CEMENT FACTORIES in Pakistan had been using ‘furnace oil’ or ‘natural gas’ as the fuel except those pre-independent plants which used coal in the beginning.

During past one year we find a dramatic change in this trend due to economic reasons. Now, most of factories have started using local coal as fuel. Some of the factories, especially those with a ‘by-pass or a wet process’, have replaced 60 per cent of their furnace oil consumption by local coal.

Coal almost halves the cost of fuel. The cost of fuel constitutes 25 per cent of the total cost of manufacturing cement. A cement factory with a capacity of 2000 tons per day can save up to Rs300 million a year by use of a mixture of local and imported coal. The capital cost of coal equipments may be recovered in less than eight months.

Coal was used traditionally in cement kilns all over the world since the introduction of rotary kiln at the end of the last century and it lasted till mid of the 1950 when a departure from the policy occurred due to economic reasons. In Pakistan, pre-independence plants such as Wah, Rohri and Dandot used coal till mid-1950. Maple Leaf cement factory (the first plant built after independence) also used coal of Makerwal collieries in the beginning.

Furnace oil was dominant fuel between 1955 and 1970 all over the world. Cement plants in Pakistan used cheap natural gas during that period. After the oil embargo in 1974, oil prices shot up and factories all over the world started using coal again . By this time, dry precalciner plants had already been introduced which were more sensitive to variation in raw meal. The problem associated with coal in Precalciner kilns has mostly been won but sensitivity of dry process plants to variation in raw meal, coal ash and sulphur remains a challenge to plant engineers. Coal is partly converted to ash after combustion in kilns. Coal thus behaves like a raw meal in the kiln. Local coal contains some minor costituents like sulphur, alkalis and chloride which poses problem if they exceed the tolerable limit.

Between 1980 and 1984, there was a general trend of switching over to coal as fuel in kilns all over the world. Pakistan remained an exception to this international trend, partly because of the negative response of state-owned plant managers and partly due to the low-cost and easy availability of natural gas. During that period, almost all factories were under the state control. Thanks to the new generation of plant owners, for their quick decision to shift to coal in past one year for economic reasons, 21 out of the 23 factories are now privately owned.

It is time that some facts about local coal are explained and the related myths discarded so that total shift to coal as cement kiln fuel was achieved without facing any complications.

Let us first see as to how experts define, the measured, the indicated, the inferred and the hypothetical. reserves.

MEASURED: Virgin bodies of coal having a high degree of geological assurance, lying within a radius of 0.4 km of point of thickness.

INDICATED: Virgin body of coal having a moderate degree of geological assurance, lies between 0.4 km and 1.2 km from a point of thickness.

INFERRED: Virgin body of coal having a low degree of assurance lying between 1.2 km and 4.8 km from a point of thickness.

Hypothetical: A class of undiscovered resources which has very low degree of assurance, the estimates are based on assuming continuity beyond inferred reserves.

The total deposit including indicated, inferred and hypothetical is 185 billion tons out of which only 4 billion tons is measured and only 218 million tons is mineable and developed at this stage. If all the plants shift to total coal firing, their production requirement will be 3.5 million tons annually. This will be in addition to 3.5 million tons of non-cement consumption of coal in Pakistan. We also see that most of developed & mineable reserves of coal is at Lakhra. This limits the selection option of cement plant managers. They will have to use Lakhra coal inspite of its high moisture, high and variable ash and high sulphur.

Heating value of the most of the coal deposit of Pakistan is around 4000 Kcal per kg of coal. Standard text on cement technology states that minimum calorific value of coal should be 5000 kcal/kg in order to provide a properly hot flame necessary for clinker formation.

The sulphur cycling calculation reveals that maximum allowable percentage of sulphur in coal should be 2.70 if C3A (Tri Calcium Aluminate) in cement is less than or equal to 7% and maximum allowable percentage of sulphur in coal should be 4 if C3A content in cement is greater than 7%.

This is therefore a myth that Pakistani coal alone can replace furnace oil in total. Some amount of high calorific value and low sulphur imported coal has to be mixed with local coal.

Lakhra coal of Sindh contains 5.72% of sulphur on average basis. But this figure may be very much deceptive. Lakhra coal field is spread over 500 sq.km of area. Sulphur content in Lakhra coal may be as low as 3% and a high as 18%. The variation is most unpredictable. It may vary from mine to mine, seam-to-seam and even in one mine from face to face.

Thar coal deposit contains only 1.16% sulphur and therefore it is most suitable for cement plant. But Thar is still in the stage of confirmation of its hypothetical, inferred and indicated reserves. Mining is yet to be started after this confirmation and the infrastructures like rail & road links are yet to be constructed. Cement factories may not expect coal from Thar at least within 5 years from now.

Some cement factories have developed indigenous coal equipments, which are being utilized with success. But coal powder is highly explosives and dangerous under certain conditions. Some minor mishaps had already occurred in some of the cement factories in equipments associated with coal grinding. It is time that standard safety provision already in practice internationally should be adopted in Pakistan to avoid serious mishaps with coal equipments.

Most of the cement factories have started using coal without any pre-blending arrangement. This will not be successful in case of total shift to coal. Local has high quantity of ash with enormous variation and then there is sulphur. A cement factory requires uniformity of sulphur and ash during the final burning process on a second-by-second and minute-by-minute basis. This control can be achieved by introducing pre-blending arrangement before grinding of coal. Experienced and qualified mining engineers may be helpful in controlling the uniformity of coal quality at the mine. They may be associated in the selection of coal mining areas for supply of coal to cement plants. They may also be associated in mining of coal with least inclusion of pyrite and carbonaceous shale. Pyrite and carbonaceous shale respectively are major sources of sulphur and ash found in local coal. It has been observed that coal mines in Pakistan supervised and controlled by qualified and experienced mining engineers have taken larger share of coal supply to cement industries.