Though blowers and conveyors are being used for short and long distance material transport respectively in cement companies, the innovative air cushion technology promises to be cost effective in the long run.
Production of cement has always been one of the most energy-intensive operations. In order to avoid expensive primary fuels such as carbon, gas and oil, and to produce in more economical and sustainable way, cement manufacturers across the world are relying on alternative fuels for the incineration process in the calciner for several years.
Thus, cement production process involves movement of bulk materials, whether it is fuel or raw materials. Use of alternative fuels and raw materials (AFR), including solid municipal waste, nowadays, is bolstering the material transportation function further in the cement manufacturing.
Internal material transport equipment for a manufacturing unit is entirely different from those used for transportation logistics, which transport goods and other materials to long distances. Material transport equipment supplier is involved in supply and installation of the whole chain from the acceptance and unloading of the delivery vehicle, up to the storing, conveying and feeding process of the solid alternative fuels for the specific user. The solution includes transport of alternative fuels from the storehouse to the rotary kiln area as well as calciner and the main burner.
Blowers
Roots blowers (Twin/Tri Lobe Roots Blower), also called Rotary Lobe Compressors, are widely used in cement production process and used in kiln burner feeding, pre-calciner, burner feeding, raw meal silo feed Aeropol, silo mixing bin aeration and surge bin aeration, to name a few. Roots blowers are also used to convey cement and fly ash in a cement manufacturing plant, which is done pneumatically by using Roots blowers.
Charging of kiln is one of the critical stages where Roots blowers are used. These blowers take normal atmospheric air at suction and compress it to the required capacity and the required pressure at discharge and supply it, so as to charge the kiln for the next process. The quality of these blowers should be excellent so that they work in the critical conditions of a cement manufacturing plant.
Since the lobes run within the casing with finite clearances, no internal lubrication is required. Thus, the air delivered is 100 per cent oil-free. These blowers deliver, practically a constant flow rate independent of the discharge pressure conditions. The flow rate is largely dependent on the operating speed.
These machines are also extensively used in applications such as pneumatic conveying, aeration, cement plants, water treatment plants for filter backwash, aquaculture, aeration etc. They are used as general utilities, more commonly where the distance is short and a large volume of air is required (during blending, aeration, fluidisation and conveying).
Selecting the correct blower model for such critical applications in a cement plant in alignment with the other equipment installed is the responsibility of the manufacturer. A quality product will always help in attaining overall optimum performance of the plant, say experts.
Conveyors
The other means of transport equipment in the cement manufacturing unit are conveyors. Some cement companies use conveyers to move these materials, for they are cost-efficient. Though pneumatic conveying lines are extremely maintenance-intensive and also susceptible to breakdown, some conveyor manufacturers have come up with pipe conveyers, the enclosed type of construction of which protects environment from material falling down and emissions. Due to its ability to navigate curves, considerably less transfer towers are required compared to other belt conveyors, resulting in cost savings.
Roller/belt and tubular/pipe conveyor systems are well known among user. But both of them require a lot of maintenance because of friction they generate due to movement of goods one a belt supported by rollers.
Friction-less conveyor
The latest technology is air cushion conveyor (ACC) system reduces friction in the system, thus, resulting in cost efficiency and movement of higher volume of materials.
"Air cushion lifts up the rubber belt, removing friction in ACC. It brings in several advantages – energy saving, environment-friendly and requiring minimal maintenance,"says Frank Wang, General Manager of Sagta Engineering, a shanghai, China, based consultancy company that is trying to introduce ACC systems in India. In a conventional belt conveyor, where belt is running on rollers, a number of rollers appear along it. "Basically the concept of ACC is very much similar to that of conventional belt conveyor, but the difference is there are no rollers in the new technology. Instead of rollers there are certain modules and on the surface of the modules there are a number of small holes through which pressurised air comes and keeps the belt afloat, so that the material loaded onto the conveyor belt moves on the airfill," says U.K. Mullick, Chief Consultant of Sagta in India, while explaining the concept further.
The majority of power consumption of a conveyor is for overcoming the frictional resistance of number of rollers present in the system. "If there are no rollers, then there is no friction, due to which the power consumption will come down drastically – estimated at 20-70 per cent, based on the length of the conveyor (longer the more)," Mullick added.
Even the lifespan of rubber belt used in the conveyor will increase manifold against its lifespan of 3-4 years in other conveyor systems. "To our surprise, the rubber belt of our first project where ACC was installed is still there even after 15 years, and no replacement needed anytime soon," says Wang. Thus, even though the innovative ACC system comes with no cost advantage in terms of initial installation, it has the ability to give operational advantage to the company installing it all through its life. Giving an inkling into the volume of power saving that can be derived with ACC, Mullick said, for a 15-km conventional conveyor power installation needed is 4,200 kW, while for ACC technology the installed capacity required is 2,500 kW.
However, ACC has its own limitations – it cannot carry material in sizes of over 50mm and cannot take a turn towards right or left, it has to be installed in a straight line. Hence the need for use of different types of conveyors, including conventional and pipe conveyors, if the route of the conveyor passes through hills and mountains.
– B.S. SRINIVASALU REDDY
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