GB1591768A - Dry cement production process - Google Patents

Description

(54) DRY CEMENT. PRODUCTION PROCESS (71) We, SERRANA S/A DE MINERACAO., a Brazilian Corporation of Av. des Estados no. 4530--Santo Andre- Sao Paulo-Brazil, do hereby declare the invention for which we pray that a Patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement:- This invention relates to a dry cement production process, that is the production process for obtaining cement clinker by the dry process for which for example 700 to 1000 kcal/kg of clinker are required.

Heating power is usually supplied to the cement kiln in this kind of process by burning at the lower end of the kiln a suitable fuel, for example gas or oil or pulverised coal. The fuel is usually injected through a jet and ignited by a blow torch and when ignited it burns at a high temperature, the hot gases passing up the length of the kiln and out either via a flue or via a by-pass into a preheating system such as a prehating tower or into a secondary combustion installation or even an auxiliary installation which uses the same fuel as the main system and is located outside the kiln.These preheating systems are employed to preheat the raw material which is usually referred to as raw meal in the art and normally comprises mineral clay and calcium carbonate and/or iron materials in such a way that the mixture of the components takes account of given chemical values of a so-called meal composition modulus. This meal is introduced at the opposite end of a kiln to the burner and combustion takes place in countercurrent with the flow of raw material.

When pulverised fuel, for example coal, is used it is necessary to have grinding, drying and controlled atmosphere installations to avoid the danger of explosion and in order to give the coal a grain size suitable for guaranteeing the formation of a flame which meets the configuration requirements, that is, the burning time and dispersion of the particles. The grain size normally used is below screen 200 (74 y). Such pulverising installations involve high costs and special care during operation in that they operate directly in series with the burner and create an explosion risk.

The heat produced by the fuel is used for heating the raw meal for decarbonisation and for sintering the clinker.

Heating and decoarbonisation may occur to a greater or less extent in the preheating system, such as a preheating tower, by using the gases originating from the kiln or by the other systems referred to above.

In the so-called precalcining installations, that is, the preheating installations, fuel can be burnt in the fuel inlet chamber and the quantities of heat therein injected may reach up to 60% of the heat necessary for the manufacture of clinker, the remaining heat being provided by the burner at the outlet end of the rotary kiln.

With the successive increases in the cost of oil, it is becoming more economical to use coal in those countries in which it is available but it has the disadvantages of (1) fluctuation in the quality of the coal, principally when a coal produces a lot of ash, which does not permit stable operation, at full charge of a preheated furnace; (2) the relatively high investment for milling and drying installations and handling of the coal which is to be pulverised; (3) the danger associated with the stocking of coal dust; and (4) the increase in consumption of electric power for the preparation of the coal.

The present invention is intended to provide a process and apparatus to reduce some of the above disadvantages.

Accordingly, the present invention consists in a dry cement production process comprising preheating cement raw meal in a preheating system and burning the preheated material in a cement kiln to form cement clinker, wherein at least some crude lump mineral coal or crude fragmented vegetable charcoal, which has not be pulverised or milled and having a moisture content of up to 15 /n by weight, is burnt in the preheating system. Said coal or said charcoal may be supplied to an inlet chamber of the kiln, hot gases from said kiln being passed to the preheating system.

Preferably, the preheating system includes a preheating tower drawing hot gases from the kiln.

The quantity of said coal or said charcoal which is used is sufficient to supply between 20 and 60van of calories consumed in the formation of cement clinker.

The invention can be performed in various ways but one embodiment will now be described by way of example and with reference to the accompanying drawing which is a diagrammatic illustration of apparatus for carrying out the process of the invention.

As shown in the drawing, the dry cement production apparatus comprises a rotary kiln indicated by reference numeral 1. The outlet end 2 of the kiln is provided with a burner 3 of known type which burns a suitable fuel, for example oil, gas or pulverised coal, the heat from the combustion passing up the kiln 1 to an inlet chamber 4 situated at the upper end of the kiln. Raw meal to be processed is supplied, by means not .shown, to a preheating tower indicated generally by reference numeral 5 down which it passes to a meal entrance 6 which allows entry into the inlet chamber 4.

The meal then enters the rotary kiln 1 and passes downwards along the kiln so that combustion takes place in countercurrent with the hot gases.

The hot gases pass upwardly along the kiln 1 and thence from the kiln 1 through the inlet chamber 4 into the preheating tower 5 where they preheat the raw meal to provide precalcining and decarbonisation and further decarbonisation and sintering takes plates in the kiln itself.

Crude mineral coal in the coarse form which is sometimes refered to as "run of mine" coal is fed to a hopper 7 whence it is transported via a conveyor 8 to an elevator 9 which lifts it upwards and deposits it in a second hopper 10 from which it is delivered to doser scales (metering arrangements) 11 which provide a predetermined coal flow through a duct 12, via a rotary valve 13, to a coal inlet 14 to the inlet chamber 4. It will be observed that this coal inlet is closely adjacent to the meal inlet 6. The inlet chamber 4 may have a separate combustion chamber within it but it is in any case arranged to allow the coal to burn within it.

The quantity of coarse coal introduced is substituted in calorific balance for the corresponding value of fuel employed in the main burner 3 which, may for example be oil. The substitution percentage that may be obtained depends basically on the process and the dimensioning of the installation but it can be arranged to be between 20 and 60V of the total number of calories consumed for the manufacture of the cement.

The addition of the coal, even of low calorific value or rejects, at 20 to 600/n of the total consumption of calories in the preheater does not necessarily save power but it permits the use of more economic fuels, thus conserving the high quality and more expensive fuel which is used at the burner end of the kiln.

It has been found that the use of mineral coal or vegetable charcoal in fragment or lump form as is normally supplied obviates the relatively high capital expenditure on coal/charcoal preparation plant and eliminates the high risk factor represented by the use of pulverised coal.

Depending on the composition of the meal and on the installation, decarbonisation levels of up to 100% can be obtained.

The results of this partial substitution of fuel have been verified on an industrial scale in a kiln with a capacity of 1300 t/day and a maximum fuel oil consumption of 5500 litres/hour.

Coals having different inorganic material contents and different calorific capacities were burned, the CO, CO2 and O2 content of the effluent gases of the preheating system were also measured constantly and samples were taken of the product (clinker) in order to investigate the influence of the new process on its quality. The following conclusions can be drawn: 1. The heating system had no negative effects on the formation of cements and no prejudicial tendencies were observed regarding the formation of disadvantageous dusts.

2. The quantity of calories supplied to the kiln by the coal permitted a significant reduction in the calorific values approximately equal to those obtained from the fuel oil supplied to the blow torch of the furnace, whereby there is also a significant reduction in the thermal load in the sintering range.

3. No negative effects were observed which could prejudice the quality of the product.

4. In the case of complete combustion of the coal, there is not appreciable production of carbon monoxide which would constitute a hazard for the electrostatic system for cleaning the gases (anti-pollution).

The coal or charcoal used in the present substitution process must meet the following requirements: Grain size: crude fragmented vegetable charcoal or mineral coal, without any fineness restriction.

Sulphur content: maximum 1.5% for alkali-free raw materials and higher when the raw materials contain alkalies.

Calorific capacity: no restriction regarding the maximum and minimum values.

Ash or inorganic material content: no restriction regarding the minimum and maximum values which are a function of the raw materials used.

Volatile product content: no restriction.

Fixed carbon content: no restriction.

Moisture content: up to 15% by weight.

WHAT WE CLAIM IS: 1. A dry cement product process comprising preheating cement raw meal in a preheating system and burning the preheated material in a cement kiln to form cement clinker, wherein at least some crude lump mineral coal or crude fragmented vegetable charcoal, which has not been pulverised or milled and having a moisture content of up to 15 /n by weight, is burnt in the preheating system.

2. A process as claimed in Clairh 1, in which said coal or said charcoal is supplied to an inlet chambers of the kiln, hot gases from said kiln being passed to the preheating system.

3. A process as claimed in Claim 1 or Claim 2 in which the preheating system includes a preheating tower drawing hot gases from the kiln.

4. A process as claimed in any one of Claims 1 to 3, in which the quantity of said coal or said charcoal which is used is sufficient to supply between 20 and 60 /n of calories consumed in the formation of cement clinker.

5. A dry cement production process according to Claim 1, substantially as described herein with reference to and as shown in the accompanying drawing.

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

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. alkali-free raw materials and higher when the raw materials contain alkalies. Calorific capacity: no restriction regarding the maximum and minimum values. Ash or inorganic material content: no restriction regarding the minimum and maximum values which are a function of the raw materials used. Volatile product content: no restriction. Fixed carbon content: no restriction. Moisture content: up to 15% by weight. WHAT WE CLAIM IS:

1. A dry cement product process comprising preheating cement raw meal in a preheating system and burning the preheated material in a cement kiln to form cement clinker, wherein at least some crude lump mineral coal or crude fragmented vegetable charcoal, which has not been pulverised or milled and having a moisture content of up to 15 /n by weight, is burnt in the preheating system.

2. A process as claimed in Clairh 1, in which said coal or said charcoal is supplied to an inlet chambers of the kiln, hot gases from said kiln being passed to the preheating system.

3. A process as claimed in Claim 1 or Claim 2 in which the preheating system includes a preheating tower drawing hot gases from the kiln.

4. A process as claimed in any one of Claims 1 to 3, in which the quantity of said coal or said charcoal which is used is sufficient to supply between 20 and 60 /n of calories consumed in the formation of cement clinker.

5. A dry cement production process according to Claim 1, substantially as described herein with reference to and as shown in the accompanying drawing.