Scrubbing our industry

Creating environmentally friendly cleaning systems for power plants

October 13, 2009
By: Professor R. Carlisle "Carl" Smith

Today's industrial scrubber technology can help make existing energy companies more environmentally friendly. Fabricators with the right equipment, capacity, knowledge, and opportunity might find a new market in making components for these systems. Find out what it takes.

Energy Plant Steam Plume

Figure 1Environmentally Friendly Steam Plume Rising From Energy Plant

The U.S. is in a mad rush to minimize air pollution from industrial and other sources. Many considerations exist besides those put forth by Al Gore in "An Inconvenient Truth." An important one is the cost of cleaning up.

I am convinced that many of our politicians and government leaders are not aware of the tremendous costs involved in manufacturing power plant scrubbers. We hear the drums beating about the excessive energy costs and the need for more and different energy-producing methods. The methods that are being proposed to solve the so-called energy crisis are far in the future. Also, the volume of energy that may be produced with wind, nuclear, geothermal, and hydro power will not meet the ever-increasing needs of our energy-dependent world.

There is no way that we will be able to meet the demand by waiting for these sources to be developed. Our fossil fuel-fed power plants are working overtime to produce the energy that we need today, and the demand is growing exponentially. We should be concentrating on clean coal and reducing emissions from natural gas-fired boilers. I believe that this is the only way to handle our immediate and near-future energy requirements.

While retrofits are being fabricated and installed to make energy companies greener, these providers will have to pass costs on to their customers. However, industry now has a handle on the design for power-plant scrubbers—fluidized gas beds and others—and fabricators have developed efficient and high-quality processes and procedures for building the equipment. This technology eventually will allow power companies to reduce energy prices once the environmental equipment is in place and working.

Looks Can Be Deceiving

The smoke coming from fossil fuel-fed power plants with scrubbers in place appears to be harmful, but in fact this smoke is steam vapor created by hundreds of gallons of water the scrubbers use. This moisture-producing process enhances plant life. The only harm it might cause is to get you a little damp on an extremely cloudy day.

The river shown in Figure 1 is actually a great fishing spot. Bass fishing tournaments are held there at least once a month, and some really nice bass and other species can be caught. Straight across the river from the plant is a boat access ramp used heavily by fishing enthusiasts and water skiers.

Environmental activists frequently are invited to participate in plant tours. Most are favorably impressed. Of course, there are those who will never give up the love for a battle with industry.

Making a Clean-air Scrubber

To withstand the corrosion involved in the air-scrubbing process, scrubbers must be made from a somewhat costly nickel-bearing stainless alloy, such as 2205 Duplex.

The welding wire used to construct them usually has higher nickel content to overcome any alloy loss in the heat-affected zone (HAZ). This is referred to as overwelding. For welding the components in the shop, an argon-helium mixture works best. Field (on-site) welding usually is done using the shielded metal arc Welding (SMAW) process because of the atmospheric wind problem with gas metal arc welding (GMAW).

Some wire producers now offer a flux-cored, gasless wire for use with a wire feeder. This recent technology development allows for a substantial increase in weld deposit rates.

Industrial Scrubber Section

Figure 2Industrial Scrubber Section

Special Handling

The material used in constructing the scrubber must be handled very carefully to avoid any contamination that may increase the possibility for corrosion. No chlorides can come into contact with the materials, and any markers used on them must be chloride-free.

No carbon steel may come into contact with the material either. Handling equipment must have stainless steel padding to prohibit the carbon steel contamination. All grinding disks must be suitable for stainless steel and cannot be used for grinding carbon steel.

Some say these precautions are unnecessary for the nonfluid side of the scrubber, but my opinion is that you should never get careless. Also, pitting on the fluid side must be avoidedbecause of the possibility of crevice corrosion.

Size Considerations

The equipment is very large, which limits the number of fabricators who can build the parts. When possible—most power plants are built near waterways—the components are barge-shipped. The general size of the actual scrubber is 60 ft. in diameter and 120 ft. high. This requires the shell to be fabricated in segments, usually 30 ft. tall. These segments are barge-shipped to the job site, where final assembly is performed(Figure 2).

Automating the Process

The shop welds usually are made with automatic or semiautomatic GMAW equipment. This equipment typically is custom-designed and built to fit the size and shape of the segments. Automation makes all the welds look the same and have consistent quality.

Figures 3 and 4 show automated systems designed for both vertical and horizontal welds. Both are equipped with man cages, so the welder can travel with the feeder and controls.

In my opinion, when the finished scrubber is completed, the unit compares well to a work of art (Figure 5).

Professor R. Carlisle

Professor R. Carlisle "Carl" Smith

Weld Inspection & Consulting
PO Box 841
St. Albans, WV 25177
Phone: 304-549-5606