Treatments method

Since process design starts with the reactor, the first decisions are those which lead to the choice of reactor. These decisions are among the most important in the whole design. Good reactor performance is of paramount importance in determining the economic viability of the overall design and fundamentally important to the environmental impact of the process. In addition to the desired products, reactors produce unwanted byproducts. These unwanted byproducts create environmental problems. As we shall discuss later in Chap. 10, the best solution to environmental problems is not elaborate treatment methods but not to produce waste in the first place. 

Let us briefly review the primary treatment methods used. Pretreatment usually starts with phase separation if the effluent is a heterogeneous mixture. 

When viewing effluent treatment methods, it is clear that the basic problem of disposing of waste material safety is, in many cases, not so much solved but moved from one place to another. The fundamental problem is that once waste has been created, it cannot be destroyed. The waste can be concentrated or diluted, its physical or chemical form can be changed, but it cannot be destroyed. 

Measurements have been made in a static laboratory set-up. A simulation model for generating supplementary data has been developed and verified. A statistical data treatment method has been applied to estimate tracer concentration from detector measurements. Accuracy in parameter estimation in the range of 5-10% has been obtained. 

The physical state of a pollutant is obviously important a particulate coUector cannot remove vapor. Pollutant concentration and carrier gas quantity ate necessary to estimate coUector si2e and requited efficiency and knowledge of a poUutant s chemistry may suggest alternative approaches to treatment. Emission standards may set coUection efficiency, but specific regulations do not exist for many trace emissions. In such cases emission targets must be set by dose—exposure time relationships obtained from effects on vegetation, animals, and humans. With such information, a Ust of possible treatment methods can be made (see Table 1). 

Low Level Waste Treatment. Methods of treatment for radioactive wastes produced in a nuclear power plant include (/) evaporation (qv) of cooling water to yield radioactive sludges, (2) filtration (qv) using ion-exchange (qv) resins, (J) incineration with the release of combustion gases through filters while retaining the radioactively contaminated ashes (see Incinerators), (4) compaction by presses, and (5) solidification in cement (qv) or asphalt (qv) within metal containers. 

The common treatment methods are acidification, neutralization, and incineration. When oxahc acid is heated slightly in sulfuric acid, it is converted to carbon monoxide, carbon dioxide, and water. Reaction with acid potassium permanganate converts it to carbon dioxide. Neutralization with alkahes, such as caustic soda, yields soluble oxalates. Neutralization with lime gives practically insoluble calcium oxalate, which can be safely disposed of, for instance, by incineration. 

S. L. Kaplan and W. P. Hansen, Plasma—The Environmentally Safe Treatment Method, Technical Notes, HIMONT/Plasma Science (now BOC Coating Technology), Concord, Calif., May 1991. 

Table 2. Purchased Scrap Categories and Treatment Methods ...

Gaseous vent streams from the different unit operations may contain traces (or more) of HCl, CO, methane, ethylene, chlorine, and vinyl chloride. These can sometimes be treated chemically, or a specific chemical value can be recovered by scmbbing, sorption, or other method when economically justified. Eor objectionable components in the vent streams, however, the common treatment method is either incineration or catalytic combustion, followed by removal of HCl from the effluent gas. 

Treatment method Mode of Operation Degree of treatment Land requirements Equipment Remarks... 

Hot Process Softening. Hot process softening is usually carried out under pressure at temperatures of 108—116°C. At the operating temperature, hot process softening reactions go essentially to completion. This treatment method involves the same reactions described above, except that raw water COg is vented and does not participate in the lime reaction. The use of lime and soda ash permits hardness reduction down to 0.5 g/gal, or... 

Waste Treatment Methods. Technical and legal specialized knowledge and experience are needed to ensure that goals are to be met when selecting waste treatment methods. A support iadustry concentrating on waste treatment process and equipment has developed. Table 3 Hsts several estabhshed waste treatment methods commonly used. 

The treatment of waste is the third element of the hierarchy and should be utilized only in the absence of feasible source reduction or recychng opportunities. Waste treatment involves the use of chemical, biological, or physical processes to reduce or eliminate waste material. The incineration of wastes is included in this categoiy and is considered preferable to other treatment methods (i.e., chemical, biological, and physical) because incineration can permanently destroy the hazardous components in waste materials (Ref. 4). It can also be employed to reduce the volume of waste to be treated. 

This is a formidable analysis problem. The number and impact of uncertainties makes normal pant-performance analysis difficult. Despite their limitations, however, the measurements must be used to understand the internal process. The measurements have hmited quahty, and they are sparse, suboptimal, and biased. The statistical distributions are unknown. Treatment methods may add bias to the conclusions. The result is the potential for many interpretations to describe the measurements equaUv well. 

A third alternative design is to ehill the gas and separate the water eontent. In this option, water and hydroearbon speeifieations may be satisfied simultaneously if the gas temperature is kept above hydrate formation. This option is the simplest proeess and most engineering studies have shown it to be the least expensive gas treatment method. 

The overall stages in handling waste are summarized in Eigure 16.2. The treatment methods applieable to it are listed in Table 17.11. 

For each waste treatment method, indicate the type of waste-stream containing the chemical that is treated. Enter the letter code that corresponds to the general wastestream type ... 

Wastestreams containing the chemical may have a single source or may be aggregates of many sources. For example, process water from several pieces of equipment at your facility may be combined prior to treatment. Report treatment methods that apply to the aggregate wastestream, as well as treatment methods that apply to individual wastestreams. If your facility treats various wastewater streams containing the chemical in different ways, the different treatment methods must each be listed separately. 

Enter the appropriate code from one of the lists below tor each on-site treatment method used on a wastestream containing the toxic chemical, regardless of whether the treatment method actually removes the specific chemical being reported. Treatment methods must be reported for each type of waste being... 

Calculate the mass or weight of chemical in the wastestream being treated by multiplying the concentration (by weight) of the chemical in the wastestream by the flow rate. In most cases, the percent removal compares the treated effluent to the influent for the particular type of wastestream. However, for some treatment methods, such as Incineration or solidification of wastewater, the percent removal of the chemical from the influent wastestream would be reported as 100 percent because the wastestream does not exist in a comparable form after treatment. Some of the treatments (e.g., fuel blending and evaporation) do not destroy, chemically convert, or physically remove the chemical from its wastestream. For these treatment methods, an efficiency of zero must be reported. 

For metal compounds, the calculation of the reportable concentration and treatment efficiency is based on the weight ot the parent metal, not on the weight of the metal compounds Metals are not destroyed, only physically removed or chemically converted from one form into another. The treatment efficiency reported represents only physical removal of the parent metal from the wastestream, not the percent chemical conversion of the metal compound. If a listed treatment method converts but does not remove a metal (e.g., chromium reduction), the method must be reported, but the treatment efficiency must be reported as zero. 

All sequential treatment steps must be indicated for the metal compound categories reported even if the treatment method does not affect the particular metal. For example, ionic exchange must be reported as a treatment method for lead, zinc, chromium, and selenium compounds, oven though the method affects only the selenium compound. 

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