US2731955A

US2731955A - Pulverized coal furnace

Info

Publication number: US2731955A
Authority: US
Publication date: 1956-01-24
Anticipated expiration: 1973-01-24

Description

2 Sheets-Sheet l Lkr/ANN ZAOEALEM E LENHART ET AL PULVERIZED COAL FURNACE Jan.

Filed Oct. 4,

kiwi? ifi Jim. 24, w56 E. L ENHART ET AL 3,731,955'

PULVERIZED COAL FURNACE Filed Oct. 4. 1951 2 Sheets-Sheet 2 /N VENTO/. EMIL L EA/HA Rr dbf-m /v/v ZAo/PALEK.

H TTUR/VEV.

2,231,955 PULVERIZED coAL FURNACE Emil Lenhart, Bonn, and Johann Zaoralek, Essen, Germany, assignors to Firma Steinkohlen-Elektrizitat Aktiengesellschaft, Essen, Germany Application October 4, 1951, Serial No. 249,654 Claims priority, application Germany October 5, 1950 2 Claims. (ci. 122-336).

It. is known that in conventional pulverized fuel fur naces about-80-90 percent of thel ash contents of the fuel are carried away by the combustion gases. These ashes cause disturbances in theoperation of they boiler served by such a furnace, depending more or less on their chemical composition, and are generally eliminated by electrical or mechanical ash removers.

A large reduction of the amounts of solids carried away by the ue gas was achieved by fusing'the ash into slag in slag furnaces or slag funnel furnaces.

The highest degree of such ash envelopment in slag was obtained, when a whirl-current burner, also called cyclone burner was employed, in which a mixture of primary combustion air and fuel is set in rotation in the center of the combustion chamber, with the secondary air introduced tangentially through one single inlet. As a result, a flue gas was produced, which contained only 15-20 percent of the original ash contents.

The desired degree of ash elimination is thus reached and the removal of the remnants may be left to simple mechanical purifiers.

The cyclone burner, however, allows only the use of fuels that contain up to a certain percentage of volatile matter and a certain percentage of ash. It also requires a certain granular size of fuel.

However, it is generally desired by the gas and power generating industry to utilize low-grade fuels of a high moisture and ash content which fuels are found as byproducts of coal washing plants or in the form of winnow or coke dusts. For fuels of this sort, the cyclone tiring is still unsuited.

There is also known a furnace for pulverized fuels, named after its inventor Burg furnace. The chamber f the Burg tiring system also forms a whirl-current furnace, however, with inlets for secondary air distributed equally over the entire circumference through which the air enters in the direction of the rotation of the burning mixture. This part of the combustion chamber is followed by another without air inlets, where the ash is separated.

This Burg firing system is well adapted to burn the above mentioned fuels, after appropriate conditioning. It does lack, however, the ash enveloping properties of the cyclone firing.

The present invention is concerned with pulverized fuel furnaces or gas generators capable of burning the above mentioned fuels and to eifectively envelop the ash by liquid slag. lts particular features are: a combustion chamber, in which a mixture of fuel and air is in rapid rotation, with secondary air inlets distributed evenly over the circumference of the chamber, through which the air is tangentially blown in the direction of the rotation of the burning fuel. This chamber is followed by another, water cooled chamber, without air inlets, where the ash is separated by centrifugal force.

lt is of advantage to provide between the combustion chamber zones, with, or without secondary air inlets, baffles, which provide guiding surfaces, which increase the Centrifugal and consequently the ash enveloping effect.

Patented Jan. 24, 1956 It appears further to be of advantage to have one zone of the combustion chamber equipped with tangentially entering secondary air inlets, extending over the entire length and circumference, and to leave onezone `without such inlets. The cooling of the combustion chamber arch with the air inlets, mayv be eected'by the airl required for the combustion, and the cooling of the arch that has no' such: air'iniets may be obtainedithrough cooling coils, inserted4 in the boiler water circulation. It is also of advantage to-arrange baflies in form of cooling coils between the zones of the combustion chamber and to give' the latter an inclined position, with theslag outliow at its lowest point.

The annexed drawing shows diagrammatically in several sections one exampIeofperforming the invention.

Fig. l is avertical View of a furnace according tol the invention adapted to heat a steam boiler;

Fig. 2 is avertical sectional view of the furnace shown in Fig. l, the sectionC being takenv alongli'ne II-II in Fig'. l;

Fig. 3 shows a vertical'section of thel furnace of Fig. l along line Ill-JH of Fig. l. A

Like parts are designated by like numerals in all figures of the drawings'.- j

AAs seen in Fig. l, the longitudinal axis of the furnace 4' declines slightly. A conical part 13 of the furnace wall extends from a front Wall 14 andcontinues into a cylin- 12'. A conventional cyclone burner 1 is insortedV inthe front wallI 1'4. It introduces a mixture of primary air and fuel rotating about and along the longitudinal axis of the combustion chamber. A water cooled barile 11 having the shape of a cross (Fig. 2) is interposed in the path of the burning mixture in chamber 4. The baille leaves passages 18 between the arms of the cross. Whereas refractory material may be used for forming the arms of the cross forming the baffle 11, the refractory material can be omitted in the center of the baie because the crossing cooling tubes form an almost solid wall in the center of the baffle. The conical wall 13 and the cylindrical wall 12 of the combustion chamber are provided with a plurality of conduits 3 extending longitudinally of the walls and terminating tangentially of the inside surface of the walls. Secondary air is introduced through the conduits 3, forcing the hot gas away from the walls and preventing deposition of ash on the walls. The amount l of air introduced through burner 1 and through conduits 3 is preferably so controlled that the temperature in chamber -1 is higher than the fusing point of the ash. Parts 12 and 13 are surrounded by an air jacket 20 which is subdivided by transverse walls 21 into a plurality of annular air chambers 22. The latter are individually supplied with air through inlets 2. The wall of the portion of the combustion chamber commencing with the baie 11 is provided with internal conduits 25 (Fig. 3) which may communicate with channels 26 in baille 11 and with pipes 27 through which cooling water is introduced and with pipes 28 through which cooling water is relieved. The rear of the combustion chamber is closed by a wall 29 having a nozzle shaped outlet 30 for the combustion gas. Wall 29 is provided with cooling channels 31. The batie 11 forces the combustion gas against the wall 12 along which the gas ilows toward the rear wall 29, depositing liquid and pasty slag on the inside of the wall 12. The slag accumulates at the bottom of the chamber between the baffle 11 and the rear wall 29. A small opening 9 is provided in the lower part of the rear wall leaving a low dam 37 over which ows the liquid slag.

Rear wall 29 extends above and below the'combustion chamber forming a chamber 6 receiving the hot combustion gas from nozzle 30. Chamber 6 contains a bafe 40 which downwardly dellects the combustion gas. Fly ash carried along by the gas is deposited on bale 40 and drops down therealong. A water-cooled screen 7 extends from the lower part of the baffle which is spaced from the bottom 41 of chamber 6. The downwardly deflected gas hits bottom 41 and is deflected upwardly to flow through the screen 7. The latter retains residual fly ash. Cooling conduits 43 are provided in the bottom 41 and cooling conduits 44 are provided in the screen 7 and in the bale 40. The cooling

conduits

43 and 44 and the cooling conduits 31 of the gas outlet nozzle 30 are interposed in a water or steam circulating system 45, forming part of a steam generator, not shown.

The liquid or pasty slag flowing through opening 9 and the ash deflected by bafile 40 and dropping from screen 7 collects on the bottom 41 and can be removed through an opening 10 which is disposed in line with the direction of movement of the gas which is downwardly diverted by baffle 40.

We claim:

l. A combustion apparatus for pulverized fuel coinprising a substantially cylindrical combustion chamber having a cyclone burner fired first portion, said first portion having a circumferential wall and secondary air admission means equally distributed all around and over the whole length of said wall for cooling said first portion exclusively by secondary combustion air, the longitudinal axis of said combustion chamber being substantially horizontal and declining somewhat in the general direction of the flow of the combustion gases, said combustion chamber having a second portion having a water-cooled circumferential wall, and guide means for the burning gases disposed in said combustion chamber between said rst and said second portion, said second portion having a rear wall and openings in said rear wall affording passage of lthe hot combustion gas to its place of use and flow of slag out of said second portion.

2. A combustion apparatus for pulverized fuel combined with a tubular steam boiler, comprising a substantially cylindrical combustion chamber having a cyclone burnerred first portion, said first portion having a circumferential Wall and secondary air admission means equally distributed all around and over the whole length of said wall for cooling said first portion exclusively by secondary combustion air, the longitudinal axis of said combustion chamber being substantially horizontal and declining somewhat in the general direction of the flow of the combustion gases, said combustion chamber having a second portion, said second portion having a circumferential wall, a cooling coil in said last mentioned circumferential wall, guide means for the burning gases disposed in said combustion chamber between said first and said second portion, and cooling tubes in said guide means.

References Cited in the file of this patent UNITED STATES PATENTS 1,618,808 Burg Feb. 27, 1927 2,357,301 Bailey et al. Sept. 5, 1944 2,357,303 Kerr et al. Sept` 5, 1944 2,625,791 Yellott 1an. 20, 1953Y FOREIGN PATENTS 576,932 Great Britain Apr. 26, 1946 y626,249 Great Britain July 12. 1949

Claims

1. A COMBUSTION APPRATUS FOR PULVERIZED FUEL COMPRISING A SUBSTANTIALLY CYLINDRICAL COMBUSTION CHAMBER HAVING A CYCLONE BURNER FIRED FIRST POSITION, SAID FIRST PORTION HAVING A CIRCUMFERENTIAL WALL AND SECONDARY AIR ADMISSION MEANS EQUALLY DISTRIBUTED ALL AROUND AND OVER THE WHOLE LENGTH OF SAID WALL FOR COOLING SAID FIRST PORTION EXCLUSIVELY BY SECONDARY COMBUSTION AIR, THE LONGITUDINAL AXIS OF SAID COMBUSTION CHAMBER BEING SUBSTANTIALLY HORIZONTAL AND DECLINING SOMEWHAT IN THE GENERAL DIRECTION OF THE FLOW OF THE COMBUSTION GASES, SAID COMBUSTION CHAMBER HAVING A SECOND PORTION HAVING A WATER-COOLED CIRCUMFERENTIAL WALL, AND GUIDE MEANS FOR THE BURNING GASES DISPOSED IN SAID COMBUSTION CHAMBER BETWEEN SAID FIRST AND SAID SECOND PORTION, SAID SECOND PORTION HAVING A REAR WALL AND OPENINGS IN SAID REAR WALL OFFORDING PASSAGE OF THE HOT COMBUSTION GAS TO ITS PLACE OF USE AND FLOW OF SLAG OUT OF SAID SECOND PORTION.