Several parameters and conditions should be taken into consideration when selecting the equipment and systems to be installed in a cement plant. The requirements of the cement manufacturing machinery vary from one region to another and depend not only on the climatological conditions of the area, but also on the situation of each particular market. In other words, when talking about the trends in the use of specific equipment or system, we need to analyze the situation and trends of that market.

To analyze the Latin American cement market, three important aspects need to be taken into consideration:

* Latin America clearly reflects a positive correlation between cement consumption and income.

* Cement consumption and population density in Latin America also are linearly correlated, supporting the theory that the greater concentration of people, the greater their need for construction.

* In 1997, the total installed capacity of Latin America reached 166.2 million mt, and had an average utilization rate of 69%. Most countries in the region have high population densities and are on the right path for economic recovery after the Tequila crisis of 1995. All this will lead to an average capacity utilization of around 85% by the year 2000, despite an expected annual 6% plant increase.

According to these points, one could conclude that Latin America is facing the new century with a great optimism, and it is hoped that an increase in regional cement consumption will occur. This has obliged most of the cement companies in Latin America to upgrade their production and dispatch systems to reduce the total production costs and be more competitive. It is important to point out that most of the dispatch systems were installed during the 1970s' cement boom, so some installations are obsolete for the requirements of this millennium.

What follows not only describes the selecting and dimensioning criteria of the cement dispatch terminals, but also the different equipment and systems recently developed for the operation of these terminals.

Dispatch in bulk or bags The cement markets in Latin America are typically consumer orientated because the majority of cement (often close to 80%) is sold in bag form, and brand loyalty often plays a role. Bulk cement, which is typically exported, is largely purchased by concrete producers, however, the major concrete suppliers in Latin America are usually owned by the cement producers. This situation is exactly the reverse in Europe and North America. The do-it-yourself and small contractor builders who operate with very basic and unsophisticated construction methods are part of the explanation.

The high percentage of cement sold in bags has obliged most of the cement plants in Latin America to install automatic bags and palletizer equipment.

Originally the bags were distributed with a standard capacity of 50 kg. However, as an answer to the local market, the use of 25-kg bags has been increased. On some islands in the Caribbean, the use of 21.4-kg bags is becoming popular.

Several companies have expanded their operations to other regions by exporting clinker. This allows for the production of cement close to the consumption centers, keeping investment and operational costs low. However, the transportation of clinker requires special equipment to avoid the emission of dust and to resist the high abrasion of this product.

Dispatch by land or sea As mentioned, about 80% of the cement produced in Latin America is dispatched locally in bags. This product is generally brought to distribution centers by trucks. It is important to point out that the use of a railway in Latin America, with a few exceptions, is not common, since most of the countries have neither an efficient railway network, nor appropriate logistic requirements.

Some cement plants located near the coasts have taken advantage of their location to deliver the cement by sea. This trend has been observed mainly in the Caribbean countries, where the cement is transported in small-sized ships from the plant to storage, packing, and distribution centers strategically located along their coasts. Since in some cases the use of trucks is very costly and risky, being able to transport small quantities of product via sea has become more important.

A dispatch facility is designed and dimensioned according to the requirements of each particular country and market. BMH has adapted the design of its dispatch systems and equipment to fulfill present and future regional market requirements. The equipment can be employed either for new constructions or for upgrade installations, the most common case in Latin America.

Several parameters should be considered for designing and choosing the optimum cement dispatch terminal. In the following sections, the criteria normally employed by BMH for selecting and dimensioning the appropriate dispatch terminal system will be described, for either land or sea.

Cement storage system Basically the configuration of the transit storage system will define the final design of the dispatch terminal, as well as the general arrangement of the equipment needed to dispatch the material either in bulk or bags. In Figure 1, the main storage systems commonly used are shown.

Generally, the selection of any of the storage systems will depend on the following parameters:

* Available area for the construction of the storage system This parameter basically will determine the main dimensions of the storage system.

* Total required storage capacity This parameter together with the available area determines the main dimensions of the storage system. The storage capacity is calculated based upon the total production capacity of the plant. Some experts recommend that the storage capacity be equivalent to three production days. The trend, however, is to have a storage capacity for five production days.

* Soil conditions Depending on the available area and the dimensions of the required storage capacity, this parameter will determine the maximum soil permissible of loads.

* Underground water level This parameter limits the discharge system to be used.

* Dispatch method Dispatch directly to trucks or any other system.

* Total dispatch capacity per hour.

* Height limitations and local regulations.

Silos This system is the most common storage system used in the cement industry. The area to be used for the construction of a silo is less than what is required by other storage systems with the same capacity. The silos have a high efficiency and the dispatch of the material is usually easy. The cement normally is fed through the upper part of the silo, which in some cases could be considered a disadvantage. The main storage silos used in the cement industry are:

Multi Extraction (ME)-Figure 2

* Central cone;

* Silo diam: 10 to 30 meters;

* Discharge capacity: 1,000+ mtph;

* Between 3 to 9 discharge points;

* Recollection hopper; and

* Capacity to 30,000 cu meters.

Expansion Chamber (EC)-Figure 3

* Expansion chamber technology;

* Silo diam: 10 to 30 meters;

* Discharge capacity: 1,000+ mtph;

* One central discharge; and

* Capacity to 30,000 cu meters.

Inspection Chamber (IC)-Figure 4

* Expansion chamber with integrated inspection camera;

* Silo diam: 10 to 30 meters;

* Discharge capacity: 1,000+ mtph;

* Between 2 to 4 discharge points; and

* Capacity to 30,000 cu meters.

Multi-cell Silo (MS)-Figure 5

* Combine the technology of different silos (ME, EC, IC); and

* Capacity to 40,000 cu meters.

The selection of the optimum storage silo then will be a direct consequence of the production process to be used by the plant:

* The multi-cell silo or several unicellular silos are used when the mill is carried out separately. In this case, the additives will be stored in each cell or silo to be mixed in a mixing plant, either through a batch system or a continuous system, before dispatching the final product.

* When additives are used in the mill, it is possible to use a multi-cell silo or several unicellular silos, but only for storing different types of cement. In this case, the use of a mixing plant is not required.

In either case, the final cement is conveyed either to the packing plant or to the truck dispatch system, preferably using an aeroslide system. This way, the final uniformity of the mixture can be assured.

Flat storage A flat storage represents a low-cost solution, especially for temporary operations or in cases where it is possible to modify an existing building. The flat storage is an ideal solution in cases when there are height or weight restrictions due to soil conditions. The capacity of the flat storage ranges between 10,000 and 25,000 mt. A flat storage can be constructed using pre-built structures manufactured of steel and concrete walls (Figure 6).

One limitation of flat storage is that it is possible to store the final product only to be dispatched and not to mix materials or to add any kind of additive. Consequently, when this type of storage system is used the preparation of final product process requires additives be introduced at the mill.

Since the filling system has to guarantee that the flat storage has been filled uniformly, the filling system is the most important part of this storage method. The filling of the flat storage is normally achieved by means of aerosides and pneumatic pipes in combination with screw pumps. A network of pipes and aeroslides suspended from the storage roof carries out the uniform distribution of the product inside the flat storage.

The reclaiming of the cement can be carried out two ways: using a front-end loader, which pushes the material through a hopper usually located in one of the corners of the flat storage. The second, more sophisticated reclaiming system uses aeration panels, with certain inclination angles, located strategically in the bottom of the flat storage. This system normally is combined with mechanical conveying equipment such as screw conveyors or bucket elevators.

One important advantage of this system is that the storage capacity can be expanded when needed by enlarging the building.

Domes Domes are capable of storing as much as 100,000 cu meters in a maximum diameter of 70 meters. The concrete dome has several advantages:

* Speed and efficiency of construction process.

* Many locations have poor or unstable soil conditions. The dome's foundation needs are generally simple compared to those of silos. Using a spread footing often eliminates or reduces the number of pilings needed to support the structure. The ring beam or tension ring supports the dome at its base while the dome's three-dimensional curve gives it strength.

* The dome's inherent strength allows heavy loads to be placed on the its apex without external supports.

* The dome requires no internal supports.

* As the dome is typically filled by conveying material from the top of the dome and dropping it through one or more fill openings, the product can be piled high against the dome walls. This means that a higher percentage of the dome's volume is utilized than in the case with flat structures, resulting in a corresponding lower cost per ton of storage.

The reclaiming of the product can be carried out two ways, either by several rings of aeration panels, with certain inclination angles, located strategically at the bottom of the dome or flat storage, or by means of mechanical discharge systems. One of the most common mechanical reclaiming systems in domes is comprised of a screw conveyor located in the center of the dome, which conveys the product to the center of the dome. Another recently developed mechanical reclaiming system is known as Bulk Reclaimer Pivot Type (Figure 7).

As with flat storage, domes have the limitation that it is possible to store the final product only to be dispatched, making it impossible to mix materials or to include any kind of additive. Consequently when this type of storage system is used, the preparation of final product process is limited to add the additives in the mill.

After defining the storage system to be used, the total amount of cement to be dispatched per hour, and the percentage of material to be dispatched in bulk and in bags, it will be possible to determine the dimensions and equipment to be used for the final dispatch of the product.

Part 2 of this series examines Latin America's approach to dispatching in bags and bulk, packing plants, palletizers, marine terminals, and loading equipment.