Manufacturing process flow
1. Quarrying and Crushing
The quarry (where the mining activity is performed) is located 0.7 km away from the plant and has the main raw materials such as Limestone and shale that is estimated to last for 100 years , the other raw materials(Iron ore , silica sand ,gypsum and pozzolana(pumice) ) are brought from near by places. Limestone provides calcium oxide and some of the other oxides, while shale and the other materials (silica sand, iron ore) provide most of the silicon, aluminum and iron oxide required for the manufacture of Portland cement. Gypsum and Pozzolana are going to be used for final cement grinding with clinker produced from kiln.
A few meters away from the quarry there is one FLS hammer crusher which can crush 550ton/hour.The crusher reduces 85% of the rock lumps from a 2meter size down to less than 25mm.
2. Raw Material Preparation
In messebo cement factory there is closed longitudinal material storage hall with 342x35meter area used to store all the raw materials mentioned above.
There were originally about 7 piles and now 9 piles (limestone additive and Pozzolana piles added).One common stacker is used for stacking the 9 raw materials which have been crushed in the crusher. limestone and shale which need homogenizing effect are stacked after Chevron method of stacking and the other piles which need no homogenization effect are stacked after cone shell method.
Two separate Reclaimers one for limestone and the other for shale are installed to homogenize the particulate materials and to convey the homogenized material from the piles to the outgoing conveyor. Silica sand and iron ore are loaded by loader on the hopper which beneath it has a conveyor that discharges them to the outgoing belt conveyor.
Gypsum, limestone additive and pumice are brought to the cement mill by loader
In this department four intermediate bins for limestone, shale, silica sand and iron ore storage are placed. Beneath each bin there are dosimat feeders which adjust their speed according to the signal given from the QCX software from the laboratory, in this way the raw materials are proportioned in order to satisfy the final chemistry requirement.
That is the chemistry of each raw materials analyzed by X-ray analysis is fed to the software, based on this the software will calculate the proportioning in percent of mass of the raw materials, this will be sent to automated system and this system will give the proportioning signal to each dosimats, each dosimats will then vary their speed based on the load sensed by the load cell positioned there. Every hour, samples (accumulated at sampler for continuous one hour) from raw mill product will be analyzed and fed to the software to correct any deviation (from the set point inserted in the computer) that may occur due to different reasons. Therefore the system does not allow big chemistry fluctuation that may have a negative effect in burning the raw meal at kiln.
4.Raw Material Grinding
The raw material grinding system is equipped with a ball mill (diameter = 5m, drying chamber length=2.2 and grinding chamber length=8.22m). The nominal capacity of the mill is 180t/h, the fineness of the product is 10% residual on 90μm sieve and moisture content in the raw meal is less than 1%. In Messebo cement factory the exhaust gas from pre-heater is used to dry the raw materials from average moisture content of 4% to less than 1% in the raw meal.
As mentioned above there are four feeding bins in raw material proportioning station (limestone bin, Shale bin, sand stone bin and iron ore bin).
The four kinds of raw materials are fed to a common belt conveyor according to the pre-set proptioning ratios by corresponding weighing feeder (dosimat feeder). Then the raw material on the conveyor is fed to the ball mill. In the raw mill drying and grinding take place and the very fine materials will go with the air as separation air and the Coarse ones go to the air slide at the outlet of the mill then to bucket elevator and then finally to the separator through an air slide.
The ground material is then classified by a sepax separator. The coarse part is returned to the mill for further grinding and the fine part as product is carried out with the gas and collected (separated) by two cyclone separators. The pre-dedusted gas is vented out and sent to some recirculated as separation air and some to the Electrostatic precipitator for further clean up and sent to the environment then after.
The raw meal collected by the two cyclones is transported to the raw meal homogenization silo (CF silo, or controlled flow silo) by and air slide and elevator.
Meal Homogenizing and kiln feeding System
Kiln feeding system is mainly comprised of CF-silo and LOW (loss of weight) unit .CF-silo is for raw meal storage and homogenizing. Kiln feed measuring is mainly accomplished by LOW system.
There are 7 extraction holes(A,B,C,D,E,F,G)at the bottom of CF-silo.3 main rotary blowers and one standby blower(Local PLC, programmable logic control),will alternatively aerate 3 segments placed at 3 different extraction holes, and simultaneously material is extracted from these 3 outlet holes.
Different extraction rates have the effect that the layers are offset during the sinking process in the silo, so that layers with different chemical compositions leave the silo simultaneously. Hence the chemical fluctuations in the discharge flow are considerably reduced relative to the fluctuations in the feline flow and the sintering in the kiln is thus kept stable.
7 extraction holes(A,B,C,D,E,F,G) at the bottom of the silo, except for the central hole(A) which is directly connected with the underlying blending tank , the rest of holes are joined with blending tank through one air slide each. The extracted material enters into the LOW hopper via blending tank through those air slides.
Under the LOW hopper, there are two extraction outlets (A and B. B is for spare use). One pneumatic shut off gate and one motorized gate are installed on each outlet. One rotary blower on each gate aerates the extraction area at the bottom of LOW hopper. Three load cells are provided at the bottom of LOW hopper, which are used to measure the material weight in the hopper. Kiln feed control is fulfilled by measuring the reduced material quantity in the hopper within a certain period of time(during emptying period) and mathematical model during filling period.
The adjustable (motorized gate) is controlled by signal from the PLC, the load cells in the tank, and set values for the feed rate from the operator at CCR.
Metered kiln feed is conveyed to the top of the pre-heater by an air slide and then by two air- lift blowers.
6. The waste Gas
Whenever the kiln is in normal operation and raw mill is stopped, the exhaust gases induced by ID fan are cooled by Gas conditioning tower(GCT) to around 150-160oC .If both kiln and raw mill are in operation, hot gases are supplied to the raw mill for drying purposes. Gases not used in the raw mill are passing the GCT and joining the gases from the raw mill, whereafter the entire gas flow is de-dedusted in the raw mill/kiln ESP.
The dust precipitated in the raw mill/kiln filter installation is returned to either the CF-silo or pre-heater.
The cooler excess air is de-dusted in a separate Electro static precipitator specially designed for clinker dust. The recuperated dust is returned to the clinker transport system.
7. Clinker Burning and
The kiln burning system is composed of a Φ3.75x57m with inline calciner (ILC precalciner) and a single five stage preheater. The kiln system is designed for 2000t/day but is now running b/n 2000- 2500t/day after some optimization works. The average specific heat consumption of the system is 710-750kcal/kg clinker. After the raw meal is preheated in pre-heater stage cyclone 1 to 5 and precalcined in precalciner, the CaCo3 calcining rate in the kiln inlet can reach 95%. The remaining 5% of the calcinations and clinkerization process will be taken place inside kiln. The ratio of firing fuel burned in the kiln for clinkerization and the precalciner is 4:6.
A grate cooler is applied to clinker cooling by cooler fans. The clinker getting out of the cooler is comminuted by the built in hammer crusher and then carried to clinker storage by means of bucket (pan) conveyor. The exit gas from the cooler partly goes to kiln as secondary air and partly to calciner as tertiary air. The surplus part is emitted to the atmosphere after cleaned by a cooler EP.
A clinker storage silo with capacity of 15000tons and an open yard with capacity of 20000tons are built up in the plant. Under the clinker silo, the rod gate and the motorized discharging gate are installed. The clinker discharged by these equipment is fed to different belt conveyors correspondingly, then carried to the clinker feed bin in cement grinding plant b means of belt conveyor.
9. Cement Grinding
A closed circuit grinding system is applied. The main equipment consists of a 4.6x12m double compartment tube mill and a sepax separator. This mill at this time produces two types of cement namely Ordinary Portland Cement (OPC) and Pozzolana Portland Cement (PPC).
OPC comprises 90%clinker, 5%additive (limestone) and 5 %( gypsum). PPC comprises 70% of clinker, 25-29%% pozzolana and 5%gypsum.
The design capacity of the mill is 120t/h for OPC cement. But currently it is working upto 120-135t/h for OPC and 135- 150 t/h on PPC. Specific surface of the product is 2800cm2/g to 3000cm2/g.
The clinker, additive (limestone, pozzolana) and gypsum are fed by the corresponding belt weighing feeders (dosimat feeders), to a common belt conveyor then the belt conveyor feed them to the tube mill.
The ground material is carried to the sepax rotor via air slides and a bucket elevator. The separator will classify the ground material into two parts – the course and the fine (product).The coarse material is fed back to the tube mill via the air slides. The product from the separator is carried to a cyclone by means of gas stream and is collected by it. Most of the air leaving the cyclones is recycled to the sepax separator, the remaining air is cleaned in a bag filter before being released to the atmosphere via the chimney. Product as cement is conveyed to cement silos via air slides, belt conveyor, screw conveyor and a bucket elevator.
10. Cement Storage
Two Φ16m concrete silos are setup as cement storage facilities; each of them has a storage capacity of 10,000ton
Air ducts are erected on the bottom of the silo for aeration of the cement for fluidization. The air is supplied to these ducts by root blowers.
On a bottom of each cement silo a discharging unit consists of a manual gate and a pneumatic flow control gate. The discharge from these gates is transported to the cement packing system via air slides and bucket elevator. Connecting with the discharging units, there is bulk loader for both silos installed for loading the bulk cement to the Lorries.
The cement flow rate to the loader can be controlled by a flow control gate, which is mounted beside the discharging unit.
11. Cement Packing
The packing line of products in powder form is equipped with different elements/machines.
The principal elements of the packing line are
1) Vibrating screen
2) Feed hopper
3) Rotary feeder
4) Packing machine
5) Discharge belt
The vibrating screen is designed to act as a filter in order to avoid the introduction of lumps in the productive cycle. It is connected, by means of bellow elastic chute, to the feed hopper.
The feeder hopper consents to dose the product and to guarantee its constant presence, when it is requested.
The actual dosing is performed by a butter fly valve and by an appropriate vane feeder whose capacity is checked.
The heart of the packing line is the bag packer and is equipped with a storage hopper connected to different cones depending on the number of spouts the packer is equipped with(8 spouts in our case).
The task of the packer is to fill, following some programmable cycles, the bags with the available product.
Each spout is independent from the other and they are all controlled by appropriate electronic units (VENTODIGIT)
The electronic units control the performance at the filling, weighing and the bag discharging.
Messebo has two such packers each having a capacity of 2500bags per hour, which together could on average dispatch 30,000 quintal cement per day.
Flow of material in the packing plant
The flow of material rises from the bucket elevator to reach the vibrating screen, where is screened, to be settled in the storage hopper. The former is equipped with control systems (called sensors) placed inside the hopper. These sensors control the extraction system and keep the level as steady as possible.
Then the flow of material passes through the rotary vane feeder equipped with alternate gear to adjust the level of material in the packer hopper. The sensor, by which the bag packer is equipped, serves the purpose of checking the rotary vane feeder in order to keep the level as steady as possible. The flow of material is in then directed to the spouts: most part of it is packed in the bag, whereas a very small of scraps, in the form of dust, overflows. The dust is sucked up and collected, by means of a sucking chute, in the lower hopper. The reject is then separated: the dust is gathered by a screw conveyor and led back into the conveying cycle.
The packed bag cement is sent out and guided to the bag cleaner and bag cutter (for those less than 50kg) by means of belt conveyor. The cleaned bags are carried by a roller conveyor and a belt conveyor to truck loaders conveyor, and then loader or trucks.
The weight tolerance of bagged cement is guaranteed by the automatic control system.
Process flow and Quality Check
The quality check of the process is continues throughout the whale process line .In which the time interval and each work-in-process products are checked for the achievement of the quality standard sated
Quality Policy of Messebo Cement
Messebo Cement Factory is committed to continuously produce cement in accordance with national and international standards.
Messebo is also committed to develop, establish and maintain quality management system as per requirements of ISO.
We will respond quickly and effectively to fulfill customers requirements to be the best of our ability.
We will review critically but constructively the usual way of doing things for potential improvement in our quality Management system.
We shall adhere to the following values in our day-to-day operations.
Guarding against errors and learning from experience will be our important principle .
The principle of integrity, transparency, impartiality ,diligence and dependability will be adhered to in all spheres of activity
Keeping the work environment human friendly by adopting rules of safety