b'a system withTAILOR-MADE RUNECO SOLUTIONS - NOsuction roll and two felt Uhle boxescapacity, also offers a higher degree of two turboCOMPROMISES (see Fig.3). Also, the vacuum level ofcontrollability and less losses resulting units allowsDepending on Tissue machine designthe suction press roll is often clearlyin a more energy efficient vacuum even higherand width, the most efficient operationlower than that of the Uhle boxes.system. Typical savings in energy operationalsometimes requires one and sometimesAnd as air is a compressible medium,consumption are 30-50% when the flexibility,two Turbo blowers. The specified airthe volume changes significantly withlosses are eliminated in a two turbo controllabilityflow capacity is typically quite highthe surrounding pressure. Thesesystem. Another advantage of a two-and energyconsisting of overall safety margin, feltunavoidable facts lead to considerableunit system is the existence of a back-efficiency.life and type margin and with liquidenergy losses in a one-unit systemup in the very unlikely malfunctioning ring pumps, e.g. pump wear and sealthrough two mechanisms - the firstsituation as the machine can be run water temperature variation margins. Inbeing the throttling losses in thewith one turbo unit only, though with normal operating conditions the neededsuction press vacuum level control,less efficiently.air flow capacity is 40-50% lower thanand the second being the loss due the specified capacity. Regardless of theto the air expansion from the lowerTable 1. shows a typical calculation, situation, RunEco system with a fullysuction press roll vacuum state to theincluding a long term cost of speed-controlled turbo blower provideshigher vacuum in the felt Uhle boxesownership, comparing the costs of a high operating efficiency at all times. and in the main vacuum header. Ansingle turbo unit and two turbo unit often used vacuum level difference ofRunEco system to a traditional vacuum During normal operation, one single- approx. 10 kPa between the suctionsystem with liquid ring pumps. stage turbo blower typically providespress roll and felt Uhle boxes can lead sufficient capacity. However, a systemto over 50% increase in the air volumeThe absolute difference is of course with two turbo units allows even higherthrough expansion and thus to a largeaffected by the local energy price. operational flexibility, controllabilityincrease in energy consumption. However, the table highlights the and energy efficiency. As an example,fundamental differences in the running Tissue machines often have three mainA two turbo blower RunEco system,method, controllability and losses vacuum consumers, namely the presswhile offering a redundant air flowbetween the systems.Table 1. Typical calculation, including a long term cost of ownership, comparing the costs of a single turbo unit and two turbo unit RunEco system to a traditional vacuum system with liquid ring pumps.TISSUE TECHNOLOGY INTERNATIONAL31'