Your Next Oxidizer--Part 2

• Mar 01, 2001

Let's look at another example that shows an uprgrade to an existing oxidizer is the most economical solution to providing VOC control for plant expansion.

Example 2

The same paint manufacturing plant from example 1 has learned that management now has decided on a major plant expansion that will double the plant's capacity. The new equipment will increase the total exhaust from the plant to 60,000 scfm.

Now what should they do? Again, the plant has several options:

1. Upgrade the existing unit to 60,000 scfm and 99 percent destruction
2. Buy two new 30,000 scfm units
3. Buy one new 60,000 scfm unit
4. Buy one used 60,000 scfm unit designed for 99 percent destruction
5. Upgrade the existing unit to 30,000 scfm and 99 percent destruction and buy a new 30,000 scfm unit
6. Upgrade the existing unit to 30,000 scfm and 99 percent destruction and buy a used 30,000 scfm unit designed for 99 percent destruction

Option 1

When the original oxidizer was purchased, the vendor stated that the capacity of the oxidizer could be doubled by adding heat recovery chambers and a new exhaust fan. By also changing the heat exchange media to structured packing and performing a valve upgrade the system is easily converted to 60,000 scfm and 99 percent VOC destruction.

Option 2, 3 and 5

New equipment offers the choice of just adding the additional capacity, putting in two half-size units, or replacing everything with one large system.

As in example 1, the existing unit is easily upgraded to 30,000 scfm. This work can be completed after a new 30,000 scfm unit is installed eliminating process down time during installation. This system also offers the advantage of redundant oxidizers. If one oxidizer malfunctions, the plant is still capable of running at half capacity.

Installing two new 30,000 scfm units yields the same advantages as option 1 with the added benefit of a new equipment warranty on the system. Also, the resale value of the existing unit can help to offset the cost of new equipment and the benefits of redundancy are included.

Installing a new 60,000 scfm unit has the advantage of giving the plant all of its needed capacity immediately and can be installed without disrupting production. In addition, the resale value of the existing system will also help to offset the capital cost.

Option 4 and 6

These options are hybrids of options 1 and 3 and have the same benefits assuming that the right sized used oxidizer can be located and brought up to date. This is an increasing possibility in today's market.

To determine which option makes the most sense, let's take a look at the economics, downtime and operating cost for each option, as detailed in Table 2.

	Figure 2. Estimated Costs
	Expand Existing	Buy 2 New 30,000 scfm	Buy New 60,000 scfm	Buy Used 60,000 scfm	Upgrade Existing & Buy New 30,000 scfm	Upgrade Existing & Buy Used 30,000 scfm
Equipment New Fan Media Valves Media Removal Installation Freight Foundations Control Modification Flush Chamber Stack Re-Sale Value of Existing Unit	$275,000 $45,000 $187,500 $36,000 $25,000 $90,000 $30,000 $30,000 $20,000 $15,000 $30,000 N/A	$700,000 Included Included N/A N/A $60,000 $40,000 $60,000 N/A Not Required Included ($130,000)	$600,000 Included Included N/A N/A $40,000 $30,000 $30,000 N/A Not Required Included (130,000)	$400,000 Included $150,000 $60,000 N/A $90,000 $30,000 $45,000 $20,000 $15,000 Included ($130,000)	$350,000 Included $112,500 $36,000 $25,000 $60,000 $23,000 $30,000 N/A $9,000 Included N/A	$175,000 Included $225,000 $36,000 $25,000 $110,000 $23,000 $30,000 N/A $18,000 Included N/A
Subtotal	$783,500	$730,000	$570,000	$680,000	$645,500	$642,000
Installation Time Warranty Redundancy Connected HP Annual Electric Cost (6000 Hr @ $0.045/kWh	30 Days 1 Year No 500 $100,710	6 Days 5 Years Yes 400 $80,568	5 Days 5 Years No 300 $60,426	12-20 Days None No 600 $120,852	15-20 Days Upgrade-1 Yr New-5 Yr Yes 450 $90,639	20-30 Days Upgrade-1 yr Used-None Yes 500 $100,710
3 Year Cost	$1,085,630	$971,704	$751,278	$1,042,556	$915,417	$944,130
Cost-Effectiveness Rating	6	4	1	5	2	3

Expansion of the existing unit is an extensive job. Although adding two chambers to the existing three chambers doubles the flow area, the fan, stack, and ductwork were probably not sized for future capacity. In the end, only the original three cans are re-used. New valves are required for destruction efficiency as well as adding chamber flushing. Additionally, to avoid the use of an extremely large fan, the media must be changed from random packed to structured. Also, an upgrade of this magnitude will require substantial down time for the oxidizer. If the plant is not permitted to run to atmosphere during this time this is an unacceptable solution. This option is also the most expensive from an initial cost and after three years of operation.

Purchasing two new 30,000 scfm units is the second most expensive option when evaluated from an initial cost standpoint, but it is more cost effective when operating costs are factored in. This option does have the advantages of redundancy and a new equipment warranty. These factors must be considered when evaluating this option.

A new 60,000 scfm unit is the most cost effective solution. A new equipment warranty is an additional benefit. The only down side to this option is that it does not offer the benefits of redundancy.

Purchasing a used 60,000 scfm system and upgrading it for this particular option is second most expensive option based on initial capital cost and operating cost. Obviously the availability and condition of the equipment to be purchased as well as the distance to site and local labor rates will greatly affect the cost for this option.

Upgrading the existing unit and purchasing a new 30,000 scfm unit for the additional capacity ranks second in the evaluation, both on initial cost and when operating costs are factored in. But, the cost is substantially higher than a single 60,000 scfm system.

The final option of upgrading the existing system and purchasing a used 30,000 scfm system, while offering the advantage of redundancy, is not price competitive.

No longer relegated to high-volume applications, RTOs are now available in sizes as small as 1,000 scfm. The latest systems offer higher destruction rates and lower operating costs than ever before. They also install in one to five days as compared to the three to five weeks required only a few years ago. Still, if you have an existing system, you may be able to extend its useful life for another 10 years for significantly less money than a new system. Many RTOs that have outlived their applications are now available for resale. With the right modifications, used equipment can provide a real emission control bargain.

To assist you, the following table will help in gathering the necessary information to make an evaluation. It is also helpful to obtain general arrangement drawings as well as model numbers for items such as fans and burners.

	Current System	Future Needs
Process data
Process flow (scfm)
Process temperature
Combustion temperature
Exhaust temperature
Removal efficiency
VOC loading (lbs/hr)
Moisture content
Particulate loadings
Physical properties
Equipment dimensions
Fan horsepower
Burner size
Valve size (diameter)
Inlet duct size
Outlet duct size
Exhaust stack size
RTO features (Y/N)
Gas injection
Hot side or cold side bypass
Recirculation
Bake-out
Variable frequency drive (VFD)

You may not be able to obtain answers to each question, but in gathering as much information as possible, you will be in a better position to determine if your existing system can be modified to meet your future needs.

Although emission control is still an overhead item, advancing RTO technology has made the costs more manageable while improving environmental performance. There are many new choices complicating the situation, but today's options are much more palatable than in the past. With the information we've covered, you're in a much better position to ask pertinent questions and make improved decisions.

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.