This week, Cemtech held an international webinar on state-of the-art monitoring and control emissions technology. The webinar discussed the reduction of NOx emissions with a brand new precalciner technology, modern particulate matter cement emission monitoring systems (CEMs), high performance fibre technology for filter bags, and an innovative gas temperature measurement technology.
Precalciner advances
Aleksandra Novakovic-Andric, FLSmidth's global chief process engineer, spoke on the company's breakthrough in low-NOx pyroprocesses, a development that forms part of its Mission Zero sustainability strategy to develop technical equipment to run zero-emission cement plants by 2030.
FLSmidth's latest low-NOx calciner was introduced in 2017, when it was first installed at a 2000tpd white cement plant. The calciner has a larger reduction zone to reduce NOx and is equipped with an elevated tertiary air duct. High-temperature operation in the bottom part of the calciner is beneficial to low NOx and the new design has cylindrical walls that help prevent build-up. The core of the burning zone is kept high at 1200˚C, while the walls remain cooler than traditional calciner walls. Harder-to-burn fuels such as anthracite and petcoke are also easier to combust in this precalciner with low O2 and good fuel contact.
There are now three of FLSmidth’s Low NOx ILC calciners in operation. The second and third case studies are on grey kiln lines with capacities of 6500tpd and 6300tpd. According to FLSmidth, optimising the calciner can be one of the most effective means of reducing NOx emissions.
Particulate matter CEMS
Simon Kirk, product and marketing manager at ENVEA UK, and Richard Woodgate, head of international sales at ENVEA France, spoke on emissions and process control.
They explained that the main changes affecting environmental monitoring are ever-tightening regulatory control, including the lowering of emission limit values (ELVs), installation of more effective filtration systems and higher requirements for greater process efficiency. Emission monitoring of particulates can be carried out on the stack (emissions to air), baghouses and for predictive bag filter row monitoring.
Scatter-based light beam systems are increasingly used to meet the lower emission limit values. These are deployed in addition to traditional cross-stack opacity systems, while forward or backscatter technologies are highly accurate at low concentration levels. Choices are predominantly made on regulatory requirements, stack diameter and temperature, but kiln stack velocities also need consideration.
Multi-compartment baghouses have become popular, replacing ESPs as the standard for highly efficient plants. New sensor technologies now offer real-time performance monitoring of filters, including features such as leak detection and predictive bag filter row monitoring. Predictive alarms can sense pulse jet spikes, the number of pulses, increases in particulates and failed filters or leaks.
Contactless gas flow measurement
Dirk Schmidt of Kima Process Control GmbH, presented a paper on contactless, precise and fast temperature and gas flow measurement. The latest product from Kima is the Gastemp 600+1500 flow for acoustic gas temperature and volumetric measurement. The gastemp measures the transit time of an acoustic pulse passing through a hot gas to give an average temperature along the measured path and it is a contactless measurement.
The speed of sound is measured both against and in the direction of gas flow to assess the volume flow from a cross-section of a duct. Gastemp 600 flow measures up to 600˚C and the 1500 product up to 1500˚C and the instruments operate in high dust content environments up to 100g/m3. Such equipment can be fitted in the downcomer at a cement plant, kiln inlet, calciner exit or to measure secondary or tertiary air temperature.
Fibre and multifilament yarn design
Günter Gasparin, R&D manager of Evonik Industries, and Dr Georg Rathwallner, an external consultant for Evonik Fibres GmbH, highlighted the performance benefits of P84® filter media for baghouse filters.
During operation, the P84 high-performance filter media establish a permanent dust cake on the filter bag, but allow no dust penetration. There is a stable and low pressure drop, and this enables long bag life of up to eight years.
The Multilobal P84® fibres allow collection of dust particles in the lobes of the P84® fibres in low-velocity areas. This offers greater surface area and enables more dust collection than the traditional round profiles of standard fibres. P84® can produce energy savings of 10-20 per cent and P84 needle felts usually have a payback period of 2-3 years.
At Oman Cement, when the P84® bags were checked after 14 months on the kiln and raw mill baghouse, bag failures occurred in only three chambers and 33 bags were damaged out of 4368. No violations of emission standards were recorded. Having replaced 700 bags in 2020 the plant had a failure rate of 1.5 per cent during the three-year warranty period.
Summary
Effective emissions control is a priority for cement producers and technology suppliers are making significant progress in delivering high-performance solutions in a range of areas. Preventative measures are gaining widescale acceptance as best practice and the onset of digital capabilities will take emission reduction to the next level. This webinar clearly demonstrated that precalciners, filter bags, gas flow measurement and fibre technology are key tools in the battle to ensure a lower emission cement industry.