Underground » Maintenance
CSIRO is developing a photocatalysis technology for more efficient and cost effective control of diesel particulate matter (DPM) emissions at underground coal mines. The technology is advanced in terms of continuous destruction of DPM at ambient and low temperatures and efficient removal of ultrafine nanosized particulates (< 100 nm) that are of greater health risk to mine workers.
Stage 1 of this project was focused on a proof-of-concept study on photocatalytic oxidation tests with the model DPM to evaluate the feasibility of DPM photocatalytic destruction. In Stage 1, a commercial carbon black Printex-U was used as the model DPM and photocatalytic oxidation was tested by loosely mixing the model DPM with photocatalysts and then illuminated with a light source. The results of Stage 1 have clearly demonstrated that the model DPM can be efficiently destructed and fully oxidised into carbon dioxide by photocatalysis. As the model DPM is comprised primarily of nanoparticles of about 25 nm, the photocatalytic process is proved to be highly efficient in eliminating ultrafine nanosized model DPM. Based on promising results of Stage 1, it is imperative to move the project to the next stage of testing the photocatalysis technology with real diesel exhaust.
Stage 2 aims to develop a prototype photocatalytic reactor for DPM destruction and test DPM photocatalytic oxidation by connecting the prototype reactor with the real diesel engine exhaust. It tested and demonstrated the performance of photocatalysis technology in removal of DPM under the real diesel exhaust conditions. Completion of the project will give better understanding how efficient the photocatalysis technology is as a novel aftertreatment technology in the control of DPM and other gaseous emissions of the diesel engine exhaust.
The prototype photocatalytic reactor was designed and developed as a flow-through reactor with the reactor windows of flat quartz plates and the insets of ceramic foam monoliths, both of which were loaded with the photocatalyst and co-catalyst. The photocatalyst/co-catalyst material that had been developed in Stage 1 with the highest photocatalytic activity on the complete oxidation of the model DPM was used for the development of the prototype reactor. Two customised LED panels were procured and used as the light source of the prototype. Both have a single wavelength of 365 nm and light intensity of up to 0.8 W/cm. The ceramic foam monoliths are very porous with large pores of millimetres, which allow the irradiation light to shine through the monolith to increase the illumination area for DPM photocatalytic oxidation and enhance the use of light irradiation.
Loading of photocatalyst and co-catalyst onto large-size quartz plates and ceramic foam monoliths has been comprehensively investigated. Detailed approaches and procedures including screen printing, spray coating and impregnation coating have been developed for the photocatalyst/co-catalyst loading. The parameters of each process including the number of coating layers, loading amounts and processing conditions were studied and optimised through the evaluation of the activity and stability of loaded catalysts by testing photocatalytic oxidation of model soot using the experimental setup and method established in Stage 1.
Prototype trials of the DPM photocatalytic reactor with real diesel engine exhaust was carried out at the engine laboratory at Queensland University of Technology using a split stream of both the raw exhaust taken directly from the engine without any aftertreatment and the water scrubbed exhaust obtained by flowing the raw exhaust through a specially-designed water scrubber.
A four-cylinder naturally-aspirated Perkins diesel engine was used for the trials, which was coupled with a dynamometer to control and maintain the engine speed, torque and power. All the tests were performed at a fixed engine speed 1,500 rpm and under four different engine loads of 25, 50, 75 and 100%. The background emission conditions of both raw and water scrubbed exhaust were measured prior to feeding into the photocatalytic reactor for comparison with those of the treated exhaust. The DPM emissions including particle mass, number and size were continuously monitored and simultaneously the concentrations of NO, NO2, NOx, CO and HC were also measured during photocatalytic reactions. A large number of engine tests were conducted under varied conditions of engine loads, exhaust flow rates and light irradiation intensities.
The results of prototype trials have shown that photocatalytic oxidation can simultaneously reduce CO and HC emissions in diesel engine exhaust. Remarkably no HC is present in the treated exhaust. There are no obvious changes of the overall NOx concentrations in the exhaust after the photocatalytic treatment, whereas the majority of NO in the exhaust is converted into NO2 by photocatalytic oxidation.
Through the project the first prototype of DPM photocatalytic reactor was designed and developed for evaluating the performance of photocatalysis technology on control DPM emissions and other gaseous emissions in diesel engine exhaust. The technology effectiveness on destructing DPM, CO and HC emissions have been well demonstrated through a range of engine tests by connecting the prototype reactor with real diesel engine exhaust.
Further improvements on the reactor design and the integration of light sources are required for developing the full-scale reactor to treat the full stream of engine exhaust. In addition, the photocatalytic reactor can be potentially deployed as an additional exhaust aftertreatment measure to some tailpipe DPM control technologies for elimination of high-toxicity nano and ultrafine soot particles and reduction of CO and HC emissions.