northern tier states by rail or via the Great Lakes waterway. Mexican exports move by rail to Texas, New Mexico, Arizona and Southern California and by vessel to East Coast, West Coast and Gulf Ports.

The major exporting countries in 1994 were Canada and Spain with 4.2 and 1.3 million metric tons respectively. In 1988, imports from Mexico were 4.5 million tons or 28% of the 15.8 million metric tons imported in that year. Countervailing tariffs of up to 57.96%, imposed as a result of a successful anti-dumping suit by U.S. cement producers in 1990, reduced Mexican cement imports to 640,000 metric tons in 1994.

Between 1980 and 1993, the mill value of Portland cement, defined as the actual value of sales to customers f.o.b. plant less discounts, allowances, freight, distribution and packaging costs, ranged from $50 to $56/short ton in current dollars. In 1994, the value increased by 9.8% to $61.88.

Cement values expressed in 1994 constant dollars indicates that the real value of cement in 1994 was 28.1% below that in 1975. Cement prices have been kept at low levels by competition for market share among domestic producers and by pressure from low cost imports.

Since cement value has not shown major fluctuations in the last 15 years, it is assumed for the purpose of this analysis that the average price of cement to consumers will remain constant in real terms between 1996 and 2015 in the base case. The price chosen for the base case to

represent the cost of cement to customers is the twenty city average price of $71.06 per short ton as reported by Engineering News-Record for the first quarter of 1996. This is converted to $78.17 per metric ton.

- domestic cement production

2.0%

1.0%

0.5%

cement imports fill the gap between demand and domestic supply

old capacity shut down at the rate of 500,000 metric tons/yr.

energy efficiency of shut down capacity is 6.43 mmBtu/t

energy efficiency of new capacity is 4.30 mmBtu/t

no significant change in fuel mix

total employment will remain constant because of productivity

gains

Real GDP is projected to grow at an average of 2% per year between 1994 and 2015. Data reported by the Department of Interior show that construction as a percent of GDP declined in real terms from 9.0% in 1975 to 7.8% in 1994. The ratio of cement to construction expressed as metric tons per $1000 decreased from 0.219 to 0.206 over the same period. Despite the fact that neither of these indicators have declined in the last four years, cement demand is projected to grow at 1% per year, half the rate of GDP. Because imports are firmly established and have shown a gradually rising trend, half the growth in demand is assumed to be supplied by imports. Domestic production in 1994 of 74.6 million metric tons consists of U.S. cement consumption plus exports less imports of cement and clinker.

In the absence of any major economic shocks, the U.S. cement industry can be expected to continue its trend towards improved energy efficiency and greater economies of scale. This will be achieved by replacement of smaller older units with larger precalciner kilns. An average annual growth in domestic shipments projected at 0.5% annually, means that about 400,000 metric tons of new capacity will be needed each year. Assuming that an average of 500,000 metric tons of old capacity is shut down annually, total new capacity will be added at an average rate of approximately 900,000 metric tons per year or about one modern plant.

This pattern of capacity closure and replacement will result in wet process kilns dropping from about 29% of installed capacity to 14% in 2015 and preheater/ precalciner kilns increasing to 57%.

Average energy efficiency over the period in question is projected to improve by about 15% dropping from 5.20 mmBtu to 4.42 mm Btu per metric ton of cement. About half of this will come from replacement of old capacity and half from general plant improvements.

Fuel mix is not projected to change significantly except that use of natural gas will decrease between 2010 and 2015 as its relative price goes up.

The use of wastes is projected to remain constant, in part because of the lack of community acceptance of the use of hazardous wastes as energy sources and the cost and uncertainty of the permitting process, and in part because the supply of non-hazardous waste fuels tends to be limited.

The case of scrap tires is a good example of the cement kiln's energy appetite dwarfing the availability of a non-hazardous waste fuel. Approximately 250 million tires, about 1 per person, are discarded each year in the U.S. Some of these are resold, others are retreaded, some are recycled into products and some are used as fuel. The majority are dumped or stockpiled. Assuming 110 scrap tires weigh a metric ton, and the heat content is 30 mmBtu per metric ton, then the total energy value of 250 million scrap tires is equivalent to 2.7 million metric tons of coal. If 30% of these tires were burned as kiln fuel, and this number is probably realistic because of competing uses and the economics of scrap tire collection, they could be used to replace 810,000 metric tons of coal. This represents only 6% of the cement industry's annual fuel requirements. In 1994, 23 cement plants burned 37 million scrap tires, thus conserving 420,000 metric tons of coal.

SECTION II. CEMENT MANUFACTURING PROCESS

Rules of Thumb

1.6 metric tons of raw mix gives 1 metric ton of clinker
because of calcination of the limestone (loss of CO2).

0.95 metric tons of clinker + 0.5 metric tons of gypsum
gives 1 metric ton of cement.

making I metric ton of clinker uses an average of 4.7 mmBtus.

making 1 metric ton of cement uses an average of 158 kWh
of electricity.

Process Description

The cement manufacturing process consists of four main steps as shown in the figure overleaf.

The method of grinding the raw meal defines the two broad classes of kilns.

Wet. In which the raw materials are ground with water to give a slurry consisting of 30-40% water that is fed into the kiln The advantage of this process is that it