3.2. Resultados inferenciales 1. Prueba de ajuste de modelos
3.2.7. Aplicaciones computacionales en Resolución de problemas
An illustration of the relative costs of phosphoric acid via the wet route or the ther-mal route is given in the succeeding text. A typical product cost sheet is structured as in the following; it lists all the cost components, usages, and cost per unit and com-prises raw materials, in order of importance; chemical services, which do not form part of the product but are essential in its processing (e.g., defoamer or the solvent in a solvent extraction plant); utilities such as steam, water, and nitrogen; direct labor, meaning personnel required to operate, maintain, develop, and supervise the plant;
maintenance, which is usually budgeted at 1%–5% of the capital or replacement cost of the plant depending on the technology; and indirects, which include administra-tive overheads, depreciation, taxes, and insurance.
Table 1.6 displays a cost sheet for sulfuric acid as the majority of phosphoric acid enterprises include a sulfuric acid plant. The wet process acid must be purified to compete
TABLE 1.6
Sulfuric Acid Plant Cost Sheet
Sulfuric Acid Plant
Capacity 2400 t/Day
H2SO4 330 Days/Year Usage/t H2SO4 Price Unit $/t H2SO4 % Raw materials
Sulfur 0.333 100 $/t 33.3 96%
Catalyst 1.0 3%
Utilities
Electricity cost 40 0.07 $/kWh 2.7 8%
Electricity credit −65 0.07 $/kWh −4.4 −13%
Steam credit −1.2 10 $/t −12.0 −35%
Water 2.0 6%
Direct labor 40 people 50,000 $ 2.5 7%
Maintenance 3.5% capital cost 1,750,000 $ 2.2 6%
Administration $ 1.0 3%
Depreciation $ 6.3 18%
35 100%
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with thermal acid so a generalized cost sheet is included (Table 1.9) for a purified acid plant; the impact of the different solvent extraction technologies on these costs will be considered in more detail in the next chapter. The key learning point is that the cost of purified acid is dominated by the cost of the feed acid (and in this situation the return acid credit), followed by maintenance, administration and depreciation costs. The cost impact of a functioning solvent extraction technology is relatively low. Tables 1.7 through 1.11 show the cost sheets for a wet phosphoric acid plant, a phosphoric acid concentrator plant, a purified acid plant, a phosphorus plant, and a thermal acid plant. The phosphate rock input costs are on the same cost per ton of P2O5 basis, as well as identical utility costs.
Comparing the total production cost of purified phosphoric and thermal acids, it is obvious that the latter is far more expensive, nearly double, for the same P2O5, utility, labor, and overhead rates. Consequently, as well as phosphoric acid, any phos-phate derivatives made from thermal acid will be much more expensive than those from purified acid. In the past, the business case for phosphorus manufacture was based on access to local rock, coal, and cheap electricity, including hydroelectricity.
Unfortunately, if, as in China at the beginning of the twenty-first century, the domestic demand for electricity grows, and as a result of local weather conditions, the hydro-electricity literally dries up in dry seasons, then phosphorus production must face the full commercial rate for electricity as well as having output limited by its restricted electricity supply. A similar argument applies for coke. Consequently, in fully devel-oped economies, the only justification for a phosphorus plant is to meet a market
TABLE 1.7
WPA Plant Cost Sheet
Phosphoric Acid Plant
Capacity 1000 t/Day
P2O5 330 Days/Year Usage/t P2O5 Price Unit $/t P2O5 % Raw materials
Phosphate rocka 3.29 158 $/t 519.8 76%
Sulfuric acidb 2.76 35 $/t 95.7 14%
Additives 5.0 1%
Utilities
Electricity 150 0.07 $/kWh 10.1 1%
Steam $/t
Water 5.33 0.25 $/t 1.3 0.2%
Gypsum disposal 2.5 0.4%
Direct labor 50 people 50,000 $ 7.6 1%
Maintenance 3.0% capital cost 3,000,000 $ 9.1 1%
Administration $ 2.4 0.4%
Depreciation $ 30.3 4%
684 100%
a Phosphate rock of 32% P2O5 concentration, usage includes total losses (5%).
b 98% H2SO4 used, calculation based on 100% H2SO4.
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TABLE 1.8
Phosphoric Acid Concentrator Plant Cost Sheet
Phosphoric Acid Concentrator Plant
Capacity 1000 t/Day
P2O5 330 Days/Year Usage/t P2O5 Price Unit $/t P2O5 % Raw materials
Phosphoric acida 1.005 684 $/t 687.2 96%
Additives 1.0 0.1%
Utilities
Electricity 25 0.07 $/kWh 1.7 0.2%
Steam 1.8 10 $/t 18 3%
Cooling water 50 0.05 $/t 2.5 0.3%
Direct labor 10 people 50,000 $ 1.5 0.2%
Maintenance 2.5% capital cost 250,000 $ 0.8 0.1%
Administration $ 2.4 0.3%
Depreciation $ 3.0 0.4%
718 100%
a Based on 30% P2O5 filter acid concentrating up to 59% P2O5 and accounting for precipita-tion and processing losses.
TABLE 1.9
Purified Phosphoric Acid Plant Cost Sheet
Purified Phosphoric Acid Plant
Capacity 250 t/Day
P2O5 330 Days/Year Usage/t P2O5 Price Unit $/t P2O5 % Raw materials
Phosphoric acida 1.454 718 $/t 1044.1 98%
Return acid creditb −0.428 574 $/t −245.9 −23%
Solvent 0.5 1.8 $/kg 0.9 0.1%
Chemicals 50 5%
Utilities
Electricity 150 0.07 $/kWh 10.1 1%
Steam 3.5 10 $/t 35.0 3%
Cooling water 20 0.05 $/t 1.0 0.1%
Process water 1 0.9 $/t 0.9 0.1%
Direct labor 30 people 50,000 $ 18.2 2%
Maintenance 2.5% capital cost 2,250,000 $ 27.3 3%
Administration $ 9.6 0.9%
Depreciation $ 109.1 10%
1060 100%
a Based on 59% P2O5 concentrated, low sulfate, acid feed, 2.5% losses.
b Return acid credit is negotiated and ranges 0%–100% of the value of the feed acid, here it is 80%.
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TABLE 1.10
Phosphorus Plant Cost Sheet
Phosphorus Plant
Capacity 110 t/Day
P4 330 Days/Year
Usage/t P4 Price Unit $/t P4 % Raw materials
Phosphate rocka,b 9.9 123 $/t 1222.0 45%
Silicac 0.24 1.5 $/t 0.4 0%
Coke 2.4 90 $/t 216.0 8%
Electrodes 130 5%
Utilities
Electricity 13,250 0.07 $/kWh 887.8 33%
Water 1 0.9 $/t 0.9 0%
Direct labor 30 people 50,000 $ 41.3 2%
Maintenance 2.5% capital cost 1,500,000 $ 41.3 2%
Administration $ 15.0 1%
Depreciation $ 165.3 6%
2720 100%
a Based on 25% P2O5 rock and 8% P4 losses.
b Rock price same as wet acid case based on P2O5 content.
c Silica requirement accounting for SiO2 content of phosphate rock (25% SiO2).
TABLE 1.11
Thermal Phosphoric Acid Plant Cost Sheet
Thermal Phosphoric Acid Plant
Capacity 180 t/Day
P2O5 330 Days/Year Usage/t P2O5 Price Unit $/t P2O5 % Raw materials
Phosphorus 0.437 2720 $/t 1188.6 92%
Water 0.4 0.9 $/t 0.4 0%
Chemicals 20 2%
Utilities
Electricity 10 0.07 $/kWh 0.7 0%
Water 1 0.9 $/t 0.9 0%
Direct labor 20 people 50,000 $ 16.8 1%
Maintenance 2.5% capital cost 625,000 $ 10.5 1%
Administration $ 15.0 1%
Depreciation $ 42.1 3%
1295 100%
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demand for phosphorus and its organic derivatives. There is now only one phospho-rus furnace in the United States, in Idaho, and one in Europe, in the Netherlands. On the other hand, the business case for the wet acid route to purified acid is also obvi-ous; that is why there are several purified acid plants around the world.
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