completed prch project on cement

7/31/2019 Completed PRCH Project on Cement

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PROCESS CHEMISTRY REPORT ON THE

MANUFACTURE OF CEMENT

GROUP MEMBERS: Dexter Bruce

Carlin Sylvester

Junior Joseph


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The Manufacture of Cement

Damian Ortega

TABLE OF CONTENTS

Introduction.Pg. 4

What are cements.Pg. 5

The manufacturing processPg. 6

Limestone excavation

Crushing

Raw milling: Primary & Secondary

Proportioning & Blending

Slurrying

Pyro-processing

Finish grinding

Finish products: Ordinary Portland & Oil-well cements...Pg. 14

By-products and their uses...Pg. 15

Environmental concerns: Manufacture..Pg. 16

Dust & particulate emissions

CO2 emissions

Wastewater/Liquid effluents

Noise pollution

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Environmental concerns: By-productsPg. 18

Control methods: Dust & particulate emissionsPg. 19

Air filtration

Dust screens

Vegetative barriers

Control methods: Wastewater treatmentPg. 20

Future of cement industry locally and abroad..Pg. 21

Illustrations..Pg. 22

Fig. 1 Cement manufacturing process

Fig. 2 Process flow from production to consumption

Fig. 3 Flow diagram of waste recycling

ReferencesPg. 25

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INTRODUCTION

Trinidad Cement Limited (TCL) was incorporated in Trinidad in 1951 and

commenced production in 1954. Through a process of diversification and

expansion, TCL has evolved from a single cement manufacturing operation into

a full-fledged group of companies with operations throughout the Caribbean.

Today, the TCL Group has become the leading producer and distributor of

cement and ready-mix products within the Caribbean. This regional

conglomerate consists of eight subsidiaries operating in Trinidad, Barbados,

Jamaica, Guyana and Anguilla. As such, we have chosen this organization as

the basis for our research and the following treatise that is based upon the

manufacture of the widespread commodity known as Ordinary Portland Cement

(Type 1) and the lesser known but equally important Oil-well Cement.

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Before we proceed any further one must gain a general concept of what are

cements. Cements are finely ground powders that, when mixed with water, set to

form a solid mass. Setting and hardening result from the hydration of the cement

compounds. By the addition of water, the submicroscopic crystals that comprise

cement agglomerate into a gel-like substance with a high surface area. By far,

the most common use of cement and its related by-products can be found within

the sphere of residential, commercial and industrial building construction.

Cements may be used alone (i.e. neat, as grouting materials), but its normal

use is in that of mortar and concrete in which the cement is mixed together with

inert materials known as aggregate.

THE MANUFACTURING PROCESS

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There are three processes by which Portland cement can be manufactured, and

these are known as the wet, dry and semidry processes. TCL uses what is

known in the industry as the wet process technology for the manufacture of

cement. The process derives its name from the fact that the basic raw material,

naturally occurring limestone (CaCO3), is crushed and mixed with water, clay and

other components to form that which is known as slurry. Though more modern

plants utilize dry process technology, TCL is forced to maintain a wet process

owing to the fact that limestone reserves are located in Mayo which is

approximately sixteen kilometers from the cement manufacturing facilities at

Claxton Bay. There are five main stages involved in the manufacture of Portland

cement:

Crushing and grinding of raw materials (Primary milling)

Blending of material in desired proportions (Secondary milling)

Mixing with water (Slurrying)

Pyro-processing (Burning)

Grinding of cement clinker (Finish grinding)

LIMESTONE EXCAVATION

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The quarrying of limestone, the main raw material used in the production of

cement, is the first step in the manufacturing process. TCL acquires limestone

from its very own quarry located at Mayo in Central Trinidad. This quarry is home

to one of three major deposits of yellow or impure limestone located in Trinidad

and Tobago. It has been estimated that these deposits can viably sustain TCLs

current production rates for approximately two hundred years. Traditionally, the

limestone was obtained by blasting which involved the use of explosives. Today,

a heightened degree of environmental awareness coupled with a renewed

consideration of the growing Mayo community with respect to noise pollution,

has led them to review their methods. Limestone is now excavated from the

earth via the use of one of the largest tractor rippers in the Caribbean, the

Caterpillar D11R.

CRUSHING

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After the process of excavation, the limestone in the form of large boulders is

transported from the excavation site to the Hazemag impact crusher. Located

within the quarry at Mayo, the crusher possesses the capacity to process 530

tonnes of raw material per hour. The crushing process serves to reduce the raw

limestone to an average size of 25mm in preparation for the process of primary

and secondary milling. Following this, the limestone is then separated according

to high or low carbon content and subsequently transported via conveyor to a

large storage and containment area.

RAW MILLING: Primary & Secondary

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In the next stage of cement production, the crushed limestone particles are

extracted from storage and transported by conveyor to the Primary Grinding Mill.

At this point the particles undergo a drastic reduction in size. The material is

ground upon a rotating table via the use of heavy, wheel-type rollers from its

previous size of 25mm to approximately 90m (micron).

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There are additional raw materials which are used in the production of Portland

cements to impart various physical and chemical characteristics, these include:

Lime (CaO)

Silica (SiO2)

Alumina (Al2O3)

Iron Oxide (Fe2O3)

They are obtained from naturally occurring materials as well other industrial by-

products. These components after being analysed in the laboratory are blended

together in the correct proportions and added to the limestone. Following this,

the mixture undergoes what is known as Secondary Milling in which it is ground

even further into a powder-like form. Based on the silica content of the raw

material, it is sometimes necessary to add sand in the grinding process; the sand

used being acquired from TCLs own quarry.

SLURRYING

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After secondary milling of the components to acquire the powdered form, water

is added. The resulting mixture, a viscous mass of limestone, water, sand and

other components is known as slurry. The slurry is stored in one of two tanks at

the Mayo quarry, from which it is pumped via pipeline from Mayo to TCLs

processing plant located at Claxton Bay, into large concrete storage tanks

commonly known as slurry basins. At this juncture, it is constantly agitated by

compressed air and revolving mechanical paddles to prevent sedimentation.

The slurry is transported to Claxton Bay through a continuous pipeline measuring

10-inches in diameter and approximately 9 miles in length. The slurry leaving

Mayo for Claxton Bay must be of a high and consistent quality. Any slurry that

does not meet the stringent quality requirements is adjusted and recycled until

the correct composition and consistency has been achieved. The slurry, which

contains 35 to 45 percent water is sometimes filtered, reducing the water content

to 20 to 30 percent as this has the effect of reducing the fuel consumption in the

subsequent step of production known as pyro-processing or burning.

PYRO-PROCESSING

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In this stage of cement production, the slurry is pumped from the basins and into

rotary kilns which are basically long, revolving, steel cylinders lined with

refractory bricks. Refractory bricks form an insulative barrier around the kiln shell

and serve to protect the kiln against relatively high temperatures. The kilns

themselves may measure up to 200m in length as well as 7m in diameter. In TCL

the largest of the kilns is 145m long and 5m in diameter. The company has two

kilns with a combined production capacity of 2160 tonnes per day. TCLs kilns

are fueled by natural gas supplied by the National Gas Company (NGC).The kiln rotates slowly on an axis that is inclined at a few degrees to the

horizontal. As this occurs, the raw feed is introduced at the upper end and moves

slowly down the kiln to the lower or firing end. In the early stage of burning, the

slurry is dried off at a temperature of approximately 230 0C while at the burning

end, the temperature ranges from 1300 0C to 1500 0C. The burned product,

known as clinker emerges from the kiln as small nodules that pass into coolers

where the incoming air is heated and the product cooled. The chemical

equations for the production of clinker are of the following forms:

3CaCO3 +SiO2 + Heat---- Ca3SiO5 + 3CO2

9CaCO3 + Al2SiO5 (OH) 4 + Heat ---- Ca3Al2O6 + 2Ca3SiO5 + 9CO2 + 2H2O

FINISH GRINDING

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In the final stage of production, the clinker nodules along with the required

amount of gypsum are ground to a fine powder in a horizontal mill similar to the

one used for grinding of the raw materials. Gypsum is added in order to delay the

setting and hardening time of the cement. The clinker may pass straight through

the mill (open-circuit grinding), or coarser material may be separated from the

ground product and recycled to the mill for further grinding (closed-circuit

grinding). The finished product is pumped pneumatically into large storage silos

from which it can be withdrawn for packaging or for dispatch in bulk containers .

FINISHED PRODUCTS

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Ordinary Portland Cement (Type 1)

Since concrete is the most widely used of all construction materials, the

production of Ordinary Portland cement is widespread with current global

production being within the vicinity of 2000 million metric tonnes annually. The

second main product derived from this type of cement is known as mortar. These

two names are used interchangeably by many even though the structural

makeup of each is very much different to the other. Mortar is cement that has

been mixed with sand or crushed stone (gravel) that must be less than 3/16

(5mm) in size, whereas concrete is a mixture of cement and crushed stone up to

1 (2.5cm) in size. Mortars are used for the binding of bricks, blocks and stone in

walls, while concrete is mainly used as a base construction product, such as in

the creation of structural foundations.

Oil-well Cements

These types of cements are used for cementing work in the drilling of oil wells

where they are subject to high temperatures and pressures. They usually consist

of Portland or pozzolanic cements with special organic retarders to prevent

premature setting. When added to Portland cements, pozzolanic materials have

the effect of greatly increasing the long-term strength and mechanical properties.

BY-PRODUCTS AND THEIR USES

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The products that can be derived from cement are seemingly endless. Without a

doubt, its main use continues to be in the manufacture of bricks and a testament

to this fact is the current construction boom taking place in faraway lands such

as Dubai, China, India and Brazil, as well as within our twin island state of

Trinidad and Tobago. Cements are also used:

In the manufacture of tiles as a binding agent.

In the production of decorative fixtures and moldings.

As a fireproofing material.

As a sealant to protect iron and steel structures from water and air

corrosion.

For the foundations of heavy machinery, bridge piers, walks, waterworks

dams and reservoir walls, dry-docks, culverts, etc.

To produce re-enforced and pre-stressed concrete (it is used in

conjunction with iron bars and wire meshing which add strength and

flexibility).

As a grouting material (by adding pigments, different colours can be

obtained)

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ENVIRONMENTAL CONCERNS MANUFACTURE

As most cement manufacturers do, TCL faces never-ending challenges in its

attempts to control dust during extraction and processing. Operations such as

quarrying, loading, transportation, and mobile crushing typically don't lend

themselves to integrated suppression techniques, yet all of these add to the

potential for releasing vast amounts of dust. Additional concerns but no less

important are those relating to noise and water pollution.

Dust and Particulate Emissions

As was mentioned previously, the main bone of contention with respect to TCLs

entire operation continues to be that of dust and particulate emissions. According

to HSE Manager Amarchandra Maharaj, there arose greater need to do more to

control the dust emissions generated as a result of the companys operations,

since past methods of dust control such as watering with hoses and sprinklers

have become obsolete. The primary target for improving dust suppression at

TCL is the mobile crushing unit. Other contributors to the emissions produced by

cement production are the milling and finish grinding stages, both of which add

significantly to the problems experienced by employees of TCL as well as

residents within the immediate vicinity of the plant.

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CO2 Emissions

The manufacture of cement contributes to greenhouse gases both directly

through the production of carbon dioxide when calcium carbonate is thermally

decomposed, producing lime and carbon dioxide, and also through the use of

energy, particularly from the combustion of natural gas, the fuel used. It is

estimated that 75-175 kg of CO2 is produced for each tonne of concrete

manufactured, with approximately 50% of it being produced as a result of the

chemical process and 40% via the combustion of fuel.

Wastewater/Liquid effluents

Because of the nature of the wastewater effluent generated by the cement

manufacturing process, it would be detrimental to both the aquatic life as well as

farmers who depend on watercourses for crop irrigation to release this effluent

without their consideration. This generally emanates from the slurrying process

in addition to other washing operations that take place throughout the plant.

Noise Pollution

Most of the noise produced is as a direct result of the heavy machinery involved

in the various processes, in particular the crushing and milling operations. In the

past limestone was extracted via the process of dynamiting, but repeated

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http://en.wikipedia.org/wiki/Calcium_carbonatehttp://en.wikipedia.org/wiki/Lime_(material)http://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Calcium_carbonatehttp://en.wikipedia.org/wiki/Lime_(material)http://en.wikipedia.org/wiki/Carbon_dioxide


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complaints by the immediate residents to the authorities led to TCL adopting a

safer approach by the introduction of heavy quarrying equipment.

ENVIRONMENTAL CONCERNS BY-PRODUCTS

As it was previously mentioned, the main concern with respect to cement

production is dust and particulate emissions and this is no different when it

comes to its related by-products. Since a large percentage of cement goes into

the manufacture of bricks, it is inevitable that some form of pollution will occur

during its production. Known as fugitive emissions, these may take the form of

cement released during the transfer of the product from the supplier to the

customer as well as from the mixing and blending operations of the

manufacturer.

Major contributors to these problems are also construction sites that are

improperly washed down, as the cement particles can inadvertently pollute

watercourses thereby causing them to become acidic as result of the suspended

colloidal particles. With respect to drilling companies, improper well cementing

techniques can result in sea pollution, and hence affects the aquatic marine life.

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CONTROL METHODS

Dust and Particulate Emissions

Air Filtration

As recently as the year 2009, TCL has installed a new system of airborne

particulate emission control known as the Dust Boss DB-60. This system has

been implemented in compliance with ISO 14001: 2004 standards as well as

Trinidad and Tobagos OSH Act and basically controls the dust emitted by the

crushing and transportation aspects of the cement manufacturing process.

Another method of dust control implemented by TCL includes the use of

electrostatic precipitators (ESPs) which filter the air and flue gas streams

generated in order to remove the fine dust and smoke particles within them.

These devices are located at strategic locations throughout the plant to collect

these harmful emissions.

Dust Screens

These are basically heavy duty mesh fabrics spread on horizontally mounted

steel frames that minimize the dust escaping from the various plant locations.

Vegetative Barriers

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Natural vegetation such as trees has been planted around the location in order to

reduce the amount of dust that affects the surrounding residents. They are also

extremely effective in aiding in the reduction of CO2 levels.

Wastewater Treatment

For this purpose, TCL has excavated gravity settling ponds in order to allow for

the sedimentation of the particles produced by the various stages of the

manufacturing process. The effectiveness of these ponds depends on an array

of factors such as:

Detention time of the wastewater.

Size and density of the suspended solids.

Temperature and viscosity of the water.

Turbulence as a result of wind.

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FUTURE OF THE CEMENT INDUSTRY LOCALLY &

ABROAD

Due to an ever-increasing construction and industrialization drive worldwide, the

production of cement has reached staggering proportions. Within Trinidad and

Tobago, due to the vast amounts of limestone available it has been estimated

that the production of cement is economically viable for at least two hundred

years. This has placed TCL in an enviable position as the largest manufacturer

and supplier of cement regionally, capable of adequately satisfying the needs of

our Caribbean neighbours.

In a global context, the monumental structures being erected in diverse lands

such as the Burg Al Arab in Dubai, the proposed Belo Monte Dam in Brazil and

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the National Academy of Performing Arts in Trinidad have only been made

possible through the use of cement and its derivatives. Once this desire for

progress remains there will always be a host of organizations such as Trinidad

Cement Limited, available to take up the mantle and keep this appetite satiated.

ILLUSTRATIONS

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Figure 1 showing the cement manufacturing process.

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Figure 2 showing the process flow from production to consumption.

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REFERENCES

www.cement.org/waste

en.wikipedia.org/wiki/Portland_cement

www.patentstorm.us/patents

www.cement.org/tech/cct_images

www.tclgroup.com

en.wikipedia.org/wiki/Electrostatic_precipitator

www.ceratechinc.com/cement.asp

Britannica encyclopaedia

Class notes
http://www.cement.org/waste/http://www.patentstorm.us/patentshttp://www.cement.org/tech/cct_imageshttp://www.tclgroup.com/http://www.ceratechinc.com/cement.asphttp://www.cement.org/waste/http://www.patentstorm.us/patentshttp://www.cement.org/tech/cct_imageshttp://www.tclgroup.com/http://www.ceratechinc.com/cement.asp

completed prch project on cement

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