Systems adopted globally
Global cement bigwigs, including Lafarge, Holcim, Italcementi, Portland, Colacem, Cementi Rossi and Buzzi Unicem, have deployed vacuum cleaning solutions from Sibilia, Italy, to counter the spillage problem in their factories.
Two issues determine the size and capacity of the vacuuming machine: one, the area susceptible to spillage, either spread over large areas or concentrated areas and second, the amount of spillage to be collected at a time. Hence, the system varies from plant to plant.
Says Sumeet Khurana of Dulevo India: “In most cement plants in India, spillage is being removed manually by contract labourers who physically pick up spillages on tractor trolleys and then carry it to the collection unit. Spillage in the initial stage of manufacturing may not be that important to some cement industries as in the later processes like in the crushing area of the quarry, under the conveyor belt, storage and milling areas of the heating section, clinker crusher in the grinding section and in the packaging area.
“There is heavy spillage as
large as one to five tonnes that need to be collected at a time. The variation of vacuuming system of picking up spillage from a small spot or from a larger area determines whether it is fixed or flexible. In a fixed system, the vacuuming is done in concentrated spillage areas and material is deposited into prefixed tanks or cilos as shown in the schematic. This is more suitable for smaller units in a small area.
“In the larger units, since the entire cement processing system extend to several meters with the conveyor belts running over half a kilometre, it is necessary to have a flexible vacuuming system. These flexible systems can run on diesel engine tractor or truck that can move easily from one area of the plant to another. This machine will play the role of collection by way of vacuuming.”
This solution from Sibilia is most suitable for heavy engineering plants. Dulevo India is distributor for Sibilia machines in India.
Talking on the second issue, Khurana says that because of spillages and production of fine material, there is a lot of fine dust on the roads, plants or the colony. All open areas in the plant, the roads, gangways, etc., there is considerable amount of dust which can be collected through heavy duty sweeping machines. The area to be cleaned and the frequency determine the size and the number of machines required for cleaning a plant alone or along with the township. “The Dulevo 1300 Star machines are running in many of the cement plants in India. Any industrial sweeping machine running in a cement plant should be capable of handling fine dust. If machines do not have capable filtration facility, it will not work in a cement plant environment.”
Further, it should be suitably designed. “Many sweeping machines use water spray for sweeping and such machines are not suitable for industries like cement or steel where water creates a problem. If water is sprayed, it cannot pick up cement as it will harden. Hence the sweeping machine should have special high filtration systems that are designed to handle fine dust without the use of water.
Further, the sweeping machines should also be so designed that its engines are well protected, as working in such high levels of dust, the engine could give way in just three months. Thus, sweeping machines applied for municipal use are much different from those designed specially for the cement or steel industry.”
The Dulevo machines are deployed in the Rajasthan plant of JK White cement and in four plants of Dalmia Cement.
Combating Challenges
The cement industry is continuously adopting upgraded technology to meet better cleanliness and standards. Most of the cement industries today are making serious efforts to minimise pollution and its effect on the environment by installing equipment at various processing stages.
Air pollution
- To reduce dust emission and arrest the dust, most of the companies have Dust Collectors and ESPs at raw mill, coal mill, clinker cooler and cement mill. High efficiency pulse jet dust collectors have been installed in place of old shaking type bag dust collector in different sections of the plant including the crusher, raw mills, cement mills and packing plant.
- To ensure smokeless chimneys in cement mills, manufacturers are installing Reverse Air Bag House replacing the stacks of Bag houses, by which emission can be completely controlled.
- Another area is the clinker cooler, where Electro Static Precipitator can be installed.
- Dust collectors, the insertable type, at the transfer points of limestone belt and coal belt conveyors helps arrest dust emission during transfer of material from one belt to another.
- Water spray arrangements over the hoppers of primary crusher and secondary crusher, multiple limestone belts and clinker belt control fugitive emission generated locally.
- Sprinklers on the roads inside the plant help minimize the fugitive emission generated due to movement of vehicles.
Depletion of natural resources
The main raw material for making cement is limestone. Many cement plants are now using waste material from other industries as raw material.
Earlier, some plants were using Chemical Gypsum, a waste product from the fertilizer plant, in place of mineral gypsum. Now, to produce Portland Pozzolana Cement, using fly ash (waste from thermal power plants) is common with many cement plants. Portland Slag Cement is produced using blast furnace slag, a waste product from steel plants.
Priority is given to production of blended cement over ordinary or high grade Portland Cement using maximum quantities of fly ash and slag, thus resulting in power saving, mineral conservation and coal saving. At the
same time, it helps other industries (viz. fertilizer plants, thermal power plants & steel plants) to reduce the environmental pollution.
The entire quantity of fly ash generated in some of the captive thermal power plants is conveyed through dense phase conveying system to the plant for cement production.
To further promote the fly ash consumption, many companies have installed a dry fly ash handling system to unload fly ash from closed tankers directly to the steel hopper without generating any dust in the environment. This ensures totally dust free handling of fly ash in the plant.
Green house gas
Cement making is highly energy intensive and is closely coupled with global warming mainly due to its process characteristics that involves burning of fossil fuel besides high electrical energy consumption. Cement manufacturing process creates CO2 in two ways, one during dissociation of carbonates of limestone and second from burning of large quantities of fossil fuel inside the kiln to generate heat, necessary for calcinations of raw material and clinker formation.
