Your Next Oxidizer--Part 1

Have changing process requirements dictated the need to upgrade your volatile organic compound (VOC) control system? Don't scrap that old RTO just yet. You now have choices like never before. Here's some practical advice on choosing the best option for your situation. This two part series will explore the many options available to industry when process changes or additions require the addition of VOC abatement capacity.

Technical innovation has changed the landscape of the regenerative thermal oxidizer (RTO) market. These advances have dramatically impacted the economics of volatile organic contaminant (VOC) control, and created new options for meeting future clean air regulations. The durability of RTOs themselves contributes to this picture. The physical structure of a RTO unit may have years of remaining life, but its operating efficiency may no longer meet current needs. So, what does a plant do when faced with changing regulations or process expansion?

There is no easy answer and multiple options need to be explored. For example, many of the new RTO innovations can be retrofit to existing units. This means you may be able to improve the VOC destruction, thermal efficiency and capacity of your existing system while lowering its operating costs and expanding process flexibility.

In addition, the growing popularity of RTOs in industry is creating an increasing supply of used systems for sale. Often these units can be cost-effectively upgraded to increase VOC destruction or add needed capacity.

Further fueling the changing face of emission control options, the price of new RTOs has dropped significantly in recent years.

The changes create more choices when deciding how to invest in emission control equipment. But in this new arena, how do you select the best option? Let's look at some examples:

Example 1

Let's consider a paint manufacturing plant having equipment with a combined exhaust of 25,000 standard cubic feet per minute (scfm). The plant's emission control equipment is a seven-year-old three-chamber RTO rated at 25,000 scfm with 95 percent thermal efficiency and 95 percent VOC destruction. The company plans to install a new process line that will add 5,000 scfm, bringing the total process exhaust to 30,000 scfm. The RTO's 350 horse power (hp) fan runs at maximum capacity, so the system, in its current configuration, cannot handle any more flow. In 1993, it cost almost one million dollars to have the system installed, so the idea of purchasing a new system is not very attractive. However, recent advances in RTO technology provide other alternatives. Assuming the plant emissions are at the permit level, let's explore some options:

  1. Upgrade the existing unit to 30,000 scfm and 99 percent destruction
  2. Buy a new 30,000 scfm system that achieves 99 percent destruction
  3. Buy a used 30,000 scfm system that is upgraded to achieve 99 percent destruction
  4. Buy a new 5,000 scfm system for the new process

Option 1

The heat recovery chambers of the system are filled with random-packed one-inch ceramic saddles. At full flow, the system's pressure drop exceeds 25 inches of water column (0.9 psi). Some of this drop is from the ductwork and flow control dampers, but most of it is from the media (saddles) itself. New structured media could replace the current bed of saddles. This would reduce the pressure drop, and allow the oxidizer to handle the additional capacity, maintaining the 95 percent thermal efficiency, and possibly reduce electrical cost. (Information on structured media will be included in part two of this article in the April 2001 issue).

This solves the volume problem, but the plant's operating permit does not allow any increase in emissions. This does not pose a problem. The VOC destruction efficiency of the existing system can also be improved. By installing new high-performance flow dampers and a chamber flushing system, the destruction efficiency can be increased from its current level of 95 percent to over 99 percent, drastically reducing overall emissions.

Option 2

A new 30,000 scfm system offers the benefits of state of the art technology including structured heat exchange media to minimize operating cost and high performance dampers to maximize VOC destruction. In addition, the cost of a new system can be somewhat offset by selling the existing system.

The new system can be installed and commissioned while the existing system remains in operation. Upon completion of start up, minimal time is required to transfer the processes to the new system.

Option 3

A used 30,000 scfm system can be purchased for less than half of the cost of a new system and can be upgraded to meet the VOC destruction requirements. This cost can also be offset by selling the existing system.

The used system also has the benefit of being installed and commissioned while the existing system continues to operate.

Option 4

A new 5,000 scfm system can be purchased to handle the exhaust from the additional process and can be installed and started without disrupting current production.

Which choice is most cost effective? Let's start by considering the first three options. Although each situation is different, the evaluation provided in Figure 1 can be applied to any system.

Figure 1 Estimated Costs

Rebuild

Buy New

Buy Used

Buy Add'l

5,000 scfm

New structured media

$112,500

Included

$112,500

Included

New valves

$33,000

Included

Included

Included

Installation

$30,000

$30,000

$80,000

$10,000

Foundation

N/A

$30,000

$30,000

$15,000

Freight

$3,000

$20,000

$20,000

$10,000

Media removal

$20,000

Not Required

Included

Not Required

Capital equipment

Included

$350,000

$175,000

$180,000

Resale value existing unit

N/A

($130,000)

($130,000)

N/A

Flush Chamber

$9,000

Included

$9,000

Included

Subtotal

$207,500

$300,000

$296,500

$215,000

Fan horsepower required

250

200

250

400

* Total connected horsepower for existing or new unit.

As in Figure 1, upgrading the existing system offers the lowest initial cost. However, the horsepower requirement translates into higher electrical usage when compared to a new oxidizer. A new system has the highest sticker price, but it offers the lowest operating horsepower, which could save up to $10,000 dollars a year in electricity. However, it would take almost 10 years to pay back the added cost of the new system. The option for an upgraded used oxidizer offers no advantages here.

Installing a new 5,000 scfm unit would cost nearly $215,000 - about the same as the total rebuild option illustrated in Figure 1. However, it may be necessary to upgrade the existing system to meet current regulations. Under the conditions, spelled out in Figure 1, a rebuild is the best choice.

When making an equipment evaluation, as in the example above, there are subjective evaluation points that also must be considered. These are more difficult to quantify and their relative importance will vary for different situations.

In general terms, the advantages and disadvantage for each major option are shown in Figure 2.

Figure 2

1) Rebuild

Advantages

Disadvantages

Operational familiarity

Short installation schedule

Lower energy bills

Hidden costs such as repainting

Limited flow through existing valves/ductwork

Process down time

Warranty

2) Buy New:

Advantages

Disadvantages

5-year warranty or better

New systems use less energy

One-week installations typical

Operator interface with modem support

Can use existing system as backup

Cost

Logistics of tie-ins

Facility Training

3) Buy Used:

Advantages

Disadvantages

Can buy larger equipment for future capacity

Lower total cost possible

Can use existing system as backup

One-year warranty or less

Older systems not modular, expensive installation

Modifications to fit process can be costly




This article appeared in the March 2001 issue of Environmental Protection, Vol. 12, No. 3, on page 74.

This article originally appeared in the 03/01/2001 issue of Environmental Protection.

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