FI62896B - DIRECTIVE EXTRACTION OF POWDER COLL - Google Patents

Description

Ι-Γ ^ ίΤΊ Γ1 NOTICE OF PUBLICATION Q Q ^ ro UTLAGGN I NGSSKRIPT 62896

Ma C Patent nycnr.c Uv 10 03 1903 • AjS (4S) Patent neddclat (51) K ».ik.Va.3 P 23 D 1/02 FINLAND — FINLAND (21) T80525 (22) Hakwntapllv · —Ameknlngi ^ 17.02 .78 (23) AJkwp «ivt — GlMghMxUf 17.02.78 (11) Tulta * fuHdMkal - UM * aff« KH | 19.08.78 fatmtti · J »rekl * terlhelllt * l · (4Λ NMittvilulpanen | a kmiL | ullulMn date -, n. A_ rltunt och mfifteratyraltan '' Anrtk ·» utltfd och wl. »Jcrtfu» i puMtavnd 30.11.o2 ( ) (33) (31) Pyfduey utuoMwu »-BfH prtorttvt 18.02.77 29.12.77 USA (US) 769995, 8657 ^ 7 (71) Combustion Engineering, Inc., 1000 Prospect Hill Road, Windsor,

Connecticut 06095, USA (72) Donald Arthur Smith, Haddam, Connecticut, Martin Edvard Smirlock,

East Granby, Connecticut, USA (US) (7M Leitzinger Oy (5M Direct ignition of powdered carbon - Direkt tändning av pulveriserat koi

Generally, pulverized coal is ignited to provide energy to provide heating or operation during low load of a coal combustion furnace by a technique that does not require the combustion of substantial amounts of liquid or gaseous fuel. According to the invention, in the direct ignition of powdered carbon, a dense phase carbon / air stream is fed to the ignition zone where it receives ignition energy, after which the mixture thus ignited is kept in the recirculation zone until its flame maintains itself.

The present invention relates to burners designed to burn pulverized coal, and more particularly to burners used in coal-fired boilers or generators. More specifically, the invention relates to a method of igniting pulverized coal without obtaining any significant amount of energy from the combustion of liquid or gaseous fuel. Given the costs and natural resources, it is increasingly advantageous to use coal instead of natural gas or oil in electricity generation plants. The carbon-fired "'.'il' 2 62896 steam generators currently in use use high quality liquid and gaseous fuels to provide both ignition and flame stabilization energy at low loads. Substantial amounts of such first-class auxiliary fuels are needed.

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The present invention avoids the disadvantages of the prior art ... by allowing direct ignition of the powdered carbon and air stream fed to the burner. According to the invention, this is achieved when the conditions of the features of the appended claim are fulfilled.

The ignited mixture is kept in the recirculation zone, whereby the hot combustion products turn back towards the injection point of the carbon air, so that the released heat energy is concentrated and a self-sustaining flame is formed. The circulation is caused by a secondary air flow. To ensure ignition and to adjust the weight ratio of air to carbon in front of the combustion chamber, the rate of the carbon-air mixture is varied according to the content of combustible substances and the degree of grinding of the carbon. The injection speed of the carbon / air mixture is suitably 18 to 23 m / s. In certain cases, the start of the secondary air flow is delayed, which causes the return of hot combustion products to the carbon / air injection point, which is especially true in high-energy arc ignition. In addition, it is preferred that only about 15% of the stoichiometric combustion air is added to the secondary air.

The invention will be explained in more detail below with reference to the accompanying drawings, in which:

Figure 1 shows a section of a pulverized carbon arc ignition burner that can be used to practice the invention.

Figure 2 is a sectional view of an apparatus for feeding powdered carbon which may be used in conjunction with the burner of Figure 1.

Figure 3 is a front view of the feeder of Figure 2.

3 62896

The device shown in the figures is an exemplary device for the direct ignition of a stream of pulverized coal and air according to the invention without the need to use a significant amount of oil or natural gas. According to the invention, a dense phase carbon / air mixture is used in which the weight ratio between the conveying air and the carbon, measured in the inlet line in front of the combustion zone, is 1.0 or less. The ignition energy source is located so that it is either located in the air / carbon stream in the combustion zone or can be moved into it. The energy released by the ignition energy source into the air / carbon mixture ignites the carbon particles. Since the ignition energy source has an electric high-energy arc, and the ignition device then operates in pulses, a series of flame pockets are created.

According to the invention, a further air flow to the combustion zone can be provided by an additional air register of the burner. The additional air register of the burner is constructed in a known manner to form a region of circulating air and combustion products (hot gases), whereby the pockets of combustible coal are recycled back to the original carbon injection point, and the energy in the recirculation area increases until its flame is self-sustaining.

The technique of the present invention has been successfully applied when using a high energy electric arc as a source of ignition energy. However, the ignition energy source can also be a resistance heat device or several such devices or possibly a non-hydrocarbon heated pilot flame with the lowest possible energy consumption. In a preferred embodiment, the igniter is removed from the flame area after the current state of the flame has been determined. When the high-energy arc brings the ignition energy, the additional air flow is delayed until the current state of the flame is confirmed.

In the burner shown in Figure 1, a carbon line 16 is used to transport carbon by compressed air to the ignition zone in the burner. In this case, the left end of the carbon line 16 of the device shown in Fig. 1 communicates with the carbon supply device shown in Figs. The igniter is located immediately behind the delivery end of the carbon line 16. In the embodiment shown, the ignition device 23 protrudes through the side of the burner and comprises a high energy arc ignition device, 4 62896, which is the type of device currently used to ignite oil. At this stage, it should be noted that it is possible to use any ignition source that supplies sufficient energy to heat the reactants sufficiently to ignite them. For this reason, a resistance heating device or a small pilot flame heated by natural gas can be used instead of a high-energy arc igniter. However, this is preferred due to its reliability and adjustability. The ignition device 23 shown in Figure 1 is typically removably mounted so that it can be removed from the combustion zone and moved to a protective area after the carbon has ignited.

The burner also includes an auxiliary air supply line 20 which is coaxial with the carbon line 16. The conduit 20 communicates with an air chamber 14, which in the model case is cylindrical and has a somewhat larger diameter than the conduit 20. The air chamber 14 has a plurality of vanes 12. These vanes are arranged to rotate the air coming from the chamber 14 into the conduit 20. The air inlet duct 10 leads to the air chamber 14 from a compressed air storage (not shown). The air line 20 terminates in a structure 24 lined with refractory material, which forms a disintegrating nozzle. In the apparatus for carrying out the invention, the carbon conductor 16 had an inner diameter of 2.5 cm, the inner diameter of the conductor 20 was 15 cm and the diameter of the structure 24 was 33 cm at the open end and the angle of disintegration was 35 °.

Figures 2 and 3 show an apparatus for supplying pulverized coal to supply a carbon-air mixture to a coal line or fuel line 16. The feeder includes a pulverized coal tank 40 which can supply coal in any known manner. The tank 40 is suitably sized to store a sufficient amount of powdered carbon to feed the burner during the heating phase of the furnace when the burner is in use. The container 40 communicates with a gravimetrically operated feeder 43. This includes a device 42 with a variable feed rate, pressure sensitive conveyor 44 and suitable control circuits, not shown. The rotational speed of the feeder 42 is determined by the amount of carbon that is allowed to fall on the important conveyor 44 and its known weight controls the rotational speed. A gravimetrically operated feeder 43 introduces carbon into a constant speed rotary feeder 46.

The feed device 46 is formed by a cylindrical chamber 622 with vanes 47, which fit into the chamber almost airtight. The lower part of the chamber has an inlet 48 and an outlet 49. The wings 47 are arranged so that there is almost no free airway between the openings 48 or 49 and the feeder 43. Therefore, it is possible for the air flow entering the opening 48 to continue out through the opening 49 without deviating to the gravimetric feeder 43. The vanes 47 rotate the powdered carbon dropped by the feeder 43 onto the vanes 47 into the air duct between the openings 48 and 49. Compressed air is supplied to the supply device 46 by means of a suitable source 50 at a controlled speed, whereby a carbon-air mixture having a predetermined weight ratio of air to carbon is fed to the burner via a line 16. According to the invention, the weight ratio of air to carbon in the carbon-air mixture, measured in line 16, is 1.0 or less, suitably 0.5 or less.

In one embodiment using Class C bituminous coal, which was ground to 70% -200 mesh, the upper limit of the air-to-carbon weight ratio rose to 1.0. The optimal air-to-carbon weight ratio varies depending on the type of carbon.

When using the burner according to Fig. 1, the ignition device 23 is moved to the inserted position and the operation is started. An arc ignition device that generates sparks with an energy of about 25 joules and a duration of about 10 microseconds each and a repetition rate of 10 Hz has been used successfully. The compressor 50 starts as soon as the igniter starts working, whereby the gravimetrically operating feeder 43 also starts. Compressed air flowing through a rotating air-locked feeder 46 carries measured amounts of powdered carbon and passes it through line 16 and through a diffuser with a hollow cone. Although the burner of Figure 1 may operate without a diffuser 22, this is considered to be advantageous for supplying a smaller amount of circulating gas during the ignition step. The carbon-air mixture that enters in the vicinity of the igniter 23 is ignited by the energy supplied by the igniter, and the resulting flame propagates through the carbon.

This results in ignition and a relatively unstable flame fluttering at the burner outlet. At this point, the observer device 26 or the automatic flame detection device determines that the ignition has taken place and provides an additional air flow (ambient air or heated air) through the air inlet duct 10. The vanes 12 cause the air flow to rotate, followed by a helical or rotating air flow that travels along line 20 and structure 24. The latter is formed by a disintegrating nozzle which amplifies the circulating effect which naturally occurs as a result of the rotational flow of air. The rotating air stream closes the combustion zone, and as a result, the hot combustion products are drawn back into the new carbon injection zone. The noticeable effect of this cycle is that the flame becomes stable and the stability of the flame is such that the igniter 23 can be turned off and retracted. Thus, the retracted ignition device 23 remains in the protected area, so that it is not damaged by the strong heat of combustion.

It is believed that the direct ignition of the pulverized carbon of the present invention is successful because it allows suitable conditions for the flame to proceed in the flowing carbon stream after the igniter has ignited some of the carbon particles.

When the weight ratio of air to carbon is greater than about 1.0, it is difficult for the flame to proceed with unheated air, and direct ignition of powdered carbon by means of an arc igniter is therefore not effective. When the furnace is started, no preheated air is available at all, which can only be obtained by using a considerable amount of energy and / or running or gaseous fuel. Appropriate flame propagation conditions are combined with a circulation zone which helps to provide stability to the carbon as well. The circulation causes the hot products to return to the combustion zone, which in turn causes the flame to cause its own ignition energy. Whatever the reasons for the success, however, the invention provides a satisfactory direct ignition of flowing pulverized carbon.

The burner according to Figure 1 can be used as a heating burner for service boilers. When using such, the boiler must be given an elevated temperature for its conventional carbon burner to function properly. According to the present invention, the burners can be used to provide a high enough temperature for the furnace to provide stable combustion in conventional burners. The invention can also be applied to provide both ignition and stabilization at low load.

The described embodiment can be modified and altered in many ways within the scope of the invention.

Claims (1)

A method for igniting and maintaining combustion of pulverized coal in a combustion environment free of other fuels and not containing sufficient internal ignition energy to ensure ignition, wherein a fuel stream (16) consisting essentially of a mixture of pulverized coal and transport air is supplied to the combustion zone. 23) a mixture in the combustion zone to ignite the carbon in the mixture, ensuring the presence of a flame from the ignition of the coal in the combustion zone, and stabilizing the flame, characterized in that a) in said mixture the weight ratio between transport air and carbon is less than 0.5 in the form of a divergent flow to the combustion zone so as to provide a recirculating flow, whereby air and relatively fine carbon particles in the mainly upward flow are diverged with respect to the axis of the fuel flow; c) the velocity of the fuel flow when fed to the combustion zone is adjusted to 18-23 m / s as a function of the carbon particle size and the content of volatile constituents, d) the transfer of ignition energy to the mixture is effected by within the fuel flow, and e) the flame is stabilized by maintaining a vortex flow of unheated secondary air into the combustion zone and substantially coaxial with the fuel flow when the presence of the flame is detected.