Dust control
Manpower for maintenance and their safety
Trapping emissions
Engineering, technical and administrative controls
Workplace hygiene and drainage
Wet bulb temperatures, rooftop ventilators and cross air circulation..
These are just some of the myriad functions that a cement plant head has to monitor. At the same time, they also need to clamp down on expenses like fuel, manpower and material handling costs, which constitute a major chunk of Opex costs.
And if this isn’t challenging enough, they are also responsible for ensuring that cement production is a zero-waste process.
How do they do it? What technology do they use? How is FM performance monitored? Kanti Lal Nanda, Plant Head, Plant Nu Vista Limited; Tikam Chand Solanki, Plant Environment Head, JK Lakshmi Cement Ltd and Ketan Vasavada, Certified Energy Manager and cement industry consultant spoke with Mrigank Warrier, Associate Editor, Clean India Journal.
In a cement plant, dust exists in two forms – in the stack, and as suspended fugitive dust. As far as the stack is concerned, it needs to have advanced pollution controlling solutions. Nowadays, efficient baghouse filters are the norm. If the dust particles are bigger, multi-cyclones or electrostatic precipitators can be considered.
Baghouse filters
Earlier, when technology was not as advanced, there used to be cyclones, which have an efficiency of around 75%. Then electrostatic precipitators came in, with an efficiency of over 99.5%, but these are sensitive to power fluctuations. Baghouse filters are designed in a way that negative pressure draws dust-laden air to pass into them. The size of their apertures is less than three microns, so practically all the dust in the air is collected.
“Bag filters are present at grinding units, loading areas and other parts where fugitive dust can be dispersed. The collected dust is discharged back into the system, preventing pollution and also avoiding raw material losses”, shared Nanda.
Fugitive dust
Spills are common when a cement bag is dropped in the packaging area or gets torn in the loading area. Suspended dust generated by this can be harmful to open-to-the-air parts of the production equipment like bearings and gearboxes. To avoid this, dust needs to be cleaned up immediately. Difficult-to-clean areas – such as under the conveyor belt – should be identified in advance, and cleaning SOPs designed specifically for them.
“To prevent escape of dust, the maximum possible parts of the plant are made covered – from storage areas of raw material and alternative fuels to conveyor belts”, said Solanki.
An adequate draught needs to be maintained in the system to ensure that the powder-like dust does not escape. Negative pressure is maintained at draught points, so that such materials will be sucked in. A perfectly sealed system – with no cracks and leakages plugged – is essential.
Core personnel like control room operators, those dealing with large motors and critical instrumentation personnel are still from the company; security, housekeeping and alternative power generation tend to be outsourced.- Ketan Vasavada
Vacuum systems
Both centralised vacuum systems with multiple points for collection, as well as mobile vacuum machines which can be moved periodically, are in use. Bag filters are installed at practically all transfer points; suction machines can be connected to them to pick up the dust.
“Vacuum systems with appropriate piping collect spilled dust, which goes back into the raw material hopper. Dust collected from road sweeping, and from the packaging plant, is also channeled here”, said Solanki.
External areas
Dust generated during material handling in open areas can be tackled with a dry fog system and water sprinkler system. Truck mounted vacuums and road sweepers are both in vogue.
One of our respondents described an automated water sprinkling system along the road from the limestone mine to the crushing unit of the plant; it switches on every 15 minutes and settles the dust left in the wake of transport trucks.
Reducing emissions
The cement industry is one of the largest emitters of carbon dioxide in the world. While some companies are working on carbon recapture, it has not yet reached commercial viability.
The main source of carbon dioxide is calcium carbonate from limestone, which releases carbon dioxide after burning. By choosing to use or blend in low-grade limestone – which has lower calcium carbonate content, but can still produce good-quality cement – some cement companies are trying to reduce their carbon emissions.
Sulphur dioxide generated by captive power plants is trapped by flue gas desulphurisation units. Selective non-catalytic reduction processes reduce emissions of nitrogen oxides. Norms for these are set by pollution control boards, and monitored online.
In a way, a cement plant is not just zero-waste, but also waste-positive. Our kilns consume large quantities of waste generated by other industries. – Tikam Chand Solanki
Alternative fuels
“In a way, a cement plant is not just zero-waste, but also waste-positive. Our kilns consume large quantities of waste generated by other industries”, said Solanki.
Cement plants generate no waste of their own. Various streams of waste are transported to a cement plant as a source of fuel – one of the major ways in which the industry gains carbon credits. As part of the circular economy, the alternate fuel systems of their integrated units use municipal waste, bio waste and plastic waste as fuel, reducing dependence on coal.
“The excess moisture content of waste from other industries can increase the amount of heat needed to evaporate it. This waste can be sticky in nature, and the moisture may block pipes and chutes. The biggest challenge is the inconsistent calorific value of such alternative fuels. The variation has to be absorbed by coal, which is the main fuel. This fluctuation affects clinker production”, warned Vasavada.
Heat recovery
Normally, the heat efficiency of the machinery which produces the raw material for cement is 65-70%. Instead of allowing the remaining 40% heat to escape, it can be reused to generate power through waste heat recovery boilers – something already done by new cement plants.
Energy generation
Solar power – both rooftop and solar farms – are gaining ground in the cement industry. Typically, the cement company provides land and pays at a predefined rate for power generated by the solar plant that is installed and maintained by a third party. No Capex investment is needed.
Outsourcing
“Earlier, the entire staff or crew used to be on the cement company’s rolls; now contractual jobs are increasing. Core personnel like control room operators, those dealing with large motors and critical instrumentation personnel are still from the company; security, housekeeping and alternative power generation tend to be outsourced. Maintenance engineers will be from the company but technicians may be outsourced”, shared Vasavada.
“Other outsourced functions – on tonnage basis – include loading and unloading, and material handling”, reported Nanda.
Monitoring
A cement plant is tremendously high-tech. Parameters like flame temperature, flame condition, gas flow and composition, fan and motor efficiency, and gearbox vibration are monitored from a central control room through data control systems. Apart from fulfilling regulatory requirements, this also helps companies find ways to improve operational efficiency, and their bottom line.
Bag filters are present at grinding units, loading areas and other parts where fugitive dust can be dispersed. The collected dust is discharged back into the system. – Kanti Lal Nanda
Future of FM
“There was a time when a 3,000 tonne/day plant would employ 3,000-4,000 people; now, this has reduced to 700-800”, revealed Vasavada. “This has become possible because of digitisation and online real-time measurement of various parameters.”
One future trend of cement plant facility management will be to find ways to extend the life of equipment, thus increasing the gap between scheduled maintenance dates from one year, to say 1.5-2 years.
Service providers who can find ways to prevent spills, and monitor maintenance parameters like oil quality and gearbox performance (to advise on how much longer it can be used beyond the OEM’s guidelines) will be favoured.
Plants that are a few decades old may struggle to reach this level and will need help; newer plants already have this, and much more, in place.