Rock Products

MAR 2013

Rock Products is the aggregates industry's leading source for market analysis and technology solutions, delivering critical content focusing on aggregates-processing equipment; operational efficiencies; management best practices; comprehensive market

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LOADING HAULING ture, load and speed,��� said Emmett. Ac��� tive regeneration requires injecting fuel into the exhaust system, increasing fuel consumption and elevating exhaust temperatures up to 1,300 F (704 C) to clean the filter. This is often done with��� out impacting truck performance, but, in extreme cases, it could require the truck to be parked while the filter is regener��� ated, lowering production potential. It is this critical balance between ma��� chine load and the particulate filter re��� generation that is at issue. Articulated dump trucks operate in a low���engine��� demand duty cycle. ���The normal duty cycle of a truck is 30 to 40 percent, which makes it difficult for the engine to clear the DPF through passive regenera��� tion,��� said Emmett. Terex has extensively studied the rela��� tionship between duty cycle of its ma��� chines and the best Tier 4i/Stage IIIB solution. ���Since Terex does not manufac��� ture engines,��� said Emmett, ���we are able to work with leading engine manufac��� turers to choose the most efficient tech��� nology to match the application. We offer EGR technology for our material handlers, which have a high���duty cycle of up to 70 percent.��� For articulated trucks, however, Terex and Scania see SCR as the more efficient approach for customers. The SCR Option The primary emission���reducing ingredi��� ent of an SCR engine is DEF, a safe, stable and non���toxic liquid. The straightfor��� ward SCR system is composed of a DEF injector, supply module and storage tank. A chemical reaction takes place in��� side the SCR chamber to convert NOX into a harmless mixture of nitrogen vapor and water. ���Even when the cost of DEF is taken into account, the combined diesel and DEF cost for the new Terex TA300 is 7 per��� cent lower than the cost of fuel in the previous Tier 3/Stage IIIA engine.��� Production of Terex articulated trucks with the Scania SCR engines began in June 2011. Scania engines are also equipped in various equipment lines within the multiple Terex business seg��� ments. ���We have hundreds of SCR tech��� nology engines operating in North America,��� said Sundell. ���One of our early SCR prototype engines was installed in a piece of Terex port equipment and now has more than 9,000 operating hours on it. We also have a Tier 4i engine in a wheel loader with more than 11,000 op��� erating hours.��� Terex Construction offers Scania SCR engines for its TA250, TA300 and TA400 articulated trucks, designed for the construction and aggregate mar��� kets. The 9��� and 13���L engines offer from 311 hp (232 kW) to 444 hp (331 kW) gross power and are fine���tuned for efficient operation, based on applica��� tion demand. Demystifying DEF While SCR may be a preferred technol��� ogy for Terex off���road trucks, DEF is a relatively new additive within the off��� highway machine industry, which can lead to some concern. ���Customers often ask me questions about DEF, based on what they have heard and on some mis��� conceptions in the marketplace,��� said Emmett. The DEF used in SCR systems is a care��� fully blended aqueous solution consist��� ing of 32.5 percent high purity urea and 67.5 percent deionized water. A com��� pound of nitrogen, urea turns into am��� monia when heated and has been used in a variety of industries, including agriculture. The 32.5 percent urea concentration gives DEF its lowest freezing point of 12 F (���11 C). Both the deionized water and urea freeze at the same rate, so as it thaws the solution does not become di��� luted or over concentrated. During vehicle operation, SCR systems are designed to heat the DEF tank and supply lines. ���The engine cooling circuit is connected to the DEF tank, and the hoses are electrically heated to keep DEF a liquid,��� says Sundell. Should the solution freeze when the ve��� hicle is shut down, the system is de��� signed to withstand the expansion and quickly return DEF to its liquid form, so vehicle operation will not be impacted. ���We have trucks dependably operating in ���40 F (���40 C) temperatures in Moscow,��� said Emmett. Sundell adds, ���I have not heard of any cases where DEF freezing has caused problems with Sca��� nia engines.��� When compared to EGR, SCR is a much simpler technology that enables the manufacturer to fine tune the engine for performance without sacrifices. ���With the SCR system,��� said Sundell, ���emis��� sions are ���taken care of��� in the after��� treatment system, which allows us to adjust the engine for lower fuel con��� sumption and better responsiveness.��� Scott Pollock, global product manager for Terex articulated trucks, continued, ROCKproducts ��� MARCH 2013 33

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