Scrubbers costs

The countercurrent gas scrubber cost vs. solvent flow rate. 

The cotmterctirrent gas scrubber — cost versus solvent flow rate. 

The electrostatic effect can be incorporated into wet scrubbing by charging the particulates and/or the scrubbing-liquor droplets. Electrostatic scrubbers may be capable of achieving the same efficiency for fine-particulate removal as is achieved by high-energy scrubbers, but at substantially lower power input. The major drawbacks are increased maintenance of electrical equipment and higher capital cost. 

List the advantages and disadvantages of using a baghouse, wet scrubber, or LSI tor particulate collection from an asphalt plant drying kiln. The gases are at 250 X and contain 450 mg m of rock dust in the 0.1-10 /rm size range. Gas flow is 2000 min. Consider initial and operation cost, space requirement, ultimate disposal, etc,... 

Collecting a sample is a costly and timecosts minimized consistent with other objectives. It makes little sense to spend 5000 on an extensive stack testing analysis to decide whether to purchase a 10,000 scrubber of 95% efficiency or to try to get by with a 7000 scrubber of 90% efficiency. 

Small solid particles, present in dust and grit emissions, have very low settling velocities (Table 4.4) The collection efficiencies of simple cyclones are tlierefore, as shown in Figure 17.3, relatively low. Fabric filters, electrostatic precipitators or wet scrubbers may be required to remove particles <5 pm in size with an acceptable efficiency. Therefore the cost of pollution control inevitably increases when dealing with particle size distributions skewed towards the lower end. 

Since power is a substantial component of the fixed operating cost of a unit, the operating cost would run approximately seven times more on a scrubber installation. The installation costs of a hot-rolled steel precipitator to handle 100,000 cfm would be between 3.50 and 4.50/cfm as opposed to 1.40 to 1.80/cfm for a venturi scrubbing system. Although the initial capital expenditure is high for the precipitator, if the total operating and capital costs are amortized over an acceptable period of time, 8 to 10 years, the precipitator will prove to be the. lore economically feasible choice because of its low operating and maintenance costs. 

It is usually not practical or cost effective to cool flue gases to temperatures below ambient values. Condensation scrubbers are generally intended to be used downstream of another scrubber (e.g., a venturi scrubber) which has already removed PM > 1.0 m aerodynamic diameter. 

The suitability of gas absorption as a pollution control method is generally dependent on the following factors 1) availability of suitable solvent 2) required removal efficiency 3) pollutant concentration in the inlet vapor 4) capacity required for handling waste gas and, 5) recovery value of the pollutant(s) or the disposal cost of the unrecoverable solvent. Packed-bed scrubbers are typically used in the chemical, aluminum, coke and ferro-alloy, food and agriculture, and chromium electroplating industries. 

These scrubbers have had limited use as part of flue gas desulfurization (FGD) systems, but the scrubbing solution flow rate must be carefully controlled to avoid flooding. When absorption is used for VOC control, packed towers are usually more cost effective than impingement plate towers (discussed later). 

Other Considerations For organic vapor HAP control applications, low outlet concentrations will typically be required, leading to impractically tall absorption towers, long contact times, and high liquid-gas ratios that may not be cost-effective. Wet scrubbers will generally be effective for HAP control when they are used in combination with other control devices such as incinerators or carbon adsorbers. 

For argument sake, let s say that 4,500 of the 6,000 total cost is for lower energy and water costs over say a wet scrubber, and that 7,000 of the 10,000 in benefits is due to utility savings one could then use them to offset each other. Mathematically, then, both the numerator and denominator of the ratio could be reduced by 4,500 with the following effect ... 

Semidry Scrubbers The advantage of semidry scrubbers is in that they remove contaminants by way of a solid waste that is easier to dispose of (less expensive). Initially, the scrubbing medium is wet (such as a lime or soda ash slurry). Then a spray dryer is used to atomize the slurry into the gas which evaporates the water in the droplets. As this takes place, the acid in the gas neutralizes the alkali material and forms a fine white solid. Most of the white solids are removed at the bottom of the scrubber while some are carried into the gas stream and have to be removed by a filter or electrostatic precipitator (discussed later). Although semidry systems cost 5-15% more than wet systems, when combined with a fabric filter, they can achieve 90-95% efficiencies. Dry scrubbers are sometimes used in a very similar fashion, but without the help of gas-liquid-solid mass transfer, these systems use much higher amounts of the solid alkali materials. 

Fabric filters can be more costly to operate and maintain than electrostatic precipitators, cyclones, and scrubbers however, fabric filters are more practicable for filtration of specific dusts. For example fabric systems are the typical control method for toxic dusts from insecticide manufacturing processes, salt fumes from heat treating, metallic fumes from metallurgical processes, and other applications. Any other control method may not be as efficient, nor economically feasible for such applications. 

The solution indicates that to reduce the CE content of the terminal wastewater stream to 7 ppmw, air stripping can be used to intercept the bottom product of the first scrubber (lu = 2) to 2.7 CE at a cost of 713,108/yr. Since air stripping... 

The basic principle of wet collectors is to wet the contaminant particles m order to remove them from the gas stream. There is a wide range in scrubber design, cost, and performance." " " Because of this wide variability, scrubbers must be carefully matched to specific applications. 

In a cost-benefit analysis (CBA), the cost of a remedial measure is weighed against the environmental benefits it creates. Is it worth investing in a new scrubber for a plant if the impacts on its surroundings decrease by 10%. ... 

On larger streams filter separators (Volume 1, Chapter 4) are used as mici scrubbers to further reduce glycol contamination and thus increa.se the life of the glycol charge. Due to their cost, filter separators are not normally used on streams less than approximately 50 MMscfd. Often on these smaller units a section in the bottom of the contactor is used i.v a vertical inlet scrubber as shown in Figure 8-5. 

There are economic and operational reasons for considering an additional stage of compression. The addition of a stage of compression requires an additional scrubber, additional cylinder or case, and more complex piping and controls. In addition, there are some horsepower losses due to additional mechanical friction of the cylinder or rotating element and the increased pressure drop in the piping. This horsepower loss and additional equipment cost may be more than offset by the increased efficiency of compression. 

Anonymous, Hybrid Scrubber Cuts Costs, Chem. Engineering, April 28, 1975, p. 66. 

Six-tenths factor, 47 Yearly cost indices, 47 Critical flow, safety-relief, 438 Back pressure, 440 Sonic flow, 438 Critical flow, see Sonic Cyclone separators, 259-269 Design, 260-265 Efficiency chart, 263 Hydroclones, 265-267 Pressure drop, 263, 264 Scrubber, 269 Webre design, 265 Deflagration venting nomographs,... 

Two new technologies have reduced the cost of alkali fuel cells to the point where a European company markets taxis that use them. One is the use of CO2 scrubbers to purify the air supply, making it possible to use atmospheric O2 rather than purified oxygen. The other is the development of ultrathin films of platinum so that a tiny mass of this expensive metal can provide the catalytic surface area needed for efficient fuel-cell operation. 

---