THE CHALLENGE
A coil coating facility purchased a new 15,000 SCFM (24,075 Nm³/hr) regenerative thermal oxidizer (RTO), which had a nominal heat transfer efficiency rate of 90% thermal energy recovery (TER). The RTO unit was designed with supplemental fuel injection (SFI), which is used during low volatile organic compound (VOC) loading conditions to help save fuel costs. While the SFI was an improvement, the owner was looking for additional ways to decrease their exhaust air temperature and reduce operating costs.
THE SOLUTION
The high exhaust temperature (above 650°F, 343.34°C) and large airflow (12,650 SCFM, 20,303 Nm³/hr) in the oxidizer exhaust stack provided an opportunity to add energy recovery measures. Because the process required a significant amount of steam, it would likely provide the quickest results for an energy recovery project.
THE RESULT
Anguil Environmental installed a skid-mounted air-to-steam waste heat recovery boiler to recover exhaust waste heat from the natural gas fired thermal oxidizer and produce 25 psig of steam. The boilers use X-ID tubing for enhanced heat transfer through the helical ribs on the inside of the tubes.
The waste heat boiler package included forced circulation, fire tube, and heat recovery steam generator. The unit has automatic, modulating, exhaust gas bypass that is controlled by steam pressure. A boiler feedwater and blowdown separator were included as part of the package.
Installing the waste heat boiler system recovered approximately 2.58 MM BTU/hr of energy, lowering the stack temperature to 338°F (170°C). The addition of the waste heat boiler on this application saved the facility $216,770 per year. The total return period for this project was less than six months, demonstrating how targeted waste heat recovery can boost efficiency, and deliver a return on investment.
