WO1990012761A1

WO1990012761A1 - Shaft kiln

Info

Publication number: WO1990012761A1
Application number: PCT/DK1989/000089
Authority: WO
Inventors: Peter Wyss; Hans Zogg
Original assignee: Rockwool International AS
Current assignee: Rockwool AS
Priority date: 1989-04-17
Filing date: 1989-04-17
Publication date: 1990-11-01
Anticipated expiration: 1991-10-17

Abstract

A shaft kiln, especially a shaft kiln for the manufacture of mineral wool, and comprising a kiln chamber (1) with a primary (1a) and a secondary (1b) burning zone and inlets (4) for primary comubstion air (4a) and inlets (5) for secondary combustion air (5a), is provided with a downwards from above in the kiln shaft axially displaceable air injection pipe (6) for feeding additional secondary combustion air (6a) into the secondary burning zone (1b) thus essentially improving the reduction of the emission of H2S (hydrogen sulphide) and CO (carbon monoxide) through the kiln exhaust gases.

Description

Shaft kiln

The present invention relates to a vertical kiln or a shaft kiln, especially a shaft kiln for the manufacture of a melt for the production of mineral wool, and comprising a kiln chamber having a primary burning zone and a secondary burning zone immediately above the primary burning zone, and means for introducing primary combustion air into the primary burning zone and through apertures in the shaft wall secondary combustion air into the secondary burning zone.

In known shaft kilns, such as cupolas described for instance in the patent specifications DE 2,428,891, DE 2,032,400, GB 1,206,976 and DE 2,316,971 combustion air is fed to a kiln shaft in the following ways:

Into a primary burning zone in the lower part of the kiln primary combustion air through air inlet pipes or tuyeres for obtaining the requested melting temperature of the kiln charge.

Through air inlet apertures in the shaft wall on a level with the secondary burning zone secondary combustion air providing further up in the kiln shaft a secondary combustion of the kiln gases thus stabilizing the kiln burning process and partly reducing the amount of polluting constituents in the kiln gases.

It has, however, turned out that the above hitherto secondary combustion has not been sufficient for reducing the contents especially of H₂S (hydrogen sulphide) and CO (carbon monoxide) of the kiln gases for satisfying the present requirements for a reduction of the air pollution, which requirements have already been introduced in some industrial countries and which are expected to be introduced in a further number of countries. Thus the upper limit of H,S emission from kiln gas has in West Germany and the Netherlands

3 been fixed for 5 mg/Nm , which request is not met by the hitherto known kinds of secondary combustion in shaft kilns.

It is therefore the object of the invention to provide a shaft kiln which remidies the hitherto disadvantages of insufficient reduction of the emission of H«S and CO from such kilns and which in addition hereto contribates to an essential cut of installation costs of a production line of which the kiln in question may be a part, and to savings of the running costs of said line in that cost demanding exhaust gas cleaning installations of the production line may be drastically reduced or may even be spared completely.

The object is obtained through a shaft kiln according to the invention, especially a shaft kiln for the manufacture of a melt of mineral wool and of the above described type, and having at least one into the kiln shaft from above downward projecting, centrally introduced pipe for- injection of further secondary combustion air into the secondary burning zone of the shaft. The pipe may be made to being axially displaced at variable distances between the shaft bottom and the pipe end facing this bottom. Further, the downwards turning outlet of the pipe may be of a frusto-conical shape and the frusto-conical part may be provided with a number of air injection outlets in its conic surface.

Injecting further secondary combustion air into the secondary zone through the thus centrally mounted pipe in addition to the secondary air fed through the apertures in the shaft wall permits an essentially improved combustion in the secondary zone through said extra added secondary combustion air due to the thus provided better distribution ϋf the air in the zone, and through a better combustion is obtained a corresponding, essentially better reduction of the noxious constituents such as H₂S and CO of the kiln exhaust gases.

Regulating the heigth above the kiln bottom of the centrally mounted pipe in the secondary zone permits the injection of additional secondary air for the obtainment of the optimal secondary combustion conditions at any time, and giving the lower end of the pipe a frusto-conical shape and providing the conic surface with a number of air injection outlets permits a further optimal distribution of the cortbustiσn air in the zone.

The invention is described in a more detailed way in the following with reference to the accompanying drawing which shows diagrammatically and without in any way being limiting a shaft kiln with air injection inlets for primary as well as for secondary air, but in which other features of a shaft kiln, such as burners, kiln charge, melt outlets and forehearth are left out for reasons of clarity and in which

Fig. 1 shows a vertical cross-sectional view of a shaft kiln equipped with a centrally mounted pipe for the injection of secondary combustion air according to the invention and

Fig. 2 also in a vertical cross-secontional view shows a detail of Fig. 1 .

A shaft kiln with a shaft 1 has sidewalls 2 and a bottom 3, and at its upper end a feed vessel 13 with a feed hopper 14 for the introduction of raw material into the kiln. The feed hopper may at its bottom be equipped with an axially displacable cone 15 for regulating the feed inlet into the shaft 1. The shaft has at its lower end (Fig. 2) a primary burning zone la and a secondary burning zone lb. Primary combustion air 4a is fed to the primary burning zone via an annular duct 9 and through air inlets or tuyeres 4, while a certain amount of secondary combustion air 5a is fed via annular ducts 10 and air inlets 5 to the secondary burning zone the inlets being placed in sections of different height levels over the shaft bottom 3. To create appropriate burning conditions in the secondary burning zone lb the amount of secondary combustion air 5a is fed to this zone and injected through the air inlets 5 into a part of the zone having a temperature of 700^β-800'C. As the location of this part of the zone in the shaft may vary in the heigth over the kiln bottom 3 according to the burning conditions of the kiln charge the amount of injected secondary combustion air is also regulated in height in that the horizontal sections of air inlets having the better placing in relation to the 700^β-800^β temperature zone is chosen for the injection of the greater amount of air, while smaller adapted amounts are injected through the inlets of the other rows, the control of the amounts of air being normally made by automatic kiln processing based i.a. upon the shaft temperature profiles. According to the invention a further amount of secondary combustion air 6a for the improvement of the burning conditions is fed to the secondary burning zone lb through a vertical air injection pipe 6 mounted axially in the shaft and projecting downward from above into the secondary burning zone. The pipe 6 is preferably in fixed connection with an approximately horisontally mounted air duct 11 for secondary combustion air. Duct 11 is mounted displacably in height in apertures 12 with appropriate sealings of known type in the kiln wall 2, the displacement clearance of the duct substantially corresponding to the displacement height of the secondary burning zone of 700^β-800"C in the shaft. To ensure the optimal distribution of secondary combustion air fed to the secondary burning zone lb through pipe 6 the downward end 7 (Fig. 2) of this pipe has a slight frusto-conical shape with by way of example an inclination of the cone of 10° to the vertical axis of the pipe and with the conic surface circumferentially having a number of air injection outlets 8 mounted for instance in two rows each with 10 outlets and with an outlet diameter corresponding to the diameter of the air injection inlets 5 in the shaftwall 2.

The duct 9 and the pipe 6 may be watercooled in a known manner to ensure their proper functioning within the kiln shaft 1.

Comparative plant trials with shaft kilns using no secondary air injection at all and using a secondary air injection through air inlet sections in the shaft wall, but without a central pipe, and with air injection both through inlets in the shaft wall and through such pipe have been made and have given test results which will

3 appear from the following table, in which Nm /min means normal cubic

3 metres per minute and mg/Nm means milligrams per normal cubic metre. _* Primary Secondary air (Nm /min) H₂S C0% air Central Upper Mid Lower (mg/Nm³) 3 (Nm /min) pipe section section section

85,0 none none none none 360 8,0 85,0 210 6,9

104,0 none 8,0 15,0 none 51,9 3,0 104,0 5,0 15,0 66,1 4,0

85,0 12,0 14,0 10,0 2,5 0,4 0,2 85,0 12,0 14,0 10,0 2,5 2, 1 0,5 78,0 12,0 14,0 10,0 2,5 2,8 1,0 78,0 12,0 14,0 10,0 2,5 4, 5 0,9 77,0 12,0 14,0 10,0 2,5 1 ,2 0,8 92,0 11 ,0 12,0 10,0 2,0 1 ,5 2,0< 93,0 11 ,0 12,0 10,0 2,0 0,52 2,0< 93,0 11 ,0 12,0 10,0 2,0 0,00 2,0< 93,0 11 ,0 12,0 10,0 2,0 3,41 2,0<

It is to be noted immediately from this table that the relatively simple construction of a central air injection pipe for secondary combustion air reduces the emission of the pollutant hydrogen

3 sulphide from a shaft kiln to below 5 mg/Nm and also contributes to a considerable reduction of the carbon monoxide contents in the kiln exhaust gases.

Claims

C l a i s

1. §Jιaft kiln, especially a shaft kiln for the manufacture of a melt for the production of mineral wool, and comprising a kiln chamber divided into a primary burning zone and a secondary burning zone infaediately above the primary burning zone, and means for feeding primary combustion air into the primary zone and secondary combustion air into the secondary zone, c h a r a c t e r i z e d in having at least one from above into the kiln shaft (1) introduced and downwards centrally into the shaft projecting pipe (6) for injection of further secondary combustion air (6a) into the secondary burning zone (lb) of the shaft.

2. Shaft kiln according to claim 1, c h a r a c t e r i z e d in that the pipe (6) is made to being axially displaced at variable distances between the shaft bottom (5) and the pipe end (7) facing the shaft bottom.

3. Shaft kiln according to claims 1 and 2, c h a r a c t e r - i z e d in that the downwards turning end (7) of the pipe (6) has a faintly frusto-conical shape and in that the frusto-conical part is provided with a number of air injection outlets in its conic surface.