WO2006081827A1

WO2006081827A1 - Improved kiln gas bypass system in cement manufacture

Info

Publication number: WO2006081827A1
Application number: PCT/EG2005/000005
Authority: WO
Inventors: Khaled Osman Zaki
Original assignee: Khaled Osman Zaki
Priority date: 2005-02-06
Filing date: 2005-02-20
Publication date: 2006-08-10

Abstract

In cement manufacturing using the dry process, and where kiln (2) gas bypass systems are installed to get rid of alkalis, chlorides and sulphates. Bypass gases at about 1000 C must be immediately quenched (3) to lower than 450 C to avoid the sticky stage of these salts at about 700 C which cause blocking og the gas routes. Using water (8) instead of air for quenching gives many benefits such as decreasing the volume of the water quenched gases, compared to if they were air quenched thus increasing the efficiency of the dust collection system and decreasing the power consumption of both the by pass fan and the quenching air fan.

Description

IMPROVED KILN GAS BYPASS SYSTEM

IN CEMENT MANUFACTURE

• Technical Field

Cement manufacture . Kiln gas bypass systems .

• Background Art

In cement manufacture, utilizing the dry process, in cases where the raw materials contain undesirable salts such as alkalis, sulphates and chlorides as in the case in Egypt and other countries with little rainfall, this necessitates bypassing a portion of the cement kiln gases, before they enter to the preheater tower, in what is called kiln gas bypass in order to get rid of most of these undesirable salts.

As soon as the gases are extracted from the kiln to the bypass system, they must be quenched to decrease their temperature from about 1000 ⁰C to less than 450 ⁰C as these salts (alkalis, sulphates and chlorides) at 1000 ⁰C are in the gaseous state, and if cooled gradually become sticky at about 700 °C and thus cause clogging on the ducts and routes where they pass through. That is why quenching to less than 450 ⁰C is necessary so that they quickly become non sticky salts which can be easily handled.

At present, the quenching of the bypass gases is done by forcing ambient air in the quenching chamber . This is the practice currently being performed in the cement industry where kiln gas bypass systems are necessary.

The problem of this method of quenching by air is that a large amount of air is needed to quench the bypass gases.

These quenched gases are then passed to the cooling tower, where water is sprayed to further decrease the gas temperature from about 45O⁰C to about 15O⁰C, and then is passed to the dust filter to precipitate the dust from the gases before exiting from the plant stack. So, the larger the volume of the bypassed gases due to the quenching air needed, the lower the efficiency of the dust filter becomes, or in other words the larger a dust filter is needed . DISCLOSURE OF THE INVENTION

The invention is the utilization of water instead of air in quenching the bypass gases in the quenching chamber, i.e. Water quenching instead of air quenching. This has the following advantages :

1) The volume of the water quenched bypass gases is much lower than the volume of the air quenched gases causing a much higher dust filter efficiency. This is explained as follows :

La) One gram of water when heated from ambient temperature, say 30 ⁰C , to 450 ⁰C absorbs about 950 calories as follows :

70 calories (from water at 30 ⁰C, to water at 100 ⁰C) + 540 calories (from water at 100 ⁰C to steam at 100 ⁰C being the latent heat of evaporation) + 350 calories (from steam at 100 ⁰C to steam at 450 ⁰C) . l .b) One gram of air when heated from ambient temperature, say 30 ⁰C, to 450 ⁰C absorbs about 126 calories as follows :

(450 ⁰C - 30⁰C) X 0.3 calorie/ gram air/ ⁰C

From La and l.b , it becomes clear that one gram of water makes the cooling effect of about 7.5 grams of air in absorbing the same amount of heat when heated up from 30°c to 450 ⁰C .

Thus water quenching leads to a much lower quenched gases volume compared to quenching the same gases by air .

2) Increasing the humidity of the quenched gases, this leads to :

2. a) Increasing the efficiency of the electrostatic dust precipitator due to the increase of the gases humidity.

2.b) Decreasing the amount of water needed to be sprayed in the cooling tower, as by water quenching in the quenching chamber we could both reach the desired cooled temperature as well as having the required humidity of the gases needed by the electrostatic dust filter for efficient operation.

This causes less probabilities of having wet bottoms in the cooling tower and thus less kiln stops that may arise to clean up the bottom of the cooling towers. The cooling tower, in some cases, could be completely stopped by making water quenching to the desired temperature for the dust filter. This will save in much of the operation and maintenance costs of the cooling tower.

3) Electric power consumption shall be saved due to decreasing the quenching air fan speed, (or even could be totally stopped) .

Also the bypass system gas fan speed shall be reduced as the total volume of bypass gases is decreased when water quenched compared to the total volume of bypass gases when air quenched. The decrease in the volume of handled gases means decrease in the fan speed and consequently causes less fan power consumption. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1: The bypass gases are taken from a point between the rotary kiln (2) and the preheater tower (1) to the quenching chamber (3) where originally it was quenched by air blown to the quenching chamber by the quenching air fan (11) via a control damper (12) which controls the amount of quenching air. The new invention necessitates installing water sprayers (8) in the quenching chamber fed by water from the water tank (10) and water pump (9) .

The quenched gases (below 450 ⁰C ) are passed through the water cooling tower (4) then to the dust filter (5) usually an electrostatic filter or a bag filter, then by the bypass fan (6) to bypass stack (7) to the atmosphere .

BEST MODE FOR CARRYING OUT THE INVENTION

By installing water sprayers [item (8) of figure 1] in the bypass gases quenching chamber [item (3) of figure 1] . These sprayers can either be connected to the water system of the existing cooling tower or could be fed by a separate water pump [item (11) of figure 1] fed by a separate water tank [item (12) of figure I]. The rate of water sprayed for quenching depends on the rate of gases to be quenched as well as to the desired quenched temperature. • INDUSTRIAL APPLICABILITY

Water quenching instead of air quenching can be industrially applied in cement manufacturing plants utilizing the dry production process and where a bypass system is necessary to bypass some of the kiln gases to get rid of most of the undesirable salts such as alkalis, chlorides and sulphates.

The bypassed kiln gases quenching chamber is to be equipped by water sprayers to achieve the required water quenching .

Claims

1 - Using water instead of air in quenching the bypassed kiln gases would result to a lower quenched gases volume with a higher humidity. This has many advantages in the bypass process system.

2- According to claim 1 Quenching the bypass gases by water instead of air, results in a lower volume of quenched gases (thanks to the high latent heat of evaporation of water) and thus the lower total volume of quenched gases would result in a higher efficiency in the bypass dust collection filter. In most cement plants, bypass dust collection is done by electrostatic filters, the efficiency of their dust collection is inversally proportional to the gas flow rate passing through it.

3- According to claim 1 Quenching the bypass gases by water instead of air, results in more humid quenched gases. When using electrostatic filters for dust collection, the higher the humidity of the gases passing through it, the higher the dust collection efficiency is. - According to claim 1 Quenching the bypass gases by water instead of air results in decreasing the quenching air fan [item (11) in drawing figure 1], and this fan could even be totally stopped. This means that the electric power consumption of this fan is largely decreased or even totally saved.

- According to claim 1 Quenching the bypass gases by water instead of air, results in a lower volume of quenched gases. This results in decreasing the speed of the bypass fan [item (6) in drawing figure I]. This means that electric power consumption is again saved.

- According to claim 1 Quenching the bypass gases by water instead of air, could partially or totally decrease the cooling and humidifying requirements needed from the water cooling tower [item (4) in drawing figure I]. This will cause savings in operational and maintenance costs of the cooling tower as well as decreasing kiln stops that may occur to clean up the wet bottoms of the cooling tower each time they occur.