Our goal of sustainability includes minimising breakdowns and achieving MTBF (Mean Time Between Failure) 160, achieving specific power consumption 78 Kwh/t cement, increasing PPC sales and fly ash addition in PPC, slag per cent in PSC, and also increasing alternate fuel substitution and AF substitution to reduce dependency on the State Electricity Board for Power, says BLN Murthy, Director – Works, Bharathi Cements. Excerpts from the interview.
How do you view the sustainability issues in the cement industry, in terms of energy efficiency?
Energy has been harnessed out of generated waste, and coal usage has been reduced proportionately by using alternate fuels such as processed chemical solid, liquid and semi-solid waste, waste wood, paint sludge, etc, from various industrial wastes. In 2012, we have consumed about 42,768 tonnes and in 2013 so far, we have consumed 29,810 tonnes of waste material received from various industries; fossil fuels have been proportionately reduced.
Efforts to substitute fossil fuels with waste have resulted in a reduction in the consumption of natural fuels by seven to eight per cent during the period 2012 and 2013. The usage of alternate fuels resulted in the elimination of the impact of hazardous waste on the environment. All waste material materials received from various chemical industries are being dealt with as per the guidelines of the Pollution Control Board.
Have you taken any water conservation measures?
Groundwater is 19.8 per cent of the total water withdrawn. The mines discharge water is being used for plantation and dust suppression systems. Efforts are on for a dry system of dust extraction instead of wet control measures, to minimise water consumption. A check dam has been constructed for storage of surface run-off water and to improve the ground water recharge.
Three farm ponds of one lakh M3 capacity have been developed and filled with mine discharge water. This water is used for plantation and dust suppression on haul roads during the summer season, so groundwater is not drawn too much.
A sewage treatment plant has been established and is in operation for the treatment of colony sewage water; the treated water is used for process applications in the cement plant. About 25 per cent of the total water requirement is met from STP recycling.
Brief us on the steps Bharathi Cement has taken to optimise energy efficiency.
Bharathi Cements has taken an initiative to optimise energy from the project stage itself. We have installed VFDs for both LT and HT drives for all process fans like pre-heater fans, RABH fans, raw mill fans, coal mill fans, cement mills fans and cooler fans, and we have installed high efficiency fans, low pressure drop cyclones in the pre-heater. We have also installed belt weighers for optimum loading of conveyors to avoid idle running of equipment, and have also provided VFDs whereever fans are operating with less than 75 per cent damper opening.
Have you used any high efficiency pollution control equipment?
In total, BCCPL has installed 120 unit bag filters, five bag houses, two RABH (reverse air bag houses) and two ESP (Electro Static Precipitators). We have installed pollution control equipment for each point of source emission in every process. With this good maintenance, we have achieved a zero discharge from emissions of the source point.
What are the steps you have initiated to reduce your carbon footprint?
In cement industries, power is a major factor that controls production costs. However, cutting power consumption is not the only option. At Vicat Sagar Cement, we have installed a 8.4 MW WHR system which is a co-generation system that can reliably supply about 30 per cent of the plant’s power needs at no extra fuel cost, reduce its carbon footprint and save precious water.
Large quantities of hot flue gases are generated from the cement industry, which is not useful for the cement manufacturing process. In cement plants, hot flue gases coming out of the pre-heater duct, cooler vent duct, cooler mid- tap can all be recovered to produce significant amount of electricity.
The oower generation process is based on the Rankine steam cycle. The steam generated in the boiler when expanded through a turbine, turns the turbine shaft, which in tandem is coupled to an electric power generator.
Depending on the carbon emission intensity of the grid power being replaced, this WHR will save more than 70,000 tonnes of CO2 a year.
The payback period for a waste heat recovery project is attractive. In fact, savings in production costs and emissions can lead to a return on investment after only a few years, depending on the cost of electricity and scale of the plant.
How do you assess the challenges on the logistics front?
We have taken the following steps to be more cost- efficient: Maximum utilisation of inbound fleet for outbound cement transport.
Use of GPS on trucks for better route planning , faster delivery and maximising number of trips to reduce cost and better utilisation of truck loads.
Efficient network planning using state- of-the- art optimisation tools.
Warehouse location chosen on the concept of minimum reverse transportation. Following the strategy of first mile bulk and last mile bag to reduce the overall cost Optimum inventory planning at warehouse to achieve zero damage targets. Laminated packaging with minimum pilferage.
Driver training for efficient and safe driving practices.Use of cross- docking to minimise handling and warehousing costs.
SUSTAINABILITY GOALS
- Minimising breakdowns and achieving MTBF (Mean Time Between Failure) 160. – Achieved MTBF 114.42.
- Achieving specific power consumption 78 Kwh/t cement – Sp. – Power consumption reduced to 79.5 Kwh /t cement
- Increasing PPC sales to 55 per cent over total sales.- PPC sales achieved 49.5 per cent.
- Increasing fly ash addition in PPC to 33 per cent – Fly ash addition in PPC increased to 30.38 per cent.
- Increasing slag per cent in PSC to 40 per cent. – Slag in PSC increased to 36.6 per cent.
- Increasing alternate fuel substitution to 30 per cent. – AF substitution increased to ten per cent.
- Reducing dependency on State Electricity Board for power.- Thermal power plant work under progress.
GREEN INITIATIVES
- Wet drilling and bag filter attachment for drilling machine to reduce dust emission during drilling.
- Water spraying on the blasted material before loading.
- Water sprinkling on haul roads.
- Water spraying in limestone dump hopper and crusher.
- Bag filters provided for all transfer points and collected dust hundred per cent utilised.
- Water spray arrangement provided on belt conveyors to suppress dust.
- Concrete roads provided in the plant to avoid dust during vehicle movement.
- Reverse air bag house provided for the kiln and raw mill where the availability is one hundred per cent, no usage of water.
- ESP provided for cooler vent gases and bag house for cement mills.
- Roto packers and bag filters installed in cement pacing plant.
- super sucker utilised for handling spillage materials to avoid dust.
- Two road sweeping machines for cleaning the roads.
- Neem plantation done all around boundary.
- Trees planted all around material handling areas.
Electrostatic Precipitators
Electrostatic precipitators are installed for dust collection from the kiln cooler gases. ESPs are designed to deal mostly with coal- fired systems to collect dust in the flue gases. They are similar to the way an ionic breeze works. They take the incoming dirty air and pass it through a filtration device that purifies the air. Any solid particles left over will fall into a large storage container called a hopper and the clean air will be brought out.
Reverse air bag house – The hot gases from pre heater exhaust fan go to the bag house when the raw mill is not in need of it. When the raw mill is working, hot gases from the pre- heater exhaust fan partly go to heat the material in the raw mill. In the process, they cool down and thus, the final temperature and volume of gases is reduced when they enter the bag house. When the raw mill is not working, it can be by- passed and the gases from the pre- heater should be cooled down to 2400 C before they enter the bag house. The gases enter the bag house through the inlet duct and then are distributed to various modules through the hopper damper. The gases then are filtered through the bags. The dust gets separated on the inside of the bag and eventually falls in the hopper, and the clean gas enters the outlet duct through the outlet poppet damper. The gases from all the modules now enters the outlet duct and then flows to the exhaust fan.
Unit bag filters and bag houses – Unit bag filters/ bag houses are working with dust laden air or gases enter through the hopper by suction or positive pressure. The heavier dust particles fall immediately into the hopper, while the light dust is distributed and deposited on the outside of the filter bags. When a uniform layer of dust has been formed on the surface of the filter bags, it is removed by a predetermined cycle of high pressure compressed air pulses. Cleaning efficacy is increased with the use of high efficiency venturi inserts that shape the initial pulse into a mass of air that travels down each filter bag, expanding it and dislodging the dust layer from its outer surface. The mass of air also draws the secondary air behind it, adding the downward air flow. The dust removed falls into the hopper and is discharged through the discharge valve.
How ESP works
Once all the previous items have been created, they are placed in a shell. This shell is basically the home of the precipitator. Almost all of the previous components are located in the shell which is typically comprised of carbon steel. It has holes on either side for the inlet and outlet ducts. The shell is also insulated to reduce the risk of condensation build- up.
Condensation will form when the flue gas which can leave the refinery at 2000 F, hits the inside of a cold precipitator. Also, condensation will interfere with the way in which the electrodes work and render them useless because condensation will collect on the walls and will begin to collect the particulate before it can be properly taken care of.
Hoppers are one of the major external elements. There are wires, piping and ductwork on the outside, but in the end, the hoppers collect the particulate. They, just like the shell, are typically made of carbon steel. Their main job is to collect what is rapped off the collecting plates. Once the particulate has been collected and the hoppers are full, rotary air locks and access doors are used to evacuate the hoppers. Below the hoppers , we have conveyors which convey the dust which will pull the particulate from the hoppers and bring it to a remote storage facility; or they have trucks driven underneath them that will physically truck the ash away. Inside the shell, the collecting electrodes are assembled parallel to the inlet duct.
The discharge electrode runs perpendicular to the inlet and collecting electrodes. As the flue gas comes out of the inlet and enters the precipitator the rigid mast discharge electrodes greet the flue gas and negatively charge them, allowing the positively charged plates that are running parallel to the inlet to collect the flue gas.
The other major external element is the rapper. It sits on top of the roof of the precipitator, and is programmed to deliver its powerful strike within a certain timed interval. The hammer end strikes the top of the collecting plates, making all the collected particulate fall into the hoppers below.
Electricity powers just about everything on the precipitator. It is used to power the electrodes, both positive and negative, and powers the rappers. It is also used to power the vacuum system on the evacuation of the hoppers, if the hoppers have this option. Most precipitators run auxiliary transformers to subsidise the amount of energy needed to keep the precipitators running.
Outlet duct is where the new clean gas will leave the precipitator. It gives the gas a final exit strategy from inside the shell where all the work had been previously done.
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