are displaced axially in the chamber (4) for predetermined controlled action of the fluid mixing in the combustion gases through mutual interaction between the pipes. 2. A method according to claim 1, characterized in that the pipes are displaced by means outside the chamber (4), preferably holding and driving means (25:16, 20) engaging at their ends, so that the pipes are completely extendable out of the chamber. 3. A method according to claim 2, characterized in that the tubes (13) are pulled out to an inactive position outside the chamber on impulse from one or more sensors which activate the pull-out mechanism at e.g. power outage or breakdown of the refrigerant supply to the plant. 4. A method according to any one of claims 1-3, characterized in that the tubes for changing the pressure, flow pattern and / or direction of the delivered fluid are also rotated about their respective longitudinal axes. 5. A method according to any one of claims 1-4, characterized in that the pipes (13) are displaced and / or rotated on impulse from sensors (42, 43, 44) arranged in or outside the chamber which sense the combustion state in the chamber. 502 285 lb 6. A method according to claim 2, characterized in that the tubes are arranged interchangeably on the holding and drive means. 7. A method according to any one of claims 2-6, characterized in that the pipes are cleaned in connection with the extraction operation. A supply device for regulating mixing conditions in a combustion or gasification plant by means of supplied fluid for optimizing flue gas or gas parameters, which plant comprises a combustion or gasification chamber (4) which receives an axially displaceable tube (13) through which the fluid is supplied to the chamber for to maintain a combustion or gasification process therein, characterized by two or more axially displaceable perforated pipes (13) accommodated in the chamber (4), holding and driving means (16) engaging towards the ends of the pipes outside the chamber (4) 20; 26; 15) for predetermined controlled displacement of the pipes for influencing the mixing of the fluid in the combustion gases by mutual interaction between the pipes, and means (eg 42-44) for controlling the displacement movements depending on the time and / or in chamber sensed combustion condition. Supply device according to claim 8, characterized by means (27, 28, 29; 21, 38, 39) for turning and / or cleaning the pipes. Delivery device according to claim 8 or 9, characterized in that the holding and driving means are arranged to allow complete extraction of the pipes (13) from the chamber and replacement of the pipes.