Energy use, maintenance and VOC emissions can all improve with a regenerative thermal oxidizer installation. Could your process application benefit?

In this hypothetical example, replacing two older-style thermal recuperative units with a new regenerative unit would reduce operating costs and energy consumption.

To gauge your company’s success, you typically measure how well you do against your primary competitors in the marketplace. But in today’s marketplace, energy costs are your unseen competitor and may be undermining your success. The energy you use in the emission control portion of your manufacturing processes is wrapped into the cost of your product and could put you at a competitive disadvantage.

Can you turn the dead overhead of energy costs into bottom-line profits? The best way to answer that is by taking a hard look at your existing oxidizer systems. Improving emission-control thermal efficiency can have a large impact on the cost of your product. Installing new regenerative thermal oxidizer technology could pay for itself in as little as two years in terms of energy savings, maintenance costs and VOC reductions.

Regenerative thermal oxidizers (RTOs) use ceramic media to recover oxidizer heat and preheat incoming process air, lowering overall operating costs. RTOs are particularly effective for process streams with low solvent loading.

In the last few years, all consumers have seen natural gas prices double. And, with new, large consumers of natural gas (e.g., electrical utility industry switching to gas-fired generation facilities), further increases are anticipated. In addition, electrical rates also have risen; private and public utilities post double-digit rate increases annually. These higher energy costs directly affect your bottom line.

Energy use is similar to purchasing a piece of invisible equipment. Imagine telling your company’s board of directors or owner that you just spent $500,000 on a piece of equipment that they will never see. Although it sounds ridiculous, that’s what companies are doing when they continue to consume energy inefficiently.

Table 1. In this hypothetical example, the processor is considering replacing two older recuperative thermal oxidizers with one regenerative thermal oxidizer.

Oxidizer Heat Exchange Systems

Consider your existing oxidizer system to help determine whether replacing it would yield energy savings. Older thermal recuperative oxidizers, introduced as cutting-edge technology in the 1970s, are still in many plants today. In 30 years, oxidizer manufacturers and processors have learned a few things about oxidizer technology.

Older thermal recuperative units use more energy due to limitations on heat-exchange efficiency. In addition, most plants are now running production around the clock. This means the unit that was new in 1980 is burning more fuel, and doing so at today’s higher energy rates. Many processes have reduced the VOC concentrations being treated by older thermal recuperative oxidizers. This results in burning more supplemental fuel to maintain destruction temperature in the oxidation system. In addition, older thermal recuperative oxidizers can suffer from metals fatigue when cycled on and off. As a result, some companies are keeping them running when the process lines are not in operation. With the lower heat exchange efficiency, this again results in added energy costs.

To help illustrate, consider a hypothetical application with an existing thermal recuperative oxidizer and compare it to an energy-efficient regenerative thermal oxidizer (table 1).

Consider the impact on annual operating costs if the existing thermal recuperative oxidizers are replaced with a new regenerative thermal oxidizer unit. Start with the existing oxidizers and evaluate what they are costing to operate (table 2). Next, look at the impact of installing a new 45,000 scfm regenerative thermal oxidizer and what the operating costs of that would be for the same application (table 3).

As you can see, the operating cost differential is noteworthy for this hypothetical processor. The operating cost been reduced by more than $500,000 per year, and the company would emit less NOX and CO2.

To develop a straightforward payback, compare the operating cost savings vs. the investment cost. The overall investment cost of the replacement regenerative thermal oxidizer can be impacted by many factors: location, re-use of existing ducting, permitting, freight costs, installation, etc. Based on similar actual projects, the oxidizer cost is projected to be approximately $550,000, depending on options for the specific application, leading to a payback of 12 to 18 months. (At times, the investment cost can be somewhat reduced; utility companies may offer rebates or similar payments for projects that result in energy savings. Investigate potential rebates as a part of the overall evaluation.)

Table 2. In the hypothetical example, the two recuperative thermal oxidizers cost $653,142 per year to operate.

Should You Upgrade?

Now that you’ve seen what’s possible, you have to decide whether an upgrade will offer the same benefits to your company. Your first step is to review results of recent preventive maintenance reports on your existing thermal recuperative oxidizer. Review any components that show signs of wear that could lead to failure. Then, assess if the required maintenance and repairs make sense by performing a cost/benefit analysis.

Also consider compliance issues. If you invest in oxidizer improvements, will you be required to retest your unit for permit renewal? If so, will it pass compliance tests?

The second step is to review your energy costs for the past few years and consider how projected increases will affect your company. Be sure to consider annual increases in natural gas costs, and use recent years’ rate increases to project potential future increases.

The third step is to determine how much of the cost of energy is passed through to your customers. Would your product be more competitive if you could decrease the price by decreasing energy costs? Or, would a bottom-line savings allow you to expand into new markets or new product development?

Table 3. In the hypothetical example, replacing the recuperative thermal oxidizer with one regenerative unit would reduce operating costs by more than $500,000.

Another potential issue to consider is the EPA’s regulation of NOX. Your systems may be in compliance for VOC regulation, but the next emission under the EPA’s scrutiny is nitrogen oxide, or NOX. Originally, regulations governing NOX emissions were fairly consistent from state to state. However, in 2004, an additional 11 states were required to control NOX to the same levels as the Northeast. This brings the list states affected under the program to Alabama, Connecticut, Delaware, Illinois, Indiana, Kentucky, Massachusetts, Maryland, Michigan, North Carolina, New Jersey, New York, Ohio, Pennsylvania, South Carolina, Tennessee, Virginia, West Virginia and the District of Columbia. Parts of Georgia and Missouri are expected to participate in the future.

If the VOCs being oxidized contain nitrogen, they can form NOX through the combustion process. Most typical VOCs, however, do not include nitrogen, and therefore most of the NOX that is created in an oxidizer is generated from the reaction of free nitrogen with free oxygen. This reaction takes place at temperatures above 2,500oF (1,371oC). The burner flame is the only location within an oxidizer that operates at temperatures in this range. Hence, the larger and hotter the flame inside the oxidizer, the more NOX it will create. Because regenerative thermal oxidizers recover energy more efficiently than thermal recuperative oxidizers, the burner fires less frequently and creates less NOX. In many applications, regenerative thermal oxidizers have enough energy released from the combustion of VOCs to sustain the combustion process and NOX emissions can be almost zero, as the burner does not fire.

You only need to go back to the hypothetical application to see how you can track the return on investment a new regenerative thermal oxidizer can provide. The next time your leadership team asks how you can cut cost out of your process, take a look at your cost of emission control. PH