Pollution Engineering - April 2009 - (Page 30) Energy Savings for VOC ABATEMENT As a coating and laminate company in South Carolina discovered, older model regenerative thermal oxidizers can be real gas hogs. But at what point is it cost effective to replace an aging RTO? By JON HOMMES, lead engineer, Dürr Systems Inc., EES fter operating two regenerative thermal oxidizers (RTOs) for the last 25 years, Soliant LLC, Lancaster, S.C., considered what repairs were needed to keep them operating reliably. The company manufactures precision coatings for durable films and laminates in support of the transportation, marine, heavy truck, recreation, consumer electronics and consumer packaging industries. They approached the original manufacturers of the RTOs, Dürr Systems Inc. EES, to assess and recommend repairs. After inspecting the equipment, the manufacturer determined A Old RTOs (2006 Avg) New RL60 RTO January ‘08 February ‘08 March ‘08 April ‘08 May ‘08 June ‘08 Average Month Gas Savings that the old oxidizers had been designed with low thermal efficiency to accommodate VOC loading significantly higher than their current levels. Under current operating conditions, the old oxidizers were gas hogs. In 2006, the oxidizers used 56,675 dekatherms (dth) at an average of $10.78/dth. This added up to over $50,913 per month. RTO replacement project In late 2007, the company installed a new rotary-valve RTO to replace the old oxidizers, which went online Dec. 17; the energy performance contract began Jan. 1, 2008. Through June of 2008, the new oxidizer had reduced the company’s gas usage for VOC abatement by 85 percent. With their long-term gas supply contract ending in June 2008, the company began looking at a spot gas price for uninterruptible service of $15/dth and a contract price of $14/dth. At their current contract natural gas price, the RTO replacement project saves the company an average of $56,500 per month. Technical Comparison Number of Fans Number of Valves/ Actuators Number of Burners Ambient Noise Level Control Panel Old Oxidizers 4 42 (14 in, 14 out, 14 purge) 2 Very high Inside plant, no HMI to display system information Natural Gas Usage (dth/mo) 4,723 (56,675dth/yr) Operating Cost ($/month @ $14/dth) $66,122/mo 734 782 650 726 609 617 686 4,037 dth/mo $10,276 $10,948 $9,100 $10,164 $8,526 $8,638 $9,604/mo $56,518/mo New RTO 1 1 RL rotary valve 1 Low Air-conditioned control room at the RTO + remote panel inside plant Figure 1: The replacement RTO system used much less fuel and energy, reducing the monthly gas bill by over $56,000 per month. Figure 2: The new system improved emissions and efficiency. 30 Pollution Engineering APRIL2009
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