基于YQP36預(yù)加水盤(pán)式成球機(jī)設(shè)計(jì)帶CAD圖
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Feasibility study requirements for a new cement plant
R.Hogg, D Frame and M.E. Asim, WS Atkins Consultants, UK, discuss the theory and practice of undertaking large cement plant projects.
FOR SPANISH AND FRENCH VERSIONS PLEASE REFER TO THE SPECIAL TRANSLATED SECTION AT THE BACK OF THE ISSUE
Introduction
The decision to start the construction of an entirely new cement plant facility, or a major capacity extension at an existing cement works, should always be based on a detailed techno-economic feasibility study. Such a study will indicate to the promoter the viability of the business in terms of the best technical solution, the overall capital and operating casts, the magnitude of the operation in terms of production and workforce needed, and the return on his investment over a period of time.
A typical feasibility study deals with the following issues:
Marketing study.
Raw materials proving.
Site studies.
Conceptual engineering and process design.
Analysis of alternatives.
Project cost including infrastructure.
Project schedule.
Investment analysis, risk assessment, development of financial structures.
Project finance.
Discussion with financing institutions.
Whilst any feasibility study must include technical aspects, it is important to realize the full implications of marketing research and accurate financial projections.
Pro-feasibility study
In order to minimize front end expenditure and to quickly obtain a firm indication of the likely project viability, a pre-feasibility study is performed.
The pre-feasibility study is carried out at low cost, but in sufficient detail to show whether a full feasibility study is justified. The pre-feasibility study will examine the market place, the raw materials, capital and operating costs, and develop a business plan to show the likely returns on the investment, and identify the risks and scale of operation involved.
Typically this exercise will take four to six weeks to complete, commencing with a site visit. However, the study is largely performed by desk research and reference to the in-house date base. The site visit is used to determine the suitability of raw materials for cement manufacture, local building and civil engineering costs, cost of land and peculiarities of the particular site location, and local cost of consumables required in the operation of the plant. The desk research concentrates upon current plant and machinery costs, financial and marketing considerations and preliminary plant sizing and determination of the process route.
In the event of the pre-feasibility study showing a clear indication that it is worthwhile to proceed with the project, then a full feasibility study can be initiated.
Full feasibility study
Market research
The objective of the market study is to establish the demand for the various types of cement in the context of the region or market area of the proposed plant. The study seeks to establish the current and forecast cement usage over a 5-7 year period. The forecast is then used together with the indicated selling prices to generate the likely revenue stream for the proposed operation.
The consultant must have considerable experience in the global cement industry and be able to approach a feasibility study with an excellent knowledge of prevailing market conditions and likely trends. Each individual company and market does, however, present a unique set of circumstances which must be fully understood. The normal approach adopted is first to study the company and identify its strengths and weaknesses, strategic direction and motivation. This is essential in providing an immediate picture of the company’s likely success in achieving its aims.
The second stage of the marketing survey, desk research, puts the initial discussions into context by examining a wide range of published data relevant to the industry.
Sources of published data are collated and compared by a team of researchers and consultants in an operation to substantiate known trends and uncover new information. It is not sufficient to rely on information several months old, and without an international perspective, trends in cement production and demand are frequently misleading.
Collecting published data is an on-going process, but having established a background to the study, information should, where possible, be verified using independent sources with firsthand accounts of the industry and its outlook. Companies, government organisations and other industry associations are often willing to provide their own assessment lf markets, but care needs to be taken not to compromise any party prepared to give its view.
Armed with a comprehensive selection of published data and industry opinion, the job of the consultant at this stage is to accurately define not only the market size for a particular product, but the likely change in that market. Such changes are often predicted by historic relationships between, for instance GDP and overall construction activity; economic growth and housing starts of cement consumption and population size. Figure 1 illustrates this point. Without taking into account subjective opinion and recognizing changing user requirements for different cement types, such forecasts can be flawed. Analysis of such factors is particularly important in lesser developed countries where impressive growth rates can change the balance of construction activity over remarkably short periods of time.
Other economic information likely to have a bearing on the market are government tariffs, import duties and sector subsidies. Even in free market areas, many aspects of economies are regarded as being of strategic importance and governments frequently strive to preserve national interests wherever possible by fixing prices of imposing import tariffs. Should import tariffs be relaxed of prices allowed to move in line with supply and demand, there will be an appreciable change in the market conditions. National companies, for instance, might suddenly find themselves uncompetitive. With cheaper imports, the balance between cement grinding and clinker production requirements could change quite dramatically. It would be up t the government to accommodate these changes, but one of the principle tasks of the consultant is to anticipate them.
This last point highlights what is perhaps the single most important yet difficult to determine aspect of a market study: competitor reaction. Knowing of others investment plans, government licensing, likely dates of completion, principle contractors involved and distribution partners is difficult and time consuming, but it is not enough. Competitors are not just nationals of those who have historically sold their product through the same predictable channels of distribution. There are an increasing number of companies who would like to reduce dependence on suppliers by vertically integrating their operations. This could entail building their own plant or developing their own deep water terminal to import cement directly. Others might decide to diversify into selling, for example, ready missed concrete. Some large users might be on verge of entering into long term agreements with one company or looking to buy form further afield. The combinations are numerous but it is up to the company investing in expensive plant and machinery to understand its customers and convince both itself and the investors that it really does have the best view of the market.
Raw materials proving
The volume and quality of the raw material deposits have to be established with accuracy. A wide ranging search for raw materials may start with desk research and consultation with National Geological Survey data and available geological mapping. The search will include examination of aerial photography records and satellite imagery e.g. Landsat or SPOT.
The desk research is followed buy site visits to the proposed location by geologists who take the study a step forward by making on-site examinations of previously identified geological horizons and outcrops. The first samples are taken by channeling from promising outcrops, road cuttings, recent excavations or from purpose excavated test pits. Field testing of the samples is required to provide an initial indication of the calcium carbonate, silica, alumina and iron content of the deposit. The testing is simple, rapid and economical and the geologist can adjust the field investigations and maximize the recovery of useful information.
The most promising samples are chemically analysed in testing laboratories and when sufficient data has been obtained in terms of chemical quality, and the probable volume established, a decision to mount a full drilling campaign can be made.
The primary raw material or limestone, is core drilled and careful records of the geological progression is made as the cores are recovered, recorded and laid sequentially in the core boxes,(Figure 2). Individual and composite samples are taken from the cores and sent to laboratories experienced in the testing of cement raw materials. In order to minimize drilling costs is essential that the initial results of the first borehole are analysed rapidly and the results known in order to make further decisions on location, angle and direction of subsequent boreholes.
The information obtained from the chemical analyses and the geological record derived from the cores in then used to establish the geological structure and the volume of the deposit. The optimum quarry developments are then developed.
The secondary raw materials, clays or shales, may be proven by means of auger drilling of by test pit excavation using mobile hydraulic excavators or in some cases by hand excavation. These materials are similarly recorded and chemically analysed as for the limestones.
Using the chemical analysis of the raw material, computerized raw mix designs can be carried out. The in-house program used has several facilities which can be called upon. Firstly, all the necessary standard equations which must be satisfied for lime saturation, silica ratio, alumina ratio, hydraulic modulus, etc., are built into the program. Secondly, the mix design can be refined by adjusting the compound composition and observing the effect upon the standard ratios. Finally, cost factors can be added to the raw materials to obtain the optimum raw mix which minimizes the most expensive raw materials, but satisfies the above criteria.
Process design
The optimum process route for a specific plant is dependent upon a number of factors including the physical and chemical nature of the raw material deposits. The selection of plant and machinery is made based on the following factors”
Disposition of the raw material deposits.
Moisture content and other physical properties of the raw materials.
Level of undesirable chemical elements.
Mineralogy (particularly the content and size of silica).
Abrasiveness, grindability and the burnability of the raw materials.
Fuel types and relative costs.
Environmental protection requirements.
Electrical power availability, cost and energy efficiency requirements.
Site topography and congstraints.
Market constraints.
Labour and maintenance constraints.
The disposition of the raw materials in terms of dip and strike and physical location dictate how the primary and secondary raw material quarries are opened up, how they are to be worked and how the access roads are to be developed. The geological method of deposition and hardness of the raw materials will also determine how the quarry is to be planned and the methods of extraction determined.
The moisture content of the raw materials and the change in their characteristics as the moisture content alters has an important effect upon the choice of the primary crusher and storage systems. The moisture content has even greater implications when considering the raw milling system to be proposed in conjunction with the optimum temperature of preheater exit gas. A balance has to be struck between the requirements of the kiln system, the number of cyclone stages that can be used, and the heat requirements of the raw mill for raw materials drying.
The level of undesirable chemical elements in the raw materials, such as potassium, sodium, magnesia, chlorides and sulfur requires careful consideration in the selection of the type of kiln system. The varying levels of impurity elements in conjunction with the sulfur in the raw material and possible additional sulfur intake from the kiln fuel, lead to the necessary decisions to be made relating to the acceptance and sizing of a bypass system.
The mineralogy can vary greatly among raw materials in different countries. The method of deposition and the occurrence of the chemical elements in each of the raw materials can have a marked effect on the characteristics of combination in the kiln burning process. Notably this leads to variations in kiln fuel conditions. Predictions upon how the raw-materials will behave when combined in the necessary proportions to obtain a commercial cement, are based upon laboratory burning and grinding tests conducted as part of the feasibility study.
Energy and fuel usage are two key matters high on the agenda of all potential and existing cement plant operators. The cement industry has always been very conscious of making the maximum use of heat energy, and to this end heat transfer from the kiln gases to the raw materials, of from the hot clinker to the combustion air, has always been utilized.
Today more than ever the efficient use of energy and fuel is sought affair and a range of plant and equipments available for consideration. Technical economy of scale is also an important factor and where the market justify large capacity plant, correspond with reductions in the cost of products are achieved.
Energy consumption is be reduced through the use of roll-milling systems for raw meal in plant of tube mills, high efficiency separators in both the raw milling and cement milling departments, low pressure drop cyclones in the preheater of the burning process, and by the preheater of high pressure grinding rolls, and recent introduction of the horizontal roller mill, the so-called Horomill. The selection of the optimum planning processes ensures that the KWh/h electrical power consumption minimised.
Fuel consumption is reduced the introduction of efficient cyclones construction with heat resistant tubes and an increase in the number of stages of preheater to mount maximum use of the hot gases leaving from the kiln. Fuel consumption is also siderable affected by the designation ancillary plant such as the kiln separators, gas ducting, kiln burner, flow control valves and instrumentation.
Another recent development is the transfer of all the hot exhausted gases form the clinker cooler back onto the raw mill, thus saving on the heat required for drying the raw material. This arrangement also has the acute advantage of reducing the capital of the plant by the elimination of a cipitator or other clinker cooler collection system and its associating equipment.
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