GB2133127A

GB2133127A - Improvements in a process of manufacturing cement

Info

Publication number: GB2133127A
Application number: GB08333928A
Authority: GB
Inventors: P Davies; G A Dickson
Original assignee: PETERS CLAUDIUS Ltd
Current assignee: PETERS CLAUDIUS Ltd
Priority date: 1982-12-20
Filing date: 1983-12-20
Publication date: 1984-07-18
Also published as: GB2133127B; GB8333928D0

Abstract

Cement manufacturing plant in which a mill 2 feeds limestone to a kiln 6 discharging to a recuperator 8. Clinker from the recuperator passes through a roller crusher 10 and carried in a bucket transporter 12 to an indirect heat exchanger 14. Hot air from the recuperator 8 is used for heating and drying the raw limestone, as combustion air, or recycled to the recuperator. The roller crusher 10 and the indirect heat exchanger 14 are able to accept clinker at temperatures up to 1000 DEG C, and thereby accommodate sudden surge discharges of clinker from the kiln without the need to provide for air supplies and atmospheric venting facilities in excess of that required for normal operation. <IMAGE>

Description

SPECIFICATION Improvements in a process of manufacturing cement This invention concerns a process of manufacturing cement in which limestone is fed into a crusher and then dried prior to being fed into a calcining kiln where the limestone is combusted and calcined to produce cement clinker which is then fed into a recuperator situated downstream of the calcining kiln.

Hitherto, the cement clinker has been aircooled in the recuperator from a temperature in the range 1 4000C to 1 500 C to 3500C before being crushed in a hammer mill and passed on to a further cooler. Since the hammer mill is unsuited to accepting a material at a temperature much in excess of 3500 C, it has been the practice to supply in excess of cooling air to the recuperator in order to guard against sudden surges in the flow of cement clinker. Thus it has been found that for each kilogram of clinker produced, some 1.4 cubic metres of cooling air are required to be supplied to the recuperator, Whilst some .9 cubic metres of this air may be used in the calcining combustion process, the remainder has to be vented directly to the atmosphere through a clean-up system.

According to the present invention there is provided cement manufacturing plant including a raw limestone crusher arranged to feed to a cement kiln delivering cement clinker to a recuperator discharging the clinker through a roller crusher to an indirect heat exchanger with a plurality of blowers connected to discharge cooling air to the recuperator and air offtakes from the recuperator to the kiln, to the raw limstone crusher and, through a re-cycling connection, to the blowers.

Such an arrangement dispenses with the need to discharge air from the recuperator direct to the atmosphere and will normally operate with an air intake of around 1.2 cubic metres of air for each kilogram of cement produced.

The invention will now be described, by way of example, with reference to the accompanying, diagrammatic, drawing of a cement manufacturing plant including a crusher mill 2 which feed crushed limestone through a feed duct 4 to a rotary calcining kiln 6 discharging cement clinker to a recuperator 8. The recuperator delivers the cement clinker to a roller crusher mill 10 which crushes the kiln clinker to a 5 cm crushed clinker which, in turn, is conveyed in a bucket transporter 1 2 and distributed by a drag link conveyor (not shown) to an indirect heat exchanger 14 consisting of air cooled tube banks over which the crushed clinker moves downwardly under the effect of gravity to an outlet 1 6.

The roller crusher mill 10 consists of four, spaced, indented, rolls, the spacing corresponding to the desired clinker size of 5 cm.

Streams of air are supplied, at intervals along the recuperator, through controllable output, fixed speed, blowers 1 8, in cross flow direction to the clinker movement and the resulting flow of heated air is split into five factions. A first faction of the heated air is utilised as tertiary combustion air and is supplied through a duct 20 to the kiln, a second faction is utilised as secondary combustion air in the kiln, flowing directly to the kiln, a third faction is taken through a duct 22 and is utilised as drying and heating air in the crusher mill 2 for limestone feed to the kiln, whilst a fourth faction is taken through a duct 24 to grit arrestors 26 and then to a duct 28 leading to the blowers 1 7 for recycling, whilst the fifth faction -- the residue - is discharged to atmosphere through filtering and cleaning plant 30 and a stack 32.

Streams of air are also supplied, at intervals along the base of the indirect heat exchanger 14, through controllable output, fixed speed, blowers 34 and, at the top of the indirect heat exchanger, are collected in a duct 36 discharging to the inlets of the blowers 1 8 associated with the recuperator 8. Alternatively, the heated air discharged at the top of the indirect heat exchanger 14 may be discharged to atmosphere or utilised for area heating in adjacent accommodation. As a further alternative, a heat transport liquid, such as water or oil, may be pumped through the indirect heat exchanger 14 instead of air, and utilised in a district or area heating scheme.

In operation, the raw, damp limestone is supplied to the crusher mill 2 and delivered to the kiln 6 in a dried and crushed state. In the kiln the limestone is calcined by combustion gases to reach a temperature, on discharge to the recuperator 8 as cement clinker, of around 1 5000C.

In the recuperator 8 the clinker is colled by the air streams from the blowers 1 8 to around 31 50C before discharge to the roller crusher mill 10.

Crushed cement clinker discharged from the roller crusher mill is conveyed in the bucket transporter 12 to the indirect heat exchanger 14 and further cooled therein to around 1 000C as it moves downwardly, by the effect of gravity, to the outlet 1 6.

Air is recycled, through the grit arrestors 26, from the downstream end of the recuperator 8 to the blowers 1 8 to maintain the flow of air across the recuperator at a rate commensurate with the required rate of heat extraction.

By utilising suitable alloys in the roller crusher mill 10 and indirect heat exchanger 14 and the bucket conveyor 12, with the ability to withstand temperatures up to 10000 C, if required, any sudden surges in the supply of cement clinker can be accommodated in the system without the necessity of providing an extra air flow, or means for venting such extra air flow to atmosphere through filtering and cleaning plant.

1. A cement manufacturing plant including a raw limestone crusher arranged to feed a cement kiln delivering cement clinker to a recuperator discharging the clinker through a roller crusher to an indirect heat exchanger with a plurality of

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Improvements in a process of manufacturing cement This invention concerns a process of manufacturing cement in which limestone is fed into a crusher and then dried prior to being fed into a calcining kiln where the limestone is combusted and calcined to produce cement clinker which is then fed into a recuperator situated downstream of the calcining kiln. Hitherto, the cement clinker has been aircooled in the recuperator from a temperature in the range 1 4000C to 1 500 C to 3500C before being crushed in a hammer mill and passed on to a further cooler. Since the hammer mill is unsuited to accepting a material at a temperature much in excess of 3500 C, it has been the practice to supply in excess of cooling air to the recuperator in order to guard against sudden surges in the flow of cement clinker. Thus it has been found that for each kilogram of clinker produced, some 1.4 cubic metres of cooling air are required to be supplied to the recuperator, Whilst some .9 cubic metres of this air may be used in the calcining combustion process, the remainder has to be vented directly to the atmosphere through a clean-up system. According to the present invention there is provided cement manufacturing plant including a raw limestone crusher arranged to feed to a cement kiln delivering cement clinker to a recuperator discharging the clinker through a roller crusher to an indirect heat exchanger with a plurality of blowers connected to discharge cooling air to the recuperator and air offtakes from the recuperator to the kiln, to the raw limstone crusher and, through a re-cycling connection, to the blowers. Such an arrangement dispenses with the need to discharge air from the recuperator direct to the atmosphere and will normally operate with an air intake of around 1.2 cubic metres of air for each kilogram of cement produced. The invention will now be described, by way of example, with reference to the accompanying, diagrammatic, drawing of a cement manufacturing plant including a crusher mill 2 which feed crushed limestone through a feed duct 4 to a rotary calcining kiln 6 discharging cement clinker to a recuperator 8. The recuperator delivers the cement clinker to a roller crusher mill 10 which crushes the kiln clinker to a 5 cm crushed clinker which, in turn, is conveyed in a bucket transporter 1 2 and distributed by a drag link conveyor (not shown) to an indirect heat exchanger 14 consisting of air cooled tube banks over which the crushed clinker moves downwardly under the effect of gravity to an outlet 1 6. The roller crusher mill 10 consists of four, spaced, indented, rolls, the spacing corresponding to the desired clinker size of 5 cm. Streams of air are supplied, at intervals along the recuperator, through controllable output, fixed speed, blowers 1 8, in cross flow direction to the clinker movement and the resulting flow of heated air is split into five factions. A first faction of the heated air is utilised as tertiary combustion air and is supplied through a duct 20 to the kiln, a second faction is utilised as secondary combustion air in the kiln, flowing directly to the kiln, a third faction is taken through a duct 22 and is utilised as drying and heating air in the crusher mill 2 for limestone feed to the kiln, whilst a fourth faction is taken through a duct 24 to grit arrestors 26 and then to a duct 28 leading to the blowers 1 7 for recycling, whilst the fifth faction -- the residue - is discharged to atmosphere through filtering and cleaning plant 30 and a stack 32. Streams of air are also supplied, at intervals along the base of the indirect heat exchanger 14, through controllable output, fixed speed, blowers 34 and, at the top of the indirect heat exchanger, are collected in a duct 36 discharging to the inlets of the blowers 1 8 associated with the recuperator 8. Alternatively, the heated air discharged at the top of the indirect heat exchanger 14 may be discharged to atmosphere or utilised for area heating in adjacent accommodation. As a further alternative, a heat transport liquid, such as water or oil, may be pumped through the indirect heat exchanger 14 instead of air, and utilised in a district or area heating scheme. In operation, the raw, damp limestone is supplied to the crusher mill 2 and delivered to the kiln 6 in a dried and crushed state. In the kiln the limestone is calcined by combustion gases to reach a temperature, on discharge to the recuperator 8 as cement clinker, of around 1 5000C. In the recuperator 8 the clinker is colled by the air streams from the blowers 1 8 to around 31 50C before discharge to the roller crusher mill 10. Crushed cement clinker discharged from the roller crusher mill is conveyed in the bucket transporter 12 to the indirect heat exchanger 14 and further cooled therein to around 1 000C as it moves downwardly, by the effect of gravity, to the outlet 1 6. Air is recycled, through the grit arrestors 26, from the downstream end of the recuperator 8 to the blowers 1 8 to maintain the flow of air across the recuperator at a rate commensurate with the required rate of heat extraction. By utilising suitable alloys in the roller crusher mill 10 and indirect heat exchanger 14 and the bucket conveyor 12, with the ability to withstand temperatures up to 10000 C, if required, any sudden surges in the supply of cement clinker can be accommodated in the system without the necessity of providing an extra air flow, or means for venting such extra air flow to atmosphere through filtering and cleaning plant. CLAIMS

1. A cement manufacturing plant including a raw limestone crusher arranged to feed a cement kiln delivering cement clinker to a recuperator discharging the clinker through a roller crusher to an indirect heat exchanger with a plurality of blowers connected to discharge cooling air to the recuperator and air offtakes from the recuperator to the kiln, to the raw limestone crusher and, through a re-cycling connection, to the blowers.

2. A cement manufacturing plant as claimed in Claim 1 , wherein a bucket conveyor is provided to receive clinker from the roller crusher and discharge the clinker to the indirect heat exchanger.

3. A cement manufacturing plant as claimed in Claim 1, or Claim 2, wherein the indirect heat exchanger is air cooled.

4. A cement manufacturing plant as claimed in Claim 3, wherein a heated air outlet from the indirect heat exchanger discharges to the recuperator.

5. A cement manufacturing plant as claimed in Claim 3, wherein a heated air outlet from the indirect heat exchanger discharges to area heating means.

6. A cement manufacturing plant as claimed in Claim 1 or Claim 2, wherein the indirect heat exchanger is liquid cooled and the liuid is circulated to area heating means.

7. A cement manufacturing plant arranged and adapted to operate substantially as hereinbefore described with reference to the accompanying drawing.