Absorption Abatement

Absorption Abatement or extended absorption refers to modifications that involve the addition of increased absorption capacity or optimization of the existing absorption system to oxidize and react the nitrogen oxides with water to form acid.. Tail gases are passed through an absorber containing either water or an aqueous solution of ammonia, urea or sodium hydroxide. When water is used as the absorbent, the resultant weak acid is recycled. This increases nitric acid yields by 1% to 3%. When other absorbents are used, the recovered NOx is typically consumed in the production of nitrogen solutions for fertilizer use. If sodium hydroxide is the absorbent, pure sodium nitrite and sodium nitrate may be recovered91,104. 

Bubble cap trays hold their liquid seal on shutdown and are therefore preferred for minimizing NOx abatement problems during start-up and 

The gas at the outlet of the absorber may vary within the following limits during stable operation  

Start-up and shutdown periods will normally increase the NOx content of the tail gas at the stack during the few hours needed for the process to stabilize or for NOx to be cleared from the plant. During the ammonia oxidation some nitrous oxide (NO2) is formed. The amount depends on combustion conditions (pressure, temperature), catalyst composition and age, and design of the oxidation reactor97. 

The minimum emission levels achieved in 2001 without added pollution abatement are  

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Absorption abatement refers to modifications that involve the addition of increased absorption capacity or optimization of the existing absorption system.91... 

Fig. 2. Dual-pressure process using extended absorption for NO abatement. RC = refrigerated cooling see Figure 1 for other definitions.

In an economic comparison of these three common abatement systems, a 1991 EPA study (58) indicates extended absorption to be the most cost-effective method for NO removal, with selective reduction only matching its performance for small-capacity plants of about 200—250 t/d. Nonselective abatement systems were indicated to be the least cost-effective method of abatement. The results of any comparison depend on the cost of capital versus variable operating costs. A low capital cost for SCR is offset by the ammonia required to remove the NO. Higher tail gas NO... 

Process Licensors. Some of the well-known nitric acid technology licensors are fisted in Table 3. Espindesa, Grande Paroisse, Humphreys and Glasgow, Rhfyne Poulenc, Uhde, and Weatherly are all reported to be licensors of weak acid technology. Most weak acid plant licensors offer extended absorption for NO abatement. Espindesa, Rhfyne Poulenc, Weatherly, and Uhde are also reported (53,57) to offer selective catalytic reduction (SCR) technology. 

Chiesa, P. and Lozza, G. (1999), CO2 emission abatement in IGCC power plants by. semi-closed cycles— Part B—with air blown combustion and COi physical absorption, ASME J. Engng Gas Turbines Power 121(4), 642-648. 

For a drug to interact with a target, it has to be present in sufficient concentration in the fluid medium surrounding the cells with receptors. Pharmacokinetics (PK) is the study of the kinetics of absorption, distribution, metabolism, and excretion (ADME) of drugs. It analyzes the way the human body deals with a drug after it has been administered, and the transportation of the drug to the specihc site for drug-receptor interaction. For example, a person has a headache and takes an aspirin to abate the pain. How does the aspirin travel from our mouth to reach the site in the brain where the headache is and act to reduce the pain ... 

ABSORPTION (Process). Absorption is commonly used in the process industries for separahng materials, notably a specific gas from a mixture of gases and in the production of solutions such as hydrochloric and sulfuric adds. Absorption operations are very important to many air pollution abatement systems where it is desired to remove a noxious gas, such as sulfur dioxide or hydrogen sulfide, from an effluent gas prior to releasing the material to the atmosphere. The absorption medium is a liquid in which (1) the gas to be removed, i.e., absorbed is soluble ill the liquid, or (2) a chemical reaction takes place between the gas and the absoibing liquid. In some instances a chemical reagent is added to the absorbing liquid to increase the ability of the solvent to absorb. 

The primary pollution problem in nitric acid plants is the abatement of NOx in tail gases. Three options exist to reduce these emissions to acceptable levels 1) Capture the NOx and convert it to additional nitric acid, 2) Capture the NOx and convert it to nitrate-nitrite sales, or 3) Render the NOx harmless by converting it to non-polluting compounds. The processes that have been developed to reduce emissions at existing and new plants can be classified into four general categories Absorption, Adsorption, Selective Catalytic Reduction (SCR) and Non-Selective Catalytic Reduction91. 

Monsanto Enviro-Chem offers NOx abatement technology that is licensed from Rhodia of France. It includes a High Efficiency Absorption (HEA) section for extended absorption and a catalytic reduction section (SCR) for Catalytic Destruction ofNOx (i.e., the DCN technology)99. 

Whereas a dual-pressure plant or a high-pressure, single-pressure plant (with high pressure absorption) may give acceptable emission levels, the medium-pressure absorption plant must be followed by an abatement system.97... 

FIGURE 9.1 I Schematic diagram of the converter section of a contact sulfuric acid plant employing an interpass absorption system for both better sulfur conversion and emission abatement. Product acid (or oleum) is cooled indirectly with process water prior to storage for sale. 

The abatement of absorption of nickelocyanide ions (26), due to reaction with silver ions, measured at 275 nm at pH 10, was applied for a fast determination of Ag in a FIA system linearity in the 10 to 400 pM range, RSD about 1%97. The anionic complex of Ag(I) with 2-carboxybenzaldehyde thiosemicarbazone (27) was extracted into a solution of Adogen 464 (28) in toluene and measured spectrophotometrically at 345 nm98. 

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