Transitioning to a low carbon economy is a challenge we all face and its better to face it with partners, especially scientists from a local University.
Lafarge’s transition to lower carbon energy has benefited greatly in recent years from collaborative work with Dalhousie University researcher Dr. Mark Gibson. Dr. Gibson has had an abiding interest in the nexus between carbon emissions and re-use and re-purpose solutions for expired goods. Working under a 5-year NSERC Discovery Grant, starting in 2015, Dr.Gibson and his student team have been investigating the re-purposing of plastics, scrap tires, and other materials as fuel in cement kilns and to use satellites to track emissions changes in kiln across North America when using alternative fuels. This earlier work included literature reviews and lab testing. This continuing partnership between Lafarge Canada Inc. and Dalhousie’s Faculty of Engineering will underly the testing of tire derived fuel as a low carbon fuel alternative in the cement industry at the Lafarge Brookfield cement plant.
Recent laboratory studies conducted by Dr. Mark Gibson, Associate Professor in Dalhousie University’s Department of Civil and Resource Engineering and his colleagues in Process Engineering and Applied Science, Dr. Michael Pegg and PhD student, Ebenezer Asamany, show that tire derived fuel has the potential to lower CO2 emissions compared with coal derived fuel when co-fired in cement kilns – and with beneficial or benign effects on other emissions.
In 2015, Dr. Gibson and his team published a report entitled Use of scrap tires as an alternative fuel source at the Lafarge cement kiln, Brookfield, Nova Scotia.
“My students and I are very pleased to see this work enter the real world. Based on our research, we expect to see significant reductions in greenhouse gas emissions from the Brookfield cement plant and thereby help Nova Scotia move one step closer to a low carbon economy,” said Dr. Gibson. “We also expect that the use of tire-derived fuel will reduce NOx emissions as well as make excellent use of scrap tires,” he added.
Lafarge Canada is committed to doing its part to move to being a lower carbon manufacturer. “It is important that we work with partners in tackling the challenging problem of climate change. Dr. Gibson’s team’s research in recent years has been essential to our understanding of how to replace fossil fuels, like coal, with lower carbon alternatives,” said Rob Cumming, Environment Director for Lafarge.
While there are a number of levers available to reduce the carbon emissions in the cement industry, one of the most promising and “shovel ready” solution is growing usage of lower carbon fuels. Thanks to different initiatives including previous work with Dalhousie’s Faculty of Engineering, the Brookfield plant has reached world class status in the percentage of its fossil fuels replaced with lower carbon fuels, in the form of front end burner injection, and has reached substitution rates as high as 30% on an energy basis by the end of this year.
350,000 scrap tires per year which is just under half of the amount of tires generated in Nova Scotia.
A team of students, specialists, and Lafarge staff, under the supervision of Dr Gibson will conduct extensive baseline tests to measure kiln performance and emissions with and without the use of scrap tires and will then compare results.
This assessment will be shared with the public. The emission tests consist of continuous emission analyzers drawing gases from the stack. In addition, for trace analysis, a team of specialists will climb the stack in order to draw out stack gases through a series of filters and solutions to capture all of the compounds. The samples are sent to specialized environmental laboratories and all of the data is put together to report on the concentrations of the compounds measured. The testing methodologies follow government approved methods and will be overseen by the research team. All of this testing is in addition to continued laboratory testing and cement quality assessments.
Waste plastics destined for landfills possess large amounts of untapped energy that could be used to fuel high temperature furnaces such as rotary cement kilns through direct combustion.
Redirecting such waste to a local cement kiln presents a dual solution to both cost and environmental concerns.
In an effort to reduce fuel costs and reduce environmental emissions, Lafarge Canada Inc., Brookfield, Nova Scotia has explored the use of waste materials substituting for coal and coke as fuel sources at their cement plant. A potential fuel source is mixed waste plastics.
The research objective was to comparatively study and to predict any potential changes in stack emissions in a cement kiln equipped with an Electrostatic precipitator (ESP) if an equivalent amount of heat was shifted from the 50-50 blend of coal/coke to an equivalent heat amount of plastics. An experimental set up at Dalhousie University’s, Process Engineering and Applied Science department comprising a tube furnace with an exhaust stream connected to emission detection devices was used in investigations. Existing literature, chemical elemental analysis, and comparative experimental data were employed to predict potential changes in major emissions such as carbon dioxide (CO2), sulphur dioxide (SO2), nitrogen oxides (NOx), airborne particulate matter (PM) and volatile organic compounds (VOCs). All results were discussed with full regard to the limitations that the experimental set up encountered in mimicking actual industrial kiln conditions.
The findings of the study as presented in this report show that based on equivalent heat amounts, 30% less plastic by mass is required to contribute the same energy as the coal/coke blend.
There was a considerable potential reduction in CO2, SO2, and fuel NOx emissions by 34%, 98% and 80% respectively. On an equal mass basis, more VOC species were detected during the combustion of plastics than for coal/coke however all VOC species would thermally degrade to CO2 and H2O given kiln temperatures in excess of 1100 to 1400°C and considerable kiln residence time. Changes in stack emissions in terms of VOCs are therefore expected to be minimal. Projections based on elemental analysis and experimental data also indicate that the particulate matter contribution from plastics lie within ranges which emission control technology such as electrostatic precipitator (ESP) presently in use at the Brookfield plant is capable of removing from the flue gas stream.
The preliminary results provide sufficient insight into the expected performance of waste plastics compared to coal/coke fuel blend under similar conditions. Proceeding to full scale field trials for plastic combustion in the cement kiln with emissions monitoring apparatus has been recommended. Field trials will provide data that will first of all, confirm experimental predictions or otherwise; and secondly fully quantify the effects of the electrostatic precipitator on the predicted changes in emissions.