2nd Global Cement EnviroCem Conference on Environmental Technology for Cement & Lime
20 - 21 March 2014 - London, UK
By Robert McCaffrey, conference convenor
The 2nd Global EnviroCem Conference took place on 20 - 21 March in London, with delegates from 16 countries in attendance and a conference programme intensely focused on reducing cement plant emissions to air. A popular mercury emissions workshop was included. The 3rd Global EnviroCem Conference will take place in London in March 2016.
Image gallery for the 2nd Global Cement EnviroCem Conference on Environmental Technology for Cement & Lime - London, March 2014 (large gallery - may take time to load)
After the first event in 2008 in Düsseldorf, the second Global EnviroCem Conference took place in London. Despite the event being organised at quite short notice, cement producer delegates representing around 450Mt of cement production capacity were in attendance, including representatives from Cemex, Holcim and Lafarge.
John Kline, of John Kline Consulting, opened the conference by looking at the cement plant of the future. He suggested that the reduction of radiation and convection from the system through improved refractories and sealing could be the only remaining areas for major process efficiency improvements, aside from waste heat recovery. Efficiency gains may also come from improvements in grinding. John suggested that the proportion and overall amount of biomass in alternative fuels (AF) must increase to be able to reduce CO2 emissions from cement. He pointed out that improved grinding of AF to produce finer particles, as well as off-line combustion including pyrolysis and torrefaction, will allow higher levels of AF use. 'Grow your own fuels' may be a refrain for future cement producers, possibly using their own land or rehabilitated quarries. John also mentioned that new clinkers are being brought out to reduce environmental impacts, including Aether, Alipre, HC's BCT, NEXT from Buzzi and Vicat's Alpenat.
Mrs Claude Lorea of Cembureau pointed out that the cement industry is confronted with a 'high policy density,' that an emission performance that might be achieved on an experimental plant might then be treated as the best available technology and that the low emissions achieved might subsequently be written into laws and be applied internationally. Claude pointed out that many kilns do not need reduction measures for SOx - typically where there is no or low levels of pyrites in the raw meal. "The proposed high environmental ambition levels - the so-called 75% gap closure scenario - are at significant risk of being unattainable." A 50% gap closure scenario is claimed by industry to be more realistic.
At the start of the next session, on avoiding emissions production, Mike Sumner of Grace Construction Materials pointed out that cement plants can happily make cement without additives. However, many plants decide to use additives in order to add a commercial advantage, as well as improving cement performance. Additives can also be used to reduce - all other things being equal - the production of emissions to air, partly by allowing producers to decrease the clinker factor. Mike pointed out that many minor elements, such as those that can be enhanced in the pyroprocessing circuit while using AF, can have a disproportionate effect on cement properties. Mike also mentioned that Grace is part of a consortium that is working on a pressure swing absorption technology for the capture of CO2.
Joep Bierman of Voith Paper CTC Technology spoke about the CTC (controlled thermal conversion) process, which converts sludge from the paper recycling process into energy and minerals, including calcium carbonate, calcium oxide and meta-kaolinite. It has been shown that the minerals are capable of capturing mercury from the flue-gas of coal-fired power plants when used as a high temperature injected sorbent, as well as various benefits in waste-to-energy plants. MinPlus is a highly-porous finely-divided non-carbon-based sorbent, that first oxides elemental mercury and then captures the oxidised mercury. The additive also absorbs chlorine, sulphur and a number of heavy metals and is subsequently captured in the baghouse or ESP. Mercury is securely bound to the absorbent at temperatures up to around 350°C and leaching levels are low. Joep pointed out that the sorbent has not yet been used in the cement industry, but that Voith is open to that possibility.
Giovanni Sghirlaznoni of FLSmidth Airtech next spoke about innovations in fabric filters. DuoClean fabric filter technology uses a single compartment, with a dual gas flow approach from the side and bottom of the bags, unique gas distribution screens, long filter bags, low can velocity and low dust re-entrainment and pre-separation of the dust before the bags. DuoClean is ideal for processes with a high dust load or when online maintenance is not required. The octagonal filter units are modular and additional units can be added to cope with higher air flows, while their design means that capital and operational expenditure is kept to a minimum.
Georg Rathwallner of Evonik Industries spoke about the use of P84 polyimide fibres for the production of filter bags. Georg suggested that filter membranes are fine, as long as the membrane is completely intact: needle felts are suggested to be more robust and Georg said that if the surface of a needle felt is damaged in some way, then the next layer of fibres will continue to 'do the job.' Georg emphasised the point that P84-based bags have a lower pressure drop than other types of filter bags. Multilobal fibres increase dust filtration and also prevent dust infiltration into the fibres after the initial conditioning of the bags. Finally, Georg stated that used bags can be used as an alternative fuel, since they have a low content of minerals and no harmful combustion gases.
John Kline came back to the podium to speak about the various options for NOx reduction in the cement industry. Nitrogen oxides are formed when nitrogen from the fuel and or combustion air is combined with oxygen during combustion. NOx creation increases with fuel nitrogen level, the amount of air available for combustion and the combustion temperature. SNCR (selective non-catalytic reduction) using NH3 is applicable only in a narrow band of temperatures of 800-1000°C, which is typically only achieved within the kiln itself. SCR (selective catalytic reduction) requires a catalyst and a reducing agent and is widely used in coal-fired power stations. SCR has a higher level of NOx reduction and a lower level of ammonia slip, but the units have much higher investment costs than SNCR and higher operating costs, as well as more down time, a larger footprint and difficulties with retrofitting. SCR units can struggle with higher dust loadings and may require gas conditioning or prefiltration. However, this can require the gas to be cooled for filtration, prior to being reheated enough (to 300-400°C) for the catalyst to work efficiently. Alternatively, the gas can be passed through an ESP, to produce a lower dust load at a higher temperature, as at Lafarge Mannersdorf. The new project at the Rezzatto plant in Italy will have high-dust SCR technology installed as part of a plant upgrade, with the gas conditioning tower situated on top of the catalyst tower and with results expected by 2015. Alternatively, or in addition, filter bags can be impregnated with catalyst, to provide an SCR solution, while ceramic catalyst 'candles' can also be used, as supplied by Trimer and FLSmidth. Regenerative thermal oxidation (RTO) takes exhaust gases from various parts of the plant and heats them to around 800°C to reduce NOx and other pollutants, while organic components in the gas and CO oxidation can lead to the RTO unit being 'self-fuelling.' Josh pointed out that low temperature catalysts will be a real game-changer for the cement industry.
Ted Reese of Cadence Environmental Energy next spoke about options to manage CO in the cement industry. Ted suggests that CO is the 'forgotten emission,' which may not even be mentioned in emissions permits, but that CO reduction represents an opportunity rather than a cost for cement plants. Larger fuel particle sizes and delayed ignition rates will tend to create more CO. Ted suggested that higher CO levels can limit production and the amount of AF that can be used, while high levels of CO tend to promote local reducing conditions in the raw material bed which can result in sulphur release. Higher sulphur release can tend towards higher blockages in the riser duct section or at the kiln inlet. Ted reminded delegates of Cadence's Mixing Air technology, which puts a fan on the outside of the kiln and which uses injected air to increase mixing and to reduce NOx and CO, with many knock-on benefits.
Stefan Kern of A TEC concluded the first day with a presentation on the processing of alkali-rich bypass dust with his company's ReduDust concept. In short, the bypass dust (composed of free lime, chlorine, sulphur, sodium, potassium and other components) is washed or leached to produce a de-salted dust rich in hydrated lime and with Cl content of less than 1% which can be reintroduced into the process, as well as a brine which is then treated and crystallised to produce salable purified KCl and NaCl salts at a rate of around 200kg/t of dust processed. An industrial plant will go into production at Holcim's Rohoznik plant in Slovakia in 2014, processing 20,000t of bypass dust and producing 4000t of salt each year and with a design efficiency of Cl removal of around 90%.
Following a convivial evening on a canal boat, Ullrich Speer of Lechler GmbH started the second day and spoke about the challenges of using SNCR for NOx reduction, including process temperatures outside the optimum temperature range of perhaps 900 - 1050°C, short residence times, dust loadings, coatings and foulings. Ullrich pointed out that there are different levels of sophistication in SNCR, from basic systems with fixed lances and nozzles, up to high efficiency options with NOx predictive capabilities (with thermography) and 'intelligent' neural-network-based control systems that learn the optimum configuration of the system.
Stefan Huemer of Scheuch spoke about his company's NOx and CO reduction solutions, including its SCR system at Lafarge Mannersdorf, which uses 'soot blowers' to clean the air channels in the catalyser honeycombs clear of dust, using a heat-exchanger to preheat the purge air. Scheuch DeCONOx technology is a combined SCR and RTO unit, which is capable of reducing NOx by around 90% and CO/VOC (volatile organic compounds, also known as THC - total hydrocarbons) by around 98 - 99% and is also capable of running in autothermal ('self-fuelling') mode.
Naresh Suchak of Linde next spoke about the LoTOx NOx control solution for cement and lime plants. LoTOx is an end-of-pipe post-combustion NOx control solution which works on dirty exhaust gas by injecting ozone to oxidise NO to soluble N2O5 while also oxidising Hg. The ozone is produced on-site, on-demand, so that the system requires a NOx measurement feedback loop from the process to gauge how much is required. The system has a fairly high cost per tonne of NOx removed, but it has very high removal efficiencies. The system can significantly be installed downstream of SNCR or SCR systems. Suchak noted that "nitrates in any collected dust must be disposed of responsibly."
Franz-Josef Zurhove of Elex CemCat next spoke about the CemCat SCR technology. He pointed out that the debates that are underway in the cement industry at the moment already took place in the power industry 20 years ago. In the power industry, high dust installations are the norm and 100mg/Nm3 and 95% NOx reduction is possible, with simultaneous VOC, dioxin and furans reduction and mercury oxidation. However, in cement, the dust load is higher and stickier; and the dust may contain clays and salts which can cause process problems and can poison the catalysts. Franz-Josef mentioned that an SCR system at Montselice encountered problems with the build-up of clay materials. The catalyst cells were redesigned and other process parameters changed and the dust encrustation problem was eliminated. Other design improvements have reduced power consumption for dust cleaning by nearly 50%. At the Mergelstetten plant, which uses up to 100% AF, the incoming NOx levels can vary widely, from 700 - 2500mg/Nm3. Higher temperatures at the plant need better dust cleaning performance than for colder gases, while on the other hand high gas temperatures can cause deactivation of the catalyst. Water injection to reduce gas temperatures proved to be an effective solution. At the Joppa plant, a long dry kiln, NOx input was 2240mg/Nm3 and was reduced to 448mg/Nm3, even with extreme dust chemistry and with a high salt fraction of up to 50%. The new SCR at Rezzato will be commissioned in the autumn of 2014 and will be integrated directly in the down-comer duct before the GCT (gas conditioning tower) and the kiln ID (induced draught) fan. Franz-Josef pointed out that an SCR is actually an oxidation system (rather than a reduction system as suggested in its name), that oxidises ammonia using any NOx that is available. He reminded delegates that CO and methane oxidation are not possible in an SCR, due to the low temperatures compared to an RTO (regenerative thermal oxidiser). He forecast that the capex of SCR will progressively reduce and that the system power consumption will reduce to around 2 - 1.8kWh/t clinker. "High-dust SCR is the way forward," he concluded.
The penultimate speech at the conference was from W L Gore and concerned its new gas phase control technology consisting of sorbent-impregnated ePTFE membranes which also have a catalytic effect and which are installed in modules. The modules capture elemental and oxidised mercury and can be installed as a stand-alone structure after the baghouse or ESP, with gas temperatures of lower than 93°C. Mercury is strongly bound within the sorbent polymer catalyst, with high temperature retort processing required to remove the mercury prior to module disposal. The modules are currently being tested in the cement industry.
The final presentation at the conference was given by Martin Krenn of CTP and was on the RTO at Wopfing cement plant. The plant suffered from odour problems which had not been fixed by other measures including injection of odour-reducing materials, ozone dosing and SCR. A pilot RTO plant proved to be effective and a full-sized unit was then installed. The five-bed unit uses regenerative thermal cycling to provide a thermal efficiency of around 95% and includes an integral SNCR system. Due to the level of VOC and CO in the inlet gas, the unit is capable of running in autothermal mode, with no internal heating required. Due to minor plugging of the ceramics - the dust load must be low, at less than 10mg/Nm3 - cleaning is required to take place only yearly. A bake-out cycle is included into operation to reduce fouling of the ceramics through condensation. The odour problem was fixed and the RTO allowed the producer to increase its AF use and to use higher levels of secondary raw materials, even if they include high levels of organic matter, potentially leading to negative raw materials cost. Martin Krenn concluded that the system may be widely applicable, although plant-by-plant testing will be required.
A half-day mercury emission abatement workshop was given by John Kline of John Kline Consulting. The workshop covered mercury regulations, mercury sources, the important topic of mercury speciation, cement plant emissions, mercury emissions abatement and mercury measurement techniques and technology.
Farewells and conference prizes
Based on attendee voting for the best presentation at the conference, Franz-Josef Zurhove of Elex CemCat was awarded third place, Ted Reese of Cadence Environmental Energy took second place, but Georg Rathwallner of Evonik was awarded first place for his paper on the use of P84 as a fibre for filter bags.
Despite its relatively small size, delegates were very positive about the 2nd Global EnviroCem Conference:
- Very good technical topics
- Thanks a lot: in general it was perfect.
- Nice diversified group of industry managers and vendors - quality people
- Another well-delivered conference, successful from my perspective. Thank you!
- General environment allowed for easy introduction to attendees
- Good atmosphere, excellent technical contents
- Great job from all members of the EnviroCem team
- Congratulations, it was a good conference
- Great to have all talks printed and on a CD - very useful
- Very friendly and helpful organising team
- Different people came from lots of countries with different experiences
- Loved the speed-dating - must get more cards printed next time - great idea!
With a show of hands, delegates unanimously agreed to meet again in two years to assess progress in the fast-moving and innovative sector of cement industry gas cleaning and environmental impact abatement. We look forward to seeing you at the 3rd Global EnviroCem Conference in London in May 2016!