Burning conventional fuels in cement plants
This week Cemtech hosted its Live Webinar 'Conventional kiln fuels - preparation, storage, firing and safety' with presentations covering the design and safety of coal mills, a new kiln burner and a project to optimise a petcoke mill.
Dr Roland Aeckerberg, senior manager of process engineering at Loesche, began the discussions with an overview of the Loesche vertical coal mill design. He stated that the mills are high explosion pressure-proofed and that they have an inerting system to reduce O2 concentration. Having described the process of how coal is ground through the Loesche coal mill with a high-efficiency separator, and looked at safety measures such as magnetic separators, gas analysers and venting, Dr Aeckerberg stressed that the best practice for coal mill operation was to have continuous operation rather than starting and stopping, which can increase O2 build-up and the chances of an explosion.
Are you operating a safe plant? Vincent Grosskopf, founder of Coal Mill Safety (Singapore), drew on decades of experience in the sector to highlight what he perceives is a lack of awareness in the industry about the measures to take to grind pulverised fuels safely. He argued that safety is often compromised in the design stage of installing a coal grinding system, due sometimes to a lack of expertise but also arising from pressure by cement producers to reduce costs, resulting in inferior explosion protection.
Mill explosions will only occur when three conditions exist: sufficient oxygen (≥12 per cent O2-in-air), the presence of an ignition source (>30mJ) and air-suspended coal dust in a bandwidth of 50-2000g/m3. Safe operation of coal mills seeks to avoid these conditions and many monitoring systems exist to provide fire and explosion protection. Constructional explosion protection is the last-ditch defence to prevent damage to equipment such as the bag filter. This involves venting, explosion isolation and flame front propagation mitigation. However, Mr Grosskopf stressed that flames travelling at velocities of 200m/s (720km/h) in the riser duct are difficult to stop.
Webinar guests were then able to learn about the new Fives Pillard Novaflam® evolution burner from Thangarasu Suresh, general manager of Technical at Fives Combustion Systems Pvt Ltd (India). The Novaflam® evolution has been designed for maximising clinker quality and production rates. Offering enhanced fuel flexibility and reduced CO2 emissions, it has been created to increase the substitution rate of alternative fuels while reducing NOx emissions. The axial/radial V-shape nozzle arrangement provides impulse efficiency with optimised thermal profile.
Burner improvements include features such as the Pillard RST™ Swirler, which optimises ignition distance for lean O2 recirculation zone and the Pillard PGZ™ nozzle, which reduces NOx. The Pillard BLUEMIX™ design also helps create low and uniform flame temperature, while an Airless stabilizer™ provides additional flame control. Additional features in of the new burner include an ASF injector to optimise residence times, a sturdier tip design, and 4.0 smart-ready technology. The new burner comes in two versions. The Novaflam® evolution mono-channel burner and the bi-channel Novaflam® evolution+.
Mr Suresh concluded with case studies of burner performance at Lehigh Cement's Union Bridge plant, USA, Ramco Cement Ltd in India, Sebryakov Cement in Russia, Holcim's Davao plant in the Philippines and Biskra Cement in Algeria.
The final speaker was Virendra Rathore, JK White Cement, who reported on the optimisation of the company's petcoke Mill No 3. A project was launched to increase the mill's output and to reduce power consumption. Action was taken to increase the baghouse fan from 1130-1350rpm. The petcoke weighfeeder intake was increased from 12-15tph, while the mill grinding pressure was raised from 95-96bar to 104-105bar. On the mill, 12 of the 48 nozzels were blocked for reduced return material and the dam ring hight was raised from 50-60mm. After all the improvements, the mill increased output from 8Mtph to 11Mtph while power consumption per tonne of material was reduced from 27kWh/t to 22kWh/t. Specific energy consumption was also lowered from 3.9 to 3.4 units/t of cement.
