In the mid -1990s, a rendering plant found itself located in the middle of an area experiencing a tremendous population boom. Neighboring citizens complained regularly about the odor emitted from the plant. While the plant used a masking agent designed for odor control, the mixture of odors proved even more offensive. In addition, two oil refineries, two feed mills, a food processing plant, and an animal food plant were also located in the area. All contributed to the odor problem. In 1997, county and state health departments began to take action to address the odor issues. As a result, the rendering plant transitioned from the masking agent it had been using to chlorine dioxide (ClO2) as an oxidizing agent to combat odor. A traditional three-precursor ClO2 generation system using sodium chlorite, hydrochloric acid, and sodium hypochlorite was installed. The system provided an immediate reduction in the odors being emitted from the plant.

The three-precursor ClO2 generation system did not have the capacity to maintain the oxidant level at the necessary ORP set point—500 mV—especially during the high-volume periods that occurred in conjunction with summer’s warmer temperatures. The generation system also required constant monitoring to ensure it was operating effectively. Operators had to adjust precursor rotometer settings every 15-30 minutes, and check for air bubbles in the lines. Eduction was used to deliver precursors into the generator. ClO2 solution was educted from the batch tank into the scrubber system. Multiple eduction processes resulted in very poor dosage control. Most importantly, if the system failed, it was not easy for on-site personnel to correct the problem.

The generation system relied on the use of a ClO2 batch tank to provide the necessary conversion of precursors to ClO2. In order to accelerate the rate of ClO2 generation, excess acid and sodium hypochlorite were used to speed production. The presence of the batch tank—containing ~1000 ppm ClO2 with excess HCl and NaOCl—posed a serious safety concern to plant operators.

Despite the use of excess acid and bleach, the ClO2 conversion only achieved 80% to 85% efficiency––far below performance expectations, especially when managers factored in the amount of time and effort operators invested in keeping the system operational. Still, the plant wanted to continue using the ClO2 molecule because it provided excellent odor control. Citizen complaints had, in fact, dropped dramatically with its use. The plant need to upgrade to a larger, safer, simpler and more reliable
ClO2 generation system.

In 1998, PureLine was very much a start-up company determined to win new customers with its innovative, safe, reliable and effective ClO2 generation technology. The rendering plant agreed to try PureLine’s two-chemical ClO2 generation system––SVP-Pure®. The SVP-Pure® system used Purate® (40% sodium chlorate/10% hydrogen peroxide) and 78% sulfuric acid solution. Advantages of the
SVP-Pure® system include:
» Improved safety, simplicity, and reliability
» Lower costs for chemical precursors
» Improved ClO2 conversion efficiency
» Less operator service time (automated feed control)
» Fewer complaints about odor

In 1998, a field trial was performed using a beta version of PureLine’s SVP-Pure® ClO2 generation technology. While the generation system was far from optimized, the plant staff was very pleased with its performance and simplicity. During the first two months of the trial, PureLine service technicians visited often to make standard changes to the ClO2 dosage settings in order to optimize the feed rate with the system flow rate. They also trained on-site personnel to help them learn how to troubleshoot problems. Once the feed rate was optimized, the generator automatically provided the appropriate ClO2 dosage via flow-pacing software built into the SVP-Pure® control system. Multiple safety interlocks and alarm features ensured safe and simple operation. On-site personnel discovered that the PureLine generator was indeed much easier to troubleshoot than the previous three-precursor generator. Service visits soon became unnecessary. Only monthly system check-ups and quarterly preventative maintenance were needed—both performed by PureLine field technicians as part of the contract.

Plant operators were no longer faced with constant monitoring or unexpected and time-consuming maintenance. Instead, their daily maintenance routine was reduced to once-a-day, five-minute system checks, as well as periodic level checks of the Purate® and sulfuric acid storage tanks. The simplicity and reliability of the SVP-Pure® allowed plant personnel to focus on other projects instead of monitoring the old generator every 15-30 minutes. The plant manager reported, “The generator just ran, and it ran well.”

Equally important, the new system did not require a batch tank since SVP-Pure® technology rapidly converts two precursors into a high purity ClO2 solution at >95% efficiency. This ClO2 product solution is then educted into the rendering scrubber water system using the generator’s automated feed control system directed by ORP. Chlorine dioxide generation without the batch tank improved the safety and simplicity of the feed system. In addition, the automated SVP-Pure® system ensured optimal feed control with minimal operator involvement.

While the SVP-Pure® generator produced the same pounds per day of ClO2, it used 25% less Purate® than the amount of sodium chlorite required by the plant’s outdated system. Even if the dollar-per-pound cost of Purate was the same as sodium chlorite, a 25% cost savings would still be achieved simply by replacing sodium chlorite with Purate®. In addition, replacement of hydrochloric acid and sodium hypochlorite with sulfuric acid generated even greater savings.

Additional savings were realized due to improved ClO2 conversion efficiency. The old, three-chemical generator operated at 80% to 85% efficiency while the SVP-Pure® system achieved 95% to 99% efficiency.

The following table compares statistics that reflect the plant’s switch first from a “masking agent” to the three-precursor ClO2 generator, and finally to the PureLine SVP-Pure® generator during the summer months

Even though the plant’s initial transition from a “masking agent” to chlorine dioxide did result in better
odor control and a drop in citizen complaints from daily to weekly, complaints did persist because of the three-precursor ClO2 generator’s poor reliability and insufficient capacity. By upgrading to PureLine’s SVP-Pure® ClO2 generator, odor complaints were dramatically reduced from weekly to quarterly.

PureLine’s SVP-Pure® ClO2 generator also provided a dramatic improvement in safety and simplicity over the old generator because it uses two rather than three chemical precursors, doesn’t have a ClO2 batch tank, has a reliable automated ClO2 feed system, and is low maintenance.

PureLine’s SVP-Pure® ClO2 generator is also more cost effective than the plant’s old three-precursor generation system because it only uses two chemical precursors, requires 25% less Purate® than sodium chlorite, and produces a 10% to 15% improvement in ClO2 conversion efficiency.