FR2556824A1 - PROCESS FOR THE COMBUSTION OF PULVERIZED COAL AND IMPROVED PRE-FIREPLACE FOR PULVERIZED COAL BOILER - Google Patents

Abstract

AROUND THE INTERNAL WALL 5 OF THE FRONT FIREPLACE 4 A COOLING COIL 6 WITH JOINING SPIRES SUCCEEDING THROUGH THE ENTIRE LENGTH OF THE LATTER, TO MAINTAIN THE TEMPERATURE BETWEEN 600 AND 900C, THE AIR INLET TERTIARY 11 IS COMPOSED OF MANY HOLES DISTRIBUTED CIRCULARLY AROUND THE OPENER 8 AND AN INDEPENDENT BLOWING CIRCUIT 15 ENDS WITH LONGITUDINAL TUBES 16, 17 ARRANGED AT THE BOTTOM AND AT THE ENTRY OF THE FRONT FIREPLACE 4 AND THE FIREPLACE TUBE 1, WHICH MAKES A GOOD REGULAR COMBUSTION OF THE PULVERIZED COAL.

Description

The subject of the invention is a process ensuring good combustion of the

  pulverized coal; it also relates to an improved pre-hearth for the combustion of pulverized coal in boilers with hearth tubes and smoke tubes. Boiler tube and smoke tube boilers are designed for the combustion of liquid or gaseous fuels. In this type of boiler, the walls of the furnace tube and the smoke tubes are strongly cooled by the water in the boiler. The temperature of these walls does not allow ignition and proper combustion of solid fuel

  such as pulverized coal. As a result, the substitute

  outright from a solid fuel to fuels

  liquid or gaseous is not possible on these boilers.

  It has been found that it becomes possible to feed

  ter in pulverized coal the boilers with tube hearth and with smoke tube, provided that the combustion is carried out in a pre-hearth which precedes the hearth. Furthermore, according to the invention, this combustion must be carried out so

  to maintain between about 600 C and about 900 C the temperature

  ture of the inner wall of the pre-hearth.

  The boiler can only allow the implementation of this process when it has specific characteristics which are also the subject of the invention. This is aimed more particularly at boilers with low-capacity fire tubes and flue tubes, that is to say those whose nominal power is less than 20 tonnes per

steam hour.

  From a pre-hearth boiler preceding a hearth tube for the combustion of pulverized coal, having a longitudinal side wall surrounded by a cooling circuit, a front wall containing a burner in the center of which is mounted a burner of pulverized coal , a primary air inlet with coal, a secondary air inlet arranged to tightly surround the braleur, a tertiary air inlet at the periphery of the opening, according to the invention the front cooling circuit -foyer is constituted by a coil wound in successive turns and which is connected, on the one hand to a supply pipe, on the other hand to a cooling pipe; the boiler water supply or water drain / turns are

  succeed each other substantially over the total

  length of pre-hearth length as much as possible

contiguously.

  Furthermore, according to an additional characteristic

  shut up, half a turn, and preferably the upper half-turn

  of each coil of the coil is in a transverse plane perpendicular to the axis of the fore-hearth however

  than the complementary half-turn, and preferably the half

  lower coil is in an inclined transverse plane

  - relative to the axis of the pre-hearth.

  It has also been found that it is preferable for the tertiary air to emerge into the fore-hearth through numerous holes spaced circumferentially at the periphery of

  the opening, these holes being preferably spaced regularly-

is lying.

  Furthermore, according to another additional characteristic,

  mentaire, it is advisable to provide in addition a blowing circuit which ends with several blowing tubes

  arranged to blow longitudinally from the front

  hearth and the hearth tube, on the one hand at the front of the fore hearth around the lower part of the outlet, on the other hand at the entrance of the hearth tube, also at its lower part, in the

  direction of flow of combustion gases.

  Preferably, there are three blowing tubes at each of the two locations, with a central tube being on the lowest generator and two tubes arranged on either side of the central tube. It is preferable that the three tubes are on an arc of

  circle from 70 to 110, preferably about 90.

  In one embodiment of the invention, the blowing tubes have a flattened orifice in the direction

  radial and widened in the circumferential direction of the front

  foyer. The blowing circuit is independent of the other combustion air circuits; it is preferably supplied with air at a pressure which can range from 6 bars

  at 15 bars, preferably 10 bars. It is used by inter-

  mittence. In fact, under certain circumstances,

  dispense with the air supply circuit.

  We will now give, without limiting intention

  tive and without excluding any variant a description of a

  preferred embodiment of the invention. We refer

  ra to the accompanying drawings in which: - Figure 1 is a general sectional view of an improved pre-hearth boiler according to the invention; Figure 2 is an enlarged detail view, in section along II-II of Figure 3 showing the lower half of the flue and an air blowing tube, - Figure 3 is a sectional view along III-III of Figure 2, - Figure 4 is a detail view along arrow F of Figure 2 showing the orifice of two air blowing tubes, - Figure 5 is an elevational view in section through a plane vertical showing the coil and a

  part of the hearth tube with an air blowing tube.

  The boiler for pulverized coal represented in FIG. 1 comprises a hearth tube 1 surrounded by a jacket of water to be heated 2 traversed by smoke tubes 3; the hearth tube 1 is preceded by a pre-hearth 4 with which it is connected coaxially. This pre-hearth 4 has an internal side wall 5, generally cylindrical, surrounded by a coil 6 for circulating water embedded in a refractory and insulating material; the fore-hearth 4 still has

  a front wall 7 comprising an opening 8 made of refractory concrete

  shutter and insulator in the center of which opens the end part of a burner 9 of pulverized coal. The latter can be

  for example of the type described in document FR-A-2,054,741.

  As is known, there exists on the fore-hearth 4, a

  primary air intake through burner 9 with coal -

  sprayed, a secondary air inlet 10 surrounding narrow

  the burner 9 in the center of the outlet 8, an inlet

  tertiary air 11 arranged to surround the opening 8.

  We will not further describe this boiler which is known as a whole; we will now explain in detail what improvements are made by the invention. The tertiary air inlet 11 is thus composed

  as can be seen in Figure 3, from a multitude of ori-

  separate files 12 drilled around the opening 8 in the t8le 13 which limits, on the side of the pre-hearth 4, an annular box 14 of tertiary air inlet. The orifices 12 can have a diameter of 15 to 25 mm, preferably

  20 mm approximately, Their number depends on the air flow

  third. For example, on a boiler capable of burning 600 kg / h of coal, there were 63 orifices 12 with a diameter of 20 mm each, regularly spaced around a circumference

1014 mm in diameter.

  According to the invention there is also on the boiler described here a blowing circuit 15 which ends in blowing tubes arranged to blow longitudinally, parallel to the axis of the fore-hearth 4 and of the hearth-pipe 1; these tubes are placed at the front of the fore-hearth 4, around the lower part of the outlet 8 and at the front of the hearth-pipe 1. In the present example, there are three tubes 16 - better visible in Figures 2, 3, 4 - mounted under the opening 8, and three tubes 17 of which only one is better visible in Figure 5. At both locations there is a central tube located in the vertical plane

  which passes through the axis of the boiler in the operating position

  sation and two side tubes. The three tubes are spaced on an arc of 70 to 110, exactly 90 in

this example.

  Each tube 16, 17 preferably ends with an orifice 18 flattened in the radial direction and widened in the circumferential direction of the boiler, as shown

Figure 4.

  The blowing circuit 15 is completely independent

  during other primary, secondary and tertiary air circuits. It is supplied with pressurized air at a value ranging from 6 bars to 15 bars, preferably 10 bars in

this example.

  According to the invention, as can be seen on

  Figure 5, the coil 6 is composed of successive turns

  sives 19, contiguous, placed side by side in the longitudinal direction

  tudinal of the fore-hearth 4, as far as possible over the entire length of the latter. In Figure 5, closer to reality, there is in the coil 6 a central gap to facilitate the connection, using two flanges 20, of two assembled parts which together make up the fore-hearth 4; this arrangement is not shown in FIG. 1. This shows that it is possible, on the contrary, to produce the pre-hearth 4 in a single piece and to mount therein a coil with turns 19 adjoining the whole of the length. One end of the turns 19 is connected to a

  supply manifold and the opposite end to a col-

  drainage reader part of a water circuit

supplying the boiler.

  To achieve good combustion, we will act on the action of the coil 6 in order to maintain between 600 and 900 C the temperature of the internal wall 5 of the pre-hearth 4, using appropriate control means known in oneself. Figure 5 also shows that the turns 19 have one half, exactly the upper half in this

  example, which is placed in a transverse plane perpendicular to

  laire to the axis of the pre-hearth 4 while the other half, the lower half consequently, is in a transverse plane inclined with respect to the axis of the pre-hearth 4.

  During the operation of the dhudière, the snake

  tin 6 allows effective control of the temperature inside the pre-hearth 4, so that the ashes

  remain in the pulverulent state, without a tendency to clump together

  merge in large masses, which would happen if they

were undergoing a merger start.

  The supply air circuit 15 is put into service cyclically, for example at time intervals ranging from 30 to 60 min, for a rather short period of 1 to 10 min. The air blown in the longitudinal direction in the lower parts of the fore-hearth 4 and of the hearth-tube 1 expels in the stream of combustion gases the heavier ashes which could have deposited and accumulate in these lower parts . However, as already mentioned, the

  temperature control in the fore-hearth via

  coil mean is paramount and can make useless

  the use of the supply air circuit.

  Keeping the temperature between 600 'and 900 C

  ture of the inner wall of the pre-hearth is done in advance

  tagging, as indicated in phantom in Figure 5, by means of a pipe 21 bypass between the inlet and the outlet of the coil 6 and on which is mounted an adjustment valve 22. Thanks to that this one

  regulates the circulation of water in the coil in function

  tion of the measured temperature, for example, using temperature detectors 23 introduced between the turns of the coil up to the proximity of the inner wall of the fore-hearth.

Claims (11)

  1. Method for the combustion of pulverized coal in a boiler comprising a hearth tube preceded by a preheat characterized in that the temperature of the wall is maintained between approximately 600 ° C. and approximately 900 ° C. interior of this fore-hearth.   2. Pulverized coal boiler with pre-hearth (4) preceding a tube hearth (1), this pre-hearth (4) having an internal side wall (5) surrounded by a cooling circuit and a front wall (7) containing a burner (8) in the center of which is mounted a coal burner (9)   sprayed, characterized in that the cooling circuit   The fore-hearth (4) is a coil (6) with turns (19) succeeding each other substantially over the entire length of this pre-hearth (4), connected at one end to a pipe. water supply   and at its other end to a pipe-   evacuation, allowing temperature control of the internal side wall (5).   3. Boiler according to claim 2 characterized in that each turn (19) has a half-turn arranged in   a transverse plane perpendicular to the axis of the front   -foyer (4) while the complementary half-turn is arranged in a transverse plane inclined with respect to the axis of the pre-hearth (4).   4. Boiler according to any one of the claims.   tions 2, 3 characterized in that the turns (19) are contiguous. 5. Boiler according to claim 2 having around the opening (8) a tertiary air inlet, characterized in that this tertiary air inlet consists of a multitude of separate holes spaced on a circle surrounding the workhorse (8).   6. Boiler according to claim 5 characterized in that the holes of the tertiary air inlet have a diameter of 15 to 25 mm, preferably 20 m.n 7. Boiler according to claim 2 characterized   in that it comprises an independent blowing circuit (15)   during ending with several blowing tubes (16, 17) arranged to blow in the longitudinal direction of the pre-hearth (4) and of the hearth-tube (1), in the direction of the combustion gases, on the one hand at the front of the pre-hearth (4) around the lower part of the outlet (8), on the other   part at the entrance of the hearth tube (1).   8. Boiler according to claim 7 characterized in that, at the two locations, the tubes are on   an arc from 70 to 110, preferably 90.   9. Boiler according to claim 7, characterized in that the blowing circuit (15) is connected to a source of air under a pressure ranging from 6 bars to 15 bars, preferably 10 bars.   10. Process ensuring good combustion with   boiler according to any one of claims 2 to 9   characterized in that the circulation of the cooling water in the coil (6) is regulated by a bypass pipe (21) so as to maintain the internal wall (5) of the pre-hearth (4) at a temperature   between 600 and 900 C in accordance with the claim cation 1.   11. Process ensuring good combustion with   boiler according to any one of claims 7 to 9,   characterized in that pressurized air is sent into the blowing circuit (15) for a period of 1 to 10   minutes at 30-60 minute intervals.