JPS593423B2 - Cement raw material calcination method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for calcining raw materials for cement.

Conventionally, there are two methods of calcination of cement raw materials: a method using a so-called air flow furnace in which heat exchange is performed by jet flow, vortex flow, or a combination thereof, and a method using a fluidized bed furnace using a fluidized bed.

This invention relates to a calcination furnace for cement raw materials, which incorporates the advantages of the above two methods and uses a calcination furnace which can also be called an airflow furnace with a fluidized bed.

In a method of firing powder raw materials such as cement raw materials, a method of calcination of cement raw materials has been known in the past, in which a calcination furnace having an independent heat source is provided between a rotary furnace and a suspension preheater to improve thermal efficiency and production efficiency. This is the technology of

This calcining furnace is conventionally equipped with a so-called air flow furnace, which exchanges heat between high-temperature combustion gas and raw materials using jet flow, swirling flow, or a combination thereof, and a flow furnace, which allows cement raw materials to float and fluidize at a high concentration. Bed furnaces have been widely used, but each method has its advantages and disadvantages.

In other words, the air flow furnace type has the advantage of having a simple device and relatively low pressure loss, but on the other hand, because the burner performs space combustion within the furnace, the formation of high-temperature localized flames cannot be avoided. There are disadvantages.

For this reason, low melting point components such as alkalis in the raw materials melt in the calcining furnace and condense on the powder raw materials and the inner walls of the furnace, causing problems such as a decrease in thermal efficiency and ventilation problems, and the flames can cause problems such as damage to the refractories in the furnace. Shorten lifespan.

In addition, the bleed air from the clinker cooler (preheated air after heat exchange in the clinker cooler) is used as the combustion air in the calciner, but the ventilation of the air duct from the clinker cooler to the air intake of the calciner is The resistance is generally higher than the ventilation resistance of the rotary furnace, so in order to introduce sufficient combustion air to the calciner, a restriction must be installed in the exhaust gas duct leading from the rotary furnace to the calciner to maintain the mutual pressure balance. ing.

This increases pressure loss, leading to an increase in the power required for the ventilator.

Moreover, this exhaust gas duct is a high-temperature part, and the alkali content in the raw material evaporated in the rotary furnace is likely to condense on the raw material powder and the wall surface in this duct.

Therefore, providing a throttle in this portion is likely to cause operational problems and has the drawbacks of making it difficult to adjust the flow rates of rotary furnace exhaust gas and combustion air.

On the other hand, in the fluidized bed furnace type, the raw material and fuel are evenly mixed and no flame is formed by combustion, so there is no bright flame radiation heat or local overheating caused by local combustion, and the fluidized bed and gas temperatures are almost equal. It has the advantage of high thermal efficiency due to its long residence time.

However, on the other hand, since fluidizing air and furnace combustion air to maintain a constant fluidized bed thickness are blown from the bottom of the fluidized bed, ventilation resistance becomes large and the power required for the ventilator increases.

Therefore, in order to increase the combustion rate in the fluidized bed, the thickness of the fluidized bed must be increased, but due to the increase in pressure loss,
The disadvantage is that the thickness of the fluidized bed cannot be increased unnecessarily.

The present invention can make the conventional cement raw material calcination method more effective by employing the cement raw material calcination method described below.

In other words, ■ In the fluidized bed section, the preheater (
Alternatively, the raw material preheated by a cyclone and the fuel supplied from the bottom of the fluidized bed are uniformly mixed, and the fuel is gasified by the heat retained in the raw material.

(2) The raw material overflowing from the fluidized bed section is lifted up by the kiln exhaust gas, and at the same time, it reaches the air flow layer in the upper part of the calciner, accompanied by the gasified combustible gas.

■ In this air flow layer, the cooler bleed gas (oxygen-containing gas) is swirled in, forming a vortex inside, and violently mixing the raw materials and flammable gas, without forming a flame, and therefore generating heat from the luminous flame radiant heat. combustion without local overheating due to local combustion.

Thereby, the feed particles are thermally calcined at relatively low temperatures and isothermally and entrained by the entire exhaust gas stream from the combustion and calcination steps.

■ In the fluidized bed section mentioned above, only the minimum amount of air necessary for fluidizing the raw material is blown from the bottom of the fluidized bed, and the air necessary for combustion is supplied to the top of the calciner. Since the raw materials in the furnace are lifted by cooler bleed air or by cooler bleed air and kiln exhaust gas, as mentioned above, a restriction is installed in the kiln exhaust gas duct in order to maintain the pressure balance between the cooler bleed air system and the kiln exhaust gas system. It was set up.

This resulted in an increase in pressure loss, but in the present invention, the raw material is lifted only by the kiln exhaust gas, so the above-mentioned throttling is not necessary.

As a result of the above, the pressure loss in the calcining furnace of the present invention is relatively small.

Next, an embodiment of the cement raw material calcination method of the present invention will be described with reference to the drawings.

A part or all of the cement raw material is introduced into the fluidized bed 18 via the raw material supply port 6 by a feeder (not shown), through the cyclones 2, 3.4, and calcined in the calciner 1.

The cement raw material calcined in the calcining furnace 1 is sent to the rotary kiln 19 via a cyclone 5.

The cement raw material is preheated in the cyclones 2, 3.4 by heat exchange with the exhaust gas of the rotary kiln 19 and the calciner 1.

For this preheating, a conventionally known cyclone heater or suspension preheater may be used.

The fluidized bed 18 has a fluidized bed 22 with a perforated plate at the bottom, and an air supply pipe 10 for supplying fluidizing air into the fluidized bed 18 from the bottom of the fluidized bed 22 and a supply pipe 9 for supplying fuel. It is equipped with

In the fluidized bed 18, the cement raw material and the fuel are uniformly mixed, and the heat retained in the raw material is combusted and gasified, and a portion of it is combusted.

The cement raw material overflowing from the fluidized bed 18 falls into the exhaust gas duct 17 of the rotary kiln 19, but is lifted by the exhaust gas ejected from the rotary kiln 19 and sent to the calciner 1.
reach the top of.

In the upper part of the calciner 1, the preheated air heat-exchanged by the clinker cooler 21 is swirled into the calciner 1 through ducts 14 and 15 as shown in FIG. Gas is combusted to heat and calcinate cement raw materials.

The cement raw material calcined in the calcining furnace 1 is passed through the exhaust gas duct 1a.
After passing through the cyclone 5 and being separated, it is introduced into the rotary kiln 19 as described above.

1 is an exhaust fan for all exhaust gas flow; 8 is a raw material inlet in the calciner; 10 is an air duct for fluidization; 11
12 is a forced draft for fluidization, 12 is a dust collector, 13 is a cooling air intake, 16 is a blowhole provided in the calciner 1 as a heat-resistant obstacle for prevention, and 20 is a burner.

Since the cement raw material calcination method of the present invention is carried out as described above, the following effects can be achieved.

(1) In conventional air flow furnaces and fluidized bed furnaces, combustion may not be completed within the furnace and the combustion zone may extend to the cyclones 4 and 5 in the preceding stage.

Therefore, the temperature of the exhaust gas from the suspension preheater increases, causing a decrease in the thermal efficiency of firing cement raw materials.

By employing this invention, complete combustion can be achieved in the calcining furnace for the reasons stated in (1) to (3) above, and thermal efficiency can be increased.

(2) Because of the reasons (1) to (2) above, the raw material particles are heated and calcined isothermally at a relatively low temperature, eliminating coating troubles in the furnace.

(3) The combustion zone at the top of the calciner has a relatively low temperature (600~
The furnace wall is protected by swirling secondary air (750°C) inflow, which enables long-term continuous operation.

(4) Due to the above reasons (1) to (2), pressure loss can be reduced.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an embodiment for implementing the cement raw material calcination method of the present invention, FIG. 2 is a sectional view taken along line A-A in FIG. 1, and FIG. 3 is a cross-sectional view taken along line B-B in FIG. FIG. 1 is an exhaust fan, 2, 3.4.5 is a cyclone, 6 is a raw material supply port, 1 is a calciner, 8 is a raw material inlet of the calciner, 8a is a raw material inlet when the preheated raw material is separated, 9 10 is a supply pipe, 10 is an air supply pipe, 11 is a forced draft fan, 12 is a dust collector, 13 is a cooling air intake, 14゜15 is a duct, 16 is an atrium provided in the calcining furnace is a heat-resistant failure prevention 17 is an exhaust gas duct, 1
8 is a fluidized bed, 19 is a rotary kiln, 20 is a burner, 2
1 is Talinkar Coola.

Claims (1)

[Claims] 1. A fluidized bed calcination furnace with an independent heat source is installed between the rotary furnace and the raw material preheating device, and high temperature exhaust gas introduced from the rotary furnace and flammable gas generated in the fluidized bed inside the calcination furnace are transferred to the calcination furnace. This mixed gas is mixed with combustion air introduced into the upper part of the calcining furnace, and combusted to calcinate the cement raw material.This combustion exhaust gas is also introduced into the raw material preheating device to increase the specific capacity of the rotary furnace. A cement raw material calcination method characterized by increasing .